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The U.S. Environmental Protection Agency (EPA) mid-Atlantic region advised D.C. Water and Sewer Authority (WASA) that it must resample for lead in homes where unreliable water samples may have been drawn this year due to incorrect sampling instructions provided by a contractor.
The error was a paragraph with instructions for collecting a second-draw water sample, which inadvertently replaced first-draw instructions. The first-draw instructions were omitted.
This is significant because in a first draw, no water is run for at least six hours, then the bottle is held under the faucet before it is turned on. In the second draw, water is run until very cold, then the sample is collected from the water stream. Two samples collected in sequence provide reliable data about the lead content of water in the home plumbing and service line.
EPA acted today out of concern that samples taken in 2004 with the incorrect procedure may not accurately reflect actual lead concentrations in the water.
WASA analyzed 1837 samples through March 8, and is expected next week to provide EPA with results of another 3,000 samples.
It is unknown at this time how many homes were sampled with the wrong instructions, and therefore sampling results are questionable. WASA is reviewing sampling data to see if it can learn which homes were sampled using incorrect instructions. The sampling and analysis were done by a contractor hired by WASA.
"It is imperative that the public have confidence in the accuracy of the results obtained from these samples," wrote Donald S. Welsh. EPA's mid-Atlantic regional administrator, in a letter to Jerry Johnson, WASA general manager.
Welsh directed WASA to immediately notify all residents whose water samples are in doubt, provide them a new sampling kit with correct instructions within 14 days, and reanalyze the results within 30 days of the pickup of the sample.
In addition, Welsh required that EPA review all changes in sampling protocols before they are made public.