Lincoln Wastewater System selected Olsson to rehabilitate both influent pump stations at the Theresa Street Water Resource Recovery Facility (WRRF). Four separate construction projects spanning several years were necessary to maintain continuous operation of the WRRF throughout the improvements. To minimize the risk of not having adequate pumping capacity during wet weather events, each phase of the work was done during seasonal dry weather periods.
Two of four mechanically cleaned bar screens were replaced with a pair of Vulcan Mensch Severe Duty bar screens. A new shafted screw conveyor brings screenings to the city’s washer compactor.
Seven of the eight pumps were replaced for a variety of reasons. Flygt CT3531 dry-pit submersible pumps (15 million gallons per day [mgd] each) were determined to best meet the city’s needs. Standardizing these pumps provided more consistent operation, alleviated vulnerability to dry well flooding, eliminated driveshaft hazards and maintenance, and standardized motor voltage to 480 volts (V).
Many of the 2,400 V and 480 V electrical switchgears serving both pump stations were replaced. Eighteen-pulse variable frequency drives (VFDs) were installed with each new pump to mitigate harmonic distortion while optimizing pump control. Installation of redundant 2,400 V primary electrical service feeders, three 1,500 kilovolt-amp transformers, and an 800 kilowatt diesel-fired generator immensely improved the facility’s resilience to electrical outages.
The pneumatically actuated ball valves were replaced with air-cushioned swing check valves to improve reliability and to simplify operations. In addition, several isolation valves and interior piping were replaced.
Much of the control hardware and logic for the two pump stations was modified. Innovative control logic was designed to optimize the efficiency of all eight pumps during dry weather while providing maximum responsiveness during wet weather events.
We designed a new HVAC system for the south pump station to meet National Fire Protection Association (NFPA) 820 and Nebraska Title 123 requirements. This new equipment was required to account for various code classifications, varying air exchange rates, and controlled pressure differences between spaces.
Several structural improvements were necessary to retrofit the 1952 and 1971 buildings for the new, larger equipment. Most notably, the south pump station required a larger roof opening to accommodate the new bar screens, and a five-ton bridge crane was installed to accommodate the new pumps.
Our ability to coordinate across multiple engineering disciplines, construction projects, and contractors while working within inflexible construction windows was of paramount importance to deliver a consistent and successful end-product.
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