This report is the fourth in a series of 11 map sets depicting geohydrologic conditions in selected aquifers in upstate New York. Geohydrologic data are compiled on six maps at 1:24,000 scale. Together the maps provide a comprehensive overview of the Schenectady aquifer, the principal aquifer in Schenectady County and the most heavily pumped aquifer in upstate New York. The maps include surficial geology, geologic sections, soil permeability, water-table altitude, aquifer thickness, estimated well yield, and land use. The maps are designed to enable planners to evaluate underground waste-disposal practices that could adversely affect the aquifer. (USGS)