*2.2. Sampling and Analysis*

Groundwater quality assessment and human health risk assessment based on 10 groundwater hydrological long-term monitoring wells set up by Shanxi Provincial Department of Water Resources in the study area. Groundwater samples were collected in 2017 and were used for the analysis of water quality parameters, including pH, total hardness (TH), total dissolved solids (TDS), sulfate (SO<sup>4</sup> <sup>2</sup>−), chloride (Cl−), fluoride(F−), cyanide, volatile phenols, chemical oxygen demand (CODMn), nitrate (NO3-N), nitrite (NO2-N), ammonia nitrogen (NH4-N), and PTEs (Fe, Mn, Hg, As, Cd, Cr6+, Pb) for each sample. Sample collection, preservation, transportation, and testing were carried out in strict accordance with the Technical Specifications for Environmental Monitoring of Groundwater [56]. Before sampling, wells were pumped for 10 min to remove stagnant water. All sampling containers were thoroughly cleaned with the groundwater to be sampled. To ensure the stability of the elements, the samples analyzed for TH, Fe, Mn, Cd, and Pb were mixed with HNO<sup>3</sup> solution, the samples for the analysis of NH4-N were mixed with H2SO<sup>4</sup> solution, and the samples for cyanide and Cr6+ analysis and for Hg and As analysis were mixed with NaOH and HCl, respectively. All samples were then sealed tightly and immediately sent to the laboratory of Linfen Hydrology and Water Resources Survey Branch for analysis (within 24 h). pH was measured directly in the field using a portable pH meter. TH was analyzed using the EDTA titration method. TDS was determined by the drying and weighing approach. SO<sup>4</sup> <sup>2</sup>−, Cl−, F−, NH<sup>4</sup> + , NO<sup>3</sup> <sup>−</sup>, and NO<sup>2</sup> − were tested using an ion chromatograph (ICS-600). Fe, Mn, Hg, As, Cd, Cr6+, and Pb were measured using inductively coupled plasma-mass spectrometry (ICP-MS). Groundwater was filtered using a 0.45 µm filter before their analysis. During the analysis, distilled water and replicates were introduced to ensure the reliability of the results. The replicates had a relative error

within ±5%, indicating acceptable analytical accuracy. IDW interpolation method has been widely used to study the spatial distribution of groundwater quality parameters. IDW uses the deterministic model method to calculate the unknown value according to the nearby points rather than the far-off ones. This interpolation method fits well for real-world parameters [37–39]. IDW interpolation results were verified by overlapping field survey data and laboratory analysis results. The pixel values of the IDW interpolation map match well with those of field verification data.
