Regulatory Policy Implications of 1,4-Dioxane - Environmental Investigation and Remediation - page 459

determination by regulatory agency health experts and proceed with testing at the same time and on the
same basis as all the other water utilities.
To determine the nature of known and potential contamination within the zones of contribution of
groundwater to water supply wells, USEPA developed a program to assess potentially contaminating
activities (PCAs) that could affect sources of drinking water. The 1996 amendments to the Safe
Drinking Water Act required that states develop Source Water Assessment Programs (SWAPs) to
delineate wellhead protection areas within zones of contribution to wells, and to inventory PCAs
that could contaminate wells. The inventory of PCAs typically focuses on known and ongoing
activities that have a potential to contaminate groundwater, as inventorying past activities typically
involves a greater level of effort. Because groundwater travels slowly, much of the contamination
occurring in water supply wells today is the result of legacy contamination from past industrial
activity. The detection of 1,4-dioxane in supply wells exemplii es legacy contamination that origi-
nated before the Montreal Protocol banned the use of methyl chloroform in 1996, when disposal of
1,4-dioxane-stabilized methyl chloroform vapor degreasing waste was the primary means by which
1,4-dioxane was released to soil and groundwater.
To anticipate 1,4-dioxane in public water supply wells, SWAPs should consider whether any of
the industrial activities that use 1,4-dioxane (listed in Chapter 2) operated in proximity to water
supply wells. This review of potential 1,4-dioxane releases should include industries that used
methyl chloroform, industries that produced 1,4-dioxane as a by-product, and destinations for 1,4-
dioxane-containing wastes such as cement kilns, landi lls, and solvent recycling facilities.
10.2.4 P REDICTING W ATER S UPPLY W ELL C ONTAMINATION
Knowledge of a 1,4-dioxane release within the zone of contribution to a supply well does not neces-
sarily predict that the well will become contaminated with 1,4-dioxane. Detailed analysis of plume
dynamics and the hydrogeologic setting is needed to coni rm that the 1,4-dioxane will arrive at the
well at detectable levels. Currently, plume characterization falls under the jurisdiction of state agen-
cies overseeing groundwater cleanups, while water supply well monitoring requirements reside with
the state agencies overseeing water utility compliance with drinking water standards. In many
states, these are two separate agencies that develop their own bureaucratic cultures and, while they
may communicate about groundwater contamination issues, that communication often does not
cause a corresponding measure of coordinated action. Drinking water agencies do not usually get
involved with interpreting data from cleanup sites, and groundwater cleanup agencies are not usu-
ally focused upon the operating features of individual water supply wells. This arrangement has its
strengths in that the two skill sets are different and the division of duties allows regulators in each
discipline to rei ne their skills and apply their knowledge to the distinct challenges of groundwater
cleanup and drinking water system permitting, inspection, and regulation. There are limitations to
this arrangement as well: the regulatory “silos” that result can diminish the effectiveness of ground-
water management strategies that must apply a holistic approach in order to succeed. Although
seldom evaluated, contaminant mass discharge (or mass l ux) should be the common interest of both
drinking water and groundwater cleanup agencies, as described below.
Regulatory agencies overseeing groundwater cleanups often require a well search to identify all
operating and inactive wells within a i xed radius of the cleanup site. This requirement to investigate
whether water supply wells may be impacted from release sites should be expanded to require that
the discharger estimates the date by which the contamination could be expected to arrive at active
water supply wells residing within the i xed radius. A further expansion to this requirement is to use
the mass discharge approach to estimate the maximum contaminant concentration that could be
expected in the well.
Determining the likelihood that a well will become contaminated involves evaluating whether
the mass of 1,4-dioxane at the release site is sufi cient to sustain migration and arrival at the well,
which requires an assessment of the capture zone of the well. Where a supply well is screened in an