In-Situ Measurement Verification of Wastewater Billing Meters: The Greater Vancouver Experience

The Greater Vancouver Regional District (GVRD) is a federation of municipal governments that covers the metropolitan area of Greater Vancouver. The GVRD provides services that are regional in nature, including the regional sewerage system. The sewerage network is broken into four collection areas, the largest of which, known as the Fraser Sewerage Area (FSA), encompasses a part or the whole of 14 municipalities and approximately 1 million people. Within the FSA, the GVRD has constructed a network of approximately 20 permanent flow meters, which are used to bill the member municipalities to recover its operations and maintenance costs. These meters measure cross-boundary flows, with the municipal contributions being calculated by a subtraction method (the municipal flow equals the sum of outflows minus the sum of inflows). Where a municipality has a through-flow that is large compared to its contribution, this approach results in a calculated contribution that is sensitive to meter inaccuracy.In order to provide greater assurance that the levies the municipalities are being asked to pay are fair, a programme of verifying meter performance has been implemented. Meters are verified insitu, through independent measurements of the flow, and the results are incorporated into the municipal billing process.A key component of the process is the use of control charts to determine the discrepancies between the measurements of the flow made by the permanent meter and the testing method. Each mean discrepancy is then treated as a measurement of the permanent meter's bias. At the time of billing, the meter measurements are adjusted to account for the mean discrepancy in an effort to minimise the meter's systematic bias.