Denver — Denver Water’s $80 million Conduit 16 replacement is successfully underway. TerraFirma Earth Technologies completed vacuum wellpoint dewatering services for its portion of the replacement of the 81-year-old pipeline that runs 8.5 miles from Ralston Reservoir to the Moffat treatment plant. Reynolds Construction is the General Contractor on this phase of Denver Water’s decade-long, $600-million North System renewal project.
According to Josh Kuper, Project Manager at Reynolds Construction, this section of the project consisted of five tunnel installations in addition to approximately 5,494 linear feet of 84-inch-diameter pipe. The tunnels crossed Hwy 93, the BNSF Main Line Railroad Track, a BNSF Railroad Spur Track north of Highway 58, Highway 58, and I-70 and Applewood in Denver. “Due to TerraFirma’s successful dewatering, crews were able to move forward quickly with the open cut portion of this complex project,” Kuper said.
David Giles, President of TerraFirma, explained the dewatering method: “We installed vacuum wellpoints for a large section of the shallower, open cut portion of the project, which is a lesser-utilized method in the Denver area due to the higher elevation; however, under the right circumstances vacuum wellpoints are the best option for the unique geology in Denver.
“Lowering the groundwater table to below the excavation meant dropping the groundwater table as close as possible to the confining bedrock. Deepwell (sump) dewatering wells would have had to be placed so close together, it would have been cost prohibitive. Even then, supplemental sumping within the excavation would have been required, adding more cost, and further slowing down production.”
Giles further described the advantage of sonic drilling methods. “Denver’s unusual geology is consistently water-bearing alluvial soils over shallow bedrock. We teamed with MW Drilling to operate the sonic drilling rig. Sonic drilling methods make it possible to efficiently drill a wide range of soil types, particularly the sand-gravel-cobble typical to Denver. While it appears to be more costly up front, it is less expensive over time, and gets the job done right.”
Ryan Haas, Denver Water’s Project Manager for the Conduit 16 replacement, added,
“Denver soils are full of cobbles and boulders – some up to 3.5 ft. in diameter. The sonic drilling method used by TerraFirma made the drilling within these difficult soil conditions much more efficient.”