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).

美国地质调查局（U.S. Geological Survey）联合艾肯县、艾肯市、布里兹希尔供水与污水处理有限公司（Breezy Hill Water and Sewer Company, Inc.）、蒙特莫伦西-库奇顿供水与污水处理区有限公司（Montmorenci-Couchton Water and Sewer District, Inc.）以及吉尔伯特-萨米特农村供水区，开发了一款适配MODFLOW-NWT与MODPATH5的数值模型，用于评估南卡罗来纳州艾肯县区域大西洋海岸平原（Atlantic Coastal Plain, ACP）含水层与基岩结晶岩含水层在开发前后的地下水流与对流运移过程。
2015—2019年，研究团队对该区域的地下水可利用性、地球化学特征以及公共供水井（public-supply wells, PSW）的地下水流路径开展了评估。2000年至2015年艾肯县人口增幅约17.6%，加之该区域当前（2022年）及潜在的经济开发活动，导致饮用水与工艺用水需求持续增长。区域内绝大多数用水需求，包括公共供水、生活供水、灌溉与工业用水，均由地下水供给。
为回应公众、私营主体与政府用户对研究区内地下水可利用性及地球化学特征的各类关切，研究团队构建了三维数值地下水流模型，并结合采用土壤水平衡（Soil-Water-Balance, SWB）模型（https://doi.org/10.5066/P9WEOGCS）的地下水补给模型，基于历史地下水位观测数据与河道基流实测值完成了模型校准。
2015—2016年，研究团队从16口公共供水井与4口监测井采集了地下水样本，这些井的滤水管分别布设至大西洋海岸平原含水层，或全部/部分穿透基岩含水层。本次调查的地下水样本数据涵盖基本物理性质、化学成分，以及镭同位素226Ra、228Ra、挥发性有机化合物（volatile organic compounds, VOC）、地下水稳定同位素组成、硝酸盐浓度，还有氯氟烃（CFCs）与溶解气体的含量。
研究开展了基准期模拟与枯水年（2012年）、丰水年（2015年）的水均衡分析，同时基于3套未来气候通用循环模式（general circulation models, GCM）设置了2017—2065年的未来地下水需求情景，并模拟了未来农业灌溉需水情况。
借助校准后的地下水流模型与地下水年龄地球化学结果，研究团队模拟了地下水粒子轨迹，以确定地下水流向特定公共供水井的运移方向与时间。本研究通过模型模拟成果，为艾肯县及列克星敦县部分区域的地下水资源最优管理提供了决策支撑。
本数据集发布包含了相关模型文档报告（https://doi.org/10.3133/sir20225036）中所述所有模拟的输入与输出文件。