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HomeMy WebLinkAbout05(K) - Resolution Approving a Work Order and Authorize Budget Amendment – Water Quality Credit Pond Project ReportK:\018998-000\Admin\Docs\018998-000 PL Subwatershed Assessment Report.docx 701 XENIA AVENUE S | SUITE 300 | MINNEAPOLIS, MN | 55416 | 763.541.4800 | WSBENG.COM Memorandum To: Pete Young, PE, Water Resources Engineer, City of Prior Lake From: Jake Newhall, PE Laura Pietila, EIT Date: April 22, 2022 Re: Prior Lake Subwatershed Assessment Report WSB Project No. 018998-000 PURPOSE The City of Prior Lake recently hired WSB to complete a subwatershed assessment of areas tributary to Prior Lake. This study focuses on stormwater management and surface water quality within the Upper Prior Lake and Lower Prior Lake watersheds and provides the following: An analysis of potential best management practice (BMP) locations on City -owned parcels. A quantification of the pollutant load reduction for each potential BMP. A quantification of the volume credits that may be received for each potential BMP. A decision matrix to compare the potential BMPs. A recommendation for the installation of one to three BMPs that will result in stormwater management credits and can be used towards meeting Prior Lake Spring Lake Watershed District ( PLSLWD) and National Pollutant Discharge Elimination System NPDES) permit requirements for future City projects. Of particular concern are achievable volume control credits to be used towards meeting PLSLWD rules and the total phosphorus (TP) loading to Prior Lake, the limiting nutrient responsible for the loss of water quality and algae growth in urban lakes. EXISTING WATERSHED CONDITIONS Prior Lake is one of the most popular water resources in the seven-county metropolitan area of Minneapolis and attracts thousands of people each year. Both Upper and Lower Prior Lake have been placed on the impaired waters list for mercury. Upper Prior Lake is also impaired for nutrients. Improving these resources is important for ecosystem health and is a high priority for the City of Prior Lake. Installing or enhancing BMPs to reduce pollutants within the waterbody’s tributary areas is a step towards improving these important water resources. METHODOLOGY The Prior Lake subwatershed assessment focuses on areas that are tributary to Upper and Lower Prior Lakes. To identify potential BMP locations within the study area, a multistep desktop analysis was completed using ArcGIS Pro, the XPSWMM City-wide model, knowledge of the watershed, and City input. BMP retrofits or new BMPs were then located and sized to estimate and maximize pollutant removal. Analysis was performed with the aid of P8, a commonly used modeling software that evaluates the removal of various pollutants (suspended sediment, Prior Lake Subwatershed Assessment Report April 22, 2022 Page 2 removal device (i.e., BMP). The achievable volume credit was then calculated for each proposed BMP. Potential BMP Location Analysis It was assumed that any potential BMPs would be located on City-owned parcels Figure 1, as attached. Each parcel within the study area was visually reviewed to determine the total tributary area, the extent of the untreated impervious area, and the location of existing BMPs. Based on the findings, each parcel was ranked as having low, moderate, or high treatment potential based on the untreated impervious area draining to the parcel, as shown on Figure 2, as attached. A technical analysis was completed for the moderate and high ranked parcels to determine the most promising BMP locations and suitable types. Factors that influence the location and type of BMP include total drainage area to a specific point, how much untreated impervious area is within the watershed, land slope, hydrologic soil group (SSURGO Soils), groundwater table depth Minnesota Hydrogeology Atlas), wetlands (National Wetland Inventory), floodplains (FEMA), drinking water management areas, and biodiversity significance. See Figure 3a and Figure 3b, as attached, for the BMP sites that were selected based on the technical analysis. Pollutant Removal Estimates - P8 Modeling Utilizing P8 version 3.5, existing and proposed water quality models were built for each potential BMP location and type. All major basins downstream of the potential BMPs were included in the P8 models to adequately determine pollutant load reductions at the outfalls to Upper and Lower Prior Lake. To determine the watershed characteristics for the existing conditions P8 model, a drainage area was delineated, impervious fraction calculated, and a pervious curve number determined from soil type and land use. The land slope was used to calculate depression storage. Topographic information (LiDAR), as-built data, and storm sewer database were used to define the characteristics of the existing basins (ponds, wetlands, minor lakes) and other BMPs. The proposed BMPs were preliminarily designed to: Maximize the runoff received, particularly from catchments not routed through other basins or existing BMPs; Emphasize infiltration and filtration capabilities (e.g., infiltration basin, filtration bench) to more effectively remove the pollutants, including the dissolved fraction as much as possible. Other assumptions employed in the P8 model development include: Because of the urban nature of the watersheds, seventy percent of the impervious areas were assumed to be directly connected and thirty percent indirectly connected. Impervious runoff coefficient of one Half of the directly connected impervious classified as swept twice a year Three decades of precipitation and temperature distributions for Minneapolis and Saint Paul (from 1986 to 2015) One inch per hour filtration rate The type of BMP (filtration or infiltration) was chosen based on SSURGO soil types. Infiltration basins may be used in lieu of filtration if additional soil borings indicate favorable conditions. Prior Lake Subwatershed Assessment Report April 22, 2022 Page 3 Volume Control Credit Volume control credits to meet PLSLWD stormwater management rules were calculated for each proposed BMP based on the total water quality volume multiplied by a conversion factor, outlined in Table D.3.1 from the PLSLWD draft rules. The volume control credit directly corresponds to a new and reconstructed or net new impervious surface area that may be offset by the construction of the proposed BMP. As stated in the PLSLWD draft rules for public linear projects, “The volume equal to either 0.5 inches of runoff from all new and reconstructed impervious surfaces, or 1.0 inches of runoff from the net increase in impervious area, whichever is greater, must be captured and treated.” RESULTS Existing total phosphorus loads from each analyzed watershed are displayed on Figure 4, as attached, showing that the area with the highest loading rate per year is out of the channel on the south side of Upper Prior Lake, largely due to the size of the watershed. Furthering the analysis, the existing pollutant loads were compared to the proposed pollutant loads as determined by the P8 analysis. The benefits provided in terms of pollutant reduction were then compared against the “costs” including construction challenges, long term maintenance, and habitat loss. A Best Management Practice Decision Matrix for TP Reduction was created to summarize the results. Habitat loss, maintenance, constructability challenges, and costs were rated with 0 (low), -0.5 (moderate), -1 (high), and -2 (exceeds). Adding values for each BMP across the matrix, a score was determined. Higher scores indicate a better cost-benefit analysis. Other numerical choices for scaling the benefits versus costs would lead to the same ranking. Absent a universal method for scaling the BMP’s effectiveness, the goal of the study was not to develop a perfect scale but to reliably identify the most effective BMPs. Towards this goal, the matrix developed serves as a robust selection tool. Prior Lake Subwatershed Assessment Report April 22, 2022 Page 4 1Primary focus of pollutant removal in treatment structures such as these is TSS. Some particulate phosphorus will also be removed associated with large particles. The anticipated volume control credit and associated impervious surface offset that may be achieved by each of the proposed BMPs are displayed in the Best Management Practice Decision Matrix for Volume Control Credit. A pre-feasibility level cost estimate is also presented for each proposed BMP. Location Best Management Practice TP Pollutant Reduction at Outfall to Prior Lake (lbs/yr) Habitat Loss Maintenance Constructability Challenges Cost Total Score Lakefront Park Iron Enhanced Infiltration Basin 7.4 -2 -1 -2 -1 1.4 Underground Filtration Gallery 18.7 0 -2 -1 -2 13.7 Panama and TH 13 Iron Enhanced Filtration Bench 22.6 -0.5 -1 -0.5 -2 18.6 Boudins Park Biofiltration Basin 0.3 -1 -0.5 -1 -0.5 -2.7 Eagle Creek Avenue Iron Enhanced Filtration Basin 17.7 0 -1 -0.5 -1 15.2 Rutledge Street V2B1 Treatment Structure 1 1.3 0 -0.5 0 0 0.8 Willows Park Underground Infiltration Gallery 2.4 0 -1 -0.5 -2 -1.1 V2B1 Treatment Structure 1 6.3 0 -0.5 0 0 5.8 Best Management Practice Decision Matrix for TP Reduction Sand Point Park Location Best Management Practice Volume Control Credit1 cf) Area of New and Reconstructed Impervious Surface Offset2 ac) Area of Net New Impervious Surface Offset 3 ac) Estimated Cost4 Lakefront Park Iron Enhanced Infiltration Basin 28,701 15.81 7.91 $ 372,200 Underground Filtration Gallery 32,966 18.16 9.08 $ 559,610 Panama and TH 13 Iron Enhanced Filtration Bench 113,247 62.40 31.20 $ 857,560 Boudins Park Biofiltration Basin 9,032 4.98 2.49 $ 107,400 Eagle Creek Avenue Iron Enhanced Filtration Basin 24,627 13.57 6.78 $ 306,880 Rutledge Street V2B1 Treatment Structure 152 0.08 0.04 $ 59,500 Willows Park Underground Infiltration Gallery 18,113 9.98 4.99 $ 426,070 Sand Point Park V2B1 Treatment Structure 152 0.08 0.04 $ 59,500 1 2 3 4 Best Management Practice Decision Matrix for Volume Control Credit Impervious offset for a project where 0.5 inches of runoff from all new and reconstructed impervious surfaces must be captured. Impervious offset for a project where 1.0 inches of runoff from the net increase in impervious area must be captured and treated. Volume Conversion Factor applied based on BMP type and PLSLWD Table D.3.1 Pre-feasibility level cost estimate based on subwatershed assessment assumptions. Prior Lake Subwatershed Assessment Report April 22, 2022 Page 5 Site summaries are included below. Lakefront Park Figure 5, as attached. o Analysis showed that a significant amount of phosphorus reduction is achieved via constructed basins and Little Prior Lake. However, additional treatment options include an iron enhanced infiltration basin downstream of Little Prior Lake or an active underground filter system used to treat Little Prior Lake stormwater via a pump system. The iron enhanced infiltration basin would likely result in significant tree/habitat loss. Access to the area, for construction and long-term maintenance, would be challenging due to steep slopes and trees. Phosphorus reduction to Prior Lake is average. The basin has a large volume credit potential because of the possible BMP footprint. The Lakefront Park Master Plan indicates several locations that may be suitable for the construction of an underground filtration chamber system: under the expanded parking lot or near the potential amphitheater location. Although pumping water from Little Prior Lake to Lakefront Park may add cost, there is a significant amount of pollutant removal and volume credit potential. The BMP was modeled to pump 2-feet of water from Little Prior Lake through the filtration gallery (modeled as StormTech MC-3500 chamber) annually. The lake water was assumed to have a phosphorus concentration of 0.3 milligrams per liter. The project will necessitate permits for pumping out of a public waterbody. Pump and force main installation may present construction challenges and long-term maintenance costs. Panama Avenue and Trunk Highway 13 Figure 6, as attached. o Based on City input and a site analysis, enhancing the existing pond near Panama Avenue and Trunk Highway 13 with an iron enhanced filter bench was considered. The improvement could result in a significant pollutant reduction and volume credit. From historic aerials, it appears that the pond was constructed between 1957 and 1992. XPSWMM modeling indicates that there are potential flooding issues in the area. Boudins Park Figure 7, as attached. o Boudins Park receives thirty-four acres of runoff with eleven acres of impervious area. An existing basin and underground treatment chamber provides 10,100 cubic feet of water quality volume. To sufficiently treat all of the impervious area to NPDES and City standards, 39,749 cubic feet of water quality volume must be provided. The direct drainage to the existing filtration basin is fully treated as well as a portion of the drainage from the west. To fully treat the western drainage area, 29,649 cubic feet of additional water quality volume must be provided. The site lacks the area to construct a sufficiently sized basin. As such, limited pollutant reduction benefits and volume control credits would be gleaned from constructing a BMP in the area. The City may wish to investigate the functionality of the existing underground treatment chamber to determine if an updated chamber design would better treat the area. Eagle Creek Avenue Figure 8, as attached. o The City owned parcel adjacent to Eagle Creek Avenue, upstream of Lower Prior Lake and north of Quincy Street, was identified in the site analysis because of the ability to capture drainage from a large untreated impervious area (thirty- seven acre drainage area of which eighteen acres are impervious) that currently Prior Lake Subwatershed Assessment Report April 22, 2022 Page 6 discharges through the Eagle Creek storm sewer directly into Upper Prior Lake. The key elements of an effective BMP involve diverting the flow from the existing storm sewer along Eagle Creek Avenue into an iron enhanced filtration basin above the ordinary high water level of Upper and Lower Prior Lakes. Under these assumptions, P8 modeling confirmed that treatment of the impervious could significantly reduce pollutant loads to Prior Lake. Moderate volume control credits could be achieved, limited by the proposed basin size. A pretreatment structure e.g., SAFL Baffle and sump) would be recommended for retention and periodical removal of the bulk of the sediment in order to reduce the long-term maintenance costs of efforts associated with the filtration area. Because Eagle Creek Avenue is a county road, coordination with the County would be required. Utilities may need to be relocated or avoided. Rutledge Street Figure 9, as attached. o The storm sewer on Rutledge Street contributes untreated stormwater directly to Lower Prior Lake. Although a filtration basin would provide the most pollutant reduction, the slopes adjacent to the roadway are very steep and prohibitive to basin construction. A V2B1 or similar treatment structure may be installed along the trunkline storm sewer. A V2B1 or similar structure primarily focuses on removal of total suspended solids. Some particulate phosphorus will also be removed associated with large particles. A treatment structure would provide a minimal amount of volume control credits. Willows Park Figure 10, as attached. o Willows Park was identified in the site analysis as a potential location for a BMP based on the adjacent untreated impervious area and favorable conditions for infiltration. Further analysis of an underground chamber system (modeled as StormTech MC-3500 chamber) proved that the overall benefit to Prior Lake would be small as there are three BMPs, a wetland, and a channel prior to discharging to the lake. However, the volume credit potential offered by the BMP is moderate. Sand Point Park Figure 11, as attached. o A significant amount of untreated impervious area enters Prior Lake south of Sand Point Park. A diversion pipe was recently installed from Birchwood Avenue to Sandpoint Beach, treating a portion of the drainage area, but P8 modeling shows that there would be additional benefits to treating more of the area. A BMP cannot be located within the park itself due to elevation and access constraints. To treat the stormwater, a V2B1 treatment structure or similar could be installed within the right of way at the intersection of Birchwood Avenue and Shady Beach Trail. A V2B1 or similar structure primarily focuses on removal of total suspended solids. Some particulate phosphorus will also be removed associated with large particles. A treatment structure would provide a minimal amount of volume control credits. During the analysis, several additional best management practice options were discussed and considered. It is important to note that quantification of credits for these improvements would be difficult, but each may present water quality benefits. Investigate the condition of the channel that flows from the wetland complex near Priorwood Street and Five Hawks Drive to Upper Prior Lake. Install stabilization measures if conditions warrant it. Treat Little Prior Lake with annual or routine alum dosage. Prior Lake Subwatershed Assessment Report April 22, 2022 Page 7 Emmons and Olivier Resources, Inc. completed a retrofit feasibility study for Prior Lake Spring Lake Watershed District in 2021. The City could consider partnering with the watershed district to construct four curbside rain gardens and up to three iron-enhanced sand filter benches alongside existing stormwater ponds adjacent to Trunk Highway 13. Combined, the retrofit projects are estimated to remove 7.1 pounds of phosphorus per year. RECOMMENDATION Based on the analysis, one BMP stands out as most effective for total phosphorus reduction as well as achievable volume control credits with reasonable secondary factors: the addition of an iron enhanced filter bench to the existing pond near Panama Avenue and Trunk Highway 13. Construction of an underground filtration gallery in Lakefront Park or an iron enhanced filtration basin adjacent to Eagle Creek Avenue should also be considered for the significant total phosphorus removal and volume control credit potential. MUSHTOWNRDSEDULUTHAVESECREEKSIDECIRSEFIVE HAWKS AVE SEV ILLA G EL A K E D R S E W ILL O W W O O D S T S E H E R I T A G E L N SET O W E R S T S E P ONDVIEW TRL SEMAPLEWOOD ST SEANNA TRL SE23 Scott County GIS 16 27 12 83 42 44 17 82 18 78 14 21 This product is for informational purposes and is not suitable for legal, engineering, or surveying purposes. This product has been produced by the City of Prior Lake for the sole purpose of geographic reference. No warranty is made by the City of Prior Lake regarding specific accuracy or completeness.0 0.04 0. 09 0.1 0.2 Miles Water Quality Credit Pond Project Council Page 1 of 2 Public Works Consultant Pool Work Order Water Quality Credit Pond Project WSB & ASSOCIATES, INCORPORATED, dba WSB This work order (“Work Order”) is issued on this 20th day of March, 2023 by the City of Prior Lake (“City”) pursuant to the Public Works Consultant Pool – Master Agreement dated April 20, 2020 (“Contract”) between the City and WSB & Associates, Incorporated, dba WSB Consultant”). Based on the mutual promises and covenants set forth herein, the sufficiency of which are hereby acknowledged, the City and Consultant agree as follows: 1.Scope of Work Order. Consultant agrees to provide, perform and complete all the services requested by the City in this Work Order and attached Exhibit 1 (“Work”), which Work shall be subject to the terms and conditions of this Work Order and the Contract. 2.Term of Work Order. All Work requested by this Work Order shall be completed by December 31, 2024. 3.Compensation for Work Order. City agrees to pay the Consultant an hourly, not-to- exceed sum of $69,400.00 as full and complete payment for the Work requested by this Work Order. 4.Consultant Representative. Consultant has designated Jake Newhall to manage the Work Order subject to the supervision of Consultant’s representative. ISSUED BY CITY OF PRIOR LAKE Mayor City Manager RECEIVED AND ACCEPTED BY WSB & ASSOCIATES, INC. Signature Title Page 2 of 2 Exhibit 1 – Scope of Work Order G:\Group Data\WATER RESOURCES\WR Proposal Folder\Prior Lake\LTR PROP-p young_Panama&13_010623.docx 701 XENIA AVENUE S | SUITE 300 | MINNEAPOLIS, MN | 55416 | 763.541.4800 | WSBENG.COM January 6, 2023 Pete Young Water Resources Engineer City of Prior Lake 4646 Dakota Street SE Prior Lake, MN 55372 Re: Proposal to Provide Final Design and Construction Pond Water Quality Retrofits at Panama Avenue and Highway 13 City of Prior Lake, MN Dear Mr. Young: Attached for your review and approval is our proposed scope of services, fee, and schedule for providing professional engineering services to complete the final design and construction for the BMP retrofits to the pond located at Panama Avenue and Highway 13. The goal of this project is to improve water quality treatment provided upstream of Lower Prior Lake consistent with the recently completed Prior Lake Subwatershed Assessment. Water quality benefits (credits) from this project will be used to offset past and future watershed permitting needs for City projects where stormwater management cannot be feasibly achieved. We are excited to continue to work with you on this project. If you are in agreement with this proposal, please sign where indicated below and return one copy. The necessary contract documents will then be provided. WSB will start work upon receipt of a signed contract. Please do not hesitate to contact Jake at 612- 990- 3576 with any questions. Sincerely, WSB Jake Newhall, PE Director Mr. Pete Young January 6, 2023 Page 2 SCOPE OF ENGINEERING SERVICES FOR POND WATER QUALITY RETROFITS AT PANAMA AVENUE AND HIGHWAY 13 FINAL DESIGN & CONSTRUCTION FOR THE CITY OF PRIOR LAKE SCOPE OF ENGINEERING SERVICES This work plan consists of the final design and construction tasks for the Pond Retrofit Project at Panama Avenue and Highway 13 in the City of Prior Lake. The following are the tasks that will be included: Task 1 – Project Management ($6,800) Project management will be performed throughout the course of the project. The following subtasks are included as part of Project Management: 1.1 Attend project update meetings with City staff to discuss draft plans, final plans, cost estimates, bidding, and other project variables. This will include developing agendas, preparing handouts and graphics, and attending meetings. 1.2 Attend watershed meetings to discuss water quality benefits and credit/debit balances and allocations. This will include developing agendas, preparing handouts and graphics, and attending meetings. 1.3 Work with project team and the City to coordinate project deliverables, schedule, and budget. Deliverables: Two (2) meetings with City staff to review draft plans and final plans. Two (2) meetings with the watershed to discuss proposed and final water quality benefits. Task 2 – Collect Background Info ($6,200) This task consists of collecting background data and relevant design information for the project. The following are the subtasks that will be included as part of the evaluation: 2.1 Collect background information including: easement information, storm sewer sizes and elevations, soils information, utility information, existing hydrologic modeling for the area, groundwater information, permitting requirements, and other relevant information. 2.2 Topographic survey and bathymetric survey of the pond area will be performed by WSB. This will include surveying property lines, storm sewer, outlet structure, trees, and other items within the anticipated construction limits. It is important to note that this task does not include geotechnical analysis as it is not anticipated to be needed. If it is determined that a geotechnical investigation is needed this can be provided as an additional service. Deliverables: Topographic Survey Information. Task 3 –Permit Coordination ($4,500) This task consists of coordinating and obtaining the required permits for the project. It is anticipated that a Prior Lake Spring Lake Watershed Permit will be needed in addition to the Mr. Pete Young January 6, 2023 Page 3 water quality benefit coordination. It is anticipated that US Army Corps of Engineers permitting will be required based on experience with similar projects. In addition, WSB will coordinate the necessary Wetland Conservation Act (WCA) no-loss and exemption application. 3.1 Wetland Delineation and Report. 3.2 US Army Corps of Engineers permitting. 3.3 WCA permitting. Deliverables: Agency Coordination Meeting, necessary permitting documentation for the US Army Corps of Engineers and WCA. This task does not include any necessary permit application fees; these will be passed on to the City if applicable. Wetland delineation is not anticipated to be needed. Task 4 – Water Quality Modeling ($9,800) WSB will complete water quality and H&H modeling to help develop and inform the most effective final design components for the pond retrofit project. Existing P8 and XPSWMM will be utilized to complete these analyses. A cost benefit analysis will be completed to help determine the optimal design from a total phosphorus standpoint and while also considering construction and ongoing maintenance costs. Task 5 – Construction Documents ($24,600) This task consists of completing construction plans, specifications, and bidding documents for the Pond Retrofit Project at Panama Avenue and Highway 13. Plans are anticipated to include cover sheet, grading plan, erosion control/restoration, storm sewer plan, and details. An updated cost estimate will be developed to verify consistency between the proposed improvements and the City project budget. This scope assumes answering questions during the bid process to help facilitate the understanding of construction expectations. 5.1 Prepare draft construction plans, specification, and updated cost estimate. 5.2 Finalize construction plans, specification, and bidding documents based on feedback from City staff. Deliverables: Final Plans, Specifications, and Bid Documents. Task 6 – Construction Management ($17,500) Construction management will be performed throughout the course of the construction schedule for the Pond Retrofit Project at Panama Avenue and Highway 13. This will include attending the pre-construction meeting as well as weekly progress meetings throughout the project, and other necessary construction coordination. This task will include part-time observation (approximately 15-20 hours per week). This will include inspection of all critical construction components as well as regular check -ins with the contractor and the City. WSB will also perform the necessary construction staking and survey work. This includes any necessary survey for record drawings. 6.1 Attend weekly construction meetings. 6.2 Part-time construction observation. 6.3 Review and approve pay vouchers. 6.4 Construction staking and record drawings. Mr. Pete Young January 6, 2023 Page 4 Deliverables: Construction Meetings, Construction Observation, Construction Staking, Record Drawings. TOTAL ESTIMATED ENGINEERING FEE The cost to provide the scope of services outlined in this proposal will be billed hourly, based on our current hourly rates. We are proposing to complete the Pond Retrofit Project at Panama Avenue and Highway 13 for an hourly not-to-exceed fee of $69,400. TIME SCHEDULE Based on the current project schedule, WSB proposes to complete the construction documents by September of 2023 to allow for bidding in the fall and construction in the winter of 2023.