4.4.1.4   Reduction of Mobility, Toxicity, or Volume Through
          Treatment -- Alternative 1

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. 
HTTD systems reduce the toxicity and volume of contaminated
material by thermally desorbing contaminants from the waste
matrix in the processor and concentrating them in oils or aqueous
streams in the condensation systems.  HTTD is not an
immobilization technology; therefore, the mobility of
contaminants is not reduced.

The ability of thermal desorbers to reduce the toxicity or volume
of contamination at a site is assessed based on the following
considerations:



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

Each of these considerations is discussed below.

Reduction in Toxicity of Contaminated Material

In most cases, HTTD systems physically remove contaminants from
materials without altering the composition or toxicity of the
contaminants.  Results from a variety of SITE demonstrations and
full-scale cleanup studies indicate that HTTD systems can
effectively remove VOCs, SVOCs, PCBs, and furans to low residual
concentrations or to below detection limits in treated solids. 
The contaminants are condensed in the vapor recovery system and
require off-site incineration to destroy them.  

Irreversibility of Treatment

HTTD systems permanently remove contaminants from wastes. 
Desorption is a physical method of treating wastes that relies on
applying heat to waste to vaporize and thereby remove
contaminants from the waste.  The contaminants are not chemically
altered; that is, their chemical structure is not changed. 
Instead, their physical state is changed.  The contaminants
transform from a liquid or solid adsorbed to a solid matrix such
as soil to a gaseous phase that is removed from the HTTD
processor and condensed.

Reduction in Volume of Contaminated Materials

The volume of contaminated materials is reduced by HTTD through
the vaporization of contaminants and condensation in a vapor
recovery system, thereby transferring the contaminants from a
solid matrix to a liquid matrix.  The concentrations of the
contaminants in the oil and water from the vapor recovery system
depend on the solubility of the contaminants.  VOCs are generally
more soluble in water than are SVOCs; therefore, the condensed
water stream is likely to contain higher concentrations of VOCs
than SVOCs.  SVOCs tend to accumulate in the oil phase.  

During the Waukegan Harbor Superfund site remediation, the ATP
system treated 12,755 tons of contaminated soil and sediment at
feed PCB concentrations of about 1 percent.  About 200 tons of
waste oil was generated during the remediation of the site. 
Other ATP treatment residuals contaminated with significant
amounts of PCBs, including the activated carbon from ATP's flue
gas and water treatment systems and preheat cyclone fines, were
recycled to the ATP for treatment.  Therefore, the amount of
contaminated material was reduced to about 1.5 percent of the
original amount of contaminated soil and sediment.