Nashua Rethinks Its Approach to Controlling Overflows

摘要

Like many cities struggling to come to grips with combined sewer overflows (csos), Nashua, New Hampshire, has begun a costly, long-term campaign to disaggregate its combined sewers. Although already several years into a 20-year effort to address csos, the city recently proposed an alternative that, if approved by regulators, could save roughly $200 million and do more for water quality than would sewer separation. Home to approximately 87,000 residents, Nashua is located along the banks of the Nashua River not far from the confluence with the Merrimack. The city has a wastewater collection and treatment system comprising 330 mi (531 km) of sewers, 12 pump stations, and a secondary wastewater treatment plant with a design flow of 16 mgd (60,600 m~3/d). Combined sewers are the rule for approximately 110 mi (178 km) of the collection system. They rely on nine overflow points to relieve pressure following wet weather, and each year roughly 30 million to 100 million gal (113,600 to 378,500 m~3) of untreated sewage overflows from the system, says Richard Seymour, the deputy director of Nashua's wastewater treatment facility.