Experts told Marriottsville residents about fracture trace analysis, baseline risk assessment and uncertainty analysis Tuesday night, but conceded they weren't ready to answer residents' main question.
"Is the water going to be safe?" asked one of the 120 people at the meeting on ground water contamination at Howard County's Alpha Ridge Landfill in Marriottsville. The landfill is about two miles south of the Carroll-Howard line.
Earlier Tuesday, several residents and Howard County officials toured the landfill site.
Toxins have not turned up in tests of selected residents' wells nearby. But Tuesday night, Ethel Doll, whose property borders the landfill, said a July 1991 test of her well showed traces of a contaminant.
Donald L. Gill, a University of Maryland Medical School professor of biochemistry and landfill activist, said the chemical found in Ms. Doll's well, tetrachlorethene, a common dry cleaning chemical, turned up in high levels in samples taken from the bedrock monitoring well.
Other chemicals found in the samples included methelene chloride, a chemical used for stripping paint; and trichloroethene, a substance used to clean grease from machinery. Each is a suspected carcinogen.
Dr. Gill noted that many people in the area use filtration systems, and that "organic compounds are taken out very easily with carbon filters."
Public Works Director James M. Irvin said subsequent tests of Ms. Doll's well turned up nothing.
Residents were given an overview of the problem, starting in 1990 with the first discoveries of volatile organic compounds (VOCs) in shallow wells north and west of the 13-year-old clay-lined landfill cell.
"This class of chemicals is commonly observed in ground water that emanates from landfills," explained Robert M. Cohen, principal hydrogeologist for GeoTrans Inc., which was awarded a county contract in November to study ground water contamination at the landfill.
In September, tests conducted by the county showed high levels of VOCs in bedrock, which residents had previously been told would be a barrier to contamination of their drinking water.
Howard County Councilman Charles C. Feaga said that to keep residents informed, the county will send a monthly or quarterly newsletter about the landfill study to people who signed up for it Tuesday night.