Information Content of Wastewater Flowmeter Data before and during a Surcharge

When local sanitary sewers discharge to regional treatment systems, flow monitoring is performed for billing purposes, but the information content of these flow data is often overlooked. Wastewater flow data provide information to: (1) quantify rainfall-derived infiltration and inflow, (2) detect flow spikes that could indicate improperly connected sump pumps, and (3) observe long-term increases in peak flow that threaten a surcharge (i.e., when the sewer fills completely). These points are illustrated through a case study from the Mansfield Heights Water & Sanitation District, Arapahoe Country, Colorado using simple methods including novel refinements. It is shown how prophylactic analysis of wastewater flow data might have predicted a surcharge that resulted in public exposure to waterborne pathogens and extensive property damage. Anecdotal estimates from the Denver, Colorado metropolitan region suggest that approximately 80% of sanitation perform flow monitoring, but essentially none evaluates these data routinely. Considering the value of flowmeter data, it is recommended that such data should be analyzed at least annually.