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HomeMy WebLinkAboutEngineering Review Memo 04192021 L:\20 FILES\20 SUBDIVISIONS\FINAL PLAT\Suite Living PL - OutlotD Eagle Creek Estates (PDEV20-00002)\Building Permit\Suite Living of Prior Lake - Engineering Review Memo 04192021.docx 701 XENIA AVENUE S | SUITE 300 | MINNEAPOLIS, MN | 55416 | 763.541.4800 | WSBENG.COM Memorandum To: Nick Monserud, Project Engineer Pete Young, Water Resources Engineer From: Kris Keller, Laura Kivisto - WSB Date: April 19, 2021 Re: Suite Living of Prior Lake City Project No. DEV20-000002 WSB Project No. 10704-000 We have completed our secondary review of the site improvement plans submitted for Suite Living of Prior Lake dated December 22, 2020 as prepared by CivilSite Group and submitted on April 12, 2021. • Full Arch. Set.pdf, March 11, 2020 • Permit Set.pdf, December 22, 2020 We have the following comments with regards to stormwater management and engineering. Greyed out comments have been addressed. Red comments are new to this review. Comments in standard text still apply. General 1. Submit for and provide copies to the City of all required permits from regulatory agencies (MCES, Minnesota Pollution Control Agency, Minnesota Department of Health, NPDES, etc.) Stormwater Management 1. Rate Control a. The proposed site is part of the larger Eagle Creek Estates development plan and is accounted for in the original HydroCAD model as PROP DA J. The site was designed for 2.13 acres of impervious; 0.9 acres of impervious are proposed. b. PROP DA J drains to NURP/infiltration basin G in the original HydroCAD model. Per the proposed contours, it appears that a portion of the site runoff will flow east towards Markley Lake, bypassing treatment. Provide a drainage area map to confirm drainage patterns. Provide documentation and calculations that the proposed drainage patterns will not increase rates from the site. i. Per plans submitted in the second submittal, storm sewer has been added to capture all runoff. c. City of Prior Lake design standards have changed since the site was designed in 2013. The original design utilizes 2-, 10-, and 100-year rainfall depths of 2.80”, 4.20”, and 6.00” respectively. Rate control was calculated by considering proposed discharge rates of 0.05 cfs per net acre for the 2-year event, 0.30 cfs Suite Living of Prior Lake April 19, 2021 Page 2 per net acre for the 10-year event, and not exceeding the existing runoff rate for the 100-year event. Due to the design standard changes, provide calculations and documentation proving that with the use of Atlas 14 rainfall events and the proposed impervious amount within the drainage area, the runoff rates from the updated proposed drainage area do not exceed the runoff rates from PROP DA J in the original model. Under the new standards, Atlas 14 rainfall values of 2.84", 4.22", and 7.39" should be used to calculate the runoff rates for the 2-, 10-, and 100-year events and a rate increase is not allowed from the site from existing to proposed conditions. 2. Volume control a. Volume control requirements of 1.0” of abstraction over all of the new impervious surfaces on site is met as indicated in the Eagle Creek Estates stormwater management report. Proposed site impervious acreage is less than the impervious design value. 3. Please provide a storm sewer structure in the southwest corner of the parking lot (near the location of MH4) to capture all the runoff from the site into the storm sewer routed to the stormwater basin. Grading 1. Maximum 4:1 slopes are allowed in “maintained” areas with a maximum 3:1 slopes allowed adjacent to natural resources. a. There are areas of proposed grading east of the building that are greater than 3:1. b. There are areas of proposed 3:1 grading south and east of the building in apparent maintained areas. 2. Maintain minimum required 2% slopes for drainage swales around the north, east, and south sides of the building. 3. Provide EOF elevations for all low point catch basins. 4. Show proposed contours covered by easement label southeast of the building. 5. There is a large area that channelizes and crosses the existing sidewalk draining to the street south of the building. a. Provide/identify drainage area. b. Propose additional structure to capture drainage. 6. Show location and elevation of existing sidewalk. Utilities 1. Identify limits of public and private sanitary sewer and water. a. Provide an access easement to the hydrants and water shutoffs for the building 2. Provide the existing watermain stub pipe diameter. a. If 8” diameter, extend 8” watermain to hydrant tee. 3. Provide whether a shutoff exists on the existing watermain stub. Suite Living of Prior Lake April 19, 2021 Page 3 a. If no existing shutoff exists, connect to the existing watermain directly with a gate valve and provide the fitting used to bend the pipe alignment. 4. Provide separate fire and domestic services with separate shutoffs to the building. 5. Fire official to review hydrant spacing for coverage of the building as well as emergency access shown in the inset on sheet C2.0. 6. Verify separation for the utility crossings where the water service is going over or under the sanitary service or storm sewer pipes. Lower watermain/service and insulate as necessary. a. There is a crossing between the bottom of the storm sewer (~928.05) and top of the water service (~927.55) that has a separation of ~0.5’ i. Lower water service to increase separation to 18” minimum and insulate 7. Install a sanitary manhole at the right of way to transition from 8” to 6” sanitary sewer and for City inspection and monitoring. 8. Call out the storm sewer size, material, and slope on the utility plan. Ensure the minimum size and slope of the storm sewer pipe used is 15-inch storm sewer at 0.5%. 9. Call out the storm sewer structure size, rim elevation, invert elevations on the utility plan. 10. Provide rational calculations to show that the storm sewer is designed for the 10-year 24- hour rainfall event and that the receiving pipe has capacity to carry the flow. a. Include a drainage area map for the runoff to each catch basin. 11. Replace details 4 and 5 with the City of Prior Lake's standard details for a standard catch basin (Plate #301) and a storm sewer manhole (Plate #300). 12. All structures in the parking area should be concrete. Revise STMH 4. 13. Verify the existing storm sewer stub material and match it with the proposed connecting storm sewer pipe material. Roadway/Parking Area 1. Increase entrance radii to meet 25’ minimum requirement per Public Works Design Manual and City Standard Plate #607 2. Is there an issue with not having a barrier for the length of ribbon curb for vehicles distinguishing between the driving area and the sidewalk? Pedestrian safety, use of bollards? Miscellaneous 1. Show building style detail drawing. 2. Add the following notes and identifiers to the City of Prior Lake Erosion Control Notes section on the erosion control plan: a. Perimeter and downstream sediment control best management practices should be installed by the contractor and inspected by the City prior to any site work. b. Slopes greater than or equal to 3:1 shall have approved erosion control best management practices installed immediately after finished grading. Suite Living of Prior Lake April 19, 2021 Page 4 3. Include applicable current Prior Lake City standard detail plates including detail plate 607 for Commercial, Industrial, and Multifamily Concrete Entrances SWPPP 1. The SWPPP narrative mentions the construction of a stormwater pond. Please revise to exclude as the site plan only indicates the construction of a building and a parking lot. 2. SWPPP must include a map of all surface waters, existing wetlands, and stormwater ponds or basins that will receive stormwater from the constructed site. Please modify the extents of the proposed SWPPP plan set to show the stormwater pond and Markley Lake or provide arrows indicating the direction and distance to the surface water. 3. Call out inlet protection for the catch basins on Credit River Road downstream of the project.