Health-Risk Assessment of Arsenic and Groundwater Quality Classification Using Random Forest in the Yanchi Region of Northwest China

High-arsenic (As) groundwater was first discovered in the Yanchi region, Northwest China, which is an arid or semiarid area, and the groundwater quality seriously affects the health of local residents. A comprehensive understanding of the spatiotemporal distribution characteristics, water quality, and health risk of high-As groundwater is indispensable for the sustainable utilization of groundwater sources and resident health. Seventy-nine groundwater samples were collected from different aquifers and seasons. The hazard quotient (HQ) and carcinogenic risk (CR) of As for adults and children were assessed. Moreover, the effects of groundwater sampling site and seasonal change on As concentration were investigated. Then, the random forest method was used to evaluate the importance of the indicators and the influence of these important indicators on groundwater classification. Thirty-three percent of the groundwater samples had HQ values > 1, and the CR values of all groundwater > 1.00 × 10−6 for children, representing a serious health risk. Twenty-one percent of the groundwater samples had health risk for adult. High-As groundwater is present at depths less than 60 m, and groundwater As concentrations are slightly affected by seasonal changes. The random forest shows that the most important indicators that affect groundwater quality are Na, TDS, TH, and F, and the least important is As. Furthermore, the optimal set of indicators contained all four of the most important indicators obtained by the random forest model, which achieved a classification accuracy of 88.21% for groundwater quality.