TJ Garbes, a civil engineer with Cochran Engineering, told the City of Washington Board of Public Works on Oct. 28 that preliminary modeling shows the Walnut Street Lift Station likely lacks the capacity to handle peak wet-weather flows that back up along Front Street.

"That large 185-horsepower pump ... pumps about 2,800 gallons a minute," Garbes said, summarizing the station layout: an 18-inch gravity sewer feeding a 37-foot-deep wet well with two 60-horsepower day pumps and a single 185-horsepower wet-weather pump. The lift station discharges through a 14-inch force main that crosses the treatment plant.

Garbes presented three broad alternatives staff and the consultant are studying: install a higher-capacity force main (the preliminary idea is to move from 14 inches to a 20-inch main), replace or supplement the storm pump(s) to increase peak pumping (the consultant mentioned a target that could approach 4,500 gallons per minute), and add on-site storage at the Walnut Street Lift Station to provide staff time to respond to failures. He emphasized the presentation was preliminary and that cost estimates will be part of the final analysis.

Kevin (staff) told the board that SCADA data and newly installed flow monitoring devices—24 "eye trackers" placed on the East End—are already helping locate problem areas. He said a recent 1.5-inch rain event caused Walnut Street's wet-well level to rise to about 9 feet and triggered the large pump, indicating the East End contributes significant wet-weather flows.

Board members and staff discussed whether to abandon the existing 14-inch cast-iron force main or install a new main in parallel. Garbes cautioned that connecting new and old pipe often creates operational choke points, and that internal buildup in an older pipe could mean the effective diameter is less than nominal. He noted that the line passes under railroad tracks, which will affect construction planning.

Garbes and staff said they expect to return with a final recommendation, including hydraulic modeling, likely alternatives, and cost estimates, at the December board meeting.

Ending: The board directed staff to continue investigation; no formal vote or procurement action was taken on the wastewater items at the Oct. 28 meeting.