STORMWATER MONITORING GUIDELINES NORTH OF DUNDAS STREET OPERATION, MAINTENENACE AND MONITORING OF STORMWATER MANAGEMENT PONDS

Transcription

1 STORMWATER MONITORING GUIDELINES NORTH OF DUNDAS STREET OPERATION, MAINTENENACE AND MONITORING OF STORMWATER MANAGEMENT PONDS Revised January 2012

2 NORTH OAKVILLE MONITORING PROGRAM GUIDELINES TOWN OF OAKVILLE Development Engineering Department TABLE OF CONTENTS 1. INTRODUCTION AND BACKGROUND PROGRAM OBJECTIVES MONITORING REQUIREMENTS BASELINE DATA AND EROSION AND SEDIMENT CONTROLS MONITORING OF MODIFIED STREAMS MONITORING FOR ASSUMPTION SURVEY AND CERTIFICATION INSPECTION MONITORING FUNCTIONAL MONITORING AND SEDIMENT REMOVAL PERFORMANCE MONITORING (WATER QUALITY AND HYDRAULICS) WATER LEVEL FLOW WATER QUALITY AND EROSION NATURAL HERITAGE SYSTEM ASSUMPTION OF SWM FACILITIES COMPLIANCE WITH NOCSS TARGETS REPORTING...11 APPENDIX A Table 1. North Oakville Monitoring for SWM Facilities Figure 1. Sample Monitoring Location Plan SWM Facility Inspection Form

3 1. INTRODUCTION AND BACKGROUND The purpose of this document is to present guidelines for the operation, maintenance and monitoring of Stormwater Management Facilities (SWMFs) located in North Oakville within the North Oakville Secondary Plan (NOSP) boundary. These guidelines were prepared in accordance with the North Oakville Creek Subwatershed Study (NOCSS), OMB Mediation Agreements, Stormwater Management Planning & Design Manual (MOE 2003) and the Storm Water Management Facility Sediment Maintenance Guide (Greenland Inc. 1999). For the purposes of this report, a stormwater management facility is defined as a treatment facility that provides water quality, water quantity and erosion controls to the receiving watercourse. In most cases, this facility takes the shape of an end-of-pipe treatment (i.e. water quality pond, extended detention pond, water quality & quantity pond). The final location and design of stormwater management facilities shall be determined as part of the Environmental Implementation Report and Functional Servicing Study (EIR/FSS). A comprehensive monitoring program shall be reviewed in conjunction with the EIR/FSS. Monitoring will include erosion and sediment controls at site alteration and the collection of baseline information prior to earthworks. It is the responsibility of the landowner to routinely inspect and monitor the stormwater management pond(s) from construction until final assumption of the pond, in accordance with this guidance document. The monitoring plan for stormwater management facilities will include monitoring of the receiving system for the effectiveness of the stormwater management facilities at the location of the outfall for the purpose of water quality monitoring, and at the location(s) to be determined through the EIR for the purpose of erosion control. A multidisciplinary monitoring program approved by the Town and Conservation Halton shall be implemented for all modified streams and shall be undertaken by the proponent of the stream modification. Additional monitoring associated with the Department of Fisheries and Oceans approvals may be required and will be the responsibility of the proponent. The Development Engineering Department will review monitoring progress reports submitted by the landowner s monitoring consultant and provide comments. All deficiencies (including landscaping) are to be addressed promptly by the landowner as not to delay the monitoring program and eventual assumption of the pond. Once all requirements of the monitoring program have been met to the satisfaction of the Town, SWM pond operations will be assumed by the Town s Engineering & Construction Department. The role of the Development Engineering Department is to work with the landowner and various Town departments in order to ensure all requirements have been met and transition the ponds through the assumption process. 2

4 2. PROGRAM OBJECTIVES It is the intent of the Monitoring Program to answer the following questions prior to the Town s assumption of SWM pond operations: 1. Is it BUILT AS APPROVED? The proponent shall provide an as-constructed survey, stamped by the design engineer, to demonstrate the pond volumes prior to operating the pond (i.e. no standing water). A qualified engineer shall certify that the pond is constructed in accordance with the approved engineering drawings and approved EIR/FSS. Staff will also evaluate the whether the plantings were installed as per the approved drawings. 2. Does it OPERATE as intended? Functional and Inspection Monitoring needed to ensure that all structural components of the stormwater facility are in good working condition and maintains the storage volumes in accordance with the Ministry of Environment Planning & Design Manual (MOE 2003). 3. Does it MEET THE DESIGN TARGETS as intended? Hydraulic and Water Quality Performance Monitoring needed to determine the SWM pond s pollutant removal efficiency, hydraulic response to rainfall events and overall conformance with the NOCSS targets. 3

5 3. MONITORING REQUIREMENTS 3.1. Baseline Data and Erosion and Sediment Controls Collection of baseline information is essential to understanding the effectiveness of the stormwater management measures applied within the watershed. The Town has undertaken some baseline monitoring at Dundas Street on East Morrison and Fourteen Mile Creeks, particularly looking at water quality for fisheries protection. Further to these efforts, additional monitoring should be undertaken by the landowner once the final locations of the SWM ponds are known, as follows: Baseline temperature and TSS monitoring be undertaken in the receiving watercourse upstream and downstream of the anticipated SWM pond outlet; Temperature monitoring be undertaken during the months of July, August and September prior to construction of the SWMF. Temperature monitoring should be carried out as per Section 5 of the Ontario Stream Assessment Protocol; and The TSS monitoring should be undertaken during 3 dry weather sampling events and during at least 4 wet weather events prior to the construction of the SWMF. Erosion and Sediment Controls (ESC) Requests for site alteration and associated earthworks shall be in keeping with the relevant approvals of the EIR/FSS. The ESC requirements shall follow applicable approved guidelines and bylaws in effect at the time of development. The site alteration design report shall include a schedule for routine inspection, monitoring and reporting. Erosion and sediment measures shall be kept in good working condition at all times and remedial action should be taken to correct deficiencies/blowouts of ESC measures. A schedule for reporting on site alteration activities and associated monitoring shall be developed in consultation with the Town of Oakville. Monitoring shall consist of the following: Routine inspections prior to and following all significant rainfall events (12mm) or days of cumulative rainfall; Water quality samples should be taken at pond outlets during four (4) wet weather events; Continued stream monitoring upstream and downstream of the pond outlet for TSS and Temperature, as described in Section for baseline monitoring; and, Photographic inventory of the erosion and sediment controls Monitoring of Modified Streams A multidisciplinary monitoring program approved by the Town and Conservation Halton will be implemented for all stream modifications. The monitoring program will be implemented by the proponent of the stream modification. 4

6 Additional monitoring associated with Department of Fisheries and Oceans approvals under the federal Fisheries Act may be required and shall be the responsibility of the proponent Monitoring for Assumption Survey and Certification Following the construction of the SWM facility, a qualified professional is required to certify that the constructed facility and structural details were monitored and inspected routinely during construction and, as such, are built in accordance with the approved design. Further status certificates may be required at the assumption of the first phase(s) of subdivision or as needed following restoration or rehabilitation works. The Design Conformance Certificate should be accompanied by a recent as-built topographic survey of the SWM pond and associated features, such as: All materials used in construction The facility volume, bottom elevation, berm elevations, outlet(s) elevations Sediment forebay features Inlet and outlet structural details Flow splitting structures to divert high flows Emergency spillway Landscaping including paths Security features or devices including fencing, warning and/or educational signage, grates and underground control chambers Plantings within the SWM Block; and Other features as specified by design Inspection Monitoring It is the responsibility for the landowner to undertake inspection monitoring from the construction to assumption of the SWMF. The ponds should be inspected at the onset of each season (minimum 4 times per year) to ensure that the pond features (inlet, outlet, spillway etc.) are in good operating condition and following every significant rainfall event to ensure proper functioning. Additional monitoring may be required following significant rainfall events or in response to public inquiries. The following is a broad checklist of concerns applicable to most SWMFs and should be included in the SWM Facility Inspection Form: Obstruction at the inlet, outlet, diversion structure and emergency spillway. Inspection of manhole structures and chambers. Inspection of outlet structures (i.e. reversed slope pipe or hickenbottom). 5

7 Oil/grease contamination (with an unnatural odour) or evidence of hydrocarbon spills (ie. gasoline) in the pond or the receiving watercourse. Accumulation of trash in or around the pond. Accumulation of algae or other form of chocking vegetation. Sediment buildup in Sediment Forebay, main cell or in the receiving watercourse at the outlet. Evidence of animal activity such as burrowing or damming within the pond or at the outlet. Evidence of hydraulic malfunctioning such as frequent overtopping of the high water level over emergency spillway or low water levels following significant rainfall events. Inappropriate or dead vegetation in and around the pond. Evidence of fish stocking in the pond. Evidence of community activities, vandalism and encroachment. Status of the pond s safety features and grading (including signage fencing, side slopes, safety grates, retaining walls and other safety features). Erosion at the outlet structures including evidence of scouring at the storm outfall to the creek valley Erosion of the berm, spillway and receiving watercourse. Signs of seepage through berms. Vegetative barriers Exercise movable parts annually to ensure they are free to operate (ie. maintenance valve, etc.) Functional Monitoring and Sediment Removal The proponent shall carry out Functional Monitoring on the entire SWM system from at source to end-of-pipe and take remedial actions as necessary. Monitoring should be undertaken from construction to assumption of the SWM pond. Sediment Accumulation in SWM Pond To ensure the continued pollutant removal efficiency and storage capabilities of SWMFs, the accumulated sediment should be removed periodically in accordance with the Stormwater Management Planning and Design Manual (MOE March 2003). The following sets out the Town s preferred protocol for sediment survey in stormwater management ponds and the receiving watercourse. The sediment monitoring component of the Monitoring Program aims to measure the sediment accumulation in the sediment forebay and main body of the pond in order to determine the need for sediment removal (cleanouts). Cross sections along the pond s flow length from the inlet structure(s) to the pond outlet should be determined in consultation with the Town. A sediment depth survey should be conducted using the disk/rod or other technique as approved by the Town. The measurement should be performed using a graduated pole with a flat plate 6

8 attached to the bottom to first measure the depth from the water surface to the sediment layer and the second measurement from the top of the sediment layer to the native soil. A marker should be placed in the pond to indicate the place(s) where a measurement should be taken. Practitioners are encouraged to consult the Stormwater Management Sediment Maintenance Guide (Greenland, August 1999) for sediment measurements, sampling, and analysis techniques. Sediment disposal is regulated through the Environmental Protection Act and other MOE Guidelines. A sediment depth assessment should be completed every 2-3 years during active construction activities, or as demonstrated based on measured accumulation rates. Storm Outfalls As it relates to the performance of the SWM ponds, the storm pond outfall to the receiving stream or tributary swale is to be monitored routinely for evidence of erosion, scouring and deposition of sediment within 2-5 meters downstream of the outfall. The structural integrity of the outfall should be noted at this time. Modifications to the outfall may be regulated by the Conservation Authority, and therefore, direct approval must be obtained directly from the Authority. Upstream Features The proponent shall include upstream features in their assessment of the stormwater management system and report on their function to the overall SWM plan. These features may include, but not limited to, oil/grit separators, infiltration trenches, diversion structures and outlets, rooftop controls, bioswales/ditches. Sediment Removal from SWM Pond The owner is required to address the following to the satisfaction of the Town of Oakville prior to sediment removal from the SWM pond: A Handling, Removal and Disposal Plan for the proposed works Written notice to local residents Temporary public notice to identify maintenance works and duration; Erosion and Sediment Control Plans; Dewatering techniques; and Sediment drying techniques (if site suitable). Truck maintenance access route All necessary permits and/or written consent from external agencies Sediment chemistry analysis in accordance with the Environmental Protection Act (EPA) Regulation 347-Leachate Test, CCME Guidelines and the Guidelines For Use at Contaminated Sites in Ontario (GCSO), (MOE 1997); and 7

9 Correspondence with local MOE staff for agreed testing parameters in the context of local site conditions prior to testing. The frequency of sediment removal is based on 5% reduction of TSS removal efficiency or 50% reduction in storage volume of the sediment forebay. Upon completion of all construction activities within a subcatchment draining to a SWMF, the developer is required to remove any accumulated sediment from the sediment forebay, main cell, and any at-source features and restore the facilities back to their approved design. Should the pond assumption linger for a significant period of time after build-out of the contributing drainage area and the pond clean-out, the Town may require an additional sediment survey be conducted to demonstrate that the accumulated sediment volume does not require additional maintenance Performance Monitoring (Water Quality and Hydraulics) Performance Monitoring is required on all Stormwater Management Facilities (SWMFs) during which time the land draining to the facility is under development, with active construction activities underway, and land exposed. During this period, erosion and sediment control programs are important in protecting downstream facilities (i.e. sewers, ponds and receiving waters) from excessive sediment loads. During construction, the landowner will undertake performance/hydraulic, functional and inspection monitoring as set out in these guidelines Monitoring parameters, methodology, frequency and duration of monitoring are described in Table 1 attached. The locations of monitoring stations for various monitoring components are illustrated on Figure 1 of Appendix A Water Level Continuous water level readings should be recorded from a secure station near the sediment forebay headwall. The suggested position is shown on the Monitoring Location Plan and labeled Location 2. Water Level monitoring is a good indicator of the SWM pond s response to rainfall events. Analysis should yield an estimate of the drawdown time for a particular rainfall event and a rough estimate of the hydrograph. It is expected that a minimum of 6-8 events will be recorded over the monitoring season from as early as construction to the Town s assumption of the facility operation and maintenance responsibilities, as deemed appropriate by the Town. 8

10 Flow Continuous flow readings are a good indicator of the SWM facility s response to rainfall events and should be measured at the inlet(s) and outlet(s) of the pond, including the emergency overflow outlet. A minimum of 6-8 events should be recorded each monitoring year and may begin at construction to the Town s assumption of the operations and maintenance responsibilities, or as deemed appropriate by the Town Water Quality and Erosion The monitoring plan shall include monitoring of the receiving system for the effectiveness of the stormwater management facilities at the location of the outfall for the purpose of water quality monitoring, and at the location or locations downstream of the stormwater management facility at the most sensitive reach as identified in the EIR for the purpose of erosion control. Water quality sampling parameters include Total Phosphorus (TP), Total Suspended Solids (TSS), Temperature and in some cases Dissolved Oxygen and Chloride. Table 1 (Appendix A) provides the monitoring parameters, protocols and targets. Automated water quality samples should be taken at the pond inlet(s) and outlet(s). An example is provided on the Monitoring Location Plan (Appendix A, Figure 1). It is expected that 6-8 samples shall be taken each year. Water quality monitoring is required from construction to assumption of the pond and a schedule shall be determined in consultation with the Town and Conservation Authority. A composite sample that includes first flush can be taken at the inlet(s) Natural Heritage System A separate monitoring program shall be implemented for all municipal services such as roads, watermains, sanitary sewers, stormwater management works or trails within the Natural Heritage System. The monitoring program approved by the Town and Conservation Halton is to be developed based on the natural features and functions that may be impacted by the specific works within the NHS. The details of the monitoring program are to be included in the EIR, and, monitoring shall be implemented by the landowner installing the stormwater management works, municipal services or trails. 9

11 4. Assumption of SWM Facilities The following Checklist shall be used to track the eligibility of the Stormwater Management Facility (SWMF) for assumption. No. Items 1 100% build-out of contributing drainage area to pond. 2 All functional components of the pond have been certified by a qualified professional(s) 3 Sediment has been removed from the sediment forebay(s) and main cell. 4 As-constructed pond drawings have been submitted. 5 Monitoring requirements per approved SWMF Monitoring Program have been satisfied. 6 Site inspection has been conducted with Town Staff. 7 All plantings, landscaping features and restoration works have been accepted by Parks & Open Spaces Department. 8 MOE Certificate of Approval for the pond has been provided. 9 The pond complies with safety requirements set out in the Town s SWM Pond Policy MS-ENG Operation and Maintenance Manual has been accepted by Town Staff. 11 Owner has satisfied all conditions of the Subdivision Agreement with respect to the pond s operation, monitoring and maintenance. 5. Compliance with NOCSS Targets It is expected that the SWM water quality ponds will meet performance targets of Enhanced Level of quality control, defined as 80% removal of suspended solids (TSS) on an average annual basis and no net increase in total phosphorus concentration in accordance with the North Oakville Creeks Subwatershed Studies (NOCSS). It is understood that the efficiencies calculated from multiple storm event sampling will vary significantly, depending on the season and storm size (volume and intensity). Accordingly, it is expected that the overall pollutant removal efficiency of the SWM facility will be based on an average efficiency rating over the total sampling period post construction of the contributing drainage area. Performance of individual ponds will be compared to the established targets with consideration for the results of similar ponds. If the SWMF performance meets the objectives of the Monitoring Program and NOCSS targets, the pond may be considered for assumption by the Town, subject to the other conditions of assumption. However, if the performance of the pond does not meet targets, the following actions will be considered by the Town in consultation with the owner: 1. Review of conformance reports to see if the pond was sized and designed appropriately 10

12 2. Review of maintenance practices to ascertain if maintenance is required, especially focusing on sediment build-up and removal 3. Consideration of other factors that could explain high TSS levels in the outlet, such as berm erosion, or short circuiting of flows 4. Consideration that efficiency of removal is low due to lower than expected TSS concentrations and loadings to the pond. 5. Modifications to the inlet or outlet works if these are considered contributing to the high TSS. 6. Additional years of monitoring by the owner before assumption by the Town. 7. Other, as may be needed. 6. Reporting The annual report should provide the status of the stormwater management facility over the operating year and results of the monitoring program. Status of the facility shall be based on Functional and Inspection Monitoring as well as details of any structural modification to the pond. Modifications to the Hydraulic/Performance monitoring component may be considered annually and may include changes to the frequency of sampling, monitoring parameters or methodology applied to monitoring. Such recommendations should be put forward for consideration in the Annual Report. 11

13 APPENDIX A Table 1: North Oakville Monitoring For SWM Facilities Figure 1: Sample Monitoring Location Plan SWM Facility Inspection Form

14 Table 1. NORTH OAKVILLE MONITORING FOR SWM FACILITIES HYDRAULIC/PERFORMANCE MONITORING MONITORING PARAMETERS TARGET ANALYSIS METHOD/EQUIPMENT SAMPLE LOCATION 4 FREQUENCY/DURATION OTHER/COMMENTS Water Level Fluctuation per approved SWM Plan and Engineering Drawings Drawdown Time; Estimate of Outflow Hydrograph Water Level Meter Datalogger w/ pressure transducer (vented) Location 2 (see attached plan) 6-8 events per year; Construction to Assumption Flow Water Quality: TSS Total Phosphorus (TP) Temperature and DO Erosion Chloride Sediment Depth See Attached: Town of Oakville Stormwater Management Facility Inspection Form Meet target flow rates at Dundas Street 80% removal of TSS; no net increase of TP; no increase over background Temp & DO not to exceed 20 deg. and 6mg/l; meet d/s erosion threshold within 5% of EIR target The greater of 5% decrease in TSS removal efficiency or 50% available forebay volume Inlet Flow; Outlet Flow; Response to Storm Events Pollutant Removal Efficiency (% Removal); Water Quality Discharge; Particle Size Distribution Available sediment Vol; Planning for next sediment removal Log book of routine inspections performed throughout the year Flow Meter Velocity Area Flowmeter; capable of submerged flow accuracy (ie. ISCO 2150) Automated sampling to capture the rising and falling limbs of the storm; Multi-parameter Water Quality Sensor Disk/Rod Method or Town-Approved Alternative Location 1, 3 and 4 Location 1 and 3 Location 3 *Notes: 1. The above program overview should be implemented in accordance with the North Oakville Monitoring Guidelines. 2. Storm events should target a minimum 10mm of precipitation or greater. 3. Monitoring equipment and techniques for sampling/measurement shall be approved by the Town of Oakville. 4. See Figure 1 for Sample locations for Monitoring SWM facilities. 6-8 events per year; Construction to Assumption 6-8 samples collected an analyzed per year; Construction to Assumption FUNCTIONAL MONITORING Sediment Forebay min. 2 Minimum requirement 1:3 years perpendicular transects, min. 5 from Construction to Assumption; points per transect (see diagram) or as deemed necessary; Sediment removal as needed Main Cell TBD based on main cell configuration INSPECTION MONITORING Observation As needed Following Rainfall Events; Minimum 4 inspections per year; Construction to Assumption SWMF discharge to the stream shall be evaluated against stream baseflow conditions of 25mg/l; Temperature and Total Phosphorus monitoring will not effect assumption of SWM facilities

15 FIGURE 1. Town of Oakville - North Oakville Stormwater Management Monitoring Program Pond Monitoring Location Plan

16 STORMWATER MANAGEMENT FACILITY INSPECTION FORM 1. General Details Inspected by: Facility Number: Facility Name: Intersection: Date of Inspection: Rainfall 24 hours prior: mm Rainfall 72 hours prior: mm Discharges to: Watershed: Facility Type: circle wet pond wetland hybrid dry pond Upstream or source controls? Yes No Describe: 2. Observations: Staff Gauge Reading: cm Water temperature at outfall: o C Water Colour: Clear Green Brown Other NOTES Foul Odour None Minor Moderate High Floating Material None Minor Moderate High algae None Minor Moderate High debris None Minor Moderate High oil/sheen None Minor Moderate High floatables None Minor Moderate High Sediment depth: cm Date of Last Sediment Survey Is sediment visible below or above water surface? yes no NOTES: 3. Inspection of Structural Components INLET NOTES Blockage/Debris None Minor Moderate High Sediment Accumulation None Minor Moderate High Cracking/damage concrete None Minor Moderate High Damage to other components None Minor Moderate High Seepage None Minor Moderate High Grate secure yes no OUTLET SWALE Blockage None Minor Moderate High Erosion None Minor Moderate High clearbrown Clarity of flow out of pond clear brown Depth sediment in receiver cm NOTES: 3. Inspection of Structural Components (continued) OUTLET EMERGENCY OVERFLOW NOTES Blockage/Debris None Minor Moderate High Sediment Accumulation None Minor Moderate High Cracking/damage concrete None Minor Moderate High Seepage/dampness None Minor Moderate High Damage to other components None Minor Moderate High Grate secure yes no Cap locked yes no outer holes clogged None Minor Moderate High inner holes clogged None Minor Moderate High outer pipe rusted None Minor Moderate High structural damage None Minor Moderate High valves function (open/close) yes no Armour stone None Minor Moderate High Erosion None Minor Moderate High Short Circuiting None Minor Moderate High

17 4. Inspection of Vegetation Evidence of overtopping yes no NOTES: NOTES Aquatic None Sparse Moderate Abundant Shoreline None Sparse Moderate Abundant Trees/Shrubs None Sparse Moderate Abundant Noxious Weeds None Sparse Moderate Abundant Re-seeding/Replanting Requirements: NOTES: 5. Overall Conditions NOTES Overall Erosion of Area None Minor Moderate High Access Roads None Minor Moderate High Fences None Minor Moderate High Gates None Minor Moderate High Locks None Minor Moderate High Signage None Minor Moderate High Evidence of Encroachments None Minor Moderate High Evidence of Beaver Activity None Minor Moderate High Evidence of Waterfowl Activity None Minor Moderate High Evidence of Fish None Minor Moderate High OTHER COMMENTS: