4.4.5.3   Long-Term Effectiveness and Permanence -- Alternative 5

The plasma torch technology can be used to treat materials
contaminated with a number of different inorganic, organic,
highly toxic, or highly concentrated chemicals.  Residual risks
may be posed by chemicals not removed from the contaminated
materials during treatment.  The following sections discuss
performance data, factors that influence performance, and
limitations of the technology.

Plasma Torch Performance

One advantage of plasma torch is the production of vitrified
solids upon the melting of soil.  Its ability to produce a mass
capable of resisting the leaching of the immobilized contaminants
when contacted by water or other liquids is important. 
Experience suggests that vitrified solids are durable.
 
A disadvantage of plasma torch is that operation experience and
performance data for the technology are limited.  Pilot-scale
performance data from demonstration tests of the plasma torch
technology conducted at the DOE's component Development and
Integration Facility in Butte, Montana, under EPA's SITE program
were collected for solids, vapor treatment system and emissions,
maintenance, and post-treatment.  The feed soil consisted of a
mixture of Superfund site soil classified as high metals-bearing
soil and 10 percent by weight No. 2 diesel oil.  The most
significant metals found in the soil were aluminum, calcium,
iron, potassium, sodium, and zinc.  Zinc oxide and
hexachlorobenzene were spiked to levels of 28,000 and 1,000 ppm,
respectively, into the mixed soil (EPA 1992d).  With a feed rate
of 120 pounds per hour and torch power of 410 to 460 kW, 800
gallons of scrubber liquid was generated for a total feed of 660
pounds.  The DRE of plasma torch for hexachlorobenzene, which is
reportedly harder to destroy than PCBs, was determined by
analyzing the feed soil and the stack gas concentrations
(Eschenbach 1993).  The mean level of hexachlorobenzene in feed
soil samples was 972 ppm.  No hexachlorobenzene was detected in
the stack gas, and the DRE ranged from 99.9968 to 99.9999.  Based
on the temperatures reached in the primary and secondary chambers
of the system, it can be expected that plasma torch completely
and irreversibly destroys PCBs in the treated soil, thus
eliminating PCB hazards to the environment and human health. 
Heavy metals are immobilized in a nonleachable vitrified slag
according to TCLP analyses performed on the treated soil.  It is
anticipated that the components in treated soil would remain
stable in the vitrified slag indefinitely; however, the vitrified
slag would be properly tested and disposed of in the 30-acre
disposal site approved by local, state, and federal agencies.

Scrubbing and cooling water used in the process would have to be
disposed of at an off-site facility in accordance with the ARARs
discussed in Section 4.4.5.2.  Provisions for cleaning and
eliminating residues in and on equipment should be planned and
implemented.  

Although performance data for the SITE demonstration are readily
available, they provide only limited information because the feed
characteristics used during the SITE demonstration are different
from the wastes at the CD sites and because a small scale unit
was used during the SITE demonstration.  No design, operation, or
testing experience is available for the larger unit.  These
reasons prevent accurate emission rates, emission constituents,
utilities requirements, supplies usage, and gas treatment costs
to be estimated.

Factors that Influence Performance

Performance of the plasma torch technology is primarily
influenced by the water content of the waste and the waste
characteristics, including the quantity and chemical
characteristics of the material.  The moisture content of the
majority of the soil and sediment at the CD sites is estimated to
be 10 percent, which is acceptable for plasma torch.  Sludge from
the Winston-Thomas Sewage Treatment Plant is estimated to be 30
percent solids.  Combustion of high moisture-containing materials
may be possible at increased residence times; however, the energy
costs would increase, making plasma torch an impractical
treatment option for materials with a high moisture content.  A
dewatering system can be implemented to decrease moisture
content. Plasma torch technology can treat highly concentrated
wastes and there is no theoretical upper bound on the contaminant
concentration that can be treated.

Chemical characteristics of the feed material are important to
assess the potential for hazardous air emissions.  The primary
contaminants of concern are PCBs, dioxins, and furans.  The
scrubber solution and operating temperatures of the gas handling
system would be selected based on the chemical composition of the
feed.  As a result, unknown contaminants could be emitted to the
atmosphere.  In addition, if unknown chemicals exist in the feed,
the interaction of chemicals in the plasma torch centrifugal
furnace can cause unwanted decomposition and formation of
hazardous gases.  Testing is recommended at all CD sites to
determine exact chemical concentrations of the feed materials.

Limitations

The limitations of plasma torch include lack of experience in
treating PCB-contaminated material, increased electrical
requirements of treating feed materials with a high moisture
content, feed material composition, and the potential for
emissions.  The lack of experience in treating PCBs with plasma
torch limits the amount of available performance data.  As a
result, it has not been sufficiently demonstrated that PCBs,
dioxins, and furans can be destroyed by plasma torch.  In
addition, utility usage and emission rates are inconclusive.  An
extensive treatability study is recommended to provide conclusive
results for plasma torch to determine PCB DRE, gas treatment
system requirements, emissions characteristics, and operating
parameters.  Plasma torch is not suitable for treating
contaminated water or materials with increased moisture content
because of the increased costs imposed by increased electrical
usage.  Other cost-effective methods exist for treatment of
materials with high moisture content.

Feed material composition limits performance because it impacts
the ability of the plasma torch vitrification process to form a
durable product.  Also, combustible materials generate gases and
volatilizes inorganics that carry contaminants throughout the
process if not treated.  These contaminants increase the quantity
of secondary contamination, complicate treatment, and at high
concentrations, may be cost prohibitive (EPA 1992c).  Extensive
testing should be conducted to determine the feed
characteristics.

Also, destruction of PCBs by plasma torch creates and potentially
emits hazardous gases to the atmosphere.   Proper design and
operation of a gas treatment system reduces the amount of
hazardous gases emitted to the atmosphere to below acceptable,
permitted standards.