Kansas Geological Survey, Public Information Circular (PIC) 6
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Kansas Geological Survey, Public Information Circular (PIC) 6
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Next Page--Regulatory and Environmental Issues
Lightweight aggregate is manufactured from certain types of shale. After mining and crushing, the shale is fed into a kiln where it is heated to temperatures that cause it to swell. Although best known to the average Kansan as the lightweight, red to brown, volcanic-looking rock that is often used for landscaping, its main use is as an aggregate in lightweight concrete, such as in the terminal buildings at the Kansas City International Airport in Missouri, and in lightweight concrete blocks. The only active plant is located near Marquette in McPherson County.
Sand and gravel are formed by the weathering of rocks. Most of the sand in Kansas river systems, such as the Kansas or the Arkansas, comes from rocks that have been washed out of the Rocky Mountains to the west. These rocks are weathered (broken, ground up, and rounded) as they are carried along by the rivers, producing sand and gravel. Kansas rocks also contribute to sand deposits in some locations. For example, chert (or flint) from rocks in the Flint Hills weathers and forms sand that is carried into the Neosho River, which drains part of the Flint Hills.
Much of the sand and gravel production in western Kansas comes from small, dry pits where front-end loaders are used to fill trucks (fig. 3). Other operations, particularly in central and eastern Kansas, produce large amounts of sand and gravel by dredging the channel or neighboring floodplains of the larger rivers, especially the Kansas and Arkansas.
Figure 3--Small gravel pit in geologically recent materials near Sand Canyon in Cheyenne County.
River dredges operate by suctioning sand from the river bed and moving it to a plant on the river bank for washing and sorting. River dredging is a relatively inexpensive method of producing sand because it does not require the removal of overlying rock and soil, called overburden. River dredging is also considered, by some, to be self-healing, because the space left by sand removal is gradually filled by sand from upstream or sediments that settle out when the river is moving slowly, a process called recharge. This material may be dredged later.
Other dredges operate on the floodplain--the land space neighboring the river that is inundated during flooding--which may contain considerable deposits of sand and gravel. In floodplain dredging, a pit is dug in land on the floodplain. Ground water fills the pit, and a dredge is floated on the water, again removing sand from the bottom for processing. Sand produced by a floodplain dredge may cost about 50% more than sand produced by river dredging because floodplain dredging has greater start-up costs. Land must be purchased or leased, and a large, shallow, sloped pit must be excavated to the water table before putting the dredge in place. Also, floodplain dredging usually requires the removal of up to 20 feet of overburden, adding to production expenses. Pits have a limited lifetime because the deposit usually changes to a less sand-rich body or the sand becomes too fine. Pits are not refilled with new material, as are river bottoms, and they require reclamation when mining is complete.
Nearly all Kansas counties have at least one sand and gravel operation (see fig. 1). As with crushed stone, most sand is produced in counties with large populations, where both the source and the demand are located. Between 1984 and 1994, for example, the population of the 12 counties along the Kansas River grew by over 125,000. This growth increased the demand for aggregates, particularly sand and gravel, for use in building roads, schools, homes, and other buildings.
Across the state, use of sand and gravel has increased dramatically, from about 1,200 pounds per person in 1920 to 9,200 pounds in 1990. Total statewide production grew from about 1,000 tons to about 11.5 million tons today. Production may have dropped slightly since the 1980's, in part because the U.S. Army Corps of Engineers gradually implemented limits on Kansas River dredge operations during 1991-94. These restrictions limited the removal of sand to the amount that was recharged. This is to stabilize the elevation of the riverbed to prevent the exposure of features such as pipelines.
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Kansas Geological Survey, Public Outreach
Web version Jan. 1997
http://www.kgs.ku.edu/Publications/pic6/pic6_2.html