The stratigraphy and hydraulic properties of tills in southern New England

Abstract

The two widely recognized tills of southern New England were deposited during two late Pleistocene continental glaciations.The surface (upper) till consists of relatively sandy tills deposited during the late Wisconsin glaciation and includes compact subglacial lodgement and meltout units and a thin overlying supraglacial meltout (ablation) unit.The drumlin (lower) till is the locally preserved till deposited during the Illinoian glaciation and consists chiefly of a compact subglacial lodgement unit.These tills are highly variable in texture, composition, thickness, and structural features, reflecting the composition of the local bedrock and older surftcial materials from which they were derived and the different modes of deposition.The hydraulic properties of tills in this region are also variable because of the differences in texture, composition, and structural features that result from different provenance and genesis.Data on hydraulic properties at 92 sites were compiled from readily available sources.The horizontal hydraulic conductivities of tills derived from crystalline (metamorphic and igneous) rocks range from 1.4 x 10' to 2.3 x 10' centimeters per second, whereas the vertical hydraulic conductivities of tills derived from these rock types range from 4.7 x 10' to 3.4 x 10' centimeters per second.The porosities and specific yields of 15 undisturbed till samples, also composed of crystalline-rock detritus, range from 22.1 to 40.6 percent and from 3.9 to 31.2, respectively.The horizontal hydraulic conductivities of tills derived from the Mesozoic (Triassic and Jurassic) sedimentary rocks of central Connecticut and west-central Massachusetts range from 2.8 x 10' to 1.2 x 10' centimeters per second, whereas the vertical hydraulic conductivities range from 1.8 x 10' to 1.2 x 10" centimeters per second.The porosity of 58 samples of till derived from these sedimentary rocks ranges from 18 to 40.1 percent.