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Lava Cap Mine

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Site Description

The Lava Cap Mine Superfund site is located in the Sierra Nevada foothills of California approximately 6 miles east of the town of Grass Valley. From 1860-1918, and from 1934 -1943, Lava Cap mine was an active hardrock gold and silver mine. During peak operation the mine processed between 300-400 tons of ore per day. Waste tailings were dumped in the Little Clipper Creek drainage and, over time, a portion of the tailings migrated downstream to Lost Lake, located approximately 1.5 miles downstream. The mine tailings have a high concentration (up to 31,200 parts per million) of arsenic, a known human carcinogen. Surface water emerging from the historic mine entrance exceeds the Maximum Contaminant Level (MCL) for arsenic set under the Safe Drinking Water Act. Surface water drainage enters Little Clipper Creek and eventually discharges into Rollins Reservoir, which is a drinking water source. Elevated levels of arsenic have also been found in shallow groundwater below the tailings at the Site. Local residents use individual water supply wells for their drinking water.

Current Site Status and Cleanup Actions to Date

  • EPA has identified a total of four operable units at the Site: Operable Unit 1 (OU1) (Mine Area); OU2 (Groundwater); OU3 (Lost Lake); and OU4 (Mine Residences). The OUs were designated to phase the work such that cleanup actions can proceed in a sequence that best protects human health and the environment, specifically by quickly controlling contamination at the source and addressing residential exposure pathways.
  • In October 1997, having determined that the failure of a log dam holding back mine tailings at the Site posed a threat to human health and the environment, EPA removed 4,000 cubic yards of tailings from upstream of the dam and reinforced the dam as a temporary measure with large diameter rock.
  • The Site was listed on the National Priorities List (NPL) in February 1999 following EPA's determination that further actions were required to protect human health and the environment.
  • In April 2003, EPA initiated a second time-critical removal action to relocate the occupants of two homes, including one with school-aged children, because it was determined that high levels of arsenic in mine tailings adjacent to the homes posed imminent risks to human health. At the same time, EPA installed water filtration units on three homes whose water supplies, drawn from individual wells, exceeded the MCL for arsenic set under the Safe Drinking Water Act.
  • EPA previously identified the Lost Lake Operable Unit (OU3) in 2003 to allow for extended study of cleanup options at this part of the Site. This was necessary due to the complexities associated with existing land use. At OU3, mine tailings have been deposited downstream of the mine on recreational/residential parcels held by multiple landowners.
  • EPA initiated an investigation of potential site-related groundwater contamination in September 2003. This investigation is ongoing under the Groundwater Operable Unit (OU2).
  • In September 2004, EPA issued the Record of Decision (ROD) for the Mine Area Operable Unit (OU1).
  • Cleanup at the Mine Area OU began in September 2005. To accelerate the cleanup, EPA split off the Mine Residences Operable Unit (OU4) from OU1. This enabled completion of this portion of the design in time for EPA to move forward with the excavation of contaminated soil (PDF) (530 K, 2 pp) from around one additional home (which was not included in the 2003 time-critical removal action detailed above) before winter 2005 (the end of the construction season). The cleanup of mine tailings at OU1 is scheduled for completion by the end of September 2006.

Current Funding Status

  • To date, EPA has spent approximately $5,662,000 for investigation work, design, and time-critical removal actions at this site.
  • To date, EPA has allocated $4,895,000 toward cleanup of the Mine Area and Mine Residences OUs.
  • EPA estimates that an additional $1,345,000 will be required in 2006 to complete the tailings cleanup at the Mine Area and Mine Residences OUs.
  • EPA projects that an additional $1,700,000 will be required in 2007 to undertake surface water cleanup at the Mine Area OU.

For more information on the projects at this site, please read the Lava Cap Mine Fact Sheet on the Region 9 Superfund Web site.

Key Accomplishments

  • To date, EPA has spent approximately $5,662,000 for investigation work, design, and time-critical removal actions at this site.
  • In September 2004, EPA issued the ROD for the Mine Area Operable Unit (OU1).
  • Design of the cleanup for the Mine Area and Mine Residences OUs began in 2005, and cleanup work started in September 2005.

 

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