Air Sparging, In Situ Bioremediation, and Soil Vapor Extraction
- System consisted of two air sparging wells drilled to 55 ft bgs, three SVE wells drilled to 52 ft bgs, and associated equipment.
- No air pollution control devices were included in this system.
- Air sparging provided 23-60 cfm of air to the saturated zone; SVE removed 400 cfm (average) from the vadose zone, at 50 inches water across the blower.
- After 18 months of operation, nutrient solution was injected into the SVE wells.
State of Alaska Underground Storage Tank Regulations [18AAC78]
|USACE Point of Contact:|
Bernard T. Gagnon
and Innovative Technology Advocate
U.S. Army Corps
of Engineers, Alaska District
P.O. Box 898
Anchorage, Alaska 99506-0898
Telephone: (907) 753-5718
Chief of Environmental Restoration
and Compliance Branch
U.S. Army, Alaska
Directorate of Public Works
730 Quartermaster Road
Ft. Richardson, Alaska 99505
Petroleum hydrocarbons - diesel range organics (DRO). Average concentrations of DRO in soil were 500 mg/kg, and diesel range petroleum hydrocarbons in groundwater ranged from 0.085 to 18.6 mg/L.
Leak from fuel line
Type/Quantity of Media Treated:
Soil (in situ) and Groundwater
- Approximately 6,300 cubic yards of contaminated soil (a portion of the soil was in the saturated zone; this portion was not quantified).
- Soils consisted mainly of sand, gravel, cobble, and silt.
- Groundwater was encountered between 23 and 50 ft bgs, with a saturated zone approximately 27 ft thick and a hydraulic gradient of approximately 0.008 ft per ft.
- Subsurface materials encountered in all soil borings were generally uniform throughout the site, from ground surface to 65 ft bgs.
Purpose/Significance of Application:
Combination of three technologies used to treat DRO-contaminated soil and groundwater in situ.
Regulatory Requirements/Cleanup Goals:
The following remedial goals were specified for soil and groundwater at the Texas Tower site: soil (total BTEX - 10 mg/kg, benzene - 0.1 mg/kg, and DRO - 100 mg/kg); groundwater (benzene - 0.005 mg/L, toluene - 1 mg/L, ethylbenzene - 0.7 mg/L, xylenes - 10 mg/L, and diesel range petroleum hydrocarbons - 0.1 mg/L) as set forth in the Alaska Department of Environmental Conservation UST regulations.
- Over two years of system operation, approximately 1,300 lbs of contaminants were extracted through the SVE wells. Those contaminants consisted of 829 lbs of DRO, 418 lbs of GRO, and 55 lbs of total BTEX compounds. The estimate above does not include contaminants removed through biodegradation, which was not measured.
- Concentrations of contaminants in treated soil and groundwater met the remedial goals in all samples with the exception of three soil sample locations and three groundwater sample locations. Because the soil samples were from locations that had not been sampled prior to the design of the treatment system, the USACE concluded that the results suggested an additional "hot spot" outside of the original treatment area. Based on the results of a "mini-risk assessment" performed by the USACE, no additional remedial activities were identified. The State of Alaska accepted the closure report for this application.
- The operations contractor cited the following reasons for why no additional remedial activities were necessary: the leaking fuel lines that had been the source of the release had been removed; highly contaminated soil had been excavated and treated off site; no compounds for which maximum contaminant levels (MCLs) have been established had been detected at concentrations above MCLs during more than two years of monitoring; and the potential for exposure from residual hydrocarbons was negligible
- The total proposed cost for the air sparging, in situ bioremediation, and SVE system at the Texas Tower site was $295,760, including $145,420 for construction, $117,230 for operation, and $33,110 for work plan preparation.
- A unit cost of treatment of $47 per cubic yard was calculated from the total cost of $295,760 to remediate 6,300 cubic yards of soil (in situ); a portion of this soil was in the saturated zone.
- Because the site is isolated, the USACE reported that the cost of transportation of the equipment to the site and setup at the site was a significant portion of the total cost of the project.
- Costs of operation were kept low by monitoring the operation of the remediation system remotely. The system was not staffed, except for monthly sampling events. This savings in operating cost was not quantified for this application.
The Texas Tower site consists of four buildings surrounded by a chain-link fence at the U.S. Army's Ft. Greely military facility, located approximately five miles south of Delta Junction, Alaska, near Fairbanks. During demolition of one of the buildings in 1990, a release of petroleum hydrocarbons was discovered, reportedly originating from an underground heating oil supply line. Site investigations determined that the release had impacted both subsurface soil and groundwater. In 1990, approximately 2,000 cubic yards of contaminated soil were excavated and transported off site for thermal treatment, and in 1993 the excavation was backfilled with clean soil.
In August 1993, the USACE contractor conducted a pilot test of an SVE and air sparging system, and a biotreatability test. On the basis of the results from these tests, the contractor concluded that the site was amenable to remediation by a combination of the three technologies. The full-scale system was installed between November 1993 and January 1994 and was operated from February 1994 to February 1996. Closure samples were collected in April 1996 and, based on the data from these samples and a "mini risk assessment", the State of Alaska accepted the closure report for this application.