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be very secure as the clays forming the overburden layer have begun the lithification process(turning <br /> into rock) and are not very prone to collapse. <br /> Between the overburden highwall and for a distance away from the wall a transportation <br /> corridor is often created that is bounded by the overburden highwall on one side and a 3 to 6 foot <br /> safety berm between the overburden highwall and the exposed gravel deposit to be mined and the <br /> mining highwall which can be 100 or more feet from the overburden highwall. This berm keeps <br /> people from driving vehicles too close to the taller and more dangerous mining highwall. <br /> This transportation corridor also provides a route for removal of overburden without having to <br /> construct haulroads on the original surface of land. Generally,the overburden is removed with a <br /> backhoe or front-end loader and, if necessary, loaded into trucks with a front end loader. Loaders are <br /> used more than dozers because the same equipment can be used to mine the gravel. It is more <br /> economical that way. If the area has a deep enough soil (A and upper B horizons)to effectively be <br /> salvaged, a dozer can strip that off first and that soil can be hauled away and stockpiled separately. <br /> Topsoil and Overburden Removal and Stockpiling <br /> A vertical cross-section of the land would show a thin and somewhat vague A-horizon in the <br /> soil that is usually only a few inches thick and has a slightly darker color than the material below it. In <br /> places the A-horizon can be up to about 18" deep in localized places. This is technically the topsoil, <br /> but its boundary with the soils below is often rather vague and more of a narrow transitional zone. <br /> Where this zone is fairly evident and deeper it is stripped and saved separately,but much more often <br /> that operation requires too much precision stripping to keep that material separate from the lower <br /> horizons down to the parent material which is usually right on the top of the gravels. In that case all of <br /> the soil/overburden is salvaged as a unit and blended together. Essentially, soil and overburden are <br /> pretty much the same in most places. This is quite typical of this whole area which is a bit closer to a <br /> high elevation desert than to a high elevation semi-arid grassland. Desert and semi-desert soils are <br /> usually poorly developed and poorly differentiated with only minor differences in chemistry and with <br /> the upper layer often having less than 1%organic matter. <br /> The overburden tends to be rather dense in texture and composed of aeolian deposits of fine <br /> silts and clays mixed with alluvial deposits. Over time it becomes rather blocky due to the types of <br /> clays and to water illuviation,but it breaks apart quite nicely upon salvage creating a silty-clay loam. <br /> (NOTE:Illuviation is a process where water soaking into the soil carries fine particles deeper into the <br /> soil leaving somewhat more coarse materials nearer the surface.) In places calcium carbonate <br /> dominated zones are found that produce local layers of white calcareous deposits that are not quite <br /> Fountain Pit Technical Revision#3 - June 2022 M-1982-155 Mining Plan Page 13 of 22 <br />