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 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).

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).

A MODFLOW-NWT model was used to simulate the water budget for Haskell Lake and Tower Creek in WI using the Lake, Streamflow Routing, and Unsaturated Zone Flow packages. Particle tracking was performed with the MODFLOW solution (using MODPATH 6). 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/sir20205024).

Three-dimensional numerical models were used to determine the permeable pathways between the HANDLEY underground nuclear test and downgradient boreholes ER-20-12 and PM-3, Pahute Mesa, southern Nevada. The SEAWAT code was used to couple MODFLOW and MT3DMS models, where the coupled model simulated groundwater-flow and tritium migration from the HANDLEY test for 50 years, from the date of detonation of the HANDLEY test (March 26, 1970) to March 26, 2020. Recharge, hydraulic-conductivity, specific-storage, and effective-porosity distributions were estimated using parameter estimation (PEST) by minimizing a weighted composite, sum-of-squares objective function. Simulated water-level altitudes in 10 wells, vertical water-level differences between 5 well pairs, aquifer-test transmissivity estimates in 9 wells, tritium concentrations in 7 wells, and drawdowns in wells PM-3-1 and PM-3-2 from groundwater withdrawals in borehole ER-20-12 were compared to measured equivalents during parameter estimation and formally defined the goodness-of-fit or improvement of calibration. This USGS data release contains data, analyses, and model files for the simulations and analyses described in the associated model documentation report (https://doi.org/10.3133/sir20215032). Supplementary data and analyses are in the ancillary directory, including transmissivity estimates (Appendix A); water-level models to estimate drawdowns (Appendix B); tritium data (Appendix C); the modified hydrostratigraphic framework in the numerical models (Appendix D); effective-porosity estimates (Appendix E); the Pahute Mesa–Oasis Valley groundwater model (Appendix F); model-calibration files (Appendix G); and pre-processing routines to build model files (Appendix H). The numerical model was calibrated using a multi-model approach and a two-step process. First, the groundwater model was calibrated, which consists of (1) a steady-state model simulating steady-state (predevelopment) groundwater flow; and (2) a transient model simulating drawdowns from groundwater withdrawals during the drilling of borehole ER-20-12. A transport model was developed that uses the best-fit estimated hydraulic-conductivity field from the calibrated groundwater model and was used to estimate dispersion and effective porosities.

A previously developed groundwater flow model (https://doi.org/10.5066/P9051RUT) was slightly modified to estimate the risk-based discrete relation between groundwater extraction and surface-water/groundwater exchange. Previously, the concept of a ''capture map'' has been put forward as a means to effectively summarize this relation for decision-making consumption. While capture maps have enjoyed success in the environmental simulation industry, they are deterministic, ignoring uncertainty in the underlying model. Furthermore, capture maps are not typically calculated in a manner that facilitates analysis of varying combinations of extraction locations and/or reaches. That is, they are typically constructed with focus on a single reach or group of reaches. The former of these limitations is important for conveying risk to decision makers, while the latter is important for decision-making support related to surface-water management, where future foci may include reaches that were not the focus of the original capture analysis. Herein, we use a MODFLOW-NWT groundwater/surface-water model of the lower San Antonio River, Texas, USA to demonstrate a technique to estimate risk-based and spatially discrete streamflow depletion potential. This USGS data release contains all of the input and output files for the simulations described in the associated journal article (https://doi.org/10.1111/gwat.13080)

This Data Release has 18 different groundwater flow simulation applications for the Woodville Karst Plain area near Tallahassee Florida with three variations of distributed parameter model approach. The site model files provided include both calibrated and uncalibrated simulations of various steady-state and transient hydrologic conditions. Simulations were accomplished with equivalent porous media models that allow laminar flow only (MODFLOW) or laminar and non-laminar flow in a model layer (MODFLOW-CFP mode 2) and hybrid model simulations (MODFLOW-CFP mode 1 one-dimensional pipe network linked to equivalent porous media model). The test examples of the application of equivalent porous media model (the sponge) with and without turbulence and a hybrid model (sponge with pipes) to the Woodville Karst Plain near Tallahassee, Florida, indicated that for annual, monthly, or seasonal average hydrologic conditions, all methods met calibration criteria (matched observed water levels and average flow). Thus, the increased effort, such as the collection of data on conduit location and the computational time of a hybrid model, is not necessary for simulation of average hydrologic conditions (simulation of non-laminar flow was not critical). However, simulation of a large storm event in the Woodville Karst Plain with daily stress periods (52-day period beginning August 13, 2008) indicated that turbulence is important for matching daily springflow hydrographs and models calibrated to average conditions did not match daily storm spring hydrographs. All models were developed from an equivalent porous media model for the area calibrated by J. Hal Davis, USGS, Tallahasee Florida Office that is documented in Davis, J.H., Katz, B.G., and Griffin, D.W., 2010, Nitrate-N movement in groundwater from the land application of treated municipal wastewater and other sources in the Wakulla Springs springshed, Leon and Wakulla Counties, Florida, 1966–2018: U.S. Geological Survey Scientific Investigations Report 2010–5099, 90 p. (https://pubs.usgs.gov/sir/2010/5099/). The hybrid model was developed by Josue J. Gallegos and documented in Gallegos, J.J., Hu, B.X., and Davis, Hal, 2013, Simulating flow in karst aquifers at laboratory and sub-regional scales using MODFLOW-CFP: Hydrogeology Journal, v. 21, no. 8, p. 1749–1760.

Coal combustion by-products (CCBs, in the form of ash) produced at the coal-fired San Juan Generating Station in San Juan County, New Mexico, have been buried in former surface-mine pits at the San Juan Coal Mine since power-generation operations began in the early 1970s. A groundwater flow model was developed by the USGS to estimate the timing of groundwater recovery after the cessation of mining and to identify potential pathways and advective travel times for groundwater transport of metals that may be leached from stored CCBs to arrive at hydrologic receptors after mining operations cease. The USGS numerical modeling package MODFLOW-NWT with MODPATH particle-tracking software was used. 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/sir20175155).

This data release contains the MODFLOW 6 models described in the related Groundwater journal article (https://doi.org/10.1111/gwat.13459). The models are generalized cross-section models of a hypothetical and idealized aquifer. The models are used to examine the effects of layered or full grid connectivity with and without the XT3D option in the Node Property Flow (NPF) package of MODFLOW 6. The data release contains the models described in the paper, the 6.5.0 binary executable for MODFLOW 6, the 6.5.0 MODFLOW source code, and the Python jupyter notebook and related Python utilities used to generate, run, and post-process the results.

The U.S. Geological Survey (USGS), in cooperation with the Water Replenishment District of Southern California, developed a regional groundwater model of the Los Angeles Coastal Plain (LACP) incorporating new data, analyses, and modeling tools to better understand the hydrogeology of the groundwater basins. The LACP covers about 580 square miles and is the largest coastal plain of semiarid southern California. This aquifer is heavily developed with mostly residential, commercial, and industrial use and relies heavily on groundwater for its water supply. There has been a heavy reliance on groundwater from the LACP for many years. The need to replenish the groundwater basins within the LACP was recognized as far back as the 1930s, when spreading grounds were first used to replenish groundwater basins and store water underground during times of water surplus to meet demands in times of shortage. Seawater intrusion resulting from fresh-water pumping became significant in the 1940s. As a result, injection of imported water through wells at what is now the West Coast Basin Barrier Project began on an experimental basis in 1951. Managed aquifer recharge from the spreading grounds and barrier wells is an important part of the LACP's groundwater supply. This study, in cooperation with the Water Replenishment District of Southern California, involved an assessment of the historical and present status of groundwater resources in the LACP and the development of tools to better understand the groundwater system. The Los Angeles Coastal Plain Groundwater Model (LACPGM) developed for this study, represents a major update of a previous groundwater model developed by Reichard and others (https://doi.org/10.3133/wri034065). The LACPGM uses the USGS model code MODFLOW-USG, which enables the use of an unstructured finite-difference grid which contains nodes one-eighth mile (mi; 660 ft) in length and width. The LACPGM incorporates 12 layers for the 13 chronostratigraphic units, with the two bottom units modeled as a single layer. MODFLOW-USG was selected for its ability to effectively represent the discontinuous and faulted chronostratigraphic layers using an unstructured grid. The LACPGM simulates groundwater flow in the LACP using quarterly stress periods from 1971 to 2015. The model was used to predict water levels under future water-management scenarios, base case wet and dry scenarios, increased pumpage wet and dry scenarios, and optimized replenishment wet and dry scenarios. The scenarios include projected future pumping rates and estimate the increases in water spreading and injection that would be needed to maintain water levels. The scenarios simulate expected future pumping rates and estimate needed increases in water spreading and injection in order to maintain water levels. This USGS data release contains all the input and output files for the simulations described in the associated model documentation report (https://doi.org/10.3133/sir20215088).