Selecting the right site
When selecting a site, there are several things to consider: how overburden will affect the cost of stripping, the sizing of the material to estimate crushing cost, material hardness, and other quality features.
By Kerry Clines, Senior Editor
For Knife River Corp.’s North Central Region, job specification requirements dictate the type of products needed, which, in turn, dictate the sites where crushing and washing operations will be set up. Local agencies — counties, cities, and townships — dictate the products that various contractors need to do their work. Those products, which are defined by specifications, are the products that Knife River searches for, produces, and keeps on hand.
“Probably 75 percent of what we produce, in terms of aggregates, is for our own construction work,” says Tim Crennen, region president, North Central Region of Knife River Corp. “I’m specifically speaking of the North Central Region of Knife River — Minnesota, North Dakota, South Dakota, Iowa, and Nebraska. It varies in different markets and in the different regions of our corporation.”
Most of the company’s sites are sand and gravel, and most of those are portable crushing and washing operations. Each site, by virtue of the gradation of the pit, determines, to a large extent, just how extensively certain products can be produced.
“Of course, you want to manufacture your product as efficiently as you can into a saleable product,” Crennen adds. “In the challenging economy we’re facing right now, we’re not really interested in sitting on piles of material, or cash so to speak, for any extended period of time. We want to be able to move these products. The commercial market is flat in our region, so there’s not much desire to go out and create a new product or market niche for fear of having to sit on that inventory for an extended period of time. We want to make sure that there is a market and a need for the products we manufacture.”
In portable operations, the customer is usually a state or county agency — a public agency. The project specifications are very well defined in terms of quality and quantity, so Knife River goes out to find a source as close to the project as possible in order to be competitive. But finding a site can be difficult.
“In some places, the geology is such that there just isn’t material,” Crennen says. “We find that quite often. So you can end up hauling material a long way.”
When a project is put out for bid by an agency, Knife River studies geological maps of the surrounding area which show where the aggregate deposits are located. When an area containing the desired product is found, company employees called prospectors start knocking on the doors of local landowners to see if any of them have an interest in selling their gravel. If so, testing of the site begins.
“We’ll go in and test their site for both quantity and quality,” Crennen says. “You need to determine how much overburden there is on the pit so you know the cost of stripping it and getting to the aggregate. Of course, you need to know the sizing of the material in the pit, so you need to test for that to estimate your crushing cost. Then you need to ensure that the rock is of sufficient quality in terms of hardness and other quality features. Samples will be pulled and tested in a lab, all ahead of the bid letting.”
The permitting process follows. Since portable plants usually only operate for somewhere between two and 12 weeks, permitting is not as difficult as it is for permanent plants. It may only take three to four weeks for permitting depending upon the location, Crennen says. Knife River has a working relationship with many of the counties in the region and has established a solid reputation with them, so, in many cases, a single meeting with the county planning and zoning board can provide the authorization for the necessary permit.
The number of different products mined from the site depends on the project. “We may go in for one certain product, but if you have a project where there may be some road reconstruction or you’re building a two-lane road into a four-lane, there will be some base course material needed, also,” Crennen says. “You may have several aggregate piles for your bituminous paving — different products that you’re producing to build that blend. Then you might have a couple of different gradings of base products. Typically, no more than five or six products for a particular project.”
Sometimes, more work comes up in the area requiring a different paving gradation, so the operation may produce more products. But that’s not always a good thing.
“It’s not necessarily better to produce a bigger variety of product unless you get paid for it.” Crennen says. “More is not always better in the crushing business — in terms of product type — that’s the way I look at it. Producing more variety of products would, essentially, require more screenings and configurations of your crusher and, therefore, increase cost. If you can sit in a pit, produce one product, and sell everything you make, it doesn’t get any better than that. We want to crush what we need and use it and convert those piles of aggregate to cash. After all, cash is king.” AM