Maine Moves Ahead On CSO Projects

Lewiston's Most Difficult Job Faced Multiple Problems
January 2014, Vol. 69 No. 1

A trenching project for a new, combined sewer overflow (CSO) separation pipeline in Lewiston, ME, led to an unexpected, emergency sliplining of a sanitary sewer line. The job also had other challenges which included a massive rock ledge, old buildings virtually on the edge of the trench along with the existing sewer that was found to be leaking effluent.

The Oak Street - Phase III Project is the third part of the city's CSO master plan. This new piping separates storm water from the existing sanitary sewer system in order to relieve capacity stress on the treatment plant and meet Maine Department of Environmental Protection requirements. With a population of 37,000, Lewiston is the second largest city in Maine and is part of the Portland-Lewiston-South Portland combined statistical area.

"There are five phases to our CSO work," stated Jeffrey D. Beaule, P.E., project engineer for the city of Lewiston. "We just finished Phase IV, but the Oak Street - Phase III portion was probably the most challenging. This is because of the location of the pipeline, the unexpected sewer rehabilitation and the geological make-up of the area.

“One of the biggest problems we had on this job,” Beaule explained, “was the rock ledge we had to go through. The buildings were right at the back of the sidewalk plus we had a gas main right next to that old sewer so we couldn't blast. They had to manually hammer 370 cubic yards of rock ledge out of there. All of that and the added sewer interceptor sliplining put a lot of pressure on the projects construction schedule."

During the course of installing the new pipe, an old 60-inch diameter concrete sewer line was found to be leaking and needed to be replaced. As an alternative to replacing the sewer pipe, it was sliplined using the same type of pipe being used for the new storm water line -- SaniTite HP pipe from Advanced Drainage Systems Inc. (ADS). Additionally, the company's N-12 corrugated high-density polyethylene (HDPE) pipe was used for some other sections of the storm drain pipeline and smaller diameter SaniTite HP was used for new sanitary sewer piping.