2009-10-16_PERMIT FILE - M2009082 (13)

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Commissioners. This affects portions of the land owned Sally A. Parsons and Livingston Leigh Livestock of Weld County, LLC. For the names of all property owners and those within 200 feet of the Parsons Mine property boundary see Appendix C. The site has historically been used as irrigated agricultural land and rangeland with approximately 98 percent pervious cover. On-site soils are 14 percent, 53 percent, 7 percent, and 26 percent Hydrologic Soil Groups A, B, C, and D, respectively according to the Soil Survey for Weld County, Colorado, Southern Part by the Soil Conservation Service (Appendix A). Portions of the site are within a Zone A floodplain according to the Federal Emergency Management Agency (FEMA) Flood Insurance Rate Map (FIRM) Community-Panel No. 080266- 0608-D, dated September 27, 1991 (Appendix A). The Corps of Engineers completed a Flood Insurance Study in October 2003 for the Cache la Poudre River in the vicinity of the Parsons site. This study is currently under review by FEMA but has not yet become the effective study. For the purposes of this Flood Hazard Development Permit, the 100-year floodplain and floodway boundaries of this pending study will be adopted as the best available information. The 100-year floodplain, floodway, and Base Flood Elevations (BFEs) are shown on the Firmette presented in Appendix A. DRAINAGE BASIN AND SUBBASINS Major Basin Description The Parsons Mine site is located in the lower portion of the Bracewell Basin. The Bracewell Basin is an unstudied basin that is located east of the Law Basin and west of the Coal Bank Creek Basin. Subbasin Description The existing drainage conditions at the Parsons Mine site are presented in Figure 1 and Exhibit 1. The existing historical drainage conditions were modeled as nine subbasins, Hl through H9. All the subbasins, with the exception of Subbasin H9, return storm water directly to the Cache la Poudre River once leaving the Parsons Mine site. Subbasin H9 passes storm water onto an adjacent property to the east. Portions of the site have historically been irrigated from the Whitney Ditch. All laterals on the site will be abandoned for both mining and reclamation phases of this project. Each existing drainage subbasin is described in more detail below. Subbasin H1 contains approximately 194 acres. The boundary extends from the north bank of the Cache la Poudre River in the southwest corner of the property north to the slough that runs through the property then northwestwards to the Whitney Ditch near its intersection with WCR 23 and from the intersection of the property with the Cache la Poudre River northwestwards to the Whitney Ditch near its intersection with WCR 23. The divide for drainage entering the slough provided the eastern boundary of this subbasin. The subbasin encompasses most of the Northwest One-Quarter of the Northeast One-Quarter of Section 36, and the Southeast One-Quarter of Section 25. The slope is generally between 0.5 percent and 2.0 percent with a subbasin average of 0.8 percent. -2- Revised P¢liminary Dminagc Rcport.docx