Provided technical advice on the effect of sewer blockages on the escape of PCE from the City sewer system. The blockages were due to grease from “restaurant row”, which was just downstream from the sites of several dry cleaners. Issues included, sags in the sewer, the effect of surcharging the sewer on the sealing layer (colmation) that tends to build up at the joints and leaks in sewer pipes and whether releases due to surcharging are sudden and accidental.