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-95/506D September 1995

Bioremediation Field 

Initiative Site Profile:

Public Service Company

of Colorado

Background

In 1987, Public Service Company of Colorado (PSC), an electric utility,

determined that used oil had leaked from a 75-gallon catch basin at

the company’s facility at 2701 West 7th Avenue in Denver, Colorado.

The catch basin served as a temporary storage container for used

automotive oil in the facility’s garage. A discrepancy between the

volume of oil deposited in the tank and the volume pumped out for

disposal led PSC to suspect the leak. Though it is unclear when the

leak first occurred, the basin had been in service for approximately 29

years before the leak was discovered.

Characterization

PSC found soil concentrations of oil and grease beneath the tank

ranging up to 9,600 mg/kg. Soil samples also showed BTEX compounds in the following concentrations: toluene, 3,200 μg/kg; ethyl

benzene, 820 μg/kg; and xylenes, 29,600 μg/kg. Ground water sampling detected low levels of BTEX compounds, though levels of

xylenes exceeded EPA’s proposed drinking water standards.

Field Evaluation

An in situ bioremediation system was operated at the site from October

1989 to March 1992. Ground water was pumped from a recovery well

downgradient of the spill at the rate of 11 gallons per minute. The

recovered water was treated by carbon adsorption to remove dissolved

hydrocarbons and reinjected into the aquifer upgradient of the spill

through two injection galleries. Ground water amended with ammonium, phosphate, and hydrogen peroxide was injected through the first

gallery. Unamended ground water was injected through the second

gallery, upgradient of the first, to sweep the amended ground water

through the spill to the recovery well. Injection rates were adjusted

periodically to optimize the delivery of nutrients and oxygen to the spill.

Figure 1 shows the plan view of the site.

A total of 10 to 15 pore volumes of ground water were exchanged over

the course of the treatment, which reduced BTEX levels in the groundwater monitoring wells to below cleanup level goals. In March 1992,

PSC submitted an application for closure to the State of Colorado and

the site entered a period of postremediation monitoring.

SITE FACTS

Location: Denver, Colorado

Laboratories/Agencies: U.S.

EPA National Risk Management

Research Laboratory (NRMRL),

U.S. EPA Region 8

Media and Contaminants:

BTEX in ground water

Treatment: In situ

bioremediation of ground water

with nutrient and hydrogen

peroxide addition

Date of Initiative Selection:

Spring 1991

Objective: To evaluate the

effectiveness of in situ

bioremediation of used oil and

the potential for future

environmental impact from

residual contaminants

Bioremediation Field Initiative

Contact: John Wilson, U.S. EPA

NRMRL, P.O. Box 1198, Ada,

OK 74820

Regional Contact: Suzanne

Stevenson, U.S. EPA Region 8,

999 18th Street, Denver, CO

80202-2466

Printed on paper that contains at least

50 percent recycled fiber.
In July 1992, the Robert S. Kerr Environmental

Research Laboratory (RSKERL) (now part of the

National Risk Management Research Laboratory) and the University of Colorado at Boulder

(UCB), with support from the Bioremediation

Field Initiative, began a retrospective evaluation

of bioremediation at the PSC site. The evaluation

consisted of aquifer sampling to assess the hydrocarbon contamination remaining at the site

after treatment, and modeling to predict whether

a plume of contamination would return after

active remediation was discontinued.

Status

RSKERL collected aquifer core samples to determine

the quantity and distribution of hydrocarbons remaining at the site. Significant hydrocarbons were

found to remain in a narrow, approximately 2-ft thick interval just below the water table. Table 1

shows the contaminant concentrations found at

eight different sampling depths in the borehole

closest to the source of the spill. These data suggest

that active remediation physically and biologically

weathered the spill, creating a cortex of material

with reduced levels of hydrocarbons surrounding

a core of material in which hydrocarbons were not

degraded significantly.

Following RSKERL’s investigation of the residual

contamination, researchers at UCB conducted hydraulic conductivity tests and three-dimensional

ground-water flow modeling to determine the velocity and trajectory of potential contaminant

plumes. The research team recommended that

compliance monitoring be continued until all of the

subplumes have reached steady-state conditions,

and that compliance wells be designed to minimize

contaminant dilution.

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; Hill Air Force Base Superfund site, Salt Lake City, UT; Escambia Wood Preserving Site, Brookhaven, MS; and Reilly

Tar and Chemical Corporation Superfund site, St. Louis Park, MN. 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.

Hydrocarbon Release

Work Pit

Existing

Service

Building

Nutrient

Recharge

Gallery

Ground-Water

Recharge

Gallery

RW-1

MW-8

MW-3

F E

C B

A

MW-2A

J

50 feet

N

D

MW-1

MW = Monitoring Wells

RW = Recovery Well

A-J = Boreholes

Figure 1. Plan view of the PSC site, showing the location of the work

pit, recovery and monitoring wells, and reinjection galleries and the

approximate area of the spill.

Table 1

Vertical Distribution of TPHs, Total BTEX Compounds, and Benzene

Found in Borehole D

Elevation

(feet above MSLa

)

TPHs

(mg/kg)

BTEX

(mg/kg)

Benzene

(mg/kg)

Color and

Texture

1609.711 to 1609.458 <44 <1 <0.2 Brown sand

1609.458 to 1609.354 227 5.1 <0.2 Brown sand

1609.354 to 1609.230 860 101 <0.2 Black sand

1609.230 to 1609.101 1,176 206 4.3 Black sand

1609.101 to 1609.050 294 27 0.68 Black sand

1609.050 to 1608.949 273 7.4 0.26 Black sand

1608.949 to 1608.821 <34 <1 <0.2 Black sand

1608.821 to 1608.492 <24 <1 <0.2 Brown to

yellow sand

a

Mean sea level.

20 meters

2