United States
Environmental Protection
Agency
SUPERFUND INNOVATIVE
TECHNOLOGY EVALUATION
Demonstration Bulletin
Steam Enhanced Remediation
SteamTech Environmental Services, Inc.
Technology Description: Steam Enhanced Remediation
(SER) is a process, in which steam is injected into the
subsurface and volatile and semivolatile contaminants are
collected in the vapor phase, in the aqueous phase, and
possibly as a nonaqueous phase liquid (NAPL). The general
approach employed is to surround the contaminated zone
with steam injection wells to displace NAPLs and groundwater
to centrally located extraction wells. Residual contaminants
are vaporized when the heat front reaches them and collected
by vacuum extraction. Steam migration is monitored using
Electrical Resistance Tomography (ERT) and thermocouples.
SteamTech Environmental Services, Inc. has successfully
applied this technology for the recovery of contaminants from
soils and aquifers, and at a fractured granite site at Edwards
Air Force Base, California. The demonstration at the former
Loring Air Force Base Quarry site was the first time that the
steam injection technology was used at a contaminated site
composed entirely of fractured limestone.
Waste Applicability: Volatile and semivolatile organic
compounds (VOCs), including chlorinated solvents, fuels, and
creosote, have been successfully recovered from field sites
using steam injection. The steam injection process is equally
effective above and below the water table. It has been used
in heterogeneous soils comprised of layered soils with widely
contrasting permeabilities. Steam injection at sites which have
a component of fractured bedrock indicate that the process
may be applicable to fractured rock. This demonstration
further tests the applicability of the process in fractured
limestone.
Evaluation Approach: The Maine Department of
Environmental Protection and U.S. EPA evaluated the SER
process at the former Loring AFB Quarry site in Limestone,
Maine. The SER process was evaluated in fractured bedrock
to determine its ability to enhance the recovery of VOC,
gasoline range organic (GRO), and diesel range organic
(DRO) NAPLs from sparsely fractured limestone.
The evaluation was initiated by characterizing the fracture
system and the contaminant distribution through rock cores,
conventional borehole geophysics, and rock chip samples
that were extracted in methanol and analyzed by EPA Method
8260. The transmissivity of the fractured rock system was
determined in 10 foot intervals by using packers to isolate
the intervals. Interconnectivity testing was used to determine
the major interconnections between boreholes. Based on
this characterization information, an injection, extraction and
monitoring system was designed which included injection into
three boreholes in the eastern part of the site. Extraction of
groundwater and vapors was conducted from 10 boreholes
in the central and western portions of the site. Daily samples
of the effluent water and vapors were collected to determine
the mass of contaminants recovered. Pre- and post- treatment
groundwater and rock chip samples will be used to evaluate
contaminant reductions. Three deep wells, two of which were
angled to go under the treatment zone, will be used to evaluate
whether contaminants were mobilized downward during the
demonstration.
Because of the low injection rates and the fact that some
extraction boreholes were not recovering a significant amount
of contaminants, some of the extraction wells were converted
to injection wells after about 30 days of injection. Injection
continued for a total of 83 days, with extraction throughout
that period and continuing for one week after injection was
halted.
Preliminary Results: Figure 1 shows that initially the effluent
water concentrations decreased with time, as is common in
groundwater pump-and-treat systems. However, after
approximately 3 weeks of steam injection, the concentrations
started to noticeably increase, eventually reaching concen-
trations that were more than an order of magnitude greater
than initial concentrations. Concentrations remained high at
the end of the demonstration. The final sample had a DRO
concentration of 17,800 pg/l (not shown on the graph):
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Lodng Aqueous Concentrations
Lorlng Vapor Phase Concentrations
Surnma Cannlstor Data
Data
Figure 1 .
Figure 2 shows notable increases in vapor phase
concentrations after 3 weeks and when pressures in the
subsurface were reduced by halting steam injection.
Subsurface temperature and ERT monitoring indicated that
steam and hot water condensate followed narrow paths in
the limestone, and only a small fraction of the rock was heated
to steam temperature.
Even though this demonstration was not taken to completion
due to funding limitations, the observed steam flow and
removal mechanisms in this highly complex system suggest
that SER can be effective for increasing the mass removal
rate compared to more traditional methods.
Figure 2.
For Further Information:
Eva Davis, Technical Lead
U.S. Environmental Protection Agency
Office of Research and Development
National Risk Management Research Laboratory
P.O. Box 1198
Ada, Oklahoma 74820
(580) 436-8548 Fax: (580) 436-8703
E-mail: davis.eva@epa.gov
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