title: Verification of a depth-integrated sample arm as a means to reduce solids stratification bias in urban stormwater sampling.
abstract: A new water sample collection system was developed to improve representation of solids entrained in urban stormwater by integrating water-quality samples from the entire water column, rather than a single, fixed point. The depth-integrated sample arm (DISA) was better able to characterize suspended-sediment concentration and particle size distribution compared to fixed-point methods when tested in a controlled laboratory environment. Median suspended-sediment concentrations overestimated the actual concentration by 49 and 7% when sampling the water column at 3- and 4-points spaced vertically throughout the water column, respectively. Comparatively, sampling only at the bottom of the pipe, the fixed-point overestimated the actual concentration by 96%. The fixed-point sampler also showed a coarser particle size distribution compared to the DISA which was better able to reproduce the average distribution of particles in the water column over a range of hydraulic conditions. These results emphasize the need for a water sample collection system that integrates the entire water column, rather than a single, fixed point to properly characterize the concentration and distribution of particles entrained in stormwater pipe flow.
authors.affiliation: US Geological Survey - Wisconsin Water Science Center Middleton, WI, USA. wrselbig@usgs.gov
authors.forename: William R
authors.initials: WR
authors.lastname: Selbig
authors.forename: Amanda
authors.initials: A
authors.lastname: Cox
authors.forename: Roger T
authors.initials: RT
authors.lastname: Bannerman
mesh_terms: D002947:Cities; D004784:Environmental Monitoring / Q000379:methods*; D019015:Geologic Sediments / Q000737:chemistry; D013223:Statistics as Topic; D014874:Water Pollutants, Chemical / Q000032:analysis*; D014877:Water Pollution, Chemical / Q000706:statistics & numerical data*
chemical_list: D014874:Water Pollutants, Chemical