The City of Ashland hired us to design its first major combined sewer overflow (CSO) control capital project and assist the City with all aspects of the project, beginning with planning and applying for SRF loan monies.  This project included expansion of two pump stations and extension of force mains through the combined sewer system (CSS) to deliver flows directly to the WWTP.  Six thousand feet of an existing 20-inch force main from the Roberts Drive Pump Station was reused in parallel with a new 20-inch force main. Normal and peak pumping rates allowed both mains along with the Sixth Street Pump Station to be manifolded into a single 30-inch force main, which was routed 1.9 miles through downtown Ashland to the WWTP.

The Roberts Drive Pump Station improvements expanded the capacity of the existing pump station from 4.8 mgd to 13.0 mgd.  Station improvements include replacement of five existing submersible pumps and controls with new 160 hp pumps, structural repairs to the existing wetwell (which suffered from hydrogen sulfide corrosion), replacement of an existing generator, and the addition of a second 20-inch force main.

The Sixth Street Pump Station improvements expanded this dry-pit submersible station from 3.75 mgd to 7.0 mgd, with three 110 hp pumps.  The first portion of the force main work was new 5,400 linear feet of 20-inch force main between the Roberts Drive and Sixth Street Stations.  In front of the Sixth Street Pump Station, the new and existing 20-inch Roberts Drive force mains were designed to be manifolded with the discharge from the Sixth Street Pump Station into a single 30-inch force main. Extension of the force mains directly to the WWTP removes higher strength wet-weather flows generated in separate sanitary areas from the central CSS and eliminates triple pumping of these flows within the CSS.

Challenges in the design of the force main portion of the project included navigating extensive existing utilities in crowded residential, commercial, and industrial corridors, and working with railroads, the Kentucky Transportation Cabinet, and the U.S. Army Corps of Engineers to coordinate close parallel alignments.  The project also included sensitive crossings of two state highways, a rail yard, one flood protection levee, and the Ohio River floodwall in three separate locations.  Overall, these upgrades have provided substantial energy cost savings through the elimination of the double and triple pumping of flow. CSO overflow volume has been reduced from 50 million to about 2 million gallons per year.

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