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Military Base Sewer System Upgraded With HDPE Pipe
The recent expansion of the sanitary sewer system at Ft. Lewis, WA, included the installation of 5,000 feet of 36 inch and 400 feet of 30 inch diameter HDPE pipe to replace the base’s vitrified clay system.
Design and construction work was done by Bristol Construction Services LLC, Anchorage, AK. Bristol provides heavy construction, construction management, civil engineering and other services to the U.S. Army Corp. of Engineers, NAVFAC and the FAA in Alaska, Washington and North Carolina.
Ft. Lewis is home to I Corp and is one of the largest military reservations in the United States. Named after explorer Meriwether Lewis, it was established in just before World War I and now has 30,000 soldiers, 11,000 civilian employees, 24,000 retirees and 47,000 family members living both on and off the post.
Recent plans called for the expansion of Ft. Lewis for which the new sanitary sewer system will provide additional capacity. This meant that the sewer system would be upgraded to include large diameter pipe. The existing 24 inch clay pipe was half-full, leaking and also taking on water that infiltrated from the soil, unnecessarily adding a burden to the treatment plant.
Originally, the replacement pipe was to be polyvinyl chloride (PVC), but because of its higher cost, Bristol selected the HDPE pipe, and the Army Corp of Engineers agreed.
“The main problem with the existing sanitary sewer line,” explained John Sharp, project manager for Bristol, “was that it was already undersized for the needs of Ft. Lewis, and would not be capable of meeting the expansion plans. In addition, the vitrified clay was taking on water, so the sewage treatment plant was having a hard time processing all that extra ground water when there was a significant storm.”
The new pipeline was installed parallel to the old one so there was little interruption to base operations. Working six days a week, the Bristol crew of eight used a CAT 365 excavator that would dig the ditch and drag the trench box along. After the ditch was excavated and the box set in place, bedding would be put down to set the grade of less than a half of a percent.
“Production was great. We made very good time on the job. The pipe was fairly light. It was moved into position with the excavator,” Sharp stated. “A three-man crew was in the trench to connect the pipe sections.”
At some locations, such as the firing range, the trench was 25-feet deep. “That particular section of pipe was passing through firing ranges so you have the normal grade of about 10 feet and then another 15 feet of berm,” he said.