Case Studies of 1,4-Dioxane Releases, Treatment, and Drinking Water Contamination - Environmental Investigation and Remediation - page 401

received a permit to inject 100% recycled wastewater in the Talbert Gap wells without blending,
accompanied by intensive monitoring (Sovich, 2001; OCWD, 2008). Over 95% of the injected water
l ows inland and contributes to basin replenishment. As of 2004, 12 MGD was injected into four
aquifers in the Talbert Gap; the injected water consisted of one-third Water Factory 21 recycled
water, one-third deep well water, and one-third made up of a blend of imported water and ground-
water (OCWD, 2004).
The advanced treatment system consisted of chemical clarii cation, air stripping (for removal of
ammonia), recarbonation, i ltration, GAC absorption, and chlorination; the system treated 15 MGD.
OCWD treated as much as 5 MGD by blending advanced treated wastewater with water purii ed
and demineralized by reverse osmosis. The injection effort was augmented by drilling and operat-
ing seven extraction wells between the injection wells and the shoreline to intercept salt water and
return it to the ocean (OCWD, 1996).
8.6.2 1,4-D IOXANE D ETECTED AT W ATER F ACTORY 21
In December 2001, 1,4-dioxane was discovered in Water Factory 21 inl uent and efl uent at concen-
trations ranging from 1 to 75 μg/L, as well as two detections at 150 and 200 μg/L. Because the
Talbert Gap injection barrier had been receiving highly treated water from Water Factory 21 for
decades, in January 2002 the OCWD staff decided to sample 19 water supply wells that drew water
from the affected aquifers. 1,4-Dioxane was detected in nine of these supply wells at concentrations
ranging from 4 to 20 μg/L—that is, above California's 3 μg/L action level, but below the threshold
for shutting down the water supply wells (Mehta, 2002a). OCWD notii ed the three affected water
agencies—the cities of Newport Beach and Fountain Valley, and the Mesa Consolidated Water
District—which made the decisions to close their wells. The nine wells served more than 100,000
people. As discussed in Chapter 6, California's 3 μg/L action level, now called a Notii cation Level,
requires notii cation of consumers when 1,4-dioxane is detected at higher concentrations, but does
not require shutting down a water supply unless the concentration exceeds the Notii cation Level by
100-fold. Local water utility ofi cials nevertheless decided to shut down the nine wells while
researching the newly discovered 1,4-dioxane problem, forfeiting approximately 34 MGD of
groundwater supply (Woodside and Wehner, 2002). The City of Newport Beach staff decision to
shut down all its wells, which supply all of the city's winter drinking water, led it to purchase costly
imported water to replace the supply. One-third of the supply to two other cities was similarly shut
off after the discovery of 1,4-dioxane (Mehta, 2002a).
OCWD was among the i rst in California to test for 1,4-dioxane after encountering it while
investigating contaminated groundwater in an industrial section of northern Orange County.
Although the industrial groundwater contamination by 1,4-dioxane did not threaten drinking
water, it led OCWD's analytical chemists (1) to adapt and rei ne analytical methods to detect
1,4-dioxane and (2) to decide to test for 1,4-dioxane at Water Factory 21 (Mehta, 2002a). OCWD's
laboratory analytical experience with 1,4-dioxane is described in a laboratory case study in
Section 4.3. Within a month of detecting 1,4-dioxane in 9 out of 19 wells, OCWD proceeded to
test 51 more supply wells, revealing one more detection in a Santa Ana supply well that was not
in use (Mehta, 2002b).
Water Factory 21 operators and OCWD water quality professionals intensii ed their monitoring
for 1,4-dioxane in the inl uent and the efl uent. The fact that inl uent concentrations of 1,4-dioxane
were highly variable suggested intermittent industrial discharges as the likely source of the observed
1,4-dioxane levels. The Orange County Sanitation District quickly reviewed potential industrial dis-
charges of 1,4-dioxane and identii ed one signii cant source, a manufacturer of cellulose acetate
membranes, ironically a producer of reverse osmosis i lters similar to those used at Water Factory 21.
The Orange County Sanitation District worked cooperatively with the discharger, who voluntarily
ceased the 1,4-dioxane discharge. Concentrations of 1,4-dioxane subsequently declined to levels
associated with domestic wastewater (near 1 μg/L, attributed to shampoos and detergents), as shown