*Article* **Groundwater Health Risk Assessment Based on Monte Carlo Model Sensitivity Analysis of Cr and As—A Case Study of Yinchuan City**

**Zhiyuan Ma <sup>1</sup> , Junfeng Li <sup>2</sup> , Man Zhang <sup>3</sup> , Di You <sup>4</sup> , Yahong Zhou <sup>4</sup> and Zhiqiang Gong 1,\***


**Abstract:** Groundwater is an important resource for domestic use and irrigation in the Yinchuan region of northwest China. However, the quality of groundwater in this region is declining due to human activities, with adverse effects on human health. In order to study the effects of chemical elements in groundwater on human health, the human health risk of drinking groundwater was calculated based on the actual situation in China and on the U.S. Environmental Protection Agency (USEPA) model. Moreover, the sensitivity of contaminant exposure in drinking water wells was quantified using Monte Carlo simulation to minimize uncertainty in conjunction with USEPA risk assessment techniques, with the aim to identify the major carcinogenic factors. In addition, Visual Minteq was used to analyze the possible ionic forms of the major factors in the hydrogeological environment of the study area. The results showed that the mean CR values for As were 2.94 <sup>×</sup> <sup>10</sup>−0.5 and 5.93 <sup>×</sup> <sup>10</sup>−0.5 for the dry and rainy seasons, respectively, while for 2018 they were 5.48 <sup>×</sup> <sup>10</sup>−0.5 and 3.59 <sup>×</sup> <sup>10</sup>−0.5, respectively. In parallel, the CR values for children for 2017 were 6.28 <sup>×</sup> <sup>10</sup>−0.5 and 1.27 <sup>×</sup> <sup>10</sup>−0.4, respectively, and 1.17 <sup>×</sup> <sup>10</sup>−0.4 and 7.67 <sup>×</sup> <sup>10</sup>−0.5, respectively, indicating a considerably higher carcinogenic risk for children than for adults. results of the sensitivity analysis of Cr6+ and As using Crystal Ball software showed association values of 0.9958 and 1 for As and 0.0948 and 0 for Cr in the dry and rainy seasons in 2017, and 0.7424 and 0.5759 for As and 0.6237 and 0.8128 for Cr in the dry and rainy seasons in 2018, respectively. Only in the rainy season of 2018, the association values for As were lower than those for Cr, indicating that As is more sensitive to total carcinogenic risk. The results of the visual coinage model analysis showed that among all the possible ionic forms of As, the activity of HAsO<sup>4</sup> <sup>2</sup><sup>−</sup> had the largest logarithmic value and that of H3AsO<sup>4</sup> had the smallest value, regardless of pH changes. This indicates that HAsO<sup>4</sup> <sup>2</sup><sup>−</sup> is the ionic form of As with the main carcinogenic factor in the hydrogeological environment of the study area. Therefore, corresponding environmental control measures need to be taken in time to strengthen the monitoring and control of As, especially HAsO<sup>4</sup> <sup>2</sup>−, in the groundwater of the study area. This study is of great significance for Yinchuan city to formulate groundwater pollution risk management and recovery.

**Keywords:** groundwater; health risk assessment; Monte Carlo model (crystal ball software); visual minteq; yinchuan
