The causes of abnormal quality of environmental water due to excavation of the underground powerhouse group of a pumped storage power station were analyzed in this study.After detecting the pH values of the environmental water in large extent and analyzing the composition of the water sampled from representative seepage fractions in the engineering area

it was discovered that the pH values

the SO2-4 ion content and the total iron content had changed significantly at some locations of the environmental water body: the water appeared strong acid with irregularly distributed high SO2-4 content and high total iron content.Combining the analysis of rock composition with the investigation of pyrite mineralized points

it is considered that the abnormal quality of the environmental water in the underground powerhouse group of the pumped storage power station was caused by the uneven-distribution of the pyrite mineralized points which had been oxidized in open conditions

and had nothing to do with the filled chemical agents used in anchor holes of the powerhouse.Considering the lack of effective materials of strong acid resistance at present time

the hydrogeology conditions

especially those in the deep stratums

should be studied thoroughly in the site investigation to understand and forecast the possible change of water quality induced by the environmental conditions in the excavation and the operation of the deep-buried underground structures for the application of some preventative measures.