Tools for Accurate Sewer Metering and Billing

When officials from the Oakland County Drain Commissioner's Office (OCDC), the operator of a regional sanitary sewer system, decided that a change was needed to the billing methodology, they recognized that the customers needed confidence that the new system was fair and accurate. Therefore, they embarked on a program to ensure that the new metering program gave customers that level of comfort. In addition to a good metering program, the following analyses were performed:Utilization of two independent methodologies to estimate flow during periods of missing data, particularly during wet weather periods, since there is a peak wet weather flow component to the billing methodology.Dye testing of meters and assigning a confidence level to the dye test based on the judgment of the field crew.Incremental flow estimation rather than just relying on meter subtraction.A Mass Flow Balance (MFB) spreadsheet that allows for the technical team to make judgments, guided by unitized flows.A methodology to estimate interceptor infiltration and inflow (I/I) as its own category, to avoid penalizing communities with large amounts of interceptors within their boundaries.Development of a hydraulic model that is used iteratively to accurately estimate incremental flow inputs, accounting for travel time and routing effects for all flows.Quarterly community review meetings to understand adjustments to the data, observe trends in the data based on their understanding of the local systems, and develop action plans for any problems.A one-year parallel program utilizing the existing Residential Equivalent Unit (REU) billing methodology as well as the new metering program methodology prior to implementing the new program.