The nonprofit public interest organization Environmental Working Group (EWG) this week released the results of a study that tested the water supplies of 35 American cities. In 31 of the 35 cities tested, the known carcinogen hexavalent chromium was present in the water supply.

The result of industrial manufacturing and processes, hexavalent chromium can seep into groundwater after being discharged, thus contaminating drinking water supplies. In 25 of the cities tested, the EWG study found hexavalent chromium in amounts greater than the maximum threshold the State of California has set as a safe exposure level. California is the only state that tests and regulates hexavalent chromium in drinking water.

As a result of the study, EWG is asking the Environmental Protection Agency (EPA) to establish a legal limit for hexavalent chromium contamination in water supplies and to conduct regular tests for the chemical compound. Similarly, Earthjustice is working to limit emissions from chrome plating facilities and is urging EPA to safeguard the health of communities exposed to hexavalent chromium.

Previous employment at an environmental engineering firm first led me to the world of hexavalent chromium. I was unfamiliar with the chemical compound and had never seen “Erin Brockovich,” the popular film that told the story of water pollution in Hinkley, Calif., resulting from a hexavalent chromium plume. As I began working in the environmental engineering field, I soon learned of the chemical compound’s dangers and the extent of the problem across California.

For environmental engineers, hexavalent chromium represents work. Contamination of groundwater with hexavalent chromium is fairly common and addressing the problem can be exceedingly difficult. Detecting the source of the contamination, mapping the extent of the plume, and finally devising a series of steps to remediate the contamination is no easy endeavor—nor is it cheap.

I was tasked with identifying hexavalent chromium sites in California where the firm I worked for might be able to sell its expertise in cleaning up the pollution. What I found amazed me. There were literally hundreds of hexavalent chromium contamination sites in California. Some of them, such as Hinkley and Willits, Calif., are well-known in environmental engineering circles, but many had not received any attention or publicity. Nearly every major population center in the state had a contamination site nearby. The research left me more than a little unsettled.

Industry continues to pressure state and federal agencies to delay regulation of hexavalent chromium, reciting the common refrain that more scientific research is needed before stopping the pollution of drinking water with carcinogens. I’m not sure what type of scientific inquiry is required to show that chemical compounds known to cause cancer do not belong in drinking water. With hexavalent chromium, some old fashioned common sense from EPA is all that’s really needed to save time, money and lives.