Stormwater particles and their sampling using passive devices

Stormwater particles and their sampling using passive devices

[Abstract]: Total Suspended Solids (TSS) is commonly used as a measure of particle concentration in stormwater. The breakdown of TSS into subgroups based on particle size is an important step in describing stormwater characteristics. A simple classification system is proposed that divides solids into four size ranges; Very Fine (VFPs, <8μm), Fine (FPs, 8-63μm), Medium (MPs, 63-500μm) and Coarse Particles (CPs, >500μm).

The use of passive samplers to obtain unbiased, flow-weighted samples of non-Coarse particles was investigated. Two alternative passive samplers referred to as a flow splitter and an orifice and weir device were designed, constructed and tested. The flow splitter outperformed the orifice and weir device in terms of sampling accuracy. Based on hydraulic testing up to 5 L/s, the flow splitter was able to accurately (±2% error) obtain a constant sample volume: flow volume ratio compared to a ±15% error for the orifice and weir. Based on sediment testing, the performance of the flow splitter in obtaining VFP and FP samples was similar to that of high frequency grab sampling. Samples collected by the flow splitter matched theoretical concentrations of particles less than 63μm to within ±2% error. All sampling methods significantly underestimated the concentration of particles greater than 63μm (MPs) and more research is needed in this area. Overall, the flow splitter is considered to have significant potential for determining the Event Mean Concentration of stormwater particles.

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