Marall Chrome Mine PA/SI Presented by Rick Weaver, Hydrologist - PowerPoint PPT Presentation

US Forest Service Pacific Southwest Region Tahoe National Forest Marall Chrome Mine PA/SI Presented by Rick Weaver, Hydrologist U.S. Forest Service

Marall Chrome Mine • The Site is a former open pit chromium mine. • Located in Foresthill off-highway vehicle (OHV) Area within the American River Ranger District, part of Tahoe National Forest. • The Site consists of a large open mine pit and tailing pile. • The area surrounding the mine contains serpentine rock outcrops and naturally-occurring asbestos (NOA) in the form of chrysotile has been detected in samples in mine pit and surrounding area. • The Site is located in an active OHV recreation area with trails used for ATVs and dirt bikes. • The Site is also used for target shooting and camping.

Marall Chrome Roads and Trails

Marall Chrome Mine Pit and Tailings

East Mine Pit Wall, Facing Southeast

Site Use Pagge Creek & Marall Rd

Evidence of Camping

Sierra Fund “Gold Country Recreational Trails and Abandoned Mines Assessment”, June 2010 • Study conducted to assess whether recreational visitors may be exposed to hazardous substances at abandoned mine sites. • In conducting the study the Sierra Fund identified trails and sites of concern for which they deemed sampling was warranted to assess whether elevated levels of hazardous substances were present. • The Marall Chrome Mine was identified as having potential public health issues as a result of the presence of elevated concentrations of chromium, lead and chrysotile asbestos in the soils in the mine pit and surrounding area.

Sierra Fund “Gold Country Recreational Trails and Abandoned Mines Assessment” Marall Chrome Mine & Loop Trails and Staging Areas Sample Results • Lead (max. 4,790 mg/kg) at Marall Chrome Mine Pit • Chrysotile asbestos (max. 40%) at Marall Chrome Mine Pit and Loop 4 Trail

Forest Service Investigation • Initiated a response action pursuant to its authorities under the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA). • In fiscal year 2011, the agency contracted with Tetra Tech EMI, Inc. to conduct a CERCLA preliminary assessment/site inspection(PA/SI) for the Marall Chrome Mine. • Purpose of which was to:  Define the nature and extent of any contamination that may be present,  Whether any contaminants that may be present pose a threat to human health and the environment, and  Whether a response action under CERCLA is warranted to mitigate these threats.

Preliminary Assessment /Site Inspection Tetra Tech collected soil, tailings, sediment, and surface water samples to identify: • Potential areas of contamination, • Evaluate whether a release of hazardous substances to the environment has occurred, • Assess potential risk to human and ecological receptors, and • Assess potential threats to water quality.

Marall Chrome: Roads and Trails Sample Results • Chrysotile asbestos was detected in 4 of 5 road and trail samples with concentrations ranging from 0.5% to 3.3% and background reported at 4.8%. • No elevated concentrations of metals were detected along the trails and roads.

Marall Chrome: Mine Pit and Tailings Sample Results • Chrysotile asbestos detected in all 5 mine pit samples with the concentrations ranging from 0.75% to 2.0%. • Lead was detected in 5 of 6 mine pit and tailings pile sample locations at concentrations ranging from 386 ppm to 32,400 ppm. • Arsenic detected in all 5 mine pit and tailings pile sample locations with the concentrations ranging from 4.7 ppm to 171 ppm. • Copper detected in all 5 mine pit and tailings pile sample locations with the concentrations ranging from 25.6 ppm to 259 ppm.

Marall Chrome: Mine Pit and Tailings Sample Results • The extensive use of the tailings pile and east pit wall as target shooting backstops has led to the accumulation of lead in soil. • Some of the lead contamination on site is associated with the use of the mine pit area as a target shooting range, other elevated lead concentrations are a result of the naturally- occurring lead within the exposed ore body.

Marall Chrome: Pagge Creek Sample Results • Cobalt, copper, lead, and nickel were detected in sediment samples downstream from mine pit at concentrations slightly exceeding upstream background concentrations.

Marall Chrome: Next Steps CERCLA Engineering Evaluation/Cost Analysis (EE/CA) • Further define nature and extent of elevated concentrations of metals and naturally occurring asbestos. • Human health risk assessment to assess the exposure hazard to recreational visitors. • CERCLA remedy assessment and evaluation. Potential response options include, but are not limited to: – Site cleanup and lead recovery from the shooting areas. – Capping – Site access restrictions

Dispersed Camping

Marall Chrome: Naturally Occurring Asbestos • NOA that is not disturbed or deteriorated poses little, if any, health risk • When asbestos containing rocks are crushed or broken through weathering and ground disturbing activities such as vehicle travel on and maintenance of roads located in NOA areas, asbestos-containing dust can be generated. • Once in the air, asbestos fibers can be inhaled and can pose a potential human health risk. • Studies have found that there is no direct correlation between the asbestos concentrations present in the soils and the levels detected in the air. • As a result there is no health based screening threshold for soils that can be used to determine areas of concern for NOA.

Serpentine Outcrops and OHV Trails

Marall Chrome: Naturally Occurring Asbestos • In order to assess actual exposure EPA has determined that site specific activity-based sampling (ABS) is required assess the actual exposure risk. • ABS is conducted to assess asbestos exposure resulting from different types of ground disturbing activities. For example: – ATV riding – Driving – Hiking – Camping • ABS will be conducted as part of the EE/CA

Tailings Pile in Mine Pit

ABS Sampling Locations

Conceptual Site Model

Naturally Occurring Asbestos • The presence of NOA is not just limited to the Marrall Chrome Mine. • NOA is commonly, but not exclusively, found in areas with serpentine and ultramafic rock formations, and is abundant in the Sierra foothills, the Klamath Mountains, and Coast Ranges. • NOA has been identified in 50 out of 58 counties in the State.

Map Showing Ultramafic/ Serpentine Formations (Red) and potential asbestos deposits on the Tahoe National Forest

Tremolite & Chrysotile on the San Bernardino

To address the wide spread presence of NOA throughout the state, the Forest Servcie prepared a public awareness fact sheet that provides: • General information on NOA and its presence on NFS lands. • Guidance on how forest visitors can reduce their potential exposure to the substance.

NOA Regional Public Awareness/Notification Direction • Each Forest with serpentine/ultramafic formations and/or areas with NOA are to have this fact sheet available for forest visitors at the forest supervisor’s office and each district office. • Copies of the respective forest/district asbestos maps that the RO has been preparing are to be made available for visitors. • Overall intent of this effort is to make the visiting public aware of the potential or actual presence of NOA on NFS lands and provide them with sufficient information as to the potential health risks as they are presently known so that they can make informed decisions.

Marall Chrome Mine PA/SI Questions/Comments??