Photo by Jon Sailer on Unsplash
Entex Technologies Expands Powder House Pass WWTP to Meet Sturgis Rally Demand
Every August, the Northern Black Hills near Lead, South Dakota, come alive with the roar of engines as more than half a million riders converge on the region for the Sturgis Motorcycle Rally. Since its first run in 1938, the rally has grown into one of the largest gatherings of its kind in the country – and each summer, that surge of visitors places extraordinary demand on the local infrastructure supporting them, including the Powder House Pass Wastewater Treatment Plant. The same seasonal spike that originally shaped the plant’s design is now driving its next chapter.
The Powder House Pass expansion project will increase the plant’s average treatment capacity six-fold, from 25,000 gallons per day to 150,000 gallons per day. Because the rally creates such a distinct and short-lived surge in flow, the system has been engineered around more than just average-day performance: it’s designed to handle a peak hour flowrate of 0.60 MGD, giving the plant the operational flexibility to manage both quiet winters and the single busiest week of the year without compromise. Even at peak loading, the upgraded system is designed to consistently achieve effluent goals of BOD under 10 mg/L and NH3-N under 1.0 mg/L.
Img 1. New construction at Powder House Pass WWTP
The expansion builds directly on the plant’s original WavTex system. In October 2024, eleven new WavTex modules joined the three currently onsite, bringing the total to fourteen aerobic modules distributed across two treatment trains. A new upfront equalization tank will help absorb the sharp influent fluctuations tied to rally week, while a new filtration stage adds a further layer of polish to the effluent before discharge. Fixed-film systems, like WavTex, are well suited to seasonal flow variations because the attached biomass naturally increases and decreases in response to changing hydraulic and organic loading conditions. The modular design of WavTex also allows capacity to be expanded incrementally, enabling facilities to add treatment as demands grow rather than replacing the existing system.
Img 2. Approximate layout for new expansion
In addition to the new WavTex modules, Entex supplied the clarifier internals, aeration grids for the equalization and sludge holding tanks, airlift pumps, valves, fittings, and instrumentation. New tankage, filtration equipment, blowers, and interconnecting piping were supplied by others.
Together, these upgrades give Powder House Pass a plant built for its busiest day as much as its average one – ready for rally season, and everything in between.