United States
Environmental Protection
Agency
EPA/540/MR-93/511
August 1993
Superfund
Treatability Study Bulletin
Mobile Volume Reduction Unit at the
Escambia Superfund Site
Technology Description: The Risk Reduction Engineering Labo-
ratory (RREL) Releases Control Branch (RGB) has developed 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
soils. The process reduces the quantity of contaminated material
that must be processed by a more expensive technology, such
as incineration or bioremediation. In some cases, soil washing
may be a successful stand-alone technology.
The Environmental Response Team (ERT) of the United States
Environmental Protection Agency (EPA) wanted to evaluate soil
washing using the VRU on contaminated soils at the Escambia
Superfund Site in Pensacola, FL This site contains approxi-
mately 250,000 yd3 of sandy soil contaminated with pentachlo-
rophenol (POP) and creosote from wood treating operations.
Thus, soil washing, a relatively inexpensive technology, might
provide a large cost savings by significantly reducing the volume
of soil requiring expensive treatment. The ERT defined the objec-
tives of the test:
Determine if the technology is effective in removing the con-
taminants.
Determine if the VRU can achieve the cleanup goals of less
than 30 ppm POP, less than 50 ppm carcinogenic creosote
compounds, and less than 100 ppm total creosote compounds.
Estimate process parameters and cost factors for 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 control, then
feeds into the mix into the soil washer's rotating trommel, where
additional 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 fines slurry were held
on-site 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 sys-
tem was not utilized.
The test used sodium carbonate as the alkali to raise the pH and
Tergitol NP-10, a nonionic surfactant.
Evaluation of Test Results: The VRU treated soil during 20 2-hr
tests over a 2-wk period in late July 1992. EPA investigated the
following variables:
Surfactant concentration 0 to 0.4 wt% of water
Temperature of washing 85 to 120 °F
pH 7to10
Liquid to solids weight ratio 6:1 to 9:1
Soils 2 onsite sources
Technicians collected four types of samples: feed soil; screen
overflowcoarse solids (>100 mesh); screen underflow (fines);
and effluent water. Laboratory analyses measured particle size
distribution and moisture content as well as the presence of PCP
and 13 creosote compounds, five of which are considered carci-
nogenic.
The two feed soils had equivalent particle size distributions, only
1% to 2% by weight less than 125 microns (~120 mesh). The
primary test soil, used in Runs 1 to 18, contained approximately
150 ppm PCP and 1,200 ppm total creosote, with 70 ppm
carcinogenic creosote compounds. A surfactant concentration of
0.4% was used. Preliminary results, which were available within
48 hr, revealed high PCP and creosote removals. Subsequent
runs utilized a lower surfactant concentration of 0.2% by weight
of water.
Since these results were so encouraging, two runs used a sec-
ond soil with higher contaminant levels. This alternate soil con-
tained 135 ppm PCP, 2,550 ppm total creosote, and 115 ppm
carcinogenic creosote.
The site action levels were easily achieved. The VRU washed
approximately 98% of the PCP from the coarse soils with water
alone. Surfactant concentration, pH, or operating temperature
had little apparent effect. Residual PCP levels ranged from 1-10
ppm. Contaminant removal efficiency for the creosote without
surfactant was about 90%. Analyses of the washed soil showed
that residual creosote levels of 60-80 ppm were readily achieved
for both soils at surfactant concentration levels of 0.20%. Re-
sidual concentrations for the carcinogenic creosote compounds
Printed on Recycled Paper
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ranged from 2-6 ppm for the runs with surfactant to 8-12 ppm for
those without. In the presence of surfactant, the impact of pH and
elevated temperature was minor.
Conclusions:
Soil washing reduced the coarse soil (>100 mesh) contaminant
concentrations to levels that met the cleanup goals at the
Escambia Site.
The addition of surfactant improved the cleanup levels for the
creosote, but had little or no impact on POP levels.
The soil washing achieved about 98% removal of the POP in the
coarse soil fraction.
A 0.2% surfactant concentration in the washing fluid enhanced
creosote cleanup, providing removal efficiencies of better than
95% for the coarse soil fraction.
EPA will publish a report to provide a more detailed discussion of
the Escambia test.
For Further Information:
EPA Project Manager:
Michael Borst
U.S. EPA RREL
2890 Woodbridge Ave.
Edison, NJ 08830-3679
(908) 321-6631 HJ.S. Government Printing Olflce: 1993750-071/80057
Contaminated
soli feed
Water
v> Alkali Surfactant
Soil feed
screening
y
Oversl
anddebri
zed soil
( .
' V
Soil washer
Vibrating
100n
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screen 1 ^
issft
r
Washed coarse
solids
Fines slurry - screen underflow
to wastewater treatment or disposal
Figure 1. VRUprocess.
United States
Environmental Protection Agency
Center for Environmental Research Information
Cincinnati, OH 45268
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EPA/540/MR-93/511
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