The mystery of the missing sludge--900,000 gallons of raw sewage that escaped into the porous subterranean world beneath a Frederick County, Md., town--continued yesterday as residents of Walkersville boiled their well water and experts prepared to pour dye down the hole where the waste disappeared.

Town officials fanned out across the town of 7,500, delivering pamphlets that cautioned people to be wary of water drawn from the three municipal wells. Bottled water quickly disappeared from store shelves.

"In Walkersville right now, it costs less to take a bath in beer than to take one in water," George Ford, 76, cracked as a friend lugged off gallon jugs of water selling for nearly a dollar each.

Officials were concerned that the waste--which spilled from a broken sewer line Friday, enough to fill about 44 swimming pools--may have spread into the town's water supply because of the area's unusual geology.

The limestone deposits under the town are extremely porous, riddled with cracks and fissures, channels that could offer the sewage a shortcut to the water supply or carry it off in another direction entirely.

The spill was an accidental byproduct of continuing suburban sprawl in the once mainly rural county. It occurred as a construction company began to convert the site of a former dairy farm--now surrounded by town houses and newly built homes--into a 265-unit development of single-family homes to be called Sun Meadow.

By Monday, when officials learned that construction workers had shattered an 18-inch sewer pipe, more than 900,000 gallons of the smelly substance was gone.

Walkersville's water comes from three wells about a mile from the spill site. Officials said the town draws water from about 22 feet below the surface.

Officials tested water at the town's treatment plant every six hours yesterday, and no unusual rise in bacteria levels had been detected, according to Elizabeth Pasierb, planning and zoning administrator for Walkersville.

Private well-water users and residents with immature or compromised immune systems--infants, the elderly, AIDS patients, people receiving chemotherapy--were advised to boil tap water. Those at-risk groups can suffer severe illness as a result of the most serious contaminants in the sewage: the chlorine-resistant microorganisms cryptosporidium and giardia. Test results for those two microorganisms are not due back for days.

"We have hired a hydro-geologist and we have an engineer, and we are hoping they will be able to tell us where this may have gone and when we can stop worrying," Pasierb said.

The detective work was set back yesterday when some county workers appeared to labor at cross-purposes.

The hydro-geologist hired by the town had been summoned to conduct tests at the construction site, where workers had scooped a 40-foot-wide, 15-foot-deep hole to repair the broken sewer pipe. Among other procedures, the specialist was going to inject a nontoxic dye into the ground and follow its path to see where it ends up and when. But other county workers began filling the hole yesterday morning "to stabilize it and make the area safe," Pasierb said.

"We may have to re-excavate now," she said. "It was just a miscommunication."

Pasierb said officials also are trying to plan for the possibility that the water may be contaminated.

"We could get a portable treatment system and run our water through that, or we could get water from some other system. . . . We might even lay temporary pipe. We're looking into everything at this point," she said.

As for who is responsible for the accident, town officials said the excavation company clearly should have known that it was working in the path of a major sewer interceptor line.

A two-person crew from Explosives Experts, of Sparks, Md., had been at the site Friday, drilling the ground for explosive charges that would clear a path for utility lines to the new development.

As required by state utility law, the construction company filed notice of its excavation plans with Frederick County, which operates the sewer system, Pasierb said. County officials visited the site and placed flags in the spot where the line runs, she said.

A spokesman for the company acknowledged that the company had been told about the sewer line and should have avoided it.

"It's just a case of human error. Yes, we blasted too close to the sewer line," said Evans Bildstein, the company's general superintendent.

Bildstein said he believes there were no county flags on the site showing the location of the sewer line, but he acknowledged that "it is on the plans. Or we could have lined up the manholes and figured it out."

Walkersville residents--even those not among the at-risk population--all seemed to be buying water or boiling their tap water.

"It is scary," said Louis Maire, 76, who describes himself as well-versed in the dangers of waterborne bacteria, such as E. coli, from his job years ago as a bacteriologist at the Baltimore health department. "Those things can be pretty bad. We're definitely boiling our water."

Betty Jane Crum, 74, dipped water out of an old enamel bucket, ladled it into a pot on her stove and worried about how long to boil it.

"Some say three minutes will do it, but I just don't know," she fretted.

What about tooth-brushing? Others wondered.

"Can you use the tap water for tooth-brushing? I've been using boiled water for that, too," Fred Eyler, 67, said as he hauled two big bottles of spring water up to the Food Lion checkout.

CAPTION: Fred Eyler leaves the grocery store with two jugs of water. "Can you use the tap water for tooth-brushing?" he asked. "I've been using boiled water for that, too." Bottled water disappeared from stores after officials warned people to be wary of water from the three municipal wells.

CAPTION: "Some say three minutes will do it, but I just don't know," Betty Jane Crum said of how long to boil her tap water.

CAPTION: Shawn Wood works at the site where a sewage pipe ruptured in Walkersville, Md. The sewage escaped into the porous world beneath the town.