Hydrogeology, water quality, and ground-water-development alternatives in the upper Wood River ground-water reservoir, Rhode Island
The 72.4-square-mile Upper Wood River study area is in the Pawcatuck River basin in southern Rhode Island. Stratified drift is the only principal geologic unit capable of producing yields greater than 0.5 Mgal/d. Transmissivity of the aquifer ranges from 7,600 to 49,200 sq ft/d. Water-table conditions prevail and the aquifer is in good hydraulic connection with perennial streams and ponds. Groundwater and surface water in the study area are generally suitable for most uses. Water is soft, slightly acidic, and contains less than 150 mg/L dissolved solids. Locally, however, groundwater has been contaminated with nitrate, chloride, and volatile organic compounds. A model of the groundwater-flow system was used to evaluate the effect of alternative schemes of groundwater development on water levels, pond levels, and streamflow. Till contacts were simulated as specified-flux boundaries, drainage divides as no-flow boundaries, and streams as leaky boundaries. The areas most favorable for development of 1 Mgal/d are along the Flat and Wood Rivers. From 50 to 65 percent of the water withdrawn from wells would be derived from induced recharge. Results of simulation of development alternatives indicate that the groundwater reservoir could sustain withdrawals of 6 to 12 Mgal/d from 11 wells under long-term average annual (1942-89) and simulated drought (1963-66) conditions without causing water-level declines of greater than 25 percent of the unstressed saturated thickness of the aquifer. Pumping 12 Mgal/d, however, would reduce flow of the Wood River at the basin outlet by an amount almost equal to the 7-day, 10-yr low flow of 20.4 cu ft/s.