2008-03-24_GENERAL DOCUMENTS - M2003016 (2)

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_~ Ma~o3~~~ C~L RES°JURCES, LLC EN GINEER9 & PLANNERS July 24, 2007 Mr. Joe Kraig Pioneer Sand Company, Inc. 3026 4"' Ave. P.O. Box 7650 Colorado Springs, CO 80933 RE: Helt Plt Stormwater Management Plan Dear Mr. Kraig: DECEIVED .~ ~I AR 2 4 200 -(0 : Division of Keclamation, Mining and Safety Civil Resources, LLC has completed our engineering analyses of the drainage and erosion control issues at the Heit Pit located in Section 13, Township 2 North, Range 67 West of the 6~ P.M in Weld County, Colorado. The Heit Pit is more commonly located as being approximately one mile west of Highway 85 and approximately 4 miles north of Highway 52. Refer to Figure 1. Drainage ditches, straw bales, riprap and silt fences will be used in this plan to direct storm flows on the site. Description of Property The property is located in Weld County, Colorado along Weld County Road 20.25 approximately 4 miles north of Highway 52. The property is bordered on the east by Weld County Road 25 on the south by WCR 20.25, and by Little Dry Creek to the west. The northern boundary is an irriga#ed tree farm. The property is approximately 100 acres in size and was historically an irrigated farm. Pioneer Sand Company is leasing the property and proposes to mine 60 acres of ht Site for sand and gravel in the near future. The existing Site topography is generally characterized as sloping northeast to the South Platte River at a 0.3 percent grade. According to the Soil Conservation Service report Soil Survey of Weld County, Colorado: Soufhem Part, the property soils are Aquolls and Aquents, Dacono clay loam, Altvan loam and Bankard sandy loam, see Appendix A, Exhibit A. Drainage Analysis The Site is located in between the Little Dry Creek Drainage and the South Platte River and is affected by both of these floodplains. The flood hazard development permit required by Weld County addresses the effects of flooding on the Site. Offsite runoff entering the Site is very limited because the basin naturally tributary to the Site located south of WCR 20.25 is below grade storage (Keonig Grave! Pit) and therefore is unlikely to produce significant runoff volume. Refer to Figure1. A diversion ditch is proposed along the south property boundary with a design flow of 20 cubic feet per second (cfs) and a sediment trap/outfall at the southwest comer of the proposed mining area. Runoff generated from on-site is also limited due to the proposed excavation associated with the gravel mining. The perimeter access road should be graded to drain toward the pit to reduce transport of sediment into the receiving streams. The drainage channels will have a minimum depth of 2 feet, have a 5 foot bottom width with 4 horizontal to 1 vertical side slopes. New channels will be designed with a 0.3 percent grade. Ditches have been directed around existing wetlands, straw bales will be used as a filter and sediment trap. Riprap protection should be provided in areas of high velocity to prevent erosion. Refer to Figure 2 and Figure 3. 323 57H STREET • P.O. Box 680 • FREDERICK, COLORADO 80530 • PHONE: 303.833.1416 FAX: 303.833.2850