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geologic structure is such that the coal seam outcrops at the top of the mountain and dips at 18 to 25 percent, while the overlying surface dips at approximately 18 to 20 percent, as shown by E:chibit 12-1. • This results in overburden thicknesses ranging from 15 to 100 feet, which lends itself to area surface mining. The relatively high angle of dip on the coal seam and surface requires some modification of what would be considered a conventional area mining pit progression. This modification will be detailed later in this section. A general description of the engineering techniques utilized in the development of an area surface mine must begin with the exploratory phase. After the initial discovery of a potential coal field has been made (generally by drilling several "wildcat" test holesl, engineers and geologists, utilizing available maps and information, will establish an exploratory drilling program [o "prove up" the coed reserves. The drill hole pattern is determined and is normally based on some convenient breakdown of the public land survey system. Additional drilling is conducted where the coal is expected to outcrop or where faulted conditions are expected. Then survey crews establish baseline control in order to loc;rte the drill holes and property corners. With this survey control available, the area of interest can be contour mapped from aerial photography. With an accurate base map and all of the necessary drilling information, the engineers can calculate the various factors necessary to establish a mining plan. In area surface mining, these factors would include acres of coal available, tons of recoverable coal expected, cubic yards of overburden to be removed, and the ratio of cubic yards of overburden removed per ton of coal produced. These factors and others are examined in the light of prevailing market conditions and a determination made as to the potential economic viability of a mine. Once a • positive determination is made and an annual output established for the mine, the engineers are required to determine the size, type, and numbers of equipment or facilities needed, including topsoil removal equipment, primary stripping machines, drills, dozers, loaders, haulage equipment, reclamation equipment, coal handling facilities, and service facilities. Standard mine engineering practices, including the examination of contour maps, borings, range diagrams, and manufacturer's specifications, are utilized in sizing the major stripping machines. Ouantities of soils to be moved las determined by soil surveys) and the distances and travel conditions involved are used to determine fleet type and size for topsoil handling equipment. Overburden borings, indicating type and amount of rock, as well as expected production rates are examined in sizing blasthole drills and pit tractors. Quantities of coal and rate of production are the major determining factors in sizing loaders and haulage equipment. The type and numbers of reclamation equipment are dependent on a number of factors, including quality and quantity of spoil material to be graded, distances spoil must be moved, projected postmine contour configuration, and weather conditions. Type and size of the coal processing facility are based upon the quality and quantity of coal produced, the type of processing required, and the transportation facilities available to handle the finished product. Service facilities such as shops, office buildings, warehouses, bathhouses, powder storage, electrical supply lines, and water lines are designed to be in conformance with all applicable State and Federal safety regulations. Table 12-1 lists the major equipment currently planned for use at Seneca II-W, 2 Revised 9/98