United States
Environmental Protection
Agency
EPA/540/MR-94/510
April 1994
SUPERFUND INNOVATIVE
TECHNOLOGY EVALUATION
Demonstration Bulletin
In Situ Steam Enhanced Recovery Process
Hughes Environmental Systems, Inc.
Technology Description: The Steam Enhanced Recovery
Process (SERP) is designed to remove volatile compounds such
as halogenated solvents and petroleum hydrocarbons, and semi-
volatile compounds from contaminated soils in situ. The vapor
pressures of most contaminants will increase by the addition of
steam, causing them to become more volatile and mobile. The
technology operates through wells drilled in the contaminated
soil. Injection wells deliver high pressure steam (15 psig) to the
soil, while extraction wells draw a vacuum on the soil. The
pressure gradient drives the steam, water, and vaporized con-
taminants to the extraction wells where they can be removed for
disposal or recycling. Figure 1 illustrates the operation of the
process beneath the soil surface.
A site to be treated with in situ SERP must have predominantly
medium to high permeability soils. A geological confining layer
below the treatment depth and a confining layer above the treat-
ment zone help to contain the flow of steam. Injection and
extraction wells are arranged on the site in a pattern designed to
promote even distribution of the steam. Site-specific factors
determine the number of wells used, their arrangement on the
site, their construction, and the above-ground process equipment
to be used.
A full-scale SERP system with 35 injection wells and 38 extrac-
tion wells was used to treat a 2.3-acre area of soil up to 40 feet
dee.p at the Rainbow Disposal site in Huntington Beach, Califor-
nia. This site was contaminated with diesel fuel'compounds.
Water for steam generation was pumped from an on-site deep
water well, treated by ion exchange and the addition of chemi-
Extractlon of Vapors
And Liquids
(to treatment systems)
EXTRACTION*
WELL
DEPTH
INTERVAL OF
TREATMENT
cals, and heated in one of two natural gas-fired steam boilers.
High pressure steam was delivered to all the injection wells using
a manifold system. Air-lift pumps were used to remove accumu-
lated oily water from the extraction wells, and a vacuum pump
maintained a negative pressure on the soil and removed the
vapors from each extraction well.
The heated liquid (condensate) from the extraction wells was
routed to a heat exchanger used to pre-heat the boiler feedwater,
and then treated in a gravimetric oil/water separator. The diesel
phase from the separator was collected in a storage tank. The
remaining water phase was then treated further using filtration
and activated carbon before being discharged directly to an
underground storm sewer. Liquids and particulates entrained in
the extracted vapor were removed using a knock-out drum. The
vapor stream was then treated in a thermal oxidizer unit which
used electrical heating to oxidize the vapor before discharging it
through a stack to the atmosphere.
The full-scale SERP system used at the Rainbow Disposal site
was operated for approximately two years. The system was
operated for 16 hours a day, 5 days a week for the first year. A
24-hour cycle of operation, 6 days a week was used for the
remaining year. During most of the treatment, steam injection
and vacuum extraction were used simultaneously. Vacuum ex-
traction alone was used when the boilers were inoperable, during
interim soil sampling activities, and at the end of the remediation.
Vacuum extraction used alone after steam injection is expected
to dry and cool the soil and remove contaminants from lower
permeability soils.
! Injection of High Quality Steam
; (from boilers)
INJECTION
WELL
Steam Front (moving
through soil)
Vapor, Water and Contaminants
INJECTION
INTERVAL
CONFINING LAYER (e.g., day layer)
Figure 1. Conceptual operation of the SERP process beneath the soil surface.
Printed on Recycled Paper
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Demonstration Approach: The U.S. EPA Superfund Innova-
tive Technology Evaluation (SITE) program became involved with
th« la situ SERP technology developer after the system was
Installed at the Rainbow Disposal site. Pre-treatment soil sam-
pling and analyses occurred prior to full SITE program participa-
tion. Therefore, the focus of the Demonstration was on the
condition of the soil after treatment to determine if the technology
met the she-specific cleanup criterion of 1,000 mg/kg (ppm) of
total petroleum hydrocarbons (TPH, diesel). An economic analy-
sis of the system was also a primary objective for the Demonstra-
tion.
Before treatment, one to four samples from each of twelve bore-
holes within the defined perimeter of contamination were sampled
by the technology developer and analyzed for TPH and benzene,
toluene, ©thyfoenzene, and xylenes (BTEX). The pre-treatment
results will be used by the SITE Program in a non-critical evalua-
tion of the removal efficiency of the treatment.
The SITE program (EPA) performed post-treatment soil sampling
and analyses, Including sampling from boreholes adjacent to
(within four feet) and at the same depths as those sampled before
treatment. Additional samples at other depths were collected in
most of these boreholes. Twelve additional boreholes were also
sampled, including six outside the defined perimeter of contami-
nation for a total of 24 boreholes. Samples collected after treat-
ment were analyzed for TPH, BTEX, and total recoverable
petroleum hydrocarbons (TRPH). Six sets of triplicate samples
were collected at randomly determined sampling locations to
assess soil contaminant spatial variability. The data collected from
post-treatment sampling and analysis has been used in a
geostatistteal model to determine the likely distribution of contami-
nation remaining in the soil and the statistical significance of the
results.
A detailed economic analysis of this full-scale technology applica-
tion will be performed utilizing monitoring data (i.e., water, chemi-
cal, and gas usage; waste generation; and maintenance needs).
This data was collected by the developer with oversight by the
SITE program during the course of operation. This analysis will
focus on the actual costs of the full-scale remediation as well as
theoretical costs at another site.
Preliminary Results: Preliminary evaluation of the post-treat-
ment data suggests the following conclusions:
• The geostatistical weighted average soil TPH concentration in
the treatment area after treatment was 2,290 mg/kg. The 90
percent confidence interval for this average concentration is
996 mg/kg to 3,570 mg/kg, which shows that there is a high
probability that the technology did not meet the cleanup crite-
rion. Seven percent of soil samples had TPH concentrations in
excess of 10,000 mg/kg.
• The geostatistical weighted average soil TRPH concentration
was 1,680 mg/kg with a 90 percent confidence interval of 676
mg/kg to 2,680 mg/kg. Levels of BTEX were below the
detection limit (6 ug/kg) in post-treatment soil samples; BTEX
was detected at low mg/kg levels in a few pre-treatment soil
samples.
• Analysis of triplicate samples showed marked variability in soil
contaminant concentration over short distances. Analogous
results for TPH and TRPH triplicate samples suggest that the
contaminant concentration variability exists within the site soil
matrix and is not the result of analytical techniques. This
inhomogeneity is the reason that confidence intervals for the
average concentrations are so large.
• The data suggests that lateral or downward migration of
contaminants did not occur during treatment.
Key findings from the demonstration, including complete analyti-
cal results and the economic analysis, will be published in an
Innovative Technology Evaluation Report. This report will be
used to evaluate the in situ SERP technology as an alternative
for cleaning up similar sites across the country. Results will also
be presented in a SITE Technology Capsule and a videotape.
For Further Information:
EPA Project Manager:
Paul dePercin
U.S. EPA Risk Reduction Engineering Laboratory
Office of Research and Development
26 West Martin Luther King Drive
Cincinnati, OH 45268
(513) 569-7797
" 'US. Governmant Printing Office: 1994 — 560-067/80252
United States
Environmental Protection Agency
Center for Environmental Research Information
Cincinnati, OH 45268
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EPA
PERMIT No. G-35
EPA/540/MR-94/510
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