Planning for the Future of New York City's Water Supply System
Using Artificial Recharge in the Coastal Plain Aquifers: A Cooperative Program between the USGS and the New York City Department of Environmental Protection

By William A. Yulinsky, P.E., NYCDEP, Paul Misut, USGS, Donald K. Cohen, CPG, Malcolm Pirnie, Inc.*

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Abstract

The New York City Department of Environmental Protection (NYCDEP) and the US Geological Survey (USGS) have been cooperating on investigations into the use of the aquifers beneath Brooklyn and Queens as a supplemental potable water supply since the mid-1980's.  Early cooperative efforts included application of the USGS Long Island-wide  groundwater flow model to Brooklyn and Queens to evaluate the potential use of the aquifers.  In the mid 1990's the USGS rediscretized the model in Brooklyn and Queens to further evaluate three specific pumping scenarios, including evaluation of natural and artificial recharge, as well as a preliminary evaluation of salt water intrusion under these scenarios.  Concurrently, the NYCDEP evaluated the engineering requirements, cost estimates, and environmental impacts associated with the scenarios.

Currently, the USGS continues to cooperate with the NYCDEP in effort to develop an overall Groundwater Management Plan, which includes planning and testing of artificial recharge to the Lloyd and lower Magothy aquifers.  The USGS has played a major role in characterizing the geologic controls and in developing the flow system analysis for this project.  It will continue to be involved in ongoing field investigations designed to help confirm model assumptions and to further characterize and model the geochemistry of the Lloyd aquifer in particular.  The USGS is also developing a more robust model to evaluate the long term movement of salt water under a variety of both transient and long term pumping scenarios, including artificial recharge and recovery of water from the Lloyd aquifer.

Planning activities for the Artificial Recharge project have identified several challenging issues.  The Lloyd aquifer is the least studied of the Coastal Plain aquifers on Long Island, requiring significant assumptions in the flow system analysis.  The location of the salt water-fresh water interface in the Lloyd aquifer is not known.  Additional research is needed on the mineralogy of the Lloyd aquifer so that more specific geochemical modeling of source water-aquifer water interactions can be conducted.  The planned use of potable water from the upstate surface water reservoirs of the New York City drinking water system as the source water poses challenges regarding changes in the chemistry of the groundwater during storage and subsequent recovery, and requires an evaluation of methods to condition the source water prior to recharge to prevent dissolution of iron and manganese from the aquifer matrix.  The use of drinking water also raises significant permitting issues in New York related to the fate of disinfection by-products (DBP's) in the aquifer.  Low concentrations of DBP's, particularly chloroform, are present in the source water at levels that are well below drinking water standards, but above the New York State effluent standard for discharges to groundwater.  However, the presence of chlorine residual in the source water should help impede the development of bacterial colonization and clogging of the wells.

In George R. Aiken and Eve L. Kuniansky, editors, 2002, U.S. Geological Survey Artificial Recharge Workshop Proceedings, Sacramento, California, April 2-4, 2002: USGS Open-File Report 02-89

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