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A Newsletter by the City of Saco, Maine	May, 2007	Return to newsletter index

Saco meets Water Quality Milestones

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Combined sewer systems are collection systems that are designed to collect rainwater runoff and domestic sewage in the same pipe. These systems are designed to transport all of their contents to the Wastewater Treatment Plant, where it is treated and then discharged to the Saco River. During periods of heavy rainfall or snowmelt, however, the wastewater volume in a combined sewer system can exceed the capacity of the collection system or treatment plant. For this reason, combined sewer systems are designed to overflow occasionally and discharge excess water directly to the Saco River.

These overflows, called combined sewer overflows (CSOs) are a major water pollution concern for the approximately 772 cities in the U.S. that have combined systems.

Communities with combined sewer systems were expected to develop long-term CSO control plans that would ultimately provide for full compliance with the Clean Water Act, including attainment of water quality standards. The City of Saco's plan originated in 1995 with a presumptive life span of 20 yrs and a total cost of $10,800,000 dollars.

In December of 2006 the city completed two major milestones of its CSO long-term control plan.

Basically, the first milestone called for construction of a new "enhanced conveyance line" that would transport more combined wastewater from the Wharf/Front ST. overflow structure down to the treatment plant. This particular structure conveys the wastewater from all the sewered areas west of Route 1 and all of the downtown area.

The second milestone dictated that we had to provide preliminary treatment and disinfection to the wastewater flowing down to the treatment plant that previously discharged directly to river. City staff decided to install a relatively new type of process called a Storm King swirl concentrator. This unit is 22 feet in diameter and will provide treatment of up to 5.63 million gallons a day. During the recent Patriots Day storm event the unit processed and disinfected 11.24 million gallons over a 5 day period that previously would have discharged untreated to the Saco River.