UNITED WATER NEW YORK GROUND-WATER SUPPLY DEVELOPMENT ROCKLAND COUNTY,
NEW YORK

In response to a long-term, system-wide decline in pump-submergence levels observed by United Water New York (UWNY) at many of its supply wells, LBG was asked to conduct a hydrogeologic assessment of regional ground-water conditions to determine if the decline was related to overpumping, reduced aquifer recharge or a combination of both. The assessment results were used to develop strategies to minimize future impacts, especially in drought conditions.

UWNY is the supplier of about 28 million gallons per day of water to several hundred thousand residents in Rockland County, New York. The water supply is derived from a mix of surface water and ground water.

Using long-term SCADA data and hydrologic records, LBG determined that during 1991 and 1992 precipitation amounts were significantly below average and temperatures above normal, resulting in a significant reduction in recharge to the bedrock aquifer. Reduced baseflow at most of the county's streams confirmed the lower recharge rates.

This lack of recharge produced substantial declines in ground-water levels, decreased pump-submergence levels at many supply wells and effectively reduced available yield.

Based on these findings, LBG recommended system-wide operational procedures to be employed during times of drought, and preventive measures to lessen the impact of future droughts. These included development and utilization of additional water sources, participation in the creation of a Rockland County stormwater management plan, and implementation of a ground and surface-water monitoring program to better evaluate future demand impacts.

LBG then evaluated the feasibility of reactivating several inactive supply wells and installed additional test supply wells. The end result will be the development of a potential additional ground-water supply of approximately 1.8 million gallons per day to meet UWNY's needs during future droughts.