HYDROGEOLOGY OF THE MA TUNUCK HILLS PONDS SOUTH KINGSTOWN, RHODE ISLAND

Abstract

A detailed hydrogeological study has been applied to a series of adjacent ponds in the vicinity of the Matunuck Hills, South Kingstown, for a period of two and a half years. This study combined physical and chemical concepts in order to evaluate the surface-water/ground-water interactions, and to interpret the hydrogeologic system of the Matunuck Hills Ponds. Three different types of indicators were specifically used to assess the hydrology of the ponds: potentiometric technique, water budget calculations, and chemical analysis. The potentiometric technique helps in determining the hydraulic gradient and evaluating the spatial distribution of recharge or discharge around the ponds. The water budget calculations help to decide the major hydrologic contributors to the ponds, and also to estimate the net ground-water inflow or outflow. The chemical analysis serves as an indicator in the evolution and interaction between the ground-water and surface-water systems, and these data support the interpretation of the flow systems. The use of these three techniques produced reliable results, enhanced the ability to characterize and identify chemically distinct water bodies. They also helped to evaluate the interaction between the ground-water and surface-water bodies, and assisted in the development of a conceptual model for the hydro logic system of the Matunuck Hills Ponds area. The pond hydrologic characteristics vary depending on its position in the flow system. Tucker, Long, Spectacle, and White ponds are flow-through ponds, Round Pond is a recharge pond, and Wash Pond is a shallow discharge, deep-flow through pond. The most dilute ponds fall in either the flow-through and/or the recharge systems, located in the northern and central sections of the study area. Wash Pond, located in the southern portion of the study area has higher solute concentrations provided by the discharge of a more chemically evolved ground water. Twenty-five surface-water and ground-water samples, collected in 1994, and nine surface-water samples, collected in 1996, were obtained for chemical analysis. Sodium was the most abundant cation, while chloride and bicarbonate were the dominant anions in the surface waters and ground water sampled during the study period. The geochemical data support the interpretation of the flow systems based on the physical parameters, and serve as a chemical indicator in the evolution of the surface-water and groundwater systems. The chemistry shows the influences from precipitation composition, and rock weathering on the concentration of major constituents in the water systems. The Matunuck Hills Ponds surface-water and ground-water systems are characterized