Data used to model and map pH and redox conditions in groundwater in the Northern Atlantic Coastal Plain aquifer system, eastern USA, are documented in this data release. The models use as input data measurements of pH and dissolved oxygen concentrations at about 3000 to 5000 wells, which were compiled primarily from U.S. Geological Survey and U.S. Environmental Protection Agency databases. The boosted regression trees machine learning method was used to build the models. Explanatory variables (predictors) describe geology, hydrology, chemistry, physical characteristics, anthropogenic influence, metrics from a groundwater flow model, and groundwater residence times in the aquifer system. Data for four models are documented--one model for pH and one model each for the probability of dissolved oxygen less than three threshold values (0.5, 1, and 2 milligrams per liter). The data are provided in data tables and raster files, organized as follows. There is one data table for the well data used to develop all four models (well data). There is one zipped group of 10 files (one for each aquifer) for explanatory input data used to make predictions at grid points (prediction input). There are 9 zipped groups of files for model output; these include 1 zip file of predictions at grid points for each of the 4 models (prediction output), 1 zip file for combined pH and dissolved oxygen predictions (combined prediction output); and 4 zip files of uncertainty intervals for predictions for each of the 4 models (uncertainty output). Filenames for prediction input and for model output are distinguished by codes abbreviating the aquifer name and position in the vertical stack of 19 regional aquifers and confining units, as follows: Surficial aquifer, 1surf; Upper Chesapeake aquifer, 3upch; Lower Chesapeake aquifer, 5loch; Piney Point aquifer, 7pipt; Aquia aquifer, 9aqia; Monmouth - Mt. Laurel Aquifer, 11moml; Matawan aquifer, 13mtwn; Magothy Aquifer, 15mgty; Potomac-Patapsco aquifer, 17popt; Potomac-Patuxent aquifer, 19popx. The data release also contains a tif-format raster file of the prediction grid and two data tables that separately describe the explanatory variables (predictors) and their sources.