Nearly two weeks after a chemical spill contaminated drinking water for 300,000 West Virginia residents, the company involved revealed that it had spilled a second chemical as well. West Virginia officials say tests of drinking water samples collected since the still so far have not detected this second chemical but they will use a more sensitive test to see if they find it in smaller concentrations. Water company officials say they don't think there was any added risk to the public from that second chemical and it's told customers they can safely drink the water again unless they're pregnant. But as NPR's Elizabeth Shogren reports, the fact that a second contaminant went undetected reveals an important truth about how drinking water supplies are tested for contaminants.

ELIZABETH SHOGREN, BYLINE: The company whose tank spilled, Freedom Industries, identified this new chemical as PPH, a mixture of polygycol ethers. It was mixed in with a chemical that washes coal. The local water treatment plant hadn't noticed this second chemical in the water even with all the testing it was doing. Experts say that's because they only find what they looking for.

BRENT FEWELL: There's thousands of chemicals in use out there. To expect a water company to monitor for thousands of chemicals, it just is not practical and it would be cost prohibitive.

SHOGREN: Brent Fewell is vice president for environment, health and safety of a company called United Water.

FEWELL: When water companies do specific tests on contaminants like this they look for a fingerprint, if you will. Every chemical has a chemical fingerprint. And so when you focus on that fingerprint and you're not focusing on other fingerprints, you very well could miss a contaminant like this.

SHOGREN: Fewell says that's why it's so important for companies to tell utilities all the chemicals that might have spilled. Jon Capacasa directs the federal Environmental Protection Agency's water protection division for the region that includes West Virginia. He says there's a simple reason the water company didn't know about the second chemical.

JON CAPACASA: The substance involved here, PPH, is not a substance for which West Virginia American Water Company is required to test for under the Safe Drinking Water Act.

SHOGREN: The EPA does require public water systems to test for about 80 contaminants. How frequently water companies have to test varies on the kind of health risk the contaminant presents.

CAPACASA: Viruses and bacteria are monitored on a very short turnaround; within hours and days.

SHOGREN: Heavy metals, radiation and chemicals that may increase cancer risk are tested much less frequently - every few months or years. But water companies don't regularly test for tens of thousands of other chemicals. There are some ways labs can cast a wider net for unknown chemicals. Andy Eaton is the technical director of a water testing laboratory in California, Eurofins Eaton Analytical.

ANDY EATON: With an analytical technique called gas chromatography mass spectrometry.

SHOGREN: Eaton says 20 years ago his company was using the technology to analyze a routine water sample.

EATON: What happened was our chemists saw something that we weren't expecting.

SHOGREN: The chemists determined it was MTBE, a gasoline additive.

EATON: And everybody sort of said what? You know, what's MTBE? What's it doing there?

SHOGREN: He says it would be too expensive to use this technology to hunt for contaminants on a daily basis. But he says there's an important take away here for water companies that face chemical spills in the future.

EATON: Learn to not take the information that you're given at face value.

SHOGREN: American Water West Virginia says now that it knows about PPH, labs will analyze samples taken over recent weeks to see how much of it was and is in the water. Elizabeth Shogren, NPR News.


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