The Usquepaug-Queen River Basin study describes the hydrogeology, water quality, and simulation of pumping from wells for selected ground-water-development alternatives in the ground-water reservoir under average (1975-90) and drought (1963-66) conditions. In general, ground-water quality is suitable for most purposes. The study provides an evaluation of the effects of simulated pumping of 4 to 11 million gallons per day of ground water on the stream-wetland-aquifer system.

Three principal geologic units underlie the Usquepaug-Queen River Basin glacial stratified deposits (stratified drift), glacial till, and crystalline bedrock. Thick and extensive deposits of saturated coarse-grained stratified deposits form the major and most productive aquifer in the Usquepaug-Queen River Basin. The 36.1-square mile Usquepaug-Queen River Basin is in the Pawcatuck River Basin in southern Rhode Island. Stratified deposits cover about 42 percent of the basin and reach a maximum known thickness of 122 feet. The stratified deposits are subdivided into coarse-grained units (dominantly fine to very coarse sand and gravel) and fine-grained units (dominantly very fine sand, silt, and clay). Transmissivity is highest in coarse-grained stratified materials, which have the capability of yielding relatively high volumes of water to wells. Transmissivity is lowest in fine-grained stratified materials, which consist predominantly of lakebottom deposits. Transmissivity of the stratified drift aquifer ranges from 1,900 to 27,800 feet squared per day, and horizontal hydraulic conductivity ranges from 25 to 470 feet per day. The stratified-drift aquifer is the only aquifer in the Usquepaug-Queen River Basin capable of producing yields of 0.5 million gallons per day or more from individual wells. Pumping from ground-water and surface-water sources in the Usquepaug-Queen River Basin averaged 0.28 million gallons per day during 1989 and 0.48 million gallons per day during 1990.

Ground water and surface water (which is primarily ground-water runoff) in the UsquepaugQueen River Basin are suitable for most purposes on the basis of a comparison of physical properties and chemical constituents to drinking-water standards. Ground water in the basin is somewhat corrosive because of its low hydrogen-ion concentration. Specific conductance and concentrations of dissolved chloride and dissolved sodium are high in ground water in parts of the Usquepaug-Queen River Basin, which indicates the effects of highway de-icing salts on groundwater quality. Nitrogen (nitrite plus nitrate) concentrations in some localized areas exceed the U.S. Environmental Protection Agency maximum contaminant level of 10 milligrams per liter for drinking water.

The effects of selected ground-waterdevelopment alternatives on ground-water levels, wetland-water levels, and streamflow in the Usquepaug-Queen ground-water reservoir were evaluated by means of a three-layer ground-waterflow model. Development alternatives were simulated for average annual (1975-90) and drought (1963-66) conditions. In general, higher simulated pumping rates produced greater drawdowns than lower pumping rates. Drawdowns generally can be reduced by distributing the total pumping over many wells; however, drawdowns were minimal (less than 1.3 feet) in well SNW 906, which was near a major stream (recharge boundary); and drawdowns were substantial (at least 12 feet) in well EXW 33, which was near the edge of the model aquifer boundary (barrier boundary). Total gains in flow from ground-water discharge for all streams in the model area were not affected by the location of wells; however, the amount of ground-water pumpage derived from induced infiltration of streamflow varies significantly. Water levels in the wetlands tend to be constant even during simulated pumping. In general, pumping during simulated drought conditions increased drawdowns fractionally and greatly reduced overall streamflow gains.

Pumping from the Usquepaug-Queen stratified-drift aquifer causes infiltration of streamflow along stream segments simulated in the ground-water-flow model. Results of simulations for average conditions show that from 56 to 75 percent of the total water pumped is derived from intercepted ground-water runoff and that the amount of well water derived from induced recharge of streamflow ranged from 20 to 39 percent. The areal extent of contributing areas for selected simulated pumping wells suggest that large areas of stratified drift may need to be protected from land-use practices that are incompatible with the development of potable ground water in the Usquepaug-Queen ground-water reservoir.