A variety of cancer-causing chemicals and other noxious material buried at an old, illegal hazardous dump site in Prairieville exceeds safety standards for long-term human exposure — in some cases at concentrations hundreds of times higher — despite a federal cleanup about 30 years ago, new state environmental testing has found.

But Louisiana Department of Environmental Quality officials said their findings show the chemicals, including several volatile organic compounds and chlorinated solvents, aren't at the surface and don't pose a risk for human contact or consumption.

With the results in hand, DEQ officials said they will clean the subsurface to safe levels and seek any lingering barrels of the hazardous chemicals underground.

"There will be a remediation plan developed for it," said Greg Langley, a DEQ spokesman.

Workers found barrels of chemicals buried at the end of Tiger Heights Road in Prairieville in the mid-1980s when the local school system was working on a bus turnaround. It's not clear who had dumped the barrels, but the barrels were probably put there years before being rediscovered.

The wooded site is about a quarter-mile from Prairieville Middle School, which is to the northwest across a bayou and through woods and a neighborhood. Underground plumes of contamination flow away from the school.

Officials had believed the U.S. Environmental Protection Agency cleaned up the barrels three decades ago, but the site remained under monitoring. This past May, with little notice to some neighbors, DEQ resumed groundwater and soil testing of the area after earlier tests had shown persistent concentrations of chemicals in the ground and turned up magnetic anomalies that suggested barrels could still be buried at the site, agency reports show. 

The latest testing found contaminants about 13 to 15 feet underground and even deeper in the soil and in an aquifer up to around 25 feet deep. Though classified as a drinking water aquifer, the contaminated groundwater is not used for drinking and is separated by clay layers from deeper aquifers that are used for human consumption, DEQ officials said.

Though groundwater in the area moves to the north-northeast in the general direction of other homes, the public school and a bayou, the latest tests show the underground plumes of contaminants are largely contained to directly under or near the 1-acre site at the end of Tiger Heights, a new report on the testing says. 

Modeling from the recent sampling, however, does show that plumes from some of the elevated carcinogenic and toxic contaminants don't fully dissipate to safe levels underground until after they are beneath the yard of a home at the end of Tiger Heights, the report says.

Langley said tests of the nearby drinking water wells in 2014 found no contamination from the site. The nearest well is about 70 feet from the site and about 390 feet deep, the report says.

But the dump site has known or suspected carcinogens like vinyl chloride; 1,1,2-trichloroethane; and 1,2-dichloroethane in the soil at maximum concentrations of 0.55 parts per million to 7.5 parts per million, according to results published in a new report on the tests.

A part per million is the equivalent of one drop in a little more than 13 gallons of water.

The contaminant levels are 4 to 25 times greater than site-specific safety standards for chronic, daily exposure to those chemicals over a 30-year period, the new results show. The tests found five different chemicals in the shallow soil that exceeded that standard.

In the groundwater, the testing found 13 known or possible carcinogenic or otherwise toxic chemicals that exceeded the chronic exposure standards and also many others that didn't exceed the standards but were still present.

The testing found some of the chemicals at high levels in the soil were also at high levels in the groundwater, including vinyl chloride and 1,1,2-trichloroethane. The 1,1,2-trichloroethane was present in the groundwater at 44 parts per million, nearly 1,050 times greater than the DEQ's site-specific, chronic exposure standard.

1,1,2-trichloroethane is an industrial solvent deemed a possible carcinogen based on tests on mice, but not on humans, the EPA says. DEQ says the chemical can harm the liver.

Also, the vinyl chloride was found in the groundwater at a maximum concentration of 5.1 parts per million, which is 300 times the site-specific standard for long-term safety.

Vinyl chloride, used in the production of plastics, including pipes, is a known carcinogen, can cause damage to the liver and other organs, and has been known to cause reproductive problems in people who work daily with the chemical, the EPA says

June Sutherlin, a DEQ toxicologist, said the chemical safety thresholds against which the contaminant concentrations were measured are site-specific and make conservative assumptions to be more protective of public health.

She explained they were calculated with a combination of DEQ criteria to factor in soil and groundwater type, the type of toxins in the ground, the cumulative effect of multiple chemicals and the expected long-term dilution of those chemicals should they migrate past the old dump's property line. 

Cedrick Johnson, 30, whose family's home is at the end of Tiger Heights, said the area should have been fully cleaned up decades ago when the barrels were first found.

He added the illegal dump is in a neighborhood where his and other families were raised. Johnson and other residents have complained about what they saw as an unusual number and variety of cancer incidences on the street.

While he acknowledged the illnesses could be a statistical coincidence, he pointed out the dump site was used as a community garden from which his family and others were fed for years. 

"We ate off of that land, man," Johnson said Wednesday. "We grew mustard greens, collard greens, watermelons, strawberries. You know, we cultivated that land for a number of years."

He said that, at a minimum, the cleanup should ensure that the contaminants won't threaten people in the future. 

DEQ's cleanup won't completely remove all the chemicals, officials said, but reduce them to levels deemed safe.

Agency officials plan to do additional sampling to create conservative cleanup standards for the various chemicals in the ground and groundwater and then reduce the contamination to meet those levels.

Email David J. Mitchell at dmitchell@theadvocate.com

Follow David J. Mitchell on Twitter, @NewsieDave.