The details
The study, which started in 2024, assessed the conditions for the city’s 70 miles of wastewater lines through flow monitoring.
According to the agenda item, flow monitoring uses equipment to read and record flow depth and rate to determine if there are blockages or inflow and infiltration occurring in sewer lines. Inflow and infiltration is groundwater or stormwater from defective manholes, pipes, connections, cleanouts and drains that enter the wastewater lines, according to a June 16 presentation to Bellaire City Council by Freese and Nichols.
Blockages reduce the capacity and efficiency of the wastewater collection system, while infiltration and inflow increase the volume of water into the wastewater treatment plant that Bellaire must treat, further reducing capacity and efficiency while also increasing costs to the city, according to the agenda item. Excessive infiltration and inflow could also cause sanitary sewer overflows, infrastructure failure, reduced infrastructure capacity and greater cost to pump higher peak flows, according to the presentation.
Ishita Rahman, a water and wastewater master planner at Freese and Nichols, said the firm installed 12 flow meters and four rain gauges throughout the city’s wastewater collection system for 100 days, monitoring dry and wet weather flows to evaluate inflow and infiltration.
The study identified eight areas, called flow meter basins, in the city where excessive inflow was discovered, with only one area with excessive infiltration found at flow meter basin 11.
What’s next?
Freese and Nichols will begin a more detailed Sanitary Sewer Evaluation Survey at a future unspecified date to identify the location and scope of rehabilitation needed for the wastewater lines identified with excessive inflow and infiltration.
Field inspections will be conducted across Bellaire, using closed-circuit television, inspecting manholes and smoke tests to identify the exact locations where the problem is occurring. After field inspections, a rehabilitation and design plan will be developed.
According to the presentation, the cost to assess, design and rehabilitate each identified wastewater line with excessive inflow and infiltration will cost the city roughly $13 million over the next eight years, starting in fiscal year 2026-27.
