Using Contributing Areas to Guide Water Quality Protection

Groundwater protection in Suffolk County, New York has been ongoing for more than 50 years and is of utmost importance to both the drinking water supply and the ecological health of streams and embayments throughout the county. More than 1.4 million people rely entirely upon groundwater as their sole source of drinking water and groundwater baseflow comprises approximately 90 percent of total flow within streams and rivers in the county.

Using three-dimensional flow and transport models, water table contributing areas and travel time analyses have been updated for more than 650 public supply wells as part of the county’s Comprehensive Water Resources Management Plan. A sample set of these contributing areas has been compared to historic land use and coupled with a water quality database to qualitatively evaluate water quality trends with changes in land use. These evaluations will help to better define the impact of land use to water quality at a community supply well.

Baseflow contributing areas to the county’s coastline and all major streams and rivers have also been delineated using the same set of models. These contributing areas can be coupled with land use and water quality databases to evaluate potential surface water quality impacts resulting from changes in land use.

The groundwater contributing areas to community supply wells and surface water features have been combined using GIS tools to identify “exclusion zones.” Exclusion zones represent areas that do not contribute groundwater recharge to community supply wells or significant surface water features within the specified travel times, or deep aquifer recharge areas, e.g. the Core Preservation Area of the Long Island Pine Barrens. These exclusion zones will be evaluated by the county to determine areas that are appropriate for smart growth initiatives and/or to potentially accommodate transfer of development rights without adversely impacting water resources.