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Carroll City officials approve $163,416.75 waterproofing change order for WWTP digester
Summary
City officials approved Change Order No. 3 to install a 120‑mil polyurethane liner in Digester No. 2 at the WWTP for $163,416.75 after testing found minor leaks; the council voted unanimously to proceed and declined an optional five‑year labor warranty of roughly $15,237.60.
Carroll City officials voted to approve Change Order No. 3 to the WWTP digester and BLR air piping improvements contract, authorizing a $163,416.75 waterproofing system for Digester No. 2.
The decision followed a staff report that the digester, refilled during clear‑water startup testing, showed leakage through its walls. The presenter described visible moisture on exterior walls and said the amount collected on the building floor was small — "probably less than 5 gallons" over a little more than a day. Staff said a full digester replacement would cost about $1.1 million, making a polyurethane liner the preferred, lower‑cost option.
City staff presented three liner options provided by subcontractors: a 60‑mil product with a 5‑year warranty, a 90‑mil product with a 10‑year warranty, and a 120‑mil product with a 20‑year material warranty. Staff recommended the 120‑mil liner and provided its price of $163,416.75, which the presenter said would bring the overall contract price cited in the meeting materials to $3,202,095.
The presenter identified McGill Brothers of Omaha as the approved applicator and Sika as the polyurethane manufacturer. He said Sika's warranty covers materials only and reported that McGill Brothers offered a separate five‑year labor warranty for an additional $15,237.60; council members asked whether the contractor would patch future leaks and whether the liner would be guaranteed to fix the current problem. The presenter said he had spoken with Sika and quoted the manufacturer as saying, "our interest ... we have a tank that doesn't leak. Period."
Staff said the contractor will sandblast the interior walls and floor as part of preparation and spray three coats of material (a primer, intermediate coat and top coat). If cracks reflect through the liner, staff said, crack injection rather than recoating may be required for repair. The presenter also said McGill Brothers will perform a water test after installation to confirm the repair.
A motion to approve the change order was made by Jason and Jeff Sackman. On roll call, Atherton, Bauer, Kaylor, Dirks, Coster and Seaman voted "yes," carrying the measure. The meeting adjourned at 5:29.
Next steps: staff will proceed with scheduling and contractor coordination to complete surface preparation, installation and post‑installation testing as outlined in the change order.
