4.4.3.3   Long-Term Effectiveness and Permanence -- Alternative 3

The long-term effectiveness of the DAVES was assessed in terms of
the risk remaining after treatment.  Risks may be posed by
chemicals not removed from the contaminated material during
treatment.  Performance data, factors that influence performance,
limitations of the DAVES technology, and additional information
needed to evaluate the technical feasibility of the technology
are discussed below.

Desorption and Vaporization Extraction System Performance

The DAVES has not been used at full scale to remediate a
hazardous waste site.  Pilot-scale tests using the full-scale
DAVES have been conducted.  Table 4-9 presents the results of 14
tests conducted on PCB-contaminated harbor sediments.  The tests
ranged in duration from 0.5 to 5.5 hours.  The test results show
that the average PCB concentration was reduced from 47.4 ppm in
untreated sediments to 1.5 ppm in treated solids.  Data
concerning the stack gas emissions are not available.  The
quality of all data available is unknown.  No data is available
concerning the effectiveness of DAVES for treating soils or
sludge.

Factors that Influence Performance

The degree to which the DAVES process is able to remove
contaminants from wastes and be cost effective depends on certain
waste characteristics.  These characteristics are discussed
below.

          Sediment particle size distribution -- Contaminants
          tend to sorb preferentially to finer-sized particles,
          and fine solids may be difficult to remove from the gas
          stream.  The DAVES process is a vertically-oriented,
          fluidized-bed system; therefore, contaminated materials
          with a large amount of fines may impact the APC
          equipment, and treatment rates for contaminated
          material treatment may be significantly reduced.  

          Organic matter -- Organic compounds with high
          octanol/water partition coefficients tend to sorb to a
          greater degree to soils and sediments that contain high
          levels of organic matter.

          Moisture content -- The DAVES process is applicable to
          wastes with a moisture content ranging from 10 to 70
          percent.  Wastes with a moisture content of greater
          than 70 percent must be dewatered, and water can be
          added to the process to increase the moisture content
          of dry wastes.

          Contaminant concentration -- RSI claims that the DAVES
          process can treat wastes with a maximum total organic
          contaminant concentration of 5 percent.  The rate of
          contaminant desorption from soils and sediment depends
          on the concentration of the contaminant.


                                 


Contaminant and Waste Treatment Limitations of Desorption and
Vaporization Extraction

The contaminant and waste limitations of DAVES are similar to
those of other HTTD systems (see Section 4.4.1.3).