1. Abstract This report presents the results of a study by the U.S. Geological Survey, in cooperation with the New Hampshire Department of Environmental Services, Water Resources Division, to describe the geohydrology and background water quality of stratified-drift aquifers in the Upper Merrimack River Basin in south-central New Hampshire. The Upper Merrimack River Basin drains 519 square miles (mi2) of which 87mi2 is underlain by stratified-drift aquifers. Ground-water withdrawal from stratified-drift aquifers in the study area is about 1.8 million gallons per day or 39 percent of total ground- water withdrawals. In 1995, five towns withdrew the stratified-drift aquifers for municipal water supply. The water-supply potential of many stratified-drift aquifers in the study area is not fully developed. The largest contiguous aquifer is in the central Merrimack River Valley and covers 45 mi2. The Soucook River and Suncook River Valleys in the eastern part of the basin contain the most productive aquifers. Saturated thickness of stratified-drift aquifers is as great as 160 feet but is generally less than 80 feet. Transmissivities locally exceed 4,000 feet squared per day (ft2/d) but are generally less than 1,000 ft2/d. Stratified- drift aquifers identified as having a transmissivity greater than 2,000 ft2/d are in only 4.3 mi2 (or 0.8 percent) of the study area. Descriptors: *Geohydrology, *Ground Water quality, *Stratified-drift aquifers, *Upper Merrimack River Basin, *Soucook River, *Suncook River, *south-central New Hampshire 2. Applications that use this data 2.1 Intended use of data This data can be used to produce maps, illustrations, and perform a geographic analysis by federal, state, and local government agencies, involved with resource management and plannning. Private engineering firms and educational institutions may also benefit from this data. 2.2 Limitations of data Transmissivity values should be considered estimates only and are a result of existing data in the study area. 3. Attribute discussion TMAX -- The upper limit of the transmissivity zone, in feet squared per day. TMIN -- The lower limit of the transmissivity zone, in feet squared per day. RANGE -- A single value that defines the transmissivity zone (in feet squared per day). The folowing table explains coding for the RANGE item. 1 = 0 2 = less than 500 3 = 0 to 1000 4 = 500 to 1000 5 = 0 to 1500 6 = greater than 1500 7 = 0 to 2000 8 = 1000 to 2000 9 = 2000 to 3000 10 = greater than 3000 11 = 2000 to 4000 12 = greater than 4000 13 = 4000 to 6000 14 = greater than 6000 15 = 4000 to 8000 16 = greater than 8000 98 = unable to contour transmissivity 99 = unable to contour transmissivity and saturated thickness For example a zone with transmissivty greater than 8000 feet squared per day has a TMAX of 99999, a TMIN of 8000, and range of 16. 4. Procedures used to create or automate data Transmissivites of stratified-drift aquifers, in feet squared per day (ft2/d), were estimated from test-boring logs by calculating hydraulic conductivity for specific intervals, multiplying these values by the saturated thickness of the interval, and summing the results. Transmis- sivity values report by published engineering consultants were used as well as calculating transmissivites from unpublished aquifer test data. The transmissivity coverage is a polygon coverage where each polygon represents a range a transmissivity; for example, 0 to 1,000 ft2/d. Some polygons are hills of till that protrude the stratified-drift and, there- fore, have a transmissivty of 0ft2/d. Transmissivities were first inter- preted on paper topographic maps, then transferred to 1:24,000 scale stable mylar USGS quadrangle maps and digitized into a geographic infor- mation system (GIS), using ARC/INFO version 7.0. The quadrangle maps were then merged into one study-wide coverage and edited for errors and discrepancies. The finished study-wide coverage was erased with the hydrography coverage ( 1:24,000 scale hydrography representaion obtained from converting USGS Digital Line Graphs (DLG) into ARC/INFO coverages), so that transmis- sivity did not extend into rivers (those that were wide enough to be a polygon in the hydrography coverage) or other surface water bodies such as lakes or ponds. 5. Revisions made to data Revision after colleague and editorial review. 6. Reviews applied to data Data was reviewed by the USGS and N.H. Dept. of Environmental Services, Water Resources Division. 7. Related spatial and tabular data sets and programs Other data sets available from this study include, aquifers boundaries, saturated thickness, water table, wells, seismic lines, and low flow sites. 8. References cited GEOHYDROLOGY AND WATER QUALITY OF STRATIFIED-DRIFT AQUIFERS IN THE UPPER MERRIMACK RIVER BASIN, SOUTH-CENTRAL NEW HAMPSHIRE. by Peter J. Steckl and Sarah M. Flanagan U.S. Geological Survey Water-Resources Investigations Report 95-4123 9. Notes: The Projection is as follows: PROJECTION STATE UNITS FEET ZONE 4676 DATUM NAD83