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SAN FRANCISCO — The tap water of at least 7 million Californians is contaminated with a chemical from rocket fuel, a problem that affects people in at least 17 other states, according to an environmental group’s study. 

After collecting data from the federal and local governments, the Environmental Working Group has found that perchlorate, a chemical that affects the thyroid, has tainted wells and river water that feeds California, and contends that suggested acceptable levels are far above where they should be. 

The group suggests an enforceable limit on the amount of perchlorate allowed in water. Currently, the U.S. Environmental Protection Agency has an advisory level of 4 parts to 18 parts per billion, and the group suggests a 4.3 parts per billion limit. California has a level that recommends that a water source be closely monitored if the perchlorate level reaches 18 parts per billion. 

The EPA completed a review in February 1999, and is now refining it for greater accuracy. 

Too much perchlorate can damage the thyroid gland, which controls growth, development and metabolism. Fetuses and children with damage to their thyroids could suffer retardation, hearing or speech loss and motor skill problems. The chemical also can cause cancer at high levels. 

Perchlorate is a salt made of ammonia and chlorine that is one of the explosive components of rocket fuel. It affects areas where rocket construction or testing have taken place. 

Places in California being cleaned up include the Baldwin Park Superfund site in the San Gabriel Valley and an Aerojet Corp. Superfund site in Rancho Cordova, near Sacramento. At both places, the cleanup goal is to get down to 4 parts per billion. 

Because there is no set regulatory level, the EPA decides on a case-by-case basis what the acceptable level of cleanup should be, according to Kevin Mayer, Region 9 perchlorate coordinator. 

The EPA is currently doing studies and testing water sources around the country to establish a basis for regulatory decisions for drinking water and Superfund sites, Mayer said. 

While at least 7 million Californians could be affected by perchlorate, the number of people around the country who could be affected is unknown because little testing has been done, the EWG reported. 

The chemical has been measured in the Colorado River and Lake Mead; in Phoenix, Tucson and other areas in Arizona; as well as cities in Indiana, Iowa and Kansas. 

Perchlorate can be cleaned up using bacteria that use the chemical to breathe when there’s no oxygen in the water, by using a resin designed to absorb the salts, or by using ions to take out charged particles. A type of filter also can be used to filter out the molecules. 

But the treatments are expensive, and EWG estimates that just for a part of cleanup at the Rancho Cordova site the cost could be $50 million and last more than 200 years. 

Perchlorate is still made and used, but disposal has improved since workers used to hose the stale perchlorate out of rockets and replace it with the fresh chemical. The result of that was to have the chemical leeching into the ground, said Bill Walker, California director of the Environmental Working Group. 

“Even in the name of national defense or the space race, we just can’t afford to be this cavalier about what we do with waste,” he said. 

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On the Net: 

http://www.ewg.org 

http://www.epa.gov