Characteristics Of Runoff Pollution Of Different Underlying Surfaces In Cultural And Educational Area Of Xi’an

The acceleration of urbanization process is accompanied by the change of urban landscape pattern,large area of hard surfaces replace the original permeable surface.Which have changed the hydrological conditions of the city and have a profound influence on the regional climate,environment and water body.With the continuous improvement of the treatment rate of point source pollution,non point source pollution,including urban surface runoff pollution,has become the second pollution source causing the deterioration of urban water ecological environment.Urban districts,one of the main components of the city,occupying a large proportion of urban area.Road,roof and grassland are three main kinds of underlying surfaces in urban districts.Comparing with urban traffic road runoff,water quality of road,roof and grassland runoff in urban districts is relatively good,but the area of urban districts account for a large proportion of urban underlying surfaces,thus runoff flow is larger,and the runoff pollution load can not be ignored.On the other hand,the large area of collection space of urban districts and relatively good water quality also provide a good foundation for the collection and utilization of rainwater resources.What’s more,the construction of sponge city,which focuses on controlling pollutants at its source through a series of management measures and is regarded as a priority solution for managing stormwater in urban areas,also need to develop and design reasonably low impact development（LID）rainwater utilization system,based on water quality and emission characteristics of various underlying surfaces runoff.Three kinds of underlying surfaces,such as road,roof and grassland at a cultural and educational area in Xi’an,Shaanxi province were selected as sampling areas,and runoff samples over the whole time range of 10 storm events and 2 snowmelt events were collected by the manual time-interval sampling method from Aug.2016 to Aug.2017.The concentrations of SS,COD,TN,TP,Pb,Zn Cu,Cd,Ni,Cr,PAHs,dissolved COD,dissolved heavy metals and dissolved PAHs,as well as particle diameter d₅₀ of samples were determined.Pollution characteristics,concentration and load emission characteristics of different underlying surfaces runoff were compared.What’s more,the concentration,pollution source and emission characteristics of PAHs in these three kinds of underlying surfaces rainfall runoff were also studied in the dissertation.Study on pollution characteristics of different underlying surfaces runoff in Xi’an cultural and educational area showed that:（1）The main contaminants of urban surface rainfall runoff were SS,COD,TN,Pb and Cr.（2）Except for COD,The occurrence state of heavy metals and runoff than the total pollutants.Compared with moderate and light rainfall events,load emission rate of road and roof runoff were more higher in rainstorm and heavy rainfall events.（5）The pollution load emission of all kinds of pollutants in road and roof runoff conformed to the power function equation,and the correlation coefficients（R²）were larger than 0.99.Study on pollution characteristics and source apportionment of PAHs in different underlying surfaces rainfall runoff in Xi’an cultural and educational area showed that:（1）The descending order of PAHs concenration in these three kinds of underlying surfaces rainfall runoff were road,roof and grassland.The concentration of PAHs in different road and roof rainfall runoff events changed little.PAHs in these three kinds of underlying surfaces rainfall runoff had similar composition spectrum,that is,2 ring PAHs were the main components,4-6ring PAHs were the second,and 3 ring PAHs are the least.Compared with related researchs at home and abroad,the content of PAHs in rainfall runoff in Xi’an cultural and educational area were at medium pollution level.（2）The occurrence state of PAHs in road,roof and grassland rainfall runoff were mainly particulate,and 73.32%,67.69%and 65.16%of PAHs were particulate.（3）PAHs was similar to other pollutants and had similar variation characteristics with runoff time.（4）Source apportionment showed that PAHs in these three kinds of underlying surfaces rainfall runoff mainly originated from leakage and volatilization of petroleum products.