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HomeMy WebLinkAboutPCR Memo 2019-05-23 Page 1 of 2 MEMORANDUM Date: 5/23/2019 To: Richard Burde Organization: City of San Luis Obispo From: Scott Yoshida Title: Project Manager Project Name: Palm & Nipomo Parking Structure Project Number: 0720-02-UR19 Topic: Preliminary Stormwater Management and PCR’s The purpose of this memorandum is to describe how the proposed development will address the Regional Water Quality Control Board Post-Construction Stormwater Requirements (PCRs). The proposed project’s new and replaced impervious area is greater than 22,500 square feet so PCRs #1, 2, 3 and 4 all apply. See the Stormwater Management Plan sheet C3 for reference. The property is located off Nipomo Street (across from the Reis Family Mortuary), bound by Monterey Street to the south (across from the Children’s Museum) and Palm Street to the north (across from the Mission Prep sports field). The property is made up of six parcels: APNs 002-412-001, 002, 003, 004, 011 and 012, which are comprised of an existing City owned surface parking lot and three existing residential dwellings with garages. The existing streets and parcels generally drain via surface flow and runoff collected and conveyed by existing concrete gutters traveling from the southeast to the northwest, heading towards the Palm Street and Nipomo Street intersection. There are no existing storm drain curb inlets or culverts along the project frontage. The proposed project includes a City owned 5-story parking structure on the northern portion and a new building with plaza areas for the San Luis Obispo Repertory Theater on the southern portion. All existing structures, improvements and appurtenances on-site are planned to be demolished and removed, while some existing trees will be preserved. Frontage Richard Burde City of San Luis Obispo May 23, 2019 Page 2 of 2 improvements are also proposed which include removing and replacing the curb, gutter and sidewalks along with curb ramps. See preliminary SLO Rep Theater civil plans prepared by Engineering Design Professionals and parking structure and frontage improvement preliminary plans prepared by RRM Design Group for reference. PCR #1 Site Design and Runoff Reduction will be achieved by directing a portion of the project’s runoff to vegetated areas. PCR #2 Water Quality Treatment will be achieved by directing some runoff to proposed vegetated stormwater treatment areas or to proposed Contech Filterra biofiltration tree boxes on Palm Street. These proposed measures are shown schematically on the Stormwater Management Plan sheet C3 and will be sized to provide the required water quality treatment volume and/or handle the minimum required flow rate. PCR #3 Runoff Retention will be achieved by proposed underground storage chambers which will retain the runoff from a 95th percentile, 24-hour storm event. These proposed chambers are shown schematically on the Stormwater Management Plan sheet C3 and have been sized to provide the required retention volume. PCR #4 Peak Management will be achieved by integrating some detention volume into the proposed underground storage chambers. During the development of construction drawings, the proposed storm drain culvert inverts and discharge outflows will be set at elevations so that post-development peak flows discharged from the site will not exceed pre- project peak flows for the 2-through 10-year storm events. A drainage analysis will be conducted, and a corresponding hydrology model will be prepared to achieve the PCR #4 requirement. See preliminary SLO Rep Theater civil plans prepared by Engineering Design Professionals and parking structure and frontage improvement preliminary plans prepared by RRM Design Group for reference. A Storm Water Control Plan (SWCP) will be developed during preparation of construction drawings for the proposed project.