Bioremediation Field Evaluation Eielson Air Force Base, Alaska
Bioremediation Field Evaluation Eielson Air Force Base, Alaska
Bioremediation Field Evaluation Eielson Air Force Base, Alaska
You also want an ePaper? Increase the reach of your titles
YUMPU automatically turns print PDFs into web optimized ePapers that Google loves.
prompting additional studies at Hill<br />
and Tyndall AFBs. <strong>Base</strong>d on successes<br />
in these warm-weather sites,<br />
the <strong>Air</strong> <strong>Force</strong> and the U.S. Environmental<br />
Protection Agency’s (EPA’s)<br />
National Risk Management Research<br />
Laboratory (NRMRL) became<br />
interested in the possibility<br />
of using bioventing in cold climates.<br />
Microbial degradation occurs<br />
slowly, if at all, however, at low<br />
temperatures. The <strong>Air</strong> <strong>Force</strong> and<br />
NRMRL decided to study the use of<br />
soil warming measures to enhance<br />
the effectiveness of bio-venting<br />
in a cold climate. They selected<br />
<strong>Eielson</strong> AFB in Fairbanks, <strong>Alaska</strong>, as<br />
the study site. In winter, soil temperatures<br />
at this site drop to about 0°C.<br />
The field evaluation at <strong>Eielson</strong> AFB<br />
was undertaken to determine<br />
whether and to what degree soil<br />
warming can enhance the effectiveness<br />
of bioventing jet fuel contaminated<br />
soil in a cold climate. The<br />
evaluation also aimed to determine<br />
whether soil warming promotes<br />
high-rate, year-round bioremediation<br />
at a lower overall cost than prolonged<br />
low-rate bioremediation at<br />
ambient temperatures. The results of<br />
the evaluation are summarized below.<br />
They have also been discussed in<br />
other publications (6-8); see those<br />
publications for additional information.<br />
Site History<br />
<strong>Eielson</strong> AFB is an active base<br />
located in the <strong>Alaska</strong>n interior,<br />
about 25 miles southeast of Fairbanks<br />
(see Figure 2). The base serves a wide<br />
variety of aircraft and maintains a<br />
high volume of traffic. The climate is<br />
subarctic, with an average annual<br />
temperature near 0°C. Ambient temperatures<br />
range from below -30°C in<br />
the winter to above 30°C in the summer.<br />
Permafrost is present in some<br />
areas on <strong>Eielson</strong> AFB, but not in Site<br />
20, the area selected for this field<br />
Figure 2. Location of <strong>Eielson</strong> AFB.<br />
evaluation. Site 20 is a 1-acre area<br />
of land centered over two pressurized<br />
lines that intersect the site.<br />
The pressurized fuel lines are suspected<br />
to be the source of the fuel<br />
release because the area where<br />
the lines intersect is the most highly<br />
and uni-formly contaminated part of<br />
the site.<br />
The <strong>Air</strong> <strong>Force</strong> conducted a site<br />
characterization in July 1991,<br />
which revealed that the surface<br />
soil at Site 20 is a mixture of sand<br />
and gravel, with silt concentration<br />
increasing to about 6 ft. The soil<br />
was contaminated with JP-4 jet<br />
fuel from a depth of roughly 2 ft to<br />
the water table at 6 to 7 ft. Total<br />
petroleum hydrocarbon (TPH) levels<br />
ranged from 100 to 3,000 mg/kg,<br />
depending on soil depth and area.<br />
A hydrocarbon sheen was visible in<br />
the ground-water monitoring wells<br />
subsequently installed, and<br />
5<br />
ground-water samples showed TPH<br />
levels of 15 to 20 mg/L.<br />
In summer 1991, the <strong>Air</strong> <strong>Force</strong> and<br />
NRMRL installed and began operating<br />
an in situ soil bioremediation<br />
system: a bioventing system consisting<br />
of an air blower plumbed to<br />
air injection/extraction (bioventing)<br />
wells. The system could operate as<br />
an injection or extraction bioventing<br />
system; the <strong>Air</strong> <strong>Force</strong> and<br />
NRMRL conducted most of the<br />
study in the injection mode, which<br />
is the generally preferred method<br />
of bioventing. Operating the<br />
bioventing system involved using<br />
the blower to inject atmospheric<br />
air into the contaminated subsurface<br />
at a rate of 25 cubic feet per<br />
minute (ft 3 /min). <strong>Air</strong> injection/extraction<br />
wells were distributed uniformly<br />
at 30-ft intervals to provide<br />
relatively uniform aeration. The <strong>Air</strong><br />
<strong>Force</strong> and NRMRL constructed