Construction of hydrogeochemistry criteria in hydrogeological exploration in coal mines

Aiming at the problem of hydrogeochemical anomalies existing in hydrogeological exploration in coal mines, Jurassic aquifer in Inner Mongalia-Shaanxi mining area was taken as research objective, analysis and construction of criteria of causes of hydrochemical anomalies were carried out. The results showed:it was insufficient that during exploration "clean water and sand" was taken as the basis for discriminating completion of well washing, the residue of cement slurry was the major factor for hydrochemical anomalies such as increase of pH and decrease of mineralization. Therefore, the results of complementary hydrological exploration and water detection and drainage in working faces in deeply buried coalfield in Inner Mongolia-Shaanxi mining area were combined, the criteria of "five factors" constituted of pH, mineralization (TDS), HCO₃^-, SO₄^2- were set up, 36 sets of water samples collected during hydrological exploration in Balasu Mine were discriminated, 8 sets of hydrochemically abnormal water samples were rapidly judged out. After rejection of hydrochemically abnormal water sample points, the hydrochemical characteristics of different aquifers in Balasu Mine might be set up clearly. Quaternary hydrochemical characteristics were close to surface water, presented as water type of low mineralization, weak alkaline and heavy calcium carbonate. The aquifer of Jurassic Luohe Formation was closely connected hydraulically with Quaternary but deeper to some extent, resulting in dissolution of certain amount of Na⁺, the chemical characteristics evolved into heavy calcium carbonate type. Anding Formation is a relatively stable regional aquifuge, inducing that lateral recharge is dominant in Zhiluo Formation and Yan'an Formation, the time of cyclic alternation of groundwater is long, forming groundwater of high mineralization(>2 500 mg/L) and sodium sulfate type characterized by deep retention. sodium sulfate type groundwater.