There are three major considerations that are a prerequisite to opening a new aggregate plant: 1) Supply and demand in the local market area; 2) the type of deposit to be mined and the processes required to mine it; and 3) obtaining the permits necessary to operate the site.

Selecting a site for a new aggregate operation begins with a study of supply and demand. Each region has a baseline demand for aggregate that responds to a continuing need for highway, road and street maintenance and construction. Superposed on this need are requirements of the cities and towns—requirements that are proportional to urban size and growth rates. Transecting all these requirements are special demands of major construction projects such as interstate highways and airports. Such projects often require large quantities of aggregate in relatively short periods of time.

Because aggregate is a high-bulk, low-cost commodity, the transportation cost to the site of use is a significant part of the total cost. Therefore, natural aggregate commonly is used within 30 to 50 miles of the place of extraction. Ultimately the supply area is controlled by the geology of the area, ownership of the land, zoning or other land-use restrictions, and transportation routes. Rural counties and their communities commonly attempt to obtain aggregate within their boundaries.

In contrast, urban areas generally meet their needs from surrounding areas. These urban areas act as distinct markets, and the demand for aggregate may greatly exceed the availability of material in the surrounding areas. Major construction projects generally need aggregate for only certain phases of construction and, therefore, it may be necessary to transport aggregate great distances to guarantee its supply.

All of the users of aggregate may compete for a supply from the same sources, and major construction projects may significantly disrupt an otherwise predictable market.

Estimating supply

Potential sources of crushed stone and sand and gravel may be extremely large, but specific land-use considerations, socioeconomic considerations, or the physical or chemical properties of the materials may limit the utility of these sources. Unless the distribution, availability and quality of aggregate are known, it is difficult to formulate a reasonable plan to set aside or develop aggregate. Therefore, in planning for future aggregate need it is necessary to determine the reserves for the planning area.

Even before field investigations begin, a geologist or an engineer with geologic experience commonly conducts a preliminary evaluation. In an urban area, the maximum economically feasible shipping distance from the market area commonly defines a crude target area.

In areas where aggregate is in short supply, the target area obviously must be much larger. Geologic and topographic maps and geologic and engineering reports aid in targeting promising areas or, conversely, aid in ruling out areas for further study. State geological surveys and highway departments and the U.S. Geological Survey can provide much of this information.

Considering the costs

Preliminary investigations may be followed by detailed studies involving aerial photography, geophysical studies and field-reconnaissance studies of the target areas to more accurately define the limits of the potential sources of aggregate. These field studies focus on natural exposures such as stream cuts, cliffs and other natural outcrops and on artificial exposures such as highway and railroad cuts, and abandoned or active pits and quarries.

These studies commonly are augmented by the use of hand-sampling techniques and portable power-auger or coring equipment. Also important are rough estimates of the areal extent and volumes of the deposits, as well as specific physical or chemical properties of the materials. Laboratory analyses provide additional information about the physical and chemical properties of specific samples. Field observations should include information related to mineralogy and texture of the materials, thickness of overburden, water availability, and road access to the area.

Detailed exploration of an identified source of aggregate may vary depending on the nature of and intended uses of the aggregate. Bulldozers, loaders or backhoes are used to collect bulk samples; bulk sampling of bedrock may require drilling or blasting. Truck-mounted power augers or drill rigs can be used to collect deeper underground samples.

In addition, seismic refraction may be used to determine the thickness of overburden and thickness of desired material, and electrical resistivity may be used to determine gross textural changes within the deposit, such as changes from gravel to sand or shale to sandstone.