Contaminants:
Trichloroethene

Reactive Media:
Fe⁰

Construction:
Funnel and gate

Point of Contact:
William A. Gallant
Versar, Inc.
Tel: 303-452-5700
Fax: 303-452-2336
Email: gallabil@
versar.com
11990 Grant Street
Suite 500
Northglenn , CO 80233

A demonstration project of a permeable reactive barrier (PRB) to remediate ground water contaminated with chlorinated hydrocarbons was initiated at Lowry Air Force Base, CO. Contamination at Lowry is a result of various base activities generating contaminants that were transferred to local ground water via storm drains, septic tanks, or direct infiltration. The total chlorinated hydrocarbon concentration was approximately 1,400 µg/L, primarily consisting of trichloroethylene (TCE).

The Lowry site is underlain by unconsolidated alluvial deposits and artificial fill that is approximately 18 ft thick. These surficial deposits overlie bedrock consisting of silty claystones and sandy siltstones. The local water table aquifer is approximately 9 ft below ground surface (bgs) and saturates alluvial material as well as the upper 10 ft of underlying bedrock in places. Local ground-water flow patterns are partly controlled by paleochannels eroded into the underlying bedrock. Hydraulic conductivity for the site averages 35 ft/day, and the average ground-water velocity is 1 ft/day. The local water table aquifer is approximately 9 ft below ground surface (bgs) and saturates alluvial material as well as the upper 10 ft of underlying bedrock in places. Local ground-water flow patterns are partly controlled by paleochannels eroded into the underlying bedrock. Hydraulic conductivity for the site averages 35 ft/day, and the average ground-water velocity is 1 ft/day.

The funnel and gate system constructed consists of a 10-ft-wide and 5-ft-thick reactive wall composed of 100% granular, zero-valent iron and two 14-ft sheet piling walls that were installed to a depth of 17 ft.

The total cost for the system was approximately $530,000. This includes design, construction, materials, and the reactive material.

Thirty-four wells located within and proximate to the wall were used to monitor the system's performance. Seven sets of samples were taken from December 1995 through June 1996. Data analysis indicates that a first-order, abiotic reaction involving reductive dehalogenation is taking place within the reactive iron wall. Chlorinated hydrocarbons are being completely degraded within the first foot of the wall. After 18 hours residence time (2 ft into the wall), all analytes degrade to their respective analytical quantitation limits. In addition, intermediate breakdown products produced during the process are also degraded. The wall was resampled in May 1997 with similar results. Since the PRB was designed and built as a short-term solution, there are no plans to continue the monitoring.

During a clogging study performed in May 1997, 18 months after installation, calcite, ragonite, "green rusts", amorphous iron hydroxides, and magnetite were observed. A porosity loss of 9.7% for the 18-month operational period was estimated from the investigation.

A slurry wall containment area was constructed in October 1997 30-50 ft upgradient of the PRB as part of a new source area remedial system.

In September 1999, nine additional wells were installed upgradient of the wall, two continuous flow direction and velocity systems (Hydrotechnics) were installed and the wall was cored. The objective of the current investigation is to assess hydraulic conditions and longevity issues associated with the current wall conditions. The work was funded by the Environmental Security Technology Certification Program (DOD) and the Strategic Environmental Research and Development Program. The work is being performed by Battelle assisted by Versar, Inc. under a contract with the Naval Facilities Engineering Service Center (NFESC) with the support of AFCEE, USACE and Lowry AFB (AFBCA) personnel. Reports documenting the results of this activity are in progress.

SITE-SPECIFIC REFERENCES