Contra Costa County's portion of the urban stormwater wasteload allocation in the San Francisco Bay PCBs Total Maximum Daily Load (TMDL) is 0.3 kilograms per year (kg/yr), which represents a 90% reduction from the TMDL's assumed 2003 baseline PCBs load.
Provisions C.11 and C.12 of the San Francisco Bay Municipal Regional Stormwater Permit (MRP) require that the Permittees prepare Reasonable Assurance Analyses (RAAs) to, among other objectives, quantitatively demonstrate that PCBs reductions of at least 0.5 kg/yr will be realized within Contra Costa County by 2040 through implementation of green infrastructure (GI) projects.
Contra Costa County's RAA reassesses the baseline PCBs load and estimates current and projected PCBs load reductions through existing, planned, and projected public and private (i.e., new development and redevelopment) GI projects. Public GI includes both regulated public projects as well as voluntary GI retrofit projects, which were incorporated into GI Plans prepared by the Permittees per MRP Provision C.3. The preliminary results of the RAA indicate that the Contra Costa County Permittees would collectively need to reduce an additional 56 grams of PCBs through GI to meet the MRP-required load reductions through GI by 2040.
For comparison, the total PCBs loads reduced through public and private GI projects countywide from 2003 – 2020 is approximately 118 g/yr (or about 7 g/yr on average). A complicating factor in the implementation of GI to achieve PCBs load reductions is that PCBs load (and therefore, potential load reduction) varies greatly depending on land use type, with "Old Industrial" (i.e., pre-1980s industrial) land uses having the greatest PCBs loads in stormwater runoff.
In this light, the Contra Costa Countywide Clean Water Program (CCCWP) has been investigating more efficient ways to implement GI to achieve the MRP-stipulated load reduction goal. Some Contra Costa County communities without opportunities to reduce PCBs via GI might potentially fund GI projects in communities that do have such opportunities, including the potential for "trading" of PCBs load reduction credit achieved through implementation of GI in more polluted areas. The Permittees would continue to consider how to balance the goals of efficient PCBs load reduction via GI (which has been demonstrated to be highly location-specific, and not obtainable by all Permittees) versus other GI multiple benefits (e.g., urban greening, other urban runoff pollutant removal, flood control, groundwater recharge, habitat enhancement, etc.).
Because resources are limited, there will ultimately be trade-offs between the goals of PCBs load reduction via GI versus the other benefits of GI. In the majority of Contra Costa communities, which have few or no locations where PCBs loads could be efficiently reduced via GI, the pursuit of a potential Countywide Attainment Strategy would require trade-offs, including minimizing the opportunities to build community engagement and local support for GI. A similar trade-off exists within the communities that do have locations where PCBs loads could be efficiently reduced via GI, as the highest-ranked load-reduction locations rarely coincide with locations where other benefits to the community would be maximized.
This presentation will provide background on status of planning for PCBs TMDL compliance using GI and will discuss the compliance approach that Contra Costa Permittees have incorporated in their GI Plans and the Countywide Attainment scenario.
- Geosyntec Authors: Lisa Austin
- All Authors: Lisa Austin, Amanda Booth
- Title: 2019 CASQA Annual Conference
- Event or Publication: Event
- Practice Areas: Urban Stormwater Management Planning and Design
- Citation: Geosyntec will make substantial technical contributions at the California Stormwater Quality Association (CASQA) Annual Conference at the Monterey Conference Center in Monterey, California on October 7-9, 2019.
- Date: October 7-9, 2019.
- Location: Monterey, California
- Publication Type: Platform Presentation