Prescott study session spotlights failing SR 89 effluent pipeline, three 15% design alternatives for roadway upgrades

Prescott City Council held a study session on Aug. 26, 2025, to review 15% design concept plans for replacement of a failing 24‑inch effluent pipeline and potential improvements to State Route 89, staff said.

Gwen Roich, public works director for the City of Prescott, said the urgency is the pipe: “the number 1 priority is the pipe.” Roich told the council the existing 24‑inch effluent line “has had more than 8 failures in the last 2 and a half years,” and staff moved the repair up in the five‑year capital plan because repeated breaks have caused road closures and public inconvenience.

The council was presented with three 15% design alternatives prepared by Kimley‑Horn and partners and a staff summary of public comments collected during an ongoing 60‑day comment period. The alternatives are: Alternative 3b (a full corridor five‑lane widening, budgetary estimate $36,700,000), Alternative 5b (a hybrid five‑lane/ four‑lane with barrier through the narrow section, estimate $35,500,000), and Alternative 2b (a non‑widening alternative focusing on safety improvements, estimate $25,200,000). Andrew Baird of Kimley‑Horn said, “we generated a full 15% concept plan for all 3 alternatives.”

Why it matters: the pipe carries treated effluent, and repeated failures have prompted the city to consider replacing the pipe and, because construction will remove most of the existing roadway, whether to widen or otherwise upgrade SR 89 at the same time. Roich said multiple pipes will be installed in the corridor — three 24‑inch pipes in total — and that “when we do that, we’re gonna destroy the road that is already there today,” which makes this a decision that affects both utilities and long‑term roadway function.

Funding and budget: Roich and staff described how costs would be allocated. For the wastewater portion, staff said about 80% of wastewater expenses would be paid by ratepayers under the city’s rate structure, with development impact fees covering roughly 20% of the wastewater cost. For the roadway portion, staff said the city’s 1¢ street sales tax fund would cover approximately 70% of the widening alternatives (with the remainder coming from impact fees where state law permits) and that the street sales tax would cover 100% of the costs if the non‑widening alternative is selected. Roich said the city currently has $38,000,000 budgeted in its capital plan toward the project and that the city is pursuing additional regional and federal funding.

Construction and timing: staff emphasized the pipeline replacement is the immediate operational priority because of repeated failures and closures. The project is at 15% design (design concept report stage). Staff said a detailed financial analysis and final construction‑level cost estimates are not produced at 15% design and will come later in the design development phase. Roich noted that a non‑widening construction approach likely would require extended full‑road closures for several months to install underground pipes, while a widening approach could allow staged construction that preserves traffic flow by shifting lanes.

Traffic, safety and modeling: Ian Mattingly, city transportation manager and traffic engineer, said the corridor currently carries about “22,000 vehicles per day.” Staff described modeling and validation steps used for the traffic study: mixed data sources, counts taken in January 2025 and May 2023, ADOT counts, city annual counts and regional modeling via SIMPO, and more than 100 VSIM simulation runs. The consultants used a 25‑year planning horizon and a 2.75% annual growth rate for traffic projections; staff said that 2.75% was the most conservative historic growth rate they could justify from available studies.

Roundabouts and signals: the 15% plans assume roundabouts at key intersections and a set of corridor safety improvements that staff said are common to all alternatives (sight‑line improvements, consolidation of access points and right‑in/right‑out conditions where appropriate). Mattingly defended roundabouts as a long‑term operational choice and cited staff calculations showing lower rates of injury crashes at roundabouts compared with comparable signalized intersections in Prescott. He said comparative analysis in the traffic study showed signalized intersections would produce larger delays as traffic grows.

Public comment and themes: Carrie Oberheim, operations manager, read public comment themes compiled by staff. Council and staff summarized repeated themes: opposition to a five‑lane widening, requests for more detail on non‑widening options (flex lanes, signals, different intersection treatments), concerns about environmental and visual impacts including rock removal, worries about property impacts near private roads such as Calvary Lane, and calls for clearer demonstration that public input was considered. Staff said they posted materials and comments at sr89improvements.com and that the pairwise ranking method used with a 15‑person advisory group influenced the technical advisory committee’s weighting of alternatives.

Engineering constraints and right‑of‑way: staff reported the corridor has a typical public right‑of‑way of about 150 feet that narrows to roughly 100 feet at one bridge location. Tim Sherwood, capital program manager, said preliminary geometry indicates roughly 12 feet of space on each side may be required to accommodate a four‑lane cross section in the narrow section, and that some roundabout designs could require additional easements. Staff said they expect to purchase any additional land needed rather than pursue condemnation.

Next steps: the council did not vote. Staff noted Resolution 20‑24‑1876 (adopted Feb. 13, 2025) set the process for two study sessions and two public hearings; the first public hearing on the project is scheduled for the 3 p.m. voting meeting as item 11b and a second public hearing is scheduled for Sept. 9. Roich urged continued written comment via sr89improvements.com. Staff said a final decision and more detailed cost analyses will follow later design phases.

Quotations used in this report are attributed to speakers who spoke at the Aug. 26 study session: Gwen Roich (public works director), Tim Sherwood (capital program manager), Andrew Baird (Kimley‑Horn), Ian Mattingly (transportation manager), and Carrie Oberheim (operations manager).