Guadalupe River Watershed Mercury TMDL

Background:

The Guadalupe River Watershed supports many beneficial uses, such as drinking water supply, sport fishing, and habitat for wildlife and endangered species. Santa Clara County has issued a fish consumption advisory for mercury contamination. Mercury concentrations in fish tissue that exceed the U.S. EPA human health mercury fish criterion (0.3 mg/kg), have been measured at numerous creeks and reservoirs in the Guadalupe River Watershed. Elevated mercury concentrations in fish tissue may also pose a threat to wildlife, such as birds, amphibians, and mammals. The Guadalupe River Watershed Mercury TMDL examined this water quality problem and provided a watershed-wide mercury management strategy. The main source of mercury in the Watershed is the New Almaden Mining District, the largest-producing mercury mine in North America. Other sources include atmospheric deposition from global and local sources, soil erosion from areas not known to contain mines, urban stormwater runoff, seepage from landfills, and Central Valley Project water inputs to Calero Reservoir. In addition to being the primary regulatory means of achieving water quality goals in the watershed, the Guadalupe River Watershed Mercury TMDL will simultaneously reduce the amount of mercury in the Bay in accordance with the San Francisco Bay Mercury TMDL's proposed requirements.

June 2012 MDL Implementation Update

You can read our third annual TMDL update report to our Board here.

Mercury mine sites: As planned, we started implementation at the top of the watershed by requiring mine site owners to evaluate and report on the potential for mining waste to erode from their properties. We reviewed these reports and determined the appropriate next steps, as follows:
 

The Santa Clara Valley Water District continued its voluntary methylmercury production and control studies, which it initiated in 2005. Solar-powered circulators were effective in suppressing methylmercury production at Lake Almaden, but not in the Almaden or Guadalupe reservoirs. Therefore, the District plans to install oxygenation systems in the two reservoirs. More information is available in their December 2011 biennial report.
 
The four entities discussed above have established a coordinated monitoring program, led by Santa Clara County Parks. Monitoring data gathered thus far is inconclusive regarding changes in mercury concentrations. A cursory analysis of prey fish monitoring data shows that fish mercury concentrations were lower in reservoirs in 2011, as compared to 2004 (see comparison plot), but higher in Lake Almaden and creek sites (see comparison plot). More prey fish monitoring is planned for 2012, partly to evaluate inter-annual variation in fish tissue mercury concentrations. More information is available in the January 2012 annual data report.

U.S. EPA gives final approval to TMDL and Water Quality Objectives for Mercury in the Guadalupe River Watershed
On June 1, 2010, the U.S. Environmental Protection Agency approved the Basin Plan amendment adopted by the Regional Water Board in October 2008. These actions establish New Water Quality Objectives and Total Maximum Daily Loads (TMDLs) and an Implementation Plan for mercury in waters of the Guadalupe River Watershed. The amendment is now part of the Water Quality Control Plan for the San Francisco Bay Basin (Basin Plan), the master planning document for water quality in the Bay Area.

Previously, the State Office of Administrative Law (OAL) approved the amendment on February 24, 2010, the State Water Board approved the amendment on November 17, 2009, and the Regional Water Board adopted the amendment on October 8, 2008.

• U.S. EPA Approval of TMDL (pdf)
• U.S. EPA Approval of Water Quality Objectives (pdf)
• OAL Approval Action (pdf)
• State Water Board Approval, see item no. 7: Resolution No. 2009-0082
• Regional Water Board Adoption: Resolution R2-2008-0089
• Adopted Basin Plan Amendment (pdf)
• Final Staff Report (pdf, 7.5MB)
  • Oversized Figures (tabloid size; also included in Staff Report (pdf, 1.3MB)