Rapid City receives 100-year water utility master plan outlining constrained and unconstrained capital plans

Consultants with Black & Veatch presented the city’s updated Water Utility System Master Plan to the Rapid City Public Works Committee on April 1, summarizing a ~600‑page final report and a multi‑thousand‑page appendix that model water demand, system condition and capital needs out to 2115.

The plan projects population and water demand across three service‑area horizons and develops both an unconstrained and a fiscally constrained 100‑year capital improvement plan (CIP). It also delivers updated hydraulic models, an asset‑condition assessment, and a prioritized pipeline replacement program for the city’s roughly 34,000 existing pipe segments.

Sean Labonde, project manager for Black & Veatch, told the committee the study updated the hydraulic model, revised population and demand projections and tested the city’s current water‑rights portfolio against three supply scenarios, including a severe multi‑year drought. Labonde said the team revised per‑capita use assumptions downward: “This master plan is based on 135 gallons per person per day.” He said that lower consumption, paired with more conservative population projections, reduces long‑term maximum‑day demand compared with older plans.

The report uses the city planning department’s population forecasts and defines short‑, mid‑ and long‑term service areas for 2025, 2045 and 2115. Labonde showed that Rapid City’s 2020 Census population (about 74,000) was modeled to rise under the city planning figures toward roughly 153,000 by 2115, and that prior master plans had over‑projected population and per‑capita use in past decades.

On supply, the consultants projected available surface and groundwater supplies under three scenarios: normal natural flow, a moderate drought in which junior rights (post‑1960 priorities) are curtailed, and a severe multi‑year drought tied to reservoir levels. Labonde highlighted the role of groundwater wells (Madison and Minnelusa aquifers) and storage rights in Deerfield and Pactola reservoirs, noting the city’s storage portfolio provides months of replacement supply. He explained the city’s outdoor‑watering ban in the ordinance that triggers when Pactola Reservoir drops below 25% and that curtailing outdoor use reduces demand in worst‑case scenarios.

The master plan establishes three project categories: ongoing system improvements (pressure, fire flow, reliability and pipeline/facility replacement), capacity improvement programs (six priority geographic pressure zones, including an East Water Treatment Plant program), and growth/hydraulic improvements that would enable buildout to the 2115 service area. Every identified project has a data sheet with a description, scope and 2021 dollar estimate.

Two CIP paths were presented. The unconstrained CIP assumes higher growth and a more aggressive replacement schedule and results in an average annual improvement cost figure cited by the consultant as about $17,500,000 (2021 dollars) over the plan horizon. The constrained CIP uses a more modest, fiscally realistic replacement pace and reduces the average annual program to about $10,600,000. The company acknowledged tradeoffs: the constrained plan would replace roughly 19% of the system pipeline length in 100 years (about 15 city blocks per year), while the unconstrained plan would replace around 76% of pipeline length (about 3.5 miles or 56 blocks per year), which may be challenging to deliver year after year.

Committee members asked about inflation and construction‑cost indices, the use of HDPE pipe versus PVC for municipal mains, and how the plan ties to recent utility rate changes. Labonde and Morgan Falcone, an engineer with Rapid City’s engineering department, said the master plan intentionally stops short of selecting a funding path: “We stopped at identifying the projects,” Labonde said, and the plans can be plugged into a rate‑study to determine necessary user rates. Falcone confirmed the city’s recent rate study incorporated the facility improvement schedule for treatment plants and pump stations but used a fiscally constrained pipeline replacement assumption that differed from the unconstrained CIP.

On materials, the consultant said HDPE is commonly used for long transmission mains with few fittings and that it “is a good product” with long life but that municipal networks with frequent tees, valves and fittings present design considerations. The committee discussed testing HDPE in competitive bid comparisons to determine market pricing and compatibility with city technical standards.

The presentation gave the city four dated hydraulic models, a facility replacement model that assessed roughly 420 assets, and a data‑driven prioritized pipeline replacement program intended to target pipes with the highest consequence and likelihood of failure. Labonde warned that ductile iron mains installed in the 1950s–1960s are beginning to reach the end of their useful lives and that constrained replacement pacing could produce increased main breaks in future decades.

The committee did not adopt a financing path at the meeting. The report and the consultant’s briefing were acknowledged; city staff and the consultant recommended using the plan to prioritize near‑term projects and to inform future rate and CIP decisions.

The master plan and appendices were provided to the committee and will be available for council and CIP committee consideration as the city weighs prioritization, funding and rate implications.