Identification of Sulfate Sources in the Groundwater System of Zaozhuang: Evidences from Isotopic and Hydrochemical Characteristics

Abstract

Karst groundwater is an important source of water supply for the industrial and agricultural proposes and drinking water in Zaozhuang City. In recent years, with the development of industrialization and increasing of domestic water consumption, the sulfate pollution of karst groundwater has become a serious problem. 36 samples of surface and different depth of groundwater were collected in southern Zaozhuang City in August, 2014. Based on the analysis of the hydrochemical composition and the isotopic characteristics of δD, δ18O-H2O, and δ34 S-SO42-, this paper analyzed the influence of hydrogeochemical evolution of groundwater and human input in the area, in order to identify the scope and ways of sulfate pollution. The results showed that the basic hydrochemical type was HCO3·SO4-Ca, formation of geochemical components mainly included the dissolution of carbonate and sulfate minerals, oxidation of pyrite and the influence of human activities. Moreover, the main recharge of groundwater in study area was the atmospheric precipitation. The hydraulic connection was closely linked between the surface water and different depth of groundwater. The variation range of groundwater δ34 S-SO42- values was from 0.2‰ to 9.3‰, and the relationship between the δ34 S-SO42- value and SO42- value of groundwater showed different sources of sulfate. The sources of sulfate in groundwater included the dissolution of gypsum, the oxidation of pyrite, the leaching of fertilizer and infiltration of domestic sewage and industrial wastewater. In addition to the original geological factors, wastewater infiltration of industrial and mining enterprises was the main reason for the increase of sulfate content in the groundwater.