klau/buena vista mine

T 26S, R 10E, SEC 33, S1/2 MT DIABLO MER

The Klau/Buena Vista Mine is located in San Luis Obispo County, approximately 12 miles west of Paso Robles, California. The Klau/Buena Vista Mine consists of two abandoned mercury mine sites (Klau and Buena Vista) that are located on adjacent properties on a northwest-southeast ridge of the Santa Lucia Range in the California coastal mountains. Mercury mining and ore processing operations occurred at the Buena Vista Mine and adjacent Klau Mine between 1868 and 1970. Buena Vista Mines, Inc. has owned the Buena Vista Mine at least since 1957 and the Klau Mine since at least 1964. The most significant contaminant of concern is mercury, a metal that can be harmful to the human nervous system. In 1999, the California Central Coast Regional Water Quality Control Board (RWQCB) requested that the EPA Region 9 Emergency Response Office assist in preventing the continued release of mercury-laden sediments and other contaminants from the site. Substantial site stabilization work was conducted. These actions have reduced the discharge of acid mine drainage (AMD) and discharge into Las Tablas Creek, but uncontained contamination remains on the site. The remedial investigation began in 2007. Phase I sampling for the remedial investigation was completed in November 2007. Soil, sediment, surface water and biota were sampled. Phase II sampling of surface water and biota was completed in April 2008. Concurrent with the remedial investigation activities, EPA Emergency Response staff returned to the site in Summer 2008 to address seepage of acid mine drainage from the Buena Vista Mine Tailings repository, fill in a new sinkhole at the Klau Mine portion of the site, and perform general site maintenance.A data summary of the Phase I and II sampling was released in October 2008 and work was begun on both the human health risk assessment and screening level ecological risk assessment. Additional sampling of a second stormwater event and the installation of groundwater monitoring wells was conducted in mid-2009. The final Remedial Investigation Report, which will incorporate the risk assessments, was available in October 2012. The Feasibility Study was completed in January 2014 and as a result of data gaps, a two year bioreactor treatability study is planned and a Feasibility Study addendum will be prepared documenting the results.

Hazardous Ranking Score

50 / 100

A score of 28.5 or higher qualifies a site for the Superfund National Priority List.

Regional Contact

Region 9
Phone: (415) 947-4251

Contact Region



Site Inspection
Preliminary Assessment
Final Listing On NPL

Contaminants & Health Effects

      Endocrine Disrupter
      Reproductive Toxin
      Persistent, bioaccumulative and toxic


        African American
        American Indian and Alaska Native
        Native Hawaiian


        People living
        within a 1 mile radius


        Average Income


        Occupied homes

        Potentially Responsible Parties

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