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

Marall Chrome Mine PA/SI

Presented by

Rick Weaver, Hydrologist U.S. Forest Service

US Forest Service Pacific Southwest Region Tahoe National Forest

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
• utcrops 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

• 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.

Forest Service Investigation

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.

• 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%.

Marall Chrome: Roads and Trails Sample Results

• 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-

• ccurring lead within

the exposed ore body.

• Cobalt, copper, lead, and

nickel were detected in sediment samples downstream from mine pit at concentrations slightly exceeding upstream background concentrations.

Marall Chrome: Pagge Creek Sample Results

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

Marall Chrome: Next Steps

Dispersed Camping

• 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.

Marall Chrome: Naturally Occurring Asbestos

Serpentine Outcrops and OHV Trails

• 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

Marall Chrome: Naturally Occurring Asbestos

Tailings Pile in Mine Pit

ABS Sampling Locations

Conceptual Site Model

• 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.

Naturally Occurring Asbestos

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
• f 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.

Questions/Comments??

Marall Chrome Mine PA/SI