NBC – Sewer Seperation Program

Owner: Narragansett Bay Commission (NBC)

Overview: The Narragansett Bay Commission (NBC) is the largest owner and operator of waste water facilities in the State of Rhode Island. The facilities service highly populated urban centers. The entire service area is comprised of a combined storm/sewer system. Combined sewer systems are designed to collect rain water runoff, domestic sewerage and industrial wastewater in the same pipe. During periods of heavy rainfall or snowmelt, the waste water in the existing combined sewer system routinely exceeded the capacity of the NBC treatment facilities. Consequently, during weather events, NBC was forced to bypass the treatment process and allow millions of gallons of untreated flow into Narragansett Bay. To eliminate this problem, NBC embarked on a $1 billion (+) sewer separation program. The design is predicated on a three mile long, 24’ diameter storage tunnel drilled deep beneath the City of Providence. Closer to ground level, a series of consolidation conduits, drop shafts, and storm drainage piping were constructed to allow for diversion of waste water to the holding tunnel. The stored waste water is then sent to a waste water facility for treatment during low flow periods, eliminating the need to discharge untreated waste into the bay. John Rocchio Corporation was awarded the following four contracts under this program.

Work: The work consisted of the construction of a 370’ (depth) drop shaft with gate and screening structure. A 54 MGD temporary bypass was required to maintain existing waste water flow during construction.

Cost At Completion:  $5,356,796

Work: The work consisted of the construction of NBC outfalls 205, 219, 220, including a regulatory screening structure, and the removal and replacement of an existing settled 48” CSO pipe. A 32 MGD temporary bypass was required to maintain existing waste water flow during construction.

Cost At Completion: $4,364,580

Work: The work consisted of the construction of approximately 18,000 l.f. of various size new drain pipe, 220 manholes and catch basins, connections and modifications to existing drains, utility relocation, and pavement restoration.

Cost At Completion: $9,333,831

Work: The work consisted of the construction of approximately 12,500 l.f. of various size new drain pipe, 160 manholes and catch basins, connections and modifications to existing drains, utility relocation, and pavement restoration.

Cost At Completion: $6,911,883