North San Francisco Bay Selenium TMDL

The North San Francisco Bay Selenium TMDL is now fully approved and effective.


The North San Francisco Bay was identified as impaired by selenium in the 1990s because selenium concentrations in North Bay biota exceeded thresholds leading to bioaccumulation in fish and wildlife. Selenium is an essential micronutrient, which in higher quantities could cause reproductive impairment. In aquatic environment selenium exhibits a complex mode of toxicity. Dietary uptake of particulate selenium is the most important exposure pathway for aquatic organisms, especially predators, and some types of food webs bioaccumulate selenium more efficiently than others. In the North Bay selenium bioaccumulation has been detected only in clam–eating bottom feeders, such as white sturgeon and Sacramento splittail. Sturgeon feeds predominantly on benthic organisms, including introduced clams (i.e. Potamocorbula amurensis) that are very efficient selenium bioaccumulators, which makes this fish susceptible to selenium toxicity. large sturgeon caught in San Francisco Bay

North Bay is currently attaining the tissue targets protective of sturgeon. For this reason, the TMDL is based on existing loads and does not call for load reductions. To ensure continued protection of beneficial uses, the TMDL imposes a cap on selenium loads to prevent load increases from the in-Bay sources and from the Delta and upstream. The TMDL Implementation Plan requires effluent limits for petroleum refineries, which are the largest controllable source of selenium in North Bay, and extensive monitoring. The Regional Monitoring Program will continue to measure selenium concentrations in fish, clams and water column to make sure that selenium levels remain low, and do not pose a risk to threatened fish and wildlife.

TMDL Approval Process

  • U.S. EPA approval - August 23, 2016
  • California Office of Administrative Law approval of regulatory action - June 2, 2016
  • State Water Board approval - March 15, 2016
  • Adoption of the TMDL and the Basin Plan amendment by the San Francisco Bay Regional Water Quality Control Board - November 18, 2015

    For more information contact:
    Barbara Baginska
    Engineering Geologist
    San Francisco Bay Regional Water Quality Control Board
    1515 Clay Street, Suite 1400
    Oakland, CA 94612
    Phone: 510-622-2474
    Fax: 510-622-2460