Environmental Engineering Reference
In-Depth Information
To put the perceived threat of 1,4-dioxane in drinking water in perspective, CDPH staff prepared
a “Q&A” sheet to assist water utilities with public outreach. The discovery of 1,4-dioxane in Water
Factory 21 efl uent was a blow to the campaign to promote the reuse of recycled water in the Talbert
Gap intrusion barrier and other recharge projects, coming only two years after the discovery of
NDMA. To deter the inevitable mentality of paralysis in which recycled water projects are opposed
because they might introduce some unknown contaminant, CDPH adopted the strategy of acknowl-
edging that recycled water projects indeed will introduce contaminants for which tests have not yet
been developed. An excerpt from OCWD's Q&A on 1,4-dioxane follows:
Q—With the discovery of NDMA in 2000, and now 1,4-dioxane this year—both cancer-causing com-
pounds put into the groundwater by reusing sewer water—shouldn't we not reuse sewer water in the
future as part of our water supply?
A—No, we will always be i nding new contaminants in water, no matter what the source—for example,
perchlorate in water from the Colorado River. Finding new possible contaminants, regardless of where
the water comes from, is part of keeping the water safe. What is important is the action that is taken
when the new compounds are found and determined to be a possible threat. The water industry has a
superior record in this area. At OCWD we routinely test our water with state-of-the-art methods to
ensure water quality. Remember, we are living longer today [owing] in large part to the new technology
that allows us to i nd these new substances.
The nine contaminated wells remained shut off during the month it took to identify and elimi-
nate the source of the 1,4-dioxane; water utilities' costs for purchasing imported water mounted.
The mayor of the City of Newport Beach reported that annual costs to purchase imported water
would be close to $4 million, an expense for which the city requested reimbursement from
OCWD, because it injected 1,4-dioxane into the groundwater basin. Similarly, the City of Costa
Mesa projected an imported water cost of $850,000 annually, for which they too sought reim-
bursement from OCWD (Mehta, 2002c). In late February, CDPH's Chief of Drinking Water,
David Spath, met with water utility ofi cials at OCWD's ofi ces to further explain the role of
Notii cation Levels and why 1,4-dioxane does not pose a risk to water utility operations in the
4-20 μg/L concentration range. Dr. Spath advised the agencies that, consistent with CDPH guid-
ance, removing the wells from service is not necessary, nor is treatment necessary to remove
1,4-dioxane at the low levels detected. However, continued and frequent monitoring was recom-
mended because the level of 1,4-dioxane exceeded the Notii cation Level (OCWD, 2002). To
reassure the public, Dr. Spath told reporters, “We feel there isn't any signii cant risk to the public
with the use of these wells” (Mehta, 2002b).
CDPH and OCWD ofi cials were coni dent that well operations could resume in large part
because of OCWD's advanced understanding of the groundwater-basin hydrogeology and water
balance. OCWD's groundwater l ow model showed that the approximate residence time of Water
Factory 21 efl uent injected in the Talbert Gap injection barrier was 20 years. Because 1,4-dioxane
is miscible and resistant to sorption, OCWD's hydrogeologists estimated that the remaining
1,4-dioxane in the aquifer would be pumped out within 20 years. Therefore, the 70-year exposure
time upon which the Notii cation Level for carcinogens is predicated would not be met, and the risk
from exposure would diminish correspondingly. * This estimate of 1,4-dioxane's fate may be neglecting
its tendency to be stored in i ne-grained sediments, as discussed in Section 3.5. Because 1,4-dioxane
migrates rapidly and resists sorption and abiotic or biologic degradation, the unintended injection of
1,4-dioxane creates a time marker for tracing the long-term movement of injected water in the
groundwater basin.
As of July 2008, two of the four affected Mesa Consolidated Water District wells had decreasing
concentrations of 1,4-dioxane, whereas two wells had increasing concentrations of 1,4-dioxane
* Personal communication with Dr. David Spath, Chief of Drinking Water, California Department of Health Services (now
CDPH), April 2003. Discussion of CDPH role in Water Factory 21 1,4-dioxane episode.
Search WWH ::




Custom Search