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Home My WebLink About2025-09-11 Stantec CUP/Site Plan Review Stantec Consulting Services Inc. Stantec 733 Marquette Avenue Suite 1000,Minneapolis MN 55402-2309 September 11, 2025 File: 193800151 Attention: Mr.Jacob Rife City of Oak Park Heights 14168 Oak Park Blvd. Oak Park Height, MN 55082 Reference: Central Automotive—Conditional Use Permit/Site Plan Review Dear Jacob: As requested, we have reviewed the information submitted regarding the proposed Central Automotive parking lot addition project. The information reviewed includes preliminary, not for construction drawings dated 7-25-2025, and a site stormwater management plan dated 7/25/2025. Following are our preliminary comments and/or recommendations: Stormwater Management Regulatory Background: 1. The development is outside the City's High Vulnerability Drinking Water Supply Management Area (DWSMA). 2. The development falls within the Middle St. Croix Watershed Management Organization's (MSCWMO) boundary. 3. Rate control and water quality protection requirements are as follows: a. Rate Control: Post development will be no greater than existing for the 2, 10 and 100-year, 24-hour storm events. b. Water Quality: i. Retain runoff volume on site for 1.1 inches of runoff from impervious surfaces provided soils meet requirements for infiltration. ii. Where infiltration is not feasible or advised MSCWMO allows for flexible treatment options. Roughly summarized, flexible treatment is retaining runoff to the extent practicable and remove at least 60%, preferably 75% of annual total phosphorus load that would otherwise leave the site. Comments: 1. Rainfall Depth: The City has standardized the rainfall depth for modeling across the City in its 2018 Stormwater Management Plan. With resubmittal the owner is asked to use the following standard rates. September 11,2025 Mr.Jacob Rife Page 2 of 5 Reference: Central Automotive—Conditional Use Permit/Site Plan Review Table 2.4—24-Hour RairfaH Depths and Frequency Recurrence Interval(yrs) 24-hr Rainfall Depth(n) 1 2.4 2 2.8 5 3.5 10 4.2 25 5.2 50 6.2 100 7.2 2. Rate Control: The site development as proposed will result in a small increase in runoff rate draining overland to 59th Street N and discharging from the ponding basin via pipe into 59th St storm pipe system. The MSCWMO in their review requested a resubmittal to reduce runoff rate to existing conditions. 3. Ponding Basin: a. Existing Conditions: The Site was originally developed in 2020/21 on the basis that the ponding basin would function as an infiltration basin. The bottom the basin supports a robust stand of cattail (a wetland plant species) indicating that the basin is not functioning as intended and the basin drains slowly below its outlet elevation. b. Recommendations: To accommodate the existing site and treat the proposed parking lot addition the following are recommended. i. Convert the basin into a wet pond or a filtration basin while expanding the basin to meet the water quality flexible treatment requirements. The existing underlying soils don't allow for meeting infiltration basin design criteria. Utilize MN Stormwater Manual's MIDS calculator for phosphorus removal efficiency. 1. MN Stormwater Manual Pond Design Requirements: https://stormwater.pca.state.mn.us/index.php?title=Stormwater ponds 2. MN Stormwater Manual Filtration Basin Design Requirements: https://stormwater.pca.state.mn.us/index.php?title=Design criteria for filtr ation and https://stormwater.pca.state.mn.us/index.php?title=Design criteria for iron enhanced sand filter ii. Maximize rate control for the pond by restricting flow through the existing 12"dia. outfall pipe. A two-stage outlet within a skimmer structure(see image below) may be needed. Focus on reducing discharge rates for the 2-year and 10-year events to reduce demand on downstream storm pipe system in 591h St. September 11,2025 Mr.Jacob Rife Page 3 of 5 Reference: Central Automotive—Conditional Use Permit/Site Plan Review xx" dia. hole In baffle wall 1' Elev.=xxx.x Hole for xx" Dia. Elev.=xxx.x 111111k T outlet pipe When feasible, set invert Outlet Elev. 7; Elev.=xxx.x O 5, for outlet pipe below the I � 5' X 1.5" designed normal water min. opening elevation to improve pipe see STO-17 + cover and minimize slope •+�� around skimmer. I55 .J •� •- • ••p ••'" 6„ p•• • •-• - When baffle wall height r, is greater than 3' above 5 Dia. t •. Outlet Elev. the following ate No. shall be required: r riprap Aggregate 1. Steps details. (MnDOT Spec. 3149H Mod.) 2. 6' Diameter MH iii. Pretreatment by a SAFL Baffle structure is not required if draining to a wet pond. 4. Erosion Control(CG101 sheet): a. The construction entrance does not meet the typical, minimum 50-foot length requirement (Detail 3 on sheet CX101) due to site constraints. Use a sectional rumble plate type entrance is recommended as they are more effective than rock entrances at a shorter length (see image below—A CAD detail can be provided). i'TYR Y'FRTICAL x.w +0 SECTION NO t:CRNER RACI.JLAC[RICK l ,NP f 7VER.,E.d71TXT1LE rAEMC 5,rv= v�J 9 rrp AS NFrO 7P� ti .. II Iii " Q BARS --�OF:HUGAtEf`"_IE�L RVN[;LE i'LAIE P4NELS TEMPORARY CONSTRUCTION ENTRANCE TYPICAL RUACLE PLATE PANEL ((" `'7) RUMBLE PLATE COSTRUCTION ENTRANCE NC.T_S. I MBER 0'Ptk'£S ASNEEDED xssED ON TRAFK, 4 50 IKM NO ED CE8RS GENERA ON vYhAE S GCNSTSI.CT ANFP 2A.01I ATFYISTING R0AGNAY IF ,-FF Q F S CAN'T STAY'A RA'.FSFNT Al.PANEL 5. F`L F PANELS ON F tSM UK AVRL:NW 504.KOOK CXi FOISTING RAYEMENT A _SxACE APFA Tf DPAN4SYAY=R(1M ENTRANC;F Y3 F^ASIBLE =Qtr_NiIL SWEEP PANES 71,EAR 0S DEBRIS...SNEEZED NAINrv.,TRAPPING EFFECTIVENESS. September 11,2025 Mr.Jacob Rife Page 4 of 5 Reference: Central Automotive—Conditional Use Permit/Site Plan Review b. Consider chipping the removed trees on site and using the mulch as a perimeter berm in place of silt fence. This is not a requirement, but will reduce use of plastic and is as effective or better BMP at trapping fine soil particles from runoff. c. Remove existing biologs (mulch or compost in polymer sock) around ponding basin perimeter left presumably from the original site development. d. Erosion Control Blanket: State requirement for natural fiber netting only General Comments 1. The City reserves the right to inspect the construction of the project. The City or its designee shall be present for stormwater facilities installation. 2. Review of issues related to parking, lighting, landscaping, tree preservation,fire department access/circulation is by others. 3. The Owner shall be responsible for obtaining all required permits. Copies of all permits shall be submitted to the City prior to the start of construction. 4. The City reserves the right to require additional erosion control measures as determined/necessary during the construction of the project. If you have any questions or require further information, please do not hesitate to contact me. Regards, Stantec Consulting Services Inc. Lee M. Mann, PE MN,WI,CA Principal Phone: 612-712-2085 Lee.Mann@stantec.com Attachment: Hydrant Specifications c. file Julie Hultman, Building Official September 11,2025 Mr.Jacob Rife Page 5 of 5 Reference: Central Automotive—Conditional Use Permit/Site Plan Review Andrew Kegley, Director of Public Works Scott Richards, City Planner Kevin Sandstrom, City Attorney