Underground Storage Tanks (USTs) Bioventing Treatment at Lowry Air Force Base (AFB), Denver, Colorado

Site Name:

Lowry Air Force Base


Denver, Colorado

Period of

Status - Ongoing Report covers - 8/92 to 4/94


Full-scale cleanup (interim results)


Engineering Science, Inc.
1700 Broadway, Suite 900
Denver, CO 80290

Bioventing - 6 piping manifolds (each consisting of two 10 ft, 2 in diameter screens) - Placed in excavation at right angles (in a horizontal plane), surrounded with 1 to 2 ft layer of pea gravel - Aerated to maintain an oxygen concentration greater than 14% - Carbon dioxide concentration maintained at less than 4%

Cleanup Authority:
State: Colorado

SIC Code:
9711 (National Security)
Point of Contact:
Lt. Tom Williams
3415 CES/DEV
Lowry AFB, CO 80230

Total Petroleum Hydrocarbons (TPH) - Total Recoverable Petroleum Hydrocarbons (TRPH) concentrations of 15 to 14,000 mg/kg were measured in soil samples below the area excavated for landfarming - BTEX concentrations in soil samples were lower than cleanup criteria

Waste Source:
Underground Storage Tank

Type/Quantity of Media Treated:
Soil - No estimates have been made of the quantity of soil treated or hydrocarbon product degraded at the time of this report - Moist, firm sandy clay in top 10-15 ft - Medium to coarse-grained sand in next 15-80 ft

Purpose/Significance of Application:
Bioventing to remediate soils contaminated with heating oil which contained relatively high concentrations of TPH and relatively low concentrations of soluble contaminants (e.g., benzene).

Regulatory Requirements/Cleanup Goals:
Treated soil - TPH < 500 mg/kg; TRPH < 500 mg/kg; and BTEX < 100 mg/kg - Cleanup conducted under EPA and State of Colorado Underground Storage Tank Regulations and the Colorado Department of Health's Remedial Action Category III (RAC III) action levels

Bioventing project was not complete at time of this report - No TRPH, BTEX, or TPH data are available at this time - Bioventing system maintained adequate O2 levels in the contaminated soil and removed CO2 from the soil

Cost Factors:
Final cost data were not available - Total Capital Cost - $28,650 (including equipment, site work, engineering, project management) - Annual Operating Costs - $32,875 per year (including electricity, maintenance, laboratory charges)

As a result of a leak of heating oil from an underground storage tank (UST) at Lowry Air Force Base in Denver, Colorado, soil was contaminated with total petroleum hydrocarbons (TPH) and benzene, toluene, ethylbenzene, and xylenes (BTEX). Following excavation of contaminated soil to a depth of 35 to 40 feet below ground level, soil sampling from the bottom of the excavation indicated that TRPH concentrations of 15 mg/kg to 14,000 mg/kg remained in the soils. A bioventing system, consisting of six bioventing piping manifolds, was installed at the bottom of the excavation and began operating in August 1992. The soil was aerated to maintain an oxygen concentration greater than 14% and a CO2 concentration less than 4%.

The bioventing of the contaminated soil at this site was ongoing as of April 1994. The target cleanup levels for the soil were TPH to less than 500 mg/kg; Total Recoverable Petroleum Hydrocarbons (TRPH) to less than 500 mg/kg; and BTEX to less than 100 mg/kg. The cleanup is being conducted under the authority of the Colorado Department of Health Underground Storage Tank Program. While no TPH, TRPH, or BTEX data were available at the time of this report, the bioventing system was found to have maintained adequate O2 and CO2 levels in the soil.

The total capital cost for this application is $28,650 and the estimated annual operating costs are $32,875. It was noted during this application that key operating parameters for bioventing are soil moisture, oxygen content, and carbon dioxide content; and that more frequent and better reported respiration test results would provide a more complete picture of the progress of the bioventing process, and indicate when final soil samples should be collected.