Engineers identify inflow as main source of extra wastewater; Bellaire staff recommends targeted rehabilitation program

Friese & Nichols presented results of a year-long sanitary sewer flow monitoring study to the Bellaire City Council on June 16, 2025, finding that inflow (stormwater entering the system) accounted for most excess wet-weather flow and recommending a prioritized sanitary sewer evaluation and rehabilitation (SSES) program.

The study installed 12 flow meters and four rain gauges and monitored flow for more than 100 days to identify wet- and dry-weather flow characteristics across the system. Friese & Nichols reported inflow as the dominant component of I&I (inflow and infiltration), with infiltration representing roughly 10% of the measured I&I. The firm ranked basins by gallons per day per 1,000 linear feet; the basin around FM 11 near the wastewater treatment plant showed the highest I&I and was the first priority for follow-up field work.

Friese & Nichols recommended a four-step SSES process: (1) flow monitoring (already completed), (2) field investigation (manhole inspections, smoke testing, CCTV camera inspection), (3) rehab design based on defect findings, and (4) rehab bidding and construction. The firm provided budgetary estimates for each basin using the city's linear footage and manhole counts, assumed that 50% of inspected lines would require some form of rehab, and applied a 5% annual inflation factor to future-year construction estimates.

City staff said the SSES work will be incorporated into Bellaire's CIP and noted previously approved bond funds for wastewater could finance early phases. Councilmembers pressed the firm on whether illegal private connections and improperly plumbed features (for example, pool drains or French drains tied into the sewer) could be identified by the field investigations; Friese & Nichols said smoke testing and CCTV commonly reveal such private-side problems and that the building department and public education would be used to pursue corrections on private property.

Friese & Nichols also confirmed the study included both dry-weather monitoring (to estimate baseline infiltration) and multiple wet-weather events (to calculate inflow contributions). City staff said ongoing metering and future post-rehab monitoring should quantify reductions in wet-weather flow and help estimate downstream cost savings once Bellaire conveys flow to the City of Houston under the pending transfer arrangement.

Councilmembers asked about links between this evaluation and an asset-management program; the consultant said an asset-management study could cover age and material condition of pipes but the SSES focused on I&I reduction. Council discussion emphasized the programmatic approach'prioritize worst basins first'and the value of targeted field inspections to avoid unnecessary construction across the entire system.

The presentation did not request council approval of immediate construction; it presented findings and program-level budget estimates and asked the council to incorporate the SSES into the CIP for phased implementation.