We developed a process-based model to predict the probability of arsenic exceeding 5 microg/L in drinking water wells in New England bedrock aquifers. The model is being used for exposure assessment in an epidemiologic study of bladder cancer. One important study hypothesis that may explain increased bladder cancer risk is elevated concentrations of inorganic arsenic in drinking water. In eastern New England, 20-30% of private wells exceed the arsenic drinking water standard of 10 micrograms per liter. Our predictive model significantly improves the understanding of factors associated with arsenic contamination in New England. Specific rock types, high arsenic concentrations in stream sediments, geochemical factors related to areas of Pleistocene marine inundation and proximity to intrusive granitic plutons, and hydrologic and landscape variables relating to groundwater residence time increase the probability of arsenic occurrence in groundwater. Previous studies suggest that arsenic in bedrock groundwater may be partly from past arsenical pesticide use. Variables representing historic agricultural inputs do not improve the model, indicating that this source does not significantly contribute to current arsenic concentrations. Due to the complexity of the fractured bedrock aquifers in the region, well depth and related variables also are not significant predictors.

We report the first chronology, using four new optically stimulated luminescence dates, on the sedimentary record of Glacial Lake Pickering, dammed by the North Sea Lobe of the British-Irish Ice Sheet during the Dimlington Stadial (24-11 ka cal BP). Dates range from 17.6 AE 1.0 to 15.8AE 0.9 ka for the sedimentation of the Sherburn Sands at East Heslerton, which were formed by multiple coalescing alluvial fans prograding into the falling water levels of the lake and fed by progressively larger volumes of debris from the Wolds. Fan formation ceased $15.8 ka, at a time when permafrost was degrading and nival-fed streams were no longer capable of supplying sediment to the fans. A further age of 10.1 AE 0.7 ka dates the reworking of coversand into the early part of the Holocene, immediately post-dating Younger Dryas periglacial structures. A 45-m lake level dates to $17.6 ka, when the North Sea Lobe was already in retreat, having moved eastward of the Wykeham Moraine; it stood further east at the Flamborough Moraine by $17.3 ka. The highest (70 m) lake level and the occupation of the Wykeham Moraine date to an earlier phase of the North Sea Lobe occupation of the Vale of Pickering. #

Methyl tert-butyl ether (MTBE) concentrations g0.2 µg/L were found in samples of untreated water in 18% of publicsupply 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 publicsupply wells and increased in 60 private-supply wells, but neither trend was statistically significant.