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

Approximately 8,000 lbs. of ozone were injected into the subsurface over a 12-month period. In
general, effective ozone transport and ozone gas mass transfer to the aqueous phase were observed.
Ozone concentrations ranging from less than 1 ppm to several hundred ppm were measured in soil
gas over the entire area of the monitoring network. These concentrations were several orders of
magnitude below the injection concentration of 5 percent (50,000 ppm), which reflects rapid
subsurface ozone reaction and degradation. Dissolved ozone concentrations up to 1.4 ppm were
measured in soil moisture samples collected from pressure-vacuum lysimeters.
Soil samples collected at paired locations prior to in situ ozonation, and during February, June, and
Oct ober 1998 showed an average 93 percent reduction in PCP and PAHs. The maximum
pretreatment soil contamination was reduced greater than 98 percent, from an initial value of 220
mg/kg PCP and 5,680 mg/kg total PAHs, to below detection limits.
Significant contaminant mass reduction was reflected not only in soils data, but also in substantial
reductions in aqueous-phase concentrations of PCP and PAHs. The lysimeter data showed several
orders of magnitude reduction in dissolved PCP and PAHs at the first sampling event, conducted
aft er approximately one month of ozone injection in the 5-spot area. In addition, an individual
lysimeter produced liquid NAPL at the beginning of the project but not after one month of treatment.
Ozone consumption was calculated at approximately 7 pounds of ozone per pound of PCP and PAHs
destroyed. This number is highly conservative, because the system was optimized for maximum
ozone loading, and not for efficient ozone usage. Combining in situ ozonation and bioremediation
can significantly decrease ozone consumption.
Point of Contact
Wilson S. Clayton, Ph.D.
Aquifer Solutions, Inc.
28599 Buchanan Drive
Evergreen, CO 80439
(303) 679-3143
wclayton@aquifersolutions.com
7. San Francisco Bay Sites managed by the California Regional Water Quality Control
Board
Five pilot- or full-scale applications of in situ chemical oxidation (using potassium permanganate
or hydrogen peroxide) were performed in 1999 at industrial sites in the San Francisco Bay area.
The contaminants of concern included perchloroethylene, trichloroethylene, vinyl chloride,
chloroethane and benzene. The soils at these sites are typical of the South Bay area, and consist
of a mix of silts, sands, and clay which is fairly tightly packed and therefore not particularly
permeable. Direct-push injectors were used to deliver the oxidants to the subsurface. Pre- and
post-injection monitoring was performed to evaluate the performance of the oxidants.
Based on the results of the post-injection monitoring, which indicated either a significant
rebound or negligible reduction of contaminant concentrations, the Regional Water Quality
Control Board concluded ISCO was “ineffective” at cleaning up the groundwater at four of these
sites, and “somewhat effective” at the fifth site. However, several aspects of these projects
contributed to the poor performance of ISCO. First and foremost, the low permeability of the
soils at the sites did not allow adequate dispersion of the oxidants or sufficient contact with the
contaminants. It is likely that preferential flow pathways were the dominant method of transport
of the oxidant, thus bypassing large volumes of the subsurface.
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