Avista Utilities will begin boring underneath the Spokane River near the mouth of Lake Coeur dAlene next week to install a 6-inch diameter natural gas pipe for nearly 1,000 feet to extend gas service to the south side of the river.


The Spokane company says that its contractor on the project, Skyview Construction, of Post Falls, will begin boring underneath the river April 10. The gas-line extension will stretch from just south of Lakewood Drive on the rivers north bank to a cul-de-sac on Canal Street on the south bank. The $600,000 project is expected to take three weeks.


There is currently no gas service on the south side between this area and Post Falls, Avista spokeswoman Catherine Markson says. We are establishing this crossing due to the growth in the area as well as the strategic benefit of being able to eventually tie in to Post Falls for reinforcement and stability.


Kris Busko, an Avista gas distribution engineer who is in charge of the project, says that on the south bank of the river, Right now, the nearest gas is all the way over at Harbor Island, near Post Falls, and that system isnt robust enough to expand. Eventually, Avista would tie its system at Harbor Island to the extension in Coeur dAlene to the rivers south bank.


Residents on Coeur dAlenes Millview Lane and Fairmont Loop, which are near where the southern end of the new gas line will reach, want gas service, and Coeur dAlene developer Marshall Chesrown wants gas service at the Cougar Ridge development south of Coeur dAlene, Busko says. Avista put in dry gas lines at Cougar Ridge when infrastructure was installed there in 2004, she says.


Hopefully, in the fall, we will run down the highway (U.S. 95) and connect with that, Busko says. Also, another businessman has said that he wants gas service extended to land he would like to develop south of the river, she says. Black Rock Development, which Chesrown heads, has two development projects, RiverWalk and Bellerive, on the north bank of the river, and the gas line will be extended from the companys property.


Skyview Construction will use a method known as horizontal directional drilling, which allows steering of drill bits, to bore underneath the river in an inverted arc that could go as deep as 50 feet beneath the stream bed, but never will be closer than 20 feet to the underside of the stream bed, Busko says. The drilling will be done in two passes, with the first pass establishing a line for the bore, and the second pass reaming the bore to size.


Drilling mud will be injected into the hole as the drilling is done for lubrication, then will be left in place to make it easier to pull the casing through and to cushion it after the casing and the gas line are in place, she says.


Skyview Construction will weld together 40-foot sections of the 10-inch steel casing, and Avista crews will weld together 40-foot sections of 6-inch rust-resistant steel gas line, Busko says. In both cases, pipe will be welded into lengths that will be practical to pull through the bore, but how long those lengths can be and still go through the bore wont be known until the line for the bore is determined, Busko says. Each 40-foot section of the casing weighs 1,200 pounds, and each 40-foot section of gas pipe weighs 700 pounds.


During the project, the pipe will be visible on a beach on the north bank of the river, where the sections will be welded, while the boring machine will be visible in the Canal Street cul-de-sac area, Busko says.


With the amount of development in that area, this is the perfect time to be working on that beach, rather than later, after costly landscaping has been put in, she says.


Skyview bored under the Spokane River for Kootenai Electric Cooperative, of Hayden, Idaho, at a site to the west near Huetter Road two years ago to put in electric cable, Busko says. As far as she knows, Avista never has bored underneath the Spokane River, but did bore beneath a much larger riverthe Snake, just upstream from Lewiston, Idaho, and Clarkston, Wash.to put in a gas line in the early 1970s, and also has bored underneath the Clearwater River, she says.


The Coeur dAlene project has been in planning for more than a year, Busko says. Tasks have included finding the right alignment, informing property owners in the neighborhood about the project, and obtaining a permit from the Idaho state Department of Lands.


We had a geologic survey done, to find the best type of material to drill through, she says.


GeoEngineers Inc., which has an office in Spokane, did the geotechnical study, sinking 100-foot holes on either side of the river. It found boulders, cobble, and gravel, but other types of rock could be encountered during drilling, Busko says. GeoEngineers will monitor the material that comes out of the bore hole as the drilling is done.


Also, she says, Avista evaluated whether the river could scour out the project during high water and established that, in the alignment it chose, the line likely wouldnt be susceptible to earthquake damage.


The project has been carefully planned, partly because the river is a significant body of water, used by and seen by lots of people, Busko says. Also, like most utility distribution improvements, its engineered to last a long time. Definitely, this isnt something we would want to revisit in our lifetimes, she says.


The project is the biggest bore-drilling job she has worked on, although its common for Avista to bore beneath highways, railroad tracks, and small creeks, she says.


Markson asserts that the project will have no environmental impact.


Access pits will be dug on either side of the river to enable the work, and all work will be performed above the high water line, she says. Any excavation will be restored to original condition with landscaping per the easement agreement. We will take nothing from and leave nothing in the river, and there will be no disturbance of the silt bottom.


When the project is completed a cane-shaped vent pipe and a test box, similar to gas-system apparatus commonly seen at highway crossings, will be visible on either side of the river, she says. The devices will remain in established easements granted by landowners.


Contact Richard Ripley at (509) 344-1261 or via e-mail at editor@spokanejournal.com.