Systematic selection of off-gas treatment at the Savannah River Site Page: 3 of 11
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full-scale cleanup of the contaminated
ground'water began with the application of
pump-and-treat using air stripping.
Schedules and activities described in the
RCRA Post Closure Care Part B permit arc the
current drivers for the corrective action
program. Projects to add three air strippers
and four soil-vapor extraction units arc
currently in the design phase. 1990
Amendments to the Clean Air Act were signed
into law at approximately the same time pre-
project activities were started for the new
systems. As a result, engineering studies now
include assessing the need for off-gas
treatment systems, as well as identifying the
most appropriate treatment technology. The
purpose of this paper is to describe results of
the study performed to address these issues.
Air stripping and soil vapor extraction, as
stand alone treatment processes, transfer VOCs
to the atmosphere where they are dispersed,
diluted, and subsequently degraded by
reaction with hydroxl radicals. The treatment
systems in the A/M areas of SRS are not
considered major emission sources under South
Carolina Department of Health and
Environmental Control (SCDHEC) regulations,
and therefore do not require emission control.
The Air Quality Control Bureau of SCDHEC
currently regulates emissions from the
systems on a tonnage/year basis.
The 1990 Clean Air Act amendments identify
TCE and PCE as two of 189 hazardous air
pollutants that will require emission control
in the near future. The Environmental
Protection Agency (EPA) must establish
categories of sources that emit hazardous air
pollutants, and then promulgate regulations to
control emissions by source category. This
approach marks a shift from the risk-based
approach of the National Emission Standards
for Hazardous Air Pollutants (NESHAPs)
program, Section 112 of the Clean Air Act, to a
technology-based approach. As Hazardous Air
Pollutants (HAPs), the TCE and PCE will be
subject to what is called a Maximum
Achievable Control Technology (MACT),
defined as the average emission limit achieved
by the best-controlled 12 percent of existing
sources. MACT standards arc to be instituted
on major existing, new, and area sources that
emit HAPs. Major emission sources are
defined as any source emitting 10 tons/yr of a
single HAP or 25 tons/yr of any combination of
Air stripping was first demonstrated in M-
Arca in 1982. A pilot-scale unit verified the
removal efficiency of the technology at greater
than 99.99%, and as a result the technology
was further pursued. A prototype unit was
placed in operation in 1984 to acquire data
needed for the design of a full-scale system.
The original project activities were culminated
in 1985 when a full-scale system was brought
on-line. A separate plume of organic
contamination was identified near the Site
Admininistrative area (A- Area) and the
Savannah River Laboratory in 1987. To address
the plume in a timely manner and make
efficient use of existing resources, the
prototype unit used in the M-Area
experimental program was relocated to A-Arca
and brought on line in March 1992.
DESCRIPTION OF TECHNOLOGIES
Thermal incineration is a very simple, clean
method for destroying VOCs. The contaminated
gas stream is contacted with a fuel such as
methane or propane and is combusted. The
high temperature of combustion (typically
about 1200 - 1500 0 F) is sufficient to convert
the VOCs to carbon dioxide and water;
conversion efficiencies must be at least 99.99%
per SCDHEC regulations. Chlorinated VOCs
such as TCE and PCE will also form HC1 in the
exhaust stream, and the process equipment
must be protected from acidic corrosion. If the
levels of HC1 are high enough to exceed SCDHEC
emission limits, currently four pounds per
hour, a caustic scrubber must be added to
neutralize the HC1. An alternative method
would be to operate the unit at a lower flow
rate to make sure that the permitted HC1
emission rate is not exceeded. Based on the
long remediation times at most locations, a
limited treatment rate was not considered an
appropriate alternative for this study.
Thermal incineration systems have a relatively
low capital cost compared to other available
treatment methods. However, the operating
costs in thermal systems are high due to the
amount of fuel which must be used to heat the
air to the combustion temperature. The
addition of a scrubber also adds considerable
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McKillip, S.T. & Rehder, T.E. Systematic selection of off-gas treatment at the Savannah River Site, article, January 1, 1992; Aiken, South Carolina. (digital.library.unt.edu/ark:/67531/metadc1072116/m1/3/: accessed October 19, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.