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Stormwater Management
PREPARED BY: PREPARED FOR: Café Zupas Sandy, UT A REPORT FOR STORMWATER MANAGEMENT Cafe Zupas Chanhassen, MN MAY 2, 2023 Stormwater Management Plan Report Cafe Zupas Chanhassen, MN Prepared For: Café Zupas ɫɭɧ Universal Circle Sandy, UT ɯɫɧɮɧ ɯɧɨ-ɯɪɬ-ɧɰɰɰ Prepared By: Westwood Professional Services ɨɩɮɧɨ Whitewater Drive, Suite ɪɧɧ Minnetonka, MN ɬɬɪɫɪ (ɰɬɩ) ɰɪɮ-ɬɨɬɧ I hereby certify that this report was prepared by me or under my direct supervision and that I am a duly Licensed Professional Engineer under the laws of the State of Minnesota. __________________________ Name: Joseph Schramm Date: ɧɬ/ɧɩ/ɩɧɩɪ License No. ɬɭɧɮɯ Project Number: ɧɧɫɩɪɨɰ.ɧɧ Date: May ɩ, ɩɧɩɪ Stormwater Management Plan | Cafe Zupas May 2, 2023 Table of Contents 1.0 Introduction ................................................................................................. 2 1.1 Project Description ....................................................................................................................................... 2 1.2 Regulatory Requirements............................................................................................................................. 2 2.0 Existing Site and Drainage Conditions .......................................................... 2 3.0 Soil Conditions ............................................................................................. 2 4.0 Proposed Stormwater Management System Design ...................................... 2 5.0 Stormwater Management ............................................................................. 3 5.1 Rate Control .................................................................................................................................................. 3 5.2 Volume Abstraction ...................................................................................................................................... 4 5.3 Water Quality ................................................................................................................................................ 4 6.0 Conclusions ................................................................................................... 5 Exhibits Exhibit ɨ: Existing & Proposed Drainage Area Maps Exhibit ɩ: Impervious Area Exhibit Appendix Appendix A: Soil Borings Appendix B: HydroCAD Model – Existing Conditions Appendix C: HydroCAD Model – Proposed Conditions Appendix D: MIDS Calculator Appendix E: Water Quality BMP Performance Confidential and Proprietary. TBPLS Firm #10074302 1.0 Introduction 1.1 Project Description This report summarizes the stormwater management design for the proposed Cafe Zupas project. The proposed Cafe Zupas restaurant is located in a proposed outlot in the existing parking lot of the Lunds & Byerly’s at W ɮɯth Street and Kerber Boulevard. The proposed project consists of a ɪ,ɧɬɧ SF building and associated drive thru and parking. Exhibit ɨ shows the existing and proposed drainage areas for this project. The drainage areas extend into the overall Lunds parcel to capture runoff from the existing and reconstructed parking areas. The two parcels are considered the project area under watershed rules. However, the stormwater calculations are included only for the proposed development site and the adjacent parking lot. The disturbed area of this project is approximately ɪɧ,ɮɨɪ square feet. 1.2 Regulatory Requirements The proposed project site is located within the City of Chanhassen and Riley Purgatory Bluff Creek Watershed District. The following rules from the City and Watershed apply: Limit peak runoff to existing conditions for the ɩ-, ɨɧ-, and ɨɧɧ-year ɩɫ-hour storm events and the ɨɧɧ-year, ɨɧ-day snowmelt event. Provide abstraction for ɨ.ɨ inches of runoff from impervious surfaces, or ɧ.ɬɬ inches for restricted sites. Provide at least ɭɧ% TP removal and ɰɧ% TSS removal on an annual average basis, and no net increase in TSS or TP from the existing conditions. Minimum ɪ’ freeboard between basin ɨɧɧ-year high water level and low building opening (City requirement). 2.0 Existing Site and Drainage Conditions The proposed property is part of the Lunds & Byerly’s parcel (PID: ɩɬɯɮɰɧɧɫɧ) and currently consists of parking lot, landscape islands, driveways, and storm sewer. To the north of the proposed outlot is the Lunds & Byerly’s grocery store development. To the west of the proposed outlot is the FedEx retail store. The existing parking lot drains to four catch basins in the southwest corner of the lot. Three of these catch basins drain south via pipes to W ɮɯth Street. The westernmost catch basin drains west to the storm sewer near the FedEx store. 3.0 Soil Conditions A Geotechnical Exploration Report was completed by Westwood on April ɨɰ, ɩɧɩɪ for the project. The soil boring logs are included in Appendix A. The site generally consists of native lean clay glacial till beneath existing pavement and aggregate base. Groundwater was not observed in the soil borings. 4.0 Proposed Stormwater Management System Design The proposed project consists of a ɪ,ɧɬɧ SF restaurant and drive-thru in the existing grocery store parking lot. Runoff from the proposed building will be routed to an underground system that also receives runoff from the drive-thru and parking lot pavement. Outflow from the Confidential and Proprietary. TBPLS Firm #10074302 underground system will be routed to the development’s existing storm sewer south of the proposed drive thru. Stormwater will ultimately discharge to W ɮɯth Street storm sewer. Table 1: Impervious Lot Coverage Cover Existing Area [ac] Proposed Area [ac] Pervious ɧ.ɪɰ ɧ.ɫɭ Impervious ɩ.ɩɯ ɩ.ɩɨ Total ɩ.ɭɮ ɩ.ɭɮ There is a net decrease of ɧ.ɧɮ acres of impervious area. The total new and reconstructed impervious area for the project is ɧ.ɬɭ acres, as illustrated on Exhibit ɩ. 5.0 Stormwater Management 5.1 Rate Control Stormwater discharges for the proposed project area have been reduced to the existing rates by utilizing the storage capacity in the underground chamber system. Discharge rates were computed using HydroCAD stormwater modeling software which incorporates Atlas-ɨɫ rainfall distributions. See Appendices A & B for the existing and proposed HydroCAD models. The tables below summarize the existing and proposed peak runoff rates at the site discharge points. Table 2: Peak Discharge Rates to West Storm Event Existing Discharge Rate [cfs] Proposed Discharge Rate [cfs] ɩ-year (ɩ.ɯɮ”) ɪ.ɰɬ ɨ.ɧɰ ɨɧ-year (ɫ.ɩɮ”) ɭ.ɪɪ ɩ.ɪɮ ɨɧɧ-year (ɮ.ɫɨ”) ɨɧ.ɬɩ ɬ.ɧɮ ɨɧɧ-yr, ɨɧ-d snowmelt (ɮ.ɩ”) ɧ.ɨɮ ɧ.ɨɨ Table 3: Peak Discharge Rates to South Storm Event Existing Discharge Rate [cfs] Proposed Discharge Rate [cfs] ɩ-year (ɩ.ɯɮ”) ɯ.ɧɧ ɫ.ɯɫ ɨɧ-year (ɫ.ɩɮ”) ɨɩ.ɫɰ ɭ.ɫɯ ɨɧɧ-year (ɮ.ɫɨ”) ɩɧ.ɪɰ ɰ.ɬɧ ɨɧɧ-yr, ɨɧ-d snowmelt (ɮ.ɩ”) ɧ.ɪɫ ɧ.ɪɰ While the rate control requirement for the snowmelt event is not met at the southern discharge point, the two discharge points converge downstream of the site and the total snowmelt runoff rate matches existing conditions. The ɨɧɧ-yr HWL of the underground system is ɰɭɰ.ɮɫ’. The low floor elevation of the proposed building is ɰɮɪ.ɧɧ’, which meets the watershed’s ɩ’ freeboard requirement and the city’s ɪ’ freeboard requirement. Confidential and Proprietary. TBPLS Firm #10074302 5.2 Volume Abstraction The Watershed requires abstraction of ɨ.ɨ inches of runoff from all new or reconstructed impervious surfaces. Based on the soil borings in the proposed project area, the site is restricted for infiltration due to the sandy lean clay soils, resulting in a reduced volume abstraction requirement of ɧ.ɬɬ inches. An infiltration rate of ɧ.ɪ”/hr was measured during an infiltration test of in-situ compacted soils on ɧɫ/ɨɰ/ɩɧɩɪ by Westwood Professional Services. A rate of ɧ.ɨɬ”/hr was assumed for design. The ɨɧ” depth rock bed under the chamber system provides an equivalent infiltration depth of ɧ.ɪɪ’ (to account for ɫɧ% voids), which will draw down in ɩɮ hours for the ɧ.ɨɬ”/hr infiltration rate. Refer to Table ɫ for a summary of volume abstraction provided by the underground chambers. Refer to the end of Appendix C for the stage storage table of the underground chamber system. Table 4: Volume Abstraction BMP Impervious Area [ac] Required Volume (ɧ.ɬɬ”) [cf] Volume Abstraction Provided [cf] UG Chambers ɧ.ɬɫɧ ɨ,ɧɮɰ ɨ,ɨɪɪ 5.3 Water Quality The Watershed requires storm water facilities to be designed to provide ɭɧ% annual removal of total phosphorus (TP), ɰɧ% annual removal of total suspended solids (TSS), and no net increase in TSS and TP compared to existing conditions. The volume abstraction from the Isolator Row of the underground chamber system is proposed to meet the water quality requirements. A sump manhole provides pretreatment. The MIDS Calculator was used to model the water quality for the proposed disturbed area. Separate models were run to calculate the removal efficiencies since the regulated impervious area differs from the actual tributary drainage area to the filter device. The first model calculates the loading of the site plus the reconstructed impervious on the adjacent property. The second model includes the entire area tributary to the BMPs to calculate the proposed load removals. This includes all the disturbed pervious areas, all new impervious areas, and all disturbed impervious areas. The treatment needed to meet the watershed rules is provided by the isolator row of the StormTech chambers. A Pɯ model was developed to determine the performance of the Isolator Row, with results of ɬɬ% TSS and ɩɭ% TP removal. Refer to Appendix E for the Pɯ modeling result for the StormTech Isolator Row, which were used as inputs for the MIDS Calculator. The MIDS modeling results from Appendix D are summarized in Table ɬ below. Table 5: MIDS modeling results-Removal efficiencies Loading [lbs/yr] Load Retained [lbs/yr] % Reduction Confidential and Proprietary. TBPLS Firm #10074302 TSS ɨɮɧ.ɬ ɪɯɪ.ɮ ɨɩɬ% TP ɧ.ɰɫ ɨ.ɬɨ ɨɭɬ% In addition, a third MIDS model calculates the runoff from the existing conditions for same watershed boundary as the proposed conditions to verify that there is no increase in TSS and TP loading from the proposed project. The MIDS modeling results from Appendix D are summarized in Table ɭ below. Table 6: MIDS modeling results-No net increase Existing Loading [lbs/yr] Proposed Loading [lbs/yr] TSS ɮɬɩ.ɧ ɪɬɩ.ɮ TP ɫ.ɨɫ ɩ.ɬɫ 6.0 Conclusions The proposed Cafe Zupas Retail development and its stormwater management facilities have been designed to meet the requirements of the City of Chanhassen, Riley Purgatory Bluff Creek Watershed District, and the MPCA NPDES permit. Rate Control The proposed site discharge rates do not exceed the existing discharge rates. Volume Reduction The proposed stormwater management systems meets the volume abstraction requirement for restricted sites (ɧ.ɬɬ” over new and reconstructed impervious areas). Water Quality The proposed BMP combine to meet the ɰɧ% TSS and ɭɧ% TP removal requirements , and provide no net increase in TSS and TP. Confidential and Proprietary. TBPLS Firm #10074302 Exhibit 1: Existing & Proposed Drainage Area Maps STOSTOSTOSTOSTOSTOSTOSTOSTOSTOSTOSTOSTOSTOST O ST O ST O STOPUG PUG PUG PUG PUGRIM=964.85INV(E)=961.44INV(W)=961.35RIM=965.34INV(E)=962.09INV(W)=961.64RIM=966.44INV(W)=962.39RIM=966.82INV(S)=963.26RIM=967.53INV(W)=963.93RIM=965.03INV(N)=962.40INV(S)=961.07RIM=971.91INV(N)=967.58INV(SW)=967.61RIM=973.57INV(N)=968.72INV(S)=968.67INV(E)=968.89RIM=973.30INV(E)=970.10INV(W)=970.10RIM=973.59INV(W)=970.29RIM=971.96INV(W)=969.26RIM=971.86INV(W)=968.66INV(E)=968.5612" RCP12 " R C P 12" RCP12" RCP12" RCP12" RCP12" RCP12" RCP12" RCP12" RCPTTSTOSTOSTO965970975980964966967968969971972973974976977 978979981970975969971972973974976977978979975971972973974976977970975969971972973974976977978 9799659709709709669679689699719719719721S0.78 AC.33,830 SF2S0.91 AC.39,595 SF3S0.94 AC.41,049 SF4S0.04 AC.1,942 SFSHEET NUMBER:DATE:Phone :hLWeZaWer 'rLYe 6XLWe Fax 0LnneWonNa 01 Toll Free LICENSE NO. I HEREBY CERTIFY THAT THIS PLAN WAS PREPARED BY ME OR UNDER MY DIRECT SUPERVISION AND THAT I AM A DULY LICENSED PROFESSIONAL ENGINEER UNDER THE LAWS OF THE STATE OF MINNESOTA VERTICAL SCALE: HORIZONTAL SCALE: DRAWN: CHECKED: DESIGNED:INITIAL ISSUE: REVISIONS:PREPARED FOR: N:\0042319.00\DWG\0042319C-DRAN.DWG 05/02/2023CAFE ZUPAS1 CHANHASSEN, MN CAFE ZUPAS EXISTING DRAINAGE MAP 05/02/2023 JAS JAS AKW 05/02/2023 460 UNIVERSAL CIRCLE SANDY, UT 84070 CAFE ZUPAS 56078 JOSEPH A. SCHRAMMNOT FOR CONSTRUCTION© 2023 Westwood Professional Services, Inc.Common Ground AllianceCall 48 Hours before digging:811 or call811.com0'20'40'60'1" = 20'. . . . . . . . . . 20' 4' or 2'PROJECT NUMBER: 0042319.00 STOSTOSTOSTOSTOSTOSTOSTOSTOSTOSTOSTOSTOST O ST O ST O STORIM=964.85INV(E)=961.44INV(W)=961.35RIM=965.34INV(E)=962.09INV(W)=961.64RIM=966.82INV(S)=963.26RIM=967.53INV(W)=963.93RIM=965.03INV(N)=962.40INV(S)=961.07RIM=971.91INV(N)=967.58INV(SW)=967.61RIM=973.57INV(N)=968.72INV(S)=968.67INV(E)=968.89RIM=973.30INV(E)=970.10INV(W)=970.10RIM=973.59INV(W)=970.29RIM=971.96INV(W)=969.26RIM=971.86INV(W)=968.66INV(E)=968.5612" RCP12 " R C P 12" RCP12" RCP12" RCP12" RCP12" RCP12" RCP12" RCPTT965970975980964966967968969971972973974976977 978979981970975969971972973974976977978979975971972973974976977970975969971972973974976977978 979965970970970966967968969971971971972ONLINEPICKUPONLYORDERDRIVETHRUPROPOSED RESTAURANT3,050 SFFFE = 973.00EXITONLYXXXXX XX 1S0.56 AC.24,479 SF2S2.02 AC.87,977 SF3S0.09 AC.3,910 SFSHEET NUMBER:DATE:Phone :hLWeZaWer 'rLYe 6XLWe Fax 0LnneWonNa 01 Toll Free LICENSE NO. I HEREBY CERTIFY THAT THIS PLAN WAS PREPARED BY ME OR UNDER MY DIRECT SUPERVISION AND THAT I AM A DULY LICENSED PROFESSIONAL ENGINEER UNDER THE LAWS OF THE STATE OF MINNESOTA VERTICAL SCALE: HORIZONTAL SCALE: DRAWN: CHECKED: DESIGNED:INITIAL ISSUE: REVISIONS:PREPARED FOR: N:\0042319.00\DWG\0042319C-DRAN.DWG 05/02/2023CAFE ZUPAS2 CHANHASSEN, MN CAFE ZUPAS PROPOSED DRAINAGE MAP 05/02/2023 JAS JAS AKW 05/02/2023 460 UNIVERSAL CIRCLE SANDY, UT 84070 CAFE ZUPAS 56078 JOSEPH A. SCHRAMMNOT FOR CONSTRUCTION© 2023 Westwood Professional Services, Inc.Common Ground AllianceCall 48 Hours before digging:811 or call811.com0'20'40'60'1" = 20'. . . . . . . . . . 20' 4' or 2'PROJECT NUMBER: 0042319.00 Confidential and Proprietary. TBPLS Firm #10074302 Exhibit 2: Impervious Area Exhibit STOSTOSTOSTOSTOSTOSTOSTO STOSTOSTOSTOSTOSTOSTOSTOSTOSTOSTOSTOSTOSTOSTOSTOSTOSTOSTOSTO ST O STOSTOSTOSTO STOEXISTING BUILDING841 SQ. FEETEXISTING BUILDINGEXISTING BUILDINGPROPOSED RESTAURANT3,050 SFFFE = 973.00SHEET NUMBER:DATE:Phone :hLWeZaWer 'rLYe 6XLWe Fax 0LnneWonNa 01 Toll Free LICENSE NO. I HEREBY CERTIFY THAT THIS PLAN WAS PREPARED BY ME OR UNDER MY DIRECT SUPERVISION AND THAT I AM A DULY LICENSED PROFESSIONAL ENGINEER UNDER THE LAWS OF THE STATE OF MINNESOTA VERTICAL SCALE: HORIZONTAL SCALE: DRAWN: CHECKED: DESIGNED:INITIAL ISSUE: REVISIONS:PREPARED FOR: N:\0042319.00\DWG\0042319C-DRAN.DWG 05/02/2023CAFE ZUPAS3 CHANHASSEN, MN CAFE ZUPAS IMPERVIOUS AREAS EXHIBIT 05/02/2023 JAS JAS AKW 05/02/2023 460 UNIVERSAL CIRCLE SANDY, UT 84070 CAFE ZUPAS 56078 JOSEPH A. SCHRAMMNOT FOR CONSTRUCTION© 2023 Westwood Professional Services, Inc.Common Ground AllianceCall 48 Hours before digging:811 or call811.com0'40'80'120'1" = 40'. . . . . . . . . . 40' 8' or 4'PROJECT NUMBER: 0042319.00EXISTING IMPERVIOUS AREANEW/RECONSTRUCTED IMPERVIOUS PAVEMENT Confidential and Proprietary. TBPLS Firm #10074302 Appendix A: Soil Borings