Hydrogeochemical Evolution and Control Mechanism of Underground Multiaquifer System in Coal Mine Area

Table 1

Sample indexes-descriptive statistics.

Parameters	The Cenozoic aquifer				The Permian aquifer				The carboniferous aquifer
	Min	Max	Mean	Skewness	Min	Max	Mean	Skewness	Min	Max	Mean	Skewness
K^++Na^+ (mg/L)	111	202.47	152.71	0.26	578.6	1550.27	1036.94	0.05	168.65	813.98	398.6	0.48
Ca^2+ (mg/L)	79.55	124.73	99.89	0.24	1.13	63.15	25.59	0.63	2.42	447.56	202.17	0.09
Mg^2+ (mg/L)	28.81	81.12	54.93	0.09	1.17	38.66	13.73	0.8	5.53	323.69	121.44	1.09
Cl^− (mg/L)	91.98	144.67	115.43	0.15	56.46	354.16	171.91	0.82	82.98	188.91	143.39	-0.37
SO4^2− (mg/L)	207.06	417.26	283.62	1.01	833.2	2524.69	1668.09	0.45	1001.36	1770.6	1404.92	-0.16
HCO3^− (mg/L)	279.83	541.86	419.79	-0.35	164.21	692.17	435.72	-0.14	129.91	340.89	240.28	0.29
TDS (mg/L)	899.23	1239.45	1058.24	0.22	2023.48	5005.01	3371.35	0.32	2020.85	3088.47	2534.47	0.02
PH	7.3	8.4	7.57	2.39	7.79	8.32	7.94	1.96	7.1	8.3	7.68	-0.6