Prescott council hears update on failing SR 89 effluent line, three design alternatives advance to 15% plans

Gwen Roach, public works director for the City of Prescott, told the City Council on April 8 that the effluent pipeline running in the SR 89 right-of-way “has broken over a dozen times in the last 6 or 7 years,” and that the city contracted Kimley Horn and Associates last November to produce a 15% design concept report evaluating alternatives for the roadway and the two wastewater mains.

The consultant team presented collected traffic counts, origin-destination analysis, geotechnical borings, crash data, and a scored evaluation of 20 initial alternatives that produced three recommended options (and one additional alternative for study) to carry into 15% plans. Andrew Baird, project manager with Kimley Horn, said the firm is “about 2 thirds of the way through their process” and will return on July 8 with the 15% design concept report and plans and the start of the 60‑day public comment period.

Why it matters: the corridor is both a functioning regional highway and a scenic, residential area. The project exists to replace a failing pressurized effluent main and to upsize a gravity wastewater main; at the same time the city must address deteriorating pavement and rising traffic demand that the consultant says already exceeds some previous 2045 projections.

Key findings and data

- Extent: the study limits run from the existing Willow Lake Roundabout north to the existing Fippin Trail Roundabout (a little over 2 miles); effluent and wastewater mains run slightly less than the full roadway limit.

- Traffic counts: Kimley Horn reported about 22,000 vehicles per day measured in January 2025 on SR 89; detour conditions in December 2024 shifted roughly 36,000 vehicles onto Willow Creek Road during a closure, and Williamson Valley Road saw an additional ~5,000 during that detour. The consultant used those counts plus Streetlight origin-destination data to model regional travel patterns.

- Growth and capacity: the team used a planning growth rate of 2.75% (based on ADOT counters and historical counts) and projects…