A previously developed steady state three-dimensional groundwater flow (MODFLOW-2005) and advective transport (MODPATH6) model was used to examine subsurface nitrate transport to wells and receiving streams in two subcatchments contributing to the Upper Chester River, Maryland. Multiple scenarios of flow and transport parameter fields (recharge, hydraulic conductivity, and porosity) were previously calibrated against groundwater levels, stream discharge measurements, and atmospheric tracer measurements, as described in https://doi.org/10.1016/j.jhydrol.2018.02.006; those multiple scenarios are also available as a USGS data release (https://doi.org/10.5066/F7SN087R). Two of the flow and transport scenarios calibrated in Zell et al. (2018) were selected to simulate nitrate transport, with MODPATH6 files updated as necessary to represent advective transport from observation wells with subsurface nitrate measurements. The development of the model input and output files included in this data release and the application of the models to nitrate transport simulation are documented in the Journal of Environmental Quality article (https://doi.org/10.2134/jeq2018.11.0408).

A steady state three-dimensional groundwater flow (MODFLOW-2005) and advective transport (MODPATH6) model was developed to examine subsurface travel times to wells and receiving streams in two subcatchments contributing to the Upper Chester River, Maryland. The model was calibrated to conditions from 1990 to 2005, the period for which groundwater levels, stream discharge measurements, and atmospheric tracer measurements were jointly available. Six calibrated model scenarios were generated and paired with First Order Second Moment (FOSM) linear uncertainty analysis tools to evaluate (i) the uncertainty of base-flow age estimates as well as (ii) the worth of future data collection. The development of the model input and output files included in this data release are documented in the Journal of Hydrology article (https://doi.org/10.1016/j.jhydrol.2018.02.006).

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.

An existing three-dimensional model (MODFLOW-2000) by Fine, Petkewich, and Campbell (2017) (https://doi.org/10.3133/sir20175128) was used to evaluate 7 water-management scenarios and predict the effects on the groundwater flow and groundwater-level conditions in the Mount Pleasant, South Carolina area. This model was originally developed in 2007, by Petkewich and Campbell (https://pubs.er.usgs.gov/publication/sir20075126), then updated and recalibrated to conditions from 1900 to 2015. Results of six previous scenario simulations (scenarios 1-6) for the Mount Pleasant Water Works are published in a U.S. Geological Survey (USGS) Scientific Investigations Report (https://doi.org/10.3133/sir20175128). The archived model input and output files are available in a USGS data release (https://doi.org/10.5066/F7S181FC). Seven additional MODFLOW-2000 scenarios (numbered 7-13), using this updated and recalibrated model, were developed to evaluate different withdrawal strategies which are included in this data release: (7) Mount Pleasant Waterworks bringing online a new well (located at the old well 5 location) at 3.51 million gallons per day (Mgal/d) in 2025; (8) Maximizing withdrawals from Mount Pleasant Waterworks wells 2 and 5 (3.51 Mgal/d each) in 2020 and 2025, respectively; (9) Same as Scenario 7, but removing well 3 from production in 2025; (10) Same as Scenario 9, but removing well 4 from production in 2025 (11) Same as Scenario 7, but converting well 3 to an injection well in 2025 (12) Same as Scenario 11, but converting well 4 to an injection well in 2030; and (13) Same as scenario 8, but with two injection wells added (one in 2025 and one in 2035) to Mount Pleasant Waterworks well field. Nine alternate simulations for scenarios 11-13 (three MODFLOW and six MODPATH) were done to evaluate the effects of different porosity on the groundwater flow system, water levels, and the time-of-travel of particles from injection wells to the main water source. This USGS data release contains all the input and output files for the simulations described above and in the readme.txt file of this data release (https://doi.org/10.5066/P9GZEE4E).

An existing three-dimensional model (MODFLOW-2000) by Fine, Petkewich, and Campbell (2017) (https://doi.org/10.3133/sir20175128) was used to evaluate 7 water-management scenarios and predict the effects on the groundwater flow and groundwater-level conditions in the Mount Pleasant, South Carolina area. This model was originally developed in 2007, by Petkewich and Campbell (https://pubs.er.usgs.gov/publication/sir20075126), then updated and recalibrated to conditions from 1900 to 2015. Results of six previous scenario simulations (scenarios 1-6) for the Mount Pleasant Water Works are published in a U.S. Geological Survey (USGS) Scientific Investigations Report (https://doi.org/10.3133/sir20175128). The archived model input and output files are available in a USGS data release (https://doi.org/10.5066/F7S181FC). Seven additional MODFLOW-2000 scenarios (numbered 7-13), using this updated and recalibrated model, were developed to evaluate different withdrawal strategies which are included in this data release: (7) Mount Pleasant Waterworks bringing online a new well (located at the old well 5 location) at 3.51 million gallons per day (Mgal/d) in 2025; (8) Maximizing withdrawals from Mount Pleasant Waterworks wells 2 and 5 (3.51 Mgal/d each) in 2020 and 2025, respectively; (9) Same as Scenario 7, but removing well 3 from production in 2025; (10) Same as Scenario 9, but removing well 4 from production in 2025 (11) Same as Scenario 7, but converting well 3 to an injection well in 2025 (12) Same as Scenario 11, but converting well 4 to an injection well in 2030; and (13) Same as scenario 8, but with two injection wells added (one in 2025 and one in 2035) to Mount Pleasant Waterworks well field. Nine alternate simulations for scenarios 11-13 (three MODFLOW and six MODPATH) were done to evaluate the effects of different porosity on the groundwater flow system, water levels, and the time-of-travel of particles from injection wells to the main water source. This USGS data release contains all the input and output files for the simulations described above and in the readme.txt file of this data release (https://doi.org/10.5066/P9GZEE4E).

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.

The U. S. Geological Survey, in cooperation with the U.S. Environmental Protection Agency, developed a numerical ground-water-flow model, using MODFLOW-2000, to simulate ground-water flow in the Pohatcong Valley including the area within the Pohatcong Valley Ground Water Contamination Site. In 1978, the chlorinated solvents trichloroethene (TCE) and tetrachloroethene (PCE) were detected in thePohatcong Valley in production wells in Washington Borough and Washington Township, Warren County, New Jersey. Subsequent investigation revealed that many domestic wells in Washington and Franklin Townships also were contaminated, and in 1989 the Pohatcong Valley Ground Water Contamination Site was added to the U.S. Environmental Protection Agency (USEPA) National Priority List. A remedial investigation, by the USEPA and CH2M Hill with technical assistance from the U.S. Geological Survey (USGS), was begun in 1999. The simulation of ground-water flow in the Pohatcong Valley described here was conducted by the USGS in cooperation with the USEPA. The ground-water-flow model, using MODFLOW-2000 and the particle–tracking program MODPATH, estimated flow paths of groundwater from known sources of contamination in Washington Borough and tested possible site contamination remediation alternatives. Five ground-water remediation alternatives (GW2a, GW2b, GW3a, GW3b, and GW4b) were simulated. In addition, a 10-year solute transport simulation was conducted, using the USGS groundwater-transport process, to illustrate the potential for dispersion to increase the width of the solute plume. 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/sir20065269).

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).

Groundwater flow models have the potential to predict spatial groundwater discharge dynamics within river networks, but models are often not evaluated against discharge dynamics. The objective of this study was to understand the variation in simulated discharge dynamics (discharge location, flowpath depth, and subsurface travel time) for models with common, but varying frameworks and assumptions. The University of Connecticut in collaboration with the United States Geological Survey developed a groundwater flow model (MODFLOW-NWT) for the Farmington River Watershed (1,570 km2) in the northeastern United States and systematically varied the type of typical calibration data (well head and stream elevation); calibration parameters; parameters related to permeability of the surficial materials, bedrock, and riverbed sediments; control of river-aquifer exchange directionality; and model resolution. Each model variation has an associated particle tracking (MODPATH) model. Subsequent work, not described in this model archive, compared with simulated spatial patterns of groundwater discharge with patterns observed with hand-held thermal infrared imagery. This dataset contains model inputs and outputs, post-processing python scripts, and pest calibration input files for 12 model variations described in the associated journal article (https://doi.org/10.1029/2020WR028027)