Army tests this week of Aberdeen drinking-water wells found no traces of a hazardous industrial chemical discovered a week ago in one of the city's 11 wells, an Aberdeen Proving Ground spokesman said yesterday.
"No perchlorate was detected in any of the wells we sampled or in the finished water," said George Mercer. "We're not really sure why that was."
Wells 7, 8, 9, 10, and 11 -- those on the base -- were tested Wednesday, he said. The other six wells are located off the base.
The "no detection" results do not mean that perchlorate, a chemical used in explosives and linked to thyroid dysfunction, is not present in the well, said Cal Baier-Anderson, a University of Maryland toxicologist who closely follows ground-water issues at the base.
"The perchlorate is hovering around the detection limits," she said. "So sometimes they'll pick it up and sometimes they won't."
Aberdeen City Manager Peter A. Dacey said the city is pleased with the results and will continue investigation and testing.
Mercer said that the city and base have devised a schedule to test the wells twice a month, and that APG would put about four dozen more probes in the area to try to detect the origin and scope of the contamination.
The detection limit used in the well tests was 1.2 parts per billion, APG officials said yesterday.
Steven R. Hirsh, a remedial project manager for the U.S. Environmental Protection Agency who works on APG cleanup issues, said the agency has devised a limit of 1.1 parts per billion in finished water from the Aberdeen site. The limit was set specifically for the site and is based on federal Superfund site risk-assessment standards, he said.
Perchlorate first was discovered in ground water in the area in March last year. Last month, the chemical was found within 300 feet of the wells, prompting further tests. The city shut down well No. 9 last week after perchlorate was detected at a level of 4 parts per billion.
Ken Stachiw, who oversees environmental cleanup projects on the base, said the base continues to move "full-steam ahead" on its investigation.