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3.10 Boron • <br />Boron is an essential minor element required for plant growth. Concentra- <br />tions range from 0.1 to 1.9 ppm in the overburden and 0.1 to 2.4 ppm in the <br />underburden. Boron levels are highest for coal and carbonaceous shale <br />scrota. Concentrations are generally between 0.1 and 0.5. Most agronomic <br />crops require at lebst 0.4 ppm boron. Therefore, spoil boron concentrations <br />are not toxic and will be adequate for successful reclamation. <br />3.11 Selenium <br />This nonmetal ranged from<0.01 to 0.32 ppm in the overburden and<0.01 to <br />0.12 ppm in the underburden. The higher concentration increments are <br />generally shale stata immediately above or below coal seams. These levels <br />of selenium are not inhibitory to successful reclamation. Normal soils <br />contain from 0.1 to 2 ppm total selenium and from 0.01 to 0.5 ppm water <br />soluble selenium (CSMRI, 1977). <br />3.12 Mercury <br />This nonessential element ranges from <IO to 230 ppb in The overburden and • <br />from <10 to 26 ppb in the underburden. The higher levels of mercury gen- <br />erally occur near the surface. The mercury content of soils is often very low <br />and averages approximately 100 ppb (CSMRI, 1977). Mercury levels at <br />Seneca are consistently less than 100 ppb. Therefore,. no reclamotion pro- <br />blems are anticipated. <br />3.13 Cadmium <br />Cadmium levels in the overburden range fromm.05 to 1.69 ppm while values <br />in the underburden range from<0.05 to 0.13 ppm. Concentrations are gen- <br />erally between 0.05 and 0.10 ppm. Higher cadmium levels are associated <br />with carbonaceous shale and organic matter in the topsoil. Cadmium levels <br />within the range described above is considered normal and nontoxic to plants <br />and animals. <br />3.14 Co er <br />Plant available copper in soil should average from 2 to 9 ppm (CSMRI, 1977; • <br />USDA, 1957). At Seneca, copper levels range from 0.4 to 11.6 ppm in the <br />overburden and 0.2 to 3.9 ppm in the underburden. The highest copper <br />Gov a s 15~, <br />6-147 <br />