Storm, contractor debris fouled pumps at Hamstring Lift Station; staff outlines repairs and possible capital fixes

Scott Murphy, wastewater manager for Infomark, told the Water and Sewer and Solid Waste Committee on July 8 that both major wastewater facilities met permit requirements for May and June but that two sanitary sewer overflows occurred after a heavy storm in early June.

Murphy said the overflows were linked to a failure at the Hamstring Lift Station during a weekend that produced about 4.1 inches of rain. "We had 2 sanitary sewer overflows that were related to, a pretty nasty storm that came through on the sixth and the June 7," Murphy said. The station’s peak flow during the event reached about 28,000,000 gallons per day, he added.

Murphy said the immediate cause was a failed comminuter (a large grinder unit) that is a single, nonredundant component at the station, combined with debris that had been left in the gravity line during earlier contractor work. "We wound up having 4 pumps affected by debris. That station holds 7 pumps," he said. Photos shown to the committee included impellers fouled with extension cords and lay‑flat hose, a damaged manual bar screen and a failed inflatable plug found in the line.

City staff and Infomark described steps taken and constraints facing repairs. The impellers and backing plates for these pumps are uncommon parts; Murphy said lead times are "on the order of 18 to 24 weeks" for replacements. He also said the station’s configuration makes access and retrofits difficult: motors are large (350 horsepower) and some internal gearboxes require crane access to remove.

Staff emphasized the role of debris in worsening the failure. A partial inventory of items recovered, which Murphy said was compiled by the contractor, listed extension cords, pressure washers, pumps and other construction materials. "There was a lot of material left in that gravity that feeds that," Murphy said. He said the city has asked the contractor for accounting of what was left and that some material appears to have remained in the pipeline long after the contractor’s work ended.

Committee members and staff discussed system‑wide remedies. Murphy said the existing comminuter is a single high‑wear piece and that prior studies priced passive alternatives (fine bar screens, a second channel/grinder) but that those options were costly. He said staff will dust off earlier studies to re‑evaluate priorities and that Infomark’s fresh operational view may help re‑set capital priorities.

The committee also discussed public outreach to reduce wipes and rag‑type debris entering sewers. Murphy and members noted many wipes sold at retail are not truly flushable; Murphy said some municipalities have banned non‑soluble wipes and others run public reminders with utility bills. "It's a really big problem for us," he said.

Why it matters: the Hamstring Lift Station is a major regional conveyance that feeds the West Side treatment plant; extended outages or long lead times for specialized parts can create service risk and raise repair costs. Staff said they will pursue near‑term repairs while evaluating longer‑term capital changes such as additional screening, a second channel or different pump technology.

Provenance: Topic intro — Scott Murphy presentation, 00:04:16 (block_256.45). Topic finish — discussion of public information and CIP, 00:27:35 (block_1326.1951).