Characteristics and source apportionment of groundwater nitrate contamination in the Hutuo River alluvial-pluvial fan regions

Based on investigation of groundwater and surface water of the Hutuo River alluvial-pluvial fan in October, 2015, the pollution mechanism of nitrate in the region were identified by using the water chemical and multivariate statistical technology. The results show that the nitrate contamination is lighter for surface water and the mean concentration of nitrate is 19.54 mg/L, and all the samples are not over the environmental quality standard for surface water in China (GB-3838—2002). For groundwater, however, the mean concentration of nitrate is 75.84 mg/L and 30.43% of the samples are over the quality standard in China (88.6 mg/L), indicating that the groundwater has suffered serious nitrate pollution. The personal annual risk caused by nitrate in three hydrogeological units of the Hutuo River alluvial-pluvial fan regions are 4.94×10-8, 1.99×10-8 and 2.61×10-9, respectively, and are lower than the maximum allowance risk level recommended by ICRP (5.0×10-5/a). Therefore, it is at an acceptable level and will not cause obvious health hazards. There are significant difference between nitrate concentration resulting from the different hydrogeological subregions and groundwater depth. However, there are no significant differences between the land use and the nitrate concentration. The mainly sources of NO-3 pollution is the domestic sewage and chemical fertilizer in the study area. In addition, the groundwater intensely exploited is a major inducing factor for the NO-3 pollution.