Hydrogeology of the Schodack-Kinderhook Area, Rensselaer and Columbia Counties, New York

Abstract

Two glaciodeltaic outwash terraces in southern Rensselaer and northern Columbia Counties, known locally as the Schodack and Kinderhook terraces, consist of ice-contact and outwash sand and gravel and together form a regional, unconfined, stratified-drift aquifer with a combined area of 18.75 square miles. The hydrogeology of these aquifers is summarized on four maps at 1:24,000 scale, that depict (1) locations of wells and test holes, (2) surficial geology, (3) altitude of the water table, and (4) altitude of the bedrock surface. Both terraces are associated with a thin and probably discontinuous confined aquifer consisting of beds of glaciofluvial sand and gravel derived from the outwash deltas that form the two terraces. The confined aquifer is overlain by thick deposits of lacustrine silt and clay. Consultants? estimates of average hydraulic conductivity, based on aquifer tests conducted at four test wells screened in thicker sections of the confined aquifer, range from 430 to 2,360 ft/d (feet per day), with a mean of 1,150 ft/d. The mean estimate of hydraulic conductivity derived from specific-capacity data from 16 test wells screened in confined and unconfined sections of the aquifer is 640 ft/d. Reported yields for domestic wells completed in unconfined sections of the Schodack and Kinderhook terrace aquifers average 16.1 and 18.3 gal/min (gallons per minute), respectively, and reported yields of domestic wells completed in hydraulically confined sections of these terraces average 15.3 and 12.8 gal/ min, respectively. Yields from public-supply wells screened in the confined sections of the Schodack Terrace aquifer range from 50 to 1,050 gal/min and average 305 gal/min. Average annual recharge to the Schodack Terrace aquifer and adjacent upland till deposits, as estimated in a 1960 U.S. Geological Survey study, were 16.3 and 7.1 inches per square mile, respectively. Bedrock that underlies the study area has been highly modified by tectonic activity, differential weathering, and preglacial erosion which produced about 900 ft of relief on the bedrock surface. A major thrust fault that runs north-south through the area separates autocthonous Ordovician rock units to the west from allocthonous Cambrian (Taconic) rocks to the east.