Recent hydrologic appraisals {S, 10) have emphasized that future 

 water management must take into account the balance of the Long Island 

 ground-water reservoir as expressed by the equation: Inflow = Outflow ± 

 changes in storage and have outlined several management alternatives and 

 their consequences. As of I968, the total fresh-water outflow from the 

 ground-water reservoir beneath the water budget area was greater than the 

 inf lowland the amount of fresh ground water in storage was declining. If 

 present management practices continue it is likely that within the water 

 budget area (1) the hydrologic imbalance will increase, (2) ground-water 

 levels will continue to decline, and (3) salty ground water will continue to 

 move slowly inland. The yield of the Long Island ground-water system is not 

 a single fixed number but will vary depending on hydrogeologic conditions, 

 the management scheme, and the extent to which certain undesirable effects of 

 development will be tolerated. 



A continuous program of hydrologic investigations is essential 

 to provide the information necessary for water management and planning. Pre- 

 sent activities that provide a continuous record of the hydrologic system 

 should be continued and further refined. More intensive study and monitor- 

 ing of water quality are required in various parts of the island and continu- 

 ing efforts should be made to define the shape and areal extent of the hydro- 

 geologic units particularly in eastern Suffolk County. 



5.3 The hydrogeologic system on the north shore of Long Island Sound 



The hydrogeologic information in the subregions of the Long 

 Island Sound Regional Study Area that lie north of the Sound varies in 

 quantity and quality. The most complete information is presently available 

 for Subregions 1, 4 and 5. On-going studies by the U.S. Geological Survey 

 are in various stages of completion in Subregions 2 and 3 whereas the part 

 of Subregion 6 in this area is deficient in data. 



The principal hydrologic unit on the north shore of the Sound is 

 the river basin drained by a perennial stream. The saturated zone beneath 

 each of these basins constitutes a fresh ground-water reservoir, the boundaries 

 of which are (1) the topographic drainage divides (2) the water table (3) the 

 streams and (k) impermeable bedrock. For small areas that border the coast 

 and are not drained by a stream the interface between fresh and salty ground 

 water is a boundary. The geologic framework of the ground-water reservoirs 

 on Figure ]k includes the upper fractured part of the bedrock and unconsoli- 

 dated layered and unlayered deposits of sand, gravel, silt, clay (termed 

 stratified drift and till respectively). 



Recharge to each ground-water reservoir under natural conditions 

 is derived solely from precipitation on the drainage basin. The amount and 

 rate of recharge varies from basin to basin and with time. In areas where 

 the surface materials are principally till and bedrock the estimated average 

 annual recharge is approximately 0.3 mgd/mi (million gallons per day per 

 square mile) and in areas covered by stratified drift it is approximately 1 

 mgd/mi^. Most recharge occurs during the period October through March of 

 each year when vegetation is generally dormant. 



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