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July 1993 -38- 923-2515 • <br />The following equation (CD4LRD 1988) is used to calculate material damage: <br />Y =relative yield <br />Y = 100 - B (ECS-AW), where: <br />B = percent yield decreases per unit salinity increase <br />ECS =Predicted conductivity of water (mmhos/cm), and <br />AW =Salinity threshold of irrigation water (mmhos/cm) <br />The values for "B" and "AW" are from Table 1 of the CMLRD guidance document (1988). <br />The relative yields for the small grains based on predicted changes in TDS loads are: <br />Wheat <br />Y = 100 - 7.1 (ECS-4) <br />(moderately tolerant) Y = 93.63 <br />Barley Y = 100 - 5.0 (ECS-5.4) <br />(tolerant) Y = 102.52 <br />= 5.9% difference <br />= 3.9% difference <br />Post-mining productivity for the 12 acre field is estimated to be 20.8 to 22.0 bushels per acre <br />of wheat and 26.1 to 27.7 bushels per acre of barley. <br />Hockett Brothers and Hockett Farms have a total of 2,000 acres in small grain production <br />(Hockett 1993). Assuming all 2,000 acres would be in either wheat or barley in a given year, <br />the percent reduction in yield is estimated to be less than 1%, well below the 10% criterion for <br />a large scale operation (CMLRD 1988). The overall impact of the predicted increase in TDS <br />of the alluvial water will, therefore, be negligible. <br />• <br />• <br />Golder Associates <br />