Destruction processes of mining on water environment in the mining area combining isotopic and hydrochemical tracer

Abstract

There is less research on the hydrological system and its destruction processes mechanism in the mining areas, especially combined application of isotope technology and chemical signals, which is a key scientific problem that need to be solved. This study takes Jinci spring area in Shanxi as a case study. It is based on the data of hydrology and mining condition from 1954 to 2015, combining monitoring experiments, O18, D, S34 and N15 tracing, chemical and model simulation. This study investigates the hydrological regularity and impacts of mining activities on water quantity and quality, and reveals the destruction process of hydrological system. The results show that: (1) Water chemical type shows an evolutionary trend of HCO3−-Ca2+-Mg2+→SO42--HCO3--Ca2+-Mg2+→SO42--Ca2+-Mg2+, due to the influence of exploitation and fault zones. Isotope tracer shows that mine pit water is formed by a mixture of pore water, karst water and surface water. (2) Although precipitation and seepage have a certain impact on the reducing of groundwater quantity, over-exploitation of water resource is still the main reason for reducing of groundwater quantity. Under the conditions of keeping the exploitation intensity at the current level or reducing it by 10%, groundwater level shows a declining trend. Under the condition of reducing it by 30%, groundwater level starts to rise up. When reducing by 50%, groundwater level reaches its highest point. Coalmining changes the runoff, recharge and discharge paths. (3) From 1985 to 2015, Water quality in the mining area is worsening. Ca2+ increases by 35.30%, SO42− increases by 52.80%, and TDS (Total Dissolved Solid) increases by 67.50%. Nitrates come from the industrial and domestic wastewater, which is generated by mining. The percentage of groundwater coming from gypsum dissolusion is 67.51%, and the percentage from coal measure strata water is 34.49%. The water qualities of river branches are generally deteriorated.