*3.5. Water Quality Index Assessment*

Table 4 shows the weight assigned to each parameter, and the relative weights are calculated using Formula (3).

**Table 4.** Relative weight of physicochemical parameters. All units for all parameter indices are in mg/L, except pH (non-dimensional).


Table 5 lists the water quality assessment results. As shown in Table 5, 37 of the samples (77.1%) are of excellent quality, 9 samples (18.7%) are of good quality, and 2 samples (4.2%) are of poor quality. The most significant parameters affecting the water quality in the study area are NO<sup>3</sup> <sup>−</sup>, F−, and Cr6+ .

Water without excellent quality is dominated by wells with low depth represented by samples TW1-052, TW1-047, TW1-041, TW2-021, TW2-66 and TW2-67 with 2, 3, 2, 3, 10, and 8 m, respectively.

The contamination source of the wells represented by samples TW1-052, TW1-047, TW1-041 might be the ravines situated nearby. These ravines may bring contaminated water that leaks in the phreatic and shallow aquifer. The other concerned wells with low depth were possibly contaminated by human activities, as they are located in residential and agricultural areas.

As depicted in Figure 5, a major part of Tongchuan is dominated by excellent water and can be used for drinking purpose. However, in some towns such as Yuhua, Wangshiao, and Chenlu, for example, groundwater quality is not suitable for drinking. Therefore, water needs pretreatment before drinking, and taking effective measures to prevent groundwater pollution is imperative. Low deep wells should also be drilled deeply to avoid contamination by surface water leakage and pollution caused by human activities.
