EPA rules cited in lead flap

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Officials with the Washington Aqueduct said yesterday federal guidelines prohibit them from changing the disinfectant used to treat the District's water supply, even though scientists now say the chemical might have caused lead contamination.

The aqueduct in November 2000 replaced pure chlorine with chloramine, a compound of ammonia and chlorine, in a move mandated by the Environmental Protection Agency (EPA). Scientists say the switch might have upset the chemical balance of the water and made it more corrosive.

"We can't go back to free chlorine and remain in compliance with EPA regulations," Thomas P. Jacobus, general manager of the aqueduct, said yesterday. "If it is true that chloramine has caused the lead problems, we didn't know it at the time. Nothing in the literature indicated it would happen."

Scientist Marc A. Edwards and EPA representatives said the switch might have led to the accelerated corrosion of service lines in the District, first shown in 2001 and 2002 monitorings conducted by the D.C. Water and Sewer Authority (WASA).

"The old plan for controlling lead leaching ... had been working reasonably well," said Mr. Edwards, a scientist from Virginia Tech and a former EPA subcontractor. "Then, a series of events that included a switch to chloramine triggered a 'perfect storm' of lead corrosion."

Excessive leaching of lead to water occurs when corrosive water contacts plumbing materials such as lead pipes.

Mr. Jacobus said the decision to change the disinfectants was made to comply with revised EPA regulations. Chloramine reacts less strongly to organic matter than pure chlorine, he said, causing fewer potentially cancer-causing byproducts.

"The EPA reduced the minimum allowable level of disinfectant byproducts in the water supply from 100 parts per billion to 80 parts per billion," Mr. Jacobus said. "We had to comply."

Earlier this month, WASA began testing contaminated residences to find out whether a change in the chemical composition at the aqueduct, not the lead-based service lines themselves, is the real cause of the lead contamination.

Officials have switched back to pure chlorine until May 7 and are testing whether the change in chemicals will affect residences with elevated levels of lead contamination.