THE UNDERLYING STRUCTURE OF SYSTEMATIC VARIATIONS IN THE EVENT MEAN CONCENTRATIONS

Urban runoff pollution can essentially be characterised by fluid quant ities and pollutant concentrations. It has been possible to construct models accounting for variations in runoff quantities with some succes s. However, although several pollutant storage and transport mechanism s have been postulated there still remains substantial unexplained var iation in pollutant concentrations. Though a series of well establishe d multivariate pattern recognition techniques the present study has ai med at disclosing the underlying structure of systematic variations in the event mean concentrations (EMC) of pollutants in combined sewers during rainfall. The statistical methods that have been applied to the pollutant concentration variables are factor analysis, cluster analys is, distribution analysis and correlation analysis. The event mean run off data considered includes eleven pollutant variables originating fr om five combined sewer catchments in Denmark and in the Netherlands. T he combined results of the analyses support earlier findings that EMCs are best described by bimodal or mixture distributions, and further s uggest that event based pollutant modelling could be improved through a recognition of these characteristics. (C) 1997 IAWQ. Published by El sevier Science Ltd.