Factors affecting declining water levels in a sewered area of Nassau County, New York

Double-mass-curve analysis of ground-water levels in Nassau County, Long Island, N.Y., shows that the average-weighted ground-water levels in a 32-mi² (83-km²) segment of a sewered area declined 11.8 ft (3.6 m) relative to an adjacent unsewered area to the east during 1953-72. Electric-analog-model analysis indicates that 4.9 ft (1.5 m) of the decline is due to pumping in nearby Queens County, west of the sewered area. Most of the remaining 6.9 ft (2.1 m) of the decline is due to sewering. Streamflow within the sewered area has also declined because of the lowered ground-water levels.