A MODFLOW-2005 model, using the SWI2 package, was developed for the Sandy Hook Unit, Gateway National Recreation Area (hereafter Sandy Hook) in New Jersey to evaluate the response of groundwater resources to expected sea-level rise (SLR) and changes in groundwater recharge associated with global climate change. The National Park Service (NPS), among other agencies, is mandated to evaluate the effects of global climate change on NPS parks and promote resiliency and sustainability of park resources to the extent possible. Sandy Hook is visited by thousands of people each year who take advantage of the historical and natural resources and recreational opportunities which are threatened by global climate change, including SLR, changes in precipitation and groundwater recharge, and changes in the frequency and severity of coastal storms. Fresh groundwater resources are important to the ecosystems of Sandy Hook. The Bayside Holly Forest, one of only two known old-growth American holly (Ilex opaca) maritime forests, is particularly vulnerable to global climate change because of the proximity of the water table to land surface in low-lying areas and the potential for saltwater intrusion and inundation. Groundwater-flow simulations completed for this study include a Baseline scenario, three SLR scenarios (0.2, 0.4, and 0.6 meters [m]), two Recharge scenarios—a 10-percent Increased Recharge scenario and a 10-percent Decreased Recharge scenario—and a scenario with 0.6 m of SLR and 10-percent increase in recharge. Understanding the possible effects of SLR and changes in recharge will allow the NPS to allocate scarce resources to best prepare for and manage climate-change-driven changes in the groundwater system and the subsequent effects on park ecosystems. This USGS data release contains all of the input and output files for the simulations described in the associated model documentation report (https://doi.org/10.3133/sir20205080).

A three-dimensional groundwater flow model, MODFLOW-NWT with the SWI2 module, was developed to provide a better understanding of the fresh groundwater system of Assateague Island, Maryland and Virginia. Groundwater flow on Assateague Island was simulated to evaluate the effects of sea-level rise and changes in recharge on the depth to freshwater below the land surface, changes in freshwater discharge, and the depth of the freshwater/saltwater interface. The model was calibrated to average 2014-15 hydrologic conditions and vegetation. The model also simulated the movement of the freshwater- seawater interface for three sea-level rise scenarios.This USGS data release contains all of the input and output files for the simulations described in the associated model documentation report (https://doi.org/10.3133/sir20205104).

A three-dimensional groundwater flow model, MODFLOW-NWT with the SWI2 module, was developed to provide a better understanding of the fresh groundwater system of Assateague Island, Maryland and Virginia. Groundwater flow on Assateague Island was simulated to evaluate the effects of sea-level rise and changes in recharge on the depth to freshwater below the land surface, changes in freshwater discharge, and the depth of the freshwater/saltwater interface. The model was calibrated to average 2014-15 hydrologic conditions and vegetation. The model also simulated the movement of the freshwater- seawater interface for three sea-level rise scenarios.This USGS data release contains all of the input and output files for the simulations described in the associated model documentation report (https://doi.org/10.3133/sir20205104).

A three-dimensional groundwater flow model was developed to simulate the effects of withdrawals on the groundwater-flow systems of five aquifers in and around Ocean County, New Jersey—the unconfined Kirkwood-Cohansey aquifer system and Vincentown aquifer, and three confined aquifers--the Rio Grande water-bearing zone, the Atlantic City 800-foot sand, and the Piney Point aquifer. A transient model was used to simulate conditions that represent no groundwater withdrawals, 2000–2003 groundwater withdrawals, and maximum-allocation groundwater withdrawals. Particle-tracking analysis, using results from two steady-state simulations, determine flow paths and travel times to near-shore wells screened in the unconfined Kirkwood-Cohansey aquifer system, the Rio Grande water-bearing zone, and the Atlantic City 800-foot sand. Sources of water to wells in both unconfined and confined aquifers and travel times based on particle-tracking analysis are used to assess the susceptibility of selected wells to saltwater intrusion from bay or ocean water. This USGS data release contains all of the input and output files for the simulations described in the associated model documentation report (https://doi.org/10.3133/sir20165035).

A regional groundwater-flow model and particle-tracking program were used to delineate areas contributing groundwater to coastal and freshwater bodies and to estimate travel times from the water table to saline water bodies under average conditions from 1968 to 1983 on Long Island, New York. The coastal waters of Long Island are important economic and recreational resources for the region. The coastal water bodies receive freshwater from inflow of both surface water and groundwater, in addition to tidal exchanges of saltwater. Excessive nitrogen inputs associated with development and urbanization in the freshwater recharge areas to coastal water bodies can adversely affect marine and estuarine ecosystems. The results from this study will be beneficial for developing informed strategies to address nutrient loading to these systems, to provide a basis for additional scientific studies, and to engage the public. This is the first phase in the development of an updated groundwater-flow model for Long Island as part of the National Water Quality assessment Program (NAWQA). The study modified and used the model documented in the publication 'Simulation of the effects of development of the ground-water flow system of Long Island, New York by Herbert T. Buxton and Douglas A. Smolensky (https://pubs.er.usgs.gov/publication/wri984069). This data release contains all of the model input and output files for the simulations described in the associated model documentation report (https://doi.org/10.3133/sir20165138).

The U.S. Geological Survey, in cooperation with the U.S. Department of the Navy, developed several 3-D groundwater flow models for used with MODFLOW-2005, MODFLOW-NWT, and SEAWAT model codes to evaluate variable-density groundwater flow and contaminant transport in Operable Unit 1 on Naval Base Kitsap in Keyport, Washington. Chlorinated volatile organic compounds (CVOCs) have migrated to groundwater beneath a former 9-acre landfill at Operable Unit 1 (OU-1). The three predominant ground-water contaminants are the chloroethene compounds trichloroethene (TCE), cis-1,2-dichloroethene (cis-DCE), and vinyl chloride (VC). A need for remedial action was identified because some of the contaminants present a potential risk to humans primarily through drinking contaminated groundwater or through ingesting seafood harvested from contaminated surface water. An ongoing effort with the U.S. Navy and U.S. Geological Survey (USGS) began in 1995 by evaluating the effectiveness of natural attenuation processes for removing and controlling the migration of CVOCs in ground water at OU-1. Additional collection of geochemical and contaminant concentration data demonstrated that biodegradation of CVOCs in shallow groundwater at OU-1 is substantial and prevents most of the mass of dissolved-phase CVOCs in groundwater beneath the landfill from discharging to surface water. However, dissolved-phase contaminant concentrations in the hundreds of milligrams per liter continue to persist in localized areas of OU-1. Data suggest that residual sources of chloroethenes in the form of non-aqueous phase liquid remain at the site, and that biodegradation is only partly effective at reducing the dissolved-phase contaminants that are generated from these sources. In 2018 an additional USGS effort was begun to simulate variable-density groundwater flow and contaminant transport in the vicinity of OU-1 using a revised hydrogeologic model of the site and a refined delineation of persistent contaminant sources. MODFLOW-2005 and MODFLOW-NWT model codes were used to calibrate a new model. Then groundwater flow and contaminant transport models were developed using SEAWAT-Version 4, a computer program based on MODFLOW and MT3DMS, to simulate three-dimensional variable-density groundwater flow coupled with multi-species solute transport. These models were used to simulate the direction and rate of groundwater flow near OU-1, estimate the CVOC mass in groundwater and the rate of mass loading, and assess possible remedial activities at OU-1. This USGS data release contains all of the input and output files for the simulations described in the associated model documentation report (https://doi.org/10.3133/sir20205066).

A previously developed groundwater-flow model of the Great Egg Harbor and Mullica River Basins, N.J. (https://doi.org/10.3133/sir20125187) by the U.S. Geological Survey (USGS) was used to analyze the effects on groundwater levels and stream base flow from possible changes in groundwater withdrawals and effluent infiltration in Winslow Township, Camden County, New Jersey. The Camden County Municipal Utilities Authority (CCMUA) infiltrated treated sewage effluent at their infiltration/percolation lagoons in Winslow Township, New Jersey, from 1985 to 2014. Increasing effluent volumes strained the capacity of the sewage-treatment plant and infiltration/percolation facility which closed in 2014. The treatment plant began pumping effluent from Winslow Township to the main CCMUA treatment facility which discharges treated effluent to the Delaware River. Eliminating infiltration of treated effluent in Winslow Township reduced groundwater recharge in the Great Egg Harbor River Basin and ultimately reducing groundwater discharge (base flow) to the Great Egg Harbor River. A study was conducted to determine the effects of eliminating the infiltration of treated effluent and reducing groundwater withdrawals from wells completed in the Kirkwood-Cohansey aquifer system on groundwater levels and base flow in the Great Egg Harbor River. The model simulates a baseline scenario with 2003-2007 withdrawals and five scenarios with different effluent infiltration conditions and 2008-2010 withdrawals using MODFLOW-2000 (version 1.18.01). This USGS data release contains all of the input and output files for the baseline scenario and five scenarios described in the associated report (https://doi.org/10.3133/sir20235002).

A previously developed groundwater-flow model of the Great Egg Harbor and Mullica River Basins, N.J. (https://doi.org/10.3133/sir20125187) by the U.S. Geological Survey (USGS) was used to analyze the effects on groundwater levels and stream base flow from possible changes in groundwater withdrawals and effluent infiltration in Winslow Township, Camden County, New Jersey. The Camden County Municipal Utilities Authority (CCMUA) infiltrated treated sewage effluent at their infiltration/percolation lagoons in Winslow Township, New Jersey, from 1985 to 2014. Increasing effluent volumes strained the capacity of the sewage-treatment plant and infiltration/percolation facility which closed in 2014. The treatment plant began pumping effluent from Winslow Township to the main CCMUA treatment facility which discharges treated effluent to the Delaware River. Eliminating infiltration of treated effluent in Winslow Township reduced groundwater recharge in the Great Egg Harbor River Basin and ultimately reducing groundwater discharge (base flow) to the Great Egg Harbor River. A study was conducted to determine the effects of eliminating the infiltration of treated effluent and reducing groundwater withdrawals from wells completed in the Kirkwood-Cohansey aquifer system on groundwater levels and base flow in the Great Egg Harbor River. The model simulates a baseline scenario with 2003-2007 withdrawals and five scenarios with different effluent infiltration conditions and 2008-2010 withdrawals using MODFLOW-2000 (version 1.18.01). This USGS data release contains all of the input and output files for the baseline scenario and five scenarios described in the associated report (https://doi.org/10.3133/sir20235002).

Improvements to an existing regional groundwater-flow model of a 160-square mile area of coastal New Hampshire (https://doi.org/10.3133/sir20085222), incorporating MODFLOW-NWT and by more accurately representing stream characteristics, were presented at the MODFLOW and More 2017 conference in an example simulating approximate changes in water use. The groundwater-flow model developed for the previous study incorporated detailed water-use information for 2003-04 and simulated the effects of projected increases in water use. At that time, population growth and increasing water demand prompted concern for the sustainability of the region’s groundwater resources in a fractured-crystalline bedrock-aquifer with little storage. However, poor stream representation may reduce the effectiveness of the heads simulated by the original model. Groundwater heads in an area of relatively large population change, near the center of the Seacoast’s fractured bedrock aquifer, were simulated with the upgraded model using published 2004 and approximated 2015 water-use rates. This USGS data release contains all the input and output files for the simulations described in the associated proceedings paper from the MODFLOW and More 2017 conference. The publication which documents this work is included in the ancillary directory of this data release.

Improvements to an existing regional groundwater-flow model of a 160-square mile area of coastal New Hampshire (https://doi.org/10.3133/sir20085222), incorporating MODFLOW-NWT and by more accurately representing stream characteristics, were presented at the MODFLOW and More 2017 conference in an example simulating approximate changes in water use. The groundwater-flow model developed for the previous study incorporated detailed water-use information for 2003-04 and simulated the effects of projected increases in water use. At that time, population growth and increasing water demand prompted concern for the sustainability of the region’s groundwater resources in a fractured-crystalline bedrock-aquifer with little storage. However, poor stream representation may reduce the effectiveness of the heads simulated by the original model. Groundwater heads in an area of relatively large population change, near the center of the Seacoast’s fractured bedrock aquifer, were simulated with the upgraded model using published 2004 and approximated 2015 water-use rates. This USGS data release contains all the input and output files for the simulations described in the associated proceedings paper from the MODFLOW and More 2017 conference. The publication which documents this work is included in the ancillary directory of this data release.