Pilot Flow Monitoring Program Tests Meter Capabilities

The Metro Wastewater Reclamation District (Metro District or District) is the wastewater treatment authority for a 715 square mile service area in metropolitan Denver and serves 1.8 million people. Since 2008, the Metro District has been refining the Transmission System hydraulic model, which has resulted in better understanding of the Transmission System flows and improved ability to identify potential capacity constraints. In 2015, the District initiated a three-year program to continue annual updates of the Transmission System model and to design, pilot and construct up to 28 new permanent metering facilities for continuous in-line interceptor flow monitoring.During the pilot program, flow meters from four manufacturers ADS, Hach, Isco and Mace were installed over a seven-month period so that the Metro District could evaluate the performance of the meters to determine which meter should be recommended for permanent installation. The pilot program included design, bidding, contracting, submittals, procurement, installation, electrical design and telemetry, performance evaluation and final recommendations.Site selection and site reconnaissance were an important early activity for the pilot program. The sites were originally identified based on planning level information in the Metro District 2013 Facility Plan. Manhole conditions, flow conditions, power availability, radio telemetry/signal strength availability and other constraints identified during the site reconnaissance survey guided and even optimized the final site selection during preliminary design of the pilot sites. Information collected during site reconnaissance activities was captured on electronic tablets using custom forms developed using a tablet based industry standard data collection application.The pilot program allowed the Metro District to evaluate equipment installation, telemetry and performance under various hydraulic conditions, as well as assess vendor support under a variety of challenges. As part of the pilot program the flow meters were rotated between two locations in order to test meter performance in different hydraulic conditions and provide a more equitable comparison of meter performance.The performance of the meters was scored against pre-defined criteria to aid the Metro District in the final selection of metering equipment. The pilot program evaluated the flow meters on the following six categories: Equipment Capabilities, Vendor Capabilities, Operation & Maintenance, Power, Communications and Cost. Within each of these six categories, 25 criteria and the relative weighted importance was developed jointly with District staff.The pilot program has benefited the Metro District by resulting in an informed and unbiased decision on the flow meter technology that best fits the needs of the District. The approach and lessons learned from this experience may benefit other agencies looking to install flow meter equipment for permanent flow monitoring in their respective collections systems.