2020-08-20_PERMIT FILE - C2009087 (2)

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RULE 2 - PERMITS RN15-01 2.05-96.1 Revision 10/17 provide passive treatment. Ongoing monitoring has documented the effectiveness of these measures in mitigating elevated selenium levels. In 2014 the Water Quality Control Commission (WQCC) granted a temporary modification of the chronic selenium TVS in both Cow Camp Creek and Grassy Creek to current conditions to allow PSCM to collect additional biologic and water quality data necessary to develop site-specific standards. In 2015 the WQCD incorporated new flow limits, compliance locations, and revised selenium limits into PSCM NPDES permit CO0048275. PSCM appealed portions of the permit including the application of flow limits for discharges that are the result of natural hydrologic processes and the implementation of water quality limits at locations prior to final treatment that do not acknowledge ambient concentrations. PSCM’s appeal remains ongoing. Nevertheless, PSCM has continued to pursue the refinement of the flow limitations through continued collection of flow measurements at the outfalls and resolution of the appropriate selenium standards for the receiving streams during the pendency of its permit appeal. In 2017, the WQCC extended the selenium temporary modification for Grassy Creek to 12/31/2022 and the temporary modification to Cow Camp Creek to 12/31/2023 to allow for additional data collection. In May 2019 the WQCD incorporated the extension of the selenium temporary modification into permit CO0048275. In June of 2019, PSCM provided an update to the WQCC on the status of the temporary modifications during the Regulation #33 rulemaking hearing, at which time the WQCC determined it was appropriate to maintain the existing temporary modifications selenium. In order to conserve available soil resources, vegetation and soil materials will be removed from all new mine disturbance areas prior to disturbance. While beneficial in terms o f soil conservation and provision of a suitable growth medium to support final reclamation and revegetation efforts, this practice exposes underlying materials to potential erosion and loss, can increase suspended sediment levels in the runoff water, and may increase sediment contributions to area drainages. To maintain effective surface drainage, mitigate erosion, prevent loss of surficial materials, and minimize additional contributions of suspended solids to area drainages, PSCM will route undisturbed drainage around disturbance areas, grade and stabilize disturbed areas to provide for effective drainage control, establish a drainage and sediment control network to collect and retain runoff from disturbed areas, reclaim disturbance areas as soon as operationally practical, and utilize other specific locali zed drainage and erosion control methods as necessary. These activities are discussed further in the following sections. In conjunction with mine development, facility installation, and ongoing coal re fuse placement, PSCM will grade, stabilize, and maintain all disturbed areas to provide for effective drainage and minimize potential erosion. Where appropriate, PSCM will utilize localized grading and stabilization measures to effectively control and route drainage and minimize flow velocities. Examples would include graveled surfaces and the yard area drainage system in the mine facilities area; diversion/collection ditches; and drainage control berms utilized to isolate disturbed area drainage. Localized drainage control and grading measures will be supplemented by PSCM’s drainage and sediment control network. This network consists of diversion ditches which route undisturbed runoff around or through disturbance areas, collection ditches which intercept disturbed area runoff and route it to sedimentation ponds, the sedimentation ponds, and associated discharge structures. The drainage and sediment control system is described in Section 2.05.3, Ponds, Impoundments, and Diversions, and design information and calculations are provided by Map 2.05.3-M4, Drainage and Sediment Control Plan, 2.05.3-M5, Operational Channel Profiles, and by Exhibit 2.05.3-E2, Drainage and Sediment Control Plan. The drainage and sedimentation control network will collect