## 3 Results and Discussion
### Human Health Risk Assessment (HHRA)  
Human health risks were assessed in areas B and C. The main reason is that these two areas have permanent settlements. Specifically, area B is designated for industrial use according to the current spatial plan, but it is mainly used for agriculture, while part of the area is residential. The expansion of services and industry is planned in the future. Area C is an exclusively residential zone. The health risk assessment in a specific area included those CLHCs that exceeded the particular IT value in groundwater (Table S3). Groundwater contamination in area B was caused by PCE, TCE and _cis_-DCE with a maximum concentration of 442 u/L, 1110 u/L and 500 ug/L, respectively. However, the effect of _cis_-DCE on the carcinogenic health risk could not be evaluated due to missing values of key parameters. According to the selected criterion, the only problematic groundwater contaminant in area C was PCE, with a maximum concentration of 138 ug/L. The results of the carcinogenic and non-carcinogenic risk assessment due to human contact (adults and children) with CLHCs in groundwater by the five most likely exposure routes (details in Supplementary Text S1) are shown in Table 1. Regarding the non-carcinogenic risk in the evaluated areas, B and C, the H\({}_{\text{Total}}\) value for both adults and children was lower than 1.0, so the existence of non-carcinogenic effects on the population was not confirmed. The greatest contribution of the three CLHCs to the total non-carcinogenic risk for both population groups was by TCE (95.3%), followed by PCE (4.0%) and _cis_-DCE with a negligible contribution (0.7%), which is consistent with the toxicological parameters of these CLHCs, while the RfD and RfC values for TCE are one order of magnitude lower than those for PCE and _cis_-DCE. A comparison of several considered exposure routes showed that dermal contact during irrigation (80.4% for adults and 55.6% for children) and indoor breathing (12.7% for adults and 28.6% for children) contributed the most to the non-carcinogenic risk for adults and children. The ingestion of home-grown vegetables and groundwater during the watering period had a less significant effect, 4.5% and 1.8% in adults and 12.4% and 3.5% in children, respectively, while outdoor breathing and the inhalation of water spray were negligible exposure routes to CLHCs. This analysis is consistent with the results of a risk assessment of human exposure to VOCs present in groundwater from Taiwan, which confirmed that water intake, indoor breathing and dermal absorption contributed the most to human health risks [127]. The IELCR values for the individual did not exceed the threshold value of \(10^{-4}\)[128,129], which represents an unacceptable carcinogenic risk (Table 1). However, IELCR values in area B above the threshold of \(1\times 10^{-6}\) could indicate a potential cancer risk. The main contributor to the IELCR\({}_{\text{total}}\) value was TCE, with almost 100% contribution and the indoor breathing and dermal contact during irrigation were predominant exposure routes accounting for 30.0% and 70.0% in adults and 55.0% and 37.8% in children, respectively. Although the human health risk assessment is limited by uncertainties (e.g., time-varying concentration of organic micro-contaminants in groundwater, other present contaminants not included in the HHRA, default weight of residents instead of their current weight or ambiguity in the consumption of home-grown vegetables), it provides approximate information about the effect of the environmental exposure of the population to these harmful organic compounds. Epidemiological studies have clearly documented a statistically significant association of increased human exposure to PCE, TCE or VC with an increased risk of developing several types of cancer and other non-cancer diseases [130, 131, 132, 133].