BRINGING THE RESULTS OF THE NEW HAMPSHIRE BEDROCK AQUIFER ASSESSMENT TO YOUR BACKYARD

The U.S. Geological Survey (USGS), in cooperation with the New Hampshire Department of Environmental Services (NHDES), investigated the yields of wells in New Hampshire's bedrock aquifer. The NHDES compiled the data set, used for the study, which includes 20,308 wells with information on yield, depth, and construction. The analysis produced a statewide GIS grid of well-yield probabilities that may be used to assess the potential for water supply in the bedrock aquifer. USGS Professional Paper 1660, Factors Related to Well Yield in the Fractured-Bedrock Aquifer of New Hampshire, documents the statistical model.

Multiple regression, using instrumental variables, was the primary method of analysis. The results indicated that well yield is generally lower in wells located on steep hill slopes and hilltops, and at a greater distance from surface-water bodies. Yields are greater in wells located in valleys, at sites with large upgradient topographic drainage areas, and within 100 feet of some types of lineaments. Well yields also correlate with 29 mapped geologic units. For example, the Frontenac and Rye Formations have high yields.

Quadrangle-scale investigations were done to determine the degree to which predictive well-yield statistical relations can be improved by local geologic mapping. Additional geologic, fracture, and lineament data were collected for the Pinardville and Windham, N.H. quadrangles, where data from numerous wells (1,682 and 1,504 wells, respectively) were used to test the value of the additional mapping information. The statistical model was applied with and without the additional data. Yield-probability maps were produced for both quadrangles with and without the added data. These maps clearly demonstrate the advantage of including detailed geologic map units and fracture-correlated lineaments when predicting well yield.

The USGS has developed an interactive web-based interface for viewing and accessing the New Hampshire Bedrock Well-Yield Probability model results. The model results can be viewed and accessed for over 25.7 million 30x30-meter grid cells covering the entire land area of New Hampshire. Report publications also include statewide lineament maps, a report on geophysical techniques, and a report on the bedrock water quality.