Permeable Reactive Barrier at East Helena site, East Helena, Montana

Site Name:

East Helena

Location:

East Helena, Montana

Period of
Operation:

Spring 2005 to Ongoing

Cleanup
Type:

Pilot Scale

Technology:
Zero-Valent Iron Permeable Reactive Barrier
-- The permeable reactive barrier (PRB) consists of a trench 30 feet long, 46 feet deep and 6 feet wide, with 175 tons of zero-valent iron (ZVI) placed in the trench.
-- The ZVI PRB system was installed 600 feet downgradient of the source area, perpendicular to the flow of contaminated groundwater.

Cleanup Authority:
CERCLA

Contacts:
Remedial Project Manager:
Linda Jacobson
U.S. Environmental Protection Agency Region VIII
Phone: (303) 312-6503
Email: Jacobson.linda@epa.gov

Project Manager:
Rick Wilkin
U.S. Environmental Protection Agency
National Risk Management Research Laboratory
Office of Research and Development
Phone: (580) 436-8874
Email: wilkin.rick@epa.gov

Contaminants:
Groundwater:
-- Heavy Metals: Arsenic (As) (20 milligrams per Liter [mg/L])

Waste Source:
Process ponds contaminated due to lead smelting operations.

Type/Quantity of Media Treated:
The ZVI PRB system is treating an arsenic contaminated groundwater plume that is 450 feet wide and extends 2,100 feet downgradient from the process ponds.

Purpose/Significance of Application:
To remediate arsenic contaminated groundwater.

Regulatory Requirements/Cleanup Goals:
The maximum contaminant level (MCL) for arsenic is 0.010 mg/L.

Results:
Initial, post-installation monitoring evaluations indicated that arsenic concentrations in the groundwater had been reduced from 20 mg/L (highest concentration) to below 0.010 mg/L. Due to the limited evaluation of the system it has not been determined if the treatment has been successful. A two year evaluation to determine if the system should be implemented at a full scale will be completed in 2007.

Cost Factors:
The ZVI PRB system cost approximately $325,000 to construct. There are no additional operation and maintenance cost associated with this system.

Description:
The East Helena site is located in East Helena, Montana. The site was added to the National Priorities List (NPL) in 1984. The site was a lead smelting facility that operated from the late 1880s to 2001. Smelting operations over a period of a hundred years have lead to heavy metal contamination of soil, surface water, and groundwater at the site.

Groundwater at the site had become contaminated with arsenic due to leaching from the contaminated process ponds located over the shallow groundwater. The arsenic plume is approximately 450 feet wide and extended 2,100 feet downgradient from the process ponds. The ZVI PRB was installed as a pilot project in spring of 2005.

The ZVI PRB includes a 30 foot long trench that is 46 feet deep and 6 feet wide. The trench is filled with 175 tons of ZVI and coarse sand. The system was constructed approximately 600 feet downgradient from the process ponds, perpendicular to the flow of the arsenic contaminated groundwater plume.

The construction of the system cost approximately $325,000. There are no operation and maintenance cost associated with this system.

The first round of post-implementation groundwater data was collected in June 2005. Based on this data, arsenic concentrations in treated groundwater had been reduced from 20 mg/L to below 0.010 mg/L. The system is currently in the process of a two year evaluation to determine if the system should be implemented in full scale.