Project Summary:

MTBE has been found in groundwater in New Hampshire since its initial use in 1979 as an octane booster and then as an oxygenate in reformulated gasoline in the 1990s, but the extent of methyl tert-butyl ether (MTBE) contamination in drinking-water wells in the state is not well documented. A 2003 study in southeast New Hampshire identified widespread, low-level MTBE contamination in untreated water from public and private drinking-water supplies. Public water suppliers monitor MTBE concentrations in their finished water, but raw water (water prior to treatment) is not routinely monitored. Based on existing finished-water data from public water-supply systems, contamination of public supplies with MTBE concentrations greater than 0.5 µg/L in New Hampshire has risen from 12.7% in 2000 to 15.7% in 2005. MTBE contamination is greatest in the four counties where reformulated gasoline (RFG) use was mandated. In three of the four counties that were required to use RFG year-round since 1995, 20% of the public supplies had MTBE above 0.5 µg/L in 2004 and 2005. RFG contained about 11% MTBE by volume in New Hampshire. This study is the first comprehensive evaluation of MTBE in untreated groundwater from public and private drinking-water wells in the state. National and regional studies show that redox, MTBE sources, biochemistry, and hydraulics are important to MTBE occurrence and that identifying factors to predict occurrence can help to understand trends. We identify physical, environmental, and anthropogenic factors associated with MTBE occurrence in public- and private-supply wells and report on preliminary trends in MTBE concentrations from paired well samples collected in 2003 and 2005.

Methyl tert -butyl ether (MTBE) concentrations =0.2 µg/L were found in samples of untreated water in 18% of public-supply wells (n = 284) and 9.1% of private domestic wells (n = 264) sampled in 2005 and 2006 in New Hampshire . In counties that used reformulated gasoline (RFG), MTBE occurred at or above 0.2 µg/L in 30% of public- and 17% of private-supply wells. Additionally, 52% of public-supply wells collocated with fuel storage and 71% of mobile home park wells had MTBE. MTBE occurrence in public-supply wells was predicted by factors such as proximity to sources of fuel, land use, and population density, as well as low pH and distance from mapped lineaments. RFG use, land-use variables, and pH were important predictors of private-well MTBE occurrence. Variables representing sources of MTBE, such as the distance to known fuel sources, were not significant predictors of MTBE occurrence in private-supply wells. It is hypothesized that private wells may become contaminated from the collective effects of sources in high population areas and from undocumented incidental releases from onsite or proximal gasoline use. From 2003 to 2005, MTBE occurrence decreased in 63 public-supply wells and increased in 60 private-supply wells, but neither trend was statistically significant.