WINDHAM — More than half of Maine’s residents get their drinking water from underground sources, but experts say the water is increasingly threatened by development and chemicals.
In 60 large municipal water systems that use ground water, contamination has shut down eight water sources, at least temporarily, in the past 12 years. Cleanup costs have run as high as $1.5 million.
Most recently, a gasoline additive was discovered in ground water near a Windham gas station.
“This North Windham case demonstrates perfectly how even a smaller development, a gas station-convenience store, can have a major impact on ground-water quality that is presently serving as a public water supply,” said George Seel, director of technical services for the state Department of Environmental Protection.
The Christy’s gas station suspected to be the source of the contaminant is less than a quarter-mile from two Portland Water District wells which supply water to about 3,000 people.
On May 1, test results showed a concentration of methyl tertiary-butyl ether, or MTBE, about three times the state’s limit.
By last week, tests showed the level of MTBE had risen to nearly eight times the limit, and one of the district’s supply wells contained traces of MTBE.
Windham is one of Maine’s fastest-growing towns, with about 100 new homes each year and a sprawling retail strip. In 1994, town officials commissioned a study of the large sand-and-gravel aquifer under the town.
The $100,000 computer model concluded that even if the town is completely developed according to existing zoning, the aquifer should remain healthy. But the model tested for pollutants from household sewage, and did not anticipate accidental releases such as a fuel spill.
“It was a very clean bill of health for the aquifer,” said Will Plumley, president of the environmental group Friends of the Presumpscot.
The contamination at Christy’s and subsequent findings at the district’s wells were especially troubling because construction of the gas station was approved based on studies conducted in 1990 that said any leak would flow west, not east toward the well.
Increased use of ground water in the area may have redirected the water’s flow and explain why it went east instead of west, experts said.
“The more development you have, the harder it is to find a location where you can say, `This is relatively free of threats to ground water,”‘ said Peter Garrett, a geologist who studied wellhead protection planning for the state in 1993.
The town’s attorney told planners that the commercial zoning that encompassed the property did not allow them to consider the threat of fuel leaks when ruling on whether the station could be built.