SEWER REHABILITATION TO REDUCE INFILTRATION AND INFLOW - A CASE STUDY

The City of North Miami Beach implemented a sewer evaluation and rehabilitation program designed to quickly reduce infiltration and inflow (I/I) by correcting the most serious collection system defects based on an expedited investigation phase. A key element of the program involved the immediate implementation of repairs following the identification of problems in the collection system, and accordingly the City set up rehabilitation capabilities early in the investigation phase so that investigation and rehabilitation could be performed in a nearly concurrent fashion. The system-wide I/I reduction program was initiated with detailed lift station evaluation; manhole insert installation; replacement of previously undetected collapsing lines in rear-yard easements; and selectively targeted television inspection to evaluate the internal condition of collection system piping and identify sources of infiltration. Limited smoke testing was performed to locate sources of inflow. Primary repair methods consisted of dig-andreplace for shallow lines in areas with limited aboveground and underground conflicts; chemical grout for structurally sound piping with limited joint leaks; and formed-in-place PVC liner installation to rehabilitate damaged gravity mains in high-traffic areas, for deep lines that would have required dewatering during excavation, in areas where other utility lines presented conflicts, and in rear-yard easements where gravity mains ran beneath customer fences, gardens, sheds, and lawns. Dramatic reductions in I/I were achieved in the first year of the program as the most serious defects were discovered and repaired. Diminishing returns have been seen in subsequent years as the program has been able to focus on less serious defects and preventive maintenance repairs. Through 2000, the City is metering a nearly 40 percent reduction in average daily flow from that measured at the start of the I/I reduction program in 1996. This reduction is translating into significant financial savings and an increase in available system capacity.