Case Studies of 1,4-Dioxane Releases, Treatment, and Drinking Water Contamination - Environmental Investigation and Remediation - page 409

groundwater removed. The plant operated between 2000 and 2700 gpm throughout most of the
1990s. AFP 44 currently has the capacity to operate approximately 25 active upper-zone and four
lower-zone extraction wells, and 10 active upper-zone recharge wells. In addition to the extraction
wells, there are 65 upper-zone and 10 lower-zone wells in which water levels and water quality are
monitored on a regular basis. The air-stripper system continues to operate today in accordance with
the 1986 RAP; however, as will be discussed subsequently, the system is being upgraded with an
advanced oxidation treatment (AOT) system specii cally to address 1,4-dioxane contamination.
Once the AFP 44 remediation system was installed and demonstrated to be operating as designed,
subsequent remedial actions focused on potential groundwater contamination sources, especially
those associated with VOCs and chromium waste. SVE systems were installed between 1994 and
1996 at solvent contamination sites 1, 2, and 3. Soil excavation and off-site disposal was conducted
at shallow metals-contaminated sites 4, 5, and 6. Additionally, DPE was conducted at site 5 to
address deep vadose zone VOC contamination. Most of these remediation systems successfully
reduced contaminant levels to below agreed-upon standards, and the sites were documented as
having remedial action complete.
An additional set of remedial actions involved in situ treatment methods including chemical
oxidation (ISCO) and bioremediation/chemical reduction. The ISCO was focused on TCE and
1,1-DCE and utilized potassium permanganate (KMnO 4 ). This oxidizer has been effectively dem-
onstrated at numerous solvent sites and was pilot-tested in a series of large-scale injection programs
in the regional groundwater beneath soil sites 2 and 3. Over 1 million gallons of water containing
more than 40,000 pounds of KMnO 4 at concentrations ranging from 0.5% to 2% were injected at
these two sites over the course of the multiyear program. VOC destruction has been encouraging:
less than 10% of the maximum-measured VOC concentrations in groundwater remained after this
massive KMnO 4 injection. Monitoring and evaluation of the program is ongoing. An in situ biore-
mediation pilot study was performed in an area with chlorinated solvent and hexavalent chromium
contamination in the deep vadose zone and groundwater. Because hexavalent chromium was pres-
ent in this area, oxidation technologies could not be used. An emulsii ed mixture of vegetable oil
and sodium lactate was injected to create chemically reducing conditions, which would lead to
chemical reduction of hexavalent chromium to the less mobile and less toxic form, trivalent chro-
mium. Additionally, the injection would create favorable conditions for the growth of indigenous
bacteria capable of consuming the chlorinated contaminants, either directly or cometabolically.
This 2006-2008 study yielded mixed results and will need to be further evaluated to determine
whether the technology warrants application on a larger scale.
The TARP plant was constructed near Irvington Road and Interstate 19, northwest of AFP 44,
and placed in operation in September 1994 to contain the leading edge of the TCE plume. The sys-
tem has been operating continuously since that time, with the exception of brief maintenance-related
shutdowns. The system includes two separate well i elds, the south well i eld, extracting approxi-
mately 1000 gpm from i ve wells in the upper zone of the regional aquifer, and the north well i eld,
extracting 4000 gpm from four wells in the undivided regional aquifer. The combined extraction of
approximately 4900 gpm is treated by using air strippers, with GAC for off-gas treatment, and then
blended with water from other sources and distributed to the community. An estimated 3500 pounds
of chlorinated VOCs was removed from the drinking water aquifer between 1994 and 2008 (ADEQ,
2008). Because this water is provided to the community, a signii cant amount of public scrutiny has
been directed at the pumping, blending, and distribution, especially with respect to concentrations
of 1,4-dioxane in the groundwater.
8.7.6 1,4-D IOXANE D ISCOVERY AND R EGULATION
In 2002, 1,4-dioxane was discovered in inl uent and efl uent groundwater at the AFP 44 GWTP at
concentrations of approximately 10 μg/L. Ultimately, the 1,4-dioxane plume was determined to
extend over 5 miles and to have a slightly wider footprint than the chlorinated VOC plume. The