Pollution characteristics of urban road runoff in Xi´an, China

Urban road runoff caused by 36 storm events were collected using self-made volume proportional collecting device at south second ring road in Xi´an, China from Mar. 2009 to Feb. 2010. Event mean concentrations (EMC) of SS, NH₃-N, total and dissolved COD, Pb and Zn were tested. Pollution intensity, as well as occurrence, correlation and seasonal variation of runoff pollutants were explored. Results showed that EMC of main pollutants varied greatly and the median EMC of SS, COD, dissolved COD, NH₃-N, Pb, Zn and dissolved Zn were 1601mg/L, 613mg/L, 143mg/L, 1.9mg/L, 0.0416mg/L, 0.2233mg/L and 0.1114mg/L respectively. EMC of SS and COD was far greater than Integrated Wastewater Discharge Standard Grade III, so SS and COD were the main pollutants of road runoff of Xi´an. The occurrence of Pb was mainly granular state, 46.2% of Zn, 26.4% of organic pollutants were dissolved. The correlation of COD, Pb and Zn with SS were significant at 0.01 level and correlation coefficients were 0.797, 0.825, 0.893 respectively, which showed that particulate matters were carrier for many other pollutants. Result of one factor analysis of variance showed that EMC of SS, COD and NH₃-N varied with seasons significantly, while the variation tendency of other pollutants, such as dissolved COD, Pb and Zn was not obvious.