Installation Date:
1999

Contaminants:
Trichloroethene, cis-1,2-Dichloroethene

Reactive Media:
Fe⁰ and Sand

Cost:
$450,000

Construction:
Continuous Trench

Point of Contact:
Michael Duchesneau
Parsons Engineering Science, Inc.
Tel: 781-401-2492
Fax: 781-401-2492
Email: michael.duchesneau@
parsons.com
30 Dan Road
Canton , MA 02021-2809

A full-scale demonstration permeable reactive barrier (PRB) system was installed at Seneca Army Depot Activity in Romulus, NY in 1999. Continuous wall trenches were chosen based on the system’s lower cost, ease of installation, expectation of less disruption in ground-water flow, and ability to treat the upper surface of the bedrock aquifer. Trichloroethylene (TCE) and cis-1,2-dichloroethylene (cis-DCE) are the contaminants of concern at the site. Following a removal action using low temperature thermal desorption (LTTD) in 1996, the concentrations dropped from 51,000 µg/L to 9,100 µg/L for TCE and from 130,000 µg/L to 1,100 µg/L for cis-DCE.

The site is an ash landfill area for a former trash incinerator used for the disposal of chlorinated solvents. A TCE/DCE ground-water plume (1200 ft long by 600 ft wide) emanated from the ash landfill source area. The geological matrix is comprised of 6 ft by 8 ft of glacial till with fractured shale to 20 ft. The depth of the water varies over the year from ground surface to 6-8 ft below ground surface (bgs). The average hydraulic conductivity of the glacial till is 1.8 ×
10^-4 in/sec and that of the fractured shale is 1.4 ×
10^-5 in/sec. The shale conductivity decreased with increasing depth. There is poor connection between the overburden and the bedrock.

The PRB is 650 ft long, 14 in wide, and 7-12 ft deep with a cover of approximately 1 ft of natural soil. It is installed from the ground surface into the top 1-2 ft of the weathered shale bedrock. The 5,525 ft³ of reactive material used is a 50/50 mixture of zero valent iron (Fe⁰) and sand. The total installation cost including construction and materials was $350,000. Design costs, including a 3-D ground-water model, were $100,000.

The cleanup goal was based on the New York State standard of 5 µg/L. Samples taken after 4 quarters of monitoring revealed 100% removal of TCE. Removal of cis-DCE was less than expected. Concentrations downgradient and within the wall were measured at 20-40 µg/L. Removal of DCE will require additional reactive iron. Future walls are pending if DCE removal can be achieved. Sampling continues intermittently as funding allows.

Lessons Learned

Monitoring results indicate that walls will need to be thicker and comprised of 100% reactive material. Incomplete treatment of cis-DCE was attributed to greater than expected PRB influent concentrations of TCE (500 as opposed to 100 µg/L) and greater than expected variability of ground-water velocities. These variations necessitate the installation of additional monitoring wells to determine concentrations and velocities. Column study tests of the reactive iron may also be needed to determine if the reactivity of the iron may have contributed to the DCE breakthrough.

SITE-SPECIFIC REFERENCES

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