Fifteen feet below Chuck Whittaker's feet lay water and, 5 feet below that, lay an uncharted, 200-year-old coal mine.

These measurements were significant because of the spot in the Hill District where Whittaker was standing yesterday morning -- about 30 feet up the slope behind the John Wesley AME Zion Church.

Officials have known for years that orange, acidic mine water was draining into the church's basement, as well as seeping out of the sidewalk along Herron Avenue below. But only since the state Department of Environmental Protection began efforts this year to eliminate the noxious flow have people realized just how close the ancient mine is to the church.

Jon Smoyer, a geologist with DEP's Bureau of Abandoned Mine Reclamation, said that proximity has forced a change in plans.

So Whittaker and Carnegie Mellon University graduate student Christopher Baker joined with DEP crews yesterday to try to map the old mine works. DEP officials will use the information to figure out how to safely divert the acid mine drainage.

Whittaker, a consultant with the university's Robotics Institute, yesterday lowered a newly developed sonar device called the Wet Ferret down several 6-inch bore holes that the DEP had drilled earlier in the week.

The sonar scans relayed back up the bore hole will be used to produce three-dimensional images of the water-filled mine, Baker said.

Though the mine is within the 4- to 6-foot-high Pittsburgh coal seam, early readings from the Wet Ferret showed that the void was only about 2¹*₂ feet high, suggesting that miners of two centuries ago had partially backfilled with mine cuttings and other debris.

"There's almost got to be gob piles in there," said Smoyer, referring to coal wastes, as he looked at the sonar scans.

A $67,000 project to divert the mine water away from the church basement and into the city sewers was announced by DEP officials in February.

Originally, they planned to excavate the mine to a level below that of the church basement and install french drains. But the mine is so close to the church that officials now worry that the excavation could unleash an unwanted torrent.

"This isn't a location where we can let a lot of water go at once," Smoyer explained. "You can't go in blind."

No maps exist for the mine, which is so old it doesn't even have a name.

Smoyer said crews are using the conventional method for exploring unmapped, abandoned mines -- drilling a number of exploratory bore holes in and around it. But this also seemed an opportunity to test mine mapping technology that the Robotics Institute developed following the Quecreek Mine inundation two years ago.

That accident was blamed, in part, on inaccurate maps for an abandoned mine located next to the Quecreek Mine in Somerset County. Robotic technology was proposed as one means of producing maps, or of validating existing maps, of old mines that are inaccessible to humans.

The DEP gave the Robotics Institute a $75,000 contract to help develop that technology and yesterday's sonar mapping will serve as the final demonstration project required by that contract, Whittaker said.

The institute has developed several devices for mapping abandoned mines, including a wheeled robot the size of a golf cart called Groundhog and a new, smaller version called Cave Crawler. A prototype has been completed of a robot called Minefish, which can be lowered down a bore hole to swim through a flooded mine.

The Wet Ferret used yesterday and Ferret 3, a similar downhole device that uses a laser scanner to map dry mines, are less complicated devices than the robots but also have more near-term applications, said Whittaker, who is operations manager of Workhorse Technologies, a CMU spinoff that is trying to commercialize the mapping technology.