Chemical Evolution Process and Quality Assessment of Seepage Groundwater in Tunnel Crossing Gas-Bearing Coal Seams

Table 2

Relative weights of groundwater quality parameters studied and reference standards.

Chemical parameter	WHO standards	Weight ()	Relative weight ()
pH	6.5-8.5	4	0.074
EC	1500	4	0.074
TDS	1000	4	0.074
HCO3^-	500	3	0.056
SO4^2-	250	5	0.093
Cl^-	250	4	0.074
NO3^-	45	5	0.093
F^-	1.5	5	0.093
Ca^2+	75	2	0.037
Mg^2+	50	2	0.037
Na^+	200	3	0.056
K^+	12	2	0.037
NH4^+	0.5	3	0.056
Fe	0.3	4	0.074
Al	0.2	4	0.074

Note: NH₄⁺ and Al refer to WHO standards and Chinese groundwater quality standards [22, 23].