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<br /> <br />-z- <br />is believed that surface manifestations would include tension cracks, a <br />general lowering of the surface (worst case = 6 feed , and possible subsidence <br />"holes". (See Subsidence vortion of [his TA.) This Dotentia.l subsidence and <br />incidental impacts Co the ephemeral drainage are believed by ~SF1 to not he <br />significant because if tension cracks did form in the channel of the ephemeral <br />stream they would tend to "heal° themselves over time due to the nature of the <br />slialy material underlying the ephemeral drainage (thus limiting water <br />inflow). However, tension cracks may interrupt stream flow for a period of <br />time and general lowering of the land surface and local Failures (e.g., holes <br />or small depressions) may adversely affect the stream's gradient. <br />In terms o.f the overall effect to surface water resources, OSM believes [he <br />impact on the ephemeral drainage due to subsidence to be of limited extent due <br />[n the reasons noted above and [he fac[ that flows from this drainage are of a <br />very limited extent and no direct water users (except further downstream along <br />Hubbard Creek) have been identified. 'Co detect any impacts on the ephemeral <br />drainage, tl~e applicant proposes a surface water monitoring station on this <br />drainage at the Point oL intersection of the stream and the southern Federal <br />lease boundary. Therefore, some baseline data will be collected prior to the <br />nu111ng of pillars. This monitoring, in concert with the required subsidence <br />monitoring, should detect any effects to this drainage and iE they should <br />prove to be signif ir_a nt, mitigation measures will he i.mplemen[ed (e.g., a <br />subsidence control plan). <br />Based on the applicant's statements and the limited analyses, OSM finds that <br />the operation is in, conformance with Che surface water protection provisions <br />of 30 CFR 817. <br />