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Delaware plans to impose stricter drinking water standards for three toxic chemicals suspected of causing cancer in people, a move that will require increased filtering of public supplies in systems serving more than 200,000 state residents.

Two water utilities would be affected immediately by the proposed lowering of allowable limits for perchloroethylene in drinking water to 1 part per billion from the current 5 ppb level. The chemical, often called PCE or “perc,” is widely used in dry cleaning, and has turned up in groundwater across Delaware and around the country.

A similar tightening is under consideration for a related solvent, tetrachloroetheylene or TCE, and vinyl chloride. All three are considered probable carcinogens. TCE and PCE are widely used as cleaning solvents in industry, while vinyl chloride is used in making plastics. 

“The bottom line for me is that Delawareans aren’t going to be drinking in or bathing in water with PCE in it, once these improvements are made,” said Lt. Gov. Matt Denn, who began urging state health officials to consider the changes last year. “From that perspective, it’s an important step forward.