MODFLOW-NWT and MODPATH5 used to evaluate groundwater availability, geochemistry, and flow pathways to public-supply wells in the Atlantic Coastal Plain and bedrock aquifers, Aiken County and part of Lexington County, South Carolina, 2015-2019

The U.S. Geological Survey, in cooperation with Aiken County; City of Aiken; Breezy Hill Water and Sewer Company, Inc.; Montmorenci-Couchton Water and Sewer District, Inc.; and Gilbert-Summit Rural Water District developed a model for use with MODFLOW-NWT and MODPATH5 to evaluate groundwater flow and advective transport under pre- and post-development conditions in the Atlantic Coastal Plain (ACP) and bedrock crystalline-rock aquifer in the Aiken County, SC area. Groundwater availability, geochemistry, and flow pathways to public-supply wells (PSW) were assessed between 2015 and 2019. A population increase by about 17.6 percent from 2000 to 2015 in Aiken County, as well as the current (2022) and potential economic development in the area, has led to an increased demand for water to meet drinking- or process-water needs. Most water demands, including public supply, domestic supply, irrigation, and industrial, are met by groundwater. To address the various concerns of public, private, and governmental users related to groundwater availability and geochemistry in the study area, a 3-dimensional, numerical groundwater-flow model, in conjunction with a groundwater-recharge model using the Soil-Water-Balance (SWB) model (https://doi.org/10.5066/P9WEOGCS), was constructed, and calibrated using historical groundwater levels and measurements of stream baseflows. The groundwater geochemistry investigation included the collection of groundwater samples, between 2015 and 2016, from 16 PSWs and 4 monitoring wells screened in the ACP aquifers or entirely or partially open to the bedrock aquifer. Basic physical properties and the chemical composition of the groundwater samples are reported along with the concentration of radium isotopes 226Ra and 228Ra, volatile organic compounds (VOC), stable isotopic composition of the groundwater, nitrates, and concentrations of CFCs and dissolved gases. A base simulation and water budgets for dry (2012) and wet (2015) year conditions, future (2017–2065) groundwater-demand scenarios based on three general circulation models (GCMs) of future climates, and future agricultural irrigation demands were simulated. The calibrated groundwater-flow model, and geochemical results of groundwater ages, were used in conjunction to simulate groundwater particle tracks to determine the direction and travel time of groundwater to a particular PSW. Model simulations are used in this study to provide information to facilitate the best management of the groundwater resources in Aiken County and part of Lexington County. This data release contains all the input and output files for the simulations described in the associated model documentation report. (https://doi.org/10.3133/sir20225036).