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OXBOW MINING, LLC -TECHNICAL REVISION TR-43 II WEST COAL REFUSE FACILITY TECHNICAL ADEQUACY COMMENTS/RESPONSES 1) In the Section 8 culvert ruing table jar the IIW tulvertr, there it a footnote that rtater that `77W it derigned to parr the peak flow from a 100 year, 24 hour event". However, the peak flown tired far IIW culvert 1 and IIW errlverf 3 appear to be firm the 10year, 24 hour event. Pleare revue the footnote, if appropriate. Response: Culverts IIW-2, IIW-3, and IIW-5 are designed to pass the peak discharge from the 100- year, 24-hour event. Culverts IIW-1 and 4 aze designed to pass the peak discharge from the 10-yeaz, 24-hour event. The table has been revised to cleazly indicate the correct design basis and copies of the revised table accompany these responses for replacement in the Mining and Reclamation Plan document. 2f In the Section 8 culvert rin~ng table for the IIW culverh, culvert IIW-3 receiver flow from the Wert Valley Diverrion, which it a ditch derigned for the 100 year, 24 hour event. However, it appearr that the culvert it derigned tiring the 10 year, 24 hour event. Pleare explain or revue the nrlvert derign. Response: The CDMG is correct in noting this discrepancy. The design for Culvert IIW-3 has been revised to reflect the 100-yeaz, 24-hour flows. Copies of the revised culvert design information accompany these responses for replacement in the Mining and Reclamation Plan document. 3J In the channel deign table far the II Wert Coa! Before Facility, then it a footnote that rtater `Flown for II Wert rhannelr bared on the 100year/24 hour rtorm". However, the bemh channelr and IIW HR (Upper) and IIW HR (L.owerJ an derigned wring the l0year, 24 hour event. Pleare clarify the footnote. Response: The channel design table has been revised to clazify which channels are designed for the 100-yeaz event. Copies of the revised channel design table accompany these responses for replacement in the Mining and Reclamation Plan document. 4) The Divirion'r copy of the TR43 rubmitlal cantainr two different Sedcad design rarer for the clean water diverrian ditch. The fiat run nralted in a peak flaw of 10.66 cfr, while the second derign run nrulted in a peak flow of 11.89 cfi. Pleare explain. Response: A superceded design was inadvertently included in the submittal package. The superceded design has been removed from the updated design package that accompanies these responses for replacement in the Mining and Reclamation Plan document. 5) Pleare provide the Sedcad hydrology derignr jar IIW nrlvert 4. Response: Designs for Culvert IIW-4 have been included in the updated design package that accompanies these responses Eor replacement in the Mining and Reclamation Plan document. 6) On rheet 5 of 5 ojDrawing 2.05-M4, the natural rtream rymbol located in the narthwett corner ojthe IIW gob pile it rhawn to parr through the clean water diverrian ditch and onto the gob pile. Pleare revue the drawing to chow that the natural rtream ttopr at the diverrian ditch. Response: Map 2.05-M4 (Sheet 5 of 5) has been revised to show that the upland diversion (IIWHR (Upper)) intercepts the existing small ephemeral drainage above the II West Coal Refuse Facility. Copies of the revised map accompany these responses Eor replacement in the Mining and Reclamation Plan document.