City briefed on need for new wastewater plant as solids limit reached; cost estimates exceed rates alone

Flagstaff’s water‑services leadership presented technical and budgetary reasons the city must plan for a new wastewater treatment plant: existing facilities are constrained by solids processing capacity even though per‑capita liquid flows have fallen because of conservation.

Lee Williams, introduced as the city’s director of water services, reviewed the two existing plants — Wildcat Hill (1979) and the Rio de Flag facility (1996) — and explained that conservation lowers average liquid flow but does not reduce the solids load in wastewater. Williams said that while the city’s combined liquid capacity is roughly 10 million gallons per day (MGD), solids‑processing constraints drive the need for new or upgraded treatment capacity.

Why it matters: the city projects eventual treatment needs of roughly 14 MGD at full buildout. Staff estimated construction costs for a new plant at roughly $25–$30 per gallon of capacity in today’s dollars, which translates to about $225–$300 million for a 10 MGD facility and $350–$420 million at 14 MGD — amounts far beyond what routine rate increases would easily support.

Technology, phasing and funding details Williams described conventional and newer approaches. The Wildcat Hill plant has been modified with IFAS (integrated fixed‑film activated sludge) to meet standards; the Rio plant uses an alternative suspended‑growth process. Staff discussed membrane biological reactor (MBR) technology as an “advanced water treatment” pathway that produces higher‑quality effluent and is relatively easy to phase in modular cells (examples exist in other Arizona communities). Williams said MBR can be phased in 2.5‑MGD increments (roughly $75 million per cell under staff’s rough assumptions), allowing construction paced to available funding and demand.

Design funding and near‑term steps The FY‑10‑year CIP includes about $25 million for design of a new plant (roughly 10% of estimated construction). Williams said the project is on an approved Water Resource Development Act (WERDA) list and that an anticipated $5 million WERDA appropriation could contribute to design if Congress funds the program. Staff and council agreed grants, low‑interest loans and other non‑rate financing will be needed for construction.

Council questions and staff request Council members pressed for timelines and effects of inaction. Williams said inaction risks capacity constraints, development limits, and potential compliance or sanitary incidents if major equipment fails; he recommended starting funding discussions immediately. Staff asked council for direction to pursue funding strategies and to continue design work that is already in the CIP.

Ending: Council directed staff to continue evaluating options; no capital appropriation was approved at the retreat. Design work is in the CIP and staff will return with more detailed cost estimates, phasing scenarios and funding strategies.