Recovery of Coliforms in the Presence of a Free Chlorine Residual

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Abstract
Despite the presence of a free chlorine residual, significant numbers of coliforms were recovered from the Grand Rapids, Mich., distribution system during the summers of 1982 and 1983. The first incident appears to have been caused by entry of a slug of contamination into the water supply. The second incident involved persistent recoveries of apparent regrowth organisms and paralleled previous incidents reported by other utilities. The subsequent discovery of several defects in the Grand Rapids water supply system points out the need to determine the source of such organisms, which, unless proved otherwise, must be considered a serious contamination problem.