By Stephen McCord

Mercury is an odd element: It is liquid under normal conditions, it forms amalgams with many other metals such as gold and silver, and it is more than 13 times denser than water.

In natural waters, mercury is a concern because of the potential toxic effects of one form, methylmercury, to humans and wildlife. Methylmercury forms as a byproduct of certain bacteria metabolizing mercury under conditions such as those found in wetlands. Its toxicity is difficult to comprehend — one standard thermometer’s volume worth of methylmercury is enough to pollute more than 3,000 Olympic-size swimming pools worth of water.

Exposure to methylmercury comes largely from eating fish that have accumulated it through their diet. Methylmercury is linked to developmental problems in fetuses and children, and affects the nervous system in adults. Similar affects are observed in wildlife.

Today, mercury is the most common cause of contaminated water bodies in the Cache Creek and Putah Creek watersheds, which drain from the Inner Coast Range eastward from Colusa, Lake and Napa counties into Yolo and Solano counties.

The state’s Office of Environmental Health Hazard Assessment has issued several fish consumption warnings (oehha.ca.gov/node/412). A recent U.S. Geological Survey study of mercury concentrations in grebes (a common fish-eating bird) at 25 lakes statewide found the highest levels at Lake Berryessa.

The Inner Coast Range is a complex mixture of rock types: sedimentary, volcanic and the delicate green- and black-flecked serpentine, the California state rock. Areas rich in serpentine tend to contain relatively high concentrations of mercury. These bare surface soils naturally erode into local creeks, and mineral springs discharge waters rich in mercury. Even more broadly, reactive mercury in global emissions of oil and coal contaminate even pristine watersheds worldwide.

There have been three eras of mercury mining in these watersheds: the Gold Rush (second half of the 19th century), two world wars (first half of the 20th century) and the Industrial Revolution (1950s to early 1970s). Mercury mining activity fluctuated with economic demand due to developments in gold mining in the Sierra Nevada and Nevada Comstock Lode, medicine, explosives, gasoline additives and atomic-energy research. We are left with the legacy of about 80 abandoned mercury mines in the upper Cache Creek and Putah Creek watersheds, and many thousands of other abandoned mines statewide.

The vast majority of this mining predated two important developments: major water projects damming and diverting large proportions of the runoff from the two watersheds, and modern environmental laws such as the Clean Water Act. Consequently, enterprising miners simply dumped their contaminated waste downhill to be swept away in the next storm, and that contaminated material still blankets floodplains and the San Francisco Bay and delta.

A key challenge to cleaning up mine sites is often, ironically, environmental laws. Common concerns for any organization interested in improving a site include: 1) “Touch it and you own it,” meaning you are liable for ongoing contamination from a site even if all you did there was try to fix the problem; and 2) “Perfect is the enemy of good,” meaning the law doesn’t easily allow only inexpensive improvements if standards are still being exceeded.

It can take years (and too much budget) to complete an adequate environmental assessment and obtain the necessary federal, state and local permits for cleaning up a mine site. Nonetheless, several organizations are taking on the challenge.

The Delta Tributaries Mercury Council (sacriver.org/aboutwatershed/mercury/dtmc), which morphed from a Cache Creek stakeholders group in 1995, is guided by its 2002 Strategic Plan to reduce the risk of mercury within the larger Sacramento River watershed. The council hosts quarterly meetings that are announced to its nearly 500 members.

The federal Brownfields program provides liability protection, funds, and technical assistance (not enforcement) to assess and clean up contaminated sites (including “mine-scarred” lands). Water managers representing four of the counties encompassing the Cache and Putah creeks watersheds recently formed a coalition to assess the mercury mines in the region as brownfields in order to improve them (westsideirwmbrownfields.org).

The local nonprofit Tuleyome is a regional leader in cleaning up abandoned mercury mine sites (tuleyome.org/projects/mercury-mine-remediation-program). Tuleyome is implementing a three-year, $2.4 million grant from the California Department of Fish and Wildlife’s Ecosystem Restoration Program to clean up the Corona and Twin Peaks mercury mines in northwest Napa County, which drain into Lake Berryessa.

— Stephen McCord is president of McCord Environmental, based in Davis. As a registered professional engineer, he has more than 25 years of consulting, research and teaching experience in the environmental engineering field throughout the United States and internationally. Tuleyome is a 501(c)(3) nonprofit conservation organization based in Woodland; the Tuleyome Tales column is published monthly. For more information, visit www.tuleyome.org