Boston’s Pilot Project to Measure CSO Flows Relies on New Technology and Scattergraphs to Detect Overflows

In 2013, the Boston Water and Sewer Commission (Commission) initiated a pilot study of ten CSO structures to determine if current technology is reliable enough to measure overflow activation, duration and volume with a high degree of confidence for public notification on the Commission’s web site. A hydraulic model is currently being used for regulatory reporting for volume, but a more immediate system is needed for public notification.The strategy was to instrument all incoming and overflow pipes in nine of the ten regulators, which are all tidally-influenced. The Commission’s goal for the pilot project was to determine 1) whether or not an overflow occurred, 2) the start and end times of a combined sewer overflow, 3) if these events and information can reliably be reported in real or near-real time in a practical manner to the notify the public.ADS Environmental Services (ADS) was selected to measure depth, velocity and flow at the locations utilizing fifteen monitoring devices with twenty-five sensors measuring all incoming combined sewer flow and overflow to receiving water bodies. The selected structures are all different, but they contain typical components of overflow weirs, baffle walls to control floatables and tide gates. In addition to the ADS monitoring equipment a NOAA tide gauge installed in Boston Harbor is used for tide level verification and all depths in the ADS system are converted to elevation data on a common Boston datum. The use of elevation data in conjunction with traditional depth and velocity data in the outfall pipes has helped determine if motion in the overflow pipe is an actual overflow or flood and ebb tides. The use of traditional methods combined with elevation data and conditional algorithms for overflow confirmation have helped improve real-time data quality and confidence for eventual public notification.The topic of this paper is an innovative method for understanding the regulator behavior and for identifying overflow events based upon repeatable patterns in scattergraphs. The incoming lines to all structures are metered with depth and velocity sensors and the scattergraphs of those data reveal patterns that, by themselves, can be used to identify and develop estimates of overflow volumes.