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access road configured and armored to facilitate the flow as it discharges into the sediment pond. 53. Appendix 10, Chicago Tunnel Site Detention Pond(p. 6) • The third paragraph implies that the entire 0.46 acre feet of storage capacity can be used to attenuate the peak flow. All spillways must be designed to pass the 100-year design flow assuming the pond is full to the lowest, non-gated, gravity flow outlet structure. So, unless there is a low level outlet,the detention pond must be assumed to be full to the spillway invert at the onset of the design storm. Please re-evaluate and re-design as appropriate all AM-I I ponds and their spillways with this approach. RESPONSE: The Sediment Pond is designed to contain two times the volume of runoff from a 10 year/24-hour storm (2 x 0.21 acre feet = 0.42 AF minimum), consistent with other EMP facilities at the site. Accordingly it is designed to contain, rather than attenuate, the storm runoff. The volume of a 100 year storm is 0.41 acre feet with over 1 foot of freeboard, and the peak inflow is 7.1 cfs. A low level outlet is not included because that would require special management,particularly if there is a spill from the portal, shop, or fuel depot. An 8 foot wide armored spillway at the one foot freeboard depth cut into the stream-side of the crest has been added to Drawing CCVSAI I-6. 54. Appendix 10, Integration of Chicago Tunnel Site (per • The last paragraph states "most of the facilities have been constructed to meet those criteria". Which facilities have not been constructed to meet the design criteria? RESPONSE: The primary sediment control facility at the Chicago Tunnel area is the Sediment Pond, which was designed and constructed to contain two times the volume of runoff from a 10 year/24-hour storm event and is consistent with other EMPs at the site. The sediment pond is the most important of the facilities since it is positioned to receive storm water discharges from the tunnel portal, the maintenance shop, and the fuel depots which constitute all potential pollutants except for sediment. Other features such as stream culverts were being upgraded at the time this report was written, hence the statement quoted above. 55. Appendix 10, Figurep. 8) • The schematic shows Basins PG-A1, PG-B1, PG-C1, and PG-F1 being routed to EMP- 09 until 2021,then after 2024 being routed to EMP-21. Where are these basins being routed to between 2021 and 2024? RESPONSE. EMP-09 has two purposes. Initially it will accept storm water from the pre-mining development of Schist Island. Beginning in approximately 2021 all of the four sediment basins comprising EMP-09 except for Basin EMP-09a will be removed by mining. When the North Cresson Mine is backfilled in that area (about 2024) the basins will be restored with similar size and capacity to accept stormwater from the backfill operations. Details of that restoration will depend on the real-time configuration of the backfill, so it is premature to provide a design at this point. Replacement of their function is the important factor. Accordingly, that period from 2021 to 2024 shown on the schematic is the time when there is no basin, and no need for sediment control. 56. Appendix 10, Revised Globe Hill Mine Perimeter • As alluded to in Comment No. 39b above, the proposed Globe Hill Mine pit interception of Poverty Gulch is potentially problematic. Plan views 1 through 13 on Drawing CCVSAI 1-10 include a callout for a"Bypass Pipeline", which is unacceptable for reclamation/closure design. Furthermore,the last bullet on p. 10 (Appendix 10) states "CC&V is evaluating an alternative design for a stream bypass system that will Page 25 of 30