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Great Falls, Montana
Great Falls Wastewater Treatment Plant Screen Replacement
Modernizing the headworks without interrupting service to the community
When the City of Great Falls needed a wastewater treatment plant screen replacement, Morrison-Maierle engineers faced a high-stakes challenge: modernize the headworks with an ineffective screen inside an active facility while maintaining continuous wastewater service. The Great Falls Wastewater Treatment Plant headworks screening replacement combined bypass pumping, confined-space rehabilitation, equipment selection, and coordinated electrical, controls, HVAC, and access improvements.
Through careful planning and flexible design, the team delivered a cost-effective, efficient solution that improves debris removal, operator safety, odor control, and long-term reliability.
Client/Owner
City of Great Falls
Location
Great Falls, Montana
Project Budget
$2.2M
Project Snapshot
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Maintained uninterrupted wastewater treatment while bypassing average flows of 5.5 to 6 million gallons per day, with capacity for up to 8,000 gallons per minute.
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Avoided an estimated $250,000 duplicate bypass-pumping event by completing the channel inspection during the planned construction bypass.
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Reused and rehabilitated the existing headworks facility, minimizing major new construction while improving long-term performance.
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Installed a compact screening and washer/compactor system that captures more debris, reduces odors, improves handling, and protects downstream equipment.
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Adapted quickly to undocumented drain lines, unexpected wastewater flows, and unusual asphalt-like material without interrupting plant operations.
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Strengthened operator and engineer safety through coordinated confined-space procedures, gas monitoring, fall protection, and adjustments that reduced hydrogen sulfide exposure.
How to Upgrade Critical Infrastructure in an Operating Plant
Approximately 60 percent of the city’s wastewater flow passes through this side of the headworks. Average bypass flows were estimated at 5.5 to 6 million gallons per day, and the temporary system was designed for up to 8,000 gallons per minute. Because flows arrived from multiple sources rather than one convenient manhole, the contractor needed to route large suction hoses through constrained access points, remove manhole tops, install strategic pipe plugs, and maintain backup plans. Morrison-Maierle involved a contractor during design to evaluate bypass strategies early, reducing construction surprises and protecting uninterrupted treatment.
A Cost-Effective Alternative to Duplicate Bypass Pumping
A separate pre-design bypass event for a brief channel inspection was estimated at approximately $250,000. Instead, Morrison-Maierle designed for conservative rehabilitation assumptions and scheduled the detailed inspection during the construction bypass, when temporary pumping was already required. This approach avoided duplicative work and cost while preserving flexibility to address actual field conditions.
Fitting Better Screening Into a Constrained Facility
The existing building and channel geometry required a compact screen that could operate vertically or at a slight angle while providing sufficient hydraulic capacity, reliable debris removal, and practical maintenance access. Morrison-Maierle compared manufacturers, configurations, bar spacing, procurement options, and washer/compactor requirements. The selected system captures more material at the front of the process and dewaters and compacts screenings, making them easier for operators to handle while helping protect downstream pumps and equipment.
Work at this excessive depth, 20-plus-feet, in a confined space required atmospheric monitoring,
venting, retrieval equipment, and an entry permit to safeguard workers and inspectors. The
engineering team entered the influent channel to review existing conditions, observe concrete repairs, and inspect completed coating work.
Three manholes were used to intercept the wastewater treatment plant influent for bypass pumping. Because the temporary bypass operation would have cost approximately $250,000 for only a short inspection window, Morrison-Maierle recommended a different approach. This decision avoided a costly duplicate bypass effort while still protecting the city from unknown
conditions.
The bypass pumping alone required significant planning because wastewater discharged to the work area was from multiple sources (three pictured here) rather than a single manhole.
A contractor helps guide the new screen down into place.
Startup produced an unexpected operational challenge when black, asphalt-like gravel began
arriving at the new screen and clogging the washer/compactor. The source appeared to be asphaltic material entering the sanitary sewer system, likely from equipment washout. Although the condition was outside the project’s design assumptions, the new screen captured the material rather than allowing it to pass downstream, highlighting the value of improved front-end screening.
Adapting to Unknown Conditions
Construction revealed undocumented drain lines, unexpected flows, and a line shown as abandoned that still carried wastewater. The team worked with the contractor to plug or abandon lines where appropriate and added a bypass pump for localized flow. During startup, asphaltlike material entering the sewer clogged the washer/compactor. Operators and engineers monitored the issue until the seasonal source stopped. Importantly, the new screen captured the material before it could travel downstream.
Managing Confined-Space Safety
Engineers also needed to inspect concrete repairs and coatings inside a narrow influent channel approximately 20 to 24 feet deep. Morrison-Maierle coordinated with its safety officer, the City, Veolia, and the contractor to address hydrogen sulfide, fall, access, and engulfment hazards. The team completed required training, assigned entry roles, used calibrated gas monitoring equipment, and provided fall-restraint and retrieval systems. When bypass splashing increased hydrogen sulfide conditions, the discharge configuration was adjusted to reduce off-gassing and support safer entry.
The Result? A More Efficient, Resilient Headworks
The completed project reused the existing facility while replacing the ineffective screen, rehabilitating the influent channel, replacing slide gates, and integrating supporting building systems. Construction finished at approximately $1.961 million—slightly below the $1.988 million bid. The upgraded headworks now captures more debris, improves screenings handling, reduces odors, protects downstream equipment, and supports safer, more reliable operations.
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