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
                                                                                             Printed on Recycled Paper

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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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