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Home My WebLink AboutMOD-0806-2021 Stormwater Control Planj' Stormwater Control Plan for Post Construction Requirements Exhibit 4 Application Submittal Where directions state "Done" that means no additional information or forms below that point needs to be filled out or furnished. See Exhibits for Watershed Management Zones, Basins, & Urban Sustainability Areas Use "n/a" where information requested is not applicable. If you are unsure regarding how to fill out any of the information, please come in and request assistance from a staff person. Project Information Step 1 Applicant Name: John Rourke Application No: Project Name: Westmont Subdivision Location Address: 468 Westmont Ave., San Luis Obispo, CA 93405 Location APN: 052-496-001 Site Zoning: R-1 Project Type: ✓ Commercial f Detached Single Family Residential Industrial Multi -unit Residential Mixed Use Public Project Phase: Project Description: 41 Lot Single -Family Subdivision with affordable housing Total Project Site Area 1216,870 (a) Total New Impervious Surface Area = 53,325 sqft (b) Total Replaced Impervious Surface Area = 20,021 sgft (c) Total Existing Impervious Area = 21,897 sgft (d) Total Impervious Area of Completed Project = 73,346 sqft 73 346 sqft q (e) Net Impervious Area: (a+b) — (c-d) = OR where (c-d) is a negative number: (a+b) _ Your project is NOT subject to Post Construction Requirements if... Step 2 gonArea (a+b) of project is < 2,500 square feet — e OR Area (a+b) of project is > 2,500 square feet, and is a project type listed below (✓ type) — ie[] Road & parking surface repair — slurry & fog & crack seal, pothole & spot patching, overlay & resurfacing & other damage repair with no expansion Road & parking shoulder grading Road & parking cleaning, repairing, maintaining, reshaping, regarding drainage systems Sidewalk & bike path / lane project — no other impervious surface created and runoff is directed to vegetated area Curb & gutter improvement or replacement — no other impervious created Underground utility project —surface replaced in kind Utility vaults — Ex: lift stations, backflows Fuel storage — above ground with spill containment Photovoltaic systems — on existing impervious surface, over pervious surface with vegetated cover, ffer strip at the most down gradient row of panels Second story — no increase in building footprint Decks & stairs & walkways — raised with space below for drainage Temporary structures — in place less than 6 months Trails and pathways, where no other impervious surfaces are replaced or created, and built to direct stormwater runoff to adjacent vegetated areas. Form revised: July 12, 2016 ALL~ Stormwater Control Plan for Post Construction Requirements Otherwise, your project is subject to the Post Construction Requirements Project Site Details Step 3 Watershed Management Zone: j wMz-i Urban Sustainability Area Name: ✓Meet USA Conditions • See Area calculations in Step 1 to compare to thresholds in each Step below • Where directions state "Go To". fill out and attach the referenced Form and any supporting documents ;tep 4 Project is > 2,500 square feet El Yes - Go To Requirement 1— Site Design & Runoff Reduction - Form 1 AND THEN Go To Step 5 itep 5 Detached single family residential project where Area (e) is > 15,000 square feet OR Project where Area (e) > 5,000 square feet III Yes - Go To Requirement 2 — Water Quality Treatment - Form 2 AND THEN Go To Step 6 ❑ No - Done tep 6 Detached single family residential project where Area (e) > 15,000 square feet OR Project where Area (a+b) > 15,000 square teet AND is in Watershed Management Zone 4,7,10 over a ground water basin OR in Zone 1,2,5,6,8,9 El Yes - Go To Requirement 3 — Runoff Retention - Form 3 AND THEN Go To Step 7 ❑ No - Done ;tep 7 Project where Area (a+b) > 22,000 square feet AND is in Watershed Management Zone 1,2,3,6,9 0 Yes -Go To Requirement 4 — Peak Management -Form 4 ❑ No - Done Exhibits 1. Watershed Management Zones 2. Groundwater Basin Location 3. Watershed Management Zone Revision Request 4. Urban Sustainability Conditions and Maps of Approved Areas Stormwater Control Plan for Post Construction Requirements Form 1 Requirement 1- Site Design and Runoff Reduction: Identify the strategies used to reduce runoff through site design. Strategies 1-5 required. Describe or attach simple plan details for 1. - 5. 1. Limit disturbance of creeks and natural drainage features and setback development from these features. Disturbance to creeks and natural drainage features minimized. 2. Minimize compaction of highly permeable soils Compaction of permeable soils minimized where possible. 3. Minimize clearing of native vegetation and grading, conserving natural areas and maximizing undisturbed areas, and developing along natural landforms. Clearing of native vegetation and grading minimized where possible. 4. Minimize impervious surfaces including roadways and parking lots Impervious surfaces minimized where possible. Do one of the following: ✓ ❑Direct roof run off into cistern, rain barrel, or vegetated area ❑Direct driveway, walkways, patios, and/or parking area into vegetated area ❑✓ construct surfaces (bike lanes, walks, driveways, parking areas,patios) with permeable surfaces 6. Other (Optional): Identify strategy(s) and describe or show how it will be done in the project. Stormwater Control Plan for Post Construction Requirements Form 2 Requirement 2 - Water Quality Treatment: (Reference Post Construction Stormwater Management Requirements for Development Projects in the Central Coast Region - Adopted July 12, 2013 California Regional Water Quality Control Board Central Coast Region - for details regarding requirements -Section B.3 and Section C. Alternative Compliance.) Treatment Location ✓ 0 On Site ❑ Off Site - Alternative Compliance Measure Used ✓ 111 1. Harvesting, infiltration, evapotranspiration L l 2. Bio-filtration I reatment (Document inability to use 1.) ❑ 3. Non -Retention Based Treatment (Document inability to use 1. or 2.) Description of structural controls: Permeable paver section Alternative compliance measures: Attachments Attach t Calment/54'Zing %ai%uiati0nI5, inClU'dirg any volume treated with of f_S;te �rnmrnlin„�nno • Attach construction and planting details and specifications for bio filtration options ■ Attach documentation regarding Treatment Measure selection • Attach infeasibility analysis where alternative compliance is proposed. Certification I Scott Stokes certify that the systems selected and sized, as demonstrated in the attached calculations, meet the Water Quality Treatment required for this project per the Post Construction Requirements adopted by the Central Coast Regional Water Quality Control Board. Where identified in the attached ume tatio , Water Quality Treatment will be met through alternative compliance. 11-11-2021 Sign ure Date Stormwater Control Plan for Post Construction Requirements Form 3 Requirement 3 - Runoff Retention: (Reference Post Construction Stormwater Management Requirements for Development Projects in the Central Coast Region - Adopted July 12, 2013 California Regional Water Quality Control Board Central Coast Region - for details regarding requirements - Section B.4 and Section C. Alternative Compliance.) • If a revision to the site's Watershed Management Zone is being requested, attach Watershed Management Revision Request Form (Exhibit) and supporting documentation. • Rainfall maps are available from the Regional Water Quality Control Board Site Assessment Measures Summary I] Attach documentation of the following information: ■ Site topography • Development envelope • Hydrologic features including natural areas, wetlands, watercourses, seeps, springs, and required setbacks • Vegetative cover including trees • Open space requirements • Location of groundwater wells used for drinking water • Depth to seasonal high groundwater • Soil types and hydrologic soil groups • Depth to impervious layer such as bedrock • Presence of unique geology (e.g. karst) ■ Geotechnical hazards ■ Existing structures, utilities, and drainage infrastructure including municipal storm drain system components ■ Existing easements and covenants • Documented soil or groundwater contamination • Source and estimated stormwater run-on from offsite, coming to project area • Drainage Management Areas (B.4.d.iii) ■ Drainage management strategies by Drainage Management Area ■ Runoff reduction measures and any structural control measures by Drainage Management Area (or full site as appropriate) ❑ Technical infeasibility limits on -site compliance ❑ 10% of equivalent impervious surface area is dedicated to retention based stormwater control measures - No alternative compliance for retention Runoff volume - compliance not achieved on -site: ❑ Alternative compliance for retention proposed Runoff volume - compliance not achieved onsite: Runoff volume - alternative compliance used: Analysis and Sizing ❑ Attach calculated Tributary Areas and Design Volumes per the Post Construction Stormwater Management Requirements -Attachment D ❑ Adjustment made for redevelopment 11 Adjustment made for being in, and meeting requirements of, an Urban Sustainability Area Stormwater Control Plan for Post Construction Requirements Form 3 Control Mechanism Site in Zone 1, 4, 7, and/or 10 and over groundwater basin 0 95" percentile event retained via infiltration ❑ Finding of technical infeasibility —Structural Stormwater Measure proposed Site in Zone 2 ❑ 95" percentile event retained via storage, harvesting, infiltration, and/or evapotranspiration ❑ Finding of technical infeasibility— Structural Stormwater Measure proposed Sit- in Zn r �wri/nr Si ❑ 85" percentile event retained via infiltration [I Finding of techniral infeasibility — Structural Stormwater Measure proposed Site in Zone 6 and/or 9 ❑ 85th percentile event retained via storage, harvesting, infiltration, and/or evapotranspiration ❑ Finding of technical infeasibility —Structural Stormwater Measure proposed Attachments aCL. A+ -+,.,.a... --+ n .- 11111r,rinnc Fnr hvrirninnir• nnnlvcit and Stormwater control measure sizina MELUI.If "LLUl.III I ICIIL V 6ull. u.aw �. v....�v. ..r v........J... •••••—•,— — -"----------- - -- ■ Attach discussion of technical infeasibility for structural stormwater measure, where proposed in lieu of preferred storage, harvesting, infiltration, and/or evapotranspiration, include justification for any non - retention based controls • Attach documentation of technical infeasibility for On -site compliance, including a site specific hydrologic and/or design analysis supporting findings • Attach description of alternative compliance project Including a summary description of pollutant and flow reduction comparing the expected aggregate results of the alternate project to the results that would otherwise have been achieved by meeting the numeric performance requirements onsite. ■ Attach Attachment E calculations for retention requirement adjustment for technical infeasibility ■ Attach Attachment F calculations for off -site retention requirements • Attach agreement for alternative compliance site use, for purposes of achieving compliance • Attach Operations and Maintenance Plan for all Stormwater control measures (include any Peak Management facilities) Post -Construction Owner Identification At the time of completion of the construction work, and the shift to post -construction stormwater controls, the below listed owner is responsible for Operations and Maintenance of stormwater control measures: (If responsibilities are divided, list all responsible owners and associated measures.) Certification I Scott Stokes certify that the systems selected, sized, and designed as demonstrated in the attached calculations, meet the Runoff Retention Performance Requirement for this project per the Post Construction Requirements adopted by the Central Coast Regional Water Quality Control Board. Where identiZehe a e documentation, Runoff Retention will be met through alternative compliance. 11-11-2021 Sign ture Date Stormwater Control Plan for Post Construction Requirements Form 4 Requirement 4 - Peak Management (Reference Post Construction Stormwater Management Requirements for Development Projects in the Central Coast Region - Adopted July 12, 2013 California Regional Water Quality Control Board Central Coast Region - for details regarding requirements - Section B.5) Show any stormwater control measures used to meet the requirements of this section, in the documentation and attachments required for Retention (Form 3), including in all mapping and Operations and Maintenance materials. Peak Management Compliance 0 Post -development peak flows, discharged from the site, do not exceed pre -project peak flows for the 2 through 10 years storm events. ❑ Technical infeasibility limits on -site compliance ❑ Alternative compliance for retention proposed Runoff volume - compliance not achieved onsite: Runoff volume - alternative compliance used: Attachments • Attach calculations showing pre -project discharge and post -project discharge for the 2 through 10 year storm events ■ Attach documentation of technical infeasibility for on -site compliance, including a site specific hydrologic and/or design analysis supporting findings ■ Attach description of alternative compliance project including a summary description of pollutant and flow reduction comparing the expected aggregate results of the alternate project to the results that would otherwise have been achieved by meeting the numeric performance requirements onsite. • Attach agreement for alternative compliance site use, for purposes of achieving compliance Post -Construction Owner Identification At the time of completion of the construction work, and the shift to post -construction stormwater controls, the below listed owner is responsible for Operations and Maintenance of the peak management control measures: (If responsibilities are divided, list all responsible owners and associated measures.) Certification I Scott Stokes certify that the systems selected, sized, and designed as demonstrated in the attached calculations, meet the Peak Management requirements for this project per the Post Construction Requirements adopted by the Central Coast Regional Water Quality Control Board. Where identified in the attached cum tati n, Peak Management will be met through alternative compliance. 11-11-2021 Sig ture Date Stormwater Control Plan for Post Construction Requirements Exhibit 1 Watershed Management Zones T C LV E N y N c C3 Q O �N ®3 O t LCl 0 CO 01 - 1