Over the course of a number of rehabilitation projects for New Castle County, Delaware conducted over the last few years, Malcolm Pirnie has collected pre- and post-rehabilitation flow data from neighborhoods and catchments being rehabilitated as well as nearby unrehabilitated "control" catchments. These data have been compared before and after rehabilitation on the basis of total system volume and peak flow rate during wet weather events and are considered for a variety of rehabilitation technologies installed singularly and in combination. Reductions in peak flow during a storm event range from 13% to 55%, averaging 36%, while reductions in total volume during storm event range from 5% to 41%, averaging 37%. Preliminary baseline or dry-weather infiltration analyses also indicate 40-50% reduction.Rehabilitation technologies used in these projects include cured-in-place mainline lining, cured-in-place lateral lining, pressure testing and packer-injection grouting of mainline joints and lateral/tap joints, and various manhole repair methods. The overarching rehabilitation philosophy has been one of holistic rehabilitation to offset the migration of water within the pipe bedding to the next easiest point of entry. It would be extremely difficult to get significant reductions by rehabilitating a pipe here and a pipe there, or by performing just mainline rehab or just manhole rehab without addressing the other, and without addressing tap/lateral leakage.
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