Regulatory Policy Implications of 1,4-Dioxane - Environmental Investigation and Remediation - page 469

readily in the subsurface. For example, 1,4-dioxane, which is used as a stabilizer for some chlori-
nated solvents, is more highly toxic, less likely to sorb to aquifer solids, and less biodegradable
than some other solvent constituents under the same environmental conditions (USEPA, 1999).
The directive also calls for identifying the TICs * and determining whether MNA will sufi ciently
diminish their concentrations and eliminate risk.
The persistent and mobile nature of 1,4-dioxane in groundwater hinders its eligibility as a candi-
date for MNA remediation; however, because 1,4-dioxane migrates at essentially the same rate as
groundwater, it will become more rapidly attenuated by physical processes such as dispersion,
matrix diffusion, and dilution from recharge. Therefore, chlorinated solvent sites with 1,4-dioxane
releases may nevertheless be suitable for MNA as a reasonable long-term remedy if the intent of the
USEPA protocol can be upheld to the satisfaction of USEPA's staff.
1,4-Dioxane plumes can become very large due to the fate and transport properties described in
Chapter 3. Where 1,4-dioxane plumes are regional in nature, the high cost of installing dozens of
extraction wells and multiple advanced oxidation treatment systems may make conventional reme-
diation impractical. The Pall Life Sciences case study in Chapter 8 proi les a regional plume where
the court-ordered remedy was to establish a groundwater exclusion zone to prevent the use of 1,4-
dioxane-contaminated groundwater in Ann Arbor, Michigan. 1,4-Dioxane within the exclusion zone
will attenuate due to physical processes as it migrates toward the Huron River, where it is expected
to be further diluted to inconsequential concentrations upon discharge to the river. In another regional
plume case involving perchlorate in Santa Clara County, California, hundreds of private wells were
impacted with low concentrations near California's 6 μg/L perchlorate MCL. Because perchlorate
exposure from groundwater occurs primarily through drinking and cooking, providing bottled water
was deemed sufi cient to eliminate most exposures. This option might not be available for a regional
1,4-dioxane plume because inhalation exposure through bathing, showering, dishwashing, and other
household water uses may pose health risks. To satisfy USEPA's MNA protocol requirements for 1,4-
dioxane plumes, dischargers must ensure that MNA is protective of human health by verifying that
there are no currently exposed receptors (especially private wells) and that benei cial uses will not
become impaired over the planned timeframe of the MNA remedy.
Regulatory agency decisions on whether MNA is an acceptable remedy have typically hinged on
whether there may be a more practical means of removing the groundwater contaminants more
quickly than would be achieved by MNA. However, 1,4-dioxane treatment using advanced oxida-
tion is very energy intensive. Consequently, the environmental impact of carbon dioxide (CO 2 )
emissions from the power generation used to supply electricity to the treatment operation may be
signii cant. Growing concerns over the contribution of CO 2 emissions to global warming are caus-
ing the groundwater remediation community to rethink the benei ts of energy-intensive pump and
treat systems. “Green remediation” focuses on including CO 2 emission considerations in the reme-
dial technology feasibility analysis. When global warming concerns are included in the evaluation
of treatment options that are equally protective of human health, MNA may be favored even though
the timeframe to complete cleanup and obtain closure may be longer.
10.4.2 1,4-D IOXANE AND N ATIONAL P OLLUTION D ISCHARGE E LIMINATION S YSTEM
E FFLUENT L IMITATIONS
The discharge or reuse of extracted and treated groundwater resulting from the cleanup of ground-
water contamination sites is regulated by the National Pollutant Discharge Elimination System
(NPDES). USEPA delegates the authority to issue NPDES permits to state regulatory agencies,
which oversee the discharge of treated groundwater to surface water. The permits specify water
quality conditions that must be maintained in the receiving water (e.g., the creek or river to which
* TICs are analytes that do not match the standard list of analytes reported in the laboratory method.