Addressing PCBs and Mercury TMDLs in San Francisco Bay through Urban Runoff Treatment Retrofits – CW4CB Pilot Project Results
The Clean Watersheds for a Clean Bay (CW4CB) project was a collaboration among the Bay Area Stormwater Management Agencies Association (BASMAA) member agencies designed to evaluate the effectiveness of stormwater treatment controls (including green infrastructure controls) for PCBs and mercury, pollutants for which there are Total Maximum Daily Load (TMDLs) for the San Francisco Bay. The primary objective of the urban runoff treatment retrofit pilot projects was to select and implement retrofit of representative urban stormwater treatment controls that could be used to evaluate the potential for achieving mercury and PCBs load reductions through treatment control retrofit across the Bay Area. First term San Francisco Bay Area Municipal Regional Permit (MRP) Provisions C.11.e. and C.12.e required the MRP Permittees to identify and conduct treatment control pilot projects in ten locations during the permit term and to document the knowledge and experience gained to provide a basis for determining the scope of implementation of treatment control retrofits in subsequent permit terms. Each county (San Mateo, Contra Costa, Alameda, Santa Clara, and Solano) was required to have at least one selected pilot project location. The 10 resulting pilot projects were designed, constructed, and monitored as part of the CW4CB project and have been grouped into five treatment categories: bioretention, multiple (including pervious pavement and Silva Cells), media filters, hydrodynamic deflector separation (HDS) units, and vegetated swale.
The 10 pilot projects were built between 2010 and 2016 and 8 of the 10 projects were monitored for varying numbers of storm events between 2012 and 2016. Pilot projects were monitored for volume-based performance and pollution reduction performance. Post-construction monitoring included whole-water, time-composite aqueous BMP influent and/or effluent samples, analyzed for PCB congeners, total mercury, total lead, total organic carbon (TOC), SSC, turbidity, TSS, particle size distribution (PSD), volatile suspended solids, and settleable solids. Monitoring also incorporated field filtering for a subset of sampling events and locations. Samples were passed through a 10 µm filter to remove solids (and adsorbed pollutants) and the field-filtered, time composite aqueous samples were subsequently analyzed for PCBs and total mercury.
Monitoring analytical results were evaluated for pollutant load reduction effectiveness. Event based results were examined, along with results combined by monitoring location. Total PCBs were found to be reduced for all locations except one HDS unit and a single bioretention cell in another project, which is believed to have been constructed incorrectly. Total mercury findings were more mixed but were found to be reduced for approximately half of the studies and were found to be increased in only a single bioretention cell, which is believed to have been constructed incorrectly. Cost effectiveness of the use of treatment control measures to achieve TMDL and MRP required PCBs and mercury load reductions was also examined.
This presentation will describe the urban runoff treatment retrofit study portion of the collaborative regional CW4CB project, including treatment retrofit pilot projects, provide evaluaion results for PCBs and mercury load reductions, cost analyses, and summarize lessons learned to help inform future green infrastructure retrofit planning and implementation.
Kelly Havens, P.E., has eight years of experience in management and technical support of projects focusing on urban, industrial, and construction-phase stormwater management, including stormwater BMP sizing, design, and evaluation, NPDES permit compliance, and development of BMP technical guidance manuals.
Lisa Austin, P.E., has over 25 years of experience in water quality and stormwater management. Ms. Austin has in-depth knowledge of industrial and municipal National Pollutant Discharge Elimination System (NPDES) permitting; municipal stormwater program planning and operations; stormwater best management practice (BMP) selection, design, and maintenance; and construction erosion control.
Brian Currier holds B.S. and M.S. degrees in Environmental Engineering from the University of California, Davis, and is a California-licensed Professional Engineer. Brian has been involved in stormwater research since 1997. He is currently a research engineer with the Office of Water Programs and occasionally teaches for the Department of Civil Engineering at California State University, Sacramento.