Case Studies of 1,4-Dioxane Releases, Treatment, and Drinking Water Contamination - Environmental Investigation and Remediation - page 375

Resources (DNR) recommended discharge of wastewater into ini ltration lagoons and removal of
natural geologic barriers between the pond bottom and the water table 15-40 ft below to facilitate
slow ini ltration to groundwater (Kellogg, 2005). The state issued a permit in 1964 to install a
three-million-gallon wastewater lagoon to hold and ini ltrate process wastes, which may have con-
tained 1,4-dioxane in concentrations as high as 25 mg/L (City of Ann Arbor, 2006; SRSW, 2006);
other sources familiar with the case state that the 1,4-dioxane concentration in wastewater may
have been higher, in the range of 200-300 mg/L. * After installing two additional lagoons in 1966
and 1967, the company still required additional wastewater capacity. In 1976, DNR granted P/GSI
temporary permission to try managing treated process wastes by using spray irrigation. Seven
months later, in May 1977, the Michigan Water Resources Commission issued a groundwater dis-
charge permit authorizing efl uent spraying onto open i elds on the company's 40-acre property.
Later, USEPA recommended that Gelman drill an injection well, which they did in 1981. The
injection well was drilled at a cost of approximately $1,000,000. The well was drilled more than 1
mile into sandstone (the Mt. Simon Formation), which is geologically isolated from shallow pro-
duction aquifers (Fotouhi et al., 2006).
In 1984, a University of Michigan graduate student from the School of Public Health, Dan
Bicknell, discovered 1,4-dioxane in Third Sister Lake near the P/GSI property in a section of the
Saginaw Forest owned by the university. The following year, 1,4-dioxane contamination was dis-
covered in nearby private wells by an investigation conducted by the Washtenaw County Health
Board. After learning of the discovery of 1,4-dioxane contamination in late 1985, P/GSI used a
water supply well to remove more than 25,000 pounds of 1,4-dioxane from groundwater near the
plant between 1987 and 1994. The contaminated water was not treated; instead, it was discharged
into the injection well under a USEPA permit. In 1994, P/GSI decided not to renew the injection well
permit because of the cost of upgrading and operating the well, and the well was sealed (Kellogg,
2005). P/GSI had permits for its wastewater disposal practices for the entire period in which
1,4-dioxane-laden wastewater was discharged; however, citizen groups allege that permit limits
were at times exceeded and other unpermitted discharges may have occurred. In any case, the per-
mitted practice of treating 1,4-dioxane-laden wastewater in unlined lagoons and spray irrigating
wastewater on lawns and i elds clearly contributed to the widespread contamination of groundwater
with 1,4-dioxane.
8.3.2 G EOLOGIC S ETTING
The advance and retreat of glaciers dei nes the highly heterogeneous hydrostratigraphy of the Ann
Arbor/Scio Township area. The subsurface consists of unconsolidated glacial outwash sediments,
tills, and lacustrine deposits. † Multiple glacial outwash channels provide high-permeability aqui-
fers facilitating rapid contaminant migration in different directions. The glacial deposits are up to
300 ft thick and overlie the Coldwater Formation of Mississippian age (i.e., somewhat older than
300 million years), which is predominantly shale (Brode et al., 2005; Fotouhi et al., 2006).
Groundwater is generally shallow, averaging 15 ft below the ground surface. Three major aquifers
were initially identii ed; they are designated as the Unit C3 (Core Area), Unit D0 (Western
System), and Unit D2 (Evergreen System) aquifers. A Unit E aquifer that is deeper was later
determined to be present.
A coni ning layer within the glacial sediments was thought to isolate deeper aquifers from
contamination. Subsurface characterization performed in 2001 revealed a window in the coni ning
layer that allowed contamination to migrate into deeper aquifers. The complex geology in the vicinity
of the P/GSI property contributes to the widespread nature of the contamination (MDEQ, 2005).
* Jim Brode (of Fishbeck, Thompson, Carr and Huber, Kalamazoo, Michigan, February 2008, personal communication).
† Lacustrine deposits are lake bed deposits.