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Mine 1, and underground discharge from the adjacent Foidel Creek Mine has converted <br />Foidel Creek from an intermittent stream to a perennial stream. Additional spoil aquifer <br />discharge may occur in Eckman Pazk azeas, thus the quantity of water ultimately supplied <br />to the Trout Creek AVF would be increased by a small amount. <br />As discussed previously, however, the elevated salinity of the spoil aquifer dischazge in <br />combination with underground mine discharge at the Foidel Creek Mine raises the <br />concern of material damage due to salt loading. <br />Rule 2.06.8(5)(6) of the Colorado Regulations specifically refers to potential increases in <br />electro-conductivity of water supplying AVFs [o levels above the threshold value at <br />which crop yields decrease as constituting material damage. The rule further cites a <br />specific paper by E.V. Maas and G.J. Hoffman of the U.S. Salinity Laboratory published <br />in the Journal of the Irrigation and Drainage Diversion, ASCE., June, 1977. <br />In their paper, Maas and Hoffman list research derived salinity threshold levels and <br />response rates for selected agricultural species and group those species as well as a <br />number of additional crops into four categories based on relative tolerance to salinity <br />(sensitive, moderately sensitive, moderately tolerant and tolerant). <br />The Division has taken the approach that a positive material damage finding would be <br />made if projected salinity increases resulting from mining would result in significant <br />decreases in production or shifts in species composition based on the Maas and Hoffman <br />paper. <br />On the Trout Creek AVF, TCC sampled, vegetative cover within a number of farmed <br />fields as denoted on Supplemental Map No. 36. Vegetative production, as well as cover <br />was sampled in one Feld, Pasture 11. A majority of [he species on the AVF would be <br />considered moderately tolerant, and on an acreage weighted basis only 18.4% of the <br />cover was made up of moderately sensitive species (salinity threshold reached at root <br />zone soil saturated paste extract electro-conductivity of 1500 umhos/cm). A number of <br />the species encountered have not been ranked by Maas and Hoffman, and other <br />references were consulted. In general, Aveneae tribe grasses and Trifolium species were <br />considered to be moderately sensitive, while Triticeae, Stipeae, and Poeae tribe grasses <br />(with the exception of Dact lis were considered to be moderately tolerant. Carex and <br />Juncus species were also considered to be moderately tolerant. <br />As shown in Table 13 of this document, projected Trout Creek water quality for flood <br />irrigation is approximately 500 umhos/cm. Assuming that a root zone saturated extract <br />soil salinity of 750 umhos/cm would result from flood irrigation water with a specific <br />conductance of 500 mmhos/cm, no decrease in crop production would occur. The <br />assumed relationship between irrigation water salinity and root zone soil salinity is within <br />the typical range reported in USDA Handbook 60. Based on leaching calculations <br />included in the application and soil sampling conducted on the Fish Creek AVF by the <br />3l <br />