APPENDIX H-3 PRELIMINARY DEWATERING EVALUATION REPORT

Transcription

1 APPENDIX H-3 PRELIMINARY DEWATERING EVALUATION REPORT

2 400 Exchange, Suite 100 Irvine, California Tel: Fax: June 30, 2008 Mr. Donald Chae and Mr. Min Chae 6940 Beach, LLC 3100 East Imperial Highway Lynwood, California / Subject: Preliminary Dewatering Evaluation Report - DRAFT Proposed Mixed-Use Development Beach Boulevard and Orangethorpe Avenue, Buena Park, California Dear Donald and Min, Summarized in this letter are the results of the preliminary dewatering evaluation for the Mixed- Use Development Project (Project) located at Beach Boulevard and Orangethorpe Avenue in Buena Park, California (Site). This report has been prepared for Arete Development to support the Environmental Impact Report (EIR) currently being prepared for the Project. For the evaluation, preliminary dewatering criteria were based on existing geologic information available for the Site and other nearby properties and on available Project information obtained from EDAW. This information is summarized below along with the results of the evaluation. To date, no specific structure foundation plans are available for the Project. Final dewatering requirements such as depth and/or duration for construction dewatering are currently not known for the Project. Based on Petra s January 2008 Geotechnical Feasibility Assessment, the depth of excavation is assumed to be 30 feet below ground surface (bgs). Based on EDAW conceptual drawings, the bottom of the subterranean parking structure appears to be approximately 35 feet bgs. Given this, the bottom of the excavation for the proposed parking structure was assumed to be 35 feet bgs. Rational for Dewatering The Site consists of approximately acres and is bounded to the north by Melrose Street, to the south by Orangethorpe Avenue, to the east by Brenner Avenue, and to the west by Beach Boulevard. Based on EDAW s conceptual drawings, the Project consists of residential towers, potential office space, a hotel, retail stores, and a three-level subterranean parking structure. The parking structure is shown as being beneath the entire Site which is square shaped and approximately 750 by 750 feet in size. In EDAW s conceptual drawings, the subterranean parking structure appears to be approximately 35 feet deep. Using a surface elevation of approximately 75 feet mean sea level (msl) as indicated by Petra (2008), the bottom of the subterranean parking structure would be approximately 40 feet msl. Based on groundwater elevation data for existing groundwater monitoring well MW-1 located at the Buena Park Car Wash, groundwater at the Site occurs at approximately 15 to 16 feet bgs (approximately 60 feet mls) and ranges in the vicinity of the Site between approximately 8 and 25 feet bgs. Based on the these data, approximately 20 to 25 feet of groundwater will need to be dewatered across the Site for construction of the subterranean parking structure and possibly permanently depending on engineering specifications for the Project. E n v i r o n m e n t a l E n g i n e e r s & C o n s u l t a n t s

3 Mr. Donald Chae and Mr. Min Chae 6940 Beach, LLC June 30, 2008 Page 2 Conceptual Geologic Model and Model Input Parameters A review of available environmental regulatory files for nearby properties was performed to find pertinent information for input to the dewatering evaluation. Pertinent information, including lithologic logs, groundwater elevation data, groundwater contaminant concentrations, and other hydraulic parameters, was available from the following properties: Buena Park Car Wash, located at the southwest corner of the proposed project area, at 6976 Beach Boulevard (Equipoise, 2007); Valero Gasoline Service Station, located at the southwest corner of the proposed project area, at 7751 East Orangethorpe Avenue (England Shahn & Associates, 1995); Chevron Gasoline Service Station, located to the west of the proposed project area, at 6971 Beach Boulevard (Conestoga Rover, 2007); Lube Facility (Former G&M Oil), located to the north of the proposed project area, at 6812 Beach Boulevard (Leighton Consulting, 2007); and Former Shell Service Station, located to the east of the proposed project area, at 7979 Orangethorpe Avenue (Wayne Perry, 2007). In addition to information from the properties listed above, information from the Phase I Environmental Site Assessment (ESA) performed by Brown and Caldwell (2008) and from the Phase II Investigation by Brown and Caldwell (2008) was also used to develop the conceptual geologic model from which the evaluation was based. Project and geologic information was also obtained from the geotechnical feasibility assessment conducted by Petra (2008) for the Site. Site Soil: Numerous shallow borings are available at, and in the vicinity of, the Site. These borings, many of which were converted to shallow groundwater monitoring wells, are typically 20 or 25 feet in depth. At the Site, only two deep borings by Petra (Borings B-1 and B-2) were drilled to depth (approximately 80 feet bgs) to characterize deeper subsurface conditions. These borings form the basis of the conceptual geologic model for the Site as summarized below. 0 to 20 feet bgs: Shallow soil at the Site to approximately 20 feet bgs consist primarily of fine to medium sand and silty sand with some minor clayey sand. 20 to 55 feet bgs: Starting at approximately 20 feet bgs, sandy sediments become silty with some silty clay and clayey silt to approximately 35 feet bgs where more competent clays are encountered. As indicated by the lithologic logs for Boring B-1 and B-2 (Petra, 2008), the sandy and silty clay unit observed at approximately 35 feet bgs (approximately 65 feet msl) may be continuous across the Site, potentially ranging up to 10 feet thick as observed at Boring B-2. Underlying the clay unit are silts, silty sands and sands, with some clayey sand. 55 to 80 feet bgs: At approximately 55 feet bgs, the Lakewood Formation is encountered. The upper Lakewood Formation at the Site consist of medium dense silty sand to approximately 65 feet bgs with underlying sandy clays and clayey silts occur to the maximum depth of the borings at approximately 80 feet bgs. Groundwater Conditions: Unconfined groundwater conditions occur that the Site with groundwater occurring in between 8 and 25 feet bgs. Groundwater at monitoring well MW-1 located at the Buena Park Car Wash occurs at approximately 15 to 16 feet below top of casing. Based on available information from groundwater monitoring wells, it is not understood if this water is perched on the upper clay unit located at 35 feet bgs or if this water is in hydraulic connection with deeper sandy units. Based on depth to groundwater measurements from the 2008_06_30 Engineering Dewatering Evaluation.doc

4 Mr. Donald Chae and Mr. Min Chae 6940 Beach, LLC June 30, 2008 Page 3 Buena Park Car Wash (Equipoise, 2007) groundwater flow at the Site is typically to the southwest (approximately 205 degrees relative to true north) at gradient of approximately At this time, no Site specific hydraulic parameters (hydraulic conductivity, storativity, or specific yield) are available to perform a detailed hydraulic evaluation. Given this, the preliminary evaluations performed have inherent uncertainty and should not be relied upon to develop final construction specifications. Further aquifer testing and pilot testing is required to reduce this uncertainty. Based on available lithologic logs, a hydraulic conductivity equal to one-foot per day was assumed to be representative of the shallow sediments at the Site. This value is typical of silty sand (Freeze and Cherry, 1979) and is consistent with the permeability values presented by Petra (2008) for the shallow alluvium sand-silt mixtures which were reported to range between 3 x 10-5 and 3 x 10-9 feet/second (i.e., 2.6 to feet per day). For all simulations, a porosity of 0.25 was assumed with a storage coefficient and specific yield of and 0.25, respectively. Preliminary Design Criteria: For the preliminary evaluation, a target depth for dewatering was set equal to the top of the upper clay unit observed at 35 feet bgs or at approximately 40 feet msl. It was assumed that this clay unit is laterally continuous through the vicinity of the Site. This depth roughly coincides with the likely depth of the subterranean parking structure based on preliminary drawings provided by EDAW. Preliminary Dewatering Simulations Preliminary simulations were performed using WinFlow (Version 3.11; Environmental Simulations, Inc. 2003), an analytical groundwater flow model. WinFlow is an interactive, analytical modeling tool that simulates two-dimensional steady-state and transient ground-water flow in the horizontal plane assuming that ground-water flow is horizontal and occurs in an infinite aquifer that is isotropic and homogeneous. The base of the aquifer is horizontal and fixed at a given elevation. In the steady-state and transient models, the top of the aquifer is also horizontal and fixed at a given elevation. In the steady-state model, however, unconfined conditions are simulated when the hydraulic head is below the top of the aquifer. In the transient model, the aquifer is always confined, even when the head falls below the top of the aquifer. Pumping rates, linesink fluxes, pond recharge, and elliptical recharge rates are constant through time. In the transient model, wells start pumping or injecting water at time zero. Wells are assumed to fully penetrate the aquifer. Wells are assumed to be perfectly efficient and linesinks are in perfect hydraulic communication with the aquifer. Simulations Performed: The following scenarios were simulated to develop a preliminary understanding of the dewatering impacts at the Site: 1. Baseline groundwater flow scenario; 2. Steady state drawdown scenarios using linesinks (French drains); and 3. Steady state pumping scenarios using wells. The analytical grid for the simulations was 10,000 feet by 10,000 feet with the southeast corner of the Site located in the middle of the grid with a x:y coordinate equal to 5000:5000 feet. For the baseline simulation, groundwater flow across the Site was simulated with a gradient of to the southwest at 205 degrees relative to north. Groundwater elevations at MW-1 (Buena Park Car Wash) in the baseline simulation were simulated to be approximately that 2008_06_30 Engineering Dewatering Evaluation.doc

5 Mr. Donald Chae and Mr. Min Chae 6940 Beach, LLC June 30, 2008 Page 4 measured at the Car Wash in late This simulation was used to calculate drawdown for subsequent simulations. To evaluate the amount of pumping required to lower water levels below the proposed subterranean structure (i.e., at 35 feet bgs), constant head linesinks were used to simulate the effects of deep perimeter drains located around the Site. Two separate scenarios were run; a) assuming that the underlying clay at 35 feet bgs is an effective hydraulic barrier to groundwater up-flow with no significant leakage from underlying sediments, and b) assuming that the underlying clay is not an effective barrier to up flow and the bottom of the aquifer coincides with the deeper clay unit observed at approximately 65 feet bgs. Given that wells will likely be used to dewater and control groundwater at the Site for construction, dewatering simulations were preformed using nine on-site wells. For these simulations, four wells were located on the upgradient side of the Site (eastern side) with three wells located on the downgradient side (western) of the Site. Two wells were located within interior of the Site. Both a competent clay unit at 35 feet bgs scenario as well as the deeper aquifer scenario with the base of the aquifer located at approximately 65 feet bgs was simulated similar to the linesink scenarios described above. Results The results of the simulations are presented below and on Figures 2 though 4. As indicated on Figure 2, streamlines 1 from the steady state scenario using constant head linesinks to simulate perimeter dewatering using French drains indicate that once dewatered, the groundwater from surrounding areas will be directed towards the Site. Once at steady state (i.e., once water level decline in close proximity of the Site has stabilized) total inflow into the drains for the simulations presented range from approximately one gallon per minute (gpm) for dewatering above a competent clay unit to approximately 10 gpm if the clay unit is not continuous and the bottom of aquifer is approximately 65 feet bgs. For the dewatering simulations using wells (Figures 3 and 4), wells were pumped at five gpm. As indicated on Figure 3 drawdown inside the Site boundary approaches approximately 20 feet after approximately 20 days of pumping (i.e., water levels inside the excavation are lowered to approximately 65 feet msl). As indicated on Figure 4, drawdown after approximately 40 days approaches approximately 25 feet. In practice, once the desired drawdown and steady state conditions are reached, pumping would be reduced with total pumping theoretically approaching the steady state extraction rates observed in the linesink simulations. Given that no preliminary foundation plans or construction details or schedule is currently available, the duration of pumping required at the Site is unknown. Moreover, since these simulations are based on assumed hydraulic parameters, further evaluation is recommended to develop final construction specifications. 1 A streamline is a line that is tangential to the direction of the instantaneous groundwater velocity vector and can be seen as the path traced out by a massless particle as it moves in groundwater. The region bounded by streamlines is called a streamtube. Because the streamlines are tangent to the flow velocity, fluid that is inside a stream tube must remain forever within that same stream tube except at points where the velocity magnitude is zero, such as at a stagnation point. 2008_06_30 Engineering Dewatering Evaluation.doc

6 Mr. Donald Chae and Mr. Min Chae 6940 Beach, LLC June 30, 2008 Page 5 Impacts of Dewatering on Nearby Groundwater Contamination The Phase I ESA identified several properties in close proximity of the Site with documented groundwater contamination, including two properties on-site with known groundwater contamination. On-Site groundwater impacts were primarily attributed to leaking underground storage tanks (USTs) at the Buena Park Car Wash and the Valero Gasoline Service Station properties. Off-Site groundwater impacts were attributed to several gasoline and waste oil USTs. The maximum concentrations of contaminants detected in groundwater at these properties are summarized in Table 1. As summarized in Table 1, groundwater contamination at the Buena Park Car Wash included gasoline-range petroleum hydrocarbons (measured as total petroleum hydrocarbon (TPH) -gasoline) ranging to 112 µg/l methyl tertiary butyl ether (MTBE) at concentrations ranging to 100 µg/l, and several volatile organic compounds (VOCs) at concentrations ranging to 4,700 µg/l (Table 1). Groundwater concentration data was not available at the Valero Gasoline Service Station; however, three HydroPunch wells were installed within the sidewalk immediately to the south of the Valero Gasoline Service Station as part of the Phase II Investigation performed by Brown and Caldwell. Groundwater sampling from the HydroPunch wells detected TPHgasoline ranging to 4,600 µg/l, MTBE ranging to 2,000 µg/l, tert butyl ether (TBA) ranging to 170,000 µg/l, and several VOCs at concentrations ranging to 47 µg/l (Table 1). Historical maximum groundwater concentrations at the Chevron Gasoline Service Station are 39,940 µg/l for TPH-gasoline, 9,250 µg/l for MTBE, and 4,900 µg/l for TBA (Table 1). Maximum historical groundwater concentrations at the Lube Facility (Former G&M Oil) are 690 µg/l for MTBE and 80,000 µg/l for TPH-gasoline (Table 1). Maximum historical groundwater concentrations at the Former Shell Service Station are 60,000 µg/l for TPH-gasoline, 230 µg/l for MTBE, 28 for diisopropyl ether (DIPE), and 66 µg/l for TBA (Table 1). Lateral Extent of Influence of Site Dewatering: The results of the simulations are presented below and on Figures 2 though 4. As indicated the Figure 2, streamlines from the steady state scenario using constant head line sinks to simulate perimeter dewatering using French drains indicate that once dewatered, the groundwater from surrounding areas will be directed towards the Site. Based on dewatering simulations using wells as presented in Figure 3 and 4, the zone of contribution for the on-site perimeter wells under steady pumping at five gpm reaches the Site boundary at approximately 120 days and extends approximately 30 feet beyond the property within a year. While these simulations are highly dependent on assumed input parameters, they indicate that off-site contamination will likely be captured by the dewatering system given enough time and pumping. The time until contaminated groundwater is captured in the dewatering system is directly dependent on the assumed effective hydraulic conductivity, storativity, and specific yield of the aquifer. Site specific values for these parameters are currently not known for the Site and vicinity. Further hydraulic testing is required to estimate these parameters to verify the simulation presented herein. Estimated Influent Concentrations for Site Dewatering: Influent concentrations for on-site dewatering were estimated by developing representative dilution factors based on the either the area of impacted groundwater for short term on-site groundwater contamination or estimated 2008_06_30 Engineering Dewatering Evaluation.doc

7 Mr. Donald Chae and Mr. Min Chae 6940 Beach, LLC June 30, 2008 Page 6 linear discharge rates (i.e., gpm per foot) along the linesinks that capture off-site groundwater contamination for long-term or permanent dewatering. The results are summarized in Table 1. Based on the simulations performed, it appears that for relatively short term dewatering (i.e.,under approximately 120 days), only the on-site contamination will be captured by the dewatering wells. Since the extent of on-site contamination is not fully delineated, the maximum concentrations of petroleum hydrocarbons and VOCs detected at the Site were used to estimate influent concentrations representative of the entire property assuming that contaminant concentrations are consistent with depth and that dilution is proportional to respective land surface areas (i.e., the ratio of contaminated property area to uncontaminated surface area at the Site). As indicated on Table 1, for short term dewatering, on-site contamination will be diluted by uncontaminated groundwater (i.e., 98% dilution factor; Table 1). Using this dilution factor, estimated influent concentrations for the dewatering system were approximately 47 µg/l for petroleum hydrocarbons, 1,740 µg/l for TBA, 20 µg/l for MTBE, and 82 µg/l for total VOCs. To refine this estimate, a more detailed evaluation is required using Site-specific hydraulic parameters (hydraulic conductivity and storativity) in addition to a better understanding of the extent of impacted groundwater on-site. For long-term or for permanent dewatering (i.e., greater than 120 days), linear discharge rates along the simulated drains from the modeling simulations were used to estimate dilution factors for off-site contamination reaching the Site in time. Based on the intersection of steady state streamlines stemming from nearby properties with known groundwater contamination, the discharge of contaminated groundwater along the linesinks was estimated and used to estimate dilution factors as presented on Table 1. Using these dilution factors, conservative maximum influent concentrations were estimated. As indicated, estimated influent concentration could reach 850 µg/l for petroleum hydrocarbons, 51 µg/l for TBA, 0.3 µg/l for DIPE, and 97 for MTBE. These results were not sensitive to the depth of the underlying clay layer. As indicated on Table 1, influent concentrations assuming the bottom of the aquifer is the deep lower clay layer (at 65 feet bgs) were very similar to those using the competent underlying clay layer at 35 feet bgs. To refine these estimated concentrations, a more detail hydraulic evaluation is required using Site-specific hydraulic parameters (hydraulic conductivity and storativity) in addition to a better understanding of the extent of impacted groundwater on-site. Conceptual Treatment and Discharge of Dewater Groundwater generated at the Site from dewatering activities will be treated at the Site and discharged to the storm drain under a National Pollution Discharge Elimination System (NPDES) permit administered by the California Regional Water Quality Control Board Los Angeles Region. If only short-term construction dewatering is required for the Project, a temporary NPDES permit would be used at the Site with a trailer-mounted treatment system using activated carbon to adsorb the contaminants prior to discharge into the storm drain. For long-term dewatering, a permanent NPDES permit would be obtained. Based on the expected groundwater extraction rates and estimated contaminant concentrations, activated carbon would also likely be the best treatment alternative for a long-term treatment system. This treatment alternative would be verified in a pilot test to be conducted at the field as part of design process to ensure that the treatment system could achieve the discharge limits. 2008_06_30 Engineering Dewatering Evaluation.doc

8 Mr. Donald Chae and Mr. Min Chae 6940 Beach, LLC June 30, 2008 Page 7 The conceptual treatment system for the Project for long-term dewatering would include a holding tank, in-line filter, transfer pumps, at least two granular activated carbon vessels, and miscellaneous gauges and controls (i.e., pressure, flow totalizer, control switches). The activated carbon will adsorb the contaminants (i.e., MTBE, TBA, and VOCs) to treat the water stream. The treatment system will encompassed an area of approximately 20 feet by 20 feet and would be secured with a fence and locking gate. The treated water will be discharged to the storm drain criteria set by the NPDES permit. The NPDES permit will establish the monitoring, testing, and reporting requirements including discharge limits for specific contaminants. The discharge limits for individual contaminants would likely be will set at California Department of Public Health maximum contaminant limits (MCLs) for drinking water. Routine operation and monitoring would be conducted on a weekly to monthly basis as specified by the permit. Conclusions and Recommendations Based on assumed hydraulic input parameters, a two-dimensional groundwater flow model was used to simulate various dewatering scenarios for the Project for the construction of a subterranean parking structure to beneath the entire Site. Assuming isotropic and homogeneous groundwater conditions, the dewatering scenarios were used to develop a preliminary understanding of potential impacts at properties with known groundwater contamination. Using linesinks to simulate perimeter French drains under steady state flow conditions (i.e., the drop in waterlevels have stabilized in proximity of the Site), streamlines indicate that groundwater from around the entire perimeter of the Site is captured by the drain system. At steady state, extraction rates vary depending on the competency of the underlying clay unit observed at approximately 35 feet bgs, with the total extraction rate ranging up to approximately 10 gpm assuming an effective hydraulic conductivity of one foot per day and that the underlying clay at 35 feet bgs is not competent. Based on the lateral extent of streamlines from the steady state simulations, if continuous dewatering is required at the Site, a French drain system will eventually capture groundwater contamination from nearby properties. Based on current extent of groundwater impacts and dilution estimates, these contaminants will be greatly largely diluted. Dewatering of the Site to approximately 35 feet bgs using wells will likely require at least nine groundwater extraction wells each pumping at least five gpm for several weeks. Once the desired water levels are obtained and steady state conditions are reached, the extraction rates could theoretically be reduced to the total extraction rates of approximately 10 gpm obtained from the constant head linesink simulation discussed above. Given the dependency of results on assumed model input parameters (hydraulic conductivity, storativity, and specific yield), Brown and Caldwell recommends that a detailed field investigation be conducted at the Site to delineate the extent of groundwater contamination on- Site and to develop Site specific estimated of key hydraulic parameters. Included in this evaluation should be an aquifer test(s) designed to 1) derive Site-specific hydraulic parameters for the shallow (0 to 30 feet bgs) sand and silty sand unit required to refine the preliminary evaluation, and 2) test the competency of the clay unit located at 35 feet bgs. Groundwater generated at the Site from dewatering activities will be treated at the Site and discharged to the storm drain under a NPDES permit administered by the California Regional Water Quality Control Board Los Angeles Region. The discharge limits for individual contaminants would likely be will set at California Department of Public Health MCLs for drinking water. For short-term construction dewatering, a temporary NPDES permit would be 2008_06_30 Engineering Dewatering Evaluation.doc

9 Mr. Donald Chae and Mr. Min Chae 6940 Beach, LLC June 30, 2008 Page 8 used at the Site with a trailer mounted treatment system using activated carbon to adsorb the contaminants prior to discharge into the storm drain. For long-term dewatering, a permanent NPDES permit would be obtained and a permanent activated carbon treatment system would be constructed. A pilot test would be conducted at the Site as part of the design process to ensure that the treatment system could achieve the discharge limits. Limitations and Certification This document was prepared for Arete Development to support the EIR currently being prepared. The results, findings and discussion of results presented in this document were based in part on information made available to Brown and Caldwell. Brown and Caldwell have not made an independent investigation as to the validity, completeness, or accuracy of such information. To date, no specific structure foundation plans are available for the Project. Actual dewatering requirements such as depth and/or duration are currently not known for the Project. In addition, since the evaluation was largely based on assumed specification and input parameters and including hydraulic conductivity, storativity, and specific yield assuming that the underlying sediments are isotropic and homogenous in nature, the actual response of the underlying sediments to pumping is not known. Brown and Caldwell recommends that a detailed field investigation be conducted at the Site to delineate the extent of groundwater contamination on- Site and to develop Site specific estimated of key hydraulic parameters necessary to develop a more rigorous understanding of the likely effects of pumping at the Site. Brown and Caldwell appreciate the opportunity to provide the services described herein. If you have any questions regarding this report, please call us at (714) Very truly yours, BROWN AND CALDWELL Juan A. Guerrero, P.G. Environmental Services Group Manager Ian Goltz, P.G. Managing Hydrogeologist Attachment: Figures Tables 2008_06_30 Engineering Dewatering Evaluation.doc

10 FIGURES

11

12

13

14

15 TABLES

16 TABLE 1 ESTIMATED GROUNDWATER CONCENTRATIONS FROM SITE DEWATERING Proposed Mixed-Use Development, Beach Boulevard and Orangethorpe Avenue, Buena Park, California Brown and Caldwell File No: i) Estimated Worst Case Groundwater Concentrations from On-Site Groundwater Contamination for Short Term Construction Dewatering Input Calculated Input / Calculated (Green Shading) Property Length of Discharge Per Total Site Impacted Un-impacted Dilution Data Impacted Linesink Length from Model Discharge from Model Site Area Site Area Factor Type Detected Petroluem Hydrocarbons and Fuel Oxygenates Maximum Groundwater Concentrations Detected Detected Other Volatile Organic Compounds TPH-gasoline TBA MTBE DIPE PCE 1,1,-DCA 1,2-DCA 1,1-DCE 1,1,1-TCA Total VOCs Buena Park Car Wash 6976 Beach Boulevard Valero Gasoline Service Station 7751 Orangethorpe Avenue feet gpm/foot gpm feet 2 feet ug/l ug/l ug/l ug/l ug/l ug/l ug/l ug/l ug/l ug/l , ,500 98% Existing Groundwater Concentration 112 ND 100 ND ,600 4,700 8,042 Estimated Steady State Dewatering Concentration 1.15 ND 1.02 ND , ,500 98% Existing Groundwater Concentration 4, ,000 2,000 ND ND 30 ND 17 ND 47 Estimated Steady State Dewatering Concentration 47 1, ND ND 0.31 ND 0.17 ND 0 Estimated Worst Case Concentrations in Extracted Water (Influent) 47 1, ND ii) Estimated Worst Case Groundwater Concentrations from Off-Site Groundwater Contamination for Permanent Dewatering with Constant Head Linesinks with Competent Underlying Clay (Bottom = 35 feet bgs) Input Calculated Input / Calculated (Green Shading) Property Length of Discharge Per Total Site Impacted Un-impacted Dilution Data Impacted Linesink Length from Model Discharge from Model Site Area Site Area Factor Type Detected Petroluem Hydrocarbons and Fuel Oxygenates Maximum Groundwater Concentrations Detected Detected Other Volatile Organic Compounds TPH-gasoline TBA MTBE DIPE PCE 1,1,-DCA 1,2-DCA 1,1-DCE 1,1,1-TCA Total VOCs Chevron Gasoline Service Station 6971 Beach Boulevard Lube Facility (Former G&M Oil) 6812 Beach Boulevard Former Shell Service Station 7979 Orangethrope Avenue feet gpm/foot gpm feet 2 feet ug/l ug/l ug/l ug/l ug/l ug/l ug/l ug/l ug/l ug/l % Existing Groundwater Concentration 39,940 4,900 9,250 ND ND ND ND ND ND ND Estimated Steady State Dewatering Concentration ND ND ND ND ND ND ND % Existing Groundwater Concentration 80,000 ND 690 ND ND ND ND ND ND ND Estimated Steady State Dewatering Concentration 836 ND 7 ND ND ND ND ND ND ND % Existing Groundwater Concentration 60, ND ND ND ND ND ND Estimated Steady State Dewatering Concentration 624 ND 2 ND ND ND ND ND ND ND Estimated Worst Case Concentrations in Extracted Water (Influent) ND ND ND ND ND ND ND iii) Estimated Worst Case Groundwater Concentrations from Off-Site Groundwater Contamination for Permanent Dewatering with Constant Head Linesinks with Deep Lower Clay (Bottom = 65 feet bgs) Input Calculated Input / Calculated (Green Shading) Property Length of Discharge Per Total Site Impacted Un-impacted Dilution Data Impacted Linesink Length from Model Discharge from Model Site Area Site Area Factor Type Detected Petroluem Hydrocarbons and Fuel Oxygenates Maximum Groundwater Concentrations Detected Detected Other Volatile Organic Compounds TPH-gasoline TBA MTBE DIPE PCE 1,1,-DCA 1,2-DCA 1,1-DCE 1,1,1-TCA Total VOCs Chevron Gasoline Service Station 6971 Beach Boulevard Lube Facility (Former G&M Oil) 6812 Beach Boulevard Former Shell Service Station 7979 Orangethorpe Avenue feet gpm/foot gpm feet 2 feet ug/l ug/l ug/l ug/l ug/l ug/l ug/l ug/l ug/l ug/l % Existing Groundwater Concentration 39,940 4,900 9,250 ND ND ND ND ND ND ND Estimated Steady State Dewatering Concentration ND ND ND ND ND ND ND Existing Groundwater Concentration 80,000 ND 690 ND ND ND ND ND ND ND % 96% Estimated Steady State Dewatering Concentration 835 ND 7.2 ND ND ND ND ND ND ND Existing Groundwater Concentration 60, ND ND ND ND ND ND Estimated Steady State Dewatering Concentration 624 ND 2.4 ND ND ND ND ND ND ND Estimated Worst Case Concentrations in Extracted Water (Influent) ND ND ND ND ND ND ND Notes: 1 " ug/l " denotes micrograms per liter. 5 " MTBE " denotes Methyl Tertiary Butyl Ether. 9 " VOCs " denotes volatile organic compounds. 2 " TBA " denotes Tertiary-butyl alcohol. 6 " TPH-gasoline " denotes Total Petroleum Hydrocarbon-gasoline. 10 " gpm "denotes gallons per minute. 3 " DIPE " denotes diisopropyl ether 7 " 1,2-DCA " denotes 1,2-Dichloroethane. 11 " 1,1,1-TCA " denotes 1,1,1-Trichloroethane. 4 " 1,1-DCA " denotes 1,1-Dichloroethane. 8 " 1,1-DCA " denotes 1,1-Dichloroethene. Table 1 Estimated GW Concentrations from Site Dewatering /Table 1 Page 1 of 1 Brown and Caldwell