Two-thirds of homes tested exceeded 15 parts per billion, some by 30 times or more.

Chemists, engineers and other water quality experts are trying to determine what caused a spike in lead levels in the tap water of thousands of homes in Washington, D.C.

Two-thirds of the more than 6,000 homes tested in 2003 by the district's Water and Sewer Authority had lead levels that exceeded 15 parts per billion set by the Environmental Protection Agency. Some residences tested exceeded the EPA lead mark by 30 times or more.

WASA actually first discovered the problem in 2002 when the agency conducted a series of random tests on a small number of homes. After more extensive tests in 2003, WASA notified homeowners last November and held a public meeting last December. But it wasn't until the Washington Post published a story in its Jan. 31 edition that homeowners first learned the extent of the problem.

“We've been receiving calls on this every day since,” contractor Mike Reavis, Blake and Wilcox, Silver Springs, Md., told us. “We'll inspect the water services of our established customers, and, for the most part, we're referring them back to the WASA for more help.”

Scientists plan to focus on whether new chemicals used to treat the district's water may have contributed to the lead contamination. They are especially interested in studying chloramine, a combination of chlorine and ammonia. The district's two treatment plants began using the chemicals four years ago to treat the water for bacteria. The plants had used chlorine alone to do the disinfection, but the EPA tightened limits on the cancer-causing byproducts that chlorine produces.

Scientists believe that chloramine has had a highly corrosive effect on service lines, allowing lead to dissolve from the pipes. The district's officials say this is the first time the district's water has shown significant lead contamination since the late-1980s.

The Washington Post also reports that further studies will be done on lowering the acidity of the treated water. Treated water typically picks up the lead when it leaves the treatment plant. Lowering the acidity of the water would make it less likely to erode lead pipes and fixtures.

There are about 130,000 service lines for residential customers in the district and about 23,000 of those are made of lead.

EPA guidelines require WASA to replace 7 percent of its lead pipes annually, estimated to cost as much as $20 million a year. WASA officials say they will begin replacing lines in neighborhoods where lead levels are the highest.

Many more homeowners are likely to have related problems inside their homes, including lead pipe, solder and leaded brass faucets. WASA foots the bill for service lines and it's up to homeowners to determine how to deal with plumbing inside their homes.

Health officials say lead can cause serious damage to the brain, nervous system, kidneys and red blood cells. Lead contamination is particularly dangerous to fetuses, babies and children.