4.4.7.6   Implementability -- Alternative 7

Implementation considerations for solvent extraction systems
include technical feasibility, administrative feasibility, and
availability of services and materials.  Additional information
is also needed to implement solvent extraction systems.  These
considerations are discussed below.

Technical Feasibility

The technical feasibility of implementing the solvent extraction
technology depends on (1) operating experience and technical
difficulties and (2) system reliability.  These considerations
are discussed below.

Operating Experience and Technical Difficulties

Planned and unexpected delays have been associated with the
implementation of this technology.  Expected delays associated
with preventative maintenance have occurred, as well as time
allowed for repairs to equipment during cleanup.  For the
B.E.S.T.  system, an average of 908 hours per year has been spent
on overall system repairs (EPA 1993d).  Assuming an 85 percent
online factor for the full-scale unit, CF Systems estimates that
an average of 850 hours per year is spent on overall LG-SX system
repairs (EPA 1990b).

During the CF Systems pilot-scale demonstration of LG-SX at the
New Bedford Harbor site in New Bedford Harbor, Massachusetts, the
vendor encountered some operational problems (EPA 1990b).  In
order to simulate a full-scale cleanup, a 5-ton-per-day
pilot-scale unit was used to treat contaminated sediment, and the
sediment waste stream was recycled.  Problems encountered are
detailed below.

          The internal surfaces of the extractor hardware and
          piping collected PCBs because PCBs are soluble in oil
          and grease, which was used to coat these surfaces.

          The unit intermittently retained feed material solids
          in equipment dead spaces and discharged them during
          subsequent passes.

          Because of poor performance of the cartridge filter,
          solids were observed in the extract samples, which were
          expected to be solids-free.

          The extractor and treated sediment hardware contained
          organic sludge from prior use of the unit at a
          petroleum refinery, thus preventing complete
          interpretation of data.

          Low-pressure dissolved propane caused foaming to occur
          in the treated sediment product tanks, which in turn
          affected sample collection and caused frequent overflow
          of treated sediment into a secondary product tank.

CF Systems attributes these complications to the fact that the
sediment stream was recycled, which would not normally occur in a
full-scale unit.  CF Systems claims that with some design
modifications and stricter operational controls, a full-scale 
LG-SX unit could be implemented successfully.  Other potential
implementability problems include the flammability of the
solvents used for extraction and the LG-SX system's
nonapplicability to waste types containing greater than 15
percent fines.  The latter limitation would pose a potential
implementation problem for the 17-acre tertiary lagoon at the
Winston-Thomas Sewage Treatment Plant site, which contains PCB-
contaminated clay.  Soils with a high clay content are difficult
to treat by solvent extraction because the PCBs are strongly
adsorbed to the fine soil particles.  

Treatability results from the NCS-Stockton site show that the
Terra-Kleen Solvent Extraction Treatment System required 57 wash
cycles to lower the PCB concentration in soil from 300 to 6.0
mg/kg (EPA 1995).  During another treatability study, soil with a
high fines content was treated using the B.E.S.T.  system at the
Paoli Railyard site in Paoli, Pennsylvania.  Results indicate
that the B.E.S.T.  system did not attain the performance criteria
of less than 2 ppm.  The PCB concentration was measured at 39 ppm
and 16 ppm for the third and sixth extraction stages,
respectively.  The soil contained an initial level of 920 ppm of
PCBs.  The PCB concentration in the treated soil after the fifth
stage was almost the same as after the sixth stage, indicating a
diminished effectiveness in the later cycles.  During the test,
it was also observed that a large amount of fine particles
remained suspended in the extract.  The settling times recorded
for these extractions was very long (Groundwater Technology
1991).  In order to minimize this settling time during full-scale
operation, the system would require the addition of a high-speed
centrifuge; therefore, lagoon clays may require additional
handling consisting of mixing the clayey waste with the lagoon
sludge so that the waste could be treated without requiring an
excessive number of wash cycles and to prevent the need for
centrifugation.

System Reliability

The only data available for cleanups in which PCBs were the main
concern are pilot-scale tests; however, RCC's B.E.S.T.  unit was
tested at full scale at a site contaminated with PCBs, but PCBs
were not the main contaminant of concern.  Therefore, the
reliability of solvent extraction has not been established for
full-scale PCB cleanups.

Administrative Feasibility

The administrative feasibility of solvent extraction depends
primarily on the ability of a solvent extraction system to
receive all necessary federal, state, and local permits.  The
solvent extraction system would have to be tested to evaluate
whether the system can meet the required performance standard for
PCB removal of 2 ppm.  An off-site TSCA regulated landfill would
have to be identified for the disposal of oversized materials. 
The landfill will need to have the appropriate capacity and be
willing to accept the waste.  In addition, state and federal
authorities would have to approve the disposal.  Common permits
for construction of required facilities and the concrete pad
would need to be obtained.  Permits may also be required for road
improvements and construction.

Availability of Services and Materials

PRC identified three vendors that supply the solvent extraction
technology.  RCC's B.E.S.T.  system has been successfully
demonstrated at full scale.  RCC's current full-scale unit is
limited to the treatment of sludges and slurries; therefore, if
this vendor is selected, either the soils must be converted to a
slurry or a unit capable of handling soils would need to be
constructed.  Both CF System's and Terra-Kleen's Solvent
Extraction Treatment System have been successfully implemented at
pilot scale, and both vendors plan to implement their systems at
full scale at the New Bedford Harbor site in New Bedford,
Massachusetts, and the NCS-Stockton site in Stockton, California,
respectively.  In order for Terra-Kleen's system to meet
remediation time requirements, a large area would be required to
set up the roll-off units.  All representative vendors should be
able to supply systems to meet the capacity requirements of the
CD sites.

The fenced area reserved for the CTF should provide adequate
space for the treatment and temporary storage of the contaminated
material.  A pad should be constructed at the location of the
system position.  In addition, storage facilities for process
equipment, chemicals, untreated materials, and treatment
residuals should also need to be constructed.  The fence
installed around the perimeter of the CTF should provide
security.  A heated enclosure should be constructed for the
system so that all-weather operations can be achieved. 
Construction of the support facilities would need to be completed
before mobilization of the solvent extraction system can begin. 
After construction is complete, the process equipment can be
transported to the site.  The length of time required for this
preliminary construction will vary depending on the requirements
of the selected system.

Additional Information Needed to Implement Solvent Extraction

In order to assess solvent extraction's potential effectiveness
in treating contaminated materials at the six   CD sites,
additional waste characterization studies would need to be
performed.  As discussed above, information regarding the
moisture content, particle size, physical characteristics, and
organic content of the wastes should be required to determine the
total extractable fraction.  Additionally, the concentration of
PCBs present and the quantity of soil, sediment, and sludge to be
treated should be determined.  With this information, a more
accurate assessment of the system's ability to treat the wastes
from the six CD sites could be made.

Treatability testing is also needed to predict the performance of
solvent extraction for removing and destroying PCBs.  The
treatability test should use a variety of solvents to determine
the best solvent for treating PCB-contaminated materials and the
approximate number of solvent washes required to reduce the PCB
concentration in the contaminated materials to below 2 ppm.