v>EPA
United States
Environmental Protection
Agency
EPA/540/MR-93/512
August 1993
Superfund
Treatability Study Bulletin
Mobile Volume Reduction Unit at the
Sand Creek Superfund Site
Technology Description: The Risk Reduction Engineering
Laboratory (RREL) Releases Control Branch (RGB) has devel-
oped a pilot-scale Mobile Volume Reduction Unit (VRU) to
determine the feasibility of soil washing for the remediation of
contaminated soils. This mobile unit, mounted on two trailers,
can process 100 Ib/hr of soil feed. Soil washing is a cost
effective technology used in conjunction with other methods for
remediating contaminated soil. The process reduces the quan-
tity of contaminated material that must be processed by more
expensive technologies, such as incineration or bioremediation.
In some cases, soil washing may be a successful stand-alone
technology.
Region VIII of the United States Environmental Protection
Agency (EPA) requested the VRU to evaluate soil washing as
a treatment for contaminated soil at the Sand Creek Superfund
Site in Commerce City, CO. This site contains approximately
14,000 yd3 of soil contaminated with pesticides. Soil washing,
a relatively inexpensive technology, might provide a significant
cost savings by reducing the volume of soil requiring expensive
treatment by incineration. Region VIII defined the objectives of
the test:
• Determine if the soil washing is effective in removing hep-
tachlor and dieldrin from contaminated soil.
• Determine whether the VRU can achieve the cleanup goals
set for the site: less than 0.553 ppm heptachlor and less than
0.155 ppm dieldrin.
• Estimate the process parameters and cost factors forthe full-
scale operation.
• Provide data for process scale-up.
The system, illustrated in Figure 1, begins by screening the
excavated soil to remove debris and large objects greater than
1/4 inch. The soil, fed into a hopper, is transferred by screw
conveyor to the soil washer feed hopper, where the surfactant
water and alkali are added. A ribbon blender in the hopper
mixes the soil and additives. A screw feeder, with speed con-
trol, then feeds the mix into the soil washer's rotating trommel,
where the wash water is added. The washed slurry flows by
gravity to vibrating screens for the separation of the cleaned
coarse soil from the fines and wash water, which contain the
contaminants.
After sampling, the washed coarse soil and the fines slurry
were held onsite pending further treatment. The VRU provides
a fines slurry treatment system for separation of solids and
dissolved contaminants from the effluent water. This slurry
treatment system was not utilized.
Two alkalis, sodium carbonate and sodium hydroxide were
used to raise the pH. Three surfactants, Tergitol NP-10, So-
dium Laurel Sulfate, Adsee 799/Witconol NP-100, were used.
Evaluation of Test Results: The VRU treated Sand Creek soil
during 23 2-hr tests over a 2-wk period in late September 1992.
EPA investigated the following variables:
Surfactant concentration — 0 to 1.5 wt% of water
Three surfactants — two nonionic and one anionic
Wash fluid temperatures — 70 to 130 °F
pH—7to10
Liquid to solids weight ratio — 6:1 to 9:1
Soils depths — 0-1 ft, 1-3 ft, 0-5 ft
Technicians collected four types of samples: feed soil, screen
overflow—coarse soils (>200 mesh); screen underflow (fines);
and effluent water. Laboratory analyses measured particle size
distribution and moisture content as well as the presence of
heptachlor, dieldrin, and other pesticides.
The three feed soils had equivalent particle size distributions:
30% to 35% by weight less than 74 microns (~200 mesh). The
primary test soil, used in 19 runs, contained approximately 250
ppm heptachlor and 20 ppm dieldrin. The other two soils, used
in Runs 13 to 16, were obtained from depths below the primary
test soil where the contaminant concentrations were an order
of magnitude lower. ,
With surfactant concentrations of approximately 1.0% by weight
of water, the VRU washed more than 90% of the heptachlor
and dieldrin from the coarse soils with residuals averaging 20
ppm and 2 ppm respectively. Without surfactant, removal effi-
ciencies of 75% to 80% were obtained. The three surfactants
achieved similar extraction efficiencies. The results for the two
secondary soils indicated removal efficiencies equivalent to
that achieved with the primary soil. The results of .varying pH,
temperature, and the liquid to solids ratio were inconclusive.
The site cleanup goals were not met. However, the test soil
came from the most contaminated areas on the site. Other
areas are significantly less contaminated. Therefore, soil wash-
ing may still be effective in reducing the quantity of Sand Creek
soil requiring processing by incineration.
For two runs, the washed coarse soil was processed a second
time through the washer. Contaminant removal efficiency in-
creased less than 50%. Several washed coarse soil samples
were subjected to a rinse at the laboratory. One run, using the
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0 - 5 ft soils, appeared to achieve the action levels for both
contaminants.
Conclusions:
• The soil washing with 1% surfactant achieved >90% removal
for the target contaminants.
• Soil washing did not reduce the coarse soil (>200 mesh)
contaminant concentrations to levels that met the cleanup
goals at the Sand Creek Site. Required removal efficiencies
(> 99%) were beyond the capabilities of the VRU.
* Addition of a surfactant improved the cleanup levels for
heptachlor and dieldrin.
• Double washing provided only a modest increase in contami-
nant removal efficiency.
• Rinsing the coarse soils resulted in a significant reduction of
heptachlor and dieldrin.
EPA will publish a report to provide a more detailed discussion
of the Sand Creek test. The report will be available from the
National Technical Information Service in Springfield, VA.
For Further Information:
EPA Project Manager:
Michael Borst
U.S. EPA RREL
2890 Woodbridge Ave.
Edison, NJ 08830-3679
(908)321-6631 «U.S. Government Printing Office: 1993—750-071/80056
ContaminatBd
soil feed
Water
Alkali Surfactant
Soil feed
screening
Oversized soil
and debris (>1/4 In.)
Washed coarse
*• solids
* sample point
Fines slurry - screen underflow
to wastewater treatment or disposal
F!guf»l. VRU process.
United States
Environmental Protection Agency
Center for Environmental Research Information
Cincinnati, OH 45268
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EPA/540/MR-93/512
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