Determination of the number of storm events representing the pollutant mean concentration in urban runoff

Abstract

Urban storm water quality monitoring is usually limited due to time and cost constraints, and thus, the determination of the minimum number of storm events that should be sampled necessary to estimate the pollutant mean concentration relative to the landuse is valuable. In this research, the minimum number of storm events was derived by considering both the variability of event mean concentration (EMC) values and the associated degree of uncertainty for a given set of measured storm events using monitored storm event data during a three-year period from 2009 to 2011 on five urban sites. Based on the findings, the required number of storm events could be determined using the propose method but representing only the 99 and 95% confidence limits of the site mean concentration (SMC) and differed depending on the pollutant. Results showed that a minimum of six to eight storm events were adequate to estimate the SMC of total suspended solids at low levels of uncertainties with relative standard error of less than 20%. The storm event sampling was preferable to be conducted five to six times during spring and summer when most of rainfall occurs while only once or twice during the fall and winter season.

Keywords:

• Event mean concentration
• Minimum number of storm events
• Monitoring scheme
• Site mean concentration
• Urban runoff

Acknowledgments

The funding for this research was financially supported by the Eco-STAR Project under the grant of the Ministry of Environment in Korea (07-II-6). The authors are grateful for their support.

Notes

Presented at the Nonpoint Source (NPS) Workshops at the Third International Conference on Rainwater Harvesting & Management, Goseong, Korea, 20–24 May 2012 and the Korea-China World Expo Exhibition Plan, Beijing Normal University, Beijing, China, 4–7 July 2012