Case Studies of 1,4-Dioxane Releases, Treatment, and Drinking Water Contamination - Environmental Investigation and Remediation - page 369

8.1.4 D ISCUSSION
Figure 8.2 shows that by 1999, conditions at the SRC site caused 1,4-dioxane to migrate about 2.3
times farther than total VOCs. Contaminant transport modeling accounting only for retardation
and dispersion, but discounting the biotransformation of contaminants, accurately predicted
1,4-dioxane migration. The model overestimated the migration of chloroethane and THF because
these contaminants are biodegradable (Nyer et al., 1991).
The remedies selected for this site—soil bioremediation, SVE, air stripping, and carbon
adsorption—are effective at removing the bulk of the chlorinated VOCs at the site, but are rela-
tively ineffective at removing 1,4-dioxane. The areal extent of 1,4-dioxane distribution changed
little between 1999 and 2008, which suggests that natural attenuation is also not actively removing
1,4-dioxane at this site. The primary means of attenuating 1,4-dioxane have apparently been by
pumping 1,4-dioxane out of the shallow aquifer and discharging to the POTW, where it is substan-
tially diluted prior to discharge to the receiving water, where it is presumably diluted further. The
part of the plume outside the inl uence of pumping wells will eventually attenuate through disper-
sion and dilution from recharge due to rainfall, irrigation, and losing streams. Risk of exposure at
this site was eliminated by connecting private well owners to the municipal water supply, which
was not contaminated by this site, and by frequent monitoring of the nearest actively used supply
wells. Maximum concentrations of 1,4-dioxane measured along the plume centerline in 1990,
~2300 ppb, were relatively low compared to the much higher concentrations seen at other solvent-
waste handling and recycling facilities. The 2300 ppb maximum was measured 10 years after the
cessation of active discharges, raising the possibility that the bulk of the 1,4-dioxane mass has
dispersed much farther downgradient.

8.2 SOLVENT SERVICES SITE, SAN JOSE, CALIFORNIA
In Silicon Valley, Solvent Service Inc. (SSI) opened a facility in 1973 to reclaim spent solvents and
other wastes from printed circuit board manufacturers, wafer fabs (semiconductor manufacturers),
and other electronics and industrial manufacturing facilities. SSI treated solvents under a treatment,
storage, and disposal facility (TSDF) permit at a facility located on a 3-acre parcel in an industrial
area of San Jose, California. Subsurface contamination was investigated beginning in 1983 when
leaking tanks were discovered (Cal EPA, 2000). SSI employed a wide range of chemical engineer-
ing processes to rei ne solvents, metal plating wastes, and other waste streams. Solvents were rei ned
through the use of distillation and gravity phase separation. As discussed in Chapter 1, distillation
of vapor-degreaser still bottoms will further concentrate the “high boiler” stabilizer compounds
such as 1,4-dioxane.
VOCs were i rst detected in shallow groundwater beneath underground solvent-storage tanks,
wash-down sumps, a drum-storage area, and an unloading area for solvent tank trucks (Cameron-
Cole, 2001). Initially, more than 20 contaminants were discovered, including VOCs associated with
production of printed circuit boards, semiconductors, and other electronic parts. The VOCs were
detected at extremely high levels, including occurrences of free-phase solvent. The chemicals
detected included methyl ethyl ketone, acetone, xylene isomers, perchloroethylene, trichloroethylene,
methyl chloroform, 1,1-dichloroethane, cis -1,2-dichloroethylene, and others. Soil concentrations of
total VOCs in some locations were in excess of 10,000 ppm (i.e.,

1%). Ethenes (perchloroethylene
and trichloroethylene) were quantii ed in soil at more than 30 0 0 ppm, and ethanes (pr ima r ily dichlo-
romethane and methyl chloroform) were present at more than 1700 ppm. In groundwater, ketones
(methyl ethyl ketone and acetone) were found as high as 21,000 ppm; ethenes were at 153 ppm, and
ethanes were at 468 ppm. In addition to having some very high concentrations of contaminants, the
site also gained notoriety for a 1992 acid leak that caused a toxic cloud and injured 11 people, as well
as for shutting down a 3-mile stretch of the U.S. 101 freeway and causing evacuation of a nearby
neighborhood (Chui, 1995). The SSI site was briel y added to the Superfund List on June 21, 1988,

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