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GeoInsighter
Fall/Winter
2004 Newsletter
Dioxane Return to the Newsletter
Index
Dioxane. 1,4-Dioxane.
1,4-Diethylene dioxide. All synonyms for an emerging constituent of
concern that is receiving increasing attention from the United States
Environmental Protection Agency (USEPA) and state regulatory agencies.
In some of its guidance documents, the USEPA has recognized 1,4-dioxane
as a stabilizer in chlorinated solvents that is more toxic and
persistent in the environment than other solvent compounds under similar
environmental conditions.
History
Dioxane is not a new compound. It has been used in industry since the
1960s, is present in chlorinated solvents at 2 to 8 percent, and can be
found in paint, varnishes, and adhesives. It is also used as a
reaction medium solvent in organic chemical manufacturing. The solvent
most closely associated is 1,1,1-trichloroethane (TCA), a commonly used
degreasing solvent, production of which uses approximately 90 percent of
the dioxane produced. Until recently, dioxane has not been considered a
constituent of concern when evaluating chlorinated solvent sites,
regardless of its widespread use with the chlorinated compounds.
However, increasing numbers of instances of dioxane impacting drinking
water wells and its USEPA classification as a probable human carcinogen
are initiating further evaluation.
Fate and Transport Properties
Compared to common chlorinated solvents, dioxane has a higher water
solubility and a lower carbon-sorption coefficient. These
characteristics make dioxane more mobile in water and less likely to
sorb to soil. As a result, a dioxane plume typically migrates more
rapidly than the associated chlorinated solvent plume, resulting in a
larger area of ground water impact. If present in soils, dioxane readily
leaches into ground water. Volatilization of dioxane from moist soils or
from solution in ground water is slow due to its relatively low Henry’s
Law Constant, but, because of its vapor pressure, it will readily
volatilize in dry soils or from dense non-aqueous phase liquid (DNAPL)
exposed to air.
Regulatory and Analytical Information
As more information is becoming known about dioxane, states have started
to develop regulations for dioxane in drinking and ground water.
Massachusetts is requiring dioxane analyses at some Massachusetts
Contingency Plan (MCP) sites and, in 2004, issued a drinking water limit
of 3 parts per billion (ppb). The Massachusetts Department of
Environmental Protection (MADEP) ground water reportable concentrations
(RCs) are 1 and 10 milligrams per liter (mg/L) for RCGW-1 and RCGW-2
category ground water, respectively. RCGW-1 category ground water refers
to ground water that has the potential to be used as a drinking water
source, public or private, and RCGW-2 category ground water refers to
all other ground water in Massachusetts. The New Hampshire Department of
Environmental Services (NHDES) is currently regulating dioxane on a
site-specific basis. As regulations are being defined, laboratory
analysis techniques are being developed. The current method of analysis
is a modified USEPA 8260B for volatile organic carbon (VOC) by purge and
trap gas chromatography/mass spectrophotometry in Selected Ion Mode.
Unfortunately, method detection limits range from 5 to 100 ppb, causing
difficulty in evaluating regulatory compliance.
Remediation Procedures
Due to its physical and chemical characteristics, common treatment
methods, such as air stripping or carbon adsorption, do not achieve high
removal efficiencies. Removal of organic compounds by air stripping is
fundamentally based upon the chemical’s ability to transfer from the
liquid and gaseous phase, defined by the Henry’s Law Constant. Dioxane
has a low Henry’s Law Constant, making it a difficult compound to
air-strip, resulting in poor removal efficiencies. The utility of
activated carbon adsorption is dependent on the carbon adsorption
coefficient (Koc). Compounds with low Koc values, including dioxane, are
not readily sorbed by activated carbon. Furthermore, dioxane remediation
is fundamentally difficult because of the presence of TCA in solvent
plumes. TCA and dioxane have significantly different chemical
properties. TCA is less soluble, has a higher Henry’s Law Constant, and
has a significantly higher Koc than dioxane, making TCA a good candidate
for removal by carbon adsorption or even air stripping. Therefore, a
treatment system designed for the remediation of TCA may not be adequate
to attain cleanup objectives for dioxane.
At this time, the most effective treatment for dioxane is advanced
oxidation using ultraviolet light with hydrogen peroxide. Chemical
oxidation has become a readily available treatment method for the
remediation of a variety of organic contaminants and is typically used
in situ. Advanced chemical oxidation is typically an ex situ treatment
alternative and, when integrated with additional treatment methods
(i.e., air stripping or activated carbon), is effective at remediation
of sites with dioxane and solvents present.
Erin L. Stanisewski
elstanisewski@geoinc.com
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