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City schedules special meeting after sewer digester began leaking during startup
Summary
City staff told the Carroll City Council that a recently repiped wastewater digester began leaking during a clear-water startup. Staff recommended a fluid-applied polyurethane lining (about $163,000, 20-year leak warranty) as a lower-cost alternative to a $1.1 million rebuild; a special meeting was set to consider a change order.
Carroll city staff alerted the City Council on April 24 that a wastewater digester taken offline for repiping began leaking when it was filled with clear water during startup testing.
Randy (staff member) said crews emptied and repiped the digester as part of converting the anaerobic system to an aerobic process. “When we filled the digester with clear water, it began leaking through the walls,” he said, describing the problem discovered during a two-day startup test.
Staff presented three options: leave the tank as-is (with ongoing leakage and eventual structural failure), apply a fluid-applied polyurethane lining to stop leaks, or demolish and rebuild the digester. The lining was priced in staff materials at just over $163,000 and would carry a warranty against leakage for 20 years; rebuilding the tank was estimated at roughly $1.1 million.
Randy explained two plausible causes for the new leaks: removal of struvite deposits (a mineral that can seal small cracks in anaerobic tanks) during the cleaning and a thermal-change effect from replacing hot, cured sludge with cold water, which may have opened existing hairline cracks. He said contractors contacted for repairs could mobilize within about 10 days and that the repair itself would take roughly four days.
To avoid delaying construction work, the city manager requested a special council meeting Wednesday at 5:15 p.m. so members could consider a change order to authorize repairs. Council members agreed to schedule the special meeting.
Next steps: the council will consider the proposed change order at the special meeting; staff recommended the polyurethane lining as the cost-effective option to preserve the digester short-term while avoiding the much higher cost of rebuilding.
