Statewide Aquifer Transmissivity for New Hampshire

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. Transmissivity values report by published engineering consultants were used as well as calculating transmissivites from unpublished aquifer test data.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, therefore, have a transmissivty of 0ft2/d. Transmissivities were first interpreted on paper topographic maps, then transferred to 1:24,000 or 1:25,000 scale-stable mylar USGS quadrangle maps and digitized into a geographic information system (GIS), using ARC/INFO version 6.0. The quadrangle maps were then merged into one study-wide coverage and edited for errors and discrepancies. The finished study-wide coverage was clipped to the hydrography coverage ( 1:24,000 or 1:25,000 scale hydrography representaion obtained from converting USGS Digital Line Graphs (DLG) into ARC/INFO coverages), so that transmissivity 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. Revisions were made after colleague and editorial review. Data were reviewed by the USGS and N.H. Dept. of Environmental Services, Water Resources Division.

Data from 13 drainage basin transmissivity datasets were merged to create one statewide shapefile. Polygons with no transmissivity data were removed. In regions where study areas overlap, numerous sliver polygons may occur. In these areas, use of the study area-level datasets may provide more consistent data.

Metadata containing available information were complied for these data.