A groundwater Nitrate Decision Support Tool (GW-NDST) for wells in Wisconsin was developed to assist resource managers with assessing how legacy and possible future nitrate leaching rates, combined with groundwater lag times and potential denitrification, influence nitrate concentrations in wells (Juckem et al. 2024). The GW-NDST relies on an ensemble of calibrated parameters to make nitrate predictions and to estimate the uncertainty of those predictions. This data release contains all of the calibrated parameter files required to run the tool. The files are packaged in a single ZIP file. To run the tool, the ZIP package needs to be downloaded and extracted within the pest/ies_parameter_ensembles/ subdirectory within GW-NDST file structure. There are eleven parameter files contained within this zip file (one for each parameter group). Each of these files are compressed numpy .npy files that contain 3-dimensional arrays of parameter values.