This groundwater-flow model archive/data release contains the model input and output files for 1) edited versions of four of the five NAWQA steady- state, inset MODFLOW-NWT models of regional model of Lake Michigan Basin (https://doi.org/10.3133/sir20185038) and 2) general models simulating the same four basins as the four inset models. Two HUC8 basins in the lower peninsula of Michigan (Kalamazoo (KALA) and Boardman-Charlevoix (BOARD) basins) and two HUC8 basins in Wisconsin (Upper Fox (UFOX) and Manitowoc-Sheboygan (MANI) basins) are represented in the inset and genera-simulation models. The inset models are designed to serve as a training area for metamodels to estimate groundwater age in glacial wells. The construction and details of the original four inset models are outlined in the U.S. Geological Survey Scientific Investigations Report 2018-5038 (https://doi.org/10.3133/sir20185038), and the construction and details of the general models are outlined in the Water Resources Research journal article (https://doi.org/10.1029/2017WR021531). The original four inset models are archived in the data release at https://doi.org/10.5066/F76D5R5V. Groundwater withdrawals from wells in the original four inset models were removed in the inset models in this archive because the general models did not have wells and to be able to compare the results from the two types of models in the archive. The boundary conditions of these ?pre-development? versions of the inset models were changed from constant-head boundaries (reflecting 2005 conditions) to no-flow boundaries. The general-simulation models apply an innovative modeling approach that allows for rapid,automated construction and calibration of models at a scale appropriate to the problem at hand (https://doi.org/10.3133/sir20215142). Results from the four general models in this archive were compared to results from the edited versions of the four inset models to evaluate the degree to which the general models reproduce behavior simulated by the inset models that use conventional flow modeling techniques. The underlying directories contain all the input and output files for the MODFLOW-NWT simulations and MODPATH particle tracking analysis for the edited versions of four inset models, and the four general models simulating the same four basins as the inset models described in the USGS Scientific Investigations Report (https://doi.org/10.3133sir20215142). The MODFLOW-NWT (v 1.0.9) and MODPATH 6 (version 6.0.1) executables and source codes, various ancillary python scripts written for this project, and model geospatial data are also included in the archive. Descriptions of the data in each subdirectory are provided to facilitate understanding of this this model archive. File descriptions are provided for select input and output files to provide additional information that may be of use for understanding this this model archive.

An extreme gradient boosting (XGB) machine learning model was developed to predict the distribution of nitrate in shallow groundwater across the conterminous United States (CONUS). Nitrate was predicted at a 1-square-kilometer (km) resolution at a depth below the water table of 10 m. The model builds off a previous XGB machine learning model developed to predict nitrate at domestic and public supply groundwater zones (Ransom and others, 2022) by incorporating additional monitoring well samples and modifying and adding predictor variables. The shallow zone model included variables representing well characteristics, hydrologic conditions, soil type, geology, climate, oxidation/reduction, and nitrogen inputs. Predictor variables derived from empirical or numerical process-based models were also included to integrate information on controlling processes and conditions. This data release documents the model and provides the model results. Included in this data release are, 1) a model archive of the R project: source code, input files (including model training and testing data, rasters of all final predictor variables, and an output raster representing predicted nitrate concentration in the shallow zone), 2) a read_me.txt file describing the model archive and an explanation of its use and the modeling details, and 3) a table describing the model variables.

This data release includes grids representing the depth and thickness of drinking-water withdrawal zones, polygons of hydrogeologic settings, an inventory of sources of well construction data, and summaries of data comparisons used to assess the depth of groundwater used for drinking-water supplies in the United States. Well construction data sources are documented in Table1_DataSources.xlsx. Data comparisons using the Mann-Whitney test to assess similarity between hydrogeologic settings were used to justify combining data where they were sparse (compare_neighbors_all_domestic.txt and compare_neighbors_all_public.txt). Water-supply-well depth varies geographically by water use and the type of well, which illustrates the need to identify the depth of domestic drinking water withdrawal and depth of public supply drinking water withdrawal zones. Water-supply-well depth also varies by aquifer; therefore median values were calculated for each Principal Aquifer (PA), Secondary Hydrogeologic Region (SHR) between PAs and PA or SHR associated with overlying sediment polygons, where present, including glacial (G), coarse glacial (GC), and stream-valley alluvium (AV) polygons (all termed hydrogeologic settings here). A polygon shape file of hydrogeologic settings is included in this data release (HG_Settings.zip) and includes well counts and median thicknesses and depths for each area. This data release documents an inventory of well construction data sources and thickness and median top and bottom of drinking water depth zones by aquifer for domestic and public supplies. This data release includes equations used for estimating information for wells missing information on the depth to the top/length of the open interval. This data release contains: HG_Settings.zip --Shape file with well counts and median depth and thickness for hydrogeologic setting areas compare_neighbors_all_domestic.txt --results of Mann-Whitney tests to assess domestic-supply well construction data similarity between hydrogeologic settings compare_neighbors_all_public.txt --results of Mann-Whitney tests to assess public-supply well construction data similarity between hydrogeologic settings Depth_of_Drinking_Water_Supplies_Metadata07232021.xml --Metadata NonReferencedDomestic.txt --An inventory of domestic-supply well data that are not published elsewhere NonReferencedPublic.txt --An inventory of public-supply well data that are not published elsewhere Table1_DataSources.xlsx --An inventory of databases, references, state web sites, and individual state contacts for data sources. The logic behind data extraction algorithms is also defined for each data source. A tab delimited text version with the same name is also available. Lithology_OpenIntervalLengthFit.txt --Parameters for equations used for estimating open intervals by lithology, overlying sediment, and well type HydrogeologicSetting_OpenIntervalLengthFit.txt --Parameters for equations used for estimating open intervals by hydrogeologic setting and well type domestic_grids.zip contains: domestic_bottom_dist_to_5.asc --Grid of domestic-supply well open interval bottom depth data density, distance to reach 5 wells with information on the bottom of the open interval domestic_open_dist_to_5.asc --Grid of domestic-supply well open interval length data density, distance to reach 5 wells with information on open interval length domestic_bottom_open.asc --Grid of domestic-supply well depth to the bottom of the open interval domestic_len_open.asc --Grid of domestic-supply well open-interval length domestic_top_open.asc --Grid of domestic-supply well depth to the top of the open interval public_grids.zip contains: public_bottom_dist_to_5.asc --Grid of the public-supply well open interval bottom depth data density, distance to reach 5 wells with information on the bottom of the open interval public_open_dist_to_5.asc --Grid of the public-supply well open interval length data density, distance to reach 5 wells with information on open interval length public_bottom_open.asc --Grid of the public-supply well depth to the bottom of the open interval public_len_open.asc --Grid of the public-supply well open-interval length public_top_open.asc --Grid of the public-supply well depth to the top of the open interval pubdom_difference_grids.zip contains: pubdom_bottom_open_diff.asc --Grid of the differences between the public-supply and domestic-supply well moving median surfaces representing the bottom of the open interval pubdom_len_open_diff.asc --Grid of the differences between the public-supply and domestic-supply well moving median surfaces representing the length of the open interval pubdom_top_open_diff.asc --Grid of the differences between the public-supply and domestic-supply well moving median surfaces representing the top of the open interval