Case Studies of 1,4-Dioxane Releases, Treatment, and Drinking Water Contamination - Environmental Investigation and Remediation - page 377

water supply is not threatened by 1,4-dioxane because the intake location is upstream of the
groundwater discharge area.
The i rst private well contamination was discovered in 1986, but it was not until the late 1990s
before full cleanup of off-site groundwater began. The delay was partly due to legal actions i led by
the State of Michigan and the city and to countersuits by P/GSI, as described in Section 8.3.6 . For
more than 10 years, off-site cleanup was limited to some extraction of contaminated groundwater
from a former supply well, and 1,4-dioxane continued to migrate away from the site. The plumes
have expanded at rates very close to the linear groundwater velocities (Fotouhi et al., 2006). 1,4-
Dioxane has migrated 3000 ft to the west of the site and as far as 9000 ft east of the site (according
to the MDEQ 85 ppb threshold) or farther when mapping is based on the limit of detection.
8.3.4 R EGULATION
Upon discovery of private well contamination by 1,4-dioxane, P/GSI provided bottled water for resi-
dents and businesses and agreed to contribute toward the cost of extending municipal water lines to
affected subdivisions (City of Ann Arbor, 2006). Because there were concerns over inhalation and
dermal exposure in addition to drinking water exposure, P/GSI arranged for families whose wells
had high levels of 1,4-dioxane to shower at a nearby hotel (Fotouhi et al., 2006). By 2000, more than
120 homes with contaminated private water supply wells had been connected to the municipal water
supply system (MDEQ, 2000). Washtenaw County staff collects regular samples from an additional
50 operating private wells near the edge of the plume. In 13 of these 50 wells, 1,4-dioxane levels
range from 1 to 24 ppb; the remainder are nondetect. P/GSI pays the costs for sampling and connect-
ing to the municipal supply (MDEQ, 2000).
Michigan does not have a state Maximum Contaminant Level (MCL) for 1,4-dioxane. Interested
elected ofi cials sought to adopt a Michigan MCL at 35 ppb. If adopted, the 1,4-dioxane MCL
would have been the i rst time that the State of Michigan developed a state drinking water MCL
that was not a federal MCL. The proposed MCL was opposed by the City of Ann Arbor, Washtenaw
County, and citizen groups as not being protective enough, while the Michigan Manufacturers
Association, P/GSI, and others objected that it was too restrictive. The basis for the proposed
MCL is explained in Chapter 6. In 1986, the State of Michigan recommended 3 ppb as a safe
standard for 1,4-dioxane in drinking water (City of Ann Arbor, 2006). In June 1995, the state
legislature amended the NREPA, increasing the generic residential cleanup criteria for 1,4-diox-
ane to 77 ppb for groundwater. In June 2000, the state adopted USEPA's methodology for calcu-
lating risk-based cleanup criteria, which resulted in the generic residential cleanup criteria and
the current drinking water criteria of 85 ppb. The 1,4-dioxane concentration in groundwater that
Michigan considers to be safe for venting to surface water used for human contact is 2800 ppb
(MDEQ, 2004).
Among the more interesting regulatory actions in the P/GSI case is the prohibition zone (PZ)
(depicted in Figure 8.4 ). In order to protect the public, the Washtenaw County Circuit Court issued an
order on May 17, 2005, to restrict the use of groundwater in portions of the City of Ann Arbor and in
Ann Arbor and Scio Townships. The order prohibits the use of groundwater that is or may become
contaminated with unacceptable levels of 1,4-dioxane in a mapped area called the PZ. A few of the
properties in this area receive their drinking water from private wells; however, most areas are already
connected to the city water supply (MDEQ, 2007). In the PZ area, the order prohibits the consump-
tion or use of well water, the installation of new water supply wells, and requires the proper destruc-
tion of all private wells at P/GSI's expense. P/GSI must also fund connecting properties within the PZ
that are on private wells to the municipal water supply. Exceptions are available for ground-source
heat-pump systems that operate with closed circulation loops and for dewatering wells used in
construction and maintenance. Property owners must disclose the order restrictions upon selling or
leasing a property within the PZ, as well as disclosing the presence of 1,4-dioxane contamination
beneath the property. Because the depth to groundwater in most areas of the PZ is about 40 ft, typical