Hydrogeology, ground-water availability, and water quality in the Titicus River valley, Ridgefield, Connecticut

Abstract

Projected needs for additional water supplies, coupled with limited alternative sources, have prompted an evaluation of the availability and quality of water in the stratified-drift aquifer within the Titicus River valley in Ridgefield, Connecticut. Previous studies indicated that this aquifer may be capable of yielding moderate to large quantities of water to wells. Hydrologic data from test drilling, seismic-refraction profiling, streamflow measurements, and water-quality analyses, coupled with groundwater model simulations, indicate that the aquifer is capable of yielding 1 million gallons per day of potable water. Stratified drift underlies 1.26 square miles of the Titicus River valley, and in places is more than 90 feet thick. Although much of the stratified drift is fine grained, poorly sorted sand and gravel layers are common, and some areas within the valley have dominantly coarse-grained sediments. Transmissivity values estimated from grain-size analyses and logs of test borings range from less than 500 to more than 5,000 feet squared per day. A mathematical model of drawdowns and yields from hypothetical wells in the most hydrologically favorable locations within the upper and lower sections of the Titicus River valley predicts maximum withdrawal rates of 0.9 and 0.4 million gallons per day, respectively. Estimates of the water available from natural and induced recharge in the upper valley area, based on empirical equations for ground-water outflow and the 30-day, 2-year low flow of streams, indicate that 0.6 million gallons per day could be sustained without causing undesirable hydrologic consequences. The total sustained long-term yield for the complete stratified-drift aquifer in the Titicus River valley is estimated to be 1.0 million gallons per day. Water quality in the aquifer generally is suitable for human consumption and most other uses, with the exception of locally elevated levels of hardness and manganese, which may limit use. Hardness is attributed to the solution of carbonate minerals in the aquifer and underlying bedrock; manganese probably is derived from decaying vegetation in swamps. Water quality of the Titicus River is similar to that of ground water but contains elevated concentrations of bacteria that are indicative of livestock sources. INTRODUCTION Population growth and industrial development are stressing water resources beyond the current capacity of some existing water-supply systems in Connecticut. This situation is particularly severe in southwestern Connecticut, where rapid population growth has resulted from the area's proximity to the New York metropolitan area, and most surface-water resources have already been developed or are committed to other uses. Additional water supplies will most likely be developed from ground-water sources, because (1) present State policy encourages ground-water development; (2) there are few areas suitable for reservoir development; and (3) reservoir construction costs are high. Stratified-drift aquifers generally are considered as the ground-water source most capable of providing the large volumes of water needed for public and industrial supplies in Connecticut. A major component of the U.S. Geological Survey's program in the State is to investigate the quantity and quality of water in stratified-drift aquifers that may have the potential as a regional water supply. As an element of this program, information on the hydrogeology, the availability of ground water, and the quality of water in the Titicus River valley was collected and assessed by the U.S. Geological Survey in cooperation with the Town of Ridgefield, Connecticut. Purpose and Scope This report presents the results of a study conducted between July 1983 and September 1985 to estimate the sustained long-term yield of the stratified-drift aquifer in the Titicus River valley and to appraise the quality of water within the aquifer and the Titicus River. This report also describes the hydrogeology of the river-aquifer system and presents estimates of the principal hydraulic properties of the aquifer that determine its water-yielding characteristics. Methods used to estimate the quantity of natural recharge to the aquifer and the potential for induced recharge from the Titicus River, and maximum pumpage from areas of high transmissivity within the aquifer are summarized. The report also includes tables listing the results of physical, chemical, and bacteriological analyses of water from wells and streams within the Titicus River valley. Location and Description Ridgefield, located in southwestern Connecticut, borders New York State and is approximately equidistant from Hartford and New York City. The Titicus River drains an area of 8.6 mi 2 (square miles) in the western half of Ridgefield and flows westward out of Connecticut into North Salem, New York, where it is tributary to the Croton River, which is tributary to the Hudson River. The stratified-drift aquifer described in this report extends over an area of 1.26 mi 2 in the Titicus River valley within the town of Ridgefield (fig. 1.). 73°27'53 4|0tt'3o«.£=