4.4.7.4   Reduction of Mobility, Toxicity, or Volume through
Treatment -- Alternative 7

This evaluation criterion addresses the statutory preference for
selecting remedial actions that employ treatment technologies
that permanently and significantly reduce the toxicity, mobility,
or volume of hazardous substances.  This preference is satisfied
when treatment reduces the principal threats at a site through
destruction of toxic contaminants, reduction of the total mass of
toxic contaminants, irreversible reduction in contaminant
mobility, or reduction of the total volume of contaminated media. 
Solvent extraction systems reduce the toxicity and volume of
contaminated material by solubilizing and removing contaminants
from the waste matrix and concentrating them in oils in the
solvent recovery systems.  The ability of solvent extraction
systems to reduce the toxicity or volume of contamination at a
site is assessed based on the following considerations:

          Reduction in toxicity of contaminated material
          Reduction in volume of contaminated material
          Irreversibility of treatment

Each of these considerations is addressed below.

Reduction in Toxicity of Contaminated Material

Toxicity of contaminated material is reduced by solvent
extraction through the removal of contaminants from waste.  The
separated contaminants are concentrated into a small volume of
oily waste that would require further treatment.  The
concentration of metals in the treated solids also affects the
disposal options for the treated solids.  Solvent extraction does
not remove metals from wastes; therefore, treatment of wastes
containing metals above the TCLP standards may produce treated
solids that exceed RCRA TCLP standards or that may pose a risk at
the site.  In this case, treated solids would require further
treatment before disposal.

Reduction in Volume of Contaminated Materials

Solvent extraction may reduce the overall volume of contaminated
material up to 0.01 percent of the original waste volume
depending on the volume of the total extractable fraction (EPA
1994b).  The nature of the contaminants present also determines
the disposal requirements for concentrated oily waste and water. 
In general, water products do not normally require further
treatment and can be sent to the local POTW, but sampling and
analysis should be conducted prior to disposal.  The concentrated
oily waste  would require further treatment such as incineration
or dechlorination.

Irreversibility of Treatment

Solvent extraction is primarily an irreversible volume reduction
process.  It does not destroy hazardous contaminants but
separates contaminants from soils, sediments, and sludges,
thereby reducing the volume of the contaminated material that
must be treated.