Delineation of the freshwater-saltwater interface on southwestern Long Island, New York, through use of surface and borehole geophysical methods

By: , and 

Links

Abstract

The U.S. Geological Survey used surface and borehole geophysical methods to delineate the freshwater-saltwater interface in coastal plain aquifers along the southwestern part of Long Island, New York. Over pumping of groundwater in the early 20th century combined with freshwater-saltwater interfaces at the coastline created saltwater intrusion in the upper glacial, Jameco, Magothy, and Lloyd aquifers. Our research indicates extensive saltwater intrusion of the Lloyd aquifer along the southwestern coast of Long Island, N.Y. Several public-supply wells in the southern parts of Nassau, Queens, and Kings Counties have been adversely affected by saltwater intrusion causing several supply wells to be shut down and abandoned.

In 2015–17, the U.S. Geological Survey collected time domain electromagnetic soundings at 12 locations and borehole electromagnetic induction conductivity logs at 9 outpost wells within the study area to delineate several saltwater intrusion wedges. Three separate wedges , (shallow, intermediate, and deep), of saltwater intrusion were delineated in the upper glacial, Jameco, and Magothy aquifer complex. In addition, reanalysis of geophysical logs collected in an open borehole of a test well in southern Queens County in 1989 revealed the Lloyd aquifer was nearly completely intruded by saltwater with an estimated chloride concentration of 15,000 milligrams per liter. This suggests the freshwater-saltwater interface was at the coastline and not miles offshore as theorized by previous studies.

Study Area

Publication type Conference Paper
Publication Subtype Conference Paper
Title Delineation of the freshwater-saltwater interface on southwestern Long Island, New York, through use of surface and borehole geophysical methods
Year Published 2021
Language English
Publisher Long Island Geologists
Contributing office(s) New York Water Science Center
Description 20 p.
Conference Title 28th Conference on Geology of Long Island and Metropolitan New York
Conference Date April 10, 2021
Country United States
State New York
Other Geospatial Long Island
Google Analytics Metrics Metrics page
Additional publication details