Perchlorate, a chemical known to disrupt the thyroid gland and linked to hormonal dysfunction, developmental delays and infertility, is considered a health risk to humans at concentrations of 1 part per billion, according to a proposed EPA standard.
The level of 80 parts per billion was detected at a construction site at Sibley Memorial Hospital, across the street from the aqueduct property.
Tests also revealed perchlorate levels of 6 to 8 parts per billion in an underground drainage ditch that carries water leaking from the aqueduct's treatment basins.
Aqueduct officials said they still strongly believe that the perchlorate cannot get into the reservoir. Jacobus said the aqueduct will nevertheless conduct tests every three months for perchlorate levels as low as 1 part per billion.
Scott C. Heuer, a Spring Valley activist, said elevated levels of arsenic turned back yards into hazardous waste sites. He said the Army should now err on the side of caution and address any buried munitions and contamination left from the World War I testing station at American University.
"It can't be stalled any longer," Heuer said. "Is what went wrong in Spring Valley going to go wrong with the aqueduct or the Potomac River?"
In California, regulators have issued emergency orders to clean up sites where levels of perchlorate reach 6 parts per billion, even in cases where drinking water is not affected. Maryland told the Army more than a year ago to clean up contaminated soil and groundwater from the Aberdeen Proving Ground testing site after finding perchlorate in drinking wells in the town of Aberdeen. But the military is mulling over the proposal, and state officials said they cannot force the cleanup unless there is a proven health emergency.
The EPA has the legal authority to require the cleanup of perchlorate in contaminated soil or water if it reaches levels of 4 parts per billion and public health is at risk. But the Defense Department has successfully argued that perchlorate cleanup at all its bases is unnecessary, costly and could jeopardize the military's war on terror.
For local activists and environmentalists, however, the District's case stands out because of the number of people who could be affected.
"It's very troubling to us that you'd have known contamination 100 meters from the water supply for the nation's capital and known or likely weapon burial sites immediate adjacent to the reservoir, " said Erik Olson, a lead attorney at the Natural Resources Defense Council. "And because the Army is not willing to ask Congress for money -- and does not really want to find a problem -- they're still waiting for years before they aggressively take action."