The Flint water treatment plant is pictured on Thursday, April 17, 2014. The City of Flint is planning on switching from Lake Huron to the Flint River as the primary water source for city residents and businesses. Samuel Wilson | Mlive.com

FLINT, MI - As concerns about Flint's water quality were mounting earlier this year, the city disregarded federal rules requiring it to seek out homes with lead plumbing for testing, potentially leading the city and state to underestimate for months the extent of toxic lead leaching into Flint's tap water.

City water officials filed certified documents with state regulators that claimed the city only tested tap water from homes where residents were at the highest risk of lead poisoning, but records obtained by The Flint Journal-MLive show those claims were false and may have delayed efforts to fix the public health emergency here.

Water samples sent to state labs for testing in the first six months of this year were all marked as having come from homes with lead service lines, but actually almost always came from homes at less risk of lead leaching - houses with underground plumbing made of copper, galvanized steel or materials that could not be identified, according to the city's own documents given to The Journal through the Freedom of Information Act.

In response to questioning, Flint Utilities Administrator Mike Glasgow said the city was struggling to collect the number of samples that were required following the city's switch to the Flint River as its water source in April 2014.

Records of the material in individual service lines were not readily available or did not exist, Glasgow said, leading the city to submit samples regardless of whether homes were at high risk of lead in water.

The U.S. Environmental Protection Agency requires that water sampling be done at "high-risk" locations whenever possible to better ensure that high levels of lead or copper are detected as soon as possible. Lead service lines are most likely to leach lead in water, and the American Water Works Association says cities like Flint should have been collecting 50 percent of samples from such high-risk homes.

That didn't happen in Flint, records show, even though the state and city have estimated that at least 15,000 homes in Flint have lead service lines.

Professor Marc Edwards, a water researcher from Virginia Tech University, said there's a reason water systems are required to search out homes with the greatest potential for lead poisoning.

"The rule is set up to test the worst-case scenario homes since you're only testing (a small number of) homes," Edwards said. "What happens if you don't is people (are) told their water is safe when their kids are being lead poisoned."

Lead is a toxic element that can damage the brain and nervous system of children, causing lower IQs, decreased ability to pay attention and underperformance in school.

In addition to testing at homes, the state eventually found toxic levels of lead in water at three Flint schools last month, including one school with water that registered lead levels more than six times the federal limit.

But that stepped up testing in Flint only came after city and and state officials spent months telling residents their water was safe and met all quality standards, using the city's arbitrary testing to support their position.

It was independent research, led by Edwards and local Dr. Mona Hanna-Attisha, that eventually led to the declaration of a public health emergency in the city.

A spokesman for the Michigan Department of Environmental Quality said the state is aware of problems with Flint's water samples this year and is investigating why samples were certified to have come from high-risk homes when they apparently were not.

Flint City Administrator Natasha Henderson referred specific questions about testing methods to Glasgow, but said the city was thrust into the business of water treatment and new sampling requirements after the abrupt switch in water sources -- from using pre-treated Lake Huron water to the Flint River in April 2014.

"I feel comfortable where we are ... I feel comfortable we're going to deal with all the issues," Henderson said.

Department of Public Works Director Howard Croft did not address why the city claimed all of 68 water samples included in 2015 testing were marked as having come from homes with lead service lines.

"We are aware of the discrepancy and have been actively working in advance of enforcement to complete a materials evaluation of the distribution system in order to produce a pool of Tier 1 sampling sites," Croft said in an email to The Journal.

A Tier 1 sampling site is a home with lead lines, according to U.S. EPA classification.

A spokesman for the EPA, which is investigating how the Flint water crisis happened, declined to comment.

Federal guidelines say community water systems must first attempt to collect water samples from homes with lead service lines when testing for lead and copper in drinking water because those are most susceptible to leaching lead.

More than 20 years ago, as stricter federal guidelines were put in place, water systems were required to develop inventories of the materials in distribution systems so that they could identify samples sites for lead and copper testing.

Flint never did, according to Glasgow, leaving it with a hodgepodge of scattered records, tens of thousands of which were individual, hand-written index cards. Sometimes the paper slips and map data had water service line information, but often it did not, records show.

As the city's water crisis unfolded, city and state officials have estimated at different times that 50 to 80 percent of homes in the city are connected to the water system with individual service lines that include lead. Glasgow said the estimates are based on anecdotal information from city utilities workers, but the city doesn't have hard data despite the federal rule requiring it.

"With no materials (inventory of the service lines), it left us in a unique spot. I have to use the information" we have and anecdotal information from workers in the city's water department, he said.

And although the city certified to the state that all its samples since the switch to the river came from homes with lead service lines, the records supplied to The Journal show the material content of those service lines is missing for 15 of 68 samples collected and counted from Jan. 1 until June 30.

More than half the sample sites have copper -- not lead -- service lines, the same records show, and there is a record of a lead service line at only eight of the 68 sample sites, according to The Journal's review.

Even though Flint's testing in the first half of this year showed the highest lead levels measured by the city in more than 20 years, the results still showed lead levels below independent testing conducted by Virginia Tech researchers.

The city's tests showed 10 percent of homes sampled had 11 parts per billion or more of lead with six of the 68 samples exceeding the federal lead limit of 15 ppb.

While city water testing showed Flint was within the limits for lead set by the EPA, testing by Edwards and researchers at Virginia Tech showed the lead problem was more widespread - exceeding the EPA limit in 20 percent of its tests.

The EPA requires that water sampling be done at "high-risk" locations whenever possible to better ensure that high levels of lead or copper are detected as soon as possible - before problems are allowed to fester and spread.

If water systems can't find enough of those high-risk homes for testing, other samples can be included, including those from apartment buildings that have lead service lines or homes with lead or lead solder indoor plumbing.

Croft said the city's most recent collection of water samples came from the random distribution of 175 testing bottles -- without regard for whether the homes were at high-risk of lead leaching. The city included every test kit that that was returned in its results, regardless of what material the home's service lines were made of, officials said.

"Going forward, we will be able to be more targeted," said Croft. "We did the best we could ... We're developing ways (to improve that)."

Croft has said previously that the city is in the process of compiling data from the tens of thousands of index cards and city maps in order to better understand its aging, underground infrastructure.

Glasgow said the information is "incomplete (and) missing a lot."

"Unfortunately, the deeper we dig the more we see how our information is lacking," Glasgow said.

Public health officials and researchers have said the river water caused lead levels to spike in Flint because it was much more corrosive than Lake Huron water that had been used for decades. Hanna-Attisha's research led to the discovery of rising lead levels in the blood of infants and young children since the city began using the Flint River.

Last month, using local, state and grant funds, Flint abandoned its use of the river and returned to purchasing treated lake water from Detroit again.

Even with the return to pre-treated lake water, the EPA warned just this month that health dangers remain with the Flint water system and advised that residents should be warned of the potential risk of increased lead in drinking water when crews perform underground work that could dislodge scale and sediment that contain lead.

The city, state and federal government have all begun investigations aimed at determining why lead levels were allowed to spike in Flint, and the DEQ has acknowledged it contributed to problem when it mistakenly allowed the city to use river water for more than 17 months without treating it to make it less corrosive.

Brad Wurfel, a spokesman for the state DEQ, said officials are "aware of the situation" in which Flint certified its most water samples came from high risk homes when other records indicate that not all did.

"The DEQ is investigating it as a potential enforcement case," Wurfel said in an email to The Journal.

Since The Flint Journal-MLive's inquiry, the state is now demanding the city supply information that it should have reported more than 20 years ago.

A Nov. 9 letter from the state agency to the city stated Flint has until Dec. 31 to supply it with the distribution system inventory that should have been completed by Jan. 1, 1992.

Edwards said the city's water testing results are suspect because of the service line issue, because of its past sampling methods and because the DEQ knowingly dropped two water test samples with very high lead levels in testing this year.

Edwards alleges the DEQ took that step in order to avoid exceeding limits for lead in federal law. The state has said the samples were dropped from the report because they did not meet testing criteria, including one of the tests having come from a home in which a water filter was used.

Flint's rush to find enough water tests to submit to the state is documented in an June 25 email from a DEQ representative to Glasgow, which warned Flint was running out of time to collect required water samples to be tested for lead.

The same email said the city's initial testing showed it was out of compliance with the federal threshold for lead in water.