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water is applied in excess of what is necessary for the species grown, and this <br />excess leaches the soil profile, thus making the assumed relationship between soil <br />salinity and irrigation water salinity a worst case assumption. The applicant <br />proposes that no decrease in production of any of the species currently grown on <br />the Trout Creek AVF would be expected unless the conductivity of the irrigation <br />water were to exceed 1 mmhos/cm. Based on species composition data submitted, <br />the applicant predicts that significant production decreases (>3% for a farm unit) <br />would not occur unless irrigation water salinity were to exceed 2.0 mmhos/cm. <br />Given the factors involved, the Division finds it is appropriate to propose an <br />irrigation water material damage suspect level of 1.5 mmhos/cm for Trout Creek, <br />from the confluence of Middle Creek to the Yampa River. Establishing the <br />suspect level at 1.5 mmhos/cm acknowledges the evidence submitted by the <br />applicant while maintaining a reasonable suspect level established through <br />research and application. <br />As a result of TR-32, the applicant has proposed a plan to discharge mine water <br />only when the stream has the dilution capacity to maintain waters at or below the <br />discharge points on Fish Creek and Trout Creek to 1.5 mmhos/cm. In summary, <br />projected flood irrigation water quality is 1.230 mmhos/cm and material damage in <br />terms of productivity declines would not be expected unless water salinity were to <br />exceed 1.5 mmhos/cm. <br />Given the minor effect of mine discharge on Trout Creek surface water quality, a <br />specific projection of alluvial ground water impact was not made. Since alluvial <br />recharge would occur in late spring and early summer when dilution due to <br />snowmelt runoff is at its peak, it follows that alluvial waters (and thus <br />subirrigation) would be less affected by mine discharge than Trout Creek surface <br />water (and flood irrigation). <br />3. The proposed operation would preserve the essential hydrologic functions of the <br />alluvial valley floor. <br />The essential hydrologic functions of the Trout Creek alluvial valley floor have <br />been identified as the capacity to support subirrigated and flood irrigated <br />agricultural activities. <br />The proposed plan would not result in any surface disturbance or undermining of <br />the Trout Creek AVF. Also, as discussed previously, no material damage would <br />result from changes in the quality of surface and ground water that supply the <br />alluvial valley floor. Thus, the essential hydrologic functions of the alluvial valley <br />floor would not be affected by the proposed operation. <br />Foidel Creek Mine 45 June 4, 2010