Errors associated with sampling and measurement of solids: Application to the evaluation of stormwater treatment devices

Solids removal often is the first parameter evaluated when testing the effectiveness of stormwater treatment devices. Therefore, it is imperative that the sources and magnitude of potential errors associated with each stage of sampling and measurement be understood and quantified. The following research examined the errors associated with the analysis of solids from collection via an automatic sampler through sample splitting with churn and cone splitters to, finally, solids concentration analysis by three common US analytical methodologies (Suspended Solids Concentration [SSC, ASTM D3977-97B] and Total Suspended Solids [TSS, by both US EPA Method 160.2, identical to ISO 11923, and Standard Methods 2540D]). Material gradient impacted the reliability of the autosampler. Sample splitting distributed representative and consistent subaliquots. SSC methodology best represented the known solids concentration in water for a representatively wide range of typical particle sizes. This research documented the magnitude of potential errors associated with each stage in solids measurement in stormwater. The question remains as to what effect these errors will have when combined into a single sampling and analysis activity. Large and variable errors may mask bias differences in the methods; also, error analysis and comprehension is a vital part of the stormwater control evaluation process.