The corrosive and damaging effects of hydrogen sulfide gas is a phenomenon with which everyone in the wastewater industry is familiar, and the City of Greenwood, Arkansas’s largest sewage lift station was a casualty of this all too common foe. Lift Station No. 1 was originally constructed with two (2) submersible wet pit pumps. As wastewater flows increased, a result of population growth and inflow and infiltration (I&I), additional pumps had to be added. Due to the lack of wet well space, two (2) suction lift pumps were added in order to meet peak wastewater flow rates. The existing suction lift pumps were occasionally failing because they were unable to maintain their prime. After an assessment of the wet well, it was agreed that turbulent flow and swirl in the wet well were the likely cause of the suction lift pumps loss of prime. During the assessment of the pumps and wet well, significant corrosion of the concrete wet well and ductile iron pipe and fittings were also observed. Due to the inadequacies of the existing lift station, the City elected to construct a new sewage lift station in lieu of rehabilitating the existing undersized and failing structure.
The available project site posed many challenges including a limited footprint; location within the 100-year floodplain; proximity to a wet weather creek; presence of groundwater; and its proximity to the Sebastian County Courthouse and Town Square. Given its location, addressing odor problems was a primary goal. A new wet pit submersible pump station was designed with four (4) submersible pumps. The lift station included two (2) wet wells, each capable of being isolated from the collection system for maintenance. Each wet well contains a dry weather submersible pump, relocated from the existing pump station, and a new wet weather submersible pump with a total lift station pumping capacity of 5 million gallons per day. A new electrical building was constructed to house the variable frequency drives, electrical switchgear, and upgraded telemetry equipment. The existing emergency standby generator was relocated and an air scrubber was added to the new lift station to remove hydrogen sulfide gas and other noxious odors from the lift station.