Monday, June 23, 2008 : 9:30 a.m.

Development and Calibration of a 100-Year, Transient, Saltwater Intrusion Model for Long Island, New York

Matthew Gamache, PE, Robert Fitzgerald, PE and Kristina K. Masterson, PE, CDM Inc.

Historically, intensive pumping in Brooklyn and Queens caused significant drawdown of groundwater head levels and damaging intrusion of salt water into the groundwater system.  From 1900 to 1950 extensive groundwater development occurred in Brooklyn and Queens, resulting in large groundwater drawdowns.  Saltwater encroachment at water supply wells in Brooklyn is documented as early as the 1920s.  In 1947, all public water supply pumping in Kings county stopped because of widespread saltwater intrusion.  Pumping in Queens then increased from approximately 52 MGD in 1950 to approximately 70 MGD in the early 1970s.  Nassau and Suffolk county withdrawals increased significantly over this period as well.  Groundwater elevations in Queens and Nassau counties decreased, and significant saltwater impacts at public supply wells in Queens occurred in the 1960s.  Queens pumping has since been reduced to less than 5 MGD, which has resulted in water level recovery of up to 35 feet during the past 25 years.

A groundwater flow model of the aquifer system beneath Kings, Queens, Nassau and Suffolk counties on Long Island, New York was developed to study groundwater flow patterns and the availability of groundwater for future public water supply. In order to evaluate the feasibility of potential future water supply projects, a 100-year (1905-2005) historical transient simulation was developed to demonstrate that the model can reasonably represent the regional salt water intrusion and groundwater head drawdowns that occurred during the 20th century.

DYNSWIM, a 3-dimensional, finite-element, dual-phase freshwater and saltwater flow code was used in this study.  DYNSWIM is part of the DYNSYSTEM suite of groundwater modeling software and was developed for use in coastal aquifer studies.  The model adequately simulates the movement of the saltwater wedge, as well as water level fluctuations associated with changes in pumping and groundwater recharge, over time.

Matthew Gamache, PE, CDM Inc. Mr. Gamache is a water resources engineer who specializes in subsurface hydrologic and contaminant transport modeling. These models have been used to assess groundwater flow paths, travel times, and contaminant concentrations for litigation support, delineation of drinking water protection zones, and design of groundwater remediation systems.

Robert Fitzgerald, PE, CDM Inc. Mr. Fitzgerald is a Senior Groundwater Modeler who has been responsible for numerous studies of groundwater flow and dissolved and separate phase contaminant transport in aquifers. Mr. Fitzgerald also has extensive experience in hydrology, hydraulics and water resources management, emphasizing the application of computer simulation models. He has been responsible for the use of models in analyzing and developing programs for groundwater management and remediation, flood alleviation, reservoir yield augmentation and water quality assessment.

Kristina K. Masterson, PE, CDM Inc. Ms. Masterson is a water resources engineer who specializes in groundwater flow and contaminant transport model simulation analysis. Ms. Masterson has conducted groundwater flow and mass transport modeling studies for site environmental assessment, remediation investigation and design, remediation performance evaluation, and water resources management projects. During the 20 years that she has worked in the water resources engineering field, Ms. Masterson has successfully applied numerical groundwater flow and mass transport models to study groundwater flow patterns and contaminant mass transport characteristics in many different hydrogeological settings.


2008 NGWA Conference on Eastern Regional Ground Water Issues