MODFLOW-NWT and MODPATH6 models used to simulate contributing areas in hypothetical sedimentary rock aquifers under extreme recharge events

MODFLOW-NWT groundwater flow models and MODPATH6 particle tracking simulations were developed to determine contributing areas (CAs) for and advective travel times to domestic wells under extreme recharge events in a small hypothetical watershed underlain by dipping sedimentary rocks. The hypothetical models are based on hydrogeologic conditions in the Newark Basin, located in New Jersey, New York, and Pennsylvania, USA. During extreme recharge events, groundwater supply wells have increased vulnerability to contaminants or pathogens originating at land surface that are flushed into the subsurface. Fractured-rock aquifers are particularly vulnerable because transport to wells can be very fast owing to preferential flow paths through high-permeability fractures with small effective porosities. A base case (BC) scenario was developed in which the flow models simulate transient extreme recharge events and twice daily pumping, and the particle tracking uses a porosity of 0.0001. Alternate transient scenarios were developed in which the models have fewer vertical fractures (FewVF), increased recharge (Rch6.4), or larger effective porosity (Por.001), and an alternate steady-state scenario (StSt) was developed that uses long-term average recharge and pumping rates. For the BC and StSt scenarios, MODFLOW-NWT simulations were run for 48 different pumping well locations (24 shallow well locations and 24 mid-depth well locations). For the FewVF and Rch6.4 scenarios, MODFLOW-NWT simulations were run for the 24 mid-depth well locations. For all scenarios, MODPATH simulations were conducted to define the CAs, the travel times from the CAs to the well, and the arrival times at the well. Transient simulations used hourly releases of particles at the water table throughout the extreme recharge event. The StSt scenario had a single release at the beginning of the simulations. Software tools are provided in this data release to post-process the MODPATH results and produce figures similar to those in the companion journal article (https://doi.org/10.xxxx/xxxxxxxxxxx). This USGS data release contains all the input and selected output files for the simulations described in the companion journal article (https://doi.org/10.xxxx/xxxxxxxxxxx).