17.24.806 ALLUVIAL VALLEY FLOORS: MATERIAL DAMAGE DETERMINATION
Criteria for determining whether a strip or under-ground coal mining operation will materially damage the quantity or quality of waters include, but are not limited to:
(1) potential increases in the concentration of total dissolved solids of waters supplied to an alluvial valley floor, as measured by specific conductance in millimhos, to levels above the threshold value at which crop yields decrease, as specified in Maas and Hoffman, "Crop Salt Tolerance--Current Assessment," Table 1, "Salt Tolerance of Agricultural Crops," unless the applicant demonstrates compliance with (2) of this rule. Salt tolerances for agricultural crops have been published by E.V. Maas and G.J. Hoffman, in a paper entitled "Crop Salt Tolerance--Current Assessment" contained in the Journal of the Irrigation and Drainage Division, American society of civil engineers, pages 115-134, June, 1977. Table 1, giving threshold salinity values is presented on pages 22-125. For types of vegetation not listed in Maas and Hoffman as specified by the department, based upon consideration of observed correlation between total dissolved solid concentrations in water and crop yield declines taking into account the accuracy of the correlations. This publication is hereby incorporated by reference as it exists on March 13, 1979. The Maas and Hoffman publication is on file and available for inspection at the Department of Environmental Quality, 1520 E. 6th Ave., Helena, MT 59620-0901;
(2) potential increases in the concentration of total dissolved solids of waters supplied to an alluvial valley floor in excess of those incorporated by reference in (1) of this rule. These increases are not allowed unless the applicant demonstrates, through testing related to the production of crops grown in the locality, that the proposed operations will not cause increases that will result in crop yield decreases;
(3) potential increases in the average depth to water saturated zones (during the growing season) located within the root zone of the alluvial valley floor that would reduce the amount of subirrigated land compared to premining conditions;
(4) potential decreases in surface flows that would reduce the amount of irrigable land compared to premining conditions; and
(5) potential changes in the surface or ground water systems that reduce the area available to agriculture as a result of flooding or increased saturation of the root zone.