Various health advisory signs were posted around a creek just west of Monterey Way between Sixth and Eighth Street where unauthorized dumping of used cooking grease was recently discovered.

A business illegally dumped several thousand gallons of cooking grease into a city manhole, causing water contamination and intensive cleanup.

“I’m concerned that somebody thought that this was OK to do or didn’t care,” said Matt Bond, city stormwater engineer. “Somebody had to have known that this was wrong and they still did it.”

Bond said the grease was dumped last week into a manhole near the intersection of West Sixth Street and Monterey Way and was of a magnitude he had not seen before. He said it isn’t yet known what business dumped the grease, but that it was done deliberately.

“It wasn’t just a five-gallon pail that somebody dropped in there,” Bond said. “It almost looks as if somebody opened up our manhole and a grease truck deliberately dumped stuff into it.”

Cooking grease — whether it be animal fat or vegetable oil — is as damaging to the environment as petroleum oil, according to the Environmental Protection Agency. Dumping oil of any kind is illegal under federal law and city ordinances that regulate pollutants, and Bond said the Lawrence Police Department is investigating the incident.

Specifically, the manhole used by the business to dump the grease is located between Hy-Vee grocery store and a strip mall that includes Chipotle, Subway and Little Caesars Pizza. The manhole and adjoining storm sewer line are located in the Quail Creek watershed. The city issued a health and stream advisory Saturday for the area near Sixth Street and Monterey Way after elevated bacteria and contaminants were detected.

After a days-long cleanup of the city sewer system and the creek, Bond said the advisory was lifted Wednesday. He said the city hired plumbers to clean the city sewer lines, a hazardous materials cleanup crew to decontaminate the creek and a septic service to collect runoff from the cleaning.

Bond said the total cost for the cleanup isn’t yet known, but that “easily dozens” of hours were spent, some of which were after regular business hours.

“Ace Pipe Cleaning came out Friday night and was here until 1:30 Saturday morning cleaning that pipe,” Bond said. “And then Monday we came out and started cleaning up the stream banks.”

Bond said before the decontamination, the creek was covered with a sheen of oil.

Dumping or spilling animal fats and vegetable oils can cause “devastating impacts” on aquatic environments, according to the EPA. A spill of only one gallon of oil can contaminate a million gallons of water. Spills can suffocate animals and plants by coating them with oil, form toxic products, produce rancid odors, clog water treatment plants and catch fire when ignition sources are present.

Dumping is illegal under the Clean Water Act, and federal regulations for the discharge of cooking oils have the same prevention and control requirements as for petroleum oil.

The Lawrence Police Department did not immediately respond to a request for additional information regarding the investigation Wednesday afternoon.