Table 7.

Hydrochemical index of sandstone fracture water from the 12 coal system.

Index	Na+	Ca2+	Mg2+	Cl–	SO42–	HCO3–
Minimum value	2.92	51.17	29.94	5.71	12.71	69.47
Maximum value	12.67	64.36	37.36	10.99	17.03	74.16
Average	7.78	59.25	32.57	8.97	15.54	71.79
Standard deviation	2.48	2.88	2.25	1.08	1.16	1.31
Coefficient of variation	0.32	0.48	0.69	0.12	0.07	0.02