Analysis of Changes in Ground‐Water Levels in a Sewered and an Unsewered Area of Nassau County, Long Island, New York

Abstract

From the 195O's to the early 1970's expansion of sanitary sewerage in southwest Nassau County contributed to progressive declines in ground-water levels. Since the early 197O's, however, 10 years after the area was fully sewered, water levels have not declined significantly, which suggests that the water table may have reached a new equilibrium position. Double-mass-curve analyses show that during 1953-76 the average weighted ground-water levels in a 32-square-mile (83-square-kilometer) part of the sewered area declined 12.2 feet (3.73 meters) more than those in the unsewered area to the east. However, by 1973 this decline was 13.5 feet (4.1 meters). Finite-difference digital-model results indicate that 3.6 feet (1.1 meters) of the relative 1953-76 decline was due to pumping in adjacent Queens County and that most of the remaining decline was a result of sewerage. Streamflow within the sewered area decreased in response to the lowered ground-water levels, and ground-water levels in the adjacent unsewered area were also lowered because of the sewerage.

EFFECTS OF URBANIZATION ON BASE FLOW OF SELECTED SOUTH‐SHORE STREAMS, LONG ISLAND, NEW YORK1

“…Cohen, et al (1968), and Franke and McClymonds (1972) outlined the general hydrologic situation and water budget on Long Island. Franke (1 968), Garber and Sulam (1976), and Sulam (1979) discussed the decline in ground-water levels that resulted from sanitary sewerage in Nassau County. Pluhowski and Spinello (1 978) analyzed the impact of sewers in reducing base flow and ground-water recharge on Long Island.…”

Assessing regional land‐use/cover influences on New Jersey Pinelands streamflow through hydrograph analysis

“…Extensive storm and/or sanitary sewering systems and the presence of retention/detention ponds for storm-water control can have a substantial effect on the hydrology of developed areas. Sulam (1979) found that wastewater sewering in Long Island, New York, with the effluent discharged outside the sewered watershed, led to decreased streamflows compared with an adjacent, unsewered area. Ku et al (1992) found that recharge basins that collect storm runoff increased ground-water recharge relative to storm-sewer systems that routed storm runoff directly to streams.…”

Effects of sanitary sewers on ground-water levels and streams in Nassau and Suffolk Counties, New York, part 1: Geohydrology, modeling strategy, and regional evaluation

“…2.) Sulam (1979), in an update of these double mass curve analyses, estimated that the effects of SDD-2 on ground-water levels had come to equilibrium in the early 1970's, and the water-table decline averaged 9 ft.…”

“…However, the available information indicates that the system was close to equilibrium in the early 1970 f s because that period represented a 10-year hiatus between construction of the older sewer systems in the 1960*s, when the drought occurred, and the construction of the new sewer districts in the mid-1970's^. Sulam's (1979) double mass curve analyses in the area indicated that the system was probably in equilibrium in the early 1970 f s. Therefore, ground-water conditions of the early 1970 f s were selected as the most appropriate initial conditions for the subregional simulations.…”