Abandoned Mine Lands
Description:
The historic Poison Lake mill tailings site is located on the north side of Comanche Reservoir and west of Buena Vista Road. The mill tailings were transported by pipeline to the Poison Lake site from the Penn Mine complex during the period that it actively mined for copper 1880?s -1942. The historic Penn Mine Mill processed the ore, extracted the copper and disposed of mine tailing wastes at this site and an adjacent downstream site in proximity to Lake Comanche. Approximately 200,000 tons of mill tailings originally were deposited at Poison Lake. The tailings dam was breached in the early 1960?s, allowing approximately 150,000 tons of tailings to discharge into the Mokelumne River watershed. Roughly 50,000 tons still exist on BLM administered land.
The Poison Lake mill tailings and waste rock has been discovered recently to contain highly elevated levels of arsenic and zinc. These tailings have discharged from the tailings dams over the last 45-year period into Lake Comanche.
Potential human health risks and regional environmental impacts may have resulted from release of arsenic and zinc-bearing tailings into the waters of the state and airborne sources. Downstream adverse impacts to biota, including sport fish, may also need to be addressed. This area has now been designated as an AML CERCLA site. Sample results from water, sediment indicate elevated arsenic and zinc level exist in the mill tailings sediments. A CERCLA non-time-critical remediation process has been implemented.
A RSI (Removal Site Investigation) document has been compiled by June, 2006. Compilation of a focused EE/CA (Engineering Evaluation/Cost Analysis) document will be contracted during 2007. Remediation options will be listed in the EE/CA. Identification and coordination of identified Responsible Parties (RP) will be required to effectively remediate and stop continued migration of arsenic and zinc-bearing tailings downstream onto downstream watershed areas.
Benefits:
Proposed improvement of human health by reduction of dermal and airborne exposure to arsenic by undertaking proposed remediation of arsenic-bearing mill and mine tailings. In-place capping or removal of arsenic-zinc contaminated sediments within active stream channel/100-year floodplain will change its present status as a pollution "nonpoint source" under the Clean Water act and prevent downstream discharge into the Mokelumne watershed. The California State Water Control Board and other regulatory agencies require that BLM mandate significant reductions in arsenic and zinc loads from its managed lands within California.
Feasibility:
This site of BLM's high priority AML 1010 sites for pilot cleanup. During FY2005 technical specialists collected water and sediment samples at the site. During FY2006 BLM specialists and BLM contractors will undertake compilation of RSI and CERCLA documentation. Specifically, emergency remediation and removal actions will be undertaken which focus on human health risk protection and mitigation of environmental impacts associated with the arsenic and zinc-bearing tailings.
Support:
There is widespread support from interagency Federal partners (USFWS, EPA), State Partners (DOC AMLU/OMR, DTSC, CWQCB, RWQCB, CA Fish&Game, CA Dept. Public Health), County Partners (Dept. Envtl Health) and various watershed stakeholders.
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