This groundwater model archive documents a transient, regional-scale numerical model of the Long Island aquifer system that simulates hydrologic conditions for the period 1900-2019 using US Geological Survey’s groundwater modeling software MODFLOW 6 (Hughes and others, 2017). The development and calibration of the numerical model is documented in Walter and others, 2024. The model input and output files included in this data release are documented in the readme.txt. The model simulates historical water levels, stream flows, and the position of the saltwater interface in response to time-varying changes in pumping and recharge stresses for the period 1900-2019. This archive also contains input and output files for scenarios developed to simulate hydrologic conditions at annual and seasonal time scales averaged for the period 2010-2019, a five-year drought, and sea level rise of 6 feet.

This data release contains the input, output, and model code used to run a transient simulation of a previously published (Walter and others, 2020) steady-state regional model of Long Island, N.Y. The original model code was updated to MODFLOW 6 (version 6.3.0) and incorporates monthly transient stress periods to simulate conditions from 2005-2019 following methods described in Walter and others (2020). Selected remedial stresses (groundwater extraction and return) were incorporated for select locations in southeastern Nassau County. No modifications were made to the hydrologic boundaries, model layers, or hydraulic properties specified in the original model. A uniform value of 0.25 was used to represent specific yield (unconfined storage) and a uniform value of 0.00001 was used to represent specific storage (confined storage) which are typical values for Long Island sediments. Monthly values for natural recharge from precipitation were calculated using a Soil-Water Balance model (Finkelstein and others, 2022). Components of anthropogenic recharge--wastewater return flow, storm water inflow, and inflow from leaky infrastructure--were estimated for monthly stress periods consistent with the methods described in Walter and others (2020). Monthly groundwater withdrawals for various sources, including public-water supply, industrial, remediation, and agricultural, were compiled or estimated for the same period. No additional calibration was conducted for this scenario and as such, it is possible that in some locations the model simulation results may not accurately represent the temporal responses to monthly hydrologic stresses.

In 2016, the United States Geological Survey (USGS) began development of a regional-scale numerical model of the Long Island aquifer system, as part of the National Water Quality Assessment (NAWQA) Program. The three-dimensional groundwater-flow model was developed to evaluate 1) responses of the hydrologic system to changes in natural and anthropogenic hydraulic stresses 2) the subsurface distribution of groundwater age, and 3) the regional-scale distribution of groundwater travel times and the source of water to fresh surface waters and coastal receiving waters. The model also provides the groundwater flow components used to define model boundaries for possible inset models used for local-scale analyses. Unconsolidated sediments underlying the Island comprise a sole source aquifer that supplies water to about 2.9 million people in Nassau and Suffolk Counties; the aquifer also contributes groundwater discharge to freshwater and marine ecosystems. Anthropogenic activities have affected both the quantity and quality of groundwater, owing to the Island's large population and the generally unconfined conditions prevalent across the aquifer system. Groundwater withdrawals, particularly in the western part of the Island, have resulted in large declines in water-table altitude and in the landward movement of the freshwater/saltwater interface encroaching on local water supplies. Subsurface contamination emanating from numerous point sources, often associated with industrial sites in developed areas in western Long Island, adversely affect downgradient water supplies. In central and eastern Long Island, nutrients emanating from non-point sources associated with residential development and agricultural activities have degraded water quality in shallow parts of the aquifer system. The model uses the numerical code MODFLOW-NWT to represent steady-state conditions for predevelopment and 2005-2015 average groundwater pumping and aquifer recharge. The particle-tracking algorithm MODPATH was used to simulate advective transport in the aquifer, to delineate the areas at the water table that contribute recharge to coastal and freshwater bodies, and to estimate total travel times of water from the water table to discharge locations. 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/sir20205091). UPDATE: In July 2021, the MODFLOW-NWT output for the steady-state 2005-2015 model were used with the particle-tracking algorithm MODPATH6 to estimate the recharge areas to 1,662 simulated public-supply wells in the aquifer system underlying Long Island, NY. An array of particles with a uniform spacing of 250 feet were specified at the water table and tracked forward to model cells containing simulated wells. The starting locations of the particles terminating in the simulated well represents the recharge area to that well. The particle starting locations were then georeferenced and used to create a polygon shapefile of individual recharge areas. This new information has been added to the ancillary directory of this data releases - December 2021.

This model archive contains files for a set of groundwater flow, particle tracking, and management optimization models that simulate the area around the Navy-Northrop-Grumman contamination plume on Long Island, New York. These models were developed as insets from the Long Island Regional “parent” Model, from which perimeter boundary conditions were inherited. In addition to input and output files for these models, this archive contains the modeling workflow python code and source data used to build the model. These materials have been included for repeatability and decision transparency.

This model archive contains files for a set of groundwater flow, particle tracking, and management optimization models that simulate the area around the Navy-Northrop-Grumman contamination plume on Long Island, New York. These models were developed as insets from the Long Island Regional “parent” Model, from which perimeter boundary conditions were inherited. In addition to input and output files for these models, this archive contains the modeling workflow python code and source data used to build the model. These materials have been included for repeatability and decision transparency.

This groundwater model archive documents transient and steady-state regional and inset numerical models of the Long Island aquifer system that simulate groundwater flow and nitrogen transport for the period 1900-2019 using the US Geological Survey groundwater modeling software MODFLOW 6 (Langvin and others, 2017 and 2022). The development and calibration of the regional groundwater flow model is documented in Walter and others (2024). The development of the regional groundwater nitrogen transport model and inset groundwater flow and nitrogen transport models are documented in Jahn and Walter (2025). The particle-tracking algorithm MODPATH 7 (Pollock, 2016) was used to simulate advective transport in the aquifer, to delineate the areas at the water table that contribute recharge to coastal water bodies, and to estimate total travel times of water from the water table to discharge locations. Model input and output files included in this data release are documented in the readme.txt.

This groundwater model archive documents coupled transient and steady-state regional and inset numerical models of the Long Island aquifer system to simulate groundwater flow and nitrogen transport using the US Geological Survey groundwater modeling software MODFLOW 6 (Langvin and others, 2017 and 2022). The regional model domain encompasses all of Long Island, New York, while the inset model domain encompasses the Long Island Sound watershed on Long Island, New York. The development and calibration of the regional groundwater flow model is documented in Walter and others (2024). The development of regional groundwater nitrogen transport models and coupled regional-inset groundwater flow and nitrogen transport models are documented in Jahn and Walter (2025). Model input and output files included in this data release are documented in the readme.txt.

Seventy-five steady-state two-dimensional groundwater flow (MODFLOW-6) models of the shallow groundwater system were developed to map depth to water and estimate effective surficial transmissivity for the contiguous United States (CONUS). The models were driven by spatially-distributed recharge estimated by Reitz et al. (https://doi.org/10.5066/F7PN93P0) using average water-budget information for 1985-2015 and calibrated against long-term average water levels in observation wells, as well as, water-level estimates derived from perennial first-order streams and wetlands. The development of the model input and output files included in this data release, as well as post-processing used to derive additional water-budget components also included in this data release, are documented in the Water Resources Research article (https://doi.org/10.1029/2019WR026724).

Seventy-five steady-state two-dimensional groundwater flow (MODFLOW-6) models of the shallow groundwater system were developed to map depth to water and estimate effective surficial transmissivity for the contiguous United States (CONUS). The models were driven by spatially-distributed recharge estimated by Reitz et al. (https://doi.org/10.5066/F7PN93P0) using average water-budget information for 1985-2015 and calibrated against long-term average water levels in observation wells, as well as, water-level estimates derived from perennial first-order streams and wetlands. The development of the model input and output files included in this data release, as well as post-processing used to derive additional water-budget components also included in this data release, are documented in the Water Resources Research article (https://doi.org/10.1029/2019WR026724).

The U.S. Geological Survey (USGS), in cooperation with the Harris-Galveston Subsidence District and Fort Bend Subsidence District, constructed a finite-difference numerical groundwater-flow model of the northern Gulf Coast aquifer region for 1897 through 2018 using MODFLOW 6 with the Newton formulation solver to simulate groundwater flow and land-surface subsidence. Model parameter estimation and uncertainty analysis were conducted with PEST++ Iterative Ensemble Smoother software. The simulated results are described in the associated U.S. Geological Survey Professional Paper 1877. The model archive provided in this U.S. Geological Survey data release includes all the necessary files to run the MODFLOW 6 model and process the results for the posterior base realization as displayed in the accompanying report. The readme_v2.txt file describes selected files and directories in the archive and provides instructions for running the model. This 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/pp1877). This data release version 2.0 has been updated from the original version to include additional model outputs. The model inputs are identical to those included in data release version 1.0 and will produce identical results.