INFILTRATION AND INFLOW REDUCTION – A PROGRAM OVERVIEW

The City of North Miami Beach is located in Southeast Florida, where the ground water table generally ranges from 3 to 5 feet below land surface and seasonal rainfall is heavy. These conditions make infiltration and inflow (I/I) reduction a priority concern for sanitary sewer systems. In 1996, almost 50 percent of the City's total 6 MGD average daily flow was estimated to be I/I. The City initiated a system-wide I/I reduction program including detailed lift station evaluation; manhole insert installation; replacement of previously undetected collapsed lines in rear-yard easements; and closed-circuit television inspection to evaluate the internal condition of collection system piping and identify root intrusion, cracks, separated joints, leaking service connections, and other sources of infiltration. The City also performed smoke testing to locate sources of inflow. After television inspection and repair prioritization, the City selected formed in-place liner installation to rehabilitate many of the damaged gravity mains. The formed-inplace pipe lining method offers benefits over traditional excavation and replacement for high-traffic areas, for deep lines that would require dewatering during excavation, for areas where other utility lines may present conflicts, and for rear-yard easements where gravity mains may run beneath customer fences, gardens, sheds, and lawns. The City selected a formed-in-place PVC liner system, which once installed meets all the requirements of SDR-27 PVC and does not depend on the structural integrity of the host pipe. This process effectively results in an entirely new gravity main with an estimated life of 50 years. Through 1999, the City has installed liner in 27,500 feet of collection system piping, and is metering a nearly 48 percent reduction in average daily flow from that measured at the start of the I/I reduction program. This reduction is translating into significant financial savings and an increase in available system capacity.