Site Name:

Altus Air Force Base, Landfill 3 (LF 3)

Location:

Oklahoma

Period of
Operation:

July 2002 to ongoing (data available through March 2003)

Cleanup
Type:

Field demonstration

Technology:
Mulch Biowall
- Biowall was 455 ft-long, 24 ft-deep, and 1.5 ft-wide; consisted of approximately 300 cubic yards of shredded mulch (generated by the city), 60 cubic yards of cotton gin compost, and 265 cubic yards of sand
- Biowall was installed using a continuous trenching machine, allowing simultaneous excavation and filling with mulch mixture
- Groundwater flows through the biowall under natural hydrualic gradient to promote contact with the slowly soluble organic matter; microbial processes in the subsurface degrade the mulch, generating breakdown products including metabolic acids, that provide secondary electron donors or fermentable substrates for hydrogen generation, the primary electron donor used in reductive dechlorination
- 10 groundwater monitoring wells and 4 soil vapor monitoring points were installed

Cleanup Authority:
Not provided

Contacts:

Contaminants:

- TCE plume originates from LF-3 and extends southeastward approximately 4,000 feet
- Concentrations of TCE in April 1999 ranged up to 6,110 μg/L

Waste Source:
Disposal of waste in a landfill

Type/Quantity of Media Treated:
Groundwater

Purpose/Significance of Application:
Use of a mulch biowall to treat groundwater contaminated with chlorinated solvents

Regulatory Requirements/Cleanup Goals:
- The objective for this project was to assess the applicability and feasibility of promoting in situ bioremediation of TCE and cDCE in groundwater, and to contain and attenuate a shallow groundwater plume to prevent surface water discharge or off-base migration

Results:
- After 3 months, the trend of decreasing TCE and increasing cDCE concentrations in groundwater was observed at all monitoring locations located within 30 ft downgradient of the biowall
- Average decrease in TCE concentrations from July 2002 to March 2003 within the biowall was 98.7 percent; the average decrease in downgradient TCE concentrations was 64.5 percent
- As of March 2003, dissolved oxygen levels were depleted in the study area and within the biowall - oxidation-reduction potential had been lowered; sulfate levels were depleted; hydrogen sulfide and methane levels were elevated; and total metabolic acids were elevated, indicating that the conditions in the biowall were highly conducive to reductive dechlorination

Cost Factors:
Capital cost for procuring materials and installing the biowall was $165,000, or approximately $360 per linear foot. Monitoring cost was approximately $17,000 per event, totaling $51,000 for three events. Future cost of O&M is estimated to be $42,000, consisting of biannual monitoring, reporting, and project management.

Description:
LF-3 is located at the eastern portion of Altus AFB. LF-3 received waste materials including garbage, wood, paper, metal, and shop wastes, construction debris, concrete, brush, and several drums of paint waste, which was buried in trenches. Site investigation identified chlorinated solvents in the groundwater, including TCE and cDCE. A TCE plume extending about 4,000 feet downgradient of LF-3 was identified at the site.

A field demonstration of a mulch biowall was conducted at the site to to assess the applicability and feasibility of promoting in situ bioremediation of TCE and DCE in groundwater. The mulch biowall was installed using a continuous trenching machine to simultaneously excavate the trench and install the biowall materials. According to the vendor, this approach eliminated the concerns associated with open trenches. Data from the groundwater monitoring wells showed that TCE concentrations were decreasing, reduced by 64.5 to 98.7 percent, and that cDCE concentrations were increasing. Geochemical parameters measured in March 2003 indicated that the conditions in the biowall were highly conducive to reductive dechlorination. Additional monitoring is planned to document the ability of the biowall to sustain biological activity and contaminant mass degradation.

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