John Wisely

Detroit Free Press

8% of water samples tested exceeded the federal limit of 15 parts per billion.

Experts warn its too early to stop precautions like tap filters and bottled water.

Flint began adding phosphates to its water Dec. 9.

State has distributed more than 23,000 test kits, though it's unclear how many will be returned.

Preliminary results from tests on Flint's drinking water done since the city switched back to Detroit's water system and added phosphates show that lead levels appear to be falling.

Experts caution that wider sampling is needed before precautions such as drinking bottled water and using filters are lifted.

So far, the Michigan Department of Environmental Quality has processed 853 samples of water drawn from Flint homes between Sept. 29 and Jan. 15. Test results obtained by the Free Press show that about 8% off the samples exceeded 15 parts per billion for lead, the level at which federal rules require water system operators to add more corrosion controls. The state has distributed more than 23,000 test kits, though it's unclear how many will be returned for analysis.

Professor Marc Edwards of Virginia Tech, who has been leading an independent study of Flint's water for months, said the early numbers appear lower than the readings his researchers were logging in August, before the switch back to Detroit's water system.

"But they still show isolated problems," Edwards said Friday. "People should keep using the bottled water and filters until an all-clear has been given."

Flint stopped drawing water from the corrosive Flint River last fall, switching back to the Detroit Water and Sewerage Department on Oct. 16.

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The early test results show:

68 samples exceeded the federal limit of 15 parts per billion, with the highest level registering 2,516 ppb.

11 samples showed more than 100 ppb.

785 samples — 92% — registered below the federal limit, including 674 — 79% — that registered below 5 ppb.

Edwards said his researchers continue to monitor some homes that have had high lead levels, and that as late as Thursday, those levels were still exceeding federal limits. He said a more statistically significant number of tests is needed to accurately gauge the safety of the city's water system.

State officials said they are still in the data-collection phase.

"This is a snapshot," DEQ spokeswoman Melanie Brown said.

The Environmental Protection Agency said Thursday that it will take over lead testing in Flint because of what it said was "inadequate transparency and accountability." It also ordered the state to create a website to disclose test results in a more timely fashion.

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On Friday, DEQ Director Keith Creagh said the state would comply with the EPA's emergency order, which also requires officials to inventory all the lead service lines in the city. But Creagh questioned the agency’s legal authority to make such demands. He also disputed EPA Administrator Gina McCarthy's contentions that the state had delayed corrective action, saying there were omitted facts and legal errors in the order.

Creagh replaced DEQ director Dan Wyant, who resigned last month as a result of the crisis. The EPA threatened to file a complaint in U.S. District Court if the state and the city didn't respond to its order within one day, adding Friday that both had agreed and that the agency will have "further discussions with the state about their legal obligations."

The test results come about six weeks after the city began adding phosphates to its water. The phosphates build up a mineral layer inside pipes that inhibits corrosion and helps prevent lead from leaching into the water.

"If they had been adding the inhibitor from the beginning, this whole thing would have been considered a success," Edwards said.

Brown said the samples were collected from homeowners who returned sample kits that were provided by the state when they picked up bottled water or when state officials knocked on their door.

Flint stopped buying water from the Detroit Water and Sewerage Department in April 2014 and began using the Flint River after the city decided to join the Karegnondi Water Authority in a move considered more cost-effective for the financially ailing city. It needed an interim water source because construction on the water authority project will not be not complete until later this year.

Water addition helps

Detroit had been using phosphates — a type of salt containing phosphorus — for years to control lead; the method has been used successfully by water systems across the country since the 1990s. But when Flint switched water sources, it didn't add corrosion controls, as the law requires for water systems that serve more than 50,000 people. DEQ officials later acknowledged that they wrongly used the protocol for smaller water systems.

Experts said the more corrosive river water wore down the mineral layer inside Flint's aging pipes and began leaching lead into the water. If lead concentrations exceed 15 ppb in more than 10% of customer taps sampled, the water system operators must take additional steps to control corrosion.

Detroit adds 1 milligram of phosphate to every liter of water it treats. On Dec. 9, Flint began adding an additional 2.5 milligrams per liter to help accelerate the buildup of the mineral layer.

Lead levels can be expected to begin falling two to three weeks after the phosphates are added and fall faster as the mineral layer builds up, said David Cornwall, a former Michigan State University professor who serves as a technical adviser to the National Drinking Water Advisory Council. But that can also vary.

For example, all water systems have areas where water flow is low, Cornwall said. That means it takes longer for the new treated water to reach those pipes.

"There are always lots of storage tanks in a distribution system," said Cornwall, who is now president of EE&T, a consulting engineering firm based in Newport News, Va. "Water can sit in those tanks for days. You've got to get this new boosted orthophosphates out to the whole system."

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Contact John Wisely: 313-222-6825, jwisely@freepress.com or on Twitter @jwisely