MORGANTOWN -- Two years after it was charged to do so, and 13 months after its original deadline, the West Virginia Department of Environmental Protection remains unable to answer a question that worries thousands in the southern coalfields: Are water supplies and human health at risk when a chemical soup from the cleaning of coal is pumped into worked-out underground mines?

"We have some concerns, to be quite honest with you,'' DEP Director Randy Huffman told The Associated Press about coal slurry injection. "We have questions we're trying to get some answers to, to make sure it's safe.''

Yet coal operators are still permitted to inject slurry at 15 locations.

The DEP cannot say precisely what's in that waste, how much is injected annually, or whether and where it migrates. Nor is it under any pressure to do so: The U.S. Environmental Protection Agency hasn't studied the practice in a decade and said in 2002 its existing rules were adequate to protect groundwater.

Slurry is created when coal is washed with water and chemicals to separate clay, rock and other impurities that keep the carbon from burning efficiently. Underground injection is one of the ways companies can legally dispose of it. It can also be stored in massive impoundments or dried and buried in earthen cells.

While EPA administers some states' injection programs, it says the use of "mine backfill wells'' for coal waste is so widespread and varied, many states -- including West Virginia -- run their own. The state regulations "vary significantly in their scope and stringency,'' EPA says.

In 1999, EPA identified 5,000 backfill wells in 17 states but estimated there were more than 7,800 others. More than 90 percent of the known sites were in Ohio, West Virginia, Idaho and North Dakota.

And even though residents of several West Virginia communities are now suing coal companies and claim to have tests showing their water is contaminated with toxins including arsenic, lead and manganese, the DEP says it's confident underground injection is not to blame.

Huffman says DEP has been unable to link the failure of a drinking water supply in West Virginia to an injection site in more than a decade, since a mid-1990s incident at a Buffalo Mining operation in Logan County.

"Sometimes you just have bad water,'' he said.

EPA says it's never found a drinking water contamination that is "directly attributable'' to slurry injection, either -- again, based on the 10-year-old report. "Although groundwater contamination is not uncommon at mining sites,'' it said, "it is generally difficult to identify the specific causes.''

"We have some concerns, to be quite honest with you,'' DEP Director Randy Huffman told The Associated Press about coal slurry injection. "We have questions we're trying to get some answers to, to make sure it's safe.''

Yet coal operators are still permitted to inject slurry at 15 locations.

The DEP cannot say precisely what's in that waste, how much is injected annually, or whether and where it migrates. Nor is it under any pressure to do so: The U.S. Environmental Protection Agency hasn't studied the practice in a decade and said in 2002 its existing rules were adequate to protect groundwater.

Slurry is created when coal is washed with water and chemicals to separate clay, rock and other impurities that keep the carbon from burning efficiently. Underground injection is one of the ways companies can legally dispose of it. It can also be stored in massive impoundments or dried and buried in earthen cells.

While EPA administers some states' injection programs, it says the use of "mine backfill wells'' for coal waste is so widespread and varied, many states -- including West Virginia -- run their own. The state regulations "vary significantly in their scope and stringency,'' EPA says.

In 1999, EPA identified 5,000 backfill wells in 17 states but estimated there were more than 7,800 others. More than 90 percent of the known sites were in Ohio, West Virginia, Idaho and North Dakota.

And even though residents of several West Virginia communities are now suing coal companies and claim to have tests showing their water is contaminated with toxins including arsenic, lead and manganese, the DEP says it's confident underground injection is not to blame.

Huffman says DEP has been unable to link the failure of a drinking water supply in West Virginia to an injection site in more than a decade, since a mid-1990s incident at a Buffalo Mining operation in Logan County.

"Sometimes you just have bad water,'' he said.

EPA says it's never found a drinking water contamination that is "directly attributable'' to slurry injection, either -- again, based on the 10-year-old report. "Although groundwater contamination is not uncommon at mining sites,'' it said, "it is generally difficult to identify the specific causes.''

In 2006, West Virginia lawmakers ordered DEP and then-director Stephanie Timmermeyer to take a comprehensive look at slurry injection, demanding such details as the chemical composition of slurry, a toxicology study on how it might affect human health and a hydro-geologic study on underground migration.

Huffman, however, will appear before the Joint Committee on Government and Finance this week with few answers. Though he will have been briefed enough to give an oral report, he told the AP a written document is not yet complete.

It was easier for legislators to ask the questions, he said, than it has been for regulators and scientists to answer them.

"It's better to be right than to rush through and meet some kind of deadline because there could be some kind of legislative changes proposed as a part of our findings,'' Huffman said. "And I'm more concerned, as is always the case, about what I don't know.''

The federal Office of Surface Mining, one of DEP's partners in the project, agrees.

"We're delving into some areas where we're looking at the composition of slurry and the chemical properties of slurry and things that are a little unusual for us to investigate, so we've had to learn some new techniques,'' said Roger Calhoun, director of the OSM Charleston field office.

The state Bureau for Public Health, meanwhile, has a year to develop recommendations once DEP's report is done.

In theory, underground injection allows slurry to separate over time, the solids settling to the bottom. If the geology remains undisturbed, the waste remains trapped.

Critics say that's a big if. Voids can be disrupted by the natural collapsing and settling of old mine works, or by blasting and other mining activities nearby. Too much rain can trigger blowouts. And old mines can be accidentally punctured.

"An abandoned mine is not a sealed tube. You can't put something in there and assume it's going to stay. As soon as you put it in there, it starts to move,'' said Marshall University environmental science professor Scott Simonton, a consultant who also serves on the West Virginia Environmental Quality Board.

The West Virginia Coal Association contends chemicals in slurry bond to the solids, rendering the water essentially clean. But Simonton calls that notion "ridiculous,'' noting many dissolve and remain suspended.