Biggars Lane Landfill Expansion Environmental Assessment Stormwater Management Assessment County of Brant

Transcription

1 R.J. Burnside & Associates Limited Leslie Street, Suite 200 Newmarket ON L3Y 0A4 CANADA telephone (905) fax (905) web Technical Memorandum Date: Project Name: Client Name: Submitted To: Biggars Lane Landfill Expansion Environmental Assessment Stormwater Management Assessment County of Brant James Hollingsworth, P.Eng. Submitted By: Harold Faulkner, P.Eng. 1.0 Introduction The County of Brant (County) is in the process of undertaking an Environmental Assessment (EA) to obtain additional landfill capacity for the County at the Biggars Lane Landfill. The EA process has been divided into three separate phases. Phase 1 involved the preparation of the Terms of Reference (TOR), which was completed by Stantec Consulting Ltd. in March 2014 and was approved by the Minister of the Environment and Climate Change (MOECC) on May 15, Phase 2 involved the identification of four alternative methods for that could achieve the necessary landfill capacity for the period from 2020 to 2050 and work plans to assess each of the alternatives. Phase 2 was completed by Golder Associates and is documented in their Report on Phase 2 Activities (May 2016, Revised October 2016) herein referred to as the Phase 2 Report. R.J. Burnside & Associates Limited (Burnside) was retained to implement Phase 3 of the EA process on behalf of the County, which consisted of completion of the EA process and obtaining EA Act approval for the landfill expansion. The Stormwater Management Assessment framework was outlined in Attachment C-2 of the Phase 2 Environmental Assessment to Expand the Biggars Lane Landfill prepared by Golder Associates in May 2016 (updated October 2016). The purpose of this memo is to: Evaluate the effects of the proposed expansion on the existing storm drainage patterns. Consider the Alternatives for the proposed expansion at the Biggars Lane Landfill site.

2 Technical Memorandum Page 2 of 9 Estimate the approximate location and size of stormwater management facilities required to address increased runoff from the proposed expansion, leading to the selection of a preferred alternative design. 1.1 Site Description The landfill site is located at 128 Biggars Lane in the County of Brant, east of Mount Pleasant as shown on Figure 1. The site currently comprises a 20.4 hectare fill area within the hectare site (property). The site operates under the Ministry of the Environment and Climate Change (MOECC) s Amended Environmental Compliance Approval (ECA) number A The surrounding land uses are as follows: North: Agricultural lands. The agricultural lands are bounded to the north by Burtch Road (County Road 26; a two-lane Rural Collector road). South: Hagan Road (a two-lane Rural Local road), Fescue s Edge Golf Club and woodlots. East: Agricultural lands. The agricultural lands are bounded to the east by Cockshutt Road (County Road 4; a two-lane Rural Arterial road). West: Agricultural lands and Biggars Lane (a two-lane Rural Local road). Figure 1 Landfill Site Location

3 Technical Memorandum Page 3 of Study Area In accordance with the approved TOR, there are three generic study areas that have been established for the purposes of the EA: the Regional, Local and Site Study Areas. These three study areas are shown on Figure 1. The Regional Study Area, highlighted in yellow, encompasses the entire County of Brant 1. The Local Study Area, highlighted in green, extends approximately 500 m in all directions beyond the landfill site property. The Site Study Area, indicated by the red boundary, comprises the ha landfill site property. 2.0 Stormwater Management Criteria The above has been completed in accordance with acceptable engineering practices, such that the post-development peak flow shall not be greater than the corresponding pre-development peak flow for the 1:2 year through 1:100 year storms. Visual OTTHYMO 3.0 (VO3) hydrologic modeling software was used to calculate runoff rates and quantify the required detention storage for all control measures. The model results also demonstrate the site s overall storm water management compliance. Intensity-Duration- Frequency curves from the County of Brant Development and Engineering Standards were used to simulate rainfall data. 3.0 Existing Conditions 3.1 Existing Drainage Stormwater runoff in the area generally drains in a south to southeast direction, to an unnamed creek flowing west to east through the south landfill buffer area. For the purposes of this assessment, the site can be separated into three drainage regions; west, central and east. Burnside s analysis omits the central region, as it is not impacted by the potential expansion of the landfill site. The west and east regions drain respectively to the west and east of the central region. The central region includes the existing landfill facility and associated stormwater management ponds (South and West SWM Ponds as described in the Stormwater Management Report Design Brief, Biggar s Lane Landfill Site, prepared by UEM Inc. in May 2006). We note the 2006 UEM Report also included an East SWM Pond, which was later deleted following a catchment area reassessment by Stantec in Currently, the west and east regions include mostly crop lands with some trees. Slopes are gentle, ranging from 1 to 3%. Three outlet locations have been established for peak flow comparison; A in the west region, and B & C in the east region as shown on the Existing Drainage Plan, Figure 2. These locations were selected to coincide with the expansion Alternatives described in Appendix A of the Phase 2 report (Golder & Associates, 2016). 1 The boundary between the County of Brant and the City of Brantford changed on January 1, This boundary change has been recognized in our assessment of the Regional Study Area.

4 Technical Memorandum Page 4 of Existing Release Rates The existing peak flows for the subject area were determined using the VO3 Hydrologic Model. NASHYD commands were used to represent the rural, undeveloped area of the site. Table 1 below summarizes the existing peak flows. Table 1 - Existing Peak Flow Rates Outlet Point Area (ha) 2-year 5-Year 25-Year 100-Year A B C Proposed Conditions The existing drainage boundaries shown on Figure 2 will be generally maintained, however, the size and slope of the catchment areas will be increased to account for the potential expansion areas. The Proposed Drainage Plan is shown in Figures 3 to 6. The Phase 2 report (Golder Associates, 2016) identified the following expansion alternatives for consideration during this Phase 3 Environmental Assessment work: Alternative 1 Development of a new landfill footprint to the west of the existing landfill, resulting in a net surplus of 92,000 m 3 of material for daily cover including an engineered low permeability cover. Alternative 2 Development of a new landfill footprint to the west of the existing landfill, resulting in a net surplus of 66,000 m 3 of material for daily cover including a base containment design and leachate collection system. Alternative 3 Development of new landfill footprints to the east and west of the existing landfill, resulting in a net surplus of 41,000 m 3 of material for daily cover, including an engineered low permeability cover. Alternative 4 Development of new landfill footprints to the east and west of the existing landfill, resulting in a net surplus of 78,000 m 3 of material for daily cover, including a base containment design and leachate collection system. 4.1 Proposed Release Rates - Unmitigated The proposed peak flow rates for the subject area were determined using the VO3 Hydrologic Model. NASHYD commands were used to represent the generally undeveloped nature of the site. Table 2 below summarizes the proposed, unmitigated peak flows. Increases in the peak flow rates are provided in Table 3.

5 Technical Memorandum Page 5 of 9 Table 2 - Proposed Peak Flow Rates Unmitigated Alternative Outlet Point Area (ha) 2-year 5-Year 25-Year 100-Year A B C A B C A B C A B C Peak flow not affected in alternative Table 3 - Peak Flow Increases - Unmitigated Alternative Outlet Point 2-year (%) 5-Year (%) 25-Year (%) 100-Year (%) 1 A A A B A C , , , , Proposed Stormwater Management Plan 5.1 Quantity Control As shown in Table 3, peak flows to the outlets are expected to increase for all Alternatives if quantity controls are not implemented. Therefore, quantity controls are proposed to reduce proposed peak flow rates to existing rates. As a result of attenuating peak flow rates, however, flow volumes for the downstream receiver typically increase. Quantity control will be achieved with one or two stormwater management ponds, depending on the Alternative. Due to grading and landfill expansion locations, Alternatives 1 and 2 require a single pond, while Alternatives 3 and 4 require two ponds. The VO3 model was used to determine the required storage volumes to control proposed peak flows to existing rates, and

6 Technical Memorandum Page 6 of 9 increases in flow volumes. Detailed orifice and weir restrictor design will be required at the detailed design stage. Table 4 provides a summary of the storage volumes required to attenuate the 100-year peak flows to the existing flow rates. 5.2 Quality Control Quality control is typically based on the amount of impervious surface area, however in this instance, the proposed land cover will remain generally pervious. As such, general sediment control is appropriate. To provide general sediment control a 100-Year pond must provide 125 m 3 of capacity for each hectare of the drainage area. This volume is typically used for temporary erosion and sediment control ponds, but can be adapted to stormwater management ponds to determine an appropriate permanent pool volume within the pond. Runoff from the 4- hour 25mm storm will be retained for a minimum 24 hours to allow for settling of sediment. The primary pond outlet pipe will also be fitted with a valve to allow for shut-off in case of a leachate outbreak. Table 4 provides the pond storage volumes for each alternative. Table 4 Pond Volume Summary Alternative Outlet Point Drainage Area Controlled by Pond (ha) 100-Year Pond Volume (m 3 ) Permanent Pool Volume (m 3 ) 1 A ,000 4,900 2 A ,000 4, Pond Design A ,000 4,400 B ,200 1,100 A ,900 4,400 C ,100 1,800 Preliminary stormwater management ponds were sized to provide the permanent and active volumes described in Sections 6.1 and 6.2. The pond outlines shown on the figures allow for a 5 m grading buffer, 1 m top of berm, and 6H:1V internal sideslopes. A permanent pool depth of 1 m, and depths ranging from 1 m to 1.5 m are provided. This preliminary design is intended to provide conservative footprints for the ponds. 6.0 Additional Stormwater Management Considerations 6.1 Climate Change The proposed expansion and stormwater management design is not expected to have an effect on climate, but should be adaptable to the potential effects of climate change. The Ontario Centre for Climate Impacts and Adaptation Resources advises southern Ontario has been

7 Technical Memorandum Page 7 of 9 impacted by many heavy rainfall and flooding events that have exceeded existing historical estimates of infrastructure design rainfall intensity-duration-frequency (IDF) values. Even though projections of total annual precipitation, into the 2050 s, suggests little change in the southern parts of Ontario, extreme rainfall events are expected to become more intense and occur more often. The effects of climate change would not be expected to have a varying impact on the Alternatives provided in this assessment, as increases or variations in rainfall intensity would occur equally across the subwatersheds. Increases in required pond storage or conveyance capacity would apply equally to each of the Alternatives. The stormwater management ponds will be designed with overflow capacity to convey the uncontrolled Regional Hurricane Hazel storm event, with a freeboard depth to prevent pond blow-out. 6.2 Existing Stormwater Management Ponds As noted in Section 4.1, two stormwater management ponds (South Pond and West Pond, UEM, 2006) exist in the central region of the site to service the current landfill area. These ponds were not considered in our assessment. However, we acknowledge a portion of the area draining to outlet A will be routed through these existing ponds. While there will be some redundancy in the design of Pond A (Alternatives 1-4), we note that the existing ponds were not designed to accommodate any additional runoff from the proposed expansion. At the detailed design stage, the as-constructed capacity of the existing ponds will be analyzed to determine the extent by which Pond A could potentially be reduced. Conveyance swales will be proposed around the perimeter of the proposed landfill areas. These swales will convey runoff to the proposed stormwater management ponds, and will be sized to convey the 100-year peak flow. The swales will be designed with flat slopes and wide bottoms where feasible, to provide additional opportunity for sediment to settle before reaching the stormwater management ponds. 7.0 Alternatives Evaluation Alternatives 1 through 4 were evaluated with respect to construction and maintenance costs, land disturbance, and runoff quality. Alternatives 1 & 2 are similar, since they result in a single stormwater management pond, while Alternatives 3 and 4 require two separate ponds. These are the key differences between the sets of alternatives from a stormwater management perspective. In order to determine the preferred method of landfill expansion, a detailed evaluation has been completed. The four alternative methods have been qualitatively evaluated based on each of the comparative assessment criteria and indicators outlined in the Phase 2 Report. The qualitative evaluation system defined in the TOR was used for the evaluations. For each criterion, a ranking was applied based on the following range/scale:

8 Technical Memorandum Page 8 of 9 Major Advantage Best / Lowest Impact Advantage Good Neutral Average Disadvantage Poor Major Disadvantage Worst / Largest Impact Based on this system, the preferred method is the one that receives that most favorable ranking for the majority of criteria and indicators. Table 5 Alternative Evaluation Criteria for Evaluating Alternative Methods Surface Water Change in surface water quantity Indicators of Effects on the Environment Predict the need for existing stormwater management infrastructure upgrades to meet O.Reg. 232/98 Predicted occurrence and degree of off-site effects on surface water flows Alternative 1 West Cell with Engineered Cover + Single pond to construct and maintain + Single outlet point for quality monitoring Alternative 2 West Cell with Engineered Base Containment + Single pond to construct and maintain + Single outlet point for quality monitoring + Lowest total pond volume + Shortest length of conveyance swales required Alternative 3 West and East Cells with Engineered Cover - Multiple ponds to construct and maintain - Additional land disturbance for ponds, access road and conveyance swales - Additional outlet point to monitor for water quality Alternative 4 West and East Cells with Engineered Base Containment - Multiple ponds to construct and maintain - Additional land disturbance for ponds, access road and conveyance swales - Additional outlet point to monitor for water quality - Highest total pond volume Ranking +low flow +lowest flow -higher flow volume volume volume increase for increase for increase for downstream downstream downstream receiver receiver receiver -highest flow volume increase for downstream receiver Ranking

9 Technical Memorandum Page 9 of 9 Alternative 2 is the preferred alternative from a stormwater management perspective. Alternatives 3 and 4 are less desirable, since they require two stormwater management facilities at two separate outlet points. Alternative 1 requires only one pond at one outlet, however, compared with Alternative 2, it results in a greater area to be redirected to outlet A, and a slightly larger stormwater management pond. Yours truly, R.J. Burnside & Associates Limited Harold Faulkner, P.Eng. Hydrotechnical Engineer HRF:bs Enclosure(s) "[List enclosures if required]" cc: "[Type Name]" Other than by the addressee, copying or distribution of this document, in whole or in part, is not permitted without the express written consent of R.J. Burnside & Associates Limited Technical Memorandum - SWM(3rd Draft) 10/25/ :11 AM