The groundwater system beneath the site is a complex, folded and fractured limestone aquifer that exhibits wide variations in seasonal water levels and well yields and that contains a well-developed epikarstic zone. Groundwater beneath the site flows to the south, discharging in a series of off-post springs about 1.5 miles from the boundary of Letterkenny Army Depot (LEAD).
Targeted Environmental Media:
 Fractured Bedrock
Major Contaminants and Maximum Concentrations:
- Trichloroethene (0 µg/L)
- 1,1,1-Trichloroethane (0 µg/L)
- Tetrachloroethene (0 µg/L)
- 1,2-Dichloroethane (0 µg/L)
- 1,1-Dichloroethene (0 µg/L)
- 1,1-Dichloroethane (0 µg/L)
- Vinyl chloride (0 µg/L)
- Chloroethane (0 µg/L)
No technologies selected.
- Bioremediation (In Situ)
- Reductive Dechlorination (In Situ Bioremediation)
Comments:
A bench-scale microcosm study indicated that the microbial degradation of the VOCs could be greatly enhanced under anaerobic conditions through the addition of sodium lactate. A 6-month pilot scale study followed. The results indicated that the discharge of VOCs to the springs was nondetectable within 1 month of injection. Biological indicator compounds, particularly methane, also showed marked increases in concentration.
In late 2000, the Army implemented the enhanced bioremediation effort on a full-scale basis. The program involves the introduction of sodium lactate, with a tracer dye, into a series of injection wells over a 30-day period every 6 to 8 months. Bi-monthly groundwater samples are collected from a series of on-site and off-site locations for analysis of lactate, dye, VOCs, and dissolved gases to track the progress of cleanup.
Not provided in information reviewed.
Analytical results indicate that the sodium lactate is distributed effectively throughout the source area and that the contaminant plume is continuing to biodegrade. VOC levels in off-post wells and springs have rapidly declined and remained below applicable or relevant and appropriate requirements (ARARs) since 2002. On-post production of medium and light molecular weight daughter products has shown a consistent decline to near ARAR concentrations in 2003, while primary solvents have generally declined and remained below ARARs since 2002.
Reference:
Landry, Paul G.; Paul R. Stone III. 2005. Enhanced bioremediation of chlorinated solvents in karst limestone bedrock using sodium lactate. The Eighth International In Situ and On-Site Bioremediation Symposium, Baltimore, Maryland. June 6-9.
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