United States
Environmental Protection
Agency
Office of Research and
Development
Washington, DC 20460
Office of Solid Waste and
Emergency Response
Washington, DC 20460
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
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 (PS C), 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 com-
pounds in the following concentrations: toluene, 3,200 |ig/kg; ethyl
benzene, 820 |ig/kg; and xylenes, 29,600 |ig/kg. Ground water sam-
pling 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 ammo-
nium, 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 ground-
water 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.
Printed on paper that contains at least
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In July 1992, the Robert S. Kerr Environmental
Research Laboratory (RSKERL) (now part of the
National Risk Management Research Labora-
tory) 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 hy-
drocarbon 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 re-
maining at the site. Significant hydrocarbons were
found to remain in a narrow, approximately 2-ft
Hydrocarbon Release MW-3
• MW = Monitoring Wells
A RW = Recovery Well
• A-J = Boreholes
Table 1
Vertical Distribution of TPHs, Total BTEX Compounds, and Benzene
Found in Borehole D
Elevation
(feet above MSLaj
1609.711 to 1609.458
1609.458 to 1609.354
1609.354 to 1609.230
1609.230 to 1609.101
1609.101 to 1609.050
1609.050 to 1608.949
1608.949 to 1608.821
1608.821 to 1608.492
TPHs
(mg/kg)
<44
227
860
1,176
294
273
<34
<24
BTEX
(mg/kg)
<1
5.1
101
206
27
7.4
<1
<1
Benzene
(mg/kg)
<0.2
<0.2
<0.2
4.3
0.68
0.26
<0.2
<0.2
Color and
Texture
Brown sand
Brown sand
Black sand
Black sand
Black sand
Black sand
Black sand
Brown to
yellow sand
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.
Mean sea level.
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 hy-
draulic conductivity tests and three-dimensional
ground-water flow modeling to determine the ve-
locity 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, LIT; 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.
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