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mineralized to the point of forming a caliche. These are usually at about one to two feet deep in the <br /> overburden but can vary. They too break up and mix into the general mass quite well. <br /> In some places,horizontal darker colored seams are found of various thicknesses at different <br /> depths in the overburden. These are likely local paleosoils that developed during brief wet periods in <br /> the history of the soil development when illuviation was vigorous and biological activity high. They <br /> are usually thin and are simply salvaged with the rest of the material. Some of these even have <br /> carbonized roots or twigs left indicating at these times the vegetation here was perhaps a shrub <br /> dominated with a rich grass understory. The shrubs were probably Salix(willow) and Alnus (alder) as <br /> today those genera are often abundant on glacial outwash plains. However,because the streams were <br /> undoubtedly braided, as shown by the extreme variability in the texture of the gravel,these vegetated <br /> areas probably did not last long before being ripped out by floods and channel shifting. Thus they are <br /> not common or large. <br /> Thus the material that is salvaged(soil+overburden) is quite similar to the overall mineral <br /> components of the native topsoils but without much structural differentiation or layering into <br /> distinctive horizons. In the past this material has produced good growths of both introduced and native <br /> species. Over time the native species tend to gain higher dominance on the soils while the introduced <br /> species and many native pioneer weedy species tend to decline considerably. This material has <br /> sufficient minus-200 particle content to retain moisture quite well and has a moderate to locally high <br /> water holding capacity,but can be erodable on steeper slopes if near the surface. Grass vegetation <br /> tends to limit erosion fairly well, but shrubs are often ineffective and tend to encourage rilling. On <br /> level land where grass is moderately dense, duff accumulates quite well which acts as natural mulch <br /> that keeps available water fairly high within a depth that plant roots can reach effectively. However, in <br /> general this is a dry steppe environment that favors grassland and deep rooted herbaceous plants that <br /> are drought tolerant. <br /> With these characteristics it is entirely possible to simply transfer salvaged soils and <br /> overburden on to areas that are completed with mining while stockpiling some for use elsewhere as <br /> needed. It appears that replacement to produce a total plant growth medium depth of about 8" to 12" is <br /> sufficient to establish good growth using the fines on the top to hold sufficient moisture to support the <br /> vegetation prior to their roots reaching more deeply into the more coarse substrate to acquire moisture <br /> and nutrients deeper or the water of perched aquifers. In short, it produces a thinner version of the <br /> natural soil without the blocky texture which will develop with time as illuviation sorts the particle <br /> sizes,but still sufficient depth to protect moisture from evaporation through strong capillary rise. <br /> So, in summary,the soil is stripped from a new mining area down to the gravel layer and either <br /> used immediately or stockpiled near areas that are being mined so the soil can be spread soon after the <br /> mining is finished in that area and the area is no longer needed. <br /> Fountain Pit Technical Revision#3 - June 2022 M-1982-155 Mining Plan Page 14 of 22 <br />