Protection of ground‐water resources from the effects of anthropogenic contamination requires definition of the source of water flowing in developed aquifers. Aquifer recharge areas for the confined Magothy and Lloyd aquifers of Long Island, New York, are estimated by using a three‐dimensional model of the Long Island ground‐water flow system and a particle‐tracking algorithm. Aquifer recharge areas under predevelopment conditions are consistent with an understanding of the ground‐water flow system operation. A budget comparison indicated that the recharge occurring in each area as calculated by particle tracking was within one percent of the flow entering that aquifer, according to the water budget computed from the flow model. Aquifer recharge areas for two stressed conditions, one at the present time and the other an estimate for the year 2020, are more difficult to define because of numerous pumped wells. Maximum and minimuitn recharge areas for each aquifer are presented for both present conditions and the year 2020 to bracket the actual aquifer recharge areas. These results also are consistent with the water budgets computed from the flow model. Results indicate that development causes large‐scale changes in flow patterns and the size and shape of aquifer recharge areas. The accuracy of defining recharge areas is limited by the model's representation of local‐scale characteristics of the flow system and the wells.
Has* trow N*w York State Department ol Iransportaiion, o Amityviite, t f»«port, Hicksvttle. Huntington MILE ?4 ooo 40 .5 1 KtLOMtTER EXPLANATION LINE OF EQUAL THICKNESS-Shows saturated thickness of upper glacial aquifer. Contour Interval 20 feet. 600 LINE OF EQUAL THICKNESS-Shows saturated thickness of combined upper glacial, magothy aquifers. Contour interval 100 feet. Figure 4-Approximate saturated thickness of upper glacial aquifer and of combined upper glacial and Magothy aquifers.
Accurate delineation of Long Island's internal hydrogeologic structure is integral to the understanding and management of the groundwater system. The irregular extent and surface configuration of Long Island's seven major hydrogeologic units give the groundwater system a complex internal structure. This report presents a computerized data base of hydrogeologic correlations for 3,146 wells on Long Island and adjacent parts of New York City. The data base includes the well-identification number, the latitude and longitude of the well location, the altitude of land surface at the well, the altitude of the bottom of the drilled hole, and the altitude of the upper surface of the major hydrogeologic units penetrated by the well. A computer program is included that allows retrievals of selected types of data for all or any local area of Long Island. These data retrievals are a valuable aid to the construction of hydrogeologic-surface maps. Knowledge of the internal hydrogeologic structure is necessary for efficient resource management, which includes (1) designing future waterdevelopment plans; (2) selecting sites for waste disposal; (3) locating and tracking the movement of contaminants within the groundwater system; and (4) mitigating other undesirable effects of man's influence on the system, such as streamflow depletion and saltwater intrusion. Previous Investigations Some previous hydrogeologic investigations that were completed on a local scale were used as a starting point for this study. Krulikas (1981) and Jensen and Soren (1971) evaluated the hydrogeology of Suffolk County, Kilburn (1980) and Kilburn and Krulikas (1986) evaluated the hydrogeology of parts of Nassau County, and Buxton and others (1981) evaluated the hydrogeology of Kings and Queens Counties. HYDROGEOLOGIC FRAMEWORK Long Island is underlain by unconsolidated deposits of clay, silt, sand, and gravel that overlie southward-dipping consolidated bedrock (fig. 2). The unconsolidated deposits are thinnest in northern Queens County (northwestern Long Island) and thicken to the south and east to a maximum thickness of 2,000 ft at the south shore. These deposits contain several distinct geologic units ranging in age from Late Cretaceous through Pleistocene, with some recent deposits near shores and along streams. These units are differentiated by age, method of deposition, and lithology in table 1.
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