Technical and Regulatory Guidance for In Situ Chemical ... - ITRC

Cont amination by PCE and TCE was found throughout the thickness of the alluvial aquifer
downgradient of the site at concentrations exceeding MCLs.
Impacted Receptors
Although the City of Wichita does not use water from the affected aquifer for municipal water
sup p ly , a few domestic wells were identified within one mile of the site. In addition, several
irrigation wells tapping the affected aquifer are present in Linwood Park and surrounding areas,
posing inhalation and contact risks to the public.
Remedial Objectives
The objective of remedial actions at this site is to reduce groundwater concentrations of PCE and
TCE to levels at or below their MCLs. Further, PCE and TCE present in the vadose zone must be
removed to prevent recontamination of the aquifer.
Selection of Technology and Design Parameters
This site was selected for implementation of innovative remedial technology, in the form of in situ
chemical oxidation, because the contamination plume was relatively small and well defined, and the
subsurface geology was simple, well characterized, and suitable for the p rocess. Injection of a liquid
solution of sodium permanganate (NaMnO
4) was selected as the remedial technology, based on its
relatively low cost (compared to traditional pump-and-treat systems), ease of implementation, and
demonstrated ability to oxidize PCE and TCE in groundwater. However, this technology was not
deemed effective at oxidizing these contaminants in the unsaturated zone, due to low permeability
and inability to evenly distribute the oxidant. Therefore, to remove PCE and TCE in the vadose zone,
a system of SVE wells was employed.
To remediate contaminated groundwater, the sodium permanganate was injected through an array
of hydraulic push probes at the source area. A 4% solution (25 mg/L permanganate) was used based
on a laboratory treatability study; however, this study did not take into account the chemical oxygen
demand of the aquifer sediments.
T o deal with vadose-zone contamination, an array of four SVE wells was installed around the
foundations of the buildings at the site, and piping was run from these wells to a master exhaust
blower. These wells were screened in the shallow clayey soils from approximately 8 to 13 feet below
ground surface (bgs), which places them just above the static groundwater level. Emissions
p ermit t ing from the SVE system were not required as the mass of contaminants removed was
anticipated to be less than 50 pounds per day.
Implementation of Technology
Prior to implementing the in situ chemical oxidation process, an array of 11 additional monitoring
wells was installed around and downgradient of the source areas to be treated. Wells were installed
in pairs, with one screened in the shallow portion of the aquifer and one in the deep portion of the
aquifer. These wells, along with existing monitoring wells adjacent to the site, were sampled prior
to and at intervals after treatment to evaluate the effectiveness of the remedy. Samples were tested
for PCE and TCE concentration, oxidation-reduction potential, pH, dissolved oxygen concentration,
conductivity, and temperature, and were examined for any free-phase oxidant solution present.
T he sodium permanganate solution was injected into an array of 33 hydraulic push probes on
November 1 to November 5, 1999. Injection depths were staggered throughout the source areas to
ensure even dispersion throughout the affected aquifer. A total of 757 gallons of 4% solution were
used, for an average of 23 gallons per well. However, due to local variations in hydraulic
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