Two methods of reducing predicted water-level declines in the Long Island ground-water reservoir were simulated on an electric-analog model. The declines result from predicted increased ground-water withdrawals due to population growth and loss of ground-water recharge due to sewerage. The first method calls for a 30-percent reduction in pumpage from 1975 to 1995; this would be effected through conservation measures. The second method simulates the importation of water from Suffolk County to replace pumpage in Nassau County Sewage Disposal District 3, in 1995. Two amounts of imported water were tested in the second method--100 percent of the total amount pumped in Nassau County Sewage Disposal District 3 in 1995 (61.7 million gallons per day or 2.70 cubic meters per second) and 50 percent of.— that amount (30.8 million gallons per day or 1.35 cubic meters per second). With Method I, the maximum decline in water levels is 3.5 m (11 ft), which is considerably smaller than the decline of 5.0 m (16 ft) predicted in companion Report I without this reduction. Method 11 would change the regional water-level distribution entirely and would even cause a water-level rise in Nassau County, when 100 percent of the withdrawals of Sewage Disposal District 3 are imported. Results of the model analysis are depicted on maps showing net change in heads in the Magothy aquifer and at the water table and in a table listing changes in streamflow for selected streams.
