Many sites have been investigated, and six dams were constructed in the Catskill region between 1907 and 1963 by the Board of Water Supply of the City of New York.

Preglacial valleys have been partially refilled with glacial sediments and soils to depths exceeding 400 feet. Some of the glacial units are permeable, others are impermeable.

Two earth-fill dams use concrete cut-off walls constructed with the aid of caissons. One utilized a similar cut off constructed in open excavation. A fourth dam has no concrete cut off to rock. The dams are designed with a central impermeable core of glacial till, with semipermeable soil shoulders. Such design is particularly adapted to the Catskill region with its abundance of acceptable construction materials adjacent to the sites.

Controls of embankment-fill soils include grain-size distribution, moisture content, and density. The permeability of glacial sediments that compose the dam foundation is determined by laboratory and field methods.

Throughout the Catskills, sources of concrete aggregates are usually deposits that have accumulated from the disintegration of local graywackes. This aggregate is of poor quality compared to deposits derived from igneous or metamorphic rocks.