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HomeMy WebLinkAbout2018-06-01 Westwood - Stormwater Analysis 7699 Anagram Drive Eden Prairie,MN 55344 Westwood Main (952)937-5150 Fax (952)937-5822 westwoodps.com (888)937-5150 MEMORANDUM Date: June 1,2018 Re: Ridgecrest Oak Park Heights I,LLC Stormwater Analysis File 0013019.00 To: Eric Johnson,City Administrator From: Shari Ahrens,PE This memorandum summarizes the stormwater management system design for the proposed redevelopment project at the vacated Eagles Club site located at the southwest quadrant of 60th Street N.and Norwell Ave N.in Oak Park Heights,MN. REGULATIONS The site is located within the City of Oak Park Heights and Browns Creek Watershed District (BCWD).BCWD rules 2.4.1 Management Standards include— Land-altering activity will not a.) Increase peak stormwater flow from the site,as compared with the pre-settlement condition,for a 24-hour precipitation event with a return frequency of two,10 or 100 years for all points where discharges leave a site. b.) Increase stormwater flow volume from all points where discharge leaves the site,as compared with the pre-settlement conditions,for a 24-hour precipitation event with a return frequency of two years,or five years within a landlocked basin or a subwatershed draining to a landlocked basin. c.) At a downgradient property boundary or to an onsite receiving waterbody or wetland, increase annual phosphorus loading as compared with the pre-development condition. SITE CONSTRAINTS • The project site is located within the City of Oak Park Heights Drinking Water Supply Management Area(DWSMA)which limits the ability to utilize infiltration as a stormwater management option. • Based upon site soil borings,the subsurface soils are primarily silt with some clayey-silt area.These soils have some,but limited infiltration capacities. Multi-Disciplined Surveying&Engineering ,ears Form ra.10074302 westwoodps.com June 1, 2018 Page 2 According to the Stormwater NPDES permit requirements, infiltration within a DWSMA is not allowed unless approved by an MS4-permitted city. It is understood that the city of Oak Park Heights is not currently an MS4 city, thus the city does not currently have the authority to approve site infiltration even if it can be demonstrated that negative impacts to the groundwater are unlikely. PROPOSED PROJECT DEVELOPMENT The proposed redevelopment project includes demolition of an existing vacant building and removal of the parking lot, and construction of two new buildings (including a restaurant with drive-thru and an office/retail building), parking lot and landscape areas. The area within the proposed boundary lines is 98.965 s.f. (2.272 acres). A summary of pre- development and proposed impervious areas within the project boundary are shown in Table 1. Table 1: Project Area Information Project Site Pre-Development Proposed s.f. Development s.f. Total Proposed Project Area 98,965 98,965 Impervious Area 60,123 (61%) 64,175 (65%) Pervious Area 38,842 (39%) 34,790 (35%) PROPOSED STORMWATER MANAGEMENT SYSTEM The proposed project will utilize an underground stormwater vault (StormTech System)for rate control and water quality. Westwood utilized the HydroCAD computer model for the analysis of stormwater management system at this site and the result of the model are attached to this memorandum. Stormwater runoff from the building, drive-thru and the parking lot will be directed to an underground detention system via storm pipes. Sump manhole structures will provide initial pretreatment with addition sediment removal via the StormTech isolator row system. The Grading Plan and Utility Plan are attached to this memo for reference. RATE CONTROL The stormwater management system design was modeled to achieve no net increase in peak discharge rates for the proposed development from pre-development conditions for the 2-year, 10-year and 100-year storm events. The pre-development and proposed peak discharge rates are shown in Table 3. June 1, 2018 Page 3 Table 3: Peak Discharge Rates Pre-development Proposed Conditions [cfs] Development [cfs] 2-yr Event 4.91 3.22 10-yr Event 8.67 5.68 100-yr Event 15.65 11.13 WATER QUALITY Water quality performance studies for the StormTech Isolator Row (attached) identify typical TSS removals of 80% and TP removals of 49%. The StormTech system is designed to contain sediment and floatable debris within the isolator row, which can then be removed as need. VOLUME CONTROL Due to site constrains previously mentioned, no volume control or abstraction is proposed for this project. Please contact Shari Ahrens at (952) 697-5760 if there are any comments or questions about this memorandum. Attachments: Preliminary Grading Plan and Utility Plan (dated 05-15-2018) Existing Conditions HydroCAD Model (dated 05-09-2018) Proposed Development HydroCAD Model (dated 05-09-2018) Drainage Area Exhibit (Updated 05-31-2018 StormTech Isolator Row-Water Quality Studies-White Paper 2 Ex R Ex Ex. Discharge from site Pre-Development t Subcat> Reach 'on. Link Routing Diagram for 18-05-09_Site Option 1_13019 OPH Prepared by Westwood Professional Services, Printed 5/15/2018 �___ HydroCAD® 10.00-14 s/n 03363 ©2015 HydroCAD Software Solutions LLC 18-05-09_Site Option 1_13019 OPH Prepared by Westwood Professional Services Printed 5/15/2018 HydroCAD®10.00-14 s/n 03363 ©2015 HydroCAD Software Solutions LLC Page 2 Area Listing(selected nodes) Area CN Description (acres) (subcatchment-numbers) 1.380 98 Existing Building and pavement area (2 Ex) 0.892 70 Pre-Development pervious area (2 Ex) 2.272 87 TOTAL AREA 18-05-09_Site Option 1_13019 OPH MN-Stillwater 24-hr S1 2-yr Rainfall=2.80" Prepared by Westwood Professional Services Printed 5/15/2018 HydroCAD®10.00-14 s/n 03363 ©2015 HydroCAD Software Solutions LLC Page 3 Summary for Subcatchment 2 Ex: Pre-Development Runoff = 4.91 cfs @ 12.10 hrs, Volume= 0.296 af, Depth= 1.57" Runoff by SCS TR-20 method, UH=SCS, Weighted-CN,Time Span= 0.00-48.00 hrs, dt= 0.05 hrs MN-Stillwater 24-hr S1 2-yr Rainfall=2.80" Area(sf) CN Description * 60,123 98 Existing Building and pavement area * 38,842 70 Pre-Development pervious area 98,965 87 Weighted Average 38,842 39.25% Pervious Area 60,123 60.75% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 10.0 Direct Entry, Summary for Reach 2 Ex R: Ex. Discharge from site Inflow Area = 2.272 ac, 60.75% Impervious, Inflow Depth = 1.57" for 2-yr event Inflow = 4.91 cfs @ 12.10 hrs, Volume= 0.296 af Outflow = 4.91 cfs @ 12.10 hrs, Volume= 0.296 af, Atten= 0%, Lag= 0.0 min Routing by Stor-Ind+Trans method, Time Span=0.00-48.00 hrs, dt= 0.05 hrs 18-05-09_Site Option 1_13019 OPH MN-Stillwater 24-hr S1 10-yr Rainfall-4.17" by Westwood Professional Services Printed 5/15/2018 HydroCAD®10.00-14 s/n 03363 ©2015 HydroCAD Software Solutions LLC Page 5 Summary for Subcatchment 2 Ex: Pre-Development Runoff = 8.67 cfs @ 12.09 hrs, Volume= 0.529 af, Depth= 2.79" Runoff by SCS TR-20 method, UH=SCS, Weighted-CN,Time Span= 0.00-48.00 hrs, dt= 0.05 hrs MN-Stillwater 24-hr S1 10-yr Rainfall=4.17" Area (sf) CN Description * 60,123 98 Existing Building and pavement area * 38,842 70 Pre-Development pervious area 98,965 87 Weighted Average 38,842 39.25% Pervious Area 60,123 60.75% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 10.0 Direct Entry, Summary for Reach 2 Ex R: Ex. Discharge from site Inflow Area= 2.272 ac, 60.75% Impervious, Inflow Depth = 2.79" for 10-yr event Inflow = 8.67 cfs @ 12.09 hrs, Volume= 0.529 af Outflow = 8.67 cfs @ 12.09 hrs, Volume= 0.529 af, Atten= 0%, Lag= 0.0 min Routing by Stor-Ind+Trans method, Time Span= 0.00-48.00 hrs, dt= 0.05 hrs 18-05-09_Site Option 1_13019 OPH MN-Stillwater 24-hr S1 100-yr Rainfall=7.22" Prepared by Westwood Professional Services Printed 5/15/2018 HydroCAD®10.00-14 s/n 03363 ©2015 HydroCAD Software Solutions LLC Page 6 Summary for Subcatchment 2 Ex: Pre-Development Runoff = 15.65 cfs @ 12.09 hrs, Volume= 1.078 af, Depth= 5.69" Runoff by SCS TR-20 method, UH=SCS, Weighted-CN,Time Span= 0.00-48.00 hrs, dt= 0.05 hrs MN-Stillwater 24-hr S1 100-yr Rainfall=7.22" Area(sf) CN Description * 60,123 98 Existing Building and pavement area * 38,842 70 Pre-Development pervious area 98,965 87 Weighted Average 38,842 39.25% Pervious Area 60,123 60.75% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 10.0 Direct Entry, Summary for Reach 2 Ex R: Ex. Discharge from site Inflow Area= 2.272 ac, 60.75% Impervious, Inflow Depth = 5.69" for 100-yr event Inflow = 15.65 cfs @ 12.09 hrs, Volume= 1.078 af Outflow = 15.65 cfs @ 12.09 hrs, Volume= 1.078 af, Atten= 0%, Lag= 0.0 min Routing by Stor-Ind+Trans method, Time Span= 0.00-48.00 hrs, dt= 0.05 hrs (1S) R1 1 P\ PROPOSED Proposed development DISCHARGE UG Basin (Subca) [ eac on. MP Routing Diagram for 18-05-09_Site Option 1_13019 OPH J Prepared by Westwood Professional Services, Printed 5/15/2018 HydroCAD®10.00-14 s/n 03363 ©2015 HydroCAD Software Solutions LLC 18-05-09_Site Option 1_13019 OPH Prepared by Westwood Professional Services Printed 5/15/2018 HydroCAD®10.00-14 s/n 03363 ©2015 HydroCAD Software Solutions LLC Page 2 Area Listing (selected nodes) Area CN Description (acres) (subcatchment-numbers) 1.473 98 buildings and pavement (1S) 0.799 70 pervious areas (1S) 2.272 88 TOTAL AREA 18-05-09_Site Option 1_13019 OPH MN-Stillwater 24-hr SI 2-yr Rainfall=2.80" Prepared by Westwood Professional Services Printed 5/15/2018 HydroCAD®10.00-14 sin 03363 ©2015 HydroCAD Software Solutions LLC Page 5 Summary for Subcatchment 1S: Proposed development Runoff = 5.16 cfs @ 12.10 hrs, Volume= 0.311 af, Depth= 1.64" Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-48.00 hrs, dt= 0.05 hrs MN-Stillwater 24-hr S1 2-yr Rainfall=2.80" Area(sf) CN Description * 64,175 98 buildings and pavement * 34,790 70 pervious areas 98,965 88 Weighted Average 34,790 35.15% Pervious Area 64,175 64.85% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 10.0 Direct Entry, 10 Summary for Reach 1R: PROPOSED DISCHARGE Inflow Area = 2.272 ac, 64.85% Impervious, Inflow Depth = 1.64" for 2-yr event Inflow = 3.22 cfs @ 12.22 hrs, Volume= 0.311 af Outflow = 3.22 cfs @ 12.22 hrs, Volume= 0.311 af, Atten=0%, Lag= 0.0 min Routing by Stor-Ind+Trans method, Time Span= 0.00-48.00 hrs, dt= 0.05 hrs Summary for Pond 1P: UG Basin Inflow Area = 2.272 ac, 64.85% Impervious, Inflow Depth = 1.64" for 2-yr event Inflow = 5.16 cfs @ 12.10 hrs, Volume= 0.311 of Outflow = 3.22 cfs @ 12.22 hrs, Volume= 0.311 af, Atten= 38%, Lag= 7.7 min Primary = 3.22 cfs @ 12.22 hrs, Volume= 0.311 af Routing by Stor-Ind method, Time Span= 0.00-48.00 hrs, dt= 0.05 hrs Peak Elev=928.98' @ 12.22 hrs Surf.Area= 5,528 sf Storage=2,132 cf Plug-Flow detention time= 7.3 min calculated for 0.310 af(100%of inflow) Center-of-Mass det.time= 7.3 min ( 824.9-817.6 ) Volume Invert Avail.Storage Storage Description #1A 928.25' 3,858 cf 38.17'W x 144.84'L x 2.33'H Field A 12,899 cf Overall-3,253 cf Embedded = 9,645 cf x 40.0%Voids #2A 928.75' 3,253 cf ADS_StormTech SC-310 x 220 Inside#1 Effective Size= 28.9"W x 16.0"H => 2.07 sf x 7.12'L = 14.7 cf Overall Size= 34.0"W x 16.0"H x 7.56'L with 0.44'Overlap Row Length Adjustment= +0.44'x 2.07 sf x 11 rows 7,111 cf Total Available Storage Storage Group A created with Chamber Wizard 18-05-09_Site Option 1_13019 OPH MN-Stillwater 24-hr S1 2-yr Rainfall=2.80" Prepared by Westwood Professional Services Printed 5/15/2018 HydroCAD®10.00-14 s/n 03363 ©2015 HydroCAD Software Solutions LLC Page 6 Device Routing Invert Outlet Devices #1 Primary 928.00' 18.0" Round Culvert L= 50.0' RCP, square edge headwall, Ke= 0.500 Inlet/Outlet Invert= 928.00'/927.75' S= 0.0050'/' Cc= 0.900 n= 0.012 Concrete pipe,finished, Flow Area= 1.77 sf Primary OutFlow Max=3.19 cfs @ 12.22 hrs HW=928.98' (Free Discharge) t-1=Culvert (Barrel Controls 3.19 cfs @ 3.72 fps) 18-05-09_Site Option 1_13019 OPH MN-Stillwater 24-hr Si 10-yr Rainfall=4.17" Prepared by Westwood Professional Services Printed 5/15/2018 HydroCAD®10.00-14 s/n 03363 ©2015 HydroCAD Software Solutions LLC Pape 9 Summary for Subcatchment 1S: Proposed development Runoff = 8.93 cfs @ 12.09 hrs, Volume= 0.547 af, Depth= 2.89" Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-48.00 hrs, dt= 0.05 hrs MN-Stillwater 24-hr S1 10-yr Rainfall=4.17" Area (sf) CN Description * 64,175 98 buildings and pavement * 34,790 70 pervious areas 98,965 88 Weighted Average 34,790 35.15% Pervious Area 64,175 64.85% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 10.0 Direct Entry, 10 Summary for Reach 1R: PROPOSED DISCHARGE Inflow Area= 2.272 ac, 64.85% Impervious, Inflow Depth = 2.89" for 10-yr event Inflow = 5.68 cfs @ 12.22 hrs, Volume= 0.547 af Outflow = 5.68 cfs @ 12.22 hrs, Volume= 0.547 af, Atten= 0%, Lag= 0.0 min Routing by Stor-Ind+Trans method, Time Span= 0.00-48.00 hrs, dt= 0.05 hrs Summary for Pond 1P: UG Basin Inflow Area = 2.272 ac, 64.85% Impervious, Inflow Depth = 2.89" for 10-yr event Inflow = 8.93 cfs @ 12.09 hrs, Volume= 0.547 of Outflow = 5.68 cfs @ 12.22 hrs, Volume= 0.547 af, Atten= 36%, Lag= 7.5 min Primary = 5.68 cfs @ 12.22 hrs, Volume= 0.547 of Routing by Stor-Ind method, Time Span= 0.00-48.00 hrs, dt= 0.05 hrs Peak Elev=929.41' @ 12.22 hrs Surf.Area= 5,528 sf Storage=3,900 cf Plug-Flow detention time= 8.2 min calculated for 0.546 af(100% of inflow) Center-of-Mass det.time= 8.2 min ( 810.9-802.7 ) Volume Invert Avail.Storage Storage Description #1A 928.25' 3,858 cf 38.17W x 144.84'L x 2.33'H Field A 12,899 cf Overall-3,253 cf Embedded = 9,645 cf x 40.0%Voids #2A 928.75' 3,253 cf ADS_StormTech SC-310 x 220 Inside#1 Effective Size= 28.9"W x 16.0"H =>2.07 sf x 7.12'L = 14.7 cf Overall Size= 34.0"W x 16.0"H x 7.56'L with 0.44'Overlap Row Length Adjustment= +0.44' x 2.07 sf x 11 rows 7,111 cf Total Available Storage Storage Group A created with Chamber Wizard 18-05-09_Site Option 1_13019 OPH MN-Stillwater 24-hr S1 10-yr Rainfall=4.17" Prepared by Westwood Professional Services Printed 5/15/2018 HydroCAD®10.00-14 s/n 03363 ©2015 HydroCAD Software Solutions LLC Page 10 Device Routing Invert Outlet Devices #1 Primary 928.00' 18.0" Round Culvert L= 50.0' RCP, square edge headwall, Ke= 0.500 Inlet/Outlet Invert= 928.00'/927.75' S= 0.0050'/' Cc= 0.900 n= 0.012 Concrete pipe,finished, Flow Area= 1.77 sf Primary OutFlow Max=5.63 cfs @ 12.22 hrs HW=929.40' (Free Discharge) L1=Culvert (Barrel Controls 5.63 cfs @ 4.27 fps) 18-05-09_Site Option 1_13019 OPH MN-Stillwater 24-hr Si 100-yr Rainfall=7.22" Prepared by Westwood Professional Services Printed 5/15/2018 HydroCAD®10.00-14 s/n 03363 ©2015 HydroCAD Software Solutions LLC Page 11 Summary for Subcatchment 1S: Proposed development Runoff = 15.88 cfs @ 12.09 hrs, Volume= 1.099 af, Depth= 5.81" Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-48.00 hrs, dt= 0.05 hrs MN-Stillwater 24-hr S1 100-yr Rainfall=7.22" Area(sf) CN Description * 64,175 98 buildings and pavement * 34,790 70 pervious areas 98,965 88 Weighted Average 34,790 35.15% Pervious Area 64,175 64.85% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 10.0 Direct Entry, 10 Summary for Reach 1R: PROPOSED DISCHARGE Inflow Area = 2.272 ac, 64.85% Impervious, Inflow Depth = 5.81" for 100-yr event Inflow = 11.13 cfs @ 12.20 hrs, Volume= 1.099 of Outflow = 11.13 cfs @ 12.20 hrs, Volume= 1.099 af, Atten= 0%, Lag= 0.0 min Routing by Stor-Ind+Trans method, Time Span= 0.00-48.00 hrs, dt= 0.05 hrs Summary for Pond 1P: UG Basin Inflow Area = 2.272 ac, 64.85% Impervious, Inflow Depth = 5.81" for 100-yr event Inflow = 15.88 cfs @ 12.09 hrs, Volume= 1.099 af Outflow = 11.13 cfs @ 12.20 hrs, Volume= 1.099 af, Atten= 30%, Lag= 6.6 min Primary = 11.13 cfs @ 12.20 hrs, Volume= 1.099 af Routing by Stor-Ind method, Time Span= 0.00-48.00 hrs, dt= 0.05 hrs Peak Elev=930.65' @ 12.20 hrs Surf.Area= 5,528 sf Storage= 7,111 cf Plug-Flow detention time= 8.9 min calculated for 1.098 of(100% of inflow) Center-of-Mass det.time= 8.9 min( 796.6- 787.7 ) Volume Invert Avail.Storage Storage Description #1A 928.25' 3,858 cf 38.17W x 144.84'L x 2.33'H Field A 12,899 cf Overall -3,253 cf Embedded = 9,645 cf x 40.0% Voids #2A 928.75' 3,253 cf ADS_StormTech SC-310 x 220 Inside#1 Effective Size= 28.9"W x 16.0"H => 2.07 sf x 7.12'L = 14.7 cf Overall Size= 34.0"W x 16.0"H x 7.56'L with 0.44'Overlap Row Length Adjustment= +0.44'x 2.07 sf x 11 rows 7,111 cf Total Available Storage Storage Group A created with Chamber Wizard 18-05-09_Site Option 1_13019 OPH MN-Stillwater 24-hr Si 100-yr Rainfall=7.22" Prepared by Westwood Professional Services Printed 5/15/2018 HydroCAD®10.00-14 s/n 03363 ©2015 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Heights I Utility Rim Summary of Water Quality Performance Studies S,tol'1YlT�h' Detention•&tenton•WaterQuality for the Isolator Row Division of lire Introduction These devices and the load removal efficiencies, Any stormwater treatment system,ranging from a particulate sizing, and concentrations are available wet pond to an underground manufactured sys- by contacting a local ADS representative, tern requires field testing and an evaluation of the pollutant removal efficiencies, These systems in a StormTech chambers feature an "isolator row" to network of BMP's can be used to model sediment provide water quality treatment of stormwater as it reduction, phosphorus removal, metal reduction enters the system. The isolator row features a typi- and other constituents. StormTech, a division of cal StormTech chamber wrapped in woven geotex- Advanced Drainage Systems,Inc.(ADS)has devel- tile fabric. Stormwater first enters the isolator row oped the summarized data for pollutant loading which traps sediments and pollutants via the filter inputs into modeling software programs. fabric and then allows stormwater to pass through The Isolator row has been tested by independent the fabric in a treated state to the adjacent cham- agencies and reports are available. These reports bers and stone material via hydrostatic flow. The have been provided to the University of MN, St. overall system typically features a 6-inch HDPE per- Anthony Falls Laboratory and evaluated for meth- forated under drain line placed along one side of the odology,oversight,and relevance to Minnesota.* excavation bottom to provide flow discharge control from the system. Because the excavation for the system is typically unlined, some infiltration of Data stormwater can be expected if sub-surface soils are To aid designers with choosing between different conducive to infiltration. BMP options the MN Stormwater Manual tabulat- ed the current median pollutant removal percent- Isolator Row(IR): ages. The University of New Hampshire Stormwater Re- search Center conducted field testing of 17 rain events from December 2006—March 2008,encom- • - :, , , ., passing 3 winter seasons. New Hampshire is of simi- lar latitude and climate with similar rain events to tructed gq 50 91 0 ,30 0 80 Minnesota. Additionally,separate field testing was tructedperformed under the direction of the University of North Carolina. Lab testing evaluated sizes for par- 35 50 ticulates from ranging from 110 microns(OK-110)to 22 microns(Sil-Co-Sil 106). Flow rates ranged from eable . _ , 1.7 gpm/sqft to 3.2 gpm/sqft. Median pollutant re- moval percentages from field testing are summa- rized. Summary of common pollutant removal percentages in MN Stormwater Monuol. TSS=Total suspended Solids,TP=Total Phosphorus,PP=Particulate Phos- Above data won measured at the University of New Hampshire Stormwater horus,DP=Dissolved Phosphorus,7N=Total Nitrogen,PHC=Petroleum Center,June 2008 report Hydrocarbons 1 Estimated assuming phosphorus concentrated fraction=55%particu- late/45%dissolved(MISS Calculator and Pitt,0.,Maestre,A., Stormwater Research Center Data Morquecho,F.,Grown,T.,Schnuh , MCiffi iella,K.,on rrAgi 0005).Evaluation of NPDES Phase 1 Mumcipol5tormwa[er Monitor- Preamble: ADS has been providing water quality mg Data."University of Alabama and the Center for Watershed Pro- tection/. devices which can be routed through a treatment 2 Charlotte,NC-Cherry Gardens,Charlotte-Mecklenburg stormwater Services. train for infiltration,filtration,and sedimentation. * Erickson,Al(2017)."Stormwater Master Class: Pollu- These devices constitute a cost effective and tants l Treatment,Filtration,Inspection,Maintenance and maintainable BMP for urban runoff. olis,tM�ater Quality Forum 1.0. Hosted by ADS. Minneop-