EPA Superfund Site

KLAU/BUENA VISTA MINE

CA | EPA ID CA1141190578

About this site’s exposure pathways: As of December 2024, the Klau/Buena Vista Mine Superfund site is currently considered Human Exposure Not Under Control. The site consists of three operable units (OUs): OU 1) the 320 acre mercury mine site property; OU 2) seven miles of Las Tablas Creek downstream from the mine, which includes a man-made reservoir of 7 acres with a 15 foot depth; and OU 3) which is Lake Nacimiento reservoir at the end of Las Tablas Creek, which covers 1,800 acres, is 14 miles long and up to 180 feet deep, and is used for irrigation and drinking water. This mercury mine has released large amounts of mercury to on-site soils and surface water bodies. Site-related contaminants have accumulated in downstream lake sediments, resulting in elevated levels of methylmercury in the tissues of the fish in Lake Nacimiento. The current complete human exposure pathway is ingestion of methyl mercury contaminated fish tissue. This exposure pathway is considered unacceptable based on EPA risk-based criteria because methylmercury concentrations in fish tissue far exceed safe consumption limits.

Currently, the planned activities to address this pathway include the EPA restricting access (e.g., fencing) to contaminants at OU 1. Access to OU 2 is similarly limited because these lands are privately owned. The State of California has issued fish consumption advisories for methyl mercury in fish tissue in Lake Nacimiento in 1994 and 2007. This advisory remains in place; however, Lake Nacimiento is a popular location for recreational fishing. Signage regarding the fish consumption advisory has been posted around Lake Nacimiento, as well as around all the smaller water bodies impacted by site-contamination between the mine site and Lake Nacimiento. A Human Health Risk Assessment was completed for OU 3 - Lake Nacimiento in 2018. Targeted outreach to Environmental Justice communities was implemented in 2014 and in 2018 additional resources were committed to renew community involvement work to target this exposure pathway. To prevent risks inherent at this site, do not trespass areas disturbed by mining and follow guidelines on fish consumption. EPA currently anticipates that human exposure will be under control by 2040 because remedial action is expected to address source control at the mine site by that time.