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San Francisco Bay Mercury TMDL


San Francisco Bay supports beneficial uses, such as sport fishing and habitat for wildlife and endangered species. Fish tissue collected from San Francisco Bay often contains relatively high concentrations of mercury. The California Office of Environmental Health Hazard Assessment has issued fish consumption advisories warning people to limit their consumption of San Francisco Bay fish. In addition, studies have shown that birds consuming fish and other organisms from San Francisco Bay pass mercury to their eggs, potentially contributing to reproductive failures.

The San Francisco Bay Mercury TMDL Project examines this water quality problem and identifies sources of mercury. Sources of mercury include runoff from historic mines, urban runoff, wastewater discharges, atmospheric deposition, and resuspension of historic deposits of mercury-laden sediment already in San Francisco Bay. Most of the historic mercury deposits date back to the Gold Rush of the 1800's, when mercury was mined throughout the Coastal Range and used in the Sierra Nevada to extract gold. The single largest source is the Central Valley, where rivers carry mercury from remote regions of California to San Francisco Bay.
Spinnakers on the Bay

TMDL Approved by USEPA

On February 12, 2008, the U.S. Environmental Protection Agency approved a Basin Plan amendment incorporating a TMDL for mercury in San Francisco Bay and an implementation plan to achieve the TMDL. The TMDL was approved by the State Office of Administrative Law and became effective on November 7, 2007. The Water Board is now implementing the TMDL on the variety of fronts described below.

Regulatory Documents
The San Francisco Bay Mercury TMDL was considered and adopted by the Water Board at hearings in September 2004 and August 2006. Follow the links below to agendas for those hearings, which link in turn to all relevant materials including Water Board resolutions.

September 15, 2004 Water Board hearing, Item 10

TMDL Implementation

The Water Board is engaged in implementing the San Francisco Bay Mercury TMDL, and we will keep you informed about implementation efforts by updating the information below as activities develop.

Watershed Permit - Discharge permit for municipal and industrial wastewater sources of mercury
On November 1, 2007, the Water Board adopted a Watershed Permit (Order No. R2-2007-0077, board hearing materials) for industrial wastewater and municipal wastewater discharges identified in the SF Bay Mercury TMDL implementation plan. This Watershed Permit is an NPDES permit that implements the wasteload allocations for these two source categories. It also implements other provisions of the TMDL requiring pollution prevention, special studies, and risk reduction actions to be conducted by the permittees. The permittees under this permit prepare an annual report of activities and loading information. Click here to get the latest (2011) Watershed Permit report.

According to the recent Watershed Permit report, municipal wastewater discharges to the Bay were well within the mass loading limits prescribed by this Board in its mercury watershed permit. In 2011, the municipal wastewater load was 2.9 kg mercury/year, the lowest loading yet recorded for this source category. The average municipal wastewater load for the past four years has been about 75 percent below its current permit limit of 17 kg mercury/year, and is also well within the final TMDL limit of 11 kg mercury/year, that does not coming into force until 2028. Municipal wastewater dischargers continue to improve their efforts at reducing mercury through source control activities. All but the smallest municipal wastewater dischargers have implemented dental amalgam control and public outreach and education programs. Additionally, municipal wastewater dischargers have continued to collect hazardous waste, fluorescent lights, thermometers, and batteries, which reduce mercury in municipal storm water runoff.

Mercury loadings from industrial wastewater dischargers are considerably lower than municipal wastewater dischargers. In 2011, the industrial wastewater load was calculated from effluent monitoring data as 0.39 kg mercury/year, which is comparable to past years and 70 percent below the final permitted allocation of 1.3 kg mercury/year. For industrial wastewater dischargers, source control projects focus on tracking and replacing mercury-containing equipment such as switches and thermostats.

Another important requirement of the Watershed Permit is that wastewater dischargers undertake a program to reduce public health impacts of exposure to mercury in San Francisco Bay/Delta fish. On March 1, 2010, the Bay Area Clean Water Agencies and the Western States Petroleum Association jointly submitted a proposed risk reduction program implementation plan. The plan focuses on characterizing mercury exposure in high risk populations and providing education about the risks and benefits of consuming local sport fish.

Municipal Regional Permit
The NPDES Municipal Regional Permit is a permit for all NPDES phase I municipal stormwater programs in the Bay Area. This permit implements all mercury-related control measures and wasteload allocations required by the TMDL for stormwater sources. There are two broad categories of mercury-related actions taking place through this permit. First, during the current permit term, there is a variety of mercury control measures being pilot tested to assess their effectiveness in reducing loads of mercury. These include recycling of mercury-containing devices, enhanced sediment removal and management practices for stormwater conveyances, on-site stormwater treatment retrofits, and diversion of dry weather flows and first flush runoff for treatment (e.g. at a wastewater treatment plant). Second, the permittees are developing a comprehensive monitoring program involving a network of fixed stations at the bottom of several key watersheds that will be maintained over time. This monitoring program will generate water quality data that can be used to estimate loads of mercury and other contaminants from local tributaries and stormwater conveyances and track these loads over time. You can learn more about the details of the permit requirements here (mercury requirements are in Section C.11 of the permit), and you can access all reports submitted each year under the municipal regional permit by clicking here.

Water Quality Monitoring
In addition to actions to reduce loads, it is also important to track progress on how the concentrations in the Bay and its biota (e.g. fish and birds) are changing over time. The following are the primary in-situ monitoring efforts for mercury in San Francisco Bay. The Regional Monitoring Program (RMP) measures mercury (and many other contaminants) in water, sediment, and fish tissue collected at several locations around the Bay each year. You can view and download these data for yourself using their versatile web query tool.

The RMP has been monitoring contaminants in prey fish (small fish consumed by birds or larger fish) for several years because these small prey fish provide useful information on the spatial and temporal patterns of contamination in the Bay because they tend not to move around as much as large fish. Moreover, these prey fish are consumed by many birds and larger fish so can provide an early warning for contamination higher in the food web (e.g. for larger predators like fish and birds). A summary report on the results of the monitoring program for small fish provides data and interpretation from monitoring efforts. Since 1994, the RMP has also been monitoring the concentrations of mercury and other contaminants in sport fish. A recent report comparing the concentrations of contaminants in sport fish caught in the Bay to those in caught offshore is also available. The figure below shows how mercury concentrations in sport fish change through time in different parts of the Bay and how these concentrations compare to the 0.2 parts per million fish tissue target from the TMDL.

Piscivorous birds (birds that consume fish) are among the organisms in the Bay that are most sensitive to mercury contamination. Scientists at the United States Geological Survey have been investigating how mercury can affect birds, particularly in the South Bay, and they describe their research and provide results at this website.

Inspection Report for Mercury Mines
This report presents an inventory of mercury mines and an evaluation of their potential to discharge mercury-polluted stormwater, as required by the San Francisco Bay mercury Total Maximum Daily Load (TMDL). We conclude that three sites present a high threat to impair water quality because of visual evidence of eroding mining wastes. One of these sites, the La Joya mine in Napa County, is already being addressed. The mine tailings have been safely excavated and landfilled on-site (see photos below). Water Board staff will now turn attention to the other two high priority sites - Bella Oaks mine in Napa County and the St. John's mine in Solano County.

Photos show the La Joya mercury mine tailings pile before (left) and after (right) the construction and remediation project to stabilize the material and prevent erosion and transport.

There are a lot of implementation activities in the Guadalupe River watershed addressing the legacy of mercury mining impacts..

Bay Area Petroleum Refineries - Fate of Crude Oil Mercury
The mercury TMDL implementation plan identified an information gap associated with Bay Area petroleum refineries. The information gap was an apparent mismatch between the potentially large amount of mercury entering the refineries in crude oil and the much smaller quantity of mercury that could be accounted for leaving refineries in various product and waste streams. In 2007, the Executive Officer of the Water Board formally ordered (download the Water Board's 13267 order to the refineries) the petroleum refineries to submit technical reports to address this information gap, and the final report for the study was received in June 2009 (click here to download final report, 5.2MB).

The study results suggest that about 220 kg/yr of mercury enters petroleum refineries in crude oil.  This amount, based on actual measurements of mercury in crude oil, is much less than the amount estimated by staff using literature values for mercury concentration in crude oil. The mass balance also suggests that the vast majority of this mercury leaves the refineries in solid waste that is transferred to off-site solid waste disposal facilities. Less than 10% of the input mercury is emitted directly to the air from stacks, and roughly 10% of the mercury leaves the petroleum refineries in various products like automobile fuel and fuel oil. Small amounts were also contained in petroleum coke (1%) and wastewater (< 1%).

Other Documents


U.S. Environmental Protection Agency

U.S. Geological Survey


For more information contact:

Carrie Austin
San Francisco Bay Regional Water Quality Control Board
1515 Clay Street, Suite 1400
Oakland, CA 94612
Phone: 510-622-1015
Fax: 510-622-2460

Richard Looker
Water Resource Control Engineer
San Francisco Bay Regional Water Quality Control Board
1515 Clay Street, Suite 1400
Oakland, CA 94612
Phone: 510-622-2451
Fax: 510-622-2460