Mount Clemens pivots sewer‑separation plan after modeling finds hospital site adds large runoff

Mount Clemens city staff reported at a work session that field checks and a small hydraulic model show the former hospital site on North Avenue discharges heavily into the combined sewer system, increasing the storage and upsizing needs for a previously proposed large‑area separation. Ashley, the project's consultant, said the finding makes the original $3,000,000 plan infeasible without far more storage or significantly larger mains.

The finding forced planners to pivot to three smaller, targeted separation projects designed to capture areas with persistent basement flooding complaints: Church Street (between Highland and Lodewick), Kendrick Street and Lois Lane. Ashley said the team proposes roughly 500 feet of new storm sewer on Church Street, about 1,000 feet on Kendrick and 700–800 feet on Lois Lane, including new catch basins and manholes.

"When we completed the model, none of the results were very good — we could not perform the separation as we would have liked," Ashley said, describing conservative assumptions (pipes filled to the top in the absence of flow metering) that showed the system needs significant storage capacity or an upsized main rather than a single 36–42 inch pipe.

The city has applied for a state high‑water/grant program to fund a citywide hydraulic study and one year of flow monitoring. Ashley said the study was estimated at about $300,000 with a 25% local match (roughly $60,000) and that, if awarded, monitoring would run a full year and the grant schedule allowed two years for surveying, model building and calibration, with a projected wrap‑up in mid‑2028.

Commissioners asked about short‑term measures. Ashley noted the city has already swapped some catch basin covers in problem areas as a low‑cost mitigation; those covers reduce basement inflow but tend to move water into the street. "You'd rather flood the street than someone's basement," she said, while warning that the measure is not a systemwide cure.

Staff also described a funding strategy that pairs the separation work with a pump‑station project to increase the city's competitiveness for a CWSRF loan. The combined ask for the pump station plus the three separation areas was estimated at about $5.5 million, inclusive of design, construction engineering and contingencies. Staff said prior loan terms for similar programs ranged around 2–2.75% depending on term and overburdened status, and that an overburdened determination could allow principal forgiveness.

Commissioners pressed staff on how state overburden calculations are applied; staff explained the state's blended calculation may require including portions of Clinton Township, Selfridge and Harrison in the city’s service area for eligibility scoring, a change that can affect whether the city qualifies as overburdened.

Ashley recommended the study even if the city advances smaller separations because monitoring and a calibrated model will tell planners whether local projects will shift flooding elsewhere and what the long‑term capital plan should be. She also sketched a possible construction schedule tied to a successful loan: staff said a loan closing could occur in May 2027, with construction starts in mid‑2028, and that work would be sequenced to limit closures and resident impacts.

The commission did not take a formal funding vote during the work session; staff said they had already submitted an intent to apply and would follow up with updated scope and budget if the grant or loan opportunities progress.