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PERMANENT IMPOUNDMENT DOCUMENTATION <br />• In conjuncrian with Technical Revision TR-79, approved Januan• 11, 2000, the CDMG approved <br />retention of Sedimentation Ponds A, B, D, and E as permanent impoundments to support dte <br />pos[mining uses of rangeland and wildlife habitat. Under applicable provisions of Rule 4.05.9(73), <br />permanent impoundments must meet the following criteria: <br />a) The quality of the impounded water shall be suitable on a permanent basis for its intended <br />use, shall meet applicable state and federal water quality standuds, and discharge of water <br />from the impoundment shall meet applicable state and federal effluent limitations and shall <br />not degrade the quality of receiving water below applicable stream standards; <br />b) The level of water shall be sufficiently stable, and the configuration of the pond shall be <br />adequate to support the intended use; <br />c) Adequate safen• and access to the impounded water shall be provided for proposed wacer <br />users; <br />d) Water impoundmrnts shall not result in diminution of the quality or quantity of wacer <br />available to water rights holders for agricultural, industrial, recreational, of domestic uses <br />except in accordance with applicable state law; <br />e) The size of the impoundment shall be adequate for its intended purposes; <br />E) The impoundment shall be suitable for the approved postmitting land use. <br />• The following sections provide the required demons ration under Rule 4.05.9(13) for the approved <br />permanent impoundments. <br />a) Water Quality Suitability <br />Typical warer quality for the proposed permanent impoundments can best be projected based on <br />historical pond discharge monitoring data. Active mining operations ceased in January 1993 and final <br />reclamation of mine disturbance areas was compleeed in 1995-7996. With renewal of the CDPS <br />Discharge Permit in July 1997, discharge monitoring requirements were reduced to flow, pH, and <br />settleable solids. Based on review of water qualit}• monitoring records for 1995 through 2003, <br />maximum TSS and total iron values exceeded normal operational effluent limits under CDPS <br />Discharge Permit COG-850037 in ]995, ]996, and 1997. In all cases, however, potential exceedances <br />occurred under documented storm-flow conditions (i.e.: > 10•yeaz, 24-hour storm event). Under <br />these conditions, the "Active Mining Alternative limitations" are applicable. Under the alternative <br />effluent limitations, the normal effluent standards for TSS and iron are suspended and compliance is <br />evaluated on the basis of a settleable solids limit of 0.5 mg/l. In all cases, dischazge water quality was <br />in compliance with the applicable effluent standards. Table 1 summarizes available water monitoring <br />data for the sedimentation ponds for the period 1995-2003 and provides applicable effluent limits for <br />reference. <br />Runoff water quality for new]}' reclaimed areas typically improves as vegetation is reestablished, since <br />increasing vegetative cover reduces erosion and sediment transport. This is consistem with the <br />findings of the Hydrologic Reclamation Evaluation previously prepared and submitted in support of <br />Ken's Application for Pactia] Phase I and Phase 11 Bond Release (9/6/00, copy attached for <br />• reference). The Hydrologic Reclamation Evaluation was based on [he results of revegetation success <br />monitoring completed by ESCO Associates in 1999. Given the available wamr quality monnonng <br />data and the results of the Hydrologic Reclamation Evaluation, current and future runoff <br />contributions to the proposed permanent impoundments should meet applicable effluent standards. <br />Since the CDPS effluen[ limits are based, in pan, on receiving scream standards, degradation of the <br />receiving waters has not occurred and is not reasonably anticipated to occur in the future. Reasonable <br />