Abstract: A process for repairing underground sewer lines by preventing the infiltration of groundwater into a leaking sewer line comprising determining the location of the leakage into the sewer line, vacuum excavating a bore into the ground to the sewer line in the vicinity of the leak, depositing a quantity of a water swellable material such as an argillaceous material selected from the group consisting of bentonite and attapulgite into the bore to a depth of at least about one foot above the sewer line, tamping the argillaceous material in the bore, depositing a quantity of gravel over the argillaceous material in the bore, and backfilling the excavation. The water-swellable material also contains a dye which will infiltrate into the sewer line until the leak is sealed. Through a downstream inspection, the presence or absence of the dye indicates whether water infiltration into the sewer line has stopped.