MTBE Found in Four New Hampshire Counties

The gasoline additive methyl tert-butyl ether (MTBE) is widespread in New Hampshire’s groundwater, particularly in Rockingham, Strafford, Hillsborough and Merrimack counties. Groundwater from these counties was more likely to contain MTBE than were samples from the rest of the state.

Statewide, however, the MTBE concentrations were significantly below the state drinking water limit and the federal drinking water advisory. These findings were released recently by the U.S. Geological Survey.

“In the four counties using reformulated gasoline, we found MTBE at or above 0.2 parts per billion (ppb) in 30 percent of public supply wells and in 17 percent of the private homeowner wells,” said Joseph Ayotte, USGS hydrologist and lead author of the study.

“One in every three wells tested in Rockingham County had MTBE. In the most densely populated areas of the county, one in two wells tested contained MTBE,” said Ayotte. “We also found that more than 70 percent of the water tested from wells serving mobile home communities in the state had MTBE.

“While levels are mostly very low, the study shows that MTBE occurs in groundwaters throughout the state. A low analytical measurement of 0.2 ppb enabled us to characterize MTBE contamination throughout the state,” said Ayotte.

For this study, scientists sampled more than 800 wells throughout New Hampshire in 2005 and 2006. Statewide, scientists detected MTBE in untreated groundwater from 18 percent of the public supply wells and 9 percent of the private wells tested. Despite the prevalence of MTBE in water samples from wells, most concentrations measured were less than 1 ppb. About 2 percent of the public and 1 percent of the private wells sampled had levels that were greater than the state of New Hampshire health-based limit of 13 ppb.

Starting in 1979, MTBE was added to gasoline as an octane booster to replace lead. In 1995, under the Clean Air Act, cleaner-burning reformulated gasoline was required for areas with the worst smog. In New Hampshire, that meant Rockingham, Strafford, Hillsborough and Merrimack counties. Reformulated gasoline in New Hampshire had about 11 percent MTBE by volume. In January 2007, New Hampshire banned MTBE use in gasoline.

No data exist on the human health effects of ingesting MTBE in drinking water, although some studies have generated concern about possible cancerous and non-cancerous effects. No federal regulatory standards have been set for MTBE, but an advisory of 20-40 ppb has been issued by the U.S. Environmental Protection Agency.

Much of New Hampshire’s public and private water supplies are derived from wells drilled into surficial and bedrock aquifers, where groundwater can travel slowly. This, in addition to factors like New Hampshire’s unique geologic formations and fractured-rock aquifers, makes it uncertain how long MTBE will persist in the state’s groundwater.

The USGS report, “Methyl tert-Butyl Ether (MTBE) in Public and Private Wells in New Hampshire: Occurrence, Factors, and Possible Implications,” is published in the journal Environmental Science & Technology.

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