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For several North American and European cities with combined sewer systems, retention tanks have become a common way to reduce pollutant loads released to receiving water bodies and to regulate hydraulic loads at the wastewater treatment plant during rainfall events. This study has two goals: (1) to characterize combined waters at the entrance and during the emptying of a retention tank during rainfall events for two main parameters: total suspended solids (TSS) and chemical oxygen demand (COD) and (2) to evaluate a mass balance of pollutants. A sampling campaign was undertaken to collect and analyse combined waters at the entrance and during the emptying by pumping of a retention tank. Analyses showed that the particles settled quickly, because large quantities of sediments were found during the first 20 minutes of pumping. Finally, mass balances showed that the retention tanks stored an important quantity of solids, preventing them from reaching the receiving water bodies during rainfall events. [ABSTRACT FROM AUTHOR]

Resume Afin d'evaluer l'impact potentiel de la vidange, les flux de nutriments et de matieres sont quantifies lors du remplissage et de la vidange d'un etang construit en derivation, a l'aval d'une chaine d'etangs. La cinetique de vidange a ete etablie a l'aide d'un modele numerique de terrain restituant la surface topographique de l'etang. Les matieres en suspension et les principaux nutriments ont ete regulierement quantifies. La qualite hydrobiologique du cours d'eau recepteur a ete controlee pendant et apres la vidange. L'etang a exporte 8.5 tonnes de matieres en suspension et des quantites de nutriments relativement elevees. Nos resultats confirment l'existence de deux phases critiques, ne concernant cependant qu'un tres faible volume d'effluent. Compte tenu des capacites elevees de sedimentation des matieres en suspension, la courte duree d'exposition associee a un lineaire de fosses suffisant pourrait limiter l'impact de ces matieres rejetees. Citation Vallod, D. & Sarrazin, B. (2010) Caracterisation de l'effluent de vidange d'un etang de pisciculture extensive. Hydrol. Sci. J. 55(3), 394-402. [ABSTRACT FROM AUTHOR]

Abstract: The modelling of pollutant transfer in freshwater systems can be refined by considering the heterogeneities of the sedimentary dynamics and of the chemical reactivities of fine suspended particles. One of the first steps is the fractionation of these fine particles into effective settling classes. Although several methods exist, most of them are based on either granulometric considerations and/or arbitrary threshold criteria. This article presents the bases of an experimental method focusing on the direct measurement of the settling velocities without considering the granulometry and/nor any threshold criteria. The experimental work consists in recording the temporal evolution of the vertical distribution of the suspended solid concentration in a settling tank. A mathematical analysis provides the number of particle groups, and the mass contribution and the settling velocity for each This procedure is described and applied for validation, as a first step, to calibrated suspensions. Additional work is needed for a further analysis of the physical constraints involved in the model, as well as for more extensive experimental validation. To cite this article: C. Brach-Papa et al., C. R. Mecanique 334 (2006). [Copyright &y& Elsevier]

Abstract: In karst systems, rain events often result in a decrease of the conductivity (a tracer of dissolved phase transport) and an increase in turbidity (a tracer of suspended solids transport) at wells and springs. This study shows that the comparison of suspended solids and solute transport by the coupled approach of curves (Turbidity–Conductivity) and autocorrelations gives evidence of the transport processes in the karst network and allows understanding the karst hydrodynamics. To cite this article: D. Valdes et al., C. R. Geoscience 337 (2005). [Copyright &y& Elsevier]