Age and location have conspired against Cleveland. The city’s century-old combined sewer system discharges into Lake Erie, a state EPA-designated “sensitive receiving water.” The end result: a 2011 consent decree giving the Northeast Ohio Regional Sewer District 25 years to lower illegal discharges from 4.5 billion gallons to 494 million gallons a year.

Begun in 2012, the second major component of the district’s $3 billion Project Clean Lake long-term control plan is a rather unusual solution to the problem of undersized wastewater facilities: a pump station 240 feet below ground that stores combined sewer overflows during peak wet weather events. Once flows subside, the facility will dewater the storage tunnels and pump flows into the Easterly Interceptor where it will be conveyed by gravity to the Easterly Wastewater Treatment Plant.

Although Chicago, Milwaukee, and Providence, R.I., also use “cavern” pump stations to dewater storage tunnels, the design is much less common than shaft-style pump stations. Scheduled for completion by the end of 2016, Cleveland’s 160 mgd facility will be one of the nation’s largest combined sewer overflow (CSO) pump stations.

The Cleveland office of engineering consulting firm MWH Global anticipates the facility will be activated about 80 times a year, the storage tunnels will completely fill about four times a year, and that equipment will operate an average of 340 hours annually.

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