Regulatory Policy Implications of 1,4-Dioxane - Environmental Investigation and Remediation - page 468

10.4 REGULATORY POLICY ON 1,4-DIOXANE REMEDIATION
AT CLEANUP SITES
The detection of 1,4-dioxane at solvent release sites often occurs years after the solvent release has
been investigated. As described in the case studies in Chapter 8, the late detection of 1,4-dioxane
may cause regulators to require the installation of additional monitoring wells to characterize the
extent to which 1,4-dioxane has migrated. The occurrence of actionable levels of 1,4-dioxane beyond
the capture zones of pump-and-treat systems that were installed to address chlorinated solvents may
require the installation of additional extraction wells or extraction trenches to capture 1,4-dioxane.
The treatment technology employed to remove chlorinated solvents will most likely require modii -
cation or additional treatment technologies to remediate 1,4-dioxane. In addition, the health risk
assessment may need to be revisited to evaluate risks posed by the presence of 1,4-dioxane. Finally,
if 1,4-dioxane is discovered to have migrated further than the solvents and impacted private or
municipal wells after assurances were given that the solvent release had been contained, the public
will lose trust in both the regulatory agency and the discharger, making it more difi cult to get pub-
lic cooperation for future remedial actions necessitated by the late discovery of 1,4-dioxane. In
short, the late detection of 1,4-dioxane at a solvent release site in the advanced stages of cleanup can
reopen the case, delaying closure and adding substantially to the cost of cleanup. Regulatory agency
staff members are faced with tough decisions and i erce opposition when pursuing additional
requirements to address the late discovery of 1,4-dioxane at solvent release sites. This section
proi les a few of the challenges faced by regulators and regulated parties.
10.4.1 M ONITORED N ATURAL A TTENUATION AND 1,4-D IOXANE
Is MNA an acceptable remedy for solvent sites where 1,4-dioxane is a co-contaminant? USEPA uses
the term MNA to refer to reliance on a variety of in situ physical, chemical, or biological processes
that, under favorable conditions, act without human intervention to reduce the mass, toxicity, mobil-
ity, volume, or concentration of contaminants in soil or groundwater (USEPA, 1999). These in situ
processes include biodegradation, dispersion, dilution, sorption, volatilization, and chemical trans-
formation or destruction of contaminants. When relying on natural attenuation processes for site
remediation, USEPA prefers those processes that degrade or destroy contaminants and indicates
that it is only appropriate to adopt MNA as a remedial strategy at sites that have a low potential for
contaminant migration (USEPA, 1999). MNA is typically used in conjunction with active remedia-
tion measures. For example, active remedial measures could be applied in areas with high concen-
trations of contaminants while MNA is used for low concentration areas, or MNA could be used as
a follow-up to active remedial measures (USEPA, 1999).
USEPA's policies for site remediation direct staff to ensure that source control measures should
use treatment wherever practicable and engineering controls such as containment where treatment is
impracticable. In addition, the maximum benei cial uses of contaminated groundwater should be
restored within a reasonable timeframe wherever practicable; when restoration is not practicable,
USEPA directs staff to seek remedies that will prevent further migration of the plume, prevent expo-
sure to the contaminated groundwater, and further reduce risk (USEPA, 1999). The USEPA directive
on MNA notes “MNA will be an appropriate remediation method only where its use will be protective
of human health and the environment and it will be capable of achieving site-specii c remediation
objectives within a timeframe that is reasonable compared to other alternatives” (USEPA, 1999).
The USEPA MNA directive includes several important points that bear on whether MNA is an
acceptable remedy for 1,4-dioxane sites. The directive notes that since engineering controls are not
used to control plume migration in an MNA remedy, decision makers need to ensure that MNA is
appropriate to address all contaminants that represent an actual or potential threat to human health
or to the environment (USEPA, 1999). The directive specii cally notes that cleanup of solvent spills
is complicated by the fact that a typical spill may include contaminants that tend not to degrade