Monday, April 23, 2018
Leah Bucco-White, Communications
An Olsson engineer on a skateboard was deep inside the big, blue pipe as he conducted his final assessment.
The 1,500-foot water pipe that was above ground just weeks ago is now buried below the Platte River. That meant boring through sand and gravel to create a path, and then slowly pulling the pipe underneath the riverbed. At its deepest point, the pipe is 50 feet below the river.
“The pipe needed to be watertight and able to withstand the forces it was subjected to as it was positioned below the river. Protective coatings inside and outside played an important role,” said Joel Jirak, an Olsson engineer who is on-site providing construction observation services.
The pipe will connect a new horizontal collector well on the east side of the Platte River to an existing transmission main that delivers water to the west side of the river and City of Lincoln’s treatment plant in Ashland, Nebraska. From there, the water will be delivered to Lincoln increasing the city’s water supply capacity.
“This is a unique project in every way. Boring a pipe this size under the river, and the type of well it will connect to isn’t exactly typical,” said Joel.
Joel explained that with a standard well, pipes and well screens are placed vertically, and water is pumped up and out. The horizontal collector well being used here contains a hollow concrete caisson which is like a shaft with pipes and well screens at the bottom that extend horizontally like spokes on a wheel. Water is drawn through the pipes and fills the caisson. Pumps in a well house above lift the water up and out.
“The city’s well fields include many vertical wells and when this project is complete, there will be an additional horizontal collector well at the city’s disposal,” said Ben Day, project manager. “During drought conditions, horizontal wells are more efficient. Adding this infrastructure increases overall system reliability and allows the city to manage all its wells, and its operational aquifer capacity, to minimize drawdown of the aquifer where the city’s water supply comes from.”
Olsson, working alongside Black & Veatch, is also providing concrete quality testing, moisture and compaction testing of soil, wetland delineation, and monitoring of threatened and endangered wildlife to ensure habitat is not disturbed during the project.
The expected completion date is later in the spring of 2018.