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The standard for production in Reclaimed Irrigated Pastureland was converted to a reference <br />area by TR -58, approved in 2009. The justification and data for this change can be seen in this <br />subsection 4.5. <br />4.5.1 Irrigated Pastureland Reference Area Soil Production Factors <br />Jim Boyd, the local NRCS representative, reviewed the capability of all soils in the reference <br />area and in the reclaimed area and assigned a relative factor to each of these soils. This letter is <br />included in Attachment 2.05.4(2)(e)-11. As can be seen from the letter, some soils are more <br />productive than others. The soil types are based on the USDA - NRCS Soil Survey of San <br />Miguel Area, which was compiled in the field from 1978 to 1984. The report was published in <br />1986. This survey can be obtained on the internet at: <br />http://offices.usda.gov/scripts/ndISAPI.dll/oip_public/USA—map. <br />Assignment of a relative production factor to each soil type allows for the calculation of an <br />acreage weighted relative production factor for the entire reference area, and for an entire <br />irrigated pastureland bond release block (based on the soil types in the bond release block prior <br />to mining). <br />Table 2.05.4(2)(e)-2 shows how the weighted average production factor for the reference area is <br />calculated. The same procedure is used to calculate a weighted average production factor for an <br />irrigated pastureland bond release block. Narrative following the table explains how the <br />weighted average factors are used to adjust the reference area sample mean for bond release <br />comparisons. The adjustment procedure elevates the production success standard in situations <br />where premining soils were potentially more productive than reference area soils, and lowers the <br />standard in situations where pre mine soils were on average potentially less productive than <br />reference area soils. <br />January 2015 TR -66 2.05.4(2)(e) - 21 <br />