Contaminants:
Trichloroethene, Tetrachloroethene

Reactive Media:
Fe⁰

Cost:
$30,000

Construction:
Continuous Trench

Point of Contact:
Stephanie F. O'Hannesin
Environmental Technologies, Inc.
Tel: 519-746-2204
Ext: 235
Fax: 519-764-2209
Email: sohannesin@
eti.ca
745 Bridge Street West
Suite 7
Waterloo , Ontario N2V2G6 Canada

A pilot-scale demonstration of a permeable reactive barrier (PRB) to remediate ground water contaminated with trichloroethylene (TCE) and perchloroethylene (PCE) was conducted at the Canadian Forces Base in Borden, Ontario, Canada. The PRB was installed in 1991. Contamination was the result of a previous site study to determine the dissolution characteristics of a mixed non-aqueous fluid. The contaminant plume was about 6.5 ft wide and 3.3 ft thick. Initial concentrations were 250,000 µg/L TCE and 43,000 µg/L PCE. The plume source was located about 13 ft below ground surface (bgs) and 3.3 ft below the water table.

The contaminated surficial aquifer is composed of medium-fine sand. Its lower boundary is a thick clay deposit located 30 ft below the surface. The upper boundary of the aquifer varies between 6.5 ft and 10 ft bgs. Hydraulic conductivity for the surficial sand aquifer is 20.5 ft/day.

Reactive material was installed using sealable joint sheet piling 18 ft downgradient from the source. Individual piles were interlocked to create a rectangular cell normal to ground-water flow direction that was 18 ft long, 5 ft wide, and 32 ft high. The pilings were then driven as a unit to a depth of 32 ft using a hydraulic vibratory driver suspended by a crane. The joints were sealed with a bentonite-based sealant, and the water table was lowered below the depth of excavation. The cell was then excavated and the native material was replaced with a mix of 22% (by weight) zero-valent granular iron and 78% coarse sand from 12.4-20 ft bgs. This mixture had a hydraulic conductivity of 124 ft/day. After emplacement of the mixture, the sheet pilings were removed.

The cost for installation, exclusive of the cost of reactive iron and labor, was $30,000. The reactive material and the labor were donated.

A total of 348 monitoring wells were installed upgradient and downgradient from the wall, as well as within the reactive material. Concentration distributions were monitored over a period of five years. The PRB reduced TCE concentrations by 90% and PCE concentrations by 86%. No vinyl chloride was detected in the samples. The low amounts of calcium carbonate precipitate detected in the wall after five years suggests that the wall's performance should persist for at least another five years. Since the residual source was remediated using permanganate flushing, there are no plans for additional sampling.

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