A recent federal finding that drinking water at seven of 10 Rockingham County mobile home parks is contaminated with a gasoline additive called MTBE is surprising scientists and spurring ongoing legal efforts by the state to get oil companies to clean up the mess.
The study, released this month in the journal Environmental Science & Technology, also found that half the private wells tested in the most populous regions of the county were similarly contaminated, as are 40 percent of the community water supplies in those areas.
Most of the tested water is considered safe to drink. But state officials and the scientists who conducted the study are concerned about the wells that were not tested and why so many mobile home parks are contaminated.
"We didn't really have the data to understand why mobile home parks had so much occurrence of contamination, but it's quite striking," said Joe Ayotte, a drinking water specialist with the US Geological Survey, the principal author of the study.
The research expanded on what has long been known about the area's drinking water supplies, according to health officials in the most heavily contaminated areas. Confidentiality agreements with the well owners in the study prevented Ayotte and others from naming specific sites of contamination, but the issue is of particular concern at two dozen mobile home parks in the Salem, Derry, and Londonderry areas.
Officials say there is not much they can do.
"There is always a concern about MTBE contamination in the water here," said Salem health officer Brian Lockhard. "But in New Hampshire, small systems like those community water systems are regulated by the state."
In September 2003, the state attorney general's office filed suit to force the region's fuel suppliers to clean up New Hampshire's MTBE-contaminated ground water. Since the 1970s, methyl tert-butyl ether has been added to the nation's gasoline supplies, first as an octane boost and later as a pollution control that cut down on auto emissions.
As underground gasoline storage tanks got old and leaky, the additive started to make its way into ground-water supplies and eventually into wells. Accordingly, neighborhoods near gas stations, particularly along Route 125, have been hardest hit, according to the study.
But the high incidence of MTBE at mobile home parks is puzzling.
"We knew from previous study in Rockingham County we'd probably expect to see MTBE present when we did this study," said Fred McGarry, a spokesman for the state Department of Environmental Services, another of the study's authors. "However, we certainly didn't expect to see it in 70 percent of the mobile home parks."
The number of auto junkyards in the area could be part of the problem, McGarry said. The nature of both the chemical and the state's ground-water aquifers also greatly adds to the problem, he said. Most of the area's wells are drilled into bedrock, drawing off rainwater that seeps into fissures and gaps. Those fissures and gaps may be to blame for the widespread nature of the contamination.
The MTBE chemically binds to the ground water, unlike other forms of pollution that can get filtered out on the way to and through the bedrock aquifer. Fissures in the bedrock can stretch for miles, facilitating the transmission of MTBE over greater distances. Worse, MTBE is resistant to breaking down into less-harmful chemicals over time. So it appears MTBE has soaked deep into the Granite State's bedrock aquifers and will be very difficult to eliminate, Ayotte said.
"It's not so much a health scare that's the issue right now; it's more the character of the contamination of the bedrock aquifer from which many of us drink," he said.
A handful of wells that tested positive for MTBE exceeded the state maximum of 13 parts per billion, while most were found to have less than 5 parts per billion, according to McGarry. The chemical is a suspected carcinogen, but at the levels found in the study, a person would have to drink about a half-gallon a day for decades to contract cancer, and even then the prospects are remote, McGarry said.
Officials fear, however, that pockets of higher concentrations of MTBE could be in the bedrock and go undetected for years, Ayotte said. Another fear is that such a widespread occurrence of MTBE could mean other chemicals are present. "It is possible," Ayotte said. "When you're doing a study of this magnitude, you can't check for everything."
The state's lawsuit is in the early phases, said assistant state attorney Maureen Smith, and possibly still years away from trial. The study just released probably will play a part if the case goes to trial.
"We appreciate the unbiased and scientific approach in this study to an issue that can become very emotional," she said. "This study is very troubling for the citizens of New Hampshire. It clearly documents the persistence of the chemical in the state's water supply."