United States Office of Research and Office of Solid Waste and

Environmental Protection Development Emergency Response

Agency Washington, DC 20460 Washington, DC 20460

EPA/540/F-95/506C September 1995

Bioremediation Field

Initiative Site Profile:

Hill Air Force Base

Superfund Site

Background

In 1988, the U.S. Air Force initiated a study at Hill Air Force Base (AFB) to examine

the potential of bioventing to remediate JP-4 jet fuel-contaminated soils. Bioventing

is the process of supplying oxygen in situ to oxygen-deprived soil microbes by

forcing air through contaminated soil at low airflow rates. Because bioventing

equipment is relatively noninvasive, this technology is especially valuable for treating contaminated soils at military bases, industrial complexes, and gas stations,

where structures and utilities cannot be disturbed.

Promising results from the Air Force’s initial study prompted the U.S. EPA National

Risk Management Research Laboratory (NRMRL) and the Air Force to conduct a

field evaluation of bioventing at Hill AFB and at Eielson AFB (see separate fact sheet,

EPA/540/F-95/506B). The main objective of the Hill AFB evaluation was to determine the effect of air injection flow rate on the effectiveness of bioventing in

stimulating biodegradation while minimizing volatilization. The evaluation also

provided an opportunity to gain experience in bioventing large volumes of soil with

plumes of fuel that extend deep beneath the surface as well as under roads, underground utilities, and buildings.

Characterization

Prior to bioventing, the Hill AFB site was contaminated with JP-4 jet fuel from a

depth of about 35 ft to the ground water 95 ft below the surface. The contaminated

soil was a mixture of sand, silty sand, and sand interspersed with gravel and clay.

Soil samples taken in September 1991 revealed an average total petroleum hydrocarbon (TPH) level of 890 mg/kg, with TPH levels at some depths reaching 5,000

mg/kg. At most depths, benzene, toluene, ethylbenzene, and xylene (BTEX) levels

ranged between about 300 mg/kg and about 800 mg/kg. The area of contamination

extended beneath a tool maintenance building, engine storage yard, and fuel

storage yard (see Figure 1).

Field Evaluation

Unlike soil venting or soil vacuum extraction, bioventing uses low airflow rates

to stimulate biodegradation while minimizing volatilization of contaminants in

soil. Higher airflow rates stimulate faster and more widespread biodegradation

but also release more volatile emissions to the surface. To study the tradeoff

between the rate and range of biodegradation and the release of volatile emissions, the Air Force and NRMRL operated a bioventing system at the Hill AFB

site from July 1991 to January 1995, changing the airflow rate about twice a year.

They conducted a total of five airflow rate evaluations: one each at 28, 67, 67, 40,

and 117 ft3/min. The 67-ft3/min evaluation was repeated to include additional

monitoring points added to the site.

Each airflow rate evaluation included:

• An in situ respiration test—measurement of the rate of oxygen uptake by microorganisms in the soil to estimate the rate of biodegradation occurring there. 

SITE FACTS

Location: Salt Lake City, Utah

Laboratories/Agencies: U.S.

Air Force, U.S. EPA National

Risk Management Research

Laboratory (NRMRL), U.S. EPA

Region 8

Media and Contaminants:

JP-4 jet fuel in unsaturated soil

Treatment: Bioventing

Date of Initiative Selection:

Spring 1991

Objective: To evaluate the

effectiveness of bioventing jet

fuel in deep vadose zone soil

Bioremediation Field Initiative

Contact: Gregory Sayles, U.S.

EPA NRMRL, 26 West Martin

Luther King Drive, Cincinnati,

OH 45268

Regional Contact: Robert

Stites, U.S. EPA Region 8, 

999 18th Street, Denver, CO

80202-2466

Printed on paper that contains at least

50 percent recycled fiber.
• Surface emissions tests—both during air injection and while the air

injection system was shut off so

that emissions rates could be compared.

• Soil gas sampling—to monitor oxygen, carbon dioxide, TPH, and BTEX

levels.

Status

The Air Force and NRMRL have collected and analyzed bioventing performance data for each of the four

airflow rates. The total rate of biodegradation increased with increasing airflow rates, because the radius of

biological activity increased. Surface

emissions rates remained about the

same with increasing airflow rates.

Moreover, surface emissions rates

during air injection were not significantly different from those during

bioventing shutdowns. This was an

important finding because it indicates

that bioventing at the airflow rates

evaluated (28 to 117 ft3/min) does not

increase emissions of volatilized contaminants.

Final soil sampling conducted in

December 1994 revealed that TPH

and BTEX levels had declined at all

but one soil depth within a 25-ft

radius of the injection well. Only

at a depth of 90 to 100 ft (at the

capillary fringe) did TPH and BTEX

levels fail to decline, suggesting

that the capillary fringe was not adequately aerated. These results help

demonstrate the feasibility and effectiveness of bioventing at the airflow

rates evaluated.

The Bioremediation Field Initiative was established in 1990 to expand the nation’s field experience in bioremediation

technologies. The Initiative’s objectives are to more fully document the performance of full-scale applications of

bioremediation; provide technical assistance to regional and state site managers; and provide information on treatability studies, design, and operation of bioremediation projects. The Initiative currently is performing field evaluations

of bioremediation at eight other hazardous waste sites: Libby Ground Water Superfund site, Libby, MT; Park City

Pipeline, Park City, KS; Bendix Corporation/Allied Automotive Superfund site, St. Joseph, MI; West KL Avenue

Landfill Superfund site, Kalamazoo, MI; Eielson Air Force Base Superfund site, Fairbanks, AK; Escambia Wood

Preserving Site, Brookhaven, MS; Reilly Tar and Chemical Corporation Superfund site, St. Louis Park, MN; and Public

Service Company, Denver, CO. To obtain profiles on these additional sites or to be added to the Initiative’s mailing

list, call 513-569-7562. For further information on the Bioremediation Field Initiative, contact Fran Kremer, Coordinator,

Bioremediation Field Initiative, U.S. EPA, Office of Research and Development, 26 West Martin Luther King Drive,

Cincinnati, OH 45268; or Michael Forlini, U.S. EPA, Technology Innovation Office, Office of Solid Waste and Emergency

Response, 401 M Street, SW., Washington, DC 20460.

Figure 1. Plan view of Hill AFB site.

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