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The U.S. Environmental Protection Agency issued recommendations Tuesday for cities on how to test for a contaminant in water that Milwaukee officials said last week has been found in the city's water system.

On Friday, city officials said their testing showed the presence of hexavalent chromium, a probable carcinogen made famous in the film "Erin Brockovich" that comes from both natural and industrial sources.

Laboratory tests of Milwaukee's water samples found the chemical in various points in the system - before and after water treatment.

City officials say there is no imminent threat to public health.

The EPA doesn't regulate hexavalent chromium, also known as chromium 6, but the federal government has a standard for total chromium.

The EPA's guidance statement recommended that water systems be tested at their point of intake. In Milwaukee's case, that would be in Lake Michigan, two miles offshore.

The agency also said water should be tested at points where treated water moves to the distribution system and at various points where the public can access tap water.

"They are recommending exactly what we did," said Carrie Lewis, superintendent of Milwaukee Water Works.

The water utility supplies Milwaukee and 15 other communities.

The EPA also recommended that systems with surface water sources test water once a quarter.

Systems such as Madison's, which uses groundwater, should have their water systems sampled twice a year.

An environmental group called the Environmental Working Group said last month that its own sampling found the presence of the hexavalent chromium in Milwaukee's and Madison's water supplies. It tested for the presence of the chemical in 35 cities and found it in 31.

The EPA recommended the same testing protocol Milwaukee used to test its water after the environmental group released its report.

Milwaukee's results showed the presence of the chemical is 0.22 parts per billion before water is treated; 0.20 parts per billion after treatment; and 0.19 parts per billion in tap water.

Last year, California took steps to limit the amount of hexavalent chromium in drinking water by proposing a public health goal of 0.06 parts per billion.

Federal standard

The federal government's standard for total chromium in drinking water is 100 parts per billion. The EPA is analyzing current science to determine whether hexavalent chromium in the drinking water would pose a health danger and, if so, at what level. It said Tuesday that the science is evolving.

The agency's assessment of the effect on human health will be completed later this year.

The EPA said no public water system is in violation of the standard for total chromium.

Paul A. Biedrzycki, Milwaukee's director of disease control and environmental health, said he saw no danger to people drinking Milwaukee's water.

He said city officials were waiting for the EPA review of health studies of the chemical, but his analysis of health data shows no increase in cancer rates, especially the kinds of cancers that the contaminant has been linked to.

Some industrial sources, such as metal plating plants, can produce hexavalent chromium.