Field Application of a Permeable Reactive Barrier for Treatment of Arsenic in Ground Water

Site Name:

ASARCO East Helena Plant

Location:

East Helena, Montana

Period of
Operation:

July 2005 — August 2007 (2 years)

Cleanup
Type:

Pilot Scale

Technology:
Permeable Reactive Barriers (PRBs)

  • The PRB consists of granular zerovalent iron that runs 9.1 meter (m) long (perpendicular to groundwater flow), 13.7 m deep, and 1.8 to 2.4 m wide (parallel to groundwater flow).
  • The PRB was installed over 3 days using bio-polymer slurry methods and excavation equipment.

Cleanup Authority:
EPA

Contacts:

Scott Brown
Superfund Remedial Project Manager
U.S. EPA Region 8, Montana Office
Federal Building
10 West 15th Street, Suite 3200
Helena, Montana 59626
Phone: 406-457-5035
brown.scott@epa.gov

Linda Jacobson
RCRA Project Manager
U.S. EPA Region 8
1595 Wynkoop St.
Denver, Colorado 80202-1129
Phone: 303-312-6503
jacobson.linda@epa.gov

Daryl Reed
Superfund Project Officer
MT DEQ
P.O. Box 200901
Helena, Montana 59620
Phone: 406-841-5041
dreed@mt.gov

Denise Kirkpatrick
RCRA Project Officer
MT DEQ
P.O. Box 200901
Helena, Montana 59620
Phone: 406-841-3983
dkirkpatrick@mt.gov

Wendy Thomi
Community Involvement Coordinator
U.S. EPA Region 8, Montana Office
Federal Building
10 West 15th Street, Suite 3200
Helena, Montana 59626
Phone: 406-457-5037
thomi.wendy@epa.gov

Contaminants:
Arsenic

Waste Source:
The ASARCO East Helena Plant is a former metal smelter that operated for over 100 years. ASARCO shut down plant operations in 2001. Past operations at the site resulted in contamination, including arsenic-contaminated groundwater.

Type/Quantity of Media Treated:
Groundwater

Purpose/Significance of Application:
The purpose of this demonstration was to evaluate the performance and efficiency of a zerovalent iron PRB for the treatment of arsenic-contaminated groundwater.

Regulatory Requirements/Cleanup Goals:
Not specified for this pilot-scale study.

Results:
Data from the demonstration site included the following:

  • Groundwater upgradient of the PRB indicated arsenic concentrations ?25 mg/L;
  • Groundwater within the PRB indicated arsenic concentrations ?0.50 mg/L; and
  • Arsenic concentrations in the shallow aquifer interval downgradient of the PRB were 0.07 to 0.65 mg/L, and generally coincide with concentrations observed within the reactive medium. Samples collected from the lower zone of the aquifer showed arsenic concentrations of 20 to 30 mg/L, respectively. These results indicate that ground water was moving beneath the pilot-PRB and transporting arsenic across the plane of the PRB. In the upper region of the aquifer where ground water was moving through the PRB, approximately 99% arsenic removal was achieved.

Cost Factors:
Not available

Description:
The ASARCO East Helena plant was a smelter located south of East Helena, Montana. The plant began operations in 1888 and operated for over 100 years. The plant was listed on the U.S. Environmental Protection Agency's National Priorities List (NPL) in 1984. Lead operations at the site left the groundwater contaminated with arsenic. ASARCO shut down its operations in 2001 and plant demolition is underway.

A pilot study was conducted at the site to evaluate the performance and efficiency of a zerovalent iron PRB for the treatment of the arsenic-contaminated groundwater. The PRB consists of granular zerovalent iron that runs 9.1m long, 13.7 m deep and 1.8 to 2.4 m wide. The PRB was installed over 3 days using bio-polymer slurry methods and excavation equipment. Forty groundwater monitoring wells were installed in July 2005 and groundwater samples were collected at month 1, 4, 12, 15, and 25 of operation.

The results concluded that the permeable reactive barrier is effective at treating arsenic-contaminated groundwater. Monitoring results indicated that groundwater upgradient of the barrier had arsenic concentrations of >25 mg/L and that groundwater within the barrier has an average arsenic concentration of <0.01 mg/L. In addition to this demonstration, this report addresses aspects of site characterization, remedial design, and remedy implementation, and monitoring results for this pilot-scale PRB effort, including a flux-based analysis for arsenic.