Errors Associated with Solids Analysis

Stormwater sampling by automatic samplers and the comparability of the suspended sediment concentration (SSC) and total suspended solids (TSS) methodologies have been a source of debate. Questions include whether autosamplers can pull up the larger, heavier particles found in stormwater, if automatic sampling has a particle size distribution (PSD) range limitation, and whether TSS and SSC recoveries are comparable. This research examined the protocols, limitations, and associated errors for solids determination. The autosampler was examined for its ability to sample simulated stormwater repeatably and accurately at various elevations above the water surface and within the water column, including the effect of PSD at all heights. Sample processing and splitting by churn and cone splitters were investigated for accuracy and repeatability in obtaining subaliquot volumes and representative PSD. Finally, two TSS methods and SSC were examined for recovering a known concentration and the comparability of the inter- and intra- methodologies.