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<br />Additional data on allyv~al around water depth and quality for the area in <br />question has been provided in Table 67 of 'the roidei Creek Lire-of-i4ine <br />application. The presence of ground water at depths of 4.3 to 5.7 feet <br />suggests that sub-irrigation would be possible. Due to relatively high <br />salinities (up to 5.4 mmhos/cm) it is probable that the site would not be <br />particularly productive, however, vegetation information has not been <br />provided. Division staff conducted field visits to the site in May and <br />August, 1986, and it was observed that a silver sage community indicative of <br />sub-irrigation existed in a relatively narrow belt along the stream. Areas <br />further from the stream appeared to have been treated at some point in the <br />past and seeded recently to pasture grasses including intermediate wheatgrass <br />and timothy. Due to the age of the stand, annual weeds were quite numerous. <br />Dased on the water level information and vegetation observations which <br />indicate the presence of sub-irrigation, the Division concludes that the <br />alluvial body in question is an alluvial valley floor. <br />Information concerning significance of the AVF to farming has not been <br />provided. Therefore, the Division will proceed by assuming the area is <br />significant and will make the three required AVF findings. <br />1. The proposed mining operations would not interrupt, discontinue, or <br />preclude farming on the alluvial valley floor. <br />Proposed mining activity would not directly impact any portion of the ;"F, as <br />it is outside of the proposed permit area and would not be disturbed by the <br />proposed operation. <br />2. The proposed mining operations would not cause material damage to the <br />quantity and quality of surface and ground water that supply the alluvial <br />valley floor. <br />Since this area was designated an AVF on the basis of sub-irrigation, it is <br />necessary to maintain the quantity and quality of water which supplies the <br />alluvial ground water system. <br />In the findings previously issued by the Division for the Foidel Creek Mine <br />(pilot project) in 1983, it was projected (based on information available at <br />that time) that concentrations of dissolved constituents such as sodium, <br />sulfate, iron and TDS would increase in the alluvial ground water. This <br />effect was predicted based on the assumption that Foidel Creek surface waters <br />affected by mine water discharge would recharge the alluvium. <br />However, data from a recent survey of the stream channel through the alluvial <br />body (Foidel Creek Life-of-i4ine Application Table 68) indicate the deposits <br />underlying the channel are clays and silty clays with very limited <br />permeability. TCC presented evidence that, due to the limited permeabilities, <br />recharge of the alluvium by Foidel Creek would be insufficient (5 x 10-4 <br />gal/day /sq.ft. of channel) to provide enough water to support sub-irrigation. <br />Evidence indicates that the alluvium in the vicinity is recharged from upper <br />Williams Fork sandstone units which occur 10-20 feet below the valley <br />surface. As result, alluvial waters would not be impacted by the increased <br />levels of dissolved constituents in Foidel Creek resulting from high TDS <br />underground mine-water discharge and i4ine 1, Eckman Park and Little i4iddle <br />Creek spoil aquifer discharge. <br />25 <br />