the landfarm and approximately 1.23 kg m2 (0.25
Bioventing plots had two evenly spaced air-
lb ft2) on the bioventing cells. Twice as much fer-
extraction lines placed horizontally, approximately
45 cm from the surface. The cells were covered by
tilizer was applied to the bioventing cells because
liner material. Air flow was created by pumping a
they were nearly twice as deep as the landfarming
vacuum on the air extraction lines in the
cells. This resulted in similar amounts of nutrients
bioventing piles. During operation, the pumps
added on a mass:mass basis.
were cycled on a schedule of five evenly spaced
1-hour intervals during 24 hours.
Sampling and analysis
After 54 days, triplicate sample bags were ran-
domly removed from each cell and sampled for
Spatial variability
We addressed the problem of spatial variabil-
Total Petroleum Hydrocarbon (TPH) fractions.
ity in soil contamination by using well-mixed
TPH extractions from the soil were done by
sonication with methylene chloride. Anhydrous
contaminated soil in buried nylon "net" bags. To
sodium sulfate was added to the soil during ex-
obtain uniform soils for the bags, we removed
traction as a drying agent. Extracts initially were
composite samples from each cell of the two con-
analyzed by gravimetric analysis and then by
taminated soils. Approximately 350 subsamples
were taken and composited for each soil.
resolu-bilizing in methylene chloride followed by
gas chromatography and flame ionization detec-
Composited samples were homogenized in a large
tion (GC-FID). For TPH, chromatograms were in-
rotary mixer. Because the total amount of the
tegrated from baseline to baseline.
composited sample of each soil was too large to
mix at once, it was divided into thirds and each
third was mixed for 30 minutes, then the three
Costs
portions were inter-mixed for 1 hour. The net bags
Estimates for this project were based on treat-
ing 500 yd3 (382 m3) for 1 year and ranged from
permitted mass and energy fluxes throughout the
yd3 (.82.41 m3) for landfarming and
soil both inside and outside of the bags, yet al-
yd3 (.30.59 m3) for bioventing.
lowed us to recover the soil for time-series sam-
pling. For each treatment, we used enough bags
Cost breakdowns are provided in Table 2.
for triplicate samples at each time-series sampling.
In this demonstration, all soil was excavated
For the landfarm, each bag was cylindrical and
from other sites and transported to the demon-
stration site at Farmers Loop; therefore, soil han-
measured approximately 5 cm in diameter and 40
dling costs were the same for both treatments.
to 50 cm in length. We made the net cylinders by
Other costs that were equal for the two treatments
rolling a portion of netting around a hollow metal
include acquisition and application of nutrients
form until two complete layers of netting covered
and, for this demonstration, monitoring.
the form, and then tying a knot in the netting to
Costs that were incurred in bioventing, but not
secure the bottom. The net-wrapped form was
landfarming, included plumbing for air flow,
filled with the well-mixed contaminated soil. Af-
blowers, wiring, electricity for operation, periodic
ter filling, the hollow form was removed from the
monitoring of the blowers, and maintenance of the
netting and the sample was placed back into the
blowers. In practice, in-situ landfarming may be
field soil.
applicable at many sites because heavier oils and
This procedure let us obtain relatively uniform
more recalcitrant compounds are typically less
field data for this study. It provided a uniform ini-
mobile. In-situ treatment would remove both liner
tial contaminant concentration level in each bag
and soil handling costs.
with a sufficient number of bags in each cell for
Remediation costs are site specific and abso-
replicate, time-series sampling.
lute values derived from a particular site can be
transferred to other sites only with caution. Typi-
Nutrient amendments
cally, costs are reported per ton or per cubic
Nutrients were uniformly spread on the surface
yard, but consideration must be given to the
of appropriate cells. Commercially available agri-
fixed costs, such as mobilization and decontami-
cultural fertilizer, granular 20-20-10, was used. The
nation of equipment, that are required regard-
less of the volume treated. With larger volumes
plied fertilizer to the surface because this method,
with a minimum of labor and machinery, is the
of soil treated, fixed costs are distributed over a
most likely to be used in the field. Application rates
greater volume of soil and result in a lower per
were approximately 0.62 kg m2 (0.13 lb ft2) on
unit cost.
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