Dr. Carl Frizzell is a hydraulics expert on various projects throughout the United States. He has experience in conducting hydraulic modeling, pump station design, pipeline design, plant hydraulics, and construction management. Dr. Frizzell specializes in pump station design for municipal water and wastewater industry. Dr. Frizzell received his B.S., M.S., and Ph.D from Clemson University. He has worked for CDM Smith 18 years and is Pump Station Design Discipline Leader.

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Ryan Keefe is a water/wastewater engineer, specializing in hydraulic projects. He has worked in may wastewater hydraulics projects throughout the Southeast United States, focusing on pump station design and hydraulic modelling. Mr. Keefe received his B.S. from the Georgia Institute of Technology and has been working for CDM Smith for 4 years.

When built in the early 1990s, the Cahaba River WRF Influent Pump Station, located in Jefferson County, Alabama, was sized at 98 MGD. Over time, this size turned out to be well above the necessary capacity. The existing pump station has seven vertical-mounted end suction solids-handling pumps: two 40-MGD pumps, two 20-MGD pumps, and three 6-MGD pumps. The two 40-MGD pumps are never used because they were oversized for the facility. Therefore, their condition is unknown due to lack of use, effectively reducing the reliable pumping capacity to 38 MGD. Jefferson County, Alabama requested CDM Smith to evaluate resizing the large pumps to increase station reliability and redundancy. CDM Smith performed an analysis of the historical average and peak flows for the Cahaba facility. The historical peak flow was determined to be 69 MGD, which was 29 MGD less than the currently installed capacity. The two 40-MGD pumps were rerated to two 20-MGD pumps, bringing the new capacity of the station to 78 MGD. This modification will increase the reliable pumping capacity by 40 MGD.

The pump station itself is a wet pit/dry pit type, with the dry pit extending about 80-feet below grade. This posed some constructability challenges during construction. For one, the pump station was not designed with access hatches above the pumps, so the elevator shaft will be used to remove the existing pumps and insert in the new pumps. Furthermore, it was determined that the suction and discharge sides of the pump were misaligned with the suction and discharge nozzles of the existing pump. This is exasperated by the slightly different dimensions of the new pumps. To account for this, custom stainless-steel reducers and reducing suction elbows are to be placed on the suction side of the pump, and an offset blind flange reducer will be used on the discharge side of the pump to expand to the discharge pipe. Additionally, since some of the suction pipes do not comply with suction side straight-pipe Hydraulic Institute standards, a physical model study was commissioned to determine if any custom baffles, straightening veins, or other hydraulic adjusting pieces are needed.

Our presentation will focus on the rerating analysis, constructability issues, and compliance with Hydraulic Institute standards and suction side physical modelling. Our presentation will also focus on how these modifications improve operability, redundancy, and maintainability of the Cahaba River WRF Influent Pump Station for Jefferson County.