Regulation and Risk Assessment of 1,4-Dioxane - Environmental Investigation and Remediation - page 277

must be tested on the scale of the particular circumstances of drinking water source contamination,
the i ndings of Abe and Moran taken together suggest that it is likely that there are many more
drinking water sources affected by 1,4-dioxane that have not yet been discovered because 1,4-di-
oxane is not commonly included in drinking water analysis. Where production wells have a history
of detections of methyl chloroform and its breakdown products, 1,1-dichloroethylene and 1,2-di-
chloroethane, screening level testing for 1,4-dioxane is advisable.
6.2 WATER QUALITY REGULATIONS: PROTECTION OF
ECOLOGICAL RECEPTORS
Remedial project managers from the regulatory and regulated communities must determine the
appropriate course of action when industrial efl uent or treated groundwater from which solvents
have been removed contains low concentrations of 1,4-dioxane. Aquatic toxicity of contaminants
discharged to streams usually drives the determination of discharge limits for surface-water dis-
charges; however, it may also be necessary to review the potential for drinking water impacts. Human
exposure becomes the driver for regulating 1,4-dioxane discharges where the surface-water body is
either used directly for drinking water or recharges an aquifer from which groundwater is pumped to
supply drinking water. Human exposure may also be the driver for discharge of 1,4-dioxane to sani-
tary sewers. The removal efi ciency of 1,4-dioxane in conventional wastewater treatment plants is
low, and where treated wastewater is recycled for irrigation of landscape or indirect potable reuse to
recharge groundwater, drinking water impacts may result. This section examines the toxicity of
1,4-dioxane to ecological receptors (i.e., algae, aquatic insects, i sh, and terrestrial animals) and
reviews examples of how 1,4-dioxane has been regulated in surface-water discharges.
6.2.1 N ATIONAL P OLLUTION D ISCHARGE E LIMINATION S YSTEM R EGULATIONS
NPDES permits are issued to dischargers of treated and untreated industrial wastewater, storm-
water, groundwater remediation efl uent, and other efl uents. The goal of the NPDES is to restrict or
eliminate impacts to aquatic life in surface water from direct discharges to streams or indirect dis-
charges to publicly owned treatment works (POTWs), including discharges with high biochemical
oxygen demand, toxic metals and organic compounds, high temperatures, foaming agents, and other
potential impacts. Preserving aquatic habitat, recreational uses, and the aesthetic value of natural
waters has grown in importance since the NPDES program was i rst introduced.
Chlorinated solvent release sites are often remediated with pump-and-treat systems using air
stripping or granular activated carbon (GAC). On numerous occasions, dischargers and regulators
alike were surprised to learn that the discharge contained additional, untreated compounds includ-
ing 1,4-dioxane and perchlorate (USEPA, 2007a). The consequences of discharging 1,4-dioxane to
streams, rivers, lakes, estuaries, and bays depend on local conditions. Aquatic toxicity is unlikely to
result from the 1,4-dioxane concentrations commonly encountered in efl uents from groundwater
treatment systems designed to treat chlorinated solvents. The benei cial uses of the surface-water
body and the interaction of surface water with groundwater may therefore be the determining fac-
tors in regulating 1,4-dioxane discharges. Where surface water is used directly for drinking water
or where it makes up a substantial proportion of the recharge to a drinking water aquifer, treatment
of 1,4-dioxane may be warranted to protect drinking water. The antidegradation policies in federal
and state water regulations may also prohibit discharge of contaminants to surface waters. To date,
the regulation of 1,4-dioxane discharges to surface waters has varied considerably by regulatory
agency and the context of the discharge.
6.2.2 T OXICITY OF 1,4-D IOXANE TO A QUATIC O RGANISMS
1,4-Dioxane is not highly toxic to aquatic organisms. The aquatic bioassay results tabulated in
this section show that 1,4-dioxane is acutely toxic to bacteria, algae, invertebrates, and i sh at