Particle concentrations : analysis methods for urban runoff

Abstract: Urban runoff often contains high concentrations of particles. Pollutants that adsorbs to surfaces of particulate material will be transported to receiving waters or a sewage treatment plant. For the recipient, the particles in the runoff are a significant cause of water quality impairment. The particles are associated with impacts of surface waters such as increased turbidity, and effects on water-living organisms and fish. The particle concentration is one of the most common parameters to measure in urban runoff.The main objective was to investigate and compare the accuracy of analysis methods for measuring total particle concentration in urban runoff. The methods to be compared are total suspended solids (TSS), suspended sediment concentration (SSC-A, SSC-B and SSC-C), and one new method; multiple filter method (MFM). General differences between the analysis methods:Handling of sample: ' SSC and MFM – analysis of entire sample ' TSS –aliquot analysisFilter pore size: ' TSS and SSC – 1.6 μm ' MFM – 0.45 μmThe studies were performed with artificial and natural runoff samples. Three studies with artificial samples were performed a) high amount of small particles, b) high amount of large particles and c) different particle intervals. The study with natural runoff samples, were performed with rainfall runoff, undisturbed snow and snowmelt runoff. The result for artificial samples showed that SSC and MFM gave comparable result irrespective of particle concentration or size, approximately 100 % of the initial concentration. TSS which measures the suspended solids underestimates the particle concentration with 55-90 %. Measured concentrations for samples with particles larger than 0.063 mm were underestimated. The underestimation increased with increased particle size.For rainfall runoff samples a statistical analysis, ANOVA test, showed that MFM gave a significantly higher result than SSC-B and TSS at a confidence level of 95 %. These result implied that small particles of size 0.45 – 1.6 μm influence the results. The ANOVA test showed no significant difference between SSC-B and TSS. The results from this study show that the particle size distribution has importance for the result and the particle concentrations showed to have no influence.