Environmental Engineering Reference
In-Depth Information
construction activities are unlikely to encounter contaminated groundwater. The order requires that P/
GSI continue monitoring the deep plume beneath the PZ and install additional monitoring wells if
concentrations change in a manner suggesting that the plume is heading in a different direction than
anticipated in the delineated PZ. The restriction on new wells is enforced by the Washtenaw County
Department of Planning and Environment, which issues well permits in the PZ.
The PZ order is an institutional control mechanism that is effective to the extent property owners
within the designated area are aware of it and adhere to its requirements. During 2006, a small lake
in west Ann Arbor showed detections of 1,4-dioxane at 6 ppb. The lake had not previously shown
any 1,4-dioxane detections. Investigation of the contamination revealed that the owners of a local
inn and restaurant were using a well to cool the buildings and water the lawns. The owners did not
realize that they were in the PZ or that there was a 1,4-dioxane contamination problem in the area.
1,4-Dioxane levels in their cooling system water, which discharges into a storm drain that drained
to the lake, was several times higher than the 85 ppb action level (Davis, 2006b). In another example
of the limitations of institutional controls, the notii cation requirements for landlords and property
sellers published as ofi cial notices in the local newspapers apparently were not uniformly heeded
in the PZ. At an April 2007 public meeting on the P/GSI case, a resident complained that she had
rented a property within the PZ for a year before buying a house, also in the PZ, and neither her
landlord nor the house seller disclosed that the properties were in the PZ. The property owner com-
plained that she now owns a house in the path of or overlying a 1,4-dioxane plume that was not
disclosed to her, but she is required to disclose it when she sells. At the meeting, state ofi cials
announced a small expansion of the PZ in light of new monitoring data and resolved to reissue noti-
i cations to property owners (Davis, 2007).
8.3.5 T
REATMENT
P/GSI embarked on a series of treatability studies in the decades following the discovery of 1,4-di-
oxane contamination in private wells. Early treatability studies focused on separation methods using
gas-phase separation, such as air stripping and steam stripping, and on solid-phase separation using
GAC. P/GSI's treatability studies also tested destructive treatment methods including chemical
destruction using hydrogen peroxide, ozone, and chlorine; physical destruction using UV light; and
combinations of physical and chemical destruction methods. Biological treatability studies included
microbial methods such as activated sludge and bioactivated carbon, enzymes, and inoculation with
engineered organisms (Fotouhi et al., 2006).
Site remediation began with contaminated soil removal. The most highly contaminated soils
were removed in 1979 and 1987 (MDEQ, 2000). Groundwater remediation near the source zone
began in 1987 with the reinjection of contaminated water from a nearby supply well. This remedia-
tion continued until 1994, when P/GSI found it too expensive and impractical to renew their injec-
tion well permit. The injection well also had limited capacity; therefore, it could not accommodate
the purge volumes produced at the site. Between 1994 and 1997, there was a hiatus in off-site
groundwater remediation while P/GSI responded to a lawsuit i led by the Michigan attorney general
on behalf of the Department of Natural Resources to force P/GSI to clean up groundwater (City of
Ann Arbor, 2006).
Remediation of the two shallow aquifers has been under way since 1997. Treated groundwater
is discharged to Honey Creek, a small ephemeral tributary to the Huron River. This remediation
has signii cantly decreased the concentration and mass of 1,4-dioxane contamination in the shal-
low aquifers.
The selected remedy for full-scale groundwater treatment was UV light
+
hydrogen peroxide
(H
2
O
2
). P/GSI operated a full-scale UV
H
2
O
2
system at its facility to remediate groundwater con-
taining high concentrations of 1,4-dioxane. As of 2004, more than 60,000 pounds of 1,4-dioxane
had been extracted from the groundwater and destroyed by UV
+
+
H
2
O
2
since treatment began in
1997 (Brode et al., 2005).
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