Technology:
Intrinsic Remediation
This remediation approach requires a demonstration, through intensive site characterization, that natural biological processes are destroying contaminants in situ and that the site will reach specified remediation goals within 30 years.
The demonstration includes:
- Observation of a stable or decreasing contaminant plume over time;
- Correlation of contaminant plumes with electron acceptor distribution; and
- Modeling studies that indicate attenuation due to processes other than dispersion, volatilization, and sorption
Eight quarterly sampling rounds were conducted to accumulate the data necessary for the remediation demonstration.
Annual long-term monitoring is required to confirm that adequate remediation is occurring.
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Cleanup Authority:
CERCLA and State Record of Decision (ROD) signed on October 17, 1996
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Contaminants:
Organic Compounds
- Volatiles (nonhalogenated)
- BTEX (benzene, toluene, ethylbenzene, and xylene)
- Maximum benzene concentrations:
- 2,000 µg/L at AOC 43G - 300 µg/L at AOC 43J |
Waste Source:
Soil and groundwater contamination at both sites was caused by leaks and spills from former gasoline and waste oil USTs. In addition, leaks and spills from the sand and gas trap at AOC 43G may have been another source of contamination. |
Type/Quantity of Media Treated:
- The contaminant plume at AOC 43G extends 320 feet downgradient from the source area and is 230 feet wide. The contaminant plume at AOC 43J extends 250 feet downgradient from the source area and is 190 feet wide. Plume dimensions were calculated based on groundwater concentrations above the maximum contaminant level (MCL) for benzene in March 1997.
- The aquifer is approximately 5 feet thick at AOC 43G and 10 feet thick at AOC 43J.
- Free product has been detected.
- Electron acceptors are present in the groundwater at varying levels. |
Purpose/Significance of Application:
This project demonstrates that intrinsic remediation is a viable treatment alternative at sites contaminated with BTEX. |
Regulatory Requirements/Cleanup Goals:
- The ROD established the preliminary remediation goals (PRGs) for AOCs 43G and 43J that must be met within 30 years. Most goals were based on MCLs. Iron and manganese goals were risk-based.
- Property boundary performance standards for AOCs 43G and 43J were based on the PRGs and the Massachusetts Contingency Plan (MCP) GW-1 standards for extractable and volatile petroleum hydrocarbons (EPH/VPH). |
Results:
- The results of the Mann-Kendall statistical trend analyses on BTEX compounds at both sites indicated that groundwater concentrations exhibit a statistically significant decreasing trend.
- At both sites, there is significant evidence of the utilization of electron acceptors and the appearance of degradation products, suggesting that contaminants are being biologically degraded and not just physically diluted or dispersed.
- Modeling indicates that the contaminant plumes at both sites will be reduced below the applicable MCLs between 8 and 15 years after the ROD was signed.
- Fate and transport modeling demonstrated that it was unlikely that the BTEX plumes would move off of Army property. |
Cost Factors:
- The total cost for the IRA was $671,642.
- The anticipated long-term monitoring and reporting costs are $50,000 per year.
- The number of wells sampled is a significant cost element because it effects the duration of field sampling events, analytical expenses, and the effort involved with tracking and assessing data. |
Description:
AOCs 43G and 43J are two former gasoline stations operated at Fort Devens. These sites were also used for motor pool operations during World War II. BTEX and TPH contamination in soil and groundwater at these sites is consistent with the historical use of the areas. The Army determined that intrinsic remediation was the most appropriate remedy for the contamination at both sites. The remedy consists of intrinsic remediation, IRA data collection and groundwater modeling, long-term groundwater monitoring and annual reporting, and five-year site reviews.
The IRAs for AOCs 43G and 43J demonstrated that intrinsic remediation is working and that the Army will not need to initiate additional cleanup actions. Specifically, modeling indicates that the concentrations of the contaminants of concern will be below groundwater cleanup levels in less than 30 years and that they will not migrate off of Army property. |
