Riverbank hears $136.1 million plan to upgrade wastewater plant; council presses for lower-cost options

At a Riverbank City Council meeting, consultants updated the council on the regional recycled-water project and the city's wastewater treatment plant upgrade, presenting a 60% design and a construction cost estimate that has risen to $136.1 million and outlining options to reduce that price tag.

The presentation by Neil Colwell, project manager for KSN, traced the project from an initial 2015 concept through planning and 15% design to a 60% design now under review. Colwell described the recommended treatment approach—oxidation ditches with robust nitrogen removal and tertiary filtration—chosen to allow continued use of the city's percolation ponds and to meet anticipated regulatory requirements. "We looked at treatment processes that had a robust ability to remove nitrogen," Colwell said, adding the oxidation ditch was selected for reliability and local operator familiarity.

The consultants said maintaining the percolation ponds reduces required seasonal storage and avoids tens of millions of dollars in added cost. Colwell said reuse infrastructure, filtration and pumping, storage, and secondary treatment are the largest cost drivers. He told council the construction estimate has risen from about $124 million to $136.1 million when projected to the midpoint of an expected construction window around 2029—2030.

Why it matters: the project is intended to increase treatment and disposal capacity, improve groundwater and surface-water quality by removing nitrogen, and create a recycled-water supply for irrigation or recharge. Council members and residents repeatedly framed the project in terms of long-term affordability and rate impacts for Riverbank customers.

Financing and rates: Eric Helgeson of Bartle Wells Associates summarized the city's rate study updates. Helgeson said updated cost and schedule assumptions mean the city could fund more of the project with cash and debt than previously modeled, and that annual rate adjustments around 6% in the years immediately following the council's existing adopted increases would likely support the project under current assumptions. The consultant also told council the projected annual operating cost for the upgraded plant had been updated to roughly $2.3 million per year once the facility is in service.

Gap remains: Colwell and the finance consultant outlined a sizable funding gap. Colwell said roughly $88.3 million in relatively firm funding sources is currently identified, including a Clean Water State Revolving Fund loan and a potential recycled-water grant of up to $15 million. He and staff reviewed other federal and state grant opportunities (EPA, Bureau of Reclamation, Department of Water Resources) and urged continued pursuit of grants while pursuing value engineering to reduce capital needs.

Options and next steps: consultants detailed phasing and value-engineering opportunities: scaling initial capacity to align with current plant limits, phasing oxidation-ditch construction, downsizing recycled-water storage, simplifying operations buildings, and evaluating alternate structural materials or staging to reduce near-term capital needs. Colwell said the 60% documents will go through a value-engineering process aimed at matching project scope to affordability before moving to a 90% design. He described an anticipated schedule of final design, potential 2028 bidding, construction in 2029-2030, and start-up around 2031.

Council direction: several council members pressed for a clear set of alternatives that lower upfront costs before advancing more design or approving a 90% design. A council member said repeatedly that residents could not reasonably be expected to absorb large additional rate increases and requested options showing (a) a downsized recycled-water project, (b) secondary-treatment-only alternatives, and (c) phased scenarios with projected rate impacts. Staff and consultants said they will return with the requested alternatives, value-engineering results and updated financial projections; Colwell said staff will review the 60% design and come back to council with proposed 90% design scope and phasing options.

The project remains in design and funding review; no formal council action to approve construction or to adopt a final financing plan occurred at the meeting. Council and staff set a near-term plan of additional analysis and directed staff to present cost-reduction options and funding scenarios for council consideration at upcoming meetings.