Study on the pollution load of the urban trunkroad runoff in Xi'an

The present paper is aimed at providing its authors' detailed analysis of the potential pollution effect of the urban trunk road runoff on their receiving water bodies by taking Xi'an city as a case study.Road runoff,as a heavily polluted part of urban environment, has been paid much attention by the researchers.There do exist some kinds of pollutants in this aspect,such as particulate matter,organic bacteria,nutrients as well as heavy metals.The total mass of the runoff pollutants,in other words,pollution load,has been widely used to represent the potential pollution effect of the trunk road runoff once they are receiving water bodies.It is just for' their harmful nature that has drawn wide interest of a lot of researchers,some of whom initiated serious schemes and programs of essential monitoring work.Both domestic and international study reports in recent years say that the degree of the archway runoff pollution seriousness seems to be different from country to country,and from region to region because many factors,such as the annual rainfall,types of surrounding land use,air pollution,road maintenance,the urban transportation management and so on,may all influence it.Such factors may often underscore the urgency of field research and as a result prevent it from getting well recognized.In this paper,we have collected urban trunk road road runoff data caused by 34 storm events,which were proportional to the total volume at the southern suburb and the second ring road in Xi'an by using a self-made volume proportional collecting device from March to November in 2009.Event mean concentration (EMC) of SS,COD,NH_4~+-N,Pb and Zn were tested and pollution loads were calculated.The multiple regression models of runoff pollution load were built up based on the analysis of influential factors. Results of our experiments show that the pollution loads of SS, COD,NH_3-N,Pb and Zn of Xi'an' s urban trunk road road runoff were 4.56-778.39 kg/hm~2,2.22-308.7 kg/hm~2,0.01-1.39 kg/hm~2,0.05-33.09 g/hm~2 and 1.38-115.82 g/hm~2.The amount of the pollutants entering into the receiving water bodies carried by the road runoff in different runoff events were quite different and caused shocking effects on the receiving water bodies.In addition, the rainfall had most significant impact on the pollution load positively and the correlation coefficient was 0.734-0.943 at the significant level of 0.01.Maximum rain intensity and duration were also positively correlated with pollution loads,though antecedent dry period(ADP) had little relationship with it.Thus,it can be concluded that the established multiple regression models of runoff pollution load passed the model test surely and can in turn be used for the road runoff pollution load forecasting.