Escherichia coli(E.coli), enterococci, and fecal coliform data were collected and comparedas potential indicators for swimmablility assessment of a brackish waterbody (Lake Pontchartrain, Louisiana). These indicators were measured during lake background conditions, in stormwater runoff (before dilution with lake water), and in the outfall plume within the lake following storm events. Microbial indicator titers associated with suspended particles and lake‐bottom sediments were also investigated. Overall reduction rate constants for fecal coliform, E.coli, and enterococci in lake water and sediment were measured and reported. Attachment of microbial indicators to suspended matter and subsequent sedimentation appeared to be a significant fate mechanism. A slower reduction rate of indicator organisms in sediment further suggested that bottom sediment may act as a reservoir for prolonging indicator organism survival and added concern of recontamination of overlaying waters due to potential solids resuspension. Results indicated that enterococci might be a more stable indicator than E.coli and fecal coliform and, consequently, a more conservative indicator under brackish water conditions.
The recreational waters near many large cities in the United States and Canada are severely impaired by pathogens that are present in the storm water runoff. In separated sewers the pathogen sources may be cross-flows between the sanitary and storm water systems. This paper presents the methodology that was used in developing a forecasting model for pathogen indicators for recreational sites in the receiving waters of multiple storm water outfalls. The objective of the model is to give a timelier indicator of beach water quality than conventional beach monitoring, which takes about 2 d for laboratory results. The model used for the study was based on the Princeton Ocean Model. The forecasting system consists of nested hydrodynamic models and a bacteria fate-transport submodel. Calibration and validation is based on 6 years of field studies, laboratory analyses, and experiments. The methodology is illustrated by a case study of the impact of storm water flows on the south shore of Lake Pontchartrain, Louisiana, which has been banned for swimming since 1985. The water quality data included: pathogen indicators (fecal coliform, Enterococci, and E. Coli), water chemistry parameters, turbidity, and nutrients.Résumé : L'eau des cours d'eau destinés aux loisirs près des grandes villes des États-Unis et du Canada est gravement détériorée par les pathogènes se trouvant dans le ruissellement des eaux pluviales. Dans des conduites d'égout séparées, les sources de pathogènes peuvent provenir d'une contamination croisée entre les systèmes d'égouts pluviaux et d'égouts sanitaires. Cet article présente la méthode utilisée pour développer un modèle prédictif des indicateurs pathogènes pour les sites récréatifs dans les eaux recevant plusieurs exutoires d'égouts pluviaux. L'objectif de ce modèle est de fournir un indicateur plus rapide de la qualité des eaux à la plage que celui offert par la surveillance conventionnelle des plages, laquelle nécessite environ deux jours pour avoir les résultats du laboratoire. Le modèle utilisé pour cette étude est basé sur le modèle océanique de Princeton. Le système de prédiction consiste en des modèles hydrodynamiques emboîtés et d'un sous-modèle de transport-destin des bactéries. L'étalonnage et la validation sont basés sur des études de terrain d'une durée de six ans, sur des analyses en laboratoire et des expériences. La méthode est illustrée par une étude de cas de l'impact du ruissellement des eaux pluviales sur la rive sud du lac Pontchartrain, en Louisiane, dans lequel la baignade est interdite depuis 1985. Les données sur la qualité de l'eau comprennent : les indicateurs pathogènes (coliformes fécaux, Enterococci et E. coli), les paramètres de chimie de l'eau, la turbidité et les nutriments.
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