New tools to define the impact of stormwater on receiving surface waters

The first flush effect brings a multitude of contaminants into surface waters from storm sewers, overflowing domestic sewers, and surface scour. Contained in the first flush are large numbers of pathogen indicators, and potentially pathogens. The pathogen indicators could represent a significant health threat to communities that use storm impacted surface waters for drinking water supplies. However, commonly used bacterial indicators do not provide information about fecal source and age, critical pieces of information required to determine potential pathogen risk and impact. Yet, municipalities face the daunting prospect of prioritizing the installation of best management practices in the absence of easily applied methodologies to sort out the numerous sources of pathogen indicators and quantify the risk each proposes. This paper will present some new analytical and modeling tools that could be of use to municipalities. The first tool is a unique bacterial ratio that varies with age relative to human sewage. The second tool is a neural network modeling approach for classification and ranking of stormwater impacts. Together these tools can point to the predominant stormwater sources in a watershed that bring the freshest, human or agricultural animal impacted, wastes into drinking water supplies. Copyright ASCE 2004.