MODFLOW-NWT and MODPATH6 files used for groundwater-flow simulation and pathline analyses in the vicinity of the Coakley Landfill Superfund site, Rockingham County, New Hampshire

A MODFLOW-NWT groundwater-flow model of the Coakley Landfill (CL) area in southeast New Hampshire was constructed from a previously published hydrologic model of the southeast New Hampshire region (https://doi.org/10.5066/P909PUIP). The CL model was used to evaluate groundwater-flow patterns and advective transport pathways from the CL as a proxy to solute transport of per- and polyfluoroalkyl substances (PFAS) compounds. The CL model was rediscretized and upgraded to include local information associated with the CL. A combination of trial-and-error and parameter estimation was done to calibrate model-computed water-level and streamflow data to observed water-level and streamflow data. The model was run in steady-state conditions indicative of a modified 2015 hydrologic condition then used to delineate groundwater discharge zones from the advective transport of particles from the CL. Several advective transport simulation scenarios were done including forward-tracking of particles and delineation of pathlines from the shallow bedrock aquifer underlying the footprint of the CL under conditions with and without the CL cap, and scenarios forward-tracking of particles from the deep surficial aquifer underlying the footprint of the CL, also with and without the CL cap. The cap was constructed in 1999 and scenarios without the cap are meant to identify the effect of the CL cap on groundwater-flow patterns. Further information on the model is provided in the associated U.S. Geological Survey Scientific Investigation Report (SIR) at https://doi.org/10.3133/sir2026xxxx. This USGS data release contains all the input and output files for the simulations described in the associated report.