Keywords: 
• road runoff /
• pollution /
• sedimentation property /
• settling test /
• event mean concentration

Abstract: Urban trunk road runoff caused by 34 storm events were collected at sampling station built at south second ring road in Xi’an city using self-made volume proportional collecting device from Mar. to Nov. 2009. Event mean concentration (EMC) of SS and COD, as well as occurrence of organic pollutant were tested. The influence of precipitation characteristics on runoff pollution was explored. Pollutant removal efficiency of sedimentation was studied by cumulative curve method using samples collected from 16 storm events in addition. Results show that EMC of SS and COD of urban road runoff vary widely and are dramatically higher than that in domestic sewage. EMC of SS ranges from 421 mg/L to 7 380 mg/L and the average EMC is 2 128 mg/L. EMC of COD ranges from 240 mg/L to 1 640 mg/L and the average EMC is 651 mg/L. Rainfall has most significant impact on pollutant concentration negatively, maximum rain intensity and rain duration are also negatively correlated with pollutant concentration, while antecedent dry period has few relationship with pollutant concentration. Organic pollutant in road runoff is mainly granular-state and the solution-state organic pollutant only accounts for 26 percent of all. The linear regression relation between SS and COD is certainly. Result of settling test shows that the sedimentation property of particles in different runoff events varies widely. In order to achieve sedimentation removal rate of 45%, 60% and 80%, surface loads of sedimentation tank are 1.1～9.3 cm/min, 0.6～5.9 cm/min and 0.1～2.7 cm/min， respectively.