- Created: Tuesday, 10 February 2009 07:31
- Published: Tuesday, 10 February 2009 07:31
U.S. Silicaís property in Ottawa, Ill., is divided by the Illinois River. The north side of this dividing line was quickly running out of coarse sands, which many U.S. Silica customers rely on. The processing plant was on the north side, so the company had to confront the problem of feeding it from the opposite side.
The notion of building a new plant on the south side quickly was dismissed. There was easier access to an interstate highway on the north side to aid in delivery. The north also provides access to three separate rail lines, which are responsible for hauling 70% of the product, says Administrative Manager Robert L. Krepps.
The company instead decided to take on a $16 million project with CNA consulting engineers to move product beneath the river. Krepps says the original plan was to build a conventional tunnel that measured 17 feet in diameter, large enough for a pickup truck. But the erosion zone was deeper than anticipated, and solid rock was as far as 160 feet below the pit floor. The cost to install a tunnel at these depths became prohibitive. The second best option was to use a horizontal directional drill (HDD) to install pipelines under the river. Moving forward with a tunnel project would have risked unleashing the Illinois River into the quarry.
ìIt was just too unstable to take a chance on it,î Krepps says. ìSo we went with what is called a horizontal directional drill.î
Guided by a computer, the HDD drilled two 12-inch-diameter pilot holes a distance of 3,300 feet. The computer communicated with two coaxial cables, spaced 30 feet apart, that stretched across the surface. The cables acted as antennae to guide the drills. After surfacing on the other side, the company reamed out two holes, one 36 inches in diameter and another 42 inches in diameter. Durable polyethylene pipes were dragged through these holes for slurry lines to feed the north-side processing plant, as well as conduit for electric power and a 24-inch steel water line for hydraulic mining.
ìIt was quite a process. Several of us came over there on the day they said it was going to surface, and we stood around for about an hour. I asked (the drilling contractor) where it was going to come out, and he pointed to a spot on the ground,î Krepps said. ìAnd it was about two feet off one way and about eight feet off the other way, but it came out essentially right there.î
The drilling began in June of 2006. The first pilot hole surfaced towards the end of July, and both borings were completed by Thanksgiving. But before work could begin, there were some loose ends to tie up. Two properties had to be purchased so the borings could pass beneath.
Also a permit had to be obtained from the Army Corps of Engineers to allow drilling beneath a navigable waterway. Krepps says it took some time, but it was not a difficult process. Being located on the waterway, U.S. Silica deals with the Army Corps regularly and has developed a positive relationship. The company also had to participate in archeological and historical studies. Local permitting was not an issue because U.S. Silica operates outside the city limits, and is grandfathered in for all county zoning.
Krepps says there was no stoppage of production during the project, as material continues to be mined from the opposite side of the river. However, there was one incident that posed problems for U.S. Silica, which this project has remedied.
The south side flooded in August 2007. As a result, the company was unable to mine and had to hire a contractor to truck sand across the river to maintain accounts. The cost of doing so was approximately six times higher. But now that the project has been completed, including adequate dewatering, U.S. Silica anticipates an uninterrupted, efficient flow for the next 40 years.