A study was done by the U.S. Geological Survey, in cooperation with the New Hampshire Department of Environmental Services, Water Resources Division, to describe the geohydrology and water quality of stratified-drift aquifers in the Middle Connecticut River Basin, west-central New Hampshire Stratified-drift aquifers discontinuously underlie 123 mi2 (square miles) of the Middle Connecticut River Basin, which has a total drainage area of 987 mi 2. Saturated thicknesses of stratified drift in the study area are locally greater than 500 feet but generally are less than 100 feet. Aquifer transmissivity locally exceeds 4,000 ft2/d (feet squared per day) but is generally less than 1,000 ft2/d. In only 17.2 mi2 of the study area are the aquifers identified as having a transmissivity greater than 1,000 ft2/d. As of 1990, total groundwater withdrawals from stratified drift for municipal supply were about 1.5 Mgal/d (million gallons per day) in the study area. Many of the stratified-drift aquifers underlying the study area are not developed to their fullest potential. The geohydrologic investigation of the stratified-drift aquifers focused on aquifer properties, including aquifer boundaries; recharge, discharge, and direction of ground-water flow; saturated thickness and storage; and transmissivity. Surficial-geologic mapping assisted in the determination of aquifer boundaries. Data from more than 1,000 wells, test borings, and springs were used to prepare maps of water-table altitude, saturated thickness, and transmissivity of stratified drift. More than 11 miles of seismic-refraction profiling at 95 sites was used in the preparation of the water-table-altitude and saturated-thickness maps. Seismic-reflection data collected along 1.6 miles of Mascoma Lake also were used in preparation of the saturated-thickness maps. Four stratified-drift aquifers in the towns of Franconia, Haverhill, and Lisbon were analyzed to estimate the water availability on the basis of analytical ground-water model simulation based on the Theis confined-flow equation adjusted to account for boundary effects commonly associated with stratified-drift aquifers. Conservative estimates of water availability during a 180-day period of no recharge were estimated to be 1.9 Mgal/d for the Meadow Brook aquifer; 1.8 Mgal/d for the Ham Branch Brook aquifer; 1.5 Mgal/d for the Salmon Hole aquifer; and 1.4 Mgal/d for the Haverhill-French Pond aquifer. Water-availability estimates would be higher if periods of recharge were accounted for and if less conservative boundary conditions were used in the model. Results of analysis of water samples from 26 observation wells, 3 municipal water-supply wells, and 1 public-supply spring show that, with the exception of dissolved iron and manganese in some samples, water in the stratified-drift aquifers generally meets the U.S. Environmental Protection Agency's primary and secondary drinking-water standards.
