South Napa Century Center, Stormwater Treatment, Storage and Reuse, Napa
Carlile • Macy's innovative stormwater treatment, storage and reuse design for the South Napa Century Center project gained unanimous agency approval for the removal of existing wetland ponds. Without this approval the project could not move forward.
South Napa Century Center development is an infill project consisting of a theatre complex and retail center to be built on property adjacent to the existing South Napa Marketplace. Stormwater wetland ponds on this property were a part of the existing stormwater runoff system for South Napa Marketplace. After numerous failed attempts by consultants to develop a creative design alternative that would remove the existing wetland ponds, yet still gain permitting and approval through the regulatory process, including Regional Water Quality Control Board, Carlile • Macy succeeded. Carlile • Macy's solution is the design of a hybrid dual-purpose subsurface water quality BMP coupled with a polishing engineered bioswale. The design replaces the stormwater ponds, allowing for the development of the property while accommodating the stormwater from South Napa Marketplace. Carlile Macy designed the stormwater treatment, storage and reuse system to work in three stages: separator, chamber system, and bioswale. The first element is a structural BMP to act as a primary clarifier, removing floatable oils, trash and large particles. The second element is a subgrade chamber and gravel filtration and storage system to be installed beneath the proposed parking lot, in the area now occupied by the existing ponds. The isolator row of the chamber system will act as a clarifier and filter for any remaining fine particulate and associated contaminants, while the chambers store 500,000+ gallons of treated stormwater which will be reused for irrigation. The third element will be the redesign of an existing discharge channel into an engineered bioswale, including a vegetated layer of bioswale soil mix over clean filtration gravel for final polishing. Construction will begin in Fall 2011.