A more refined test of the water in the Washington Aqueduct has revealed the presence of perchlorate, a toxic chemical typically found in weapons and explosives, federal officials said yesterday.
The discovery of the chemical in the water supply challenges the prevailing theory of the U.S. Army Corps of Engineers, which has argued that contamination from buried World War I munitions in the Spring Valley neighborhood to the north poses no threat to Dalecarlia Reservoir along MacArthur Avenue NW.
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Thomas P. Jacobus, chief of the Washington Aqueduct, said perchlorate in the reservoir measured between 1.2 and 1.8 parts per billion (ppb) and did not pose a health risk. He said he has ordered weekly tests of the water and is recommending that the corps accelerate its search for the source of perchlorate contamination.
"I'm obviously concerned about anything that has to do with drinking water. . . . But there is no cause for alarm," Jacobus said.
The corps operates the aqueduct, which supplies drinking water to more than a million people in the District, Arlington County and the city of Falls Church. It is also overseeing a multimillion-dollar cleanup of chemical contamination in Spring Valley.
Environmental Protection Agency and District government officials said last night that there was no need for immediate action but agreed that aggressive monitoring of perchlorate was now needed.
"I have a level of concern, given the context of that site," Gregg A. Pane, director of the D.C. Department of Health, said. "While there are no immediate steps called for, we are going to be taking a close look and be very vigilant about this."
Perchlorate -- a chemical that disrupts the thyroid and is linked to hormonal dysfunction, developmental delays and infertility -- is considered a health risk to humans. The EPA has said perchlorate could harm humans at levels of 1 ppb.
There is no federal standard for the chemical. The EPA is awaiting a recommendation from a scientific panel to set one. In the meantime, the agency can require the cleanup if contamination levels reach 4 ppb.
The EPA last summer detected much higher levels of perchlorate within 200 yards of the reservoir. The aqueduct, which had argued until last month that there was no immediate reason to monitor nearby groundwater or determine the source of the contamination, began more refined testing at the reservoir after the EPA findings were made public last month.
For residents in Spring Valley, the test results released yesterday justified their earlier demands for immediate investigation.
"This is exactly what we've been worrying about," said Peter deFur, a scientist hired by residents to review the contamination. "Why the heck has the aqueduct been waiting so long to use the more sophisticated tests, I don't know.
"I think we have to assume it's been going on for a long time," deFur said, referring to possible exposure to perchlorate. "This is serious."
Tom Voltaggio, deputy director of the EPA's mid-Atlantic office that oversees the District, said the agency will closely monitor the new tests and push for more aggressive efforts to find the source of the contamination.
Bob Nelson, a spokesman for the corps, said there are no plans to change the current strategy. But he said the agency will continue to work with regulators to identify perchlorate in the area and take appropriate measures as needed.