Geology and Hydrogeology Existing Conditions Final Report

Transcription

1 Clean Harbors Canada, Inc. Lambton Landfill Expansion Environmental Assessment Geology and Hydrogeology Existing Conditions Final Report Prepared by: Tel: Fax: RWDI AIR Inc South Service Road Suite 324 Hamilton, Ontario, Canada L8E 0C5 OCTOBER 2014

2 Executive Summary Clean Harbors Canada, Inc. (Clean Harbors) is undertaking an Environmental Assessment (EA) to provide additional landfill disposal capacity for hazardous waste at its Facility in Lambton County Ontario. A Terms of Reference (ToR) for the undertaking was submitted to the Minister of Environment and approval was received in December The EA considers two alternatives for providing the additional disposal capacity. One involves construction a vertical expansion over the current landfill and the second involves the development of a new landfill on property owned by Clean Harbors immediately to the south of the existing Lambton Facility property. As outlined in the EA ToR, the existing environmental conditions within the Lambton Landfill Expansion study area are to be described and documented in a series of reports. This Existing Conditions Report (this Report) describes the geology and hydrogeology conditions within the study areas identified in the ToR for the discipline. These study areas include a broader Regional Study Area extending beyond Lambton County, and a Local Study Area that encompasses the Clean Harbors Lambton Facility property and the lands immediately to the south. The Report has been revised from an earlier submission dated July The revision addresses comments received from the technical representatives for the Walpole Island and Aamjiwnaang First Nations, the Ministry of Environment and the St. Clair Township Peer Review Team on earlier drafts of this report. The goals of this revision are to provide greater clarity of content, to present an update on the results of ongoing investigations into groundwater issues at the Facility and the results of an enhanced water use survey conducted in the Local Study Area. It is recommended that the Report be reviewed in conjunction with the most recent groundwater monitoring report (2012/2013) for the Facility, which was issued on November Geology: The geology within the Regional and Local Study areas is relatively uniform, consisting of a thick sequence of clay and silt dominated sediment deposited in and adjacent to proglacial lakes during the Late Wisconsinan substage of the Quaternary. The overburden is about 20 m thick in the Petrolia area, 35 to 40 m thick in the general vicinity of the Lambton Facility property and up to 70 m thick near the St. Clair River. The stratigraphy within the Local Study Area from surface (youngest) to depth (oldest) includes: a discontinuous, thin (<4 m) deposit of silt and sand; 10 to 15 m thick silt to clayey silt till (St. Joseph Till); 15 to 25 m thick stony silt to clayey silt till (Black Shale Till); and a discontinuous thin (<4 m) stony, sandy clayey silt till (Basal Till). A thin, discontinuous layer of glaciolacustrine sediment derived through the erosion of the underlying Black Shale Till has been identified locally at the contact between the St. Joseph and Black Shale tills. The till units contain sand bodies/pockets and thin lens/layers of sand and silt with limited areal extent. The upper few metres of the St. Joseph Till are intensely weathered and fractured. The bedrock encountered below the Lambton Facility is the Kettle Point Formation, a distinctive, thin-bedded, dark brown to black bituminous shale with infrequent interbeds of green shale. The unit is 6 to 15 m thick in the area. The Kettle Point Formation is locally underlain by the Hamilton Group, a brown to grey, argillaceous limestone/shale.

3 Hydrogeology: The geologic units have been subdivided on the basis of their ability to convey water into distinct units of varying hydraulic activity. The upper 5 to 6 m of clayey silt till is weathered and fractured, therefore hydraulically active. Groundwater movement is primarily horizontal, through the fractures from topographic highs to adjacent low areas. The intensity of weathering/fracturing, the associated hydraulic conductivity, and hydraulic activity decrease with increasing depth below surface. While there is evidence of minor hydraulic activity to depths of 10 to 15 m locally, groundwater movement through the underlying unfractured clayey silt till is extremely slow and the till acts as an aquitard. The Basal Till, where present, and the upper of the shale bedrock where fractured, have a comparatively high hydraulic conductivity and have been exploited regionally and locally as a source of water supply. This zone of hydraulic activity is referred to as the Interface Aquifer. The direction and magnitude of the vertical hydraulic gradient across the till has varied over time. Prior to the development of the Interface Aquifer as a source of groundwater supply, the vertical hydraulic gradient as inferred from profiling of conservative ions such as chloride and environmental isotopes ( 18 O and 3 H) has been flat to slightly upward. With development of the aquifer, the pressure head in the aquifer was reduced and hydraulic gradient reversed to downward. Following the expansion of the Lambton Area Water Supply System into the Local Study Area in the late 1980s, groundwater use has declined significantly and fluid pressure in the Interface Aquifer has increased. Recent observations at monitoring wells on the Lambton Facility property confirm the increasing fluid pressures in the Interface Aquifer and an upward gradient have remerged at wells located in the north western corner of the site. Groundwater movement through the Interface Aquifer across the Lambton County is primarily from east to west, with the direction and rate of movement influenced by local water takings. Groundwater recharge occurs primarily in the eastern portion of the Lambton County, where the overlying aquitard is relatively thin. Water samples collected from wells installed in this area have detectable Tritium, a δ 18 O signature that is consistent with modern day water and a low mineral content. In contrast, samples from wells installed in the Interface Aquifer below the western portion of Lambton County have no detectable Tritium, a depleted δ 18 O signature (-17.5 to ) and are mineralized. It has been interpreted in the literature that the water was recharged during the Pleistocene. The clay aquitard in the immediate area of the Lambton Facility and further west, is relatively thick (>35 m). The limited recharge when combined with the low hydraulic conductivity of the Interface Aquifer and near flat hydraulic gradients, produce stagnate groundwater flow conditions in the aquifer. The underlying unfractured shale, which has a low hydraulic conductivity, acts as an aquitard. The shale separates the Interface Aquifer from the deeper bedrock formations that have been exploited both as a source of oil and gas, and subsequently for the disposal of oil-field brine and industrial waste. Groundwater flow through the shale is vertical and is very slow. Groundwater Chemistry: The groundwater samples collected from shallow wells installed in the upper, weathered clayey silt till (Active Aquitard) are enriched in alkalinity, calcium, magnesium and sulphate resulting from the chemical dissolution of carbonates and sulphide minerals in the till. The concentrations of these parameters decrease with depth in the clay till.

4 Groundwater samples collected from wells installed in the Interface Aquifer contain elevated concentrations of sodium and chloride, and are depleted in sulphide. The chloride and sodium originate in the shale bedrock and the occurrence in the aquifer is attributed to upward diffusion from the bedrock. With the decrease in groundwater use noted above, the hydraulic pressure in the Interface Aquifer is expected to continue to increase, which in turn will affect (flatten) the vertical and horizontal hydraulic gradients enlarging the zone of groundwater stagnation. The corresponding reduction in groundwater flow will result less fresh water available to dilute constituents of the bedrock that are diffusing outward from the matrix of the bedrock. Effects of Lambton Facility on Groundwater: The Lambton Facility property has been in active use as a waste management facility since the early 1960s. The chemistry of the shallow groundwater internal to the existing Lambton Facility property has been affected by site operations. This is expected and addressed through various control measures on site that mitigate the effects. Facility operations that are contributing to shallow groundwater quality impacts and the control measures that have been implemented are discussed below: It is recognized that constituents in the landfill leachate will diffuse upward through the landfill cap towards the surface and will move outward from the waste cells through the sidewalls of the cells. This movement is influenced by the local topography and has been effectively managed by controlling groundwater levels adjacent to the cells by the installation of passive features including perimeter berms and a network of internal drainage ditches. Groundwater mounding below the perimeter berms acts as a shallow groundwater divide that prevents movement from the waste cells beyond the perimeter berms. The ditches depress the water table and induce shallow groundwater and contaminant solute (i.e., leachate) towards the ditch. The ditches convey surface runoff and shallow intercepted groundwater/leachate through retention ponds and a water treatment plant prior to its release off-site. The shallow groundwater quality in the vicinity of the berms is impacted by weathering of the clay till used in constructing the berms. The clay till was derived from excavation of the waste cells. This weathering leads to the dissolution of carbonates and oxidation of sulphide minerals in the clay. Various major ions including alkalinity, calcium, magnesium, sodium and sulphate are detected in shallow wells installed near the berms at concentrations that are slightly elevated in comparison to samples collected from wells removed from the berms. Boron has also been detected at a concentration above the Ontario Drinking Water Standards in samples collected at one of the wells (TW46-99S) installed in the fill of the north perimeter berm and at concentrations exceeding the Provincial Water Quality Objectives (PWQO) at two wells (OW32-90S and OW35-90S) located external to the berm at the west side of the property. The wells are a significant distance removed from the surface water ditch along Petrolia Line, which would be the point of discharge for groundwater. The boron concentrations in water samples collected from the Petrolia Line ditch (AECOM, 2013) are about 50% of the PWQO for boron. There is no basis for mitigating the boron at the observed wells. Sodium and chloride have been detected at increasing concentrations in a shallow monitoring well (TW45-99S) near the west boundary of the Lambton Facility property.

5 The well is located between Telfer Road and the Facility s maintenance garage and vehicle parking lot, and is immediately southwest of the weeping bed for the Facility s sewage system. An investigation to identify the source(s) was undertaken. Based on the distribution of sodium and chloride in samples obtained from sewage effluent, and soil and groundwater samples, the contamination is attributed the use of de-icing salt along roadways and parking areas internal to the Facility property and along Telfer Road. The impact from de-icing salt usage masks the smaller contribution of chloride from the weeping bed. The process area east of the well has been in active use for several decades and there is an expected loading of salt and other potential contaminants in the fill within this area. While shallow groundwater movement is confined through internal ditches, the potential exists for outward movement of chloride and sodium from this area under major precipitation events. Wells installed during the investigation have been incorporated into the monitoring well network and are sampled routinely. Sodium and chloride concentrations at TW45-99S have since declined significantly. Surface water samples are also collected from ditches near TW45-99S following major precipitation events. Parameter concentrations remain elevated in the surface water. Conservative, chemical constituents in the landfill waste/leachate are predicted to move downward through the base of the waste cells by the combined processes of advection and chemical diffusion and will eventually reach the Interface Aquifer. From contaminant transport modeling conducted during the last EA, it was projected that three parameters (boron, fluoride and chloride) would breakthrough to the aquifer for the period modeled (10,000 years) at concentrations that would exceed the MOE Guideline B- 7 criteria. The effect on groundwater quality in the Interface Aquifer would be gradual and widespread over the area occupied by the waste cells. Mitigation of this effect, when determined to be necessary, would be through the installation of low capacity purge wells installed in the Interface Aquifer below the Facility property. These wells would be pumped to maintain a hydraulic gradient that is inward to the property, thus controlling groundwater movement. The water on extraction would be managed as leachate. This mitigation measure has been evaluated through the installation of test wells and the performance of pumping tests, and established to be effective. Localized, abrupt changes in groundwater quality can and have occurred under situations where a pathway between the shallow subsurface and Interface Aquifer has been formed that would allow shallow waters to enter the aquifer. This pathway could be a damaged well casing, abandoned borehole or pressure relief fracturing of the Aquitard, as was induced during excavation of Sub-cell 3, Cell 18. Failure of a well casing at a monitoring well (PW2-S) located central to the Facility between Cell 17 and Cell 18, and flooding of a large area centred on Sub-cell 3 in 2011 (which resulting in the overtopping of the well casing of a second well [PW2-S(R11)] in the same area), has introduced shallow groundwater and surface water into the Aquifer. The effect is evident as a spike in the sulphate concentration in samples collected from monitoring wells installed in the Aquifer in the area. Well PW2-S was decommissioned in accordance with to Facility protocols. PW2-S(R11) and a second well to the north (PW1-N) of where these incidents occurred, are being actively pumped to extract the water that was introduced. The cone of influence generated by this pumping has expanded outward and encompasses much of the north western portion of the Facility property.

6 Trace concentrations of chlorinated volatile organic compounds (VOCs) [trichloroethylene (TCE), cis-1,2- dichloroethylene (cis-1,2-dce), trans-1,2-dichloroethylene (t-1,2-dce), and tetrachloroethylene (PCE)] have been detected at monitoring well TW22-99D located at the northwest corner of the property about 100 m south of Petrolia Line, between Telfer Road and the western perimeter berm. The well is screened against the overburden/shale bedrock interface (Interface Aquifer) and is part of the compliance monitoring well network at the Lambton Facility. TCE was initially detected at TW22-99D in 2005 and has been observed in all samples from this well since that time. Cis-1,2-DCE and t-1,2-dce, which have been detected sporadically, are common to the degradation of TCE under anaerobic conditions similar to what are present in the Interface Aquifer. PCE was detected in a single sample from this well in 2009, during a program to evaluate a new sampling methodology and has not since been observed. The cause/source of these chlorinated VOCs has been under investigation for a number of years. Although there is anecdotal information that the TCE may have been accidentally introduced on equipment used at the well, other possible sources for the VOCs that have been investigated are: a liquid waste spill in the vicinity of the well; solute movement from the landfill; and upward movement from deep bedrock formation due to historical deep well disposal practices. Most recently, boreholes were advanced with continuous coring methods and additional wells were installed in the Interface Aquifer and overlying clay till in the general vicinity of TW22-99D to better characterize the geology and hydrogeology, and groundwater chemistry. One of the new wells (TW60-13D) was installed immediately adjacent to TW22-99D to the same depth. No VOCs have been detected in the two samples that have been collected at TW60-13D. A second deep well (TW61-13D) installed between TW22-99D and the landfill to the east, has a very low hydraulic conductivity and samples from this well have chemistry indicative of a mixture of drill water and formation water. Additional development of this well is required. Based on the recent data that has been collected, there is no clear mechanism by which the TCE could have reached TW22-99D. There is no evidence of a chemical spill and the shallow groundwater in the vicinity of the well is not impacted. Hydraulic gradients in the Interface Aquifer have consistently been from TW22-99D towards the landfill to the east and the groundwater mound that has developed within and immediately below the perimeter berm would preclude shallow movement of TCE westward beyond the berm. Samples from a well installed in the Interface Aquifer adjacent to the former deep disposal wells exhibits no evidence of contamination. The newly installed wells have been incorporated into the site-wide network of monitoring wells. These wells and TW22-99D are being sampled on a bimonthly basis with the samples submitted for the analysis of Volatile Organic Compounds. The various deep wells that are installed in the Interface Aquifer have been equipped with transducer/data logger to record the groundwater levels. The water level information is used to establish the groundwater flow pattern in the northern portion of the Facility property.

7 Executive Summary Table of Contents 1.0 Introduction Background Report Organization Project Team Clean Harbors Lambton Landfill Expansion Study Area Hydrogeology Work Plan, Implementation and Organization Implementation Process Review of Background Information Supplemental Investigations Available Secondary Source Information Geology and Hydrogeology Investigations Lambton Facility Groundwater Monitoring Program Facility History and Operations Background Landfill Operations and Design Pre-1986 Landfill Operation Landfill Operation ( ) Cell 18 Sub-Cell Landfill Operation (2000 to Present) Current Limits of Waste Disposal Volume of Waste Waste Composition Leachate Levels and Composition Closure of the Existing Landfill Site Contingency Plans Topography and Drainage Topography Drainage Geology Regional Geology Paleozoic Bedrock Geology Petroleum Exploitation and Waste Disposal Wells Bedrock Topography and Overburden Thickness Quaternary Geology Local Geology Bedrock Geology Bedrock Topography and Overburden Thickness Overburden Geology... 50

8 7.0 Hydrogeology Scope of Previous Investigations Regional Hydrogeology Hydrostratigraphy Hydraulic Conductivity Groundwater Flow Groundwater Chemistry Local Hydrogeology Hydrostratigraphy Hydraulic Conductivity - Overburden Hydraulic Conductivity Compacted Clay Hydraulic Conductivity Interface Aquifer Hydraulic Conductivity Bedrock Formations Influence of Natural Gas on Hydraulic Conductivity Groundwater Flow Background Groundwater Chemistry Existing Water Supply and Groundwater Use Regional Study Area Local Study Area Effect of Existing Lambton Facility on Local Groundwater General Discussion of Effects Effects from Routine Facility Operations Effects Associated with Excavation and Construction Effects Associated with Contaminant Movement from Landfills Existing Groundwater Chemistry (2013) Groundwater Quality- Active Aquitard Groundwater Quality - Interface Aquifer Summary of Existing Conditions Regional and Local Geology and Hydrogeology Effects of the Existing Lambton Facility on Groundwater Declaration References Geology Hydrogeology Clean Harbors Canada, Inc. Lambton Facility Landfill Specific Consultant Studies Landfill Annual Compliance Monitoring Reports Referenced Province of Ontario Regulations Deep Well Disposal Practices Other References Glossary of Terms

9 List of Figures Figure 2-1. Site Layout and Study Area Figure 3-1. Southern Expansion Area Footprint - Data Sources Figure 3-2. Location of Wells Installed in Waste Cells Figure 3-3. Location of Shallow Overburden Monitoring Wells Figure 3-4. Location of Interface Aquifer Monitoring Wells Figure 4-1. Clean Harbors Lambton Facility Features Figure 4-2. Locations of Seeps in Sub-cell Figure 4-3. Sub-cell 3 Remedial Structure Plan View Figure 4-4. Sub-cell 3 Remedial Structure Cross Section Figure 4-5. Current Limit of Waste Disposal (September 2013) Figure 5-1. Physiographic Regions within Lambton County Figure 5-2. Surface Topography in Vicinity of Lambton Facility Figure 6-1. Bedrock Geology within Lambton County Figure 6-2. Oil and Gas Well Drilling Locations and Petroleum Pools Figure 6-3. Bedrock Topography Figure 6-4. Overburden Thickness Figure 6-5. Surficial Geology (Ontario Geological Survey, 2010) Figure 6-6. Northeast to Southwest Cross Section - Lambton Facility Property Figure 6-7. Bedrock Surface Topography - Lambton Facility Figure 6-8. Overburden Thickness - Lambton Facility Figure 6-9. Thickness of Basal Till Figure 7-1. Typical Hydraulic Gradients /Distribution of Conservative Parameters Figure 7-2. Conceptual Model of Regional Geology/Hydrogeology Figure 7-3. Groundwater Geochemistry Monitoring Locations (Hamilton, 2010) Figure 7-4. Interface Aquifer Thickness Lambton Facility Figure 7-5. Hydraulic Conductivity Distribution, Interface Aquifer Lambton Facility Figure 7-6. Groundwater Elevations for Shallow Monitoring Wells (2013) Figure 7-7. Cross Section Extending Southward from the Pre-1986 Landfill Area Figure 7-8. Hydrographs for Representative Shallow Wells Figure 7-9. Potentiometric Surface in Interface Aquifer 1980 and Figure Potentiometric Surface in Interface Aquifer 1991 and Figure Potentiometric Surface in Interface Aquifer 2000 and Figure Potentiometric Surface in Interface Aquifer March and September Figure Hydrographs for Representative Wells - Interface Aquifer Figure Distribution of Vertical Hydraulic Gradients (2013) Figure Locations of Referenced Wells (Novakovic, 1991) Figure Series Wells Installed in Undisturbed Areas of Property Figure 9-1. Site Features and Drainage Areas Figure 9-2. Pathways for Contaminant Movement from Landfill Cells Figure 9-3. Borehole LM4-11 Observed and Simulated Chloride Profiles (Cell 16) Figure 9-4. Borehole LM9-11 Observed and Simulated Chloride Profiles (Cell 18) Figure 9-5. Chloride Concentration with Lapsed Time since Waste Placement Cell Figure 9-6. Cross Section through TW45-99S. 188 Figure 9-7. Cross Section throughtw22-99d and Sub-cell 3 Remedial Structure. 189

10 List of Tables Table 3-1. Work Plan Revisions Based on Comments Received... 6 Table 3-2. Annual Groundwater Monitoring Program Chemical Parameters...16 Table 3-3. Natural Groundwater Sources Indicator Parameters Concentrations...18 Table 4-1. Lambton Facility - Development History...21 Table 4-2. Landfill Areas History and Physical Dimensions of Waste Cells...28 Table 4-3. Leachate Sources Indicator Parameters Concentrations (2012 Data)...31 Table 6-1. Devonian Bedrock Stratigraphy Lambton County (Johnson et al., 1992)...39 Table 6-2. Devonian Bedrock Stratigraphy...41 Table 7-1. Parameter Concentrations (Hamilton, 2010)...67 Table 7-2. Hydraulic Conductivity Values for Overburden (Pre-1994 Investigations)...69 Table 7-3. Hydraulic Conductivity Values for Overburden (Post Investigations)..70 Table 7-4. Compilation of Hydraulic Conductivity Values by Depth...73 Table 7-5. Range in Hydraulic Conductivity Values for Interface Aquifer...75 Table 7-6. Summary of Hydraulic Conductivity Data for Bedrock Formations...78 Table 7-7. Shallow Groundwater Levels in the Vicinity of the Facility Berms...80 Table 7-8. Water Level Elevations and Hydraulic Gradients in Shale Aquitard...88 Table 8-1. Summary of Household Water Use...96 Table 9-1. Summary of 2012/2013 Chemistry Shallow Monitoring Wells Table 9-2. Summary of 2012/2013 Chemistry Deep Monitoring Wells Table 9-3. Summary of Chemistry - Interface Aquifer and Shale Wells Table 9-4. Evolving Chemistry at Well TW47-00D

11 Volume II Appendices (Computer Disc) Appendix A. Technical Work Plan - AES International Environmental Consultants (March 2011) Appendix B. Geology Supporting Information Appendix B.1. Logs for Lambton Facility Monitoring Wells (Existing and Older) Appendix B.2. Geophysical Survey (CRA, 2010) Appendix B.3. Summary Information Petroleum Exploration and Production Wells Table B.3-1. Summary of Oil, Gas and Disposal Wells Identified Within 1.5 km Boundary Table B.3-2. Geology South Option Appendix C. Technical Memorandum Revised Groundwater Use Survey Appendix D. Groundwater Database Appendix D.1. Groundwater Levels and Chemistry Appendix D.1.1 Hydrographs for Monitoring Wells Appendix D.1.2. Hydrographs for Wells Installed in Waste Appendix D.1.3. Fall 2013 Groundwater Database Appendix D.2. Summary of Hydraulic Conductivity Data Active Aquitard Appendix D.3. Regional Laboratory Analyses Table D.3-1. Laboratory Analyses (Ontario Geological Survey) Appendix D.4. Technical Memorandum Leachate Chemistry Tables D.4-1 Leachate Chemistry Summary Tables Appendix D.5. Technical Memorandum Landfill Cap Assessment Appendix D.6. Summary of Chemistry (Weaver, 1994) Appendix D.7. Summary of Chemistry for Wells Installed in Shale

12 1.0 Introduction 1.1 Background This report identifies and describes the existing geology and hydrogeology conditions associated with the proposed expansion of the Clean Harbors Canada, Inc. (Clean Harbors) Lambton Landfill Expansion Environmental Assessment Study Area (see Section 2.0) in accordance with the Hydrogeology Work Plan (Appendix A). The approved Terms of Reference (ToR) included a preliminary description of the existing environmental conditions in the vicinity Study Area with the commitment that the description would be expanded upon in the Environmental Assessment (EA). In accordance with the approved ToR, investigative studies of the following environmental components were carried out for the purposes of generating a more detailed description and understanding of the environment for use in the assessment and evaluation of the two alternative landfill expansion options during the EA: Atmospheric Environment Geology and Hydrogeology Surface Water Natural Environment Agriculture Archaeological and Cultural Heritage Technical Socio-economic The drafts of the Geology and Hydrogeology Existing Conditions Report (February 2013, January 2014 and July 2014) prepared by RWDI AIR Inc. (RWDI) was distributed to the St. Clair Township and appropriate review agencies, First Nations and Métis organizations, and the public for their information. Comments on the report were received from the technical representatives for the Walpole Island and Aamjiwnaang First Nations, the Ministry of Environment (Southwest Regional Office) and the St. Clair Township Peer Review Team. A number of revisions have been made to the Existing Conditions Report to provide greater clarity of content and to document the results/findings of two investigations that are ongoing. One is being conducted to identify the source(s) of increasing chloride concentration at a shallow well (TW45-99S) located near the west boundary of the property. The second is to investigate the source of Trichloroethylene detected in a deep well (TW22-99D) near the northwest corner of the property. In addition, the previously completed water use survey that was conducted in the Local Study Area by phone and mail enquiries was enhanced by a door-to-door survey. Structural changes to the report were primarily focused on the Appendices (provided in a CD at the back of the report). Included on the CD is a menu with links to specific referenced documents, monitoring wells, and monitoring results. This linkage format was adopted from the 2012/2013 Groundwater Monitoring Report and includes a portion of the database from the report. 1

13 This report, Geology and Hydrogeology Existing Conditions Report (October 2014) is a supporting document to the submitted EA Report and can be obtained from the EA project website. 1.2 Report Organization This document consists of two volumes including Volume I the interpretive report (Report), which contains reference tables and figures, and Volume II, which contains supporting appendices. Section 1 through Section 3 describes the undertaking. Section 4 presents a general history of the site and background information on the landfill operations. The topography and drainage are described in Section 5, the geologic setting in Section 6, the physical and chemical Hydrogeology in Section 7, and the existing water supply and water use in Section 8. A summary discussion of the effects of landfill development on local groundwater resources is provided as Section 9. The Report s contents are summarized in Section 10 - Summary of Baseline Conditions. References cited in the Report are listed in Section 12. Sections 5 through 9 are structured in a manner that focuses in from the broader regional discussion on the geology, physical and chemical hydrogeology, and groundwater use, to observations local to the Lambton Facility property and the area for the proposed off-site landfill alternative to the south of the existing Lambton Facility property. Volume II is fully contained on a computer disc that is included in the back of the Report. The content is organized as follows: Appendix A - Technical (Hydrogeology) Work Plan; Appendix B - Supporting Information (Borehole Logs and Well Records); Appendix C - Water Use Survey; and Appendix D - Groundwater Database. 1.3 Project Team The analysis and documentation was completed by the hydrogeology project team that includes staff from RWDI AIR Inc. and S.S. Papadopulos & Associates, Inc. The Project Team included the following individuals: Field Supervision, Data Collection, Compilation and Presentation Support Timothy Boc, B.E.S, Senior Field Technician, RWDI AIR Inc. Aldis I. Zandbergs, B.Sc., P.Geo., Geologist, RWDI AIR Inc. Sonia S. Lee, B.Sc. Eng., EIT, EPt., RWDI AIR Inc. Data Interpretation and Reporting Gunther H. Funk, B.Sc., P.Geo., Hydrogeologist, RWDI AIR Inc. Peter-James A. Mauro, B.Eng., EMPD, P.Eng., Senior Project Manager, RWDI AIR Inc. Contaminant Transport Modeling and Analysis Christopher J. Neville, M.Sc., P.Eng., Hydrogeologist, Associate, S.S. Papadopulos & Associates This work effort was supported and reviewed by Dr. R. Kerry Rowe P.Eng. (Department of Civil Engineering, Queen s University). 2

14 2.0 Clean Harbors Lambton Landfill Expansion Study Area The existing approved landfill operation, including all historical fill areas, has a footprint of 56 hectares out of the entire 121 hectare licensed property (see Figure 2-1). As documented in the approved ToR, two landfill expansion options for the Existing Lambton Facility have been identified. These are: Alternative Method 1: This method involves a vertical expansion of the existing landfill site with waste being placed in engineered cells constructed within the previously approved and landfilled areas of the Lambton Facility. The cells will either be excavated below grade in areas that have not previously received waste or constructed directly above previously filled cells. Alternative Method 2: This method involves the construction of a landfill on adjacent lands already property owned by Clean Harbors Canada, Inc. that is located south of the existing landfill site. Waste will be placed in a m deep excavation and covered with 5.1 m clay cap. The Study Area considered in the ToR includes the licensed Lambton Facility property, the property immediately to the south of the Facility, and the potentially affected surrounding area. From a geology and hydrogeology perspective, landfill developmental effects are assessed in terms of the potential for the landfill to alter groundwater quantity and quality, and thereby affect its end use. In addition, surface water flow is in part sustained by groundwater discharge, and the quantity and quality of this discharge can affect aquatic life and the recreational use. The study area for the geology and hydrogeology discipline is therefore defined by the physical extent of the geologic units through which groundwater movement occurs, and the direction and length of the groundwater flow paths. In the general vicinity of the Lambton Facility, groundwater movement occurs primarily through the near surface weathered/fractured portion of the clay overburden and at a zone of variable thickness and continuity at the overburden and bedrock contact. The shallow groundwater flow pathways are short, with recharge occurring over topographically elevated areas and discharge occurring in adjacent lows. The Study Area for shallow groundwater flow (referred to as the On-Site Study Area) is coincident with the surface water catchment areas, the limits of which are delineated by topography. At the Lambton Facility, the areas that have been landfilled are internal to the property and features that act as passive hydraulic barriers limiting shallow groundwater flow. These include large perimeter berms, below which the water table is mounded, and retention reservoirs and drainage ditches that act as groundwater sinks under low stage conditions. There is a component of shallow groundwater flow at the property boundary, which originates from the water table mounding below the berms, and from the reservoirs and ditches under high stage water levels. This flow is towards the network of roadside ditches and to shallow swales that drain to the ditches at the boundaries of the Facility property. 3

15 The deeper groundwater zone at the overburden bedrock contact has historically been exploited as the primary source of water supply for residences and farms located in the general vicinity of the Lambton Facility property. This zone is referred to as the Interface Aquifer based on this usage. The Interface Aquifer while regionally extensive (underlying the County of Lambton and beyond), has variable productivity and water quality. The direction of groundwater movement within the Interface Aquifer is influenced by various factors including: the regional and local topography; the volume of recharge and the distribution of residences/farms that relied on groundwater as a primary source of supply. The regional topography slopes to the west from a high along the east side of the County of Lambton. The clay overburden is thinner along the east portion of Lambton and thickens to the west, and recharge of the Interface Aquifer is correspondingly higher in the east. Most residences/farms are located adjacent to roadways resulting in a grid-like distribution of groundwater use, which is higher along the roadways and non-existent near the middle of the concession blocks. The potentiometric surface in the Interface Aquifer would therefore be depressed near the roadways and relatively unaffected away from the roadways. As discussed later in this document, groundwater taking as a source of supply has decreased significantly over the last few decades following the expansion of the Lambton Area Water Supply System across Lambton County. The declining water use has resulted in a readjustment (i.e., increase) in the potentiometric surface. The general pattern of groundwater flow through the Interface Aquifer is from east to west across the County. The Lambton Facility overlies a regional topographic high and the potentiometric surface in the Interface Aquifer is elevated below the property. Based on the current mapping of the potentiometric surface in the Interface Aquifer below the Facility property, flow is outward from a potentiometric high that extends north to south near the western property boundary. The Study Area for the Interface Aquifer because of its use as a source of water, is defined as an area extending fully around the Lambton Facility and the southern property (Alternative Method 2) and as shown in Figure 2.1 (depicted as the area encompassed by the dashed boundary) to a distance of 1.5 km outward from the boundary of the subject properties. It is noted however that many of the published maps and reports, and technical studies that were relied on to describe the geology and hydrogeology existing condition encompass a much larger regional area, which in some instances extends beyond Lambton County. This information has been considered in this study and is referenced where applicable. 4

16 3.0 Hydrogeology Work Plan, Implementation and Organization In keeping with the EA process outlined in the ToR, a Hydrogeology Work Plan (refer to Appendix A) was initially prepared and shared with the government agencies and other stakeholders. The work effort identified in this Work Plan revolves around two primary components, one focused on the preparation of a comprehensive document characterizing the existing condition, namely this Report (Geology and Hydrogeology Existing Conditions Report), and a second component, the discipline-specific assessment of the two landfill design expansion alternatives, which will be documented separately. It is intended that the contents of the Report and the most recent Annual Groundwater Monitoring Report (RWDI, 2013) for the Lambton Facility represent the baseline condition against which the potential effects of the landfill alternatives are to be assessed. The work proceeded by assembling and cataloguing available published and unpublished maps, reports, studies etc., on the geology and hydrogeology of Lambton County and that for the Clean Harbors Facility in Lambton. The product of this effort is the Bibliography presented in Section 4 of the Work Plan. As the Report is to incorporate the most recent information available for the site on the status of the groundwater condition (i.e., quantity and quality per ToR, Appendix B criteria), effort was initially directed at a thorough review of the last comprehensive assessment of site conditions, which had been completed by Jagger Hims Limited (1996) in support as the EA for the Cell 18 expansion. The Report therefore builds on and updates the content of this earlier work by incorporating the findings of the major studies completed in the general area and at the Facility Property since For example, the Annual Landfill Report, which is prepared as a requirement of the Facility s Provisional Certificate of Approval, presents a yearly snap shot of conditions at the site developed through a prescriptive groundwater monitoring program. At the time the Work Plan was prepared, the 2010 Annual Landfill Report had been issued and the initial monitoring event for the subsequent year had been completed and the data compiled. Also with the selection of the two landfill alternatives for the ToR, came the recognition that there was limited information on the geology/hydrogeology in the area south of the existing Facility Property, where one of the alternatives would be located. A work program involving the compilation of the geology from available borehole/well information, completion of a geophysical survey to establish the relative overburden thickness and bedrock topography, and a drilling/well installation program was completed in this area in 2009/2010. The results of this effort are incorporated into the Report. In reviewing the Jagger Hims Limited (1996) report, the 2010 Annual Landfill Report and the secondary information sources listed in the Work Plan Bibliography, it became apparent that some of the information was dated and the reinterpretation of the existing condition would benefit from the collection of more recent information. A supplemental field program was developed, which is outlined in some detail in the aforementioned Work Plan (copy provided in Appendix A). The Hydrogeology Work Plan was distributed to St. Clair Township, First Nations, and the Ministry of the Environment. Comments that resulted in revisions to the Geology and Hydrogeology Existing Conditions Work Plan have been integrated in this report and are outlined in Table

17 Table 3-1. Work Plan Revisions Based on Comments Received Reviewer Comments Clean Harbors Response Existing Conditions Report Reference St. Clair Township June 24, 2011: The analyte list for leachate testing in Table 2 on page 9 of the Hydrogeology Work Plan should be expanded to include comprehensive lists of heavy metals, volatile organic chemicals, and polycyclic (polynuclear) aromatic hydrocarbons. Also the liquid levels in the proposed leachate wells should be measured for a period of one year, rather than the 3 months proposed. August 5, 2011: The analyte list was established in 1996 based on detailed analysis of bulk waste samples and leachate, and chemical transport modeling conducted at that time for the last EA. These analytes were identified as being present in the waste at significant concentrations and based on their chemical behaviour (not readily degraded and comparative mobility) were identified as suitable surrogates for the broader list of chemicals present in the waste. See Section 9 and Appendix D October 23, 2011: Unsatisfactory. [Note: The list of analytes was extensively reviewed by the MOE and has been employed since 1996 for compliance monitoring purposes. The reviewer is directed to the hydrogeology reporting conducted in 1996 that describes the process followed in developing the list. November 15, 2011: It was agreed that the PRT will review the 1996 Jagger Hims Report, which provides background rationale and methodology for the selection of the proposed list of analytes. This matter can be discussed further following that review. Clean Harbors agrees to measure liquid levels in the leachate wells for a period of greater than three months and up to a year if the vertical expansion alternative is identified as preferred. The information collected from the liquid level monitoring in the leachate wells to be installed in the waste cells is intended to be used/considered during the comparative assessment of the two landfill options and by the engineering team in its design of the vertical option. If the vertical option is carried forward as the preferred option, monitoring will continue and extend out to a full year or possibly longer. 6

18 Table 3 1. Work Plan Revisions Based on Comments Received (continuation) Reviewer Comments Clean Harbors Response Existing Conditions Report Reference St. Clair Township June 24, 2011: The ToR indicates that Step 3 of the EA alternatives evaluation is to predict the environmental effects of each landfill design alternative. The proposed work plan for Task 2 does not describe how this step is to be followed in terms of assessing impacts on the basis of each of the relevant EA criteria (groundwater quality and quantity, and surface water quantity and quality). A detailed discussion of how the environmental effects of each landfill design alternative are proposed to be assessed needs to be provided. October 23, 2011: Unsatisfactory. A broader list of parameters should be used in assessing leachate impacts on groundwater quality and surface water quality. The leachate quality testing proposed under PRT Comment #8 will help determine which parameters should be used. August 5, 2011: Section 4.5 and 4.6 of the approved Terms of Reference describes the methodology for predicting the potential effects and assessing and evaluating the alternatives based on the criteria, indicators and data sources included in Appendix B of the ToR. The EA alternatives evaluation will be sufficiently detailed to facilitate comparison of the alternatives based on the potential chloride loading of surface water and groundwater through transport from the waste. The scenarios to be analyzed through modeling will be consistent with our current knowledge of conditions at the site based on almost 40-years operations and associated observations. Constrains imposed by the available data (and uncertainty) will be assessed through sensitivity analysis. November 15, 2011: It was agreed that the PRT will review the 1996 Jagger Hims Report, which provides background rationale and methodology for the selection of the proposed list of analytes. See Section 9 and Appendix D To review all comments received on the various Work Plans and associated Clean Harbors responses, please refer to the Clean Harbors Work Plan Comment Response Summary Report. Note that this Report will also be documented in the Environmental Assessment Record of Consultation. The following modifications to the scope of the supplemental field program were undertaken based on the comments that were received: Initial Work Plan called for liquid level monitoring to continue for a 3 month period following well installation. The period of time over which liquid level monitoring was conducted was increased to 12 months (August 2012 to August 2013). To accommodate this request, a more robust well design was adopted (i.e., use of stainless steel well casing and screen) and pressure transducers - data loggers were acquired to collect a near continuous record of liquid levels over the period. The list of chemical parameters to be analyzed for samples collected from the new well installations has been expanded to include additional metals, mercury, VOCs, PAHs, dioxins and furans, and PCBs. 7

19 As noted in Section 1.0, earlier drafts of the Report were distributed to various groups participating in the EA and comments were received with respect to groundwater issues that have been identified through the groundwater monitoring that has been conducted at the Facility. This Report has therefore been updated to address the comments that have been received to the end of September Implementation Process The work effort represented by this Report involved the compilation and review of available information on the geology, hydrogeology and facility operations initially, the development of the Hydrogeology Work Plan (Appendix A) to conduct supplemental investigations to address identified gaps in the existing information, and the implementation of the work program outlined in the Work Plan, as amended through interaction with St. Clair Township and First Nations (refer to Table 3-1). At the time that the initial draft Report was prepared, a number of investigations were underway at the Lambton Facility. The findings of these ongoing investigations have been incorporated into this Report. The implementation process is described herein Review of Background Information The description of the geology and hydrogeology relies extensively on available secondary source information. Copies of this information (published and unpublished reports and maps) were obtained and reviewed, and applicable regional and local information was compiled and summarized. The following were produced: an inventory of available published and unpublished reports, papers and maps, university thesis, construction drawings, historical and current photography, laboratory analysis reports, and field note books [Note: References cited in this Report are included in Section 11]; site plans generated from current aerial photography that show major features including roadways, process facilities, landfill areas, berms, drainage features, etc., and the locations of boreholes and monitoring wells; compendium of borehole logs, residential water well records, oil and gas well records and tabular summaries compiled from these logs and records [Records are contained in Appendix B and Appendix C of this Report]; a relational database (water levels and groundwater chemistry) that is referenced to individual data points (i.e., boreholes and monitoring wells) and location [Information considered is included in Appendix D with the most recent data (November 2013) collected for the Lambton Facility provided in Appendix D.2]; and figures (in plan and cross section) presenting assembled information on the geology (overburden thickness and bedrock surface topography), observed potentiometric surfaces, distribution of hydraulic conductivity and landfilled areas. 8

20 3.1.2 Supplemental Investigations The available information on existing conditions has been supplemented and updated through the completion of the following investigations: Enhanced Definition of Geology/Hydrogeology South of the Lambton Facility: With the selection of the Shallow Entombment Landfill Off-Site Alternative as one of the two landfill alternatives identified in the ToR, came the recognition that there is limited high quality information on the geology/hydrogeology south of the existing Lambton Facility in the proposed location of the alternative. To address this deficiency for the purposes of the EA and the comparative evaluation, a work program was initiated in late 2009, which involved the following elements: compilation of geology from boreholes/wells installed south of the Lambton Facility property, from water well records and from petroleum exploration well logs; geophysical (seismic) survey to establish the relative thickness of the overburden and the bedrock topography underlying the property to the south of the Lambton Facility; installation of two wells (well pair), one deep well in the primary water-bearing unit, namely the Interface Aquifer (located at the overburden/bedrock contact) and a second shallow well in the upper weathered zone of the overburden, which has also been used as a source of water; and groundwater level and water quality monitoring at the two installations [Note these wells are now part of the annual monitoring program and four years of monitoring data are available for the installations]. The survey lines and well locations and are shown in Figure 3-1. The borehole/well logs are in the data base that is included in Appendix B (on the Computer Disc at that is provided in a pocket at the back of the Report). The information obtained has been incorporated into Sections 6 and 7 of this Report. Groundwater Use: Information on groundwater use in the vicinity of the Lambton Facility is compiled from surveys completed by Hydrology Consultants Limited (1980 and 1984a), Novakovic (1991), Jagger Hims Limited (1996) and Dillon Consulting Limited in association with Golder Associates Ltd. (2004). With the extension of watermains to the vicinity of the Lambton Facility in the 1980s, the area is municipally serviced however a few residences still rely on wells to supplement the municipal supply. A survey of properties within a 1.5 km radius of the Lambton Facility Landfill was completed in November/December 2012, to obtain current information on the status of groundwater use. The survey was conducted in conjunction with a Residential/Business Survey and involved contacting property owners within this area initially by mail (letter including a description of the undertaking and an enclosed well reconnaissance survey form) and subsequently by telephone. An invitation was extended for the form to be completed on-line, over the telephone or in person. 9

21 A technical memorandum was produced that discusses the results of the water well survey (Appendix C). The information obtained is summarized in Section 8 of this Report. The MOE in its review of the initial draft of this Report commented that it would beneficial to conduct a door-to-door survey of the residential/farm properties within the survey area as opposed to relying strictly on written and verbal in input to the survey form. Clean Harbors agreed and the survey was conducted in October The water use report provided in Appendix C was updated to reflect the results of the additional survey work. Chemical Source(s) and Movement: The composition of the waste received and landfilled at the Facility has varied significantly over the years, being influenced by changing waste streams (different waste generators or new/modified production processes), and modifications to regulatory requirements. The existing base of information on the liquid level and chemistry of the leachate within the various waste cells was assembled in 1995/1996, as part of a comprehensive hydrogeological investigation conducted at that time (Jagger Hims Limited, 1996). This information was collected through the installation of wells in the Pre-1986 and Cell 16 landfill areas, and from the analysis of bulk waste samples. Additional information on the composition of the waste leachate was obtained in 2010/2011. This effort involved the collection of liquid samples from the leachate retention reservoir. Review of the analytical data indicates the samples are an admixture of leachate from a number of the open sub-cells in Cell 18 and surface water, and therefore the chemistry was not representative of the composition of leachate in the waste cells. In recognition that there is a general lack of recent data (i.e., leachate level and leachate chemistry) in the waste cells, a field program was developed to collect this information (see Hydrogeology Work Plan, Appendix A). The work effort to collect recent leachate data was completed in two steps. First Step: The initial step involving the installation of monitoring wells in waste cells at the landfill to measure the leachate level in the cells and to collect samples of leachate for analysis. The field program to install the wells was undertaken in November/December 2011 and involved advancing 10 boreholes through the landfill cap in the various cells of the Lambton Facility and installation of wells in the waste below the cap. The borehole/well locations are shown in Figure 3-2. An initial round of well sampling was conducted in mid-august 2012 and the boreholes were instrumented with transducers/data logger in late-august A second sampling event was completed in November The leachate samples were submitted to Exova Accutest, a commercial laboratory, for chemical analysis. As part of this work effort, soil cores were obtained from two of the boreholes (LM4-11 and LM9-11). Each core was sectioned with the individual sections analyzed for chloride and moisture content. The collected data were plotted to produce a graph of chloride concentration with height above the waste. The profile of chloride concentration with height above the waste prepared for each core was subsequently compared with theoretical curves for a chloride diffusion front generated using a onedimensional solute transport model. 10

22 The results were used to verify available information on the chloride diffusion coefficient to be applied to future work (i.e., predictive modeling conducted to compare the landfill expansion alternatives). The results of this program to characterize the leachate and to update information on the rate of chloride diffusion through the cap are documented in stand-alone technical memoranda (Appendices D.4 and D.5) and summarized in Section 9. Included in the memoranda are: tabular summaries of the liquid levels observed at the new well installations; the laboratory analysis reports; and the results of the diffusion profiling of the cap (i.e., chloride profiles and computer generated curves). Monitoring of liquid levels in the various waste cells was continued to September Hydrographs generated for the 10 wells that were installed are presented in Appendix D.1.2. Second Step: The second step was to involve the compilation of information on the composition of the leachate produced from the treated waste at various Clean Harbors owned landfill facilities located in the United States. Processes to treat waste at these facilities, which is similar in composition to that received at the Lambton Facility, were implemented at the United States facilities in response to the Land Disposal Restrictions (LDRs) Program introduced in 1986 under 40CFR Part 268. The LDRs were introduced gradually over several years but were in full effect in the United States by the late 1990s. In reviewing the available information for these facilities, it was noted that the data collected are prescriptive to the compliance monitoring programs at these facilities and are limited to the chemical parameters that have regulatory criteria. Information on inorganic constituents of the treated waste including various major cations/anions considered germane to the analysis of conditions local to the Lambton Facility because of their persistence in the environment and historical use as tracers was not available. Further, no information is available on parameters in the post-treated waste that could form a precipitate and potentially affect the service life of a leachate collection system. The parameters of interest include ph, TDS, and the major ions (calcium, magnesium, potassium and sodium) and major anions (alkalinity, chloride and sulphate). To provide this information, samples representative of the various waste materials received at the Lambton Facility were obtained by sampling the waste immediately post-treatment at the process area (solidification product and thermal desorber residue). Sampling in the process areas, involved the collection of at least two samples each day (morning and evening) in each area, for a period of one week, which were stored in sealed containers. At the end of the week, the contents of the containers were combined (mixed) and a single sample collected for subsequent leaching/analysis. The process was repeated for a period of several weeks to ensure that the waste sampled is representative of the wide range of waste material processed at the facility. The composite samples were processed by a modified Toxic Characterization Leaching Procedure analysis (Ontario Regulation 327). The primary change was using a 1:1 extraction completed with Milli-Q TM, ultrapure Type 1 water instead of acid extraction to better represent leaching by precipitation. The extract for a total of five (5) composite samples, representing 5 weeks of waste receipts were analyzed for calcium, magnesium, sodium and potassium. 11

23 Subsamples of the five composite samples were then obtained, composited (Composite Sample 6), extracted and analyzed for the parameters listed in the following table: Parameter Grouping General Indicators Ions Parameters ph, TDS Alkalinity, Chloride, Sulphate, fluoride, bromide, nitrate and nitrite The results of this work are included in a Technical Memorandum (Appendix D.4) and summarized in Section 4.6. Shallow Groundwater Impacts: Two parameters (chloride and boron) have been detected at locations on the Clean Harbors property at concentrations that are of potential concern and required the collection of additional information. One of the concerns was the observation of a statistically significant increasing trend in chloride concentration at shallow monitoring well TW45-99S that is part of the Facility monitoring well network. Well TW45-99S is located near the western boundary of the Clean Harbors Canada, Inc. property between the main entrance to the Facility and Gate 1 (shipping/receiving) entrance just east of Telfer Road. The well, which is 5.2 m deep, is screened in the upper weathered/fractured portion of the overburden referred to as the Active Aquitard. The investigation involved drilling and well installation, water level monitoring and groundwater sampling. The information collected, is discussed in the report titled Investigation of Increasing Chloride Concentration at Well TW45-99S (RWDI, 2014b). The second concern was with respect to the detection of boron in a shallow well installed in the fill of the northern perimeter berm at concentrations exceeding the Ontario Drinking Water Objectives (ODWS) and the Provincial Water Quality Objectives (PWQO) and at two wells along the east property boundary above the PWQO. The nearest point of discharge for shallow groundwater at these locations is the south ditch adjacent to Petrolia Line. This ditch drains to the northeast (Perch Creek and Lake Huron). Samples of surface water were collected upstream and downstream of the Facility property and submitted for the analysis of boron. The information collected, is included in the aforementioned report (RWDI, 2014b) and has been summarized herein. Deep Groundwater Impacts: Chlorinated volatile organic compounds (VOCs) [primarily trichloroethylene (TCE) and cis-1,2- dichloroethylene (cis-1,2-dce)] have been detected at monitoring well TW22-99D located at the northwest corner of the property about 350 m south of Petrolia Line, between Telfer Road and the western perimeter berm. The well is screened against the overburden/shale bedrock interface (referred to as the Interface Aquifer). TW22-99D is part of the compliance monitoring well network at the Lambton Facility. TCE is not naturally occurring in groundwater indicating an anthropogenic source. An investigation was initiated to identify the potential source(s) of the TCE. The assessment of the source and pathway was largely focused on the possible movement of TCE from the landfill. The investigation involved drilling and well installation, water level monitoring and groundwater sampling. 12

24 The information collected and summary conclusions are provided in the Interim Report titled Investigation into the Source of VOCs Detected at Compliance Monitoring Well TW22-99D (RWDI, 2013c) and its Addendum titled Trichloroethylene (TCE) Investigation at TW22-99D (RWDI, 2014c). 3.2 Available Secondary Source Information There is a considerable volume of secondary source information on the geology and hydrogeology of Lambton County in general and the Clean Harbors property and the surrounding area, specifically. The sources considered in this document are referenced in the text of this report where applicable, and are listed in Section 11 - References Geology and Hydrogeology Investigations Regional Studies: The summary description of the regional geology and hydrogeology (Sections 6 and 7) is based on maps and reports completed by and for various public and private organizations including the Ministries of Environment and Northern Development and Mines, Geological Survey of Canada, Sarnia-Lambton Environmental Association (SLEA) and St. Clair Region Conservation Authority. The regional assessment also considered published and unpublished studies completed within Lambton County by University of Waterloo and University of Western Ontario staff and students to pursue academic interests. Many of the academic studies examined the processes that affect groundwater and chemical movement in the clay-enriched overburden present in Lambton County. Local Studies: Much of the secondary source information considered herein was generated over 40 years of investigative effort by consultants retained by Clean Harbors and its predecessors firms, and through University research conducted at the site. The various investigation reports and studies are identified in Section 11 and are referenced in the following text where applicable. A chronology of the various hydrogeology studies, which assessed existing conditions at the site, follows. The initial groundwater sampling program to characterize conditions at the Lambton Facility was completed by James F. MacLaren Limited (1974). This early work involved the installation and sampling of five monitoring wells. Additional wells were installed in 1979 by Hydrology Consultants (1980) and Conestoga Rovers & Associates (1980). The 1974 and 1979 series wells formed the groundwater monitoring network and monitoring (sampling/analysis) was focused on these installations until about A comprehensive assessment of groundwater conditions was undertaken by Hydrology Consultants Limited (1984) to support development of Cell 16 and Cell 17. The 1983/1984 investigations contributed substantially to the knowledge of the groundwater movement patterns and the spatial distribution of major/minor ions below the property. The Certificate of Approval issued in 1987, required that number of investigations to confirm/verify that the movement of solutes at the property was primarily through the process of chemical diffusion. 13

25 Additional wells were installed between 1984 and 1990 to satisfy these conditions and complete the compliance monitoring well network. In addition to the various investigations under Tricil (Sarnia) Limited and subsequently Laidlaw Environmental Services ownership, the companies provided the University of Waterloo and Geologic Survey of Denmark and Greenland with access to undeveloped areas of property to conduct a number of studies. These studies [Desaulniers (1980, 1986), D Astous and Ruland (1986), Ruland (1988), Balfour (1991), McKay (1991), Solomon (1991), Harris (1994), Murphy (1994), Cloutier (1994), Weaver (1994) and Klint (1996)] were directed at: improving the understanding of the local geology, groundwater flow, groundwater chemistry and the distribution of environmental isotopes; assessing the effects of groundwater resource water taking and oil/gas exploitation on hydraulic gradients and groundwater flow patterns; and assessment of the effects of weathering and fracture development on groundwater flow and contaminant movement. The two volume groundwater conditions study completed by Jagger Hims Limited (1996) presents the most detailed assessment of hydrogeological conditions at the Lambton Facility. This work was undertaken in support of the Cell 18 landfill expansion. The next significant hydrogeological investigation is incorporated into the reporting of the gas and water venting issue at Sub-Cell 3 of Cell 18 by Safety Kleen Inc. (2000) for the Ontario Ministry of the Environment. This work involved extensive drilling/well installation, water and gas sampling, and pumping tests. Additional hydrogeological studies that have contributed to the understanding of the geology, hydrogeology and geochemistry in the immediate are of the Lambton Facility property include: investigations in the northwest corner and along the west property boundary of the Facility property that involved the collection of soil core, and installation and monitoring of wells; and sampling of existing deep wells installed in the shale aquitard. The results of these studies are incorporated in this Report. The following is a list of the major hydrogeological investigations conducted at the Lambton Facility. Conestoga-Rovers & Associates (1980), and Hydrology Consultants Limited (1980), initial investigations to characterize the physical setting (hydrology, geology, hydrogeology and hydrochemistry). Hydrology Consultants Limited (1984a) investigation to support Tricil (Sarnia) Limited application for the expansion of the existing landfill operations (Cell 16/Cell 17). Dames & Moore, Canada (1992b) summary review of the hydrogeology undertaken pursuant to Condition 17 of the Provisional Certificate of Approval A (August 29, 1986) requiring a review of predicted groundwater impacts on the landfill extension area and the comparison of these impacts with monitored results collected over five years (1986 through 1991). 14

26 Dames & Moore, Canada (1992c/1993) investigation to assess the shallow groundwater system and to delineate the contaminant (chloride) plume adjacent to Pre-1986 landfill. Jagger Hims Limited (1996) investigation to support Laidlaw Environmental Services application for the expansion of the existing landfill operations (Cell 18). Safety Kleen Ltd. (1999/2000) investigation into the water/gas venting observed within Sub-cell 3 of Cell 18. This document was prepared by the consulting team engaged in this investigation. 3.3 Lambton Facility Groundwater Monitoring Program As a requirement of the Facility s operational permit, groundwater monitoring is conducted on a yearly basis at the Lambton Facility with the results of this monitoring documented in an annual groundwater monitoring report. These reports form part of the Annual Landfill Report that is generated by Clean Harbors to document the overall operations and compliance monitoring effort. Annual groundwater monitoring reports are available for the property extending back to 1982/1983. These reports present an overview of the work conducted during the year, a compilation of groundwater level and quality data, and a discussion of the major findings. If monitoring trends trigger an investigation, the results of the supplemental work effort are typically included in the annual report. The groundwater monitoring database for the Lambton Facility is large with water level and water quality data having been having been collected as part of routine monitoring at the Facility since Monitoring events have typically been completed on one or two occasions annually. The current (2013) monitoring program involves the completion of two monitoring events per year, employing a network of 50+ monitoring wells that were installed between 1992 and 2013 (locations shown in Figure 3-3 and Figure 3-4). The results of the most recent monitoring (period extending between September 2012 and September 2013) are provided in the 2012/2013 Groundwater Monitoring Report. Monitoring involves the measurement of groundwater levels, and the collection and analysis of groundwater samples. The water level monitoring is undertaken to establish the hydraulic head distribution in the hydraulically active geologic units below the Lambton Facility. This information is compared with historical data to identify trends in groundwater level elevations. The groundwater samples are submitted to commercial laboratories and analyzed for the parameters identified in the Table 3-2. The groundwater level and chemistry data are compiled, examined in the context of previous monitoring results and summarized annually for inclusion in the Annual Landfill Report for the Facility. 15

27 Table 3-2. Annual Groundwater Monitoring Program Chemical Parameters Parameter Grouping General Indicators Major Ions Minor Ions Metals* Anions Cations Nutrients Miscellaneous Aromatic Hydrocarbons** Parameters ph, Conductivity, TDS Alkalinity, Chloride, Sulphate Calcium, Magnesium, Potassium, Sodium Ammonia (shallow wells only), Nitrite, Nitrate Bromide, Cyanide, Fluoride Arsenic, Barium, Boron, Cadmium, Chromium, Iron, Lead, Nickel, Mercury, Zinc Benzene, Toluene, Ethylbenzene, Xylenes Halogenated hydrocarbons** Note: Chloroethane, 1,1-Dichloroethane, 1,2-Dichloroethane, 1,1,1- Trichloroethane, Trichloroethylene, 1,2 Dichlorobenzene, 1,4 Dichlorobenzene, Methylene Chloride (*) Analyzed on an annual basis during the spring sampling event. (**) VOCs are analyzed sitewide every two years The chemistry data for the yearly sampling event are initially compared with the full database for past monitoring events to flag any outliers or anomalies in the year s data. Any outliers or anomalies in the data are assessed in greater detail to determine if a statistically significant trend is emerging. Actions triggered by this review may include repeat sampling/analysis. Comparison of Annual Data with Provincial Water Quality Criteria: On a yearly basis, the chemistry data are compared with the Ontario Drinking Water Standards (ODWS) and Guideline B-7 values derived from the ODWS. The shallow groundwater data are also compared with the Provincial Water Quality Objectives (PWQO). Guideline B-7 was established by the MOE as a mechanism to evaluate whether the concentrations of chemical parameters moving outward from a waste disposal site through the groundwater have the potential to affect its use as a source of supply. This guideline, which is applied at the property boundary, is intended to be protective of both existing and potential reasonable use of water on adjacent properties. The comparison with the PWQO is undertaken because the shallow groundwater eventually discharges to drainage swales and roadside ditches where its mixes with surface runoff. Use of Indicator Parameters: The analysis of trends has focused on a subset of parameters (chloride, sodium, sulphate, potassium, fluoride, barium, bromide and boron), the concentrations for which provide an indication of the potential source of the groundwater (i.e., shallow overburden or bedrock). It has been established that parameter concentrations differ significantly between each of the sources. These parameters are also present in the leachate at elevated concentrations and their detection at increasing concentrations in monitoring wells may be indicative of a water quality impact by contaminant movement from the landfills. 16

28 Table 3-3 list the indicator parameters and concentrations observed for samples collected from monitoring wells installed in the Active Aquitard, Inactive Aquitard, Interface Aquifer and Shale Aquitard. The chemistry data are compiled from Jagger Hims Limited (1996) and were collected from areas that were undisturbed by landfilling activities at the time the wells were installed. Also included in Table 3-3 are ratios of parameter/chloride concentrations, calculated from the average concentrations. Chloride and sodium concentrations increase with depth, and sulphate concentrations decrease. Potassium, barium and boron concentrations are comparatively elevated in samples from wells installed in the Shale Aquitard. The high average boron concentration in the Inactive Aquifer is most likely an anomaly (data from a single well installation). The parameter/chloride concentration ratios decrease with depth. The indicator parameter data for each well and sampling event are initially compared with the average parameter concentrations and parameter/chloride concentrations established for groups of wells installed at similar depths and location. For example, the shallow wells are assigned to a broad group, which is subdivided based on the wells location (off-site, near berms, near waste cells, etc.). The deep wells are similarly assigned to a single group, which is also subdivided based on the wells location (wells located off-site, internal to the property and along the perimeter of the property). Increases/decreases in indicator parameter concentrations in samples from the monitoring wells outside the typical range established for the well and well group are highlighted triggering additional review. The monitoring event-specific average concentrations for four of the indicator parameters (chloride, sodium, sulphate, potassium) for each well and group of wells are graphed, to visually identify any trends in these parameters and the data for the individual wells are analyzed statistically (linear regression approach) to establish if there is an emerging trend in the concentration for the well. Shewhart derived Upper Control Limits or UCLs (Starks, 1989), are applied to the graphed chemical data for individual wells to distinguish between long-term trends in parameter concentrations and any short-term concentration spikes that occasionally occur in a data set. The UCLs are calculated from the following equation: UCL = + ZS where: = mean background concentration of the parameter; Z = constant [a value of three (3) standard deviations has historically been used at the Lambton Facility in preparing the control charts]; and, S = standard deviation of the sample set. Using a Z constant of three (3), the probability of a random sample (i.e., spurious value) exceeding the UCL is not greater than [1/(3) 2 x 100%] or 11%. The parameter specific UCLs are calculated using the mean parameter concentration and standard deviation derived from the initial eight (8) sampling events for the well. This use of early time data is premised on the awareness that chemical movement through the clay till is by molecular diffusion which is a very slow process. Therefore, the monitoring wells installed in the Interface Aquifer, at the time of their installation, are not expected to be affected by Facility operations including landfilling. 17

29 Table 3-3. Natural Groundwater Sources Indicator Parameters Concentrations Active Aquitard (Undisturbed Areas) Inactive Aquitard Interface Aquifer Shale Aquitard Chloride Range [mg/l] 4 to to to 389 5,850 to 20,000 Average [mg/l] ,900 Range [mg/l] 20.9 to to to 530 5,320 to 11,000 Sodium Sulphate Potassium Fluoride Barium Bromide Boron Average [mg/l] ,160 Concentration as a Ratio of Chloride Range [mg/l] 55.3 to 1, to 77 <5 to 15 <5 to 7 Average [mg/l] Concentration as a Ratio of Chloride E-4 Range [mg/l] 2 to to to to 20 Average [mg/l] Concentration as a Ratio of Chloride E-3 1.4E-3 Range [mg/l] <0.05 to to to to 0.65 Average [mg/l] Concentration as a Ratio of Chloride E-3 5.0E-5 Range [mg/l] <0.002 to to to to 6.24 Average [mg/l] Concentration as a Ratio of Chloride 2.9E-3 7.3E-3 7.7E-4 3.1E-4 Range [mg/l] <0.5 <0.5 <0.5 <5 Average [mg/l] <0.5 <0.5 <0.5 <5 Concentration as a Ratio of Chloride <0.03 <5.9E-3 <1.9E-3 <3.9E-4 Range [mg/l] <0.03 to to to 7.66 <0.5 to Average [mg/l] Concentration as a Ratio of Chloride 1.4E E-3 4.0E-4 Notes: Data from Tables D.1-4 Supplemental Sampling Program, Table D.1-8, Table D.1-9 and D.1-10 Jagger Hims Limited (1996a). The chloride ratios are calculated from the average parameter value. 18

30 Any parameter that exceeds the UCL would trigger an investigation into what caused the UCL value to be exceeded. For shallow wells this would likely represent a localized contaminant release at the Facility. For wells in the Interface Aquifer, considering that contaminant movement downward through the clay till is expected to be very slow, a sudden increase in concentrations would be indicative of either an open borehole or pathway by which contaminants could move downward under advection or possibly a faulty annular seal around the well casing or damage to the monitoring well allowing mixing of shallow and deep groundwater. 19

31 4.0 Facility History and Operations 4.1 Background The 121 hectare property occupied by the Lambton Facility, has undergone a number of ownership changes, starting with Goodfellow Enterprises (Sarnia) Limited acquiring the property in 1960 for the purpose of developing a waste management facility. Figure 4-1 shows the locations of the major above ground structures and the approximate locations of the various waste cells on the property. Property ownership and the progression of development of the property are presented in Table 4-1. The Lambton Facility, which is operated under Certificate of Approval A031806, includes an analytical laboratory, transportation terminal, high temperature incinerator, physical chemical treatment/process area and a secure landfill. Clean Harbors Canada, Inc. currently manages pretreated and untreated solid and liquid hazardous waste originating primarily in the Province of Ontario, as well as the rest of Canada and the United States. The Lambton Facility is operated in accordance with the Facility s Design and Operations report, the most recent version is dated August 6, Landfill Operations and Design The following history of the landfill operations is compiled from information provided in Jagger Hims Limited (1996) and various Design and Operations reports that have been prepared to document changing site operations. The locations of the various waste cells referenced below are shown in Figure 4-1. General information on the landfill operation and size of the landfill area is provided in Table Pre-1986 Landfill Operation The Goodfellow Enterprises (Sarnia) Limited landfill operation involved relatively shallow (5 m to 10 m) isolated excavations (referred to as Cells C through I, which were reportedly used as lagoons for liquid waste and sludge retention, and two larger cells A and B that were excavated to depths of between 12 m and 18.3 m and received industrial waste, construction debris and municipal solid waste. The S-Pit, which was excavated to 18.3 m, contains styrene sludge. Tricil (Sarnia) Limited on acquiring the property in 1976, drained the various lagoons (liquids being processed or incinerated) and backfilled the lagoons with waste to grade. The cells were covered with 1 m to 2 m thickness of excavated clay. The S-Pit was not backfilled and remains open. [Note: Conestoga and Rovers Associates Limited undertook a field investigation of the S-Pit in 2009, which involved the advancement of three angled boreholes through the sidewall of the pit and into the base. The depth of the pit was determined to be between 8 m and 9 m.] Between 1976 and 1981, the landfill operation continued to involve the excavation of isolated cells to depths ranging from 9.2 m to 18.3 m below ground surface, with sidewall slopes as steep as 2V:1H (63 from the horizontal). The cells were backfilled with waste to 2 m to 4 m above grade and covered with 1 m to 2 m of excavated clay. 20

32 Table 4-1. Lambton Facility - Development History Property Ownership Goodfellow Enterprises (Sarnia) Limited Interval Progression of Development 1960 to 1973 Installation of liquid waste incinerator (1968), various storage tanks and conversion of exploration well for use as a deep disposal well (1961). Installation of second deep disposal well (1973). Excavation of several shallow pits/lagoons, including S-Pit for temporary liquid waste storage and excavation of isolated landfill cells A through I, (5.5 m to 9 m deep) for industrial and municipal waste disposal. Tricil (Sarnia) Limited 1973 to 1990 Landfilling restricted to industrial/hazardous waste. Laidlaw Environmental Services Decommissioning of pits/lagoons, except for S-Pit (between ). Construction of new liquid waste incinerator (1983), demolish of original incinerator (1986). Use of deep disposal wells discontinued in 1976 and wells sealed in Between 1976 and 1979, excavation and placement of waste in isolated landfill cells 1 to 2c (9 m to 15.3 m deep). Between 1979 and 1981, excavation and placement of waste in isolated landfill cells 3 to 11 (15.3 m to 18.3 m deep). Between 1981 and 1985, excavation and placement of waste in continuous trench 12 to 15 (9.2 m to 18.3 m deep). Between 1985 and 1986, placement of waste above existing waste cells A, I, 2a, 2b, 2c, 14 and 15, and re-graded area. Construction of physical/chemical pre-treatment plant (1986) Approval of EA to continue landfilling operations (Cells 16 and 17 ). Adopt shallow entombed landfill concept (excavation to 18.3 m and placement of cap from 6.1 m to grade). Between 1986 and 1990, excavation and placement of waste in continuous trench Cell 16 (18.3 m deep) to closure of continuous trench 16 (18.3 m deep). Between 1990 and 1997, excavation and placement of waste in continuous trench Cell 17 (18.3 m deep) Approval of EA to continue landfill operations (Cell 18). Continuation of shallow entombed landfill concept (excavation of primary cell to 14 m and a series of trenches depth between 14 m and 24.4 m. Reduction in waste cap thickness to 5.1 m. Between 1997 and 1998, excavation and placement of waste in continuous trench 18, Sub-cells 1 and 2. Safety-Kleen Inc.* 1998 to 2002 Between 1998 and 1999 continued landfill (Cell 18), waste sub-cells 1 and 2 Clean Harbors Canada, Inc. September 6, 2002 to present excavated to 24.4 m un-stable bottom conditions during excavation of Trench 18, Sub-cell 3. Sub-cell 3 isolated with placement of barrier (2001). Landfill base for subsequent sub-cells decreased to maximum depth of 18.3 m landfill design modified to recover waste capacity lost as a result of the isolation of Sub-cell 3. Infilling of western area between Cell 17 and Cell 18, raising top of waste over west end of Cell 18 by 4 m. Cap thickness remains same (5 m) LDR Facility for treatment of inorganic waste stream LDR Thermal Desorption Treatment and Recycling Plant. (*) Laidlaw Environmental Services acquired Safety-Kleen Inc. in 2000 and operated the facility under this adopted company name until 2002, when Clean Harbors Inc. purchased the then chemical waste management division of Safety-Kleen Inc. 21

33 The landfill design for Cells 12 through 15 was modified in 1981 to a progressive trench and fill methodology. The trench, with sidewall slopes of 2V:1H, was excavated to a maximum depth of 18.3 m. As the excavation and filling progressed, the open area of the waste was covered by 1 m to 2 m of compacted clay obtained from the advancing face. Tricil (Sarnia) Limited submitted an application to expand the landfill in 1984 and was undergoing an environmental assessment in 1984 through The process took longer than expected and by late 1985, the area available for landfilling had reached capacity. With Ministry of Environment approval, landfilling was continued in the area encompassing Cells A, I, 2a, 2b, 2c, 14 and 15. This involved stripping a portion of the cap, placement of waste and replacement of the cap. The height of the landfill after cap placement over these cells was raised to as much as 7 m to 8 m in some areas (Cells A, B and 15). The area of the landfill occupied by waste cells that pre-dates 1986 is referred to as the Pre-1986 Landfill Landfill Operation ( ) A Certificate of Approval was issued by the Ministry of Environment for extending Landfill operations (i.e., Cells 16 and 17) in Landfill cell design was modified with the initiation of the entombment concept of landfilling. This design involves the isolation of waste below the near surface weathered zone in which active ground water movement occurs. The operation continued to employ a cut and fill approach with a trench excavation to a depth of 18.3 m. Waste is placed from the base of the cell trench to a height of about 12.2 m below grade and capped with 6.1 m of clay. The sub-cells are separated at the base of the excavation by small sub-cell berms of undisturbed till about 3 m high with a top width of about 2 m and a bottom width of 5 m. These berms segregate leachate produced at the toe of the waste from clean surface water runoff that accumulates in the next sub-cell. Ponded leachate is pumped from a shallow sump at the base of the active sub-cell to the existing contaminated water reservoir for subsequent use as process water for the incinerator operation. Surface water runoff is removed from the excavation in a similar fashion and discharged to perimeter collection ditches adjacent to Cells 16 and 17. Laidlaw Environmental Services acquired the Tricil assets in In 1994 the company initiated a number of studies to support an application to the MOE to expand the landfill. This expansion (referred to as Cell 18) was approved by the MOE after extensive stakeholder review and consultation in Construction of Cell 18 was initiated late in 1996 at the west side of the property by extending a trench northward from Cell 17. The landfill design was modified by increasing the depth to 24.4 m below grade and adjusting the cap thickness to 5.1 m. The initial Sub-cell (Sub-cell1) was advanced by the same progressive trench and fill methods employed for the previous cells to produce an initial open excavation to an elevation of 186 masl. A series of trenches were then excavated at the base of the sub-cell to elevations between 182 masl and 176 masl, which were immediately backfilled with waste. As construction progressed northward additional waste was placed above the lower trenches to fill the western portion of the sub-cell to within 5.1 m of surface (elevation of 195 masl). 22

34 This process was repeated as the excavation advanced northward to the northern limits of the Sub-cell 1. The operations for Sub-cell 2 were generally similar, with the excavation advancing southward. The size of the individual trenches was increased, while excavation depth was maintained between 175 masl and 179 masl. As a consequence, the size of the open excavation was enlarged. Waste placement occurred from east to west across the two cells until the eastern portion of Sub-cell 1 was brought to grade after which it was capped with compacted clay to complete the sub-cell. Leachate and surface water runoff continued to be managed separately in the manner described above for Cells 16/17. Laidlaw Environmental Services acquired Safety-Kleen Inc. in 1998 and continued operations as Safety- Kleen Inc. By late August 1999, the western portion of Sub-cell 2 had been partially backfilled with the waste surface sloping upward from the bottom of the east side of the sub-cell into Sub-cell 1. Excavation had proceeded into Sub-cell 3, advancing from the south to the north. Trench (Trench 313) at the southwest corner of Sub-cell 3 had received waste and a portion of the west central area of Sub-cell 3 (Trenches 304, 307 and 310) had been excavated below the primary cell depth of 186 masl to an elevation of about 176 masl Cell 18 Sub-Cell 3 During excavation of Sub-Cell 3 of Cell 18, seepage/venting of gas and water was observed during routine inspection on September 3, 1999 at the base of a berm that separate the initial excavated trench (Trench 313) from the next trench to the north (Trench 310). Waste placement in Trench 313 was discontinued and efforts were directed to isolating the seep and to characterize its source. It was established that the water exhibited chemistry similar to that of the groundwater at the overburden and bedrock interface. Excavation of the northern and eastern portions of Sub-cell 3 continued without incident until September 17, 1999, at which time an additional seep was observed at the base of the excavation (Trench 304). All construction and landfilling activities in Sub-cell 3 ceased. In total three vents/seeps referred to as Seep A, Seep B and Seep C were identified (locations shown in Figure 4-2). Various meetings were held with the MOE to review the situation and to discuss methods for isolating the seeps from the adjacent excavated areas that had received waste. These measures included installing casing over the seeps to maintain access for monitoring purposes, widening and increasing the height of the separation berms and the placement of 4 m of compacted clay in the base of the trench excavations to load the base of the excavation and stabilize the berms. From the date of discovery through February 2000, the three seeps became the focus of a detailed investigation that involved the installation of several wells, collection of water samples and the performance of pressure tests. It was determined that the water and gas flow originated in the Interface Aquifer. 23

35 Considering the source of the water/gas, it was concluded that conduits (i.e., fissures) had formed between the location of the seep in the base of the sub-cell and the bedrock. The fissures provided an upward pathway for the release of the higher hydrostatic pressure in the Interface Aquifer and the venting of natural gas. Following an in-depth assessment of the phenomenon, it was determined that a combination of factors caused the formation of the conduits. The most important factor was the presence of an elevated bedrock ridge below Sub-cell 3 (shown in Figure 6-7). As the cell was being excavated to the approved depth of 24.4 m, this bedrock ridge resulted in a thinning of the clay layer separating the excavation from the bedrock high. This thinning of the clay layer, in combination with high hydrostatic head pressures in the Interface Aquifer, created high shearing stresses causing vertical fractures to develop in the clay, along with shallow tensile cracking (a normal product of excavation). A full description of the investigations that were conducted is provided in Safety-Kleen Ltd. (2000). As the distribution of these factures at depth can be determined there was no measure available to seal the fractures. It was therefore concluded that the only practical was for dealing with the vents/seeps was to install a remedial structure consisting of gravel-filled perimeter trench (installed around the affected areas) connected to a gravel blanket placed over and in hydraulic connection with the fractures. This gravel layer would allow for the continued upward movement of the gas/seepage and its accumulation in the gravel. The design also called for the entombment the gravel in a thick clay barrier. It was intended that wells would be installed in the gravel and pumped at a controlled rate to maintain a water level in the gravel that is lower than both the potentiometric level in the Interface Aquifer and the leachate level in adjacent landfill cells containing waste. The purpose of this action is to create an inward pressure gradient, which would maintain an upward pressure/flow from the bedrock into the gravel. This would eliminate the potential for water/leachate to move downward through the fractures to the bedrock. The gravel layer (and the wells used to maintain water levels in the gravel) is referred to as Hydraulic Control Layer or HCL. A remedial plan outlining the proposed mitigation was developed and submitted to the MOE on March 31, 2000, initially in draft, and was subsequently finalized (Safety-Kleen Ltd. (2001) and presented to the Township of St. Clair, the Public Liaison Committee, Walpole Island First Nation, and other interested parties. The remedial structures (HCLs) are shown in plan and in cross section in Figure 4-3 and Figure 4-4, respectively. The northern HCL encompasses Seep B and the immediate surrounding area. The southern HCL encompasses Seep A and Seep C, and the adjacent area. The clay layer that was placed above and around each of the HCLs includes a 5 m thick compacted clay liner, a compacted clay key (both constructed to achieve a specified degree of compaction), and clay backfill above the liner. The clay key constructed around the perimeter of the clay liner is intended to reduce the volume of water that could potentially move through tension fractures formed at the base of the excavated cell below the clay liner towards the HCLs. The clay backfill placed above and adjacent to the clay liner is intended to provide structural support to the clay liner and to provide physical protection for the clay liner. 24

36 In preparation for construction: waste and leachate in Sub-cell 2 and in Trench 313 of Sub-cell 3, was moved and drained (March 2001); additional geotechnical monitors were installed to assess stability of slopes and at the base of the excavation (March-April 2001); and, pumping from two wells installed in the Interface Aquifer was initiated to reduce the hydraulic pressure head in the Aquifer in the affected area with the goal of improving the basal stability of the excavation during construction of the HCLs and clay barrier(in April 2001). Approval was received from the MOE in May 2001, to initiate construction of the clay liner and HCLs. This work was started in late-may 2001 and continued until mid-october 2001 with the placement of clay backfill to provide winter protection of the clay liner constructed over the HCLs. Boreholes were drilled in November 2001 through the clay liner/backfill into the HCLs and extraction wells (EW1a-01 and EW2a- 01) were installed in each borehole. The screened portion of each extraction well was set against the gravel in the HCL. The extraction wells were then equipped with pumps and pumping was initiated to draw the water level in the HCLs down to a prescribed level below the potentiometric head in the Interface Aquifer, to maintain inward hydraulic gradient. Pumping of the Interface Aquifer to reduce the hydraulic pressure head was then discontinued. A monitoring program that involves measurement of water levels and collection and analysis of water samples at the various wells was implemented to assess the performance of the remedial structure. The water level data are collected to confirm that an appropriate pressure head differential between the HCLs and Interface Aquifer is maintained. The discharge streams from the HCL extraction wells are sampled at a semi-annual frequency as part of the routine groundwater program performed at the Lambton Facility. The monitoring results are documented in the Annual Groundwater Monitoring Report. In accordance with the remedial plan, additional wells were installed in the HCL for monitoring purposes and if necessary in the future could be equipped with pumps to draw the water level in the HCLs down to maintain inward hydraulic gradients. The final grade at Sub-cell 3 was not achieved until early The additional wells (EW1b-13, EW1c-13, EW2b-13 and EW2c-13) were installed mid Monitoring conducted to assess the performance also includes to existing monitoring wells installed in the Interface Aquifer [PW1-N and PW2-S/PW2-S(R11)]. The locations of the various wells are shown in Figure 4-3. The volume of water extracted from the two HCLs is monitored using flow accumulators on the pumps. The total extracted over the last three years (September 1, 2010 through August 31, 2013) is summarized below: Extraction Period HCL Pumping Wells Southern Well (EW1a-01) Northern Well (EW1a-01) Sep 1, 2010 to Aug 31, m m 3 Sep 1, 2011 to Aug 31, m m 3 Sep 1, 2012 to Aug 31, 2013 counter malfunctioned, averaged daily pumping rate between 6.5 and 10.7 L/day m 3

37 The water is discharged onto the cap of Sub-cell 3 and moves as overland flow to a perimeter ditch north of Sub-cell 3. For the most part, the HCL extraction system is functioning as design, maintaining hydraulic gradients that are inward into the HCL. Problems were however experienced in 2011 as a result of wide-spread flooding of Sub-cell 3 and portions of Sub-cell 2. Water ponding in the vicinity of the two extraction wells and one of the monitoring wells [PW2-S(R11)] installed in the Interface Aquifer rose to a level over toping the protective well casings allowing surface water to enter the wells. The wells were not accessible for a period of time and pumping at the two extraction wells ceased. The water levels rose to above the level in the Interface Aquifer resulting in a reversal of the hydraulic gradients. This incident and corrective measures that were undertaken are described in detail in 2012 Annual Groundwater Monitoring Report Landfill Operation (2000 to Present) Landfilling operations, which resumed in 2000 at Cell 18 Sub-cell 4, involved limiting the total depth of the excavation to 18.3 m (elevation of about 182 masl). The isolation of Sub-cell 3 and reduction in excavation depth for Sub-cells 4 through 12 resulted in a 600,000 m 3 reduction in landfill capacity. Clean Harbors Canada, Inc. acquired the Safety-Kleen Inc. chemical management division in The company approached the MOE in 2003 with a proposal to regain the approved landfill capacity lost as a result of Sub-cell 3 and the subsequent reduction in the cell excavation depth. The proposal called for the following modifications to the design: expansion of the waste limits of Cell 18 (Sub-cells 8 through 12) by approximately 4 m to the north (consistent with initial landfill dimensions per 1996 approval); increasing the height of the waste within the footprint of Sub-cell 4 through 12 to a depth of about 0.6 m below natural grade (elevation of masl); and construction of a new Sub-cell (Sub-cell 14) between Cell 18 and Cell 17. The thickness of the compacted clay cap above the waste was maintained at 5.1 m but was extended outward from Cell 18 into a bench ( key ) cut along the sidewall of the cell. This proposal was reviewed and approved by the MOE in 2003 and subsequently implemented. Sidewall instability occurred during excavation of Sub-cell 14 resulting in flatter sidewalls and an estimated loss in landfill capacity of 101,700 m 3. Clean Harbors submitted a plan to the Ministry of Environment (MOE) that involves the construction of a new sub-cell (Sub-cell 15) consisting of three shallow trenches to be excavated in the existing cap of Cell 17, and that overlying part of Sub-cell 1 and Sub-cell 2 of Cell 18. The design for Sub-cell 15 calls for trenches to be excavated to a depth of masl, with a portion of the existing cap over Cell 17/18 to remain in place. The trenches will receive approximately 2.7 m of waste to a top of waste elevation of masl, which is below the existing ground surface elevation (201 to 202 masl) and on completion, the waste will be capped. 26

38 The plan was approved by the Moe (Amendment to Environmental Compliance Approval, Number A031806, Notice No. 8, Issue Date: May 3, 2013). 4.3 Current Limits of Waste Disposal Waste is currently being placed in Sub-cell 14 located between the eastern portion of Cell 18 and Cell 17. This sub-cell has a base elevation of approximately 182 masl. The current limit of waste disposal is presented in Figure 4-2. A detailed description of landfill construction activities during the 2012/2013 monitoring period is available in Appendix F of the 2013 Annual Landfill Report. 4.4 Volume of Waste The volume of waste received at the Lambton Facility and the current available approved capacity is summarized in Table 4-2. Once the available capacity has been achieved, the landfill will occupy about 56 hectares of the 121 hectare property and contain approximately 4.28 million m 3 of waste. 4.5 Waste Composition The composition of the waste received and landfilled at the Facility has varied significantly over the years, being influenced by changing waste streams (different waste generators or new/modified production processes) and adjustments to the Facility s Provisional Certificate of Approval. Goodfellow Enerprises (Sarnia) Ltd. initially accepted industrial and domestic/municipal solid waste for landfilling and industrial aqueous waste for deep well disposal and incineration. Following the Tricil (Sarnia) Limited acquisition of the site in 1973, landfilling was restricted to waste that was not acceptable for disposal at municipally-owned sanitary landfill sites. The deep well disposal operations were discontinued in The waste following its characterization and acceptance at the Facility, and treatment if warranted, is placed in the landfill. This treatment historically may have involved neutralization, dewatering and mixing/solidification with incinerator ash at the site s physical chemical treatment units to improve stability. The waste management operations were extensively modified following the promulgation of Land Disposal Restriction (LDR) and the subsequent amendment of Regulation 347 (O. Reg. 347) of the Revised Regulations of Ontario, 1990, made under the Environmental Protection Act (EPA) in As a consequence, all waste directed for disposal in Ontario landfills starting in 2007 is to be treated either at the generators facility or at the receiving facility prior to disposal. To accommodate its customers, Clean Harbors Canada, Inc. constructed a Landfill Pre-treatment System Plant in 2007 for treatment of the inorganic waste stream and added a Thermal Desorption unit in 2010 for the organic waste streams. 27

39 Table 4-2. Landfill Areas - History and Physical Dimensions Cell Years of Waste Type Landfill Type Maximum Depth Maximum Waste Height Waste Cap Thickness Estimated Cell Estimated Waste Notes Designation Operation of Excavation (m) Thickness (m) above Grade (m) (m) Surface Area (m2) Volume (m3) A 1960 to 1973 isolated cell , ,000 several small cells, additional waste placed in 1985/1986 and area regraded B 1960 to 1973 isolated cell , ,000 several small cells C 1960 to 1973 lagoon/isolated cell ,900 34,000 D 1960 to 1973 Hazardous Industrial Waste, lagoon/isolated cell ,700 E 1960 to 1973 Construction Debris, Liquid lagoon/isolated cell ,800 72,000 several small cells F 1960 to 1973 Waste & Municipal Solid Waste lagoon/isolated cell ,680 10,000 G 1960 to 1973 lagoon/isolated cell ,500 9,000 H 1960 to 1973 lagoon/isolated cell ,000 12,000 I 1960 to 1973 lagoon/isolated cell ,400 63,000 several small cells, additional waste placed in 1985/1986 and area regraded TOTAL 61, ,700 S-Pit 1960 to 1973 Liquid Industrial lagoon 9 9 na open 2,700 na Depth and size based on CRA drilling program and airphoto interpretation to 1979 Industrial Waste isolated cell ,000 48, to 1979 Industrial Waste isolated cell ,600 71,000 several small cells 2a 1976 to 1979 Industrial Waste isolated cell ,075 80,000 additional waste placed in 1985/1986 and area regraded 2b 1976 to 1979 Industrial Waste isolated cell ,375 15,000 additional waste placed in 1985/1986 and area regraded 2c 1976 to 1979 Industrial Waste isolated cell ,900 49,000 additional waste placed in 1985/1986 and area regraded to 1979 Industrial Waste isolated cell ,600 35, to 1979 Industrial Waste isolated cell ,825 37, to 1981 Industrial Waste isolated cell , to 1981 Industrial Waste isolated cell , to 1981 Industrial Waste isolated cell , to 1981 Industrial Waste isolated cell , to 1981 Industrial Waste isolated cell ,000 21, to 1981 Industrial Waste isolated cell ,380 27, to 1981 Industrial Waste isolated cell ,400 38,000 TOTAL 54, , to 1982 Industrial Waste progressive trench and fill ,375 14, to 1982 Industrial Waste progressive trench and fill ,000 10,000 13a 1981 to 1982 Industrial Waste progressive trench and fill ,070 17, to 1984 Industrial Waste progressive trench and fill , ,000 additional waste placed in 1985/1986 and area regraded to 1985 Industrial Waste progressive trench and fill , ,000 additional waste placed in 1985/1986 and area regraded TOTAL 54, ,000 Cell 16 and Cell 17 Landfill Area to 1990 Industrial Waste entombment , , to 1994 Industrial Waste entombment ,125 1,000,000 TOTAL 140,000 1,460,000 Cell 18 Landfill Area 131,150 1,910,000 Cell 18, Subcells 1 and to 1999 Industrial Waste entombment ,820 Sub-Cell 3 (Capacity Loss) , ,000 Cell 18, Subcells 4 and to 2011 Industrial Waste modified entombment dimensions adjusted see below 69,690 modification to cell design to recover airspace, additional waste placed to 0.6 m of grade TOTAL 109,510 1,310, Landfill Capacity Recovery 600,000 Cell 18, Waste placed in Subcells 4 to 12 to 0.6 m below grade 2004 to 2011 Industrial Waste modified entombment ,550 New Subcell 14, Trench to 2013 Industrial Waste modified entombment ,266 76,000 New Subcell 14, Trench to 2013 Industrial Waste modified entombment ,689 48,000 New Subcell 14, Trench to 2013 Industrial Waste modified entombment ,571 56,200 Projected Capacity, Trench 1401 and Current Industrial Waste modified entombment ,500 Cell 18, Sub-cell 14 Side wall instability Capacity Loss -12, ,700 footprint of excavation reduced TOTAL 15, , Landfill Capacity Recovery Cell 17, Sub-cells 19-25, Cell 18, south portion of Subcells 1 and 2 Industrial Waste modified entombment , ,700 would involve 3 to 4 m deep excation into existing cap over Cells 17 and 18 Note: Table modified March 14, 2013 from Table A.1-1, Appendix A.1, Jagger Hims Limited, 1996

40 The inorganic waste stream undergoes treatment prior to placement in the landfill. The treatment processes include neutralization and solidification/stabilization. Solidification involves the addition of cement, fly ash and other agents that alters the physical properties of the waste through pozzolanic reaction. Treatment renders the waste non-corrosive, lowers the solubility of the inorganic constituents in the waste and alters the physical properties of the waste by binding the particulates to the materials that are added. The solidified waste mass on landfilling is expected to have a lower hydraulic conductivity making it less prone to leaching. As the process involves chemical additions, the total volume of the waste after treatment, increases. Waste containing listed LDR organic constituents starting in 2011, been treated at the Lambton Facility by the process of thermal desorption. The waste is heated to volatilize the organic constituents from the solid matrix and the off-gas is subsequently cooled to condense the volatilized contaminants. The liquids are collected and recycled. The off-gas is piped to the on-site incinerator for destruction of any residual organics in the gas. The waste after treatment is either landfilled directly or if necessary, depending on other constituents, stabilized employing the treatment method for the inorganic waste streams. In October/November 2012, Clean Harbors staff collected daily samples of treated waste and generated weekly composites that were processed by a modified Toxic Characterization Leaching Procedure analysis (Ontario Regulation 327). The extract for a total of five (5) composite samples, each representing one week of waste receipts were analyzed for calcium, magnesium, sodium and potassium. The results are presented in the following table. Sample I.D. Calcium [mg/l] Magnesium [mg/l] Sodium [mg/l] Potassium [mg/l] Composite , Composite Composite , Composite , Composite Average , Composite Sample 6 represents 16 days of waste receipts, was processed using a 1:1 extraction completed with Milli-Q TM, ultrapure Type 1 water instead of acid extraction and analyzed for general chemistry and anion parameters as follows: Composite 6 Parameter Concentration (mg/l) Parameter Concentration (mg/l) Alkalinity (expressed as CaCO3) 501 Nitrate 8 ph 9.24 Nitrate 17 TDS 10,000 Bromide 99 Fluoride 81 Sulphate 2,317 Chloride 1,518 29

41 4.6 Leachate Levels and Composition As indicated in Section 3.1.2, a field program was undertaken as part of the supplemental work program to collect additional information on liquid levels and the composition of the leachate in the waste cells. This work builds on the database assembled in 1995 as part of the investigations completed to support the Landfill Expansion EA (Jagger Hims Limited, 1996). The field program involved advancing 10 boreholes through the landfill cap in the various cells of the Lambton Facility and installation of wells in the waste below the cap. Schlumberger Micro-Diver dataloggers were installed in the wells in late August 2012 to record liquid levels and barometric pressure at frequency of once per hour for a period of one year. Leachate samples were collected from the wells in August and November The liquid levels were adjusted to compensate for density. The borehole/well locations are shown in Figure 3-2. A Technical Memorandum documenting the results of this field program is presented in Appendix D.4 of the Report. A discussion of the findings is presented herein. Hydrographs generated for the wells that cover the period August 2012 through August 2013 are included in Appendix D.1.2. Chemical parameters detected at measurable concentrations and the range in concentrations, are listed by well location (Pre-1986 Landfill, Cells 16/17 and Cell 18) in Tables D.4-1 through D.4-3 (Appendix D.4). Included in the compilation are data collected in 1995 and that for the most recently installed wells. Summary information on the range in concentrations for chemical parameters that have been used at the Lambton Facility to distinguish between sources of groundwater (Section 3.3) for leachate samples collected from monitoring wells installed in waste cells is presented in Table 4-3. With the exception of boron, the concentrations of the indicator parameters are one to three orders of magnitude higher than that observed for groundwater. The composition of the leachate exhibits significant spatial variability being influenced by the composition of the waste in the vicinity of the wells. The concentrations of the inorganic and organic parameters detected in the leachate for wells installed in the same cell, vary by one to three orders of magnitude. Trends evident in the data are briefly highlighted below: Pre-1986 Landfill Area: The concentrations of the many inorganic and organic constituents in the leachate are lower in samples from wells installed in the Pre-1986 Landfill Area, than samples collected from wells installed in Cells 16, 17 and 18. The major and minor ions, metals and Polynuclear (Polycylic) Aromatic Hydrocarbons (PAHs) average concentrations in samples collected in 1995 and 2012 are generally similar. Of note, most of the Volatile Organic Compounds (VOCs) were detected at lower concentrations in the 2012 samples in comparison with the 1995 samples. This difference may be caused by volatilization/degradation of the VOCs over the last 17 years or may just be reflective of the spatial variability in concentrations. 30

42 Table 4-3. Chloride Leachate Sources Indicator Parameters Concentrations (2012 Data) Pre-1986 Landfill Area Cell 16 Landfill Area Cell 17 Landfill Area Cell 18 Landfill Area Range [mg/l] 7,680 to 15,200 16,640 to 94,900 20,600 to 34,100 28,200 to 43,900 Average [mg/l] 11,500 38,700 27,200 33,700 Range [mg/l] 4,690 to 12, ,000 to 20,500 20,600 to 25,000 21,000 to 42,600 Sodium Sulphate Potassium Fluoride Barium Bromide Average [mg/l] 8,290 17,300 22,900 28,500 Concentration as a Ratio of Chloride Range [mg/l] 23 to 1,910 1,070 to 10,600 4,420 to 8,470 3,580 to 23,040 Average [mg/l] 779 5,500 6,430 10,700 Concentration as a Ratio of Chloride Range [mg/l] 152 to to 10,000 5,160 to 6,930 3,940 to 8,580 Average [mg/l] 252 4,870 6,400 6,210 Concentration as a Ratio of Chloride Range [mg/l] 1.36 to to to to 95 Average [mg/l] Concentration as a Ratio of Chloride E-4 3.7E-4 9.2E-4 Range [mg/l] 0.02 to to 0.5 <0.5 <0.5 to 2.3 Average [mg/l] < Concentration as a Ratio of Chloride 1.2E-5 1.0E-5 <1.8E-5 6.8E-5 Range [mg/l] 2.5 to to to to 1,940 Average [mg/l] ,240 Concentration as a Ratio of Chloride Range [mg/l] 0.2 to to 10 8 to 27 8 to 100 Boron Average [mg/l] Concentration as a Ratio of Chloride 3.2E-5 2.9E-4 6.2E-4 9.2E-4 Note: Data for monitoring wells installed in waste cells as part of the supplemental investigation program (Appendix D.1). Cell 16 and Cell 17: Waste Cell 16 is known to have received a significant volume of dross, an aluminum smelting by-product, which has a high salt content. Samples from wells installed in this cell are enriched in sodium and chloride. With the exception of VOC concentrations in samples from Cell 16, the concentrations of most major ions, metals and PAHs in samples from Cell 16 and 17 are generally similar. 31

43 VOC concentrations in samples from Cell 16 are significantly lower in comparison with samples from Cell 17, Cell 18 and Pre-1986 Landfill Area. This may again be related to the volatilization/degradation of the VOCs or alternatively the waste placed in the cell had a lower VOC content. Cell 18: The concentrations of most inorganic and organic parameters in the samples from wells installed in this cell are elevated in comparison with samples from the older cells. 4.7 Closure of the Existing Landfill Site Section 7 of the D&O Report for the Existing Landfill (Clean Harbors Canada, Inc., 2010) presents conceptual information on measures to be taken during the closure and post closure phases of the Lambton Facility. It is reported that, In the closure phase, support infrastructure, such as maintenance, water collection and treatment, analysis and incineration, will still be available for the upkeep of the closed landfill and associated treatment/control works including the HCLs installed in Sub-cell 3. In the post-closure phase, none of the existing support infrastructure will be available. For the most part, control of contaminant migration and release into the environment will be through natural, passive systems. These systems will require minimal maintenance and monitoring. The exception is the remedial operation (i.e., pumping) of the HCLs that have been constructed in Sub-cell 3. The HCLs will be actively operated for an indefinite period of time. Closure will involve the following items: the cap over the landfill will be constructed to its final elevation, contoured and vegetated; perimeter fencing, access and internal roadways and other earthen works (such as berms, drainage ditches and swales, surface water reservoirs, etc.) will be maintained in the condition described for the operational life of the landfill; surface water runoff will continue to be collected, treated and discharged as required in a fashion identical to that specified for the operating landfill; noise, dust and lighting abatement measures will also be maintained as for the operating landfill; existing groundwater and surface water monitoring programs will be continued, but possibly modified to accommodate knowledge of site conditions at site closure; and the current leachate reservoirs constructed on the Cell 17 cap will be decommissioned. While the specifics of post-closure are to be defined in the future, it is reported that all waste management activities conducted on the site will have ceased. The various buildings, tanks and processing equipment will have been decommissioned and demolished and any surface contamination (within the central operating area) will have been removed. 32

44 There is expected to be greater reliance on passive systems will control the off-site release of contaminants to surface water. However there is recognition that there will be an ongoing requirement to maintain surface water drainage systems and that support service/structures will need to be developed. The D&O Report provides general assumptions specific to the conceptual design of a passive surface water management system and the monitoring/evaluation of the system to assess its operational effectiveness. With regards to groundwater, it is stated that substantial modifications to the monitoring program may be made based upon the groundwater quality data collected over the operating life of the landfill and its closure phase. It was further observed that It is not reasonable at present to precisely define a monitoring program to be instituted during the post-closure period. However, the current program of semi-annual grab sampling from a widely dispersed network of piezometers may not be technically appropriate. An alternative monitoring strategy was proposed in the D&O Report. This monitoring strategy involves the use of low capacity pumping wells (purge wells) installed in the Interface Aquifer, that would be intermittently operated (pumped) and sampled. The cone of influence generated by pumping would extend outward from the purge wells and samples collected would be representative of a much larger capture zone. Once conservative contaminants in the waste reach the Interface Aquifer by advection/diffusion the purge wells would be activated as a protective measure to prevent movement of contaminants beyond the property boundary. As described in the D&O Report, the system will consist of small diameter, low flow rate, pumping wells installed into the underlying aquifer. These pumping wells would depress the hydraulic pressure head in the Interface Aquifer and create a hydraulic trap for the capture of migrating contaminants. During negotiations for the Certificate of Approval issued for Cell 18, it was agreed that a demonstration program would be conducted to assess the viability of this technology given conditions at the Facility property. The test program was initiated in 2001 and involved the sequential purging of number of wells installed in the Interface Aquifer (Gartner Lee Limited, 2001). Testing was initiated in January 2001 and involved wells located near the centre and the northwest corner of the Facility property, The pumping rates at the individual wells varied (due to iron and sulphate bacteria clogging, and subsequent chemical disinfection measures) and between well locations due to formation properties. On termination of the testing in August 2001, the steady state pumping rates varied between 2 and 6 L/minute. Water level response to pumping was monitored at most of the wells installed on-site. A groundwater model (MODFLOW) was developed and calibrated to site conditions, and subsequently used to simulate the hydraulic head response in July 2001 after several months of active pumping. There was a reasonable match in the test data and the simulation within the central area of the Facility property. The drawdown cone, with the exception of the northeast corner of the property and an area along the west property boundary west of the Process Area, encompassed most of the Facility property. It was concluded that low capacity purge wells could be effectively employed as a preventative measure to control the movement of contaminants beyond the property boundary. 33

45 Additional testing was conducted in 2007/2008 using two additional purge wells (Gartner Lee Limited, 2008). The evaluation included 12-hour and 48-hour pumping tests, and an evaluation of formation properties. Monitoring was conducted at adjacent wells. As part of future operations, there is an ongoing need to continue to operate the pumping wells installed in the HCLs within Sub-cell 3 to maintain an inward hydraulic gradient. The liquid discharge from the HCLs in the future will be composed of a mixture of groundwater and leachate (resulting from lateral diffusion/advection from the adjacent waste cells). Potential management strategies that are identified including: collection of the water from the HCL for off-site disposal; collection and on-site treatment; discharge to an on-site retention/evaporation pond and periodic treatment/off-site management as necessary; and discharge to a containment basin planted with phreatophyte vegetation and periodic treatment/offsite management, if necessary. 4.8 Contingency Plans Plans are provided in Section of the D&O Report (Clean Harbors Canada, Inc., 2010). These include the retention of the existing surface water treatment plant throughout the closure and post-closure phases for long as required. Early detection of contaminants in the Interface Aquifer would lead to activation of the purge wells installed in the Interface Aquifer. The lateral movement of leachate through the shallow weathered clay (Active Aquitard), if not adequately addressed and managed through the internal surface water system and treatment plant, would be mitigated through the installation of a perimeter drain system where necessary. The collected water/effluent would be treated and discharged or transported off-site for disposal. 34

46 5.0 Topography and Drainage 5.1 Topography The topography in the Regional Study Area encompassed by most of St. Clair Township (Figure 5-1), is generally flat to slightly undulating. The land surface slopes towards the St. Clair River to the west. The Wyoming Moraine is the most significant topographic feature in St. Clair Township (Township). In the eastern portion of the Township, the Moraine forms a southwest trending topographic high that is most evident at the community of Wyoming, north of Petrolia (Figure 5-1). The Moraine delineates the extent of the advance of the Huron Lobe of the Wisconsin Glaciation ice sheet (Barnett, 1992). Within the Wyoming Moraine the surface is slightly hummocky (i.e., occasional shallow depressions formed in the ground surface by the melting of blocks of ice enclosed in the glacial material). The land surface in the area of the Moraine was modified by wave erosion in proglacial lakes producing shoreline features including beveled bluffs and beach bar type deposits (beach strand) extending off of topographic highs. The topographic high of the Wyoming Moraine, and stream channels and drainage ditches, which have cut erosional channels in the drift, provide local topographic relief. Beyond the Moraine, the St. Clair Clay Plain is characteristically flat to slightly undulating. A washboardlike relief consisting of sub-parallel ridges and drainage swales has developed, as evident in aerial photography (Jagger Hims Limited, 1996). The relief between the ridges and adjacent swales is typically on the order of ±1 m. As discussed in later sections, these features influence the distribution/extent of surficial fracturing. The topography in the vicinity of the Lambton Facility property is depicted in Figure 5-2. The site lies on a topographic high with the surface sloping to the northeast and the southwest. Prior to development, the Lambton Facility property was relatively flat (198 masl to about 201 masl). Although the surface has been extensively modified as a result of the facility operations starting in about 1960, areas peripheral to the site, such as the old cemetery located immediately north of the entrance to the Lambton Facility and the large wood lots at the south east and south west corners of the site, are relatively undisturbed and indicative of the former topography. Of note, the ground surface at the cemetery is about 2 m to 3 m (202 masl to 203 masl) higher than the surrounding area. The rise is the western trace of a proglacial lake beach strand deposit, which extends as a narrow band running to the east-southeast. Although remnants of the deposit are still evident at the cemetery and near the wood lot at the southeast corner of the property, the granular material over the balance of the Lambton Facility property was excavated as a source of construction aggregate. Historical aerial photography for the site (1955 through 1981) presented in Jagger Hims Limited (1996) shows the ridge and swale topography that is characteristic of a beveled till plain. Locally the sub-parallel ridges and swales trend north to south creating a washboard effect with runoff directed from the ridges to the neighbouring swales. The swales prior to site development, drained to the north to the roadside ditch along Petrolia Line. 35

47 Starting in the 1960s and extending through to today, the topography of the property has been altered as a result of the extensive development of the waste management facilities. There has been ongoing excavation of the clay till to create waste cells, and retention ponds and drainage channels. Much of the clay has been displaced to the perimeter of the site to be used in the construction of screening berms, and following placement of waste in the cells, the clay has been used to cap the waste. The berms form a topographic high (about 8 m to 12 m above the surrounding ground surface) that extends around the northern perimeter of the site. A shallower berm (about 4 m to 5 m high) has been constructed along the south property boundary. The placement of a layer of waste above existing waste in the Pre-1986 Landfill Area raised the ground surface locally by about 5 m to 8 m above grade (205 masl to 208 masl). 5.2 Drainage Regional and local surface water drainage is described in Thames Sydenham and Region Source Protection Area or TSR-SPA (2007) and Environmental Hydraulics Group (1996), respectively. The On-Site Study Area (immediate vicinity of the Lambton Facility) straddles the drainage divide for three drainage systems including: Perch Creek, which drains to Lake Huron (northeast area); Talfourd Creek, which drains westward to the St. Clair River; and Bear Creek, which is a subwatershed of the Sydenham River Watershed that drains to Lake St. Clair. In the vicinity of the Lambton Facility, drainage is enhanced by ditches excavated adjacent to the major roadways. The low relief, flat slopes and clay soils contribute to poor drainage characteristic. Therefore the majority of the agricultural fields are tile drained with the outlets discharging to the roadside ditches. Flow in the roadside ditches is intermittent because of the small drainage areas that discharge to the ditches. Regional water balances presented in TSR-SPA (2007) and Environmental Hydraulics Group (1996) are summarized below: Budget Components (Estimated Average Annual) TSR-SPA (2007)* Environmental Hydraulics Group (1996)** Precipitation 919 mm 953 mm Evapotranspiration 578 mm (62.9%) 633 mm (66.4%) Runoff 174 mm (18.9%) 315 mm (33%) Shallow Groundwater 145 mm (15.8%) Infiltration 5 mm (0.05%) Balance 22 mm (2.4%) (*) Considers data from Petrolia Climate Station ( ) and streamflow data ( ) from the Hydrometric Station on Bear Creek at Brigden. (**) Water budget calculation using data for Petrolia Climate Station ( ). 36

48 Agricultural land use, roadway development and the subsequent development of the site as a waste management facility has obscured most of the original drainage pattern in the vicinity of the Lambton Facility. Drainage was diverted to deep road side ditches through field tiles, ditches and drains from adjacent fields. These ditches in turn drain towards one of Waddell Creek (northern portion of the property outside the facility operating areas) and Sydenham River system (internal operational areas and south portion of property). With the development of the facility, drainage internal to the property is directed through a network of drainage ditches, retention ponds and a water treatment plant, to the roadside ditch along Telfer Road, where it flows southwards towards Bear Creek and in turn to the Sydenham River. The reader is directed to the more expanded description of the regional and local hydrology provided in the AECOM (2013) report titled Surface Water Existing Conditions Report, Clean Harbors Lambton Landfill Expansion EA. 37

49 6.0 Geology 6.1 Regional Geology The Study Area is located in southwestern Ontario on the western flank of a major bedrock structural feature known as the Algonquin Arch, which is a broad ridge in the Precambrian crystalline bedrock that extends from the northeast to southwest into the southwestern Ontario peninsula. The Algonquin Arch separates two depositional basins, the Michigan Basin, which is centered on the lower peninsula of the State of Michigan and the Appalachian Basin, an elongated structural low that extends southward, crossing New York, Pennsylvania, eastern Ohio, West Virginia, western Maryland, eastern Kentucky, western Virginia, eastern Tennessee, northwestern Georgia, and northeastern Alabama. The bedrock geology in Lambton County is characterized by a thick sequence of Paleozoic sedimentary rock overlying Precambrian crystalline rock. The Paleozoic sediments thicken towards the centre of the Michigan Basin to about 4,900 m near Mackinaw City, Michigan and thin to the northeast where the Precambrian rocks outcrop north of Lake Simcoe. The Paleozoic sedimentary rock is about 1,100 m to 1,500 m thick below Lambton County (Sarnia-Lambton Environmental Association Monograph, 2005). Overlying the bedrock is a thick (between 25 and 55 m) sequence of clay-rich unconsolidated sediments. The area lies within the Lambton Clay Plain, a sub-region of the St. Clair Clay Plain physiographic region (Figure 5-1) as defined by Chapman and Putnam (1984) Paleozoic Bedrock Geology As noted above, Lambton County is underlain by a thick sedimentary sequence of Paleozoic rock formations overlying Precambrian crystalline rock. The uppermost (youngest formations) date to the Middle to Late Devonian Period. The Paleozoic bedrock units in the County are described in several regional reports, with excellent summaries presented in Armstrong and Carter (2006), and Johnson et al. (1992). These summaries are in part based on exploration work undertaken to assess the oil and gas potential (Johnson, 1985; Johnson et al., 1985; Johnson et al., 1989; Bailey and Cochrane, 1985; Coniglio and Cameron, 1990; and Hamblin, 1998, 2006 and 2010). The Devonian bedrock units and the underlying Upper Silurian units in the Lambton County area are identified in Table 6-1. Of the regional bedrock units, only the Port Lambton Group, the Kettle Point Formation, and the Hamilton Group subcrop below Lambton County (Sanford and Brady, 1955; Armstrong and Carter, 2006; and Johnson et. al., 1992). The areal distribution of these three bedrock units is shown in Figure 6-1. The bedrock dips gently to the southwest (0.2 to 0.5%), with the various formations subcropping in northwest to southeast trending bands. The Kettle Point Formation and the deeper Marcellus Formation were the focus of a drilling program conducted by Ontario Geological Survey in the early 1980s as part of a hydrocarbon energy resources evaluation (Johnson et al., 1985 and Johnson, 1995). 38

50 Table 6-1. Devonian Bedrock Stratigraphy Lambton County (Johnson et al., 1992) Period Bedrock Group/Formation Lithology Devonian Silurian Upper Middle Lower Upper Port Lambton Group Hamilton Group Detroit River Group Sunbury Brea Bedford Black, organic-rich shale Grey sandstone interbedded with grey shale Grey shale with silty/sandy interbeds in upper part of unit Kettle Point Black, organic rich shale and siltstone, minor grey-green interbeds of organicpoor shale and siltstone Ipperwash Widder Hungry Hollow Arkona Grey-brown bioclastic limestone, richly fossiliferous Grey calcareous shale and argillaceous limestone interbeds Grey shale and brown argillaceous and bioclastic limestone interbeds Blue-grey shale, occasional thin argillaceous limestone interbeds Rockport Quarry Grey-brown limestone with shale interbeds Bell Blue-grey, shale and thin limestone interbeds with organic-rich shale in lower part of unit Dundee occasional bituminous partings and Brown fossiliferous limestone, cherty Bois Blanc Lucas Light grey-brown limestone and dolostone, bituminous and cherty, local anhydrite and/or gypsum Amherstburg Sylvanian Bass Islands Salina Tan to grey-brown bioclastic limestone and dolostone, bituminous and cherty White sandstone Green-gray to grey-brown cherty limestone and dolostone, locally shaly partings Dark Brown to buff dolostone Evaporites, dolostone and shale ( ) hydrocarbon potential. ( ) known oil and gas producing field. ( ) salt beds. 39

51 A number of boreholes were advanced as part of this work effort, to collect core to assess the lithology and collect samples for chemical analysis. The borehole locations in the general vicinity of the Clean Harbors Lambton Facility are shown in Figure 6-1. The thicknesses of the Port Lambton Group, the Kettle Point Formation, and the Hamilton Group at the borehole locations are summarized in Table 6-2. The bedrock units are described in greater detail below: Port Lambton Group: The Port Lambton Group encompasses three bedrock formations (Sunbury, Brea and Bedford). These formations are comprised of grey shale, siltstone and sandstone, and subcrop in the western area of Lambton County, near the St. Clair River. The total thickness of the Port Lambton Group is about 110 m. The lowest formation (Bedford) was encountered in two boreholes (OGS-82-1 and KP-24) advanced by the Ontario Geological Survey (Johnson et al., 1985 and Johnson, 1995) in the western part of Lambton County near the Clean Harbors Lambton Facility (see Figure 6-1). The Bedford Formation is described in the borehole log for OGS-82-1 as dark grey shale, thinly bedded non-fossiliferous. The unit at borehole KP-24 located near Kimball is described as grey shale, very silty, non-fossiliferous with no pyrite mineralization. The unit s thickness at OGS-82-1 exceeds 33 m. Kettle Point Formation: The Kettle Point Formation is a brown to black, organic-rich (3 to 15%) shale with occasional interbeds of greenish-grey organic-poor shale and siltstone that are concentrated primary in the lower and upper beds of the unit. The Formation is exposed along the Lake Huron shoreline and subcrops over the central portion of St. Clair Township. The name Kettle Point, originates from the name of the community of Kettle Point near its exposure along Lake Huron. This name was derived from the occurrence of large (>1 m) spherical calcite concretions within the shale beds, which at their point of exposure at the Formation s outcrop resemble cooking kettles (Johnson et. al., 1992). The concretions are described in considerable detail in Daly (1900), and Coniglio and Cameron (1990). The Kettle Point Formation is not present in the north-eastern area of the St. Clair Township and it pinches out near the eastern edge of the Township over the Algonquin Arch. Formation thickness ranges between 30 and 75 m (Johnson et al., 1992). As noted above, the Kettle Point Formation (and the deeper Marcellus Formation) was assessed by the Ontario Geological Survey (borehole locations in Figure 6-1). The formation thicknesses, as compiled from published borehole logs, are provided in Table 6-2. The Kettle Point per the borehole logs varies in thickness from between 31.7 m (at OGS-82-1) to 71.1 m (at KP-24). The Kettle Point Formation is described in the borehole log at Borehole OGS-82-1 as dark grey shale, with minor grey-green lamina, silty, unfossiliferous with occasional pyrite blebs and partings. The description in the log for borehole KP-24 (which extends fully across the unit) is generally consistent. The upper 26 m of the unit at KP-24 is described as grey-black to brown-grey with little to no pyrite. This is underlain in succession by a 2.5 m thick zone of green-grey to brown-grey shale, a 39 m thick section of dark brown-grey shale with occasional pyrite nodules, 1.3 m of grey-green shale and 2 m of dark browngrey with alternating green-grey lamina. 40

52 Table 6-2. Devonian Bedrock Stratigraphy Bedrock Unit Elevation & (Thickness) Borehole OGS-82-1 KP-25 KP-24 KP-27 Location Courtright south of Sarnia near Kimball near Wanstead Surficial Deposits Port Lambton Group Bedford Formation 192 to 131 masl (61 m) to 97.7 masl (>33.4 m) to masl (33.5 m) not observed to148.2 masl (42.1 m) to masl (>5.4 m) to masl (31.85 m) not observed Kettle Point Formation Hamilton Group Ipperwash Formation to 31.4 masl (31.7 m) to 29.4 masl (2.0 m) to 87.4 masl ( >59.7 m) not observed to masl ( 71.1 m) to masl (2.5 m) to masl (>24.7 m) not observed Widder Formation Hungry Hollow Formation Arkona Formation Rockport Quarry Formation to 8.0 masl (21.4 m) to 6.0 masl (2.0 m) to 26.1 mbsl (20.1 m) to 31.9 mbsl (5.8 m) end of core 78.2 masl (>9.2 m) end of core 63.8 masl (>5 m) end of core masl (>7.7 m) Bell Formation to 46.4 mbsl (14.5 m) Hamilton Group: The Hamilton Group is a series of formations comprised mainly of mudstone and shale, with thin carbonate (limestone) horizons (Johnson et al., 1992). The Hamilton Group subcrops in the eastern portion of St Clair Township and underlies the Kettle Point Formation in the central and western portions of the Township. This unit is subdivided into six formations, which from youngest to oldest are Ipperwash, Widder, Hungry Hollow, Arkona, Rockport Quarry and Bell. The Hamilton Group s thickness is reported in Sanford and Brady (1955) to exceed 90 m. The total thickness observed at borehole OGS-82-1 (Johnson et al., 1985) is 65.8 m (Table 6-2). The Ipperwash Formation in the OGS-82-1 borehole log is described as a dark grey-brown finely crystalline limestone that is richly fossiliferous. The underlying Widder Formation consists of interbedded limestone, shale and shaly limestone. The limestone is grey to grey brown, partly bioclastic and otherwise fossiliferous. Dark blue-green shale is dominant strata (80%). The Hungry Hollow Formation is an interbedded brown to blue grey, limestone (fossiliferous to bioclastic) and shale. The Arkona Formation is described as dark blue-grey, moderately calcareous shale with minor limestone beds and shell detritus. The Rockport Quarry Formation is a dark grey to brown-grey, fossiliferous limestone with shaly partings and shell detritus within specific horizons. The Bell Formation is dark blue-grey shale that is silty and calcareous. 41

53 6.1.2 Petroleum Exploitation and Waste Disposal Wells Background: Oil was first discovered in the Town of Oil Springs in 1858 and since then, thousands of exploratory drill holes have been advanced in Lambton County. The significant oil and gas bearing units include the Dundee Formation of the Hamilton Group, the Lucas Formation of the Detroit River Group, the A-1 and A-2 Formations of the Salina Group and the Guelph Formation (Middle Silurian). Deep bedrock wells in Lambton County were used between 1954 and 1976 for the disposal of liquid industrial waste including caustics, phenols, steam condensate water with ammonia and carbon dioxide, waste oils, chlorides, ethers and sulfuric acid. By 1973, a total of 18 disposal wells had been installed or were in use, with 15 the wells completed in the Detroit River Group and three wells completed in the Salina Group (URM, 1984). The disposal of industrial waste was discontinued in Information on disposal practices is provided in Jagger Hims Limited (1996), McLean (1968), URM (1984), Vandenberg et al. (1977) and Kent et al. (1986) and Dillion Consulting Limited in association with Golder Associates (2004). In Ontario, deep wells advanced for petroleum exploration (oil and gas) and production, oil field fluid disposal, hydrocarbon storage and salt solution mining are regulated by the Oil, Gas and Salt Resources Act (OGSRA), which is administered by the Ministry of Natural Resources (MNR). The Act requires that all wells drilled for these purposes be registered, and any wells no longer in use or wells that are unproductive be decommissioned by setting plugs in the well bore and/or filling the well bore with cement to prevent the movement of fluids along the well bore. The disposal of oil field fluids, which contain salts produced as a by-product of oil in active wells, continues on a limited basis under Regulation 341/90 of the Environmental Protection Act. The Act specifies that such disposal may occur into the lost circulation zone in the Detroit River Group, except within five miles of the St. Clair River. [The lost circulation zone is described in Section ] There are currently 28 active brine disposal wells licensed in Lambton County (Oil, Gas and Salt Resources Library web accessed data base current to December 2011). Caverns completed within the A-1 and A-2 Formations of the Salina Group are used for the temporary storage of hydrocarbons and liquefied petrochemicals. There are currently 78 active storage caverns licensed in Lambton County (Oil, Gas and Salt Resources Library web accessed data base current to December 2011). The brine extracted from the creation of the caverns was injected in the Detroit River Group. Oil and Gas Pools in Vicinity of Lambton Facility: Oil and gas have been produced locally from the Dundee and Lucas Formation (see Table 6-1). Figure 6-2 shows the locations of oil and gas pools in the general vicinity of the Lambton Facility. A brief description of the pools follows: Petrolia Pool is a large exhausted oil pool that is located to the north and east of the Lambton Facility and within a portion the Study Area. The pool extends east of the Town of Petrolia. Oil is reportedly still be extracted in the eastern half of the oil pool. 42

54 Moore 2-14-VII Pool is a small active oil pool located approximately 1.8 km southwest of the Study Area between Moore Line and Rokeby Line. The single active well (License #T007209) in this pool terminates in the Guelph Formation at a depth of 719 m. The production for this well for the previous five years is as follows: Moore 2-14-VII Pool Oil Production (m 3 ) Moore 5-11-VI Pool is a small active oil pool located approximately 2 km south of the Study Area. The active well (License #T008533) terminates in the Goat Island Formation at a depth of 699 m. The oil production at this well for 2010 and 2011 was 459 m 3 and 412 m 3, respectively. Moore 15-VIII Pool and Moore 2-13-VIII Pool are active natural gas pools located approximately 2 km and 0.9 km west of the Study Area between Waubuno Road and Kimball Road. The wells in these pools terminate in the Goat Island and Gasport Formations at depths between 732 m and 755 m. The production for these pools for the previous five years is as follows: Moore 15-VIII Pool Oil Production (m 3 ) Gas Production (10 3 m 3 ) Moore 2-13-VIII Pool Gas Production (10 3 m 3 ) Kimball-Colinville Pool is a natural gas storage pool located approximately 4.2 km west of the Study Area. The pool contains numerous active and abandoned wells. Logierait Pool is a depleted natural gas pool located approximately 1.6 km west of the Study Area. Oil, Gas and Disposal Wells in Vicinity of Lambton Facility: Figure 6-2 shows the locations of wells in the vicinity of the Lambton Facility that are on file with the Ontario Oil, Gas and Salt Resources Library. Summary information for the deep wells that fall within or near the 1.5 km of the Lambton Facility is presented in Appendix B. Of the 33 deep wells listed, 29 wells are petroleum exploration and/or production gas wells, three are disposal wells and one is an observation well. The well depths range between 145 and 780 m. Of the six producing wells, five are between 148 to 197 m in depth, and one is completed to a depth of 738 m. The majority of wells with unknown status are wells that were drilled prior to A brief discussion of the most noteworthy wells follows: Ref. ID 32 (in Figure 6-2): This reference ID is assigned to MNR License No. T This is an observation well (referred to as LD-90-3) that was installed on the Lambton Facility property by the University of Waterloo as part of a research project in

55 Well LD-90-3 is a 145 m deep, multi-level installation, with five open intervals set against the Kettle Point Formation shale (1 interval), Hamilton Group shale (2 intervals), Hamilton Group carbonates (1 interval) and Dundee Formation carbonates (1 interval). Well LD-90-3 is no longer being monitored and its condition is unknown. The well is scheduled to be decommissioned as part of a larger Facility-wide program to seal wells that are not in use. Ref. ID 11: This is a former waste disposal well (MNR License No. T000963) located at the Lambton Facility property. The well was initially drilled in 1961 to depth of 421 m as a petroleum exploration well (identified as C.B. Lewis No. 26). The well was converted for use as a disposal well (Goodfellow Disposal No. 1) in 1968 with casing extended to the top of the Detroit River Group. The lower portion of the well was open through to the upper dolostones of the Salina Formation. The well was used between 1961 and 1973 for liquid waste disposal (Jagger Hims Limited, 1996). The well was decommissioned (sealed) in Ref. ID 33: This deep well referred to as Goodfellow Enterprises Disposal Well No. 2 (MNR License No. T003685) was completed in 1973 to a depth of 214 m. The well was cased to a depth of 174 m and open to the Detroit River Group below this depth. Although the well is classified as a brine well in the Oil, Gas and Salt Resources database, it was used between 1973 and 1976 for liquid industrial waste disposal. The well was also decommissioned in Ref. ID 12: Refers to Amalgamated Liquid Disposal No. 1 (MNR License No. T003132), a former oil field brine disposal well, located approximately 200 m west of Brigden Road approximately halfway between Petrolia Line and La Salle Line. The well was completed in 1970 to a depth of 304 m in the Bois Banc Formation. The well is cased to a depth of 176 m in the Lucas Formation of the Detroit River Group and is open hole to its base. The well was formally decommissioned in No annual status reports or oil field fluid disposal reports for this well could be located at the Oil, Gas and Salt Resources Library and it is therefore not possible to confirm whether this well was used for disposal purposes. Ref ID 19: Range et al. Moore No. 1 (T009546) is an active gas well that is located approximately 200 m west of Telfer Road and 600 m south Rokeby Line. The well was drilled in 2000 to a depth of 738 m. The natural gas production for the well for the previous five years follows: Range et al. Moore No Gas Production (10 3 m 3 ) The effect of oil and gas production on hydraulic gradients in the bedrock is discussed in Section Bedrock Topography and Overburden Thickness The bedrock topography and overburden thickness in the Regional Study Area are shown in Figure 6-3 and Figure 6-4, respectively. The figures were reproduced from a map compilation that is available in Gao et al. (2006). 44

56 The bedrock surface and overburden thickness maps were constructed by the Ontario Geological Survey using the logs for geotechnical boreholes, water wells and petroleum exploration holes. As shown in Figure 6-3, the bedrock surface slopes downward towards the west from an elevation of about 185 masl in the Petrolia area to a low of about 125 masl to 130 masl along the St. Clair River. The bedrock surface is slightly undulating with the Study Area overlying a broad northwest to southeast trending bedrock high. Although not fully evident in the bedrock surface mapping, there is a buried bedrock valley in the Sarnia Corunna area that runs roughly parallel to and between 300 m and 1 km east of St. Clair River. The bedrock valley extends to a depth of about 30 to 35 m below the surrounding bedrock and about 60 m to 70 m below ground surface (Interra Technologies Ltd., 1992). The pattern in the slope in the bedrock is reflected in the thickness of the overburden (Figure 6-4). The overburden is about 20 m thick in the Petrolia area, 35 m to 40 m thick in the general vicinity of the Lambton Facility and up to 70 m thick near the St. Clair River Quaternary Geology The Quaternary geology refers to the strata that overly the bedrock and includes both postglacial (recent) sediments and the thick sequence of sediments of glacial origin found throughout the area. The Quaternary geology of Ontario is described in the compilations by Karrow and Calkin (1985) and Barnett (1992). The reader is directed to these documents for a through overview of the depositional history, and the associated glacial deposits and landforms. Glacial history and lake development in the Lake Huron Basin is summarized in Hough (1953), Dreimanis and Karrow (1972) and Lewis et al. (1994). The glacial sediments in Lambton Country were deposited during the Late Wisconsinan substage of the Quaternary. The Late Wisconsinan coincided with the advance of the Laurentide Ice Sheet into Southern Ontario about 23,000 years before present, and incorporates three Stades (Nissouri, Port Bruce and Port Huron) marked by ice advances that are separated by warmer Interstades (Erie and Mackinaw) during which the ice retreat (Dreimanis and Karrow,1972). Glacial lakes existed during both the colder Stades and the warmer Interstades. Drainage during the later stages of the Mackinaw Interstade was eastward via the Mohawk Valley to the North Atlantic (Barnett, 1992). The final advance of the ice sheet (Port Huron Stade) closed the eastern drainage outlet, with the Wyoming Moraine roughly demarcating the limits of the advance. Glacial Lake Whittlesay was formed at this time, with drainage directed through the Michigan Basin (Glacial Lake Saginaw and Grand River of Michigan channel) and eventually the Mississippi River (Barnett, 1992). The meltwater from the subsequent retreat of the ice sheet produced a series of glacial lakes (Warren I, II and III, Wayne, Grassmere and Lundy). As described in Barnett (1992), the ice margin oscillated, resulting in changing drainage patterns depending on the position of the ice front and the level of the water ponded behind the ice front. Drainage during the Lake Warren I and II phases was through the Michigan Basin and the Mississippi River. 45

57 Lake Wayne (a lower water stage) was formed between Lake Warren II and Lake Warren III, at which time the retreating ice mass had retreated sufficiently to allow drainage to move eastward (probably Syracuse Channels). Re-advance of the ice front closed this outlet, raising the water level forming Lake Warren III, with drainage again to the west towards the Mississippi River. Drainage from Lakes Grassmere and Lundy was towards the east and west respectively. The major depositional period concluded with the retreat of the glacial ice mass and draining of the glacial lakes about 13,000 to 12,000 years ago (Barnett, 1992). The Quaternary geology in this area of Southwestern Ontario is described in several maps and reports completed by the geologists of the Ontario Geological Survey. The publications by the Ontario Geological Survey, which were considered include: Preliminary Map P2222 covering the Sarnia - Brights Grove (Fitzgerald et al.,1979); Preliminary Map P for the Wallaceburg St. Clair Flats Area (Fitzgerald and Hradsky, 1980); Open File Map 163 covering the Chatham-Wheatley Area (Kelly, 1991); Open File Report 5885 for Essex County (Morris, 1994); Report 188 for the Grand Bend-Parkhill Study Area (Cooper 1979); Report 298 for the Long Point-Port Burwell area (Barnett,1998); and Report 283 for the Stratford-Conestogo area (Karrow, 1993). Given the extensive thickness of the overburden and the absence of deep erosional features, the Quaternary sequence is not fully exposed in the area. The lithological descriptions and stratigraphic correlations presented in these references relied extensively on the examination of available erosional and man-made exposures, shallow soil sampling, and driller logs for water wells/petroleum exploration wells and the occasional deep geotechnical borehole. The mapping was conducted by different geologists, at different levels of study intensity, over a period of several years. Map 2556, Quaternary Geology of Ontario Southern Sheet (Barnett et al., 1991) is a compilation of the surficial geology mapping available to the Ontario Geological Survey in This mapping has since been superseded by Surficial Geology of Southern Ontario, Miscellaneous Release - Data 128 (Ontario Geological Survey, 2010). [Note: this latest mapping incorporates supplemental data collected by Bajc et al., in 2001.] The Quaternary geology in the Study Area was mapped by Fitzgerald et al. (1979) and is presented in Preliminary Map (P2222). It is reported in the Marginal Notes of P2222, that there is evidence of at least six tills, two of which are mapped at surface. These include the St. Joseph Till, which is at surface along the Wyoming Moraine and northward, and a second till, (informally referred to as the Black Shale Till), which is present at surface south of the Wyoming Moraine in the area south of Bear Creek (vicinity of the community of Brigden). Fitzgerald et al. (1979) description of the St. Joseph Till (younger of the two tills) is limited to it being clayey silt till with a clast content of less than 5%. The older/underlying Black Shale Till is also described as clayey silt till but with a higher content of black shale fragments. The two tills are separated by a massive to laminated, sometime contorted, lacustrine deposit of sandy silt to clay. 46

58 In describing the logs for deep boreholes advanced north of the Wyoming Moraine, Fitzgerald et al. (1979), indicated that the northern flank of the Moraine was underlain by multiple till and lacustrine units, and a possible Catfish Creek Till equivalent (citing Terasmae et al., 1972). In the logs for boreholes advanced south of the Wyoming Moraine, Fitzgerald et al. (1979) observed two subsurface tills, separated by massive to laminated silt and clay. The two subsurface tills were described as being similar to the Black Shale Till. A very hard silty till with abundant shale clasts directly overlying bedrock, was also reported in a borehole south of Petrolia. The surface topography has been modified by glacial lake erosion and deposition. Several shoreline features (bluffs and sandy ridge - beach strand deposits) were mapped by Fitzgerald et al. (1979) along the Wyoming Moraine and along topographic highs located further to the west. Fitzgerald et al. (1979) with reference to Taylor (1909), and Leverett and Taylor (1915), correlate the elevations of the shoreline features with glacial lakes: Lake Warren (216 to 226 masl); Lake Grassmere (195 masl); Lake Lundy (189 masl); and Lakes Algonquin and Nipissing (181 to 184 masl). Hough (1953) assigned the following elevations to the lake stages of the Huron Basin: Late Lake Warren (212 masl); Lake Grassmere (194 masl); Lake Lundy (189 masl); and Lake Algonquin (185 masl). Remnant shoreline features in the general vicinity of the Clean Harbors Lambton Facility property are attributed to glacial lakes Grassmore and Lundy. The Lake Grassmore shoreline features are mapped along the topographic high of the Wyoming Moraine near Petrolia, and as a distinct line of shallow sand ridges extending from a location north of Mandaumin to Froomfield near the St. Clair River. Shallow gravel ridges associated with Glacial Lake Lundy are limited to series of small deposits that extend from north of Mandaumin to just east of Errol along the Lake Huron shore. The field investigations conducted by Cooper (1979) in the Grand Bend-Parkhill area (northeast of the Study Area) provide a more detailed description of the Quaternary stratigraphy and the lithology. In addition, the interpretation is supported by laboratory analysis (grain-size, carbonate percentages, calcium/dolomite ratios and heavy mineral percentages). The laboratory analysis results from Cooper (1979) are compiled along with data presented in other Ontario Geological Survey reports in Table D.3-1, Appendix D.3. Cooper (1979) identified five (5) distinctive till units in the Grand Bend-Parkhill area, some of which are separated by sediments associated with glacial lakes that formed along the margins of the ice sheets. The Late Wisconsian units from youngest to oldest are: local veneer of glaciolacustrine sediment representing near-shore and deep water deposits associated with proglacial lakes Grassmere, Warren, and Whittlesey (Port Huron Stade); St. Joseph Till - silt to clayey silt till located at surface on and north of the Wyoming Moraine (Port Huron Stade); glaciolacustrine sediment probably associated with deposition in Glacial Lake Arkona (Mackinaw Interstade); a silt to clayey silt till that was identified at surface at the southern edge of the map area, and which Cooper informally labeled southern till based on its geographic location on the southern edge of the map area (Port Bruce Stade); 47

59 Rannock Till - a stony silt to clayey silt till, present at surface in the eastern part of the Study Area, east of the Wyoming Moraine - Ausable River (Port Bruce Stade); a stony till observed along a creek bank southeast of Thedford and beneath the St. Joseph Till in the Thedford shale pit; a stony sandy silt till in borehole near Brinsley (possible Nissouri Stade); and a clay till resting on bedrock, encountered in a stratigraphic borehole near Brinsley (possible Nissouri Stade). The proglacial lake deposits include linear shoreline features (shore bluffs and linear gravelly sand deposits) and deep water deposits (massive to laminated finer textured sediment). The St. Joseph Till is widely referenced as having been deposited during Port Huron Stade, the last major advance of the Laurentide Ice Sheet (Cooper and Clue, 1974; Fitzgerald et al., 1979; Cooper, 1979; and Barnett, 1992). Underlying the St. Joseph Till is glaciolacustrine sediment attributed to deposition during the Mackinaw Interstade in Glacial Lake Arkona. The name Arkona is based on shoreline features that are exposed near the town of Arkona, which are traceable towards the southwest to Birnam. Cooper (1979) also reports gravelly sand deposits below St. Joseph Till that may be correlated to Lake Arkona in Terasmae et.al (1972) and as part Cooper s mapping at a location near Thedford. The southern till unit was assigned by Cooper (1979) to the Port Bruce Stade on the basis of its stratigraphic position (underlying sediment of the Mackinaw Interstade). Cooper (1979) notes that the St. Joseph Till and southern till have generally similar textural characteristic (overlapping grain size distributions) and that the total carbonate content and calcite to dolomite ratios are not distinctly different. The heavy mineral content is the most distinctive attribute, with the southern till having a higher heavy mineral content. The Rannock Till was mapped at surface along the eastern side of the Grand Bend-Parkhill area. A stony silt till observed in exposures in the Thedford area, was reported as having a physical appearance similar to the Catfish Creek Till and Cooper (1979) cites Terasmae et.al (1972) in which a possible correlation with the Catfish Creek Till is suggested. The two deepest tills reported in Cooper (1979) were observed in a borehole located near the hamlet of Brinsley and there is uncertainty about their age and correlation with other Quaternary Deposits. Ontario Geological Survey Map 2556 (Barnett et al., 1991) reproduced in part in Figure 6-5, shows the St. Joseph Till at surface as a broad band extending along the Lake Huron shoreline between Courtright on the St. Clair River and Port Elgin. Bounding the St. Joseph Till to the south and east in Map 2556 is the Rannock Till. As mapped, the Rannock Till incorporates both the Black Shale Till (Fitzgerald et al., 1979) and the southern till (Cooper, 1979). Additional definition is provided in the most recent mapping by Ontario Geological Survey (Surficial geology of Southern Ontario, Miscellaneous Release - Data 128; 2010) where Black Shale Till and southern till are classified as geological deposits and are grouped with Rannock Till (which is assigned formation status). 48

60 There is wide-spread acceptance by the academic community and consultants engaged in studies at the Lambton Facility of the interpretation of the stratigraphy presented in Fitzgerald et al. (1979). To minimize confusion the use of the geologic unit name Black Shale Till is continued herein. The basal sandy silt till unit that is encountered in many of the deep boreholes in the Study Area may be the equivalent of the Catfish Creek Till. 6.2 Local Geology Figure 6-6 presents cross sections A A and B B that extend through the Lambton Facility property from the northeastern limit of the 1.5 km Study Area to the southwest limit. The cross sections were prepared using logs for petroleum exploration/production wells, and deep boreholes installed on the Lambton Facility property. The borehole logs for well referenced in the following Sections are provided in Appendix B of this Report. The locations of the wells are shown either in Figure 3-3, Figure 3-4 or with regard to older wells in specific figures that were prepared as part of this compilation Bedrock Geology The Kettle Point Formation is the bedrock unit that subcrops below the Lambton Facility and is observed in the deep boreholes in the general area of the site. The unit is a distinctive thin-bedded, dark brown to black bituminous shale with infrequent interbeds of green shale. Deep boreholes TW31-94, TW32-94 and TW38-94 advanced in the northeastern portion of Lambton Facility property, encountered the Kettle Point Formation between elevations of: masl to masl (thickness of 8.7 m); masl to masl (thickness of 5.9 m); and mASL to masl (thickness of 13.9 m), respectively. The upper 0.7 m to 4.3 m of the unit (average thickness of 1.3 m) was reported as weathered/fractured. [Note: Well locations are shown in Figure 3-4.] The bedrock unit underlying the Kettle Point Formation locally is the Hamilton Group. This unit is described as brown to grey, argillaceous limestone/shale. The University of Waterloo borehole LD-90-3 (T in Figure 6-6) is located at the southwest corner of the Lambton Facility property. The borehole extends through the Kettle Point Formation and Hamilton Group, into the Dundee Formation to a depth of m (approximate elevation of masl). The borehole log for indicates the bedrock sequence consists of: the Kettle Point Formation (154.1 masl to masl, thickness of 15.6 m); Hamilton Group (138.5 masl to 50.8 masl, thickness of 87.7 m); and Dundee Formation (87.7 masl to termination of the borehole at masl). Deep boreholes advanced on neighbouring properties at locations TW36-94 and TW37-94 about 500 m east of the site, penetrated the full thickness 1.6 m ( masl to masl) and 5.7 m ( masl to masl) of the Kettle Point Formation, respectively, and extended into the shale of the Hamilton Group. A deep borehole (TW35-94) advanced off-site to the west encountered the Kettle Point Formation at a depth of masl and was terminated in the Kettle Point Formation at a depth of 2.4 m below the overburden contact. 49

61 A deep borehole advanced at location TW55-09 about 1 km south of the property boundary, encounter grey shale at masl Based on the depth at which it was encountered and the location, the shale is likely the Kettle Point Formation Bedrock Topography and Overburden Thickness The local bedrock topography has been defined through a combination of regional and local data sources including water well records and petroleum exploration/production wells, and boreholes/wells installed at the Lambton Facility and adjacent properties. The bedrock topography is shown in Figure 6-7. The bedrock rises in the northwestern area of the Lambton Facility property forming a shallow north to south trending ridge, the apex of which is at an elevation of masl. The bedrock surface slopes downward from the ridge to an elevation of about 160 masl along the west property boundary and to an elevation of about masl along the east side of the property. Based on logs for water wells and petroleum exploration wells within a 1.5 km radius of the Lambton Facility property and southern alternative, the bedrock surface slopes downward both to the northeast and to the west. The elevation of the bedrock surface at the southeast corner and southwest corner of the Lambton Facility property is at about 158 masl and masl respectively. The bedrock surface to the south of the Lambton Facility dips gently southward to masl at TW55-09 (about 1 km south of the site). The results of an electrical resistivity survey conducted in 2009, on neighbouring property to the south, indicate the bedrock topography is relatively flat to slightly undulating (Geophysical Survey Report provided in Appendix B.2). A bedrock rise (possibly a shallow ridge) is observed near the northern end of the eastern most survey line (line runs north-south parallel to the roadway along the western edge of Cell 16. The crest of the rise is estimated to be >160 masl. The overburden thickness from boreholes that have been advanced in the immediate vicinity of the Lambton Facility property is shown in Figure 6-8. The overburden thins above the bedrock ridge noted in the previous section to about 36 m and thickens to 43 m in the northeast corner of the site, and to 44.4 m about 1 km south of the property Overburden Geology Four overburden units have been identified at the Lambton Facility, specifically the beach strand deposit, St. Joseph Till, Black Shale Till and Basal Till. The St. Joseph Till and Black Shale Till with a combined thickness of between 37 m and 44 m, dominate the stratigraphic sequence. The four overburden units are described below: Beach Strand: Remnant beach sediments are evident on the Clean Harbors Lambton Facility property forming a shallow ridge like feature (approximate elevation of 203 masl) starting just north of the main entrance to the Facility (at the cemetery). This ridge at one time extended to the southeast through the Facility property. 50

62 A thin veneer (<1 m) of sandy silt at surface is still evident near a woodlot located at the southeast corner of the property. Considering the elevation of the sandy sediments (between 195 and 203 masl) on the property, they may be associated with proglacial Lake Grassmere. The sand from a borehole (BH20-95) advanced near the cemetery, is described as medium to silty fine to coarse sand. The log for a test pit advanced near the woodlot describe the material as ranging from a silty sand to coarse sand with some gravel (Jagger Hims Limited,1996b). St. Joseph Till: The St. Joseph Till is characterized as a massive to laminated clay/silt with thin (0.2 to 4 cm thick), discontinuous layers of silty sand and isolated pockets/lenses of sand. Occasional stones and boulders, largely consisting of limestone, have been observed. The St. Joseph Till extends from near surface to an average depth of about 14 m with the upper 3 m to 4 m being weathered. The depth of weathering is identified by a colour change from a lighter grayishbrown to a deeper grey, with the average depth of visible weathering reported in Jagger Hims Limited (1996) as 4.3 m. Fractures are numerous to about 3.5 m, infrequent to about 5.0 m, and are occasionally observed below 6 m. Mckay (1991) observed that the fracture density decreased with depth with an average of 40 fractures per metre recorded at a depth of 1 m and an average of 0.5 fractures per metre at a depth of 6 m. This observation is consistent with the fracture mapping conducted by Klint (1996). McKay and Fredericia (1989) and Klint (1996) provide excellent summary descriptions of the St. Joseph Till and the upper few metres of the Black Shale Till, and commentary regarding the genesis and depositional history of these deposits. These two detailed studies were conducted at the Lambton Facility property and involved geological logging of fresh sidewall exposures in deep excavations. This work examined the fabric of the till, inclusions in the till, and the nature and distribution of fractures to the approximate depth of the waste Cell 17 excavation (18.3 m). A lithology profile presented in Klint (1996) for an exposed section along the western face of the landfill Cell 17 excavation, identified sand bodies/pockets up to 7 m long and 3 m thick, and thin lenses/sheets (<4 cm) of fine sand extending over 15 m long at a depth horizon of between 6 m and 10 m of ground surface. [Note: The observations in Klint (1996) are generally consistent with those reported by consultants retained by Clean Harbors and its predecessor firms, during quarterly inspections of the excavation slopes. Silt and sand lens/layers are occasionally reported in the logs for boreholes advanced on property however, the overall impression of the till from drilling is that of a massive and continuous layer of clay-silt, with only isolated inclusions of silt and sand.] The sediment observed near the contact with the underlying Black Shale Till (between 14.5 m and 18 m) is described as dominated by a laminated and layered sequence of clay and silt with minor sand layers and black shale fragments. The sequence includes massive layers of clay-rich till. The laminated layers are locally distorted (folded) and it is suggested by Klint (1996) that the glacier advanced over or settled on top of the previous deposits and sheared and compressed them. These layers appear to mark the erosional contact with the underlying Black Shale Till with the sediment at this erosional surface likely derived from the till. 51

63 Grain size analysis for the St. Joseph Till reported in Jagger Hims Limited (1996), indicate an average of 37% clay-sized particles, 44% silt-sized particles, 16% sand-sized particles and 3% gravel-sized particles. The coarse-grained lenses were reported to consist of 18% clay-sized particles, 25% silt, 28% sand and 11% gravel. Additional analyses completed during the Sub-cell 3 investigation (Safety-Kleen Limited, 2000) indicated an average of 46.2% clay-sized particles, 37.4% silt-sized particles, 14.2% sand-sized particles and 2.2% gravel-sized particles. McKay and Fredericia (1989) observed that there is substantial evidence supporting the interpretation that the St. Joseph Till and the exposed upper part of Black Shale Till were deposited in water, possibly below a floating ice shelf. Specifically, there is a lack of orientation and dip in the clasts contained within the till, the presence of steeply dipping stones in the fabric, the presence of dropstones and irregular sand lenses/bodies). The interpretation in Klint (1966) is consistent with that of McKay and Fredericia (1989) but it is suggested that it might be appropriate to substitute the term till with diamict to reflect the sediment origin in a proglacial environment. The term till is retained in the Report to minimize confusion. Black Shale Till: Within the local Study Area, the Black Shale Till extends from the base of the St. Joseph Till to a depth of between 37 m and 45 m, and has an average thickness of about 15 m. The landfill excavation extends into the upper few metres of the Black Shale Till exposing the contact with the upper St. Joseph Till. The Black Shale Till is similarly massive to laminated clayey silt however the dominant clast composition is shale. A few thin, discontinuous lens and/or pockets of gravely silty sand and silt have been observed in boreholes advanced through this unit. These lens/pockets are generally less than 2.0 m thick and occur primarily between 25 m and 29 m below ground surface. Cores were retrieved from six shallow boreholes that were advanced downward from the base of Sub-cell 3 at an elevation of about 176 masl to a depth of about 6 m (to 170 masl) as part of the Sub-cell 3 investigations (Safety-Kleen Limited, 2000). The Black Shale Till was logged as a massive to laminated silty clay with a trace of disseminated sand and gravel. One of the six boreholes encountered a 40 cm thick layer of laminated fine sand/silt/clay at an approximate elevation of 172 masl. Grain size data compiled in Jagger Hims Limited (1996) indicate the unit has an average composition of 48% clay, 41% silt, 9% sand and 3% gravel. Larger boulders to 1 m in diameter have been observed in the landfill excavation. Additional analyses completed during the Sub-cell 3 investigation (Rowe, 2000) indicated an average an average of 60% clay-sized particles, 36% silt-sized particles, 3% sand-sized particles and 1% gravel-sized particles. Basal Till: The Basal Till is a discontinuous layer of dense to hard stony, sandy clayey silt till with shale fragments and occasional pockets and lens of fine gravel and coarse sand that is encountered below the Black Shale Till at the bedrock contact. The Basal Till in the vicinity of the Lambton Facility from borehole logs is up to 4.2 m thick but is typically less than 1 m thick (Figure 6-9). 52

64 7.0 Hydrogeology 7.1 Scope of Previous Investigations The regional hydrogeologic setting in the County of Lambton within the St. Clair Clay Plain has been extensively studied and is well defined. Several studies have been completed in Lambton County that involved the compilation of regional scale information contained in Ministry of Environment (MOE) Water Well Records and Ministry of Natural Resources Petroleum Well data, and in some cases, the collection of water samples from residential wells (Mellary and Kilburn, 1969; Intera Technologies Ltd., 1986; Middleton et al., 1988; Hughes-Pearl et al., 1993; Beaton, 1993; Husain, 1996; Singer et al., 2003; Husain et al., 2004; Dillion Consulting Limited in association with Golder Associates, 2004; Waterloo Hydrogeologic, Inc. 2007; and St. Clair Conservation Authority, 2008). These reports/studies include figures and maps showing the geology, the water table and potentiometric surface in deeper units, the distribution of major ions and stable isotopes, and an interpretation of the findings. Other studies involved detailed field investigation at locations in Lambton County to advance research interests and/or to characterize the local geology/hydrogeology (Desaulniers, 1980 and 1986; Interra Technologies Ltd., 1987 and 1992; Balfour, 1991; Ruland, 1988; McKay, 1991; Solomon, 1991; Hydrology Consultants Ltd., 1984, 1992 and 1993; Cloutier, 1994; Weaver, 1994; Husain, 1996; and Jagger Hims Limited, 1996a and 1996b). The referenced studies typically involved one or more of the following activities: the advancement of boreholes to visually characterize the geology and to collect samples for testing of the geotechnical properties, and chemical and isotope analysis; installation of wells and piezometers at various locations across the St. Clair Clay Plain and at various depths between the shallow overburden to the deep bedrock, for the purpose of measuring fluid pressures and estimating the hydraulic conductivity of the unit against which the well/piezometer are screened; collection of water samples from newly installed wells/piezometers and existing residential supply wells and analysis of major ion chemistry, tritium ( 3 H) and stable isotopes ( 2 H, 18 O and 37 Cl); compilation and plotting of the collected data (water level, hydraulic conductivity, and chemistry and isotope data) to examine its spatial and temporal distribution; and calculation of hydraulic gradients, definition of groundwater flow patterns and velocity, and solute transport modeling to evaluate and simulate the behavior of conservative chemical parameters such as chloride (Cl - ), tritium and stable isotopes under diffusion and advection in clay-rich overburden. These studies contributed significantly to the understanding of the hydrostratigraphy, the pattern of groundwater flow and groundwater quality, and in many instances advanced the science, addressing specific aspects of the hydrogeologic environment, such as the depth of active weathering/fracturing within the St. Clair Clay Plain, chemical transport/movement through clay-rich overburden, and the influence of petroleum and groundwater extraction on the pattern of groundwater movement. 53

65 The interpretations presented in these studies, relied on plots and profiling of the data to illustrate its distribution in two dimensions (horizontal and vertical), and with time. Typical profiles developed for groundwater levels, major ions and environmental isotopes are illustrated in Figure 7-1. Inferences drawn from the profiles have helped characterize the hydrogeology in the Sections of the Report, which follow. Physical Hydrogeology: The conceptual model of the regional geology and hydrostratigraphy that has been developed and referenced in many of the studies is presented in Figure 7-2. The basis for this figure is a generalized stratigraphic column initially produced in 1995 by the University of Waterloo for the Lambton Industrial Society (now referred to as the Sarnia Lambton Environmental Association). It was generally concluded that groundwater flow in the dominant water bearing zone at the overburden/bedrock contact (referred to as the Regional Aquifer or Interface Aquifer), is east to west towards the St. Clair River over much of Lambton County with a component of flow towards Lake Huron to the north. Groundwater recharge is most pronounced in the eastern part of the County with discharge occurring in the west below lakes Huron and Erie. Studies conducted at sites along the St. Clair River established that the thick clay deposits underlying the River hydraulically isolate the River from the Interface Aquifer and therefore the River is not a discharge boundary. It has been convincingly demonstrated in various multi-faceted studies that the fluid pressures in the bedrock and the hydraulic gradients across the overburden are in disequilibrium as a result of changing groundwater use, reduced exploitation of petroleum resources and brine disposal practices. The effects of changing groundwater use and petroleum resource exploitation on groundwater levels are illustrated conceptually in the first column in Figure 7-1. The hydraulic head in the Interface Aquifer and underlying shale has increased and the hydraulic gradient across the overburden as decreased with declining exploitation (Weaver, 1994; Husain, 1996; Husain et al., 1998; and Husain et al., 2004). Major Ion Chemistry (Cl -, SO 4 2-, HCO 3 -, Na +, Ca 2+, Mg 2+ and K + ): These parameters are present at variable concentrations in the overburden and bedrock reflecting their originating source and the chemical and redox reactions that occur between ions and the medium in which they are present. The glaciolacustrine sediments and clay till were derived from erosional processes and deposited in fresh water proglacial lakes. The mineralogy of the unweathered material (Quigley and Ogunbadejo, 1973) is dominated by quartz (40%), carbonates (35%) and clay minerals [chlorite (10%); illite (14%); and smectite (2%)] with minor amounts of sulphide minerals (e.g., pyrite). Within the weathered zone, much of the carbonate has been leached, and the clay mineralogy has been altered through oxidation and leaching of ferrous iron (Fe 2+ ) in chlorite to ferric iron (Fe 3+ ) producing smectite. The brown colouring is attributed to oxidation of the ferrous iron. Oxidation of sulphides also occurs in the weathered zone producing sulphate and a weak acid. This reaction contributes to carbonate dissolution and increases calcium, magnesium and bicarbonate alkalinity concentrations in the shallow groundwater. Ion exchange releases sodium into solution. The shallow groundwater is enriched in SO 2-4, HCO - 3, Ca 2+, Mg 2+ and Na +. These parameters decrease near the base of the weathered zone with the precipitation of carbonates, and the bacterial reduction of sulphate. 54

66 The typical concentration profile developed for these parameters shows elevated concentrations in the hydraulically active weathered zone, which decrease near its base. This is illustrated conceptually in the SO 4 2- profile in Figure 7-1 (see second column). The analysis of water samples from piezometers installed between ground surface and the deep bedrock, established that Cl - and Na + concentrations increase with increasing depth, and in the lower few metres of the overburden approach concentrations in the underlying bedrock. The bedrock (Kettle Point Formation and Hamilton Group) was deposited in a marine environment and the pore water in the rock is enriched in salt (chloride and sodium). In contrast, the clay till and lacustrine sediment was deposited in fresh water with low salt concentrations. Movement of chloride and sodium upward from the bedrock into the clay till has produced a uniform concentration profile (i.e., decreasing chloride concentrations with height above the bedrock). The Cl - profile is illustrated conceptually in Figure 7-1 (second column). There is a general increase in the salinity of the groundwater in the regional aquifer moving from the east to the west across Lambton County. This is reflected in the chloride (Cl - ) concentration, which increases from less than 50 mg/l in the east of the County to over 500 mg/l in the west. The higher Cl - in the western part of the County is attributed to sluggish groundwater flow conditions resulting in less available fresh groundwater (from recharge through the overburden and lateral flow through the Interface Aquifer) to dilute Cl - diffusing outward from the matrix of the shale bedrock. Tritium: The atmospheric testing of thermonuclear devices starting in the 1950s and continuing into the late 1970s significantly increased the concentration of tritium ( 3 H) in the atmosphere and precipitation. Because tritium has a relatively short half-life (12.4 years), it has been a useful indicator of the relative age of the groundwater following infiltration and downward movement. The detection of tritium is typically limited to the active zone of groundwater movement. Its occurrence at detectable concentrations in samples collected below a depth of about 10 m in the clay till would be indication of movement by advection as opposed to diffusion. This could occur through a leaky well seal or damaged well. The typical tritium profile [per Figure 7-1 (third column)] illustrates that the Tritium content is elevated in the shallow weathered zone of the clay till and decreases to non-detect values within a few metres below the deepest hydraulically active fractures. Stable Isotopes ( 2 H, 18 O and 37 Cl): The relative abundance of the naturally occurring isotopes 2 H (deuterium) and 18 O (oxygen-18) in water samples, has been employed in numerous groundwater studies to differentiate between recent infiltration and water that infiltrated under a colder climatic period. The stable isotope content in a groundwater samples is calculated as the difference between the ratio of the isotope ( 2 H/ 1 H and 18 O/ 16 O) and that of a reference standard (Vienna Standard Mean Ocean Water or V- SMOW) defining the isotopic composition of freshwater. The stable isotope content in a sample is expressed in units of delta (δ), (i.e., parts per thousand or 0 / 00 ). Oxygen-18 and deuterium enriched water molecules in the atmosphere are heavier than the standard molecule and therefore are proportionally slower to evaporate and condense faster (process of fractionation). Consequently under colder conditions oxygen-18 and deuterium are depleted and the δ 2 H and δ 18 O values are correspondingly lower. 55

67 The following table presents δ 2 H and δ 18 O values for modern day water (Birks et al., 2003): Present Day (Simcoe, ) range (amount weighted mean annual value) δ 2 H ( 0 / 00 V-SMOW) -10 to -210 (-62.5) δ 18 O ( 0 / 00 V-SMOW) -1 to -26 (-9.4) The broad range in values in the above table is indicative of the time of the year during which the samples were collected with the more depleted values for samples collected during winter months. The profiles developed for 2 H and 18 O in the various references show a generally similar pattern [see profile for 18 O in Figure 7-1 (fourth column)]. Specifically, there is a general decrease in δ 18 O (and δ 2 H) values in pore water and groundwater samples with increasing depth. The δ 2 H and δ 18 O values in samples collected from hydraulically active weathered zone of the clay are between -70 to / 00 and -10 to -8 0 / 00, respectively. Samples collected near the base of the clay aquitard have δ 2 H and δ 18 O values of between -120 to / 00 and - 17 to / 00, respectively. The depleted values at depth are considered to be representative of water present in the sediment at the time of its deposition under the much cooler climatic conditions during the Pleistocene Epoch (Desaulniers, 1980 and 1986; Desaulniers et al., 1981; Beaton, 1993; Solomon, 1991; Hydrology Consultants Ltd., 1984; Weaver, 1994; Husain, 1996; and Jagger Hims Limited, 1996; Husain et al., 1998; and Husain et al., 2004). The gradual depletion in the isotope values with depth is attributed to mixing of the preexisting Pleistocene water with modern water recharging from the surface (Desaulniers, 1986). Chlorine stable isotopes (chlorine-37 and chlorine-35) have been used to assess solute transport by advection/diffusion processes because chlorine isotopes are relatively abundant with the heavier isotope chlorine-37 ( 37 Cl) accounting for 24.2% of natural chlorine and the lighter isotope chlorine-35 ( 35 Cl) accounting for 75.8%. The isotopes are present in the oxidative state as the chloride ion (Cl - ), which is relatively stable/non-reactive. Chlorine isotope measurements are also reported in units of 0 / 00 and are expressed in units of delta (δ), which is the difference between the isotropic ratio ( 37 Cl/ 35 Cl) and its referenced standard (standard mean ocean chloride). As noted, the interstitial water of the shale bedrock is enriched in Cl -, which has diffused upward from the bedrock into the clay till. Desaulniers, 1986 and Desaulniers et al. (1986) applied δ 37 Cl analyses to evaluate the upward diffusion process at two sites in Lambton County. It was determined that 37 Cl become progressively depleted with distance upward from the bedrock as this isotope has lower diffusion mobility relative to 35 Cl. Cloutier (1994) expanding this early effort to additional sites in Lambton County to pursue research interests specific to the distribution of Cl - and δ 37 Cl in the clay aquitard and the interface aquifer. The findings confirmed that δ 37 Cl is a useful tracer. 56

68 7.2 Regional Hydrogeology Hydrostratigraphy As described in the geology section, the area of Lambton County considered in this study is underlain by 20 m to 70 m of overburden dominated by clay-rich till and lacustrine deposits. A thick sequence of shale underlies the overburden. Discontinuous layers/pockets of coarser grained sediment of lacustrine origin deposited in proglacial lakes have been mapped at surface locally and are observed in boreholes in the clay-rich overburden. Per Figure 7-2, these geologic units have been subdivided on the basis of their ability to convey water into distinct units of varying hydraulic activity. The units are described below: Active Aquitard: The upper few metres of the clay-rich till and lacustrine sediments are influenced by atmospheric weathering and are characterized by fracturing and chemical oxidation producing a blocky structure. The open fractures in this interval are conductive to groundwater movement and allow for the rapid dispersion of infiltrating precipitation. Because of the fracturing, the hydraulic conductivity is comparatively larger than that of the underlying unweathered/intact clay till. The zone of hydraulic activity has been referred to in earlier studies as the Active Zone (Desaulniers, 1986; and Cloutier, 1994) and the Active Aquitard (Jagger Hims Limited, 1996; Husain, 1996 and Husain et al., 1998). The use of Active Aquitard was adopted in annual reporting for the Lambton Facility starting in 1998 and is continued herein. The properties of the weathered zone, hydrochemistry within this zone, distribution of fractures and solute movement through the fractures have been extensively studied (Quigley and Ogunbadejo, 1973; Desaulniers, 1980 and 1986; Desaulniers et al., 1981; Desaulniers et al., 1984; D Astous and Ruland 1986; Abbott, 1987; Adomait 1988; D Astous et al., 1989; Johnson et al., 1989; Balfour, 1991; Ruland et al., 1991; McKay, 1991; Solomon, 1991; Hydrology Consultants Ltd., 1984, 1992 and 1993; McKay et al., 1993; Cloutier, 1994; Harris, 1994; McKay and Fredericia, 1995; Husain, 1996; Klint, 1996; Jagger Hims Limited, 1996; Husian et al., 1998a; Corrigan, 1998; and, McKay et al., 1998). General conclusions that can be drawn from this large body of work follow: The upper weathered zone to a depth of about 3 m is characterized by a brown to brown grey coloured clay matrix with a blocky appearance attributed to the existence of a well-developed network of fractures generated through a combination of desiccation and freeze-thaw processes. Between 3 m and about 5 m, the colour changes gradually from grey brown to grey and the frequency and spacing of fractures decrease. The fractures are predominately vertical and are identified primarily by oxidation staining of the clay around the fractures and precipitation of iron and magnesium oxides and carbonates (calcite and gypsum) along the walls of the fractures. The precipitates cement the grains and may reduce the permeability and porosity of the clay matrix adjacent to the fractures. A rapid response to precipitation is observed in piezometers installed above an approximate depth of 5.0 m, with slower responses occurring below this depth. 57

69 Tritium has been detected at comparatively elevated concentrations (>10 Tritium Units or TU) in piezometers and soil pore water to depths of about 6 m. Tritium concentrations exceeding detection limits ( 1TU) have been reported to depths of about 12 m in a pore water sample from a soil core obtained along the sidewall of deep excavations at the Lambton Facility (Solomon, 1991). The occurrence of tritium at depths below 6 m is attributed to a combination of rapid precipitation movement to the base of open fractures and sand lens/pockets, and downward diffusion through intact soil clay. The presence of the landfill excavation would induce a hydraulic gradient that would accommodate movement by advection through fractures. Below about 5 m the clay takes on the appearance of the underlying unweathered/intact clay material (dominate dark grey colouring) with only infrequent fractures observed. Fractures have reportedly been observed in drill core to depths exceeding 10 m. Transition Zone: It is apparent from the studies identified above and detailed drilling conducted at the Lambton Facility that the fracture frequency, degree of fracture openness and interconnection of fractures decrease with depth. The zone of decreasing fracture intensity and corresponding decrease in hydraulic activity is referred to as the Transition Zone (Figure 7-2). The thickness of this zone depends on the depth of vertical fracturing and whether these fractures encounter underlying layers/pockets of sand/silt. Observations related to changes in the slope of vertical profiles of stable isotopes (δ 18 O and δ 2 H) and chloride concentration profiles suggest that the transition zone below the hydraulically active zone, may extend to depths of about 15 m (Weaver 1994). Cloutier (1994) found enriched δ 37 Cl in the shallow subsurface at two sites (BRP and Laidlaw) that were sampled, attributing this to possible anthropogenic sources of chloride (deicing salt and/or fertilizer use). The break in the slope of the δ 37 Cl profile occurs between 12 and 16 m at the BRP site and between 9 and 18 m at the Laidlaw Site. The large depth range at the Laidlaw site is related to the absence of information between the depths of 9 and 18 m. The Transition Zone may locally extend to the contact between the St. Joseph Till and the Black Shale Till. The contact is an erosional surface identified in some boreholes advanced within St. Clair Clay Plain and is often identified by the presence of a thin layer of silt and sand. The sandy deposits are referenced in Fitzgerald et al. (1979) and have also observed in studies conducted at the Lambton Facility including Hydrogeology Consultants (1984), Klint (1996) and Jagger Hims Limited (1996). Inactive Aquitard: Groundwater movement through the underlying unweathered/intact till (lower portion of the St. Joseph Till and the Black Shale Till), is extremely slow (on order of millimetres per year). The till is therefore referred to as the Clay Aquitard or Inactive Aquitard (Figure 7-2). Thin discontinuous layers and pockets of sand and silt are occasional observed within the Aquitard. Although the silt and fine sand has a significantly higher hydraulic conductivity, groundwater movement through these layers/pockets is controlled by the lower hydraulic conductivity of the surrounding clay till. Saturated layers and pockets of sand/silt encountered along the landfill excavation sidewalls will typically exhibit seepage for a short period of this. This suggests that these units are of limited areal extent. Interface Aquifer: A thin layer of sandy to gravelly till (Basal Till) is encountered overlying the bedrock surface in many of the boreholes and wells advanced/installed in Lambton County. 58

70 The Basal Till where present, and the upper fractured shale bedrock, have historically been used as a source of water for private residences, farms and commercial establishments, throughout the County. Based on its historical use, the Basal Till and fractured shale are referred to as the Interface Aquifer (Figure 7-2). Shale Aquitard: Within Lambton County, the shale of the Kettle Point Formation and Hamilton Group, below the upper few meters of the bedrock surface, typically shows little fracturing Hydraulic Conductivity Hydraulic conductivity values obtained from laboratory and in-situ testing are reported in most of the references cited above that involved field investigation. The summary discussion presented herein relies on compilations of available data presented in some of these references (Harris, 1994; Weaver, 1994; Husain, 1996; Husain et al., 1998; Intera Technologies Ltd., 1992; and Jagger Hims Limited, 1996a and 1996b). The results of in-situ and laboratory tests completed at the Lambton Facility property are provided in Section 7.3. Active and Inactive Aquitard: There is a general decrease in the bulk hydraulic conductivity of the clay till with increasing depth, as would be expected considering the degree of fracturing decreases with depth. A compilation of available hydraulic conductivities, presented in Husain et al. (1998) is reproduced below: Weathered Zone (<6 m depth) In-Situ Testing Laboratory Testing In-active Zone (>6 m depth) In-Situ Testing Laboratory Testing No. Tests Hydraulic Conductivity (m/s) Range Geometric mean 1 x 10-6 to 3 x x x 10-9 to 8.9 x x x 10-8 to 2.9 x x x to 2.7 x x Interface Aquifer: This thin discontinuous aquifer includes the coarse textured Basal Till, where present and the upper portion of the bedrock where fractured. The hydraulic conductivities vary by several orders of magnitude (10-4 to m/s). Intera Technologies Ltd. (1992) presents the results for in-situ tests conducted on 29 wells in the Sarnia area that were completed in the Interface Aquifer. The estimated hydraulic conductivities vary between 3 x m/s and 2 x 10-4 m/s with the average reported as 5 x 10-6 m/s. The hydraulic conductivity of the aquifer within the buried bedrock valley south of Sarnia was estimated as 1 x 10-4 m/s due to the presence of coarser material. Bedrock Formations: The hydraulic conductivity of the underlying bedrock formations is generally low but variable. 59

71 The range in hydraulic conductivity values for the deeper bedrock units reported in the following table from Jagger Hims Limited (1996) was compiled from earlier studies (Intera Technologies Ltd., 1992 and Weaver, 1994). The values were derived from slug tests, recovery tests, packer tests and cavern in-flow rates. Bedrock Unit Hydraulic Conductivity (m/s) Kettle Point Formation 2 x 10-3 to 1 x Hamilton Group (shale) 1.6 x to 1 x Hamilton Group (carbonate) 1 x 10-6 to 1 x Dundee Formation (carbonate) 7 x 10-7 to 4 x The Intera Technologies Ltd. (1992) data were compiled from testing completed on deep installations near the St. Clair River. The Weaver (1994) values are from hydraulic conductivity testing conducted on the bedrock formations at the University of Waterloo Dow and Laidlaw research sites. Summary: It is apparent from the available hydraulic conductivity data that there is substantial variability between the reported values for each of the hydrostratigraphic units. Generally, the hydraulic conductivity reflects the degree/intensity of fracturing, which for the clay-rich overburden decreases with depth. Hydraulic conductivities for the thin Interface Aquifer vary by five orders of magnitude depending on the presence of coarse textured Basal Till and the degree of fracturing in the underlying bedrock. The deeper bedrock formations also exhibit significant variability per the above table. Waterloo Hydrogeological Inc. (2007) constructed a groundwater flow model (FEFLOW) for six conservation authorities including the St. Clair Region Conservation Authority. The model encompasses a significant portion of Lambton County. The following model calibrated hydraulic conductivity values were assigned to the hydrostratigraphic units for the modeled area within the Lambton County: Fine Grained Tills & Lacustrine Sediments Horizontal 8 x 10-7 m/s Vertical - 8 x 10-8 m/s107 Basal Sand & Gravels (Basal Till) Horizontal- 7 x 10-5 m/s Vertical - 7 x 10-6 m/s Horizontal 1 x 10-4 m/s Overburden/Bedrock Contact Zone to 7 x 10-5 m/s Vertical - 1 x 10-5 m/s to 7 x 10-6 m/s Hamilton Group Horizontal 1 x 10-6 m/s Vertical - 1 x 10-7 m/s107 The model calibrated hydraulic conductivities are about one to two orders of magnitude higher than values reported in the literature Groundwater Flow Active Aquitard: Groundwater movement in the shallow subsurface occurs primarily through shallow coarse textured lacustrine deposits and weathered/fractured clay (Active Aquitard). The water table developed in this hydrostratigraphic unit mirrors the surface topography with movement occurring from topographic highs to adjacent lows. 60

72 The pattern of flow is influenced by the depth of the hydraulically active fractures and occurrence / distribution of coarser textured deposits. As the density and openness of these fractures decrease with depth, flow would be primarily horizontal towards the nearest topographically low drainage features that intersect the water table such as streams, ditches and tile drains that can convey groundwater discharge. Pumping from shallow wells can depress the water table locally and will therefore have a local influence on the water table. Inactive Aquitard: Movement of groundwater through the underlying clay aquitard is expected to be very slow considering the low hydraulic conductivity of the clay. Groundwater movement through the aquitard is expected to be vertical, with the direction influenced by the hydraulic gradient between the water table and the hydraulic head pressures developed in the Interface Aquifer at the overburden/bedrock contact. A number of the referenced studies undertaken to characterize the aquitard involved the installation of piezometers at various elevations across the full depth of the aquitard and the collection of water level and hydraulic conductivity data, and water samples for major ion chemistry and stable isotope analysis (Desaulniers, 1980 and 1986; Desaulniers et al., 1982; Hydrology Consultants Ltd., 1984; Cloutier, 1994; Weaver, 1994; Jagger Hims Limited 1996a; Husain, 1996; and Husain et al., 1998). Desaulniers (1980 and 1986) and Desaulniers et al. (1982) based on hydraulic head profiles at the time the work was completed, report that the hydraulic gradient at the sites studied in Lambton County was downward. Sampling of the various piezometers established that the δ 18 O values in the shallow groundwater were consistent with the isotopic composition for modern day recharge and the δ 18 O values at depth where representative of water originating under cold weather conditions (glacial). It was also noted that Cl - concentrations decreased with increasing height above the bedrock and it was concluded that the chloride source was the bedrock. Based on the low hydraulic conductivity values (and the low calculated groundwater velocities) and the profiles developed for the δ 18 O and δ 2 H values, and Cl - concentrations, it was concluded that movement of these conservative parameters through the clay was primarily by diffusion under a small, downward advective component. Analytical solutions that incorporate advection (average linear velocity) and dispersion (mechanical dispersion and molecular diffusion) were employed in an effort to simulate the observed δ 18 O values and Cl - profiles. Good agreement was obtained for the observed and simulated profiles for δ 18 O and δ 2 H where the profiles were displaced to an 8 m depth to accommodate the weathered zone and rapid percolation of precipitation to this depth. The best fit simulations of the Cl - profiles occurred for assigned groundwater velocities that are lower than the velocities estimated by the Darcy equation. Possible mechanisms to explain the difference include uncertainty with respect to the estimated hydraulic conductivity values and possible changes in the magnitude of the hydraulic gradient over time. It was also hypothesized (Desaulniers, 1986) that there is a threshold gradient below which Darcy s law was not valid. The investigations completed by Weaver (1994) and Husain (1996) significantly expanded the base of information on the clay aquitard and Interface Aquifer. Additional sites were instrumented, water levels and hydraulic conductivity data were collected and a substantial number of water samples were submitted for analysis for major ions and stable isotopes. 61

73 This work generally confirmed earlier conclusions that solute transport was dominated by diffusion. Information was also collected on groundwater use and the exploitation of petroleum hydrocarbon resources, and an assessment of how this usage has influenced hydraulic gradients in the subsurface. To explain the differences between observed and predicted chloride profiles reported in Desaulniers (1980 and 1986) and Desaulniers et al. (1982), Weaver postulated that the fluid pressures in the bedrock and the hydraulic gradients across the overburden/bedrock were in disequilibrium. Specifically, the downward hydraulic gradients across the clay aquitard were induced by the extraction of water from wells installed in the Interface Aquifer for water supply purposes (fairly recent phenomenon), whereas the chloride (Cl - ) concentration and isotope (δ 18 O and δ 2 H) profiles were more representative of diffusion under long-term, flat or slightly upward hydraulic gradients. This was demonstrated through solute transport modeling, which involved altering the magnitude and the direction of the vertical hydraulic gradient across the clay aquitard and the comparison of predicted chloride and isotope profiles with observed profiles. A relatively good fit between the observed and predicted profiles was obtained where a small, long-term upward gradient (0.01) was applied to the simulation of the downward diffusion of stable isotopes and the upward diffusion of chloride. Husain (1996) undertook additional investigations that were directed at assessing the influence of groundwater takings on the hydraulic gradient across the clay aquitard and on the persistence of Pleistocene aged groundwater in the Interface Aquifer. Included in the thesis is a description of the history of groundwater development in Lambton County (described in further detail later in the Section) and the influence of water takings on the potentiometric surface in the aquifer and the resulting propagation of the hydraulic gradient upward into the overlying clay aquitard. One dimensional solute transport modeling was completed to simulate the upward movement of chloride from the shale bedrock through the aquitard and the model results were compared to field defined chloride profiles. The assessments presented in Husain et al. (1998) and Husain et al. (2004) expand on this work. The earlier paper examines the transient response in the aquitard to the area-wide exploitation of the aquifer for water supplies (between the 1940s and late 1960s) and the subsequent cessation/reduction in the water taking as a result of municipal servicing of the area. The second paper (discussed under Interface Aquifer, which follows) assesses the origin and persistence of the Pleistocene age groundwater underlying the western portion of Lambton County. Incorporating hydraulic head profiles that encompass a period from 1983 to 1996 (developed in Desaulniers, 1980 and 1986; Weaver, 2004; and Husain,1996) Husain et al. (1998) illustrated in a series of figures how the hydraulic head and calculated gradient across the aquitard has changed in response to the rise in the potentiometric surface in the aquifer. With reference to the results of one dimensional solute transport modeling, a good fit was achieved between observed and simulated profiles by diffusion with little advection within a time span of 15,000 to 18,000 years (approximate lapsed time since deposition of the Black Shale Till). A transient flow model was also developed and employed to estimate the hydraulic diffusivity for the clay aquitard. This involved a sensitivity analysis where the hydraulic conductivity and specific storage were altered and compared to field data. A reasonable fit was achieved between the model output and the observed hydraulic head profiles for a hydraulic conductivity of 2 x10-10 m/s and an average specific storage of m

74 The model applying these representative values was subsequently used to generate theoretical aquitard response curves that reflect 40 years of aquifer use and 15 years of aquifer recovery. Weaver (1994), Husain (1996) and Husain et al. (1998) concluded that the downward hydraulic gradients across the clay aquitard were induced by the extraction of water from wells installed in the Interface Aquifer for water supply purposes (fairly recent phenomenon) whereas the chloride and isotope profiles were more representative of diffusion under long-term, flat or slightly upward hydraulic gradients. Interface Aquifer: Information on the regional pattern of groundwater flow in the thin, discontinuous Interface Aquifer is provided in several studies completed in the area (Mellary and Kilburn, 1969; Vandenberg et al., 1977; Hydrology Consultants Ltd., 1984; Interra Technologies Ltd., 1992; Novakovic, 1991; Middleton et al., 1988; Hughes-Pearl et al., 1993; Beaton, 1993; Weaver, 1994; Husain, 1996; Jagger Hims Limited, 1996a; Singer et al., 2003; Husain, et al., 2004; Waterloo Hydrogeologic, Inc., 2007; and Dillion Consulting Limited in association with Golder Associates Ltd., 2004). From available potentiometric mapping, groundwater flow on a regional scale is east to west towards the St. Clair River over much of Lambton County with a component of flow towards Lake Huron to the north. Groundwater recharge is inferred from potentiometric mapping (Vandenberg et al., 1977; Hughes-Pearl et al., 1993; Beaton, 1993; Weaver, 1994; Singer et al., 2003; and Dillion Consulting Limited in association with Golder Associates Ltd., 2004), and the observed distribution of major ions and the stable isotopes 18 O and 2 H (Vandenberg et al., 1977; Beaton, 1993; Husain, 1996; and Husain, et al., 2004) to occur over a broad area located east of Bear Creek approximately centred on the Watford - Warwick area. Cooper (1979) identified surface exposure of glaciofluvial outwash and ice contact drift in the area. The overburden in this area is generally thinner (<20 m) than observed further to the west. Groundwater flow is outward from a potentiometric high located in the Watford - Warwick area towards the west and northeast. On a local level, the pattern of groundwater flow may vary depending on the extent of past groundwater extraction and the distribution of zones of higher and lower hydraulic conductivity within the aquifer. As discussed under Inactive Aquitard above, there is indication from long-term water level trends that the aquifer is re-pressurizing. As some residents (see Section 8) are still extracting water from the aquifer for no-potable use, this re-pressurization is not likely occurring uniformly. It is therefore reasonable to conclude that there will be some change to the general pattern of groundwater flow as the hydraulic head in the aquifer readjusts. This change is projected to result in increased hydraulic heads in the Interface Aquifer, which in turn will lead to a general decrease in vertical and horizontal gradients. Husain (1996) and Husain et al. (2004), referencing many of the studies listed above, developed a conceptual model of the regional groundwater flow system. It was determined that the Interface Aquifer could be divided into distinct age zones based on δ 18 O signature of the water. These zones are briefly described below: 1) Groundwater recharge occurs primarily in the eastern portion of the Lambton County as reflected in a modern-day δ 18 O signature (-10 ±1 ) in samples collected from the aquifer. The chloride concentrations in this area are typically <50 mg/l. 63

75 This area is characterized by a comparatively thin aquitard (10 m to 20 m) and an aquifer zone with relatively higher hydraulic conductivity. The area is referred to as the Modern Zone. The δ 18 O signature decreases and the chloride concentration increases in samples collected from residential wells further to the west. 2) Groundwater with a depleted δ 18 O signature (-17.5 to ) and a higher chloride concentration (>400 mg/l) is evident in samples collected from the aquifer along the western portion of Lambton County near the St. Clair River. This is interpreted as evidence of a large zone of Pleistocene age groundwater and is suggestive of stagnate groundwater flow conditions. The area of stagnate flow is referred to as the Pleistocene Zone. The aquitard in this area is thicker (>35 m) and the hydraulic conductivity of the aquifer zone is lower. The zone of low hydraulic conductivity promotes a northward and southward divergence of the generally westward pattern of regional groundwater flow. 3) The area between the Modern and Pleistocene zones is referred to as the Transition Zone having a δ 18 O signature of between 16.0 to ) and an intermediate chloride concentration (>50 mg/l and <400 mg/l). The aquitard in this area is between about 20 m and 35 m thick. This area has been influenced by domestic/farm water takings from individual wells, resulting in the influx of younger aged water from the eastern portion of Lambton County. 4) A typical δ 18 O profile with depth in the western area of Lambton County indicates modern-day water within the weathered zone of the overburden (Active Aquitard), decreasing δ 18 O values with depth to the Pleistocene signature in the aquifer. Employing water budget calculations based on the water use history in the County, Husain (1996) estimated that about 2 x 10 7 m 3 of water had been extracted from the aquifer. Two scenarios were evaluated to explain the origin of the extracted water. The first considered that the water withdrawn from the aquifer was supplied through lateral flow through the aquifer. This would result in shrinkage of the perimeter of the Pleistocene zone boundary with modern age groundwater displacing the older water. The second scenario considered the water being sourced from the overlying clay aquitard due to moderate compressibility of the aquitard. It was basically concluded that volume of water extracted could have been supplied from storage in the Quaternary deposits, lateral groundwater flow in the aquifer or a combination of the two sources. The Lambton Facility property (i.e., Study Area) from the depleted δ 18 O signature and high chloride concentrations reported in earlier studies (Desaulniers, 1986; Weaver, 1994; and Jagger Hims Limited, 1996a), lies within the Pleistocene Zone as defined by Husain et al. (2004). Bedrock Units: Research conducted by Weaver (1994) involved the installation of detailed monitoring well nests including the deep bedrock monitoring well (LD-90-3) at the Laidlaw site (Clean Harbors site) and a similarly deep installation referred to as the Dow site, located a few kilometres to the north west. The multi-level deep wells installed at the two sites included screened intervals in the Dundee Formation, the overlying Hamilton Group and the Kettle Point Formation. The wells were used to collect information on the fluid pressures and hydraulic conductivity of the bedrock zones against which they were screened and to collect samples for the analysis of major/minor ions and environmental isotopes. 64

76 As part of this research, Weaver evaluated the role played by the shallow Devonian shale in controlling groundwater flow directions and rates between the deeper bedrock exploited for oil production and waste disposal, and overburden/bedrock contact zone that was historically used as a source of water supply. The major findings specific to fluid pressures and hydraulic gradients in Weaver (1994), follow: Petroleum hydrocarbon (oil) was discovered east of the Lambton Facility at and in the shallow subsurface, in the vicinity of the current community of Petrolia in the 1860s (initial find dated to 1856). The early oil wells drilled into the underlying bedrock reportedly flowed at surface (elevated fluid pressures and upward hydraulic gradients). With the subsequent introduction of active pumping to extract oil, the gradients between the shallow system and the primary oil-bearing zones in the bedrock reversed. [Note: The zone of low fluid pressure is referred to, in the Environmental Protection Act (R.R.O. 1990, Reg.341), as the lost circulation zone, a zone in the Detroit River Group into which waste can be discharged without positive pressure]. Between the 1950s and 1970s, liquid industrial waste was injected under pressure into the Detroit River Group and more recently (referencing back to early 1990s), oil field brine is being drained under gravity into the lost circulation zone. Fluid pressures exceeding hydrostatic conditions were observed in the Kettle Pont Formation shale during drilling at the Dow Chemical sites, and shale cores retrieved at both the Dow and Clean Harbors sites from the Hamilton Group released gas bubbles. Flowing artesian conditions combined with gas discharge was observed at the Clean Harbors site during development of wells installed in the Kettle Point Formation. Low fluid pressures (about 70% of hydrostatic conditions) were observed in the Dundee Formation. Two explanations are provided, one being that the low fluid pressure was induced from depressurization of the Dundee Formation due to long-term petroleum production and the second being that the low fluid pressures contain a significant content of natural gas affecting fluid density and in turn the calculated hydraulic head. Similarly, low fluid pressures were observed in the overlying Hamilton Group; however, steady state conditions may not have been reached given the low hydraulic conductivity of the bedrock. There was some divergence in the pressure data for the Kettle Point Formation at the two sites. At the Dow site, the fluid pressure remained below the hydrostatic condition whereas at the Clean Harbors site, the fluid pressure was approaching the hydrostatic condition. At the Dow site, the hydraulic heads measured in the various intervals (after adjusting for fluid density) indicate a downward hydraulic gradient between the Interface Aquifer and the deeper screened intervals. At the Clean Harbors site, the adjusted hydraulic head for the screened interval in the Kettle Point Formation is higher than that for the Interface Aquifer and the deeper bedrock. It was concluded, based on the field monitoring program, that groundwater flow is probably focused in more permeable regions of the bedrock interface zone and the Kettle Point Formation, and the Dundee Formation. Further, there is no evidence of large scale groundwater flow across the Hamilton Group shale, and if such movement were to occur, it would be limited to fractures and open boreholes. 65

77 No information was located with regards to current fluid pressures in the deep bedrock units (i.e., Hamilton Group and Dundee Formation). There is a reasonable expectation that given the cessation of oil production combined with the continued use of the bedrock unit for oil field brine disposal that the fluid pressures have increased Groundwater Chemistry A number of the previously referenced studies involved the collection of groundwater samples from existing residential wells and the chemical analysis of the samples. These wells were installed to satisfy/supplement water supply requirements and were therefore installed either in shallow sand deposits, the hydraulically active zone of the clay-rich overburden (Active Aquitard) or in the regional aquifer (Interface Aquifer) at the overburden/bedrock contact. Studies that lead to the regional characterization of groundwater chemistry in these hydrostratigraphic units include: Mellary and Kilburn, 1969; Vandenberg et al., 1977; Intera Technologies Ltd., 1992; Beaton, 1993; Husain, 1996; Singer et al., 2003; and Husain et al., Maps/figures are presented in most of these reports showing the distribution of various major ions. The regional groundwater resources report prepared by Dillion Consulting Limited in association with Golder Associates (2004) includes a compilation of the major ion chemistry data for the regional aquifer initially reported in Beaton (1996), Intera Technologies Ltd. (1992), Golder Associates Ltd. (1991) and Morrison Beatty Limited (1984). The referenced Golder and Morrison Beatty reports, are for the Sarnia and Warwick landfill sites, and while listed in Section 11, were not accessed for this Report. With reference to the mapping and interpretation in the above reports and various other reports (Mellary and Kilburn, 1969; Vandenberg et al., 1977; and Weaver, 1994; and Husain, 1996), Dillion Consulting Limited in association with Golder Associates (2004) concluded that: chloride and sodium concentrations increase from east to west across Lambton County, with 55% and 69% of the dataset exceeding the ODWS for chloride of 250 mg/l and for sodium of 200 mg/l, respectively; the water is comparatively fresh in the eastern part of the County and brackish in the west near the St. Clair River, with the higher chloride possibly an indication of localized upwelling of deeper formation waters (from waste disposal or possibly regional groundwater discharge); sulphate concentrations are typically low (<50 mg/l) and there is no apparent regional trend in its distribution; nitrate concentrations in the aquifer are low, iron is commonly above 0.3 mg/l; and 35% of the analysis results for fluoride exceed 1.2 mg/l (OWDS is 1.5 mg/l) with the higher concentrations reported for wells in the southern and eastern part of the County being associated with soft water. 66

78 The Ontario Geological Survey Miscellaneous Release Data MRD 283 (Hamilton, 2010) contains ambient groundwater geochemistry data for Southwestern Ontario collected from shallow and deep water wells between 2007 and The locations and reference numbers for the wells are presented in Figure 7-3 and the full dataset for selected wells is presented in Tables D-1 through D-2, Appendix D. Table 7-1 includes parameter concentration data (major and minor ions of interest) for five (5) shallow overburden wells and 12 bedrock wells (11 wells in the Kettle Point Formation and 1 well in the Hamilton Group) installed within the regional Study Area. Table 7-1. Parameter Concentrations (Hamilton, 2010) Select Parameter Range in Reported Parameter Concentrations Overburden Wells Bedrock Wells Calcium 29.6 to mg/l 18.2 to 189 mg/l Magnesium 10.4 to 30.2 mg/l 5.7 to 73.5 mg/l Potassium 0.66 to 16.5 mg/l 2.1 to 8.1 mg/l Sodium 1.9 to mg/l 12.4 to 446 mg/l Bicarbonate Alkalinity (HCO 3) 168 to 472 mg/l 116 to 400 mg/l Sulphate <0.4 to 62.4 mg/l <0.4 to 506 mg/l Chloride 7.8 to 186 mg/l 18.2 to 588 mg/l Bromide <0.1 to 0.56 mg/l <0.1 to 1.22 mg/l Fluoride 0.13 to 1.49 mg/l 0.17 to 1.59 mg/l Boron to 1.27 mg/l to 1.27 mg/l Iron to 1.26 mg/l to 1.26 mg/l Barium 19.5 to 122 µg/l 54.3 to 375 µg/l Methane (CH4) Measured 0 to 70,000 ppmv 90 to 80,000 ppmv In comparing the chemistry for samples from overburden and bedrock wells, the concentration ranges for the parameters overlap. Sodium and chloride concentrations generally increase from east to west across the Study Area, whereas there is no obvious regional trend in the concentrations of the remaining parameters. There is dissolved methane in most of the surficial and bedrock wells. Hydrogen sulphide was detected in some of the bedrock wells. In examining the full data set, sulphate concentrations are low (<20 mg/l), with the exception of two samples, one collected from a well (08-AG-066) located about 15 km southeast of the Study Area in an area where the overburden is relatively thin (<18 m) and a second sample collected from a well (08-AG- 092) located on Rokeby Line south of the Lambton Facility. Well 08-AG-092 reportedly corresponds with MOE Water Well Record No Per the well record, this is a drilled well that was advanced downward from an existing 30 m deep bored installation. The chemistry for this well is anomalous being more typical (i.e., low chloride and sodium concentrations) of samples from overburden wells. It appears likely that the water in the well is a mixture of deeper groundwater from the shale and shallower groundwater from the overburden. 67

79 7.3 Local Hydrogeology Hydrostratigraphy The hydrostratigraphy observed at the Lambton Facility property is consistent with that observed regionally and depicted in Figure 7-2. Most of the monitoring wells installed at the Lambton Facility are screened against the Active Aquitard and Interface Aquitard. This is because the water level in these wells responds to an induced stress (water withdrawals) in a relatively short period of time, making them suitable for monitoring purposes. Wells installed in the aquitards (clay overburden and deeper shale bedrock) are very slow to respond and are impractical to use for compliance monitoring purposes at the site. The locations of well installed in the Active Aquitard and Interface Aquitard that are routinely monitored are shown in Figures 3-3 and 3-4. There is some uncertainty with regards to the thickness of the Active Aquitard. Fractures are known to extend to depths in excess of 10 m based on indirect evidence (e.g., detectable tritium) but the general consensus in the references cited in Section that are local to the Facility property, is that the degree of hydraulic activity declines significantly below 5 to 6 mbgs. This is attributed to the presence of few if any horizontal fractures that would convey flow laterally. The Active Aquifer at the Facility property can be subdivided into two portions based on the intensity of fracturing and the expected hydraulic activity. This includes an upper portion to a depth of about 3 mbgs and a lower portion to the base of the Active Aquitard (5 to 6 mbgs). The division into two units and the assigned thicknesses are subjective, being based on numerous references (e.g., Ruland et al., 1991; Figure 2) that indicate the intensity of weathering and fracturing decreases significantly below about 3 m. Groundwater flow is expected to be preferentially through the fractures and it is reasonable to conclude that the volume of lateral flow would similarly decrease below 3 m. This is evident in various profiles of bromide concentrations that are included in McKay, Gillham and Cherry (1993). Bromide is a commonly applied tracer that is not readily attenuated and would be expected to move with groundwater. As illustrated in this reference, bromide concentrations are attenuated below 3 m, indicating the bulk of the injected bromide is moving with groundwater above this depth Hydraulic Conductivity - Overburden Historical Data Base: Studies and investigations that have contributed substantially to the base of knowledge on the hydraulic properties of the overburden and the distribution of hydraulic conductivity in the overburden are discussed below. An initial compilation of the hydraulic conductivity data for the overburden is presented in Jagger Hims Limited (1996) from studies and investigations conducted on-site prior to These data are summarized in Table 7-2. It was determined in the late 1980s that the method of well installation has a significant influence on the field derived hydraulic conductivity. 68

80 Table 7-2. Hydraulic Conductivity Values for Overburden (Pre-1994 Investigations) Reference Hydraulic Conductivity Range (m/s) Active Aquitard and Transition Zone Aquitard Hydrology Consultants Limited (1984) Test/Analysis Type Installation Method 1 x to 8 x 10-9 Slug test/ Hvorslev (1951) Direct auger Desaulniers (1986) 1 x to 1 x 10-9 Slug test/ Hvorslev (1951) Direct auger Ruland (1988) 3 x 10-9 to >1 x 10-8 Slug test/ Hvorslev (1951) Overcore with Shelby Tube D Astous et al. (1989) 1 x to 1 x Slug test/ Hvorslev (1951) Direct auger 1 x 10-8 Slug test/ Hvorslev (1951) Direct push reverse taper Balfour (1991) 9 x 10-9 to 2 x 10-7 Slug test/ Hvorslev (1951) Over-core with Shelby Tube McKay (1991) 1 x to 3 x 10-7 Slug test/ Hvorslev (1951) Direct push reverse taper Harris (1994) 8 x to 1 x 10-4 Slug test/cooper (1967) Direct push reverse taper Harris (1994) 9 x 10-8 to 4 x 10-7 Pumping Test/Neuman (1975) Direct push reverse taper Dames and Moore Canada (1992) Inactive Aquitard Hydrology Consultants Limited (1984) 1 x Slug test/ Hvorslev (1951) Direct push reverse taper 1 x to 2 x 10-9 Slug test/ Hvorslev (1951) Direct auger Desaulniers (1986) 4 x to 2 x Slug test/ Hvorslev (1951) Direct auger Ruland (1988) 9 x to 1 x 10-9 Slug test/ Hvorslev (1951) Over-core with Shelby Tube McKay (1991) 8 x to 3 x Slug test/ Hvorslev (1951) Direct push reverse taper Dames and Moore Canada (1992) 4 x Slug test/ Hvorslev (1951) Direct push reverse taper D Astous et al. (1989) in assessing well installation methods at various sites in Southwestern Ontario concluded that the hydraulic conductivity estimated for wells installed in boreholes advanced by straight augering was typically low and similar to that measured in the laboratory on intact clay till samples. This was attributing to the smearing of the clay during augering. When the smear zone was removed or reduced by overcoring the borehole with a sharp-edged Shelby Tube, the measured values of hydraulic conductivity were 1 to 2 orders of magnitude higher. Most wells in the clay overburden within the Study Area since the late 1980s have been installed by a direct push/reverse taper drilling methodology that minimizes smearing of the borehole wall. The method employs a continuous sample that is pushed through the target zone. The sampler is then retrieved and a reverse taper cutting shoe is added and the sample is then pushed back into the borehole to remove any smearing. The hydraulic conductivity estimates established in the wells installed by this methodology are considered to be more reliable. Single well response tests (slug tests) are conducted on all new wells installed on site. The estimated hydraulic conductivity values for new/replacement shallow wells installed on site since 1994 are listed in Table

81 Table 7-3. Hydraulic Conductivity Values for Overburden (Post Investigations) Reference Safety-Kleen Ltd. (2000) Safety-Kleen Ltd. (2001) Safety-Kleen Ltd. (2001) Clean Harbors Canada, Inc. (2004) Clean Harbors Canada, Inc. (2008) Clean Harbors Canada, Inc. (2012) Clean Harbors Canada, Inc. (2013) Hydraulic Conductivity (m/s) Type of Test 1.2 x 10-9 to Range in hydraulic conductivity values based on Single Well <1 x Response Test (slug tests) results for shallow wells installed in x Laboratory testing of samples of intact Till samples (Lambton Facility). 3.4 x Average hydraulic conductivity from Single Well Response Tests (slug tests) at MW x 10-9 Single Well Response Test (slug test) at TW53-03S. 1.4 x 10-8 Single Well Response Test (slug test) at TW55-09S. 2.6 x 10-8 to Single Well Response Tests (slug tests) at TW56-11S, TW57-11S 2.6 x and TW58-11S. 5.9 x 10-8 Single Well Response Test (slug test) at TW59-13S. RWDI (2013c) 1.5 x 10-8 Single Well Response Test (slug test) at TW61-13I. All boreholes advanced using direct push reversed taper methodology to reduced potential for smearing/remolding during drilling. It was also determined in early studies that the physical size/scale of the test zone has an influence on the measured hydraulic conductivity. Hydraulic conductivities representative of larger volumes of soil were obtained by D Astous et al. (1989) and McKay (1991) by monitoring water level recover responses at large scale structures. This testing was conducted at sites located within the footprint of current Cell 17 (Figure 4-1). The study by D Astous et al. (1989) involved two test, one where the water level recovery at a large diameter 1.1 m borehole was monitored and the second conducted at two parallel 3.1 m deep trenches located about 2 m apart. At both locations, the smeared zone along the sidewalls was removed. At the trench location, water containing a tracer was added to one of the trenches to maintain a constant head of water and extracted at the second trench to maintain a near constant head. The second trench was also equipped with seepage collectors installed along the sidewall at 1 to 4 m depths. The hydraulic conductivity was estimated by applying Darcy s Law (using the measured seepage and the averaged hydraulic gradient between the two trenches). The bulk hydraulic conductivity values for the large scale structures are listed below: Reference D Astous et al. (1989) Range in Hydraulic Conductivity (m/s) 6 x 10-8 for shallow collectors 1 x 10-7 for deep collectors Type of Test Flow into Seepage Collectors. 70

82 A similar, albeit more comprehensive testing of large scale structures was completed by McKay (1991). The work involved the excavation of three parallel trenches 7 m long and 4.0 m and 6.2 m apart to a depth of 5.5 m, and the manual removal of the smear zone along the sidewalls of the trenches. The fractures and weathered features exposed in the trenches were mapped. It was reported that the till exposed along the sidewalls of the trenches was highly weathered and fractured to a depth of 3 m, and there was extensive staining throughout the interval. Fractures were much less frequent below 3 m and staining occurred mainly on the fracture surfaces. Hydraulic conductivity and specific storage values were obtained through laboratory oedometer consolidation testing on samples of the weathered and unweathered till. The measured values were interpreted as being representative of the matrix of the till. There was no significant difference between the weathered and unweathered samples with mean hydraulic conductivity and specific storage values of 2 x m/s and 2 x 10-3 m -1, respectively. Large scale testing was conducted at the three trenches to estimate the bulk hydraulic conductivity. The central of the three trenches was used as a source trench and the outer two trenches were the receiving trenches. The two outer trenches were instrumented with 35 (0.25 m diameter) seepage collectors placed against the adjoining trench sidewalls at depths between 1.5 m and 4.5 m. PVC liners were placed against the upper 1.2 m of the central source trench and to a depth of 5.5 m against the outside sidewall of the receiving trenches. Sumps were installed in the outside trenches and the three trenches were subsequently backfilled with granular material. Water was added to the central trench and the water level was maintained at a constant depth of 1 m, while extracting water from the sumps in the outside trenches. The injection and sump discharge volumes, the seepage volume into each of the collectors and the hydraulic gradient between the trenches were recorded. The bulk hydraulic conductivity for the 5.5 m trench excavations was estimated by applying Darcy s Law to the average seasonal injection and withdrawal of water. The bulk values cited in the report are 1.6 x 10-7 m/s and 2.6 x 10-7 m/s (geometric mean of 2.1 x 10-7 m/s). McKay (1991) reported that the hydraulic conductivity values for the seepage collectors decreased with depth and that the variability at any single depth horizon was one to three orders of magnitude. The hydraulic conductivity estimated by trench seepage was interpreted as representative of bulk hydraulic behavior useful for estimating flow into an excavation. The hydraulic conductivity estimated from the seepage volume into each of the collectors and an average hydraulic gradient between the trenches ranged between <5 x m/s to 1.3 x 10-6 m/s (geometric mean of 8.9 x 10-9 m/s). A number of piezometers were also installed between the trenches, and hydraulic conductivity values were estimated through collected from the on and slug testing. The hydraulic conductivity from the slug tests presented in McKay (1991) ranged from to 3 x10-7 m/s. 71

83 McKay, Cherry and Gillham (1993), in comparing the hydraulic conductivity values in McKay (1991) obtained for piezometers and the higher values from the large scale testing conducted by using parallel trenches, observed that because the water level in the source trench was maintained at 0.3 mbgs, flow through the shallow uppermost weathered/fractured zone (above 1.6 m) would be significant. There is no observations or conclusions in McKay (1991) or in the subsequent papers that relied on this work (McKay, Cherry and Gillham, 1993 and McKay Gillham and Cherry, 1993) to suggest that the mean hydraulic conductivity value (2 x 10-7 m/s) obtained for the large scale experiment would apply to the full cross sectional 5.5 m depth of the trenches. There is also some suggestion that stress relief fractures induced during trenching could influence the hydraulic conductivity. A more recent detailed study conducted by Jagger Hims Limited (1996b) involved the evaluation of a pilot-scale remedial system that consisted of three 30 m long trenches excavated to 1.2 m, 6 m and 4 m east of the Pre-1986 Landfill and south of the East Retention Pond in The system was installed to determine its effectiveness to hydraulically control groundwater flow. Water was either added or extracted from the trenches to manipulate the water table and control the direction of groundwater flow. As part of the assessment program, several wells were installed adjacent to the trenches for monitoring purposes. The wells were instrumented with transducers. The hydraulic conductivity of the clay overburden was estimated based on the wells response to the injection/extraction of water level at the trenches. The range of hydraulic conductivity values follows: Active Aquitard/Transition Zone (15 wells) screened between 1-4 mbgs Range in Hydraulic Conductivity (m/s) 2 x to 4 x 10-8, geometric mean of 8 x Inactive Aquitard (3 wells) screened between 8-10 mbgs 6 x to 5 x 10-10, geometric mean of 2 x Summary of Hydraulic Conductivity Data for Shallow Overburden: The hydraulic conductivity data reported in studies conducted since 1991 (McKay, 1991; Balfour, 1991; Dames and Moore, 1992; Harris, 1994; Gartner Lee, 1999; Gartner Lee, 2003; AES International, 2009; RWDI, 2011; and RWDI, 2013) were compiled and assessed by the depth of the installation (Appendix D.2). The data base includes collectors installed in trenches and wells installed by methods that removed the smear zone (overcoring, and Shelby tubes). The hydraulic conductivity data reported in the studies was processed by various methods. Specifically, the Darcy equation was applied to seepage into collectors and water level response data for single well response testing were processed by Hvorslev (1951), Cooper (1967), Dagan (1978), Bower and Rice (1989) and Hyder et al. (1994). Table 7-4 is a summary of the hydraulic conductivity by 1 m depth increments (<2 m depth, 2 to 3 m, 4 to 5 m, and 5 to 6 m). [Note: Response test values were assigned based on position of the test interval. Where the test interval straddled one or more depth intervals, the depth that was assigned was based on top of screen interval.] 72

84 Table 7-4. Compilation of Hydraulic Conductivity Values by Depth Depth No. of Tests Geometric Mean Hydraulic Conductivity (m/s) < 2 m x 10-9 m/s 2 m to 3 m x 10-9 m/s 3 m to 4 m x 10-9 m/s 4 m to 5 m x 10-9 m/s 5 m to 6 m x 10-9 m/s The geometric mean hydraulic conductivity for the depth interval 3 to 6 m (total of 67 tests) is estimated as 3.8 x 10-9 m/s. The equivalent horizontal hydraulic conductivity (K eff ) for the Active Aquitard (full depth of 6 m) is calculated as follows: = Where, the upper portion of the weathered zone with extensive fracturing to a depth of about 3 m is assigned the bulk hydraulic conductivity (2 x 10-7 m/s), estimated in for seepage influx into collector trench (McKay, 1991); and the the lower portion of the weathered zone with less intensive fracturing between 3-6 m is assigned the geometric mean hydraulic conductivity (3.66 x 10-9 m/s rounded to 4 x 10-9 m/s) based on the compilation of hydraulic conductivity values for single response testing (Table 7-4). The hydraulic conductivity for the unweathered/intact clay is estimated as 2.6 x m/s as per the results of consolidation testing presented in McKay (1991) Hydraulic Conductivity Compacted Clay There have been extensive earthmoving activities on site that involved excavation of the clay overburden and its subsequent reuse to construct perimeter berms and as cover over the waste cells. Information on the hydraulic conductivity of the compacted clay fill is available from slug tests conducted on wells installed in the berm along the northern landfill perimeter. The berm design called for the placement of the clay material in thin lifts to be compacted to a minimum of 95% of its Standard Proctor maximum dry density. The slug test results for wells installed in the northern berm follow: 73

85 Reference Hydraulic Conductivity (m/s) Method and Well Tested Jagger Hims Limited (1996a) 3.2 x to 3.9 x Single Well Response Tests (slug tests) at TW39-99S and TW46-99S. RWDI (2013c) 5.7 x Single Well Response Test (slug test) at TW61-13S. The D&O Report specifies that the clay cap over the waste in the various cells is to be installed in shallow lifts and compacted to 90-95% of Standard Proctor density to achieve a design criterion for hydraulic conductivity of 1 x 10-9 m/s. Laboratory testing has been conducted on various occasion, which involve the compaction of representative samples to various Standard Proctor densities. The initial testing conducted by Trow Ltd. (1987) established that the till could be compacted to 4 x 10-7 cm/s (4 x 10-9 m/s ) at 88 % Standard Proctor density to 2 x 10-8 cm/s (2 x m/s) at 95% Standard Proctor. Extensive additional compaction testing was conducted in 2001 to determine the achievable hydraulic conductivity for placement of a liner at the base of Sub-cell 3 of Cell 18 (Safety-Kleen Ltd., 2001). Representative samples of both the St. Joseph Till and the Black Shale Till were collected in the field and submitted to the University of Western Ontario for Standard Proctor and modified Proctor compaction testing. It was reported that a hydraulic conductivity of less than 2 x m/s could be achieved for the till with a mean value of approximately 1 x m/s where the samples were compacted to between 0% and 2% above Standard Proctor optimum water content. As part of the Sub-cell 3 investigation a test pad was constructed using till samples and the samples were subsequently evaluated in the laboratory. The hydraulic conductivity of the compacted and remolded liner material ranged from 0.42 x m/s to 0.76 x m/s with an average of 0.59 x10-10 m/s. The moisture content of the clay till varied between 14.6 % and 17%. Samples of cap material are routinely collected by Clean Harbors geotechnical consultants and submitted for Standard Proctor testing, with the results consistently below the design criterion 1 x 10-9 m/s Hydraulic Conductivity Interface Aquifer The estimated hydraulic conductivities for the aquifer compiled from the following referenced reports are summarized in Table 7-5. early work (pre-1994),which is summarized in Jagger Hims Limited (1996); Sub-cell 3 investigation (Safety-Kleen Ltd., 2000 and Safety-Kleen Ltd., 2001); Groundwater Purge Well Program under Condition 9 of the Provisional Certificate of Approval No. A [2001 test results are documented in Safety-Kleen Ltd (2001) and 2007 testing documented in Clean Harbors Canada, Inc. (2008)]; and single well response tests on new and replacement well installations (Safety-Kleen Limited, 2000 and Clean Harbors Canada, Inc., 2004; 2006; 2008; 2010; and 2011). 74

86 Table 7-5. Range in Hydraulic Conductivity Values for Interface Aquifer Reference Jagger Hims Limited (1996a) Safety-Kleen Ltd. (2000b) Safety-Kleen Ltd. (2001) Safety-Kleen Ltd. (2001) Clean Harbors Canada, Inc. (2004) Clean Harbors Canada, Inc. 2006) Clean Harbors Canada, Inc. (2008) Clean Harbors Canada, Inc. (2010) Clean Harbors Canada, Inc. (2011) Clean Harbors Canada, Inc. (2012) Hydraulic Conductivity (m/s) & no. of Tests 3 x 10-8 (16) 2 x 10-7 (24) Type of Test Geometric mean hydraulic conductivity (number of wells tested) based on Single Well Response Test for pre-1994 wells. Geometric mean hydraulic conductivity (number of wells tested) based on Single Well Response Test results for 1994 series wells. 1 x 10-5 Pumping Test at OW1-92, hydraulic conductivity decreased during testing, influenced by natural gas. 6 x 10-8 Pumping Test at TW32-94-II, analysis of water level recovery data at test well, influenced by natural gas. 4.3 x 10-6 to 4.0 x x X 10-5 to 8.7 X x X 10-5 to 2.2 X x 10-7 (8) 3.2 x 10-7 to 8.1 x x 10-9 (3) Short-term (48 hour) pumping test at TW1. Geometric mean hydraulic conductivity based on most reliable sets of data. Note: Testing influenced by natural gas. K calculated from the mean transmissivity and assumed aquifer thickness of 3 m. Long-term (5 day) pumping test at TW1, water level response observed at same observation wells. Geometric mean hydraulic conductivity based on most reliable sets of data. Note: Testing influenced by natural gas. K calculated from the mean transmissivity and assumed aquifer thickness of 3 m. Range in hydraulic conductivity values based on Single Well Response Test results for 1999 series wells. Geometric mean hydraulic conductivity (number of wells tested) based on Single Well Response. Range in hydraulic conductivity values based on Single Well Response Test (slug tests) results for 2000 series wells. Geometric mean hydraulic conductivity (number of wells tested) based on Single Well Response. 7.2 x 10-6 Single Well Response Test (slug test) at TW53-03D. 1.4 x 10-6 Single Well Response Test (slug test) at TW35-05D. 9.1 x 10-6 & 2.1 x 10-8 Single Well Response Tests (slug tests) at PW4-03 and PW x 10-4 Short-term (12 hour) pumping test at PW4-03, water level response observed at adjacent well OW1-92. Calculated from the transmissivity and an assumed aquifer thickness of 2.2 m. 1.0 x 10-8 & 8.6 x 10-8 Single Well Response Test (slug test) at TW54-09D and TW55-09D. 7.0 x 10-7 Single Well Response Test (slug test) at PW2-S(R11). 1.2 x 10-5 & 1.3 x 10-6 Single Well Response Tests (slug tests) at TW56-11D and TW56-11D. RWDI (2013b) 1.1 x 10-4 Single Well Response Test (slug test) at TW59-13D. RWDI (2013c) 8.3 x 10-8 & 2.8 x Single Well Response Tests (slug tests) at TW60-13D and TW61-13D. 75

87 The thickness of the Interface Aquifer from available borehole logs at the Lambton Facility is shown in Figure 7-4. The distribution of hydraulic conductivity in the Interface Aquifer at the Lambton Facility is shown in Figure 7-5. The reported hydraulic conductivities were estimated from single well response tests (slug tests). Pumping tests were undertaken on-site as part of the investigations to expand the landfill [i.e., Cell 18 in 1997 (Jagger Hims Limited, 1996)], the Sub-cell 3 investigation (Safety-Kleen Ltd., 2000) and the purge well program (Safety-Kleen Limited, 2001 and Clean Harbors Canada, Inc., 2008). A discussion of this work follows: Cell 18 Environmental Assessment Investigation: Low-volume pumping tests were undertaken at wells OW1-92 and TW32-94-II. Both pumping tests were influenced by the discharge of natural gas (see discussion in a following section). The pumping rate at OW1-92 decreased as the test proceeded as a result of degassing, resulting in a decrease in the calculated hydraulic conductivity from 6 x 10-5 m/s to 6 x 10-6 m/s. It is assumed that gas displaced water in the fractures in the formation, acting as a barrier to water movement to the well. The pumping test at TW32-94-II was affected by the presence of gas was terminated early due to gas cavitation within the pump and the drawdown response was not analyzed. A hydraulic conductivity of 6 x 10-8 m/s was estimated from the water level recovery data. Sub-cell 3 Investigation: A 48-hour pumping test was completed using well TW1-99 installed immediately north of Sub-cell 3. TW1-99 was pumped at an initial rate of 4 L/minute, which was reduced after 14 hours to 3 L/minute. Monitoring data were collected at the pumping well and a number of observation wells TW39-99(D), TW40-99(D), TW2-99, TW3-99 and TW4-99. A maximum water level drawdown of 13 m was observed at the pumping well (TW1-99). Water level responses were observed at TW2-99 (1.81 m) located about 23 m to the east, TW3-99 (1.72 m) located about 25 m to the west, TW4-99 (0.36 m) located about 98 m to the east, TW40-99(D) (0.51 m) located about 166 m to the northeast and TW39-99(D) (0.03 m) located about 256 m to the northwest. This initial test was followed by an extended (19 day) pumping test. Well TW1-99 was pumped on its own for the first 168 hours of the test, followed by pumping at Well TW4-99. The following is based on the water level response during the testing of TW1-99. Wells OW1-92, OW2-92, TW32-II(D), TW39-99(D), TW40-99(D), TW46-99(D), TW2-99, TW3-99 and TW4-99 were monitored during the test. Well TW1-99 was pumped at an initial rate of 4 L/minute, which was reduced after a few hours to between 2.5 and 3 L/minute. A maximum water level drawdown of 14.6 m was observed at the pumping well (TW1-99) about 99 hours into the test. Water level responses were observed at TW2-99 (2.77 m), TW3-99 (1.66 m), TW4-99 (3.77 m), TW40-99(D) (1.73 m) and TW39-99(D) (0.12 m). The geometric mean transmissivity estimated from the 48-hour and 168-hour tests was 3.6 x 10-6 m 2 /s and 4.0 x 10-6 m 2 /s, respectively. The hydraulic conductivity values are included in Table

88 Purge Well Program: The use of purge (extraction) wells was introduced in 1997 during negotiations for the Provisional Certificate of Approval for Cell 18, as a protective measure to control the movement of any contaminants introduced into the Interface Aquifer beyond the property boundary (see Section 4.7 and 4.8). Safety Kleen Ltd. (predecessor to Clean Harbors Canada, Inc.) was subsequently required to undertake a demonstration program to determine the viability of applying this technology at the Lambton Facility. The work involved pumping of four wells (OW1-92, PW1-N, PW2-99 and TW1-99) for varying intervals starting in January 2001 with OW1-92, adding PW1-N and TW1-99 in March 2001 and PW2-92 in May Pumping continued at all four wells to August 28, 2001, at which time the test was terminated. The test duration was intended to simulate near steady state conditions in the vicinity of the wells. The information collected during the test was compared with output from a groundwater flow model, which was developed to assess the influence of purge pumping on the Interface Aquifer. The test results and predicted drawdown from the model simulation show a reasonable match within the central area of the Facility property that overlies a zone of higher hydraulic conductivity (Figure 7-5). Beyond this zone, the modeled heads diverged from the observed values indicating a poor match. It was interpreted that steady state conditions (during pumping) had not been achieved in the low conductivity zones. The model was subsequently employed to optimize the locations of purge wells for capturing groundwater below the landfill footprint. The simulation suggested that a well located central to the Lambton Facility property (such as near OW1-92) would be capable of capturing groundwater from most of the site footprint with the exception of the northwest corner of the property and possibly the central western portion. It was recommended that that additional purge wells be installed. These wells, (PW5-03) located close to the northeast corner of the Lambton Facility property and (PW4-03) located in the vicinity of OW1-92, were installed in The testing was undertaken in July A drawdown response during pumping at PW4-03 was observed at OW1-92. The analysis solution resulted in a transmissivity of 8.1 x 10-4 m 2 /s. The estimated hydraulic conductivity is included in Table Hydraulic Conductivity Bedrock Formations Information on the hydraulic conductivity of the shale bedrock below the Interface Aquifer at the Lambton Facility is limited to single response tests (slug tests) completed at two wells (TW32-94-I and TW ) installed near the northeast corner and central area of the property and at a deep installation (LD-90-03) installed by the University of Waterloo, near the southwest corner of the property. The estimated hydraulic conductivity data are listed in Table

89 Table 7-6. Summary of Hydraulic Conductivity Data for Bedrock Formations Reference Hydraulic Conductivity (m/s) Type of Test Jagger Hims Limited (1996a) 1 x 10-7 Single Well Response Test (slug test) at TW32-94-I completed in Kettle Point Formation just above contact with Hamilton Group. 5 x 10-7 Single Well Response Test (slug test) at TW38-94-I completed at Kettle Point Formation/Hamilton Group contact. Weaver (1994) 1.6 x 10-7 Single Well Response Test (recovery test) at LD (Kettle Point Formation). 1.6 x 10-11, 7.5 x 10-8, 3.4 x Single Well Response Tests (recovery tests) at LD , LD and LD (Hamilton Group) Influence of Natural Gas on Hydraulic Conductivity The presence of natural gas has been noted in many of the boreholes and wells advanced/installed on the property. It is not uncommon to experience an upward surge in the water level and gas discharge during well development and purging or testing, which is induced as the confining head of water is reduced and degassing occurs. For example, wells OW12-83-I(D), OW31-90D, OW1-92, TW32-94-I, TW35-94-I, TW36-94-I, and TW37-94-I have exhibited gas induced surging, and wells TW22-99D, TW33-94-I, TW46-99D, TW55-09D, TW56-11D, TW57-11D, TW59-13D, TW60-13D and TW61-13D have a minor gas releases noticeable as bubbling/gurgling when purged. The presence of gas is expected to influence the hydraulic conductivity test results in the following ways: will reduce the fluid density, resulting in a higher calculated hydraulic conductivity then estimated based on a water response alone; and gas present in pore spaces and fractures will block fluid movement towards the well, resulting in a lower hydraulic conductivity. The hydraulic conductivity values for the above listed wells (Figure 7-5) should be viewed with this knowledge. Weaver (1994) observed that the Kettle Point Formation at the Clean Harbors Facility investigation site (southwest corner of the property) contained up to 20% by volume gas and offered the commentary that when the effect of this gas was incorporated in the hydraulic head calculations, density-corrected head values were up to 12 m higher than those calculated assuming pure water. The occurrence of natural gas in the bedrock ridge below Sub-cell 3 combined with the zone of higher hydraulic conductivity along the ridge and the thinning of the overlying till are contributing factors to the formation of fissures at the base of the sub-cell through which groundwater and gas were released. 78

90 7.3.7 Groundwater Flow Active Aquitard and Transition Zone: Groundwater movement in the overburden is influenced by weathering and fracturing, and the occurrence and distribution of coarser-grained deposits. As noted in Section 7.2, seasonal desiccation and freeze-thaw cycles, and solute dissolution, movement and reprecipitation have physically/chemically altered the shallow fine-grained glacial deposits (till and glaciolacustrine sediments). The intensity of this alteration (i.e., fracturing) decreases with depth from the surface, with only infrequent fractures observed below a depth of 4 m to 5 m. Water movement occurs preferentially through fractures and coarse-grained deposits. Because the hydraulically active zone is shallow, the flow path is short, being influenced both by the local undulating topography (ridges and swales) and manmade features such berms, ditches, deep excavations, or drainage tiles. The granular materials (medium to fine sand and silt) are locally present at surface as remnant nearshore deposits and are observed within the clay rich overburden as isolated pockets or lens. The pockets/lens of granular will influence hydraulic activity within the fractured zone. Below the fracture zone the units are hydraulically isolated within the aquitard and will have little influence on groundwater flow. The lower hydraulic conductivity limits the downward percolation of precipitation and promotes lateral movement through the shallower hydraulically active zone. The zone of decreasing hydraulic activity is typically less than about 8 m but may extend to a depth of 12 m or more locally (from observed tritium concentrations). Pattern of Groundwater Movement: Groundwater levels expressed as elevation levels for the shallow wells installed in the Active Aquitard including wells installed in the waste cells for the March and September 2013 monitoring events are compiled in Figure 7-6. The groundwater elevations generally mirror the local ground surface topography. The water level is mounded below topographic highs (i.e., perimeter screening berms and the Pre-1986 Landfill area) and depressed in the vicinity of drainage trenches, retention ponds and open landfill cells. The influence of the berms on groundwater levels is illustrated in Table 7-7, which lists 2013 water level elevations for wells within and adjacent to the berm. Well locations are shown in Figure 3-3. With reference to Table 7-7, the water levels recorded at shallow wells (TW39-99I, TW46-99I and TW61-13S) installed in the weathered/fractured clay overburden immediately below the fill of the northern berm are generally within a range of 2 m to 3 m higher than wells [TW21-94II(S), TW22-94(S), TW32-94IV(s) and TW35-90(s)] installed at similar depths exterior to the berm. The height of this berm is between 10 m and 12 m above the original ground surface. The southern berm extends about 4 m to 4.5 m above the original ground surface. The head differential between shallow wells (TW50-02B, TW51-02B and TW52-02B) installed in the weathered/fractured clay overburden immediately below the berm fill and wells (TW50-02A, TW51-02A and TW52-02A) installed north of the berm at similar depths, ranges between a few centimeters and few metres. The mounding within the berm acts as a barrier to the shallow movement of groundwater flow below the berm. This is illustrated in cross section in Figure 7-7. The cross section extends southward from the Pre Landfill area, across the drainage ditch to the south berm. 79

91 Table 7-7. Shallow Groundwater Levels in the Vicinity of the Facility Berms Northern Berm Wells Installed in Berm Nearest Wells Removed from Berm TW39-99S (in Berm) TW39-99I (below Berm) TW21-94-II(S) TW22-94(S) Mar. 29, 2013 Sept. 24, 2013 Mar. 29, 2013 Sept. 24, 2013 Mar. 29, 2013 Sept. 24, 2013 Mar. 29, 2013 Sept. 24, TW46-99S (in Berm) TW46-99I (below Berm) TW32-94-IV(S) OW35-90(S) Mar. 29, 2013 Sept. 24, 2013 Mar. 29, 2013 Sept. 24, 2013 Mar. 29, 2013 Sept. 24, 2013 Mar. 29, 2013 Sept. 24, TW61-13S (in Berm) TW61-13I (below Berm) TW22-94(S) Mar. 29, 2013 Sept. 24, 2013 Mar. 29, 2013 Sept. 24, 2013 Mar. 29, 2013 Sept. 24, 2013 NA NA Southern Berm TW50-02B (below Berm) TW50-02A Mar. 29, 2013 Sept. 24, 2013 Mar. 29, 2013 Sept. 24, TW51-02B (below Berm) TW51-02A Mar. 29, 2013 Sept. 24, 2013 Mar. 29, 2013 Sept. 24, TW52-02B (below Berm) TW52-02A Mar. 29, 2013 Sept. 24, 2013 Mar. 29, 2013 Sept. 24, The water table is mounded within the landfill area, depressed at the ditch and mounded below the berm. Groundwater movement is towards the ditch from both the landfill and the berm. The berm around the northern perimeter of the property combined with the drainage ditches installed to the interior of berms influence shallow groundwater and leachate movement in a similar manner. Groundwater movement through the shallow fracture zone (Active Aquitard) is governed by the following equation: where: v = average linear velocity (m/s), k = hydraulic conductivity (m/s), i = hydraulic gradient (m/m), and n = porosity (unitless). The hydraulic gradients in the shallow subsurface will be influenced by the local topography, being comparatively large near features such as berms and ditches, and is essentially flat within the clay plain where relief is influenced by the local ridge and swale topography. As examples, the hydraulic gradient calculated from water level data for wells located in and adjacent to the southern berm (Figure 7-7) is estimated as 0.07 m/m. The hydraulic gradient for the clay plain (ridges and swales, which have a water table elevation differential of 0.1 m to 0.3 m, and are typically spaced about 50 m to 75 m apart) is between m/m and m/m. 80

92 The linear velocities calculated for flow through the matrix of the clay and through fractures in the clay for the range of conditions follow: Hydraulic Parameter range Conductivity (m/s) Hydraulic Gradient (m/m) Porosity (unitless) Linear Velocity (m/day) Fracture Flow 2.1 x 10-7 * x 10-4 * 1 x 10-3 * Matrix Flow 2 x ** ** 0.345** 3.8 x x 10-8 (*) geometric mean hydraulic conductivity and porosity values as reported in McKay et al. (1993). (**) hydraulic conductivity and porosity values from McKay (1991). Groundwater Level Fluctuations: Water level data have been collected at wells installed in the overburden on the Lambton Facility property since the initiation of groundwater monitoring in the 1970s. Depending on the location, well depth and geology, the water level fluctuates by 2 m to 4 m, showing seasonal variation (i.e., high water levels in the spring and lower levels in the fall). Hydrographs for all shallow monitoring wells are provided in Appendix D.1.1. Hydrographs for four representative monitoring wells around the perimeter of the site [OW32-90S, OW35-90S TW32-92-IV(S), and TW22-94] and for four representative off-site wells [TW35-94-II, TW36-94-II, TW37-94-II and TW42-99S] are presented in Figure 7-8 (locations shown in Figure 3-3). Depending on the well s location, depth and the local geology, the water level at individual wells fluctuate between 2 and 4 m, showing seasonal variation (i.e., high water levels in the spring and lower levels in the fall). Ten wells were installed in the waste cells in 2011 as part of the investigations being conducted for the Environmental Assessment that is currently underway. The locations of the wells are shown in Figures 3-3. These wells were equipped with data loggers in August 2012 and monitoring was conducted for a period of one full year (to August 28, 2013). Manual measurements were obtained at the time the transducers were installed (August 16, 2012) and each time the transducers were downloaded (November 14, 2012, March 18, 2013 and August 28, 2013). The transducer data were compensated for barometric pressure and the resulting levels were subsequently adjusted for leachate density. The calculation employed in making this adjustment follows: Well Fluid Elevation = (A - B) x C +B, where A = Measured Fluid Elevation (masl); B = Elevation of Base of Screen (masl); and C = Calculated fluid density = [measured density (g/cc) E-03 x TDS (% w/w)]. The hydrographs for the ten (10) wells installed in the waste cells are provided in Appendix D.1.2. For presentation purposes the hydrographs for the wells are grouped by the location of the well (Pre-1986 Cells, Cell 16, Cell 17 and Cell 18). Included in the hydrographs is precipitation data from the Sarnia Climate Weather Station located at Chris Hadfield Airport in Sarnia, Ontario. 81

93 The pressure head of leachate at most of the wells is above the landfill cap/waste interface. The notable example is LM5-11 (north end of Cell 16) where the hydrostatic pressure potential in the waste extends between 1.65 m and 1.85 m above ground surface. The elevated leachate head is attributed to this area being surrounded by topographically raised areas (berm to east and Pre-1986 Landfill to west, and to presence of a large stockpile of clay that has been placed on the cap just east of the well. The stockpile covers an area of about 23,000 m 2 and has an estimated volume of 107,000 m 3. As illustrated in the hydrographs, the pattern of response over the period of record (August 2012 and August 2013) is influenced by precipitation events and changes in barometric pressure. The overall amplitude of fluctuation for the one year of record is generally less than 1 m and the general trend, with a few exceptions, is flat. The leachate level for well LM3-11 installed in the northeast portion of Pre-1986 Landfill (Appendix D.1.2), increased by over 0.5 m between October 31 and November 4, 2012 and remained elevated until early June 2013, after which the level declined. The initial increase corresponds to a major rainfall event (i.e., Sarnia Climate weather station recorded a total of 71 mm of precipitation between October 28 and 31, 2012). The leachate level at other wells installed in the waste show a smaller increase, which subsequently declines as is typical of recession following a precipitation event. There is no explanation for the sustained increase in the level at LM3-11 between the end of October 2012 and June The leachate levels at LM7-11, LM9-11 and LM10-11 exhibit a slight increase (0.5 m) over the period of record. The decline in the leachate level at LM7-11 in late August 2013 (Figure D.1.2) is related to the displacement of soil associated with the excavation of a new cell in the landfill cap near this well. Interface Aquifer: The deep wells of the monitoring well network are installed such that the well screen either straddles the overburden/bedrock contact if the Basal Till (sandy/silty till) is encountered, or if absent, the screen is set fully within the upper meter or so of the bedrock. This contact zone, which has historically been exploited as a source of water, is referred to as the Interface Aquifer. With the installations of municipal water servicing throughout St. Clair Township, groundwater takings from the aquifer in the vicinity of the Facility have declined significantly, with only a few wells used for non-potable purposes. The hydraulic head in the aquifer has been increasing as water takings have decreased. Pattern of Groundwater Movement: A series of figures (Figure 7-9, Figure 7-10, Figure 7-11 and Figure 7-12) were prepared to illustrate hydraulic head changes in the Interface Aquifer in the vicinity of the Lambton Facility property using historical water level data provided in Annual Landfill Reports. Figures 7-9 through Figure 7-11 present the contoured groundwater hydraulic head elevations within the Interface Aquifer for 1980, October 1993, September 1991, May 1995, June 2000 and September The outlines of the major waste disposal areas and Petrolia Line and Telfer Road are imposed on the figures to assist with location reference. The hydraulic head elevations for March and September 2013 are presented in Figure The level of detail provided in these figures increases as additional monitoring wells are installed at the Facility. Also, as the period covers three decades, various wells have been decommissioned and replaced with newer installations to reflect changing well construction standards. The earliest data sets (1980, 1983 and 1991) show groundwater flow to be towards the east northeast from a high centred near well OW

94 With the installation of well nest TW35-94 west of the Facility in 1994, the contouring shows the potentiometric surface to be mounded below the property (Figure 7-10). The Lambton Facility property is on regional topographic and bedrock surface highs. The ground surface at the property has also been loaded with the placement of waste and displacement of excavated native soil material to the periphery of the landfill cells. The June 2000 dataset (Figure 7-11) shows the effects of active groundwater pumping in the vicinity of Sub-cell 3 (Cell 18), which was undertaken to during construction of the remedial structure installed in the sub-cell. The contours close around the pumping wells that were employed at that time to reduce the hydraulic head pressure in the aquifer for remedial construction within Sub-cell 3. Pumping was discontinued in 2001 and the September 2006 dataset (Figure 7-11) shows the water level had largely recovered. Contoured groundwater hydraulic head elevations within the Interface Aquifer for March and September 2013 are presented in Figure The September 2012 and March 2013 groundwater elevation contours indicate flow within the Interface Aquifer to be outward from a groundwater high (potentiometric high) that extends to the southeast from well TW39-99D through TW22-99D towards TW33-94-I(D). Well TW22-99D is under artesian conditions and the water level has consistently been above ground surface. Wells PW1-N and PW2-S(R11) were being actively pumped starting in February 2012 to extract surface water introduced into the aquifer as a result of flooding that occurred in 2011 in the vicinity of Sub-cell 3. The drawdown induced by this pumping is evident in Figure The drawdown cone is elongated expanding outward from the pumping wells along the more permeable zone in the Interface Aquifer and truncated to the west where the hydraulic conductivity of the aquifer below is lower. Groundwater Fluctuations in Deep Wells: Figure 7-13 shows the water level (hydraulic head) response with time at representative Interface Aquifer wells located on the Facility property [TW40-99D, TW32-94-II(D), OW35-05D and OW1-92] and off the Facility property [TW35-94-I(D), TW36-94-I(D), TW37-94-I(D) and TW49-00D]. The downward response observed in the hydrographs generated for TW40-99D and OW1-92 in 1999 was initiated by pressure release of groundwater and gas through stress fractures that formed in the base of Subcell 3. Depressurization pumping from the Interface Aquifer was subsequently undertaken during implementation of remedial measures at Sub-cell 3. A test program involving two wells (OW1-92 and PW1-N) was conducted in 2001 to assess the viability of using purge wells to control groundwater movement in the Interface Aquifer. The water level at OW1-92 and TW40-99D (Figure 7-13) was drawn down in response to the pumping conducted at these wells and posttesting recovered to pre-1999 levels. Pumping was initiated at PW1-N and PW2-S(R11) in Spring 2012 to remove surface water that had been introduced at PW2-S(R11) as a result of flooding that occurred in The response to pumping is evident in the hydrograph for well TW40-99D (Figure 7-13). Well TW40-99D is located about 100 m north of PW-1N. 83

95 The water levels measured at wells TW32-94-II(D) and OW35-90D (and its replacement well OW35-05D) located at the northeast corner of the Facility property, and at wells TW36-94-I(D) and TW37-94-I(D) located to the east of the site exhibit a near continuous rising trend. The increase in the water levels at these wells is attributed to the reduction/discontinuation of groundwater extraction from wells for supply purposes at the residences and farms along Petrolia Line following the extension of the West Lambton Water Supply System into the area in the early 1990s. With the resulting availability of a ready source of high quality water, the use of private wells declined. The hydrograph for well TW35-94-I(D) also shows rising trend although the response is more muted. This well is located about 1 km south of Petrolia Line and the water level at TW35-94-I(D) would be less influenced by the water takings at the residential/farm wells along Petrolia Line. The general rise in the potentiometric surface in the Interface Aquifer is consistent with commentary in Weaver (1994) and Hussain (1996). Both observed that, as the aquifer readjusts to the declining water taking, the regional pattern of groundwater flow and the hydraulic gradients in the area will change. This adjustment was predicted to result in an increased hydraulic head in the Interface Aquifer, which in turn would lead to near-flat vertical and horizontal gradients. The early portion of the hydrograph for well TW49-00D (Figure 7-13) exhibits the effects of prolonged development of the well to remove drilling mud. Following development the water level fully recovered. Whereas most of hydrographs exhibit minor seasonal fluctuations on the order of a few to tens of centimeters, the water level at TW49-00D fluctuates seasonally by one to two metres. There is no current explanation for the largely seasonal fluctuation at TW49-00D. The calculated linear velocity for groundwater movement through the Interface Aquifer is provided in the following table: Parameter range Hydraulic Conductivity [m/s]* Movement to West 4 x 10-6 Movement to East/ Northeast to 5.1 x 10-6 Hydraulic Gradient [m/m] (pre-pumping) (2013 data) (pre-pumping) (2013 data) Estimated Porosity [unit less] Notes: (*) Geometric mean hydraulic conductivity from pumping test data (Safety Kleen Limited, 2000) Linear Velocity [m/year] 20 to 70 6 to 22 Vertical Hydraulic Gradients between Active Aquitard and Interface Aquifer: Groundwater movement across the intact/unfractured clay between the two hydraulically active units (i.e., Inactive Aquitard and Interface Aquifer) is very slow being influenced by the low hydraulic conductivity of the intact clay. The direction of movement is dependent on the vertical hydraulic gradient between the overlying Active Aquitard and the underlying Interface Aquifer. The hydraulic gradients across the Inactive Aquitard have been calculated using water level data for 2013 at the nested shallow and deep monitoring wells. The distribution of the gradients is shown in Figure A negative value indicates an upward hydraulic gradient at the referenced location. 84

96 Calculated Vertical Hydraulic Gradient (m/m) Geology and Hydrogeology Existing Conditions Final Report The vertical gradient below the site has been evolving as a result of changes in the potentiometric head in the Interface Aquifer. As discussed in the previous section, water levels at wells screened against the Interface Aquifer in the general vicinity of Petrolia Line have been increasing. This has in turn, resulted in a general decrease in the downward hydraulic gradients at many of the wells in this area and in some instances the emergence of upward gradients, as illustrated in the following graph Upward Gradient Downward Gradient TW22-94/99 (S/D) TW39-99 (I/D) TW21-94-II/TW47-00D TW46-99S/I/D TW32-94-II/IV TW35-94S/D & TW59-13S/D Well TW22-99D is under artesian conditions and groundwater levels have consistently been above ground surface. The hydraulic gradient at the well nest (TW22-94S/TW22-99D) has also been consistently upward at this location. The gradient at well nest TW39-99 has been relatively flat fluctuating between slightly upward and downward. [Note: The gradient at well nest TW39-99 is calculated using the water level data observed at the intermediate depth well TW39-99I (installed in the native clay unit below the berm) and the data for deep well TW39-99(D) at this location.] The drawdown induced by pumping of PW1-N and PW2-S(R11) is evident in the hydraulic gradients at well nests (TW22-94S/TW22-99D and TW39-99) starting in late The gradient between well pair TW47-00D and TW21-94S shows the largest response over time. The gradient at this well nest was predominately downward but decreased steadily between 2003 and 2009, and reverse (to upward) between 2009 and With the initiation of pumping at PW1-N and PW2- S(R11) in 2012, the hydraulic gradient has reversed again and now downward. 85

97 Calculated Vertical Hydraulic Gradient (m/m) Geology and Hydrogeology Existing Conditions Final Report The downward hydraulic gradients at nests TW32-94-II/IV, TW35-94S/D/TW59-13S/D and TW46-99S/D have similarly decreased as a result of the general recovery in the water levels at the deeper well installations. As illustrated in the graph that follows, the hydraulic gradients at well nests located further removed from Petrolia Line are somewhat flatter and exhibit seasonal fluctuations Upward Gradient TW37-94 TW41-99 OW32-90 TW30-94S/TW30-99D TW42-99S/TW49-00D TW43-99 Specifically, the hydraulic gradient at most of the well nests (with the exception of TW30-90 and TW42-99S/TW49-00D) fluctuates between downward and upward on a seasonal basis. The hydraulic gradient at TW30-90 and TW42-99S/TW49-00D is downward, although the magnitude of the gradient changes seasonally. The March and September 2013 plots in Figure 7-14 presents the hydraulic gradients across the clay aquitard after 14 months and 20 months of pumping from wells PW1-N and PW2-S(R11). The hydraulic gradient below the waste cells as inferred from the measured leachate levels at the waste wells and the potentiometric surface in the Interface Aquifer is primarily downward with a few exceptions. Vertical hydraulic gradients estimated at wells LM7-11, LM8-11 and LM9-11 (located at the western end of waste Cells 17 and 18) are flat to slightly upward. This may be an artifact of contouring reflecting the distribution of the data points (i.e., majority of wells being located west of screening berm). 86