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Mr Midve' BmJay <br />Dici¢m of Mv+erals aril Gmlo~ <br />Jarwmy 28, 1999 <br />Pate 13 <br />timothy and smooth brome. Therefore, a 25 percent mixture each of these four crop species will <br />be utilized to estimate yield values. The relative yield for the imgated grass hay crop species can <br />be calculated from the following equation (Banta, 1988): <br />Y =100 - B(ECw - At>>) <br />where: Y =relative yield (percent); <br />B =yield decrease per unit salinity increase (percen[); , <br />ECw = predicted conducuviry (imgation water) (rrunhos/cm); and, <br />Aw =Salinity threshold (imgation water) (mmhos/cm). <br />Variable values and results are swnmarized in Table 17-43a, Summary of Projected Impacts to <br />Downstream Imgated Crops. Results suggest a total crop reduction of 3.3 percent, slightly <br />greater than the 3.0 loss criterion for small operations presented in the CMLRD guidance <br />document cited. However, the 0.3 percent discrepancy between the estimated value and the <br />guidance standard is easily within the margin of error inherent in the equation, especially since <br />variables presented for two of the potential hay grasses present (smooth brome and timothy) are <br />experimental values not yet accepted by industry. Also, crop reduction will be partially offset by <br />increased summer stream base flow. The spoil aquifer upstream acts as a reservoir, decreasing <br />spring run-off but increasing summer base flows. <br />Comment 35 -The "Rcgicvwl lmul Use Map"pnntdal in Tab 4 does not shoal irrigate! /mtds altng Dry G~k <br />and Nzrblrrxvt Guldt v/nd~ are sEourt in Exhibit 16-1. please revise tix "R~ianal Laird Use Map" to include all <br />!oral irrigate!/arrtls. <br />Please refer to the section titled, "Premining Land Use", on page 5 of the narrative for this tab. <br />SCC states that land use associated with the proposed Seneca II-W coal mining operation was <br />examined at two different scales: (1) Regional Patterns; and (2) Adjacent Areas and Mine Pemut <br />Area. For regional patterns, the narrative is discussed on pages 6 through ]0 and utilizes Figure 1, <br />Regional Land Use Map. Likewise, for adjacent areas and mine permit area, the narrative is <br />discussed on pages 10 through 15 and utilizes Exhibit 4-1, Land Use. The irrigated lands along <br />Dry Creek and Hubberson Gulch are depicted on Exhibit 4-1. This exhibit was overlooked by <br />SCC in the original submittal and has been revised to show the additional permit boundary <br />associated with this pemtit revision. Because of the scale differences between Figure 1 and <br />Exhibit 4-1, 1"=10,000' and 1"=2,000' respectively, and the relative size of these two areas they <br />would simply not show up on Figure 1. Therefore, SCC believes the information depicted on the <br />respective items should suffice. <br />Comment 36 - We am muiervng the strrfam ~ertter salinity lading cirlaJatians for Dry and Sage Cr»ks, re/atite to <br />dx QoraJatite lfjridogic Assessment for tle Yrmxpx Basin. Additiaml injanrwtion reluests may le fonamda! to <br />SCC f questions arise cGrrvzg tins trtierax <br />Thank you for the update. SCC has updated salinity calculation and predications for Dry Creek, <br />see revised pages 93 and 94, Tab 17. <br />