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Corpus Christi Caller-Times via Associated Press, Gabe Hernandez
In this Thursday, Dec. 15, 2016 photo, a woman reaches for bottles of water after a recent back-flow incident in the industrial district according to a city news release, at H-E-B in Corpus Christi, Texas.

DALLAS — A chemical leak from an asphalt plant that led Corpus Christi officials to warn its 300,000 residents not to drink the water this week was apparently reported a week earlier, according to an email from a state environmental official.

The internal email sent Wednesday by Susan Clewis, a regional director for the Texas Commission on Environmental Quality, contained an incident report that described the leak as a "backflow incident from a chemical tank impacting the public water system." It was reported Dec. 7 at a plant run by Ergon Asphalt and Emulsions.

The email, obtained Friday, doesn't say who initially reported the leak or to whom. It says the state environmental agency was notified around 3 p.m. Wednesday. City officials notified the public that evening.

"Obviously we are concerned about that initial report, that this may have been known for seven days and it may have been going on for that long. And why did it take so long for TCEQ to get notified?" asked Luis Moreno, chief of staff for state Sen. Juan Hinojosa, whose district includes Corpus Christi. "Those are all things that I think are starting to be figured out right now."

Mayor Dan McQueen has said local officials also only learned of the leak Wednesday. Neither Clewis nor city officials responded to requests for comment Friday, when many schools were closed for a second day.

It's the latest in a string of water scares for the Gulf Coast city. In May, the city issued its third boil-water advisory in a year as a precaution after nitrogen-rich runoff from rain flowed into the water system, resulting in low chlorine disinfectant levels in the water supply.

The TCEQ report indicates that a combination of Indulin AA-86 and hydrochloric acid leaked into the water supply. Indulin is an asphalt-emulsifying agent that's corrosive and can burn the eyes, skin and respiratory tract if a person comes into contact with concentrated amounts. The amber liquid is considered a hazardous material by the Occupational Safety and Health Administration.

"You don't expect to see it in water," Texas Commission on Environmental Quality spokesman Terry Clawson said.

Up to 24 gallons of indulin may have seeped into a pipeline carrying water, allowing it to move to other areas of the city, city spokeswoman Kim Womack said Thursday.

Ergon has said it has been in contact with the TCEQ and was "working cooperatively to provide all information to ensure state officials can remedy the situation as quickly as possible." Company spokesman Bill Miller declined to explain Friday how a hazardous chemical may have entered the water supply.

State and city officials have referred to a "backflow problem" at the plant, and Womack said inspectors didn't find a device that prevents contaminated water from flowing backward into a potable water supply. Ergon has argued that the plant does have a prevention device, Womack said.

Miller said Ergon Inc. is leasing the property for manufacturing purposes. The privately held Flowood, Mississippi-based conglomerate's Corpus Christi subsidiary makes paving and pavement preservation products.

State and federal environmental records list no problems at the plant over the past five years. A Texas Commission on Environmental Quality record lists an emergency response March 24 as having been closed. Clawson said he had no details.

Nationwide, the Environmental Protection Agency reports no current "significant violations" at Ergon facilities but shows seven receiving fines since 2010, the highest $17,200 at a Vicksburg, Mississippi, refinery.

Meanwhile, city officials eased restrictions Friday on the use of tap water while workers flushed water pipes to make sure any remnants of the chemical are removed.

Residents in some parts of the city are now allowed to consume water however they wish, but authorities urge no use at all in other parts. Some neighborhoods can only use the water for showering and washing clothes, but not drinking.

Officials said plenty of bottled water has been donated to help residents.

No one has turned up at hospitals with symptoms that might indicate they were sickened or burned by the chemical, officials say. City councilman Michael Hunter told the Corpus Christi Caller-Times it was unlikely the leaked chemical was concentrated enough to do harm, but that every precaution must be taken.

Bajak reported from Houston. Associated Press writer Paul J. Weber in Austin contributed to this report.