Regulation and Risk Assessment of 1,4-Dioxane - Environmental Investigation and Remediation - page 285

Permissible discharges of 1,4-dioxane to the sewer decrease with increasing l ow rates. Discharges
of 10, 20, and 30 gallons/min are allowed to contain 1,4-dioxane at 5930, 3950, and 2970 μg/L,
respectively (MWRD, 1999). As discussed in Chapter 7, aerobic wastewater treatment is not expected
to effectively remove 1,4-dioxane, but it can dilute concentrations to below detection limits. In a
1988 chemical analysis survey of sewage sludge from 208 wastewater treatment plants, 1,4-dioxane
was detected in sludges from three plants (USEPA, 1988).
6.2.5.2 Recycled Water Regulations
Groundwater recharge projects in California using recycled water from POTWs in which 1,4-di-
oxane is present in the sewer inl uent must use reverse osmosis and advanced oxidation to achieve
at least 0.5 log reduction in concentration. Post-treatment concentrations can be no greater than
California's NL for 1,4-dioxane, 3 μg/L (CDPH, 2007b).
In Orange County, California, 1,4-dioxane was detected in wastewater treated by advanced
methods and subsequently in nine municipal wells. The wells draw from a groundwater basin in
which the treated wastewater had been reinjected for more than a decade to provide a hydraulic
barrier to seawater intrusion. The advanced treatment, including reverse osmosis and UV light with
hydrogen peroxide, was insufi cient to remove 1,4-dioxane. * The nine wells in three cities were
temporarily shut down, requiring replacement of 34 million gallons/day of groundwater with
imported surface water. 1,4-Dioxane concentrations in the inl uent to the advanced wastewater
treatment plant ranged from nondetect to episodic peaks as high as 200 ppb, but mostly less than
100 ppb. The presence of 1,4-dioxane in the inl uent was traced to a manufacturing facility that used
1,4-dioxane to produce cellulose acetate membrane i lters, whose discharger voluntarily ceased the
discharge, and the 1,4-dioxane declined to 1 ppb, the level generally associated with domestic
wastewater (Woodside and Wehner, 2002).
A solvent remediation site in Tampa, Florida, found 1,4-dioxane concentrations in extracted
groundwater at less than 20 μg/L; however, treated efl uent in Florida may not exceed 5 μg/L, the
Florida drinking water standard. Because discharge from the treatment system is to the sanitary
sewer, water agency ofi cials required reduction or elimination of the 1,4-dioxane discharge, which
could end up in reclaimed water being used to recharge groundwater (J.C. Alonso, personal com-
munication, 2001).
6.3 AIR QUALITY REGULATIONS: OCCUPATIONAL HEALTH
AND SAFETY AND AMBIENT AIR QUALITY
As described in Section 2.7, ambient air sampling at 45 locations in 12 cities during the early 1980s
coni rmed the presence of 1,4-dioxane concentrations ranging from less than 1-30 ppb. Because
90% of the 1,4-dioxane produced for the United States was for stabilizing methyl chloroform, it is
likely that the source of 1,4-dioxane in ambient air was from vapor degreasing with methyl chloro-
form, as well as the other direct industrial uses of 1,4-dioxane and the industries that produce
1,4-dioxane as a by-product. Section 6.5.3 summarizes occupations in which a potential existed for
inhalation of 1,4-dioxane when methyl chloroform was in widespread use.
The explosion hazard of 1,4-dioxane should not be underestimated. 1,4-Dioxane is a hazardous
material that presents i re and explosion dangers from its direct use as a solvent. 1,4-Dioxane is a
highly volatile and highly l ammable liquid with an explosive/l ammability limit of 2% in air at
standard temperature and pressure. In addition, the vapor density of 1,4-dioxane is about three times
denser than air, causing its vapors to sink. The combination of 1,4-dioxane's volatility, l ammability,
* The combination of UV light and peroxide is effective at removing 1,4-dioxane when used in a coni guration optimized
for 1,4-dioxane, as described in Chapter 7. The level of peroxide at this plant, 5 mg/L, was too low; 10-15 mg/L peroxide
is more effective at removing 1,4-dioxane (Woodside and Wehner, 2002).