The probability of obtaining 40 gallons of water per minute from a 400 foot-deep well in New Hampshire

This geographic raster dataset presents statistical model predictions for the probability of exceeding 40 gallons per minute well yield from a 400 foot deep well, and is based on the available data.   The model was developed as part of the New Hampshire Bedrock Aquifer Assessment.  
The New Hampshire Bedrock Aquifer Assessment was designed to provide information (including this raster) that can be used by communities, industry, professional consultants, and other interests to evaluate the ground-water development potential of the fractured-bedrock aquifer in the State. The assessment was done at statewide, regional, and well field scales to identify relations that potentially could increase the success in locating high-yield water supplies in the fractured-bedrock aquifer. Statewide, data were collected for well construction and yield information, bedrock lithology, surficial geology, lineaments, topography, and various derivatives of these basic data sets. Regionally, geologic, fracture, and lineament data were collected for the Pinardville and Windham quadrangles in New Hampshire. The regional scale of the study examined the degree to which predictive well-yield relations, developed as part of the statewide reconnaissance investigation, could be improved by use of quadrangle-scale geologic mapping. 
Beginning in 1984, water-well contractors in the State were required to report detailed information on newly constructed wells to the New Hampshire Department of Environmental Services (NHDES). The reports contain basic data on well construction, including six characteristics used in this study—well yield, well depth, well use, method of construction, date drilled, and depth to bedrock (or length of casing). The NHDES has determined accurate georeferenced locations for more than 20,000 wells reported since 1984. The availability of this large data set provided an opportunity for a statistical analysis of bedrock-well yields. Well yields in the database ranged from zero to greater than 500 gallons per minute (gal/min). 
Multivariate regression was used as the primary statistical method of analysis because it is the most efficient tool for predicting a single variable with many potentially independent variables. The dependent variable that was explored in this study was the natural logarithm (ln) of the reported well yield. One complication with using well yield as a dependent variable is that yield also is a function of demand. An innovative statistical technique that involves the use of instrumental variables was implemented to compensate for the effect of demand on well yield.  Results of the multivariate-regression model show that a variety of factors are either positively or negatively related to well yields (see USGS Professional Paper 1660).   
Model results are presented statewide as the probability of exceeding 40 gallons per minute well yield from a 400 foot deep well.  Probability values represented in this raster (ranging from near 0 to near 100) have all been multiplied by 100 in order to store the data more efficiently as a raster.

Tags: geoscientificinformation, usgs-5d5aead0e4b01d82ce8ed1cb, well-yield-probability
Organization: Department of the Interior