**1. Introduction**

Water resources are one of the most important natural resources on earth and indispensable and irreplaceable for the survival of all living beings, as well as for human life and production activities [1–3]. Groundwater is an important component of the Earth's water resources; compared to other water sources, it has the advantages of good quality, lower investments required for its exploitation, lower susceptibility to pollution, and

**Citation:** Ma, Z.; Li, J.; Zhang, M.; You, D.; Zhou, Y.; Gong, Z. Groundwater Health Risk Assessment Based on Monte Carlo Model Sensitivity Analysis of Cr and As—A Case Study of Yinchuan City. *Water* **2022**, *14*, 2419. https:// doi.org/10.3390/w14152419

Academic Editor: Adriana Bruggeman

Received: 24 June 2022 Accepted: 28 July 2022 Published: 4 August 2022

**Publisher's Note:** MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.

**Copyright:** © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

multi-year regulation [4]. These characteristics are an important guarantee to maintain the virtuous cycle of the water resources system and have a positive impact on national livelihood, people's health and safety, and sustainable social development [5,6]. In recent years, groundwater extraction in China reached about 2.7 billion cubic meters per year, a number that is currently increasing. Moreover, 400 Chinese cities and about 45% of agricultural irrigation rely on groundwater as a source of water supply. Agricultural, industrial, and domestic activities are the main sources of groundwater pollution [7], mainly consisting of heavy metals [8,9], organic matter [10,11], As [12–14], and chromium contamination [15].

At present, groundwater pollution is a serious problem in China. According to the results of a statistical analysis of groundwater quality in 118 cities and regions nationwide, the majority of urban groundwater suffers from a certain degree of point-source and surface pollution, with 64% of urban groundwater severely polluted, 33% mildly polluted [16], and only 3% of urban groundwater basically clean [17,18]. Due to groundwater pollution, an increasing number of cities and regions are suffering from water shortage, posing rising risks to human health. According to the World Health Organization (WHO), 80% of the diseases suffered by third-world citizens are caused by water pollution [19]. Most cities in northwestern China use groundwater as their only drinking water supply. In these areas, the contamination of groundwater is expected to directly affect the health of citizens who use it for drinking purposes. Especially, the large land development projects in the Loess region and the proposed revival of the Silk Road Economic Belt may have a significant impact on the quantity and quality of groundwater, and require urgent and comprehensive research [20–22].

The study area of the present research is adjacent to the upper reaches of the Yellow River; it includes Xingqing District, Xixia District, Jinfeng District, Yongning County, and Helan County. It borders the Helan Mountains to the west and the west bank of the Yellow Rivulet River to the east. The exploited groundwater resources in Yinchuan are equal to 4.8842 <sup>×</sup> <sup>10</sup><sup>8</sup> <sup>m</sup>3/a, accounting for 28.8% of the exploitable groundwater resources, equal to 16.9317 <sup>×</sup> <sup>10</sup><sup>8</sup> <sup>m</sup>3/a, indicating a serious over-exploitation of groundwater in local areas. Groundwater is used mainly for urban domestic purposes, and also for industrial, and rural human and animal drinking water purposes [23]. In general, the ecological environment in the study area is very fragile [24].

Chen et al. found different degrees of carcinogenic and non-carcinogenic health risks from drinking groundwater in Yinchuan Plain; moreover, the health risks from inorganic contaminants such as arsenic, lead, and Cr(V) were found to be greater than those from organic contaminants such as benzene, trichloroethylene, toluene, 1.2-dichloroethane, and 1.1-dichloroethylene. More in detail, the carcinogenic and non-carcinogenic risk rates of arsenic were found to be equal to 47.3% and 8.6% respectively, i.e., considerably greater than those from other protective layer, which are also considered priority control contaminants for groundwater in Yinchuan Plain [25]. Therefore, considering the importance of groundwater in this region, in this study a health risk assessment of groundwater was conducted for the study area.

Currently, most of the health risk assessment site methods are based on the EPA health risk assessment model [26], but due to the uncertainty of the input parameters, the resulting health risk calculation results are highly uncertain. However, the Monte Carlo model can solve this problem by probabilistic methods.

The main objectives of this study are as follows: (1) to analyze the current groundwater distribution in the Yinchuan Plain through a data survey; (2) Monte Carlo and visual coinage are used to determine the main influencing factors and possible ion forms in hydrogeology, and conduct a health risk assessment of groundwater in Yinchuan City, providing support for strengthening the supervision and control of groundwater in the region.
