Impact of dry weather discharges on annual pollution from a separate storm sewer in Toulouse, France

The city of Toulouse with its separate sewer system is ideal for studying stormwater. However, during dry weather, the storm sewer also discharges water into the environment, and it is the impact of these discharges on annual pollution from storm sewer that is the object of this study. Samples have been taken from the outlets of two storm drains located in heavily and moderately urbanized areas. Sampling has been undertaken during wet weather and during dry weather between January 2010 and February 2011. Three dry weather and two wet weather samples have been taken every three months and from each outlet. The overall pollution parameters have been analyzed (chemical oxygen demand, biological oxygen demand, total nitrogen, ammonium, nitrate, total phosphorus, suspended solid matter, volatile suspended matter, pH, conductivity, turbidity). Characterization has been completed by analysis of trace organic compounds: polycyclic aromatic hydrocarbons, total hydrocarbons, methyl tert-butyl ether, diethylhexylphthalate, nonylphenols, hormones (estradiol, ethinylestradiol). For certain parameters, the results obtained did not conform to legislative requirements concerning discharge into the natural environment. Correlations between these parameters have been studied, and identified between several of them using principal component analysis. The most important correlation observed was between conductivity and concentration in total phosphorus for one of the outlet. Results showed that dry weather had an impact on annual pollution load from separate storm sewer and that level of urbanization was also a factor. The effect of season has been studied but no significant impact was found

Monitoring of stormwater between 2002 and 2010. What is the evolution of stormwater quality ?

The city of Toulouse with its separate storm sewer system is ideal for studying stormwater. That is why since 2002, three stormwater sampling campaigns were conducted. Samples were taken from the outlets of two storm drains located in heavily and moderately urbanized areas. Sampling was undertaken during wet weather and dry weather during the year 2002 for the first campaign, during the year 2007 for the second one and during the year 2010 for the last one. The overall pollution parameters were analyzed (chemical oxygen demand, biological oxygen demand, total nitrogen, ammonium, nitrate, total phosphorus, suspended solid matter, volatile suspended matter, pH, conductivity, turbidity) and the presence of some micropollutants was studied (6 PAHs, MTBE and total hydrocarbons). Results showed an evolution of stormwater quality between the three campaigns and an improvement of nutrient and suspended solid concentrations. They indicated also that dry weather had an impact on annual pollution load from separate storm sewer and that level of urbanization was also a factor whatever the year of sampling

Impact du temps sec sur la qualité des eaux pluviales de la ville de Toulouse

National audienc

Evolution of stormwater quality between 2002 and 2010 for the city of Toulouse, France

International audienc