2010-11-16_PERMIT FILE - M2010055 (6)

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October 18, 2010 Mr. Clay Kimmi Weld County Public Works Department 1555 North 17th Ave. Greeley, CO 80631 Re: Drainage Letter - Konig Borrow Pit Mr. Kimmi, s ! SELINE ---- iarior.ffao The purpose of this letter is to document drainage conditions associated with the Konig Borrow Pit Use by Special Review Permit application. Background The site is located in the NW 1/4 of Section 11, Township 10 North, Range 62 West of the 6rn P.M., Weld County, Colorado. The purpose of the proposed borrow pit is to extract fill dirt material to be used for construction of access roads and pads for oil and gas operations in this area. The proposed pit boundary is 35 acres and will be mined in two phases. Porter Creek is an intermittent drainage located 950 feet to the east of the proposed pit boundary. This area has not been mapped by FEMA. Refer to the Mining Plan and Reclamation Plan Maps for more information. Off-Site Drainage Attached is an Off-Site Drainage Map that shows the proposed pit boundary, location of adjacent county roads, and delineation of the off-site drainage basins. Also attached are calculations for off-site flows associated with these basins. Basin 01 is approximately 6.3 acres and is located to the north and west of the pit. This basin is bordered to the north by Weld County Road 120 which is a paved road. The south half of the paved roadway is included in this basin. There is a roadside ditch along the south side of CR 120. There are no cross culverts at the intersection of CR 120 and CR 81. There is no defined roadside ditch along CR 81 in this area. Therefore it was assumed that flows will cross CR 81 and flow towards the east within the existing depression located along the north boundary of the pit. Flows within this basin are generally in a sheetflow condition to the southeast over moderately sloping agricultural land. A diversion ditch will be constructed along the north side of the pit to capture these off-site flows from basin 01 and prevent these flows from entering the pit. The diversion ditch will transition back to existing grades at the north central corner of the pit boundary, returning flow to existing conditions. This diversion ditch will be 1 foot deep with a 1 foot wide bottom and 3:1 sideslopes, which will convey the 100-yr flows for basin 01. Basin 02 is approximately 2.3 acres and is located to the west and north of the pit. Again there is no defined roadside ditch along CR 81 in this area. Therefore is assumed that flows from this Corporate Headquarters High Plains Wyoming Rocky Mountains Denver West Once Park Building 4 Downtown Greeley Montgomery Building Pentagon West Building 1536 Cole Boulevard, Suite 220 71011th Avenue, Suite 105 109 East 1r Street, Suite 1 2740 Acre Lane, Suite 205 Golden, Colorado 80401 Greeley, Colorado 80631 Cheyenne, Wyoming 82001 Steamboat Springs, Colorado 80487 Ph 303.940.9966 Ph 970.353.7600 Ph 307.635.1734 Ph 970.879.1825 Fax 303.940.9959 Fax 970.353.7601 Fax 866.242.9106 Fax 866.242.9106