Scattergraph Principles and Practice: Characterization of Sanitary Sewer and Combined Sewer Overflows

Sewer overflows pose a significant threat to public health and the environment, contributing to beach closures, contamination of drinking water, and other concerns. Knowing when and where they occur — as well as their duration, volume, and frequency — are important pieces of information needed to assess their impact and minimize their future occurrence. Sewer overflows are readily identified by evaluating flow monitoring data on a scattergraph. Practical examples from flow monitoring locations throughout the United States are provided, demonstrating the scattergraph signatures of sanitary sewer overflows (SSOs) and combined sewer overflows (CSOs) under various conditions. Techniques are also developed to estimate their duration and volume from flow monitor data.