United States
Environmental Protection
Agency
Hazardous Waste Engineering
Research Laboratory
Cincinnati OH 45268
Research and Development
EPA/600/S2-87'110 Feb. 1988
Project Summary
Field Studies of In Situ Soil
Washing
James H. Nash
The EPA and U.S. Air Force
conducted a research test program
to demonstrate the removal of
hydrocarbons and chlorinated
hydrocarbons from a sandy soil by in
situ soil washing using surfactants.
Contaminated soil from the fire
training area of Volk Air National
Guard Base, Wisconsin, was first
taken to a laboratory for
characterization. At the laboratory
the soil was recompacted into glass
columns creating a simulated in situ
environment. Under gravity flow, 12
pore volumes of aqueous surfactant
solutions were passed through each
of the columns. Gas chromatograph
(GC) analyses were used on the
washing effluent and soil to
determine removal efficiency (RE).
The results of these tests were
highly encouraging. RE's of field
tests run at the fire training area
were evaluated by GC, total organic
carbon (TOC) and oil and grease
data. Ten one foot deep holes were
dug in the surface of the fire pit.
Surfactant solutions were applied to
each hole at a rate of 1.9 gallons per
square foot per day. Soil samples,
taken from the undisturbed layers
beneath each hole, were analyzed for
residual contamination. Samples
experiencing a flow through of nine
to fourteen pore volumes of
surfactant solution still had
contaminant levels comparable to
5,000-10,000 ng/g prewash
conditions.
The field study also included the
development of a groundwater
treatment process. Measurements of
TOC, VOA and biochemical oxygen
demand (BOD5) were decreased by
50%, 99%, and 50%, respectively.
Treated effluent was discharged
directly to the on-base aerobic
treatment lagoons.
This Project Summary was
developed by EPA's Hazardous Waste
Engineering Research Laboratory,
Cincinnati, OH, to announce key
findings of the research project that is
fully documented in a separate report
of the same title (see Project Report
ordering information at back).
Introduction
Surface and near-surface
contamination often serve as the source
for groundwater contamination
Percolation of rainwater through spill sites
quickly carries soluble and semi-soluble
contaminants away from the point of
origin Contaminants considered
"insoluble" above parts per million
nevertheless migrate more slowly. Gross
contaminant sources supply pure product
that over many years, flows deeply
through unsaturated soils.
Part of the EPA's Superfund site
cleanup research has been directed at
washing such contaminated soil with the
aid of aqueous surfactant solutions. The
research takes two directions. The first is
to excavate the soil and mix it m a wash
solution. The second research objective
concentrates on the application or
injection of a surfactant solution into
undisturbed soil in situ. A segment of this
in situ research is the subject of this
project summary.
This demonstration effort grew out of
mutual need between the EPA and the
U.S. Air Force. From 1982 to 1985 the
EPA researched soil washing technology
using surfactants in laboratory studies.
Recompacted soils were used in these
studies to simulate in situ conditions
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Truly undisturbed contaminated soil was
not tested up to that time. The U.S. Air
Force, as part of its Installation
Restoration Program, was seeking
processes to clean up 128 fire training
pits at Air Force installations. The Air
Force selected the Air National Guard
Base in Camp Douglas, Wisconsin, as a
candidate site for the EPA to test either
excavated or in situ soil washing. The
EPA and the Air Force representatives
chose in situ washing after further
consideration.
The Laboratory Study
Previous laboratory work identified a
50/50 blend of two commercially
available surfactants that work well in
removing contaminants from soil. They
are Adsee 799 and Hyonic PE-90, sold
by Witco Chemical and Diamond
Shamrock, respectively To determine if
this same blend would work at the Volk
Field fire training pit, contaminated soil
samples were collected
Five physical tests characterized the
soil. They were: grain size, TOC, cation
exchange capacity (CEC), mineralogy by
x-ray diffraction, and permeability The
grain size of the contaminated soil was
98% sand. By x-ray diffraction, alpha-
quartz comprises the major portion of the
soil with a minor amount of feldspar
being present. TOC was as high as
14,900 ng/g. The cation exchange
capacity of 5 milliequivalents.100 g was
not significant to the contamination
levels, however, it did support the x-ray
diffraction mineralogic findings. The
permeability of the fire pit soil, at 10-3
and 10'4 cm/sec, was one to two orders
of magnitude less than adjacent
uncontaminated soil
Chlorinated hydrocarbons were part
of the volatile contamination.
Dichloromethane, chloroform, 1,1,1-
trichloroethane (TCA), and
trichloroethylene (TCE) at concentrations
up to 3 ppm and total chlorinated
solvents up to 3.5 ppm were determined
by the VOA procedure. Other
hydrocarbons are aliphatic, aromatic and
polar constituents. The level of
hydrocarbon contamination is in the
hundreds of ng/g based on the laboratory
analysis.
Contaminated groundwater, a
significant problem, from the aquifer
below the fire training pit, was also
characterized in the lab study. VOA,
TOC, and ultraviolet spectroscopy (UV)
was used. The investigations determined
that the groundwater contains chlorinated
and non-chlorinated hydrocarbons in
excess of 300 ppm
The soil adsorption constant (K) is a
measure of a pollutant's tendency to
adsorb and stay on soil. A value of 2,000
for PCB's indicates a two-hundred-fold
greater adsorption (holding power) than
benzene at K=10. Benzo(a)pyrene, a
toxic substance, and oil have similar
values - K = 30,000 - 40,000. Grouping
contaminants according to a K value and
evaluating removal efficiencies (RE)
gives order to an otherwise complex
collection of chemical classes. This is a
report of the EPA's and the U.S. Air
Force's field evaluation of in situ soil
washing of compounds having K values
between 101 and 106
The Field Study
The field study was conducted by
laying out ten 2' x 2' x 1' pits, dug into
the contaminated surface of the fire
training area, which served as reservoirs
that held various surfactant solutions.
Field technicians applied wash solutions
into the holes at the maximum rate of 1 9
gallons per square foot per day The
daily dosage was applied m four
increments Since each hole percolated
the solutions at different rates, the time
interval between doses varied from hole
to hole. Testing in three of the pits
stopped when the time intervals for the
next application approached ten hours
indicating unacceptable permeabilities
being created. Following seven days of
washing, the pits received rinses with
local, potable well water
A combination of infrared
spectroscopy (IR) and gravimetric
determinations of soil extracts was used
to evaluate "before and after"
contaminant concentrations. To
determine contaminant concentration,
soil samples were taken after the rinse
process, extracted with carbon
tetrachlonde, and analyzed by IR
spectrophotometer for spectral
absorbance by the carbon hydrogen
bond The extracts were then air dried
and weighed to determine gravimetrically
the contaminant concentration (non-
volatile).
The contaminant concentration
before soil washing was based on the
extracts of soil samples taken adjacent to
the test holes No samples were taken
directly from the test holes before
washing in order not to bias permeation
rates
Based on both the gravimetric and
IR determinations of contaminant
concentrations, there was no measurable
decrease in contaminants following as
many as 14 pore volumes of soil washing
in the field tests.
In addition to the soil washing,
field crew conducted a bench-s>
groundwater treatment study. From
study a treatment system was asseml
and operated which successfully redi
TOC, VOA and BOD5, by 50, 99,
50%, respectively. At these effh
levels, discharge to the local aen
sewage lagoon was below the Wisco
Department of Natural Resources' pe
limits A total of 320,000 L of c
tammated groundwater was treatec
rates of 15,000 to 45,000 Lday.
The bench-scale study investig,
the use of lime, alum, ferric sulf
hydrogen peroxide, polymeric elec
lytes and mineral acids. The apphce
of these chemicals was guided
conventions appropriate to wastew
treatment plants. The resulting w
treatment process (shown in Figure
was based on the addition of lime ;
g;L. The lime created a flocculatior
iron oxides and organics. "
contaminant plume contained up to
mg/L iron. Particulate sedimentation
clanfier, followed by additional reside
time in a holding lagoon, reduced
TOC, BOD5, and VOA to accept;
discharge levels. A final polishing of
volatiles m an air stripper was the I
step in the process Table 1 i:
summary of the analytical data
Conclusions
1. In situ soil washing of the Volk Fi
fire training pit with aquec
surfactant solutions was r
measurably effective It is likely t
this same ineffectiveness would oc
at other chronic spill sites that h;
contaminants with high soil-sorpt
values (K >1Q3).
2. In situ soil washing requires groui
water treatment. Groundwa
treatment at this site was ve
successful with the simple addition
lime Air stripping effectively remov
the volatile organics. Advantages
this site were its remoteness
workable air emission limits tl
facilitated groundwater treatrm
operations and a local sewa
treatment system owned by t
responsible party TOC levels of
recovered groundwater were reduc
to one half the initial values
precipitation with lime which allow
for direct discharge to the aerol
treatment lagoons. Obviously, not
waste sites have these favorai
conditions Other fire pit sites w
lower effluent limits would requ
systems with greater retention time:
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Volatiles
Lime
2
I
t
*
—
Flash
Mix <
JB1 ~~ta
Clarifier
^
Lagoon
Air
To Aerobic
Lagoon
Well
Figure 1. Volk Field pilot treatment for water.
Table 1
Pt No.
Analytical Tests and Sampling Points for the Water Treatment Process
Description
Tests Performed
Approximate Values, Average or
Range
1 Individual we/I head
2 Well field effluent
3 Flash mixer effluent
4 Clarifier effluent
5 Air stripper feed
6 Air stripper effluent
7 Clarifier
8 Clarifier bottom
9 Soil
volatile organic
total organic
chemical oxygen demand
oil and grease
pH
volatile organic
total organic
iron
pH
chemical oxygen demand
flow rate
total organic (dissolved)
suspended solids
pH
flow rate
total organic
suspended solids
pH
flow rate
volatile organic
total organic
temperature
flow rate (water)
oil and grease
volatile organic
total organic
flow rate (air)
oil and grease
biochemical oxygen demand
chemical oxygen demand
suspended solids
suspended solids
oil and grease
70-20 mgiliter
60-760 mgiliter
6-500 mgiliter
0 2-46 mgiliter
5.7-62
70-20 mgiliter
250 ± 14% mgiliter
32 mglliter
6.0 ± 0.2
41 mgiliter
.25 - 2 Mer.sec
7 60 mg 'liter
350 mgtliter
68-9.7
.5 - 2 liter'sec
205 ± 7% mgiliter
13 6-W4 mgiliter
76
.5 - 2 liter,'sec
3.5 - 7.0 mgiliter
151 ± 73% mgiliter
6-I5"C
95 - 7 26 /ifer/sec
3.6 mgiliter
0.3-05 pgMer
146 mgiliter
101 //sec
3.6 mgiliter
2.5 mgiliter
180 mgfliter
4.4 mgiliter
2331 mgiliter
800-16000 mgikg
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James H. Nash is with Mason and Hanger-Silas Mason Co., Inc., Leonardo,
New Jersey 07737
Richard P. Traver is the EPA Project Officer (see below).
The complete report, entitled "Field Studies of InSitu So/7 Washing" (Order No. PB
88-1468081 AS; Cost: $14.95, subject to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Releases Control Branch
Hazardous Waste Engineering Research Laboratory-Cincinnati
U.S. Environmental Protection Agency
Edison, NJ 08837
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
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