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NORTHFIELD PROJECT <br />DRAINAGE AND SEDIMENT CONTROL PLAN <br />1.0 INTRODUCTION <br />Northfield Partners LLC has proposed the development of underground coal reserves approximately <br />3 miles west of the town of Florence in Fremont County, Colorado. Processing, storage, and transfer <br />facilities for the Northfield Project will primarily be located in the northwest quarter of Section 13, <br />Township 19S, Range 70W of the 6~' Principle Meridian. The proposed facilities will be constructed <br />adjacent to Chandler Creek and entirely within the Chandler Creek drainage basin. To control <br />stormwater run-off from disturbed areas, diversion structures, collection ditches, and a sediment pond <br />will be used to manage site drainage. A haul road will be constructed from Fremont County Road 79 <br />and across Chandler Creek to access the facilities. <br />r Drainage and sediment control evaluations and design for the mining activities have been conducted <br />to address Section 4.05; Hydrologic Balance, and Section 4.09; Disposal of Excess Spoil, of the <br />Regulations of the Colorado Mined Reclamation Board for Coal Mining (Revised September 14, <br />' 2005). Once mining and use of the facilities is complete, the reclamation plan proposes returning the <br />majority of the disturbed area to the approximate original topography. In general, drainage structures <br />included in this report are not anticipated to remain following reclamation. Only the South Run-on <br />Diversion Ditch upgradient of the mine waste stockpile is expected to remain following final <br />reclamation of the site. <br />Conceptual design of the sediment pond and ditches was performed utilizing the SEDCAD4 <br />` computer model program developed by Civil Software Design (January 2004). The SEDCAD4 <br />model performs hydrologic, hydraulic, and sedimentation calculations to provide run-off flow and <br />sediment quantity estimates. The model also provides sizing information for the design of drainage <br />and sediment control structures. <br />The design information provided in this report is understood to be conceptual and not for <br />construction purposes. Final sizing and design of drainage and sediment control structures should be <br />incorporated into the final site grading plan and performed with additional information from on-site <br />geotechnical material sampling and testing and detailed topography. <br />2.0 HYDROLOGIC CALCULATIONS <br />SEDCAD4 is a comprehensive, computer-based model used to evaluate stormwater run-off, erosion, <br />and sediment control management techniques. The SEDCAD4 model calculates run-off and peak <br />flow with a numerical modeling technique based on user inputs of a design storm event (i.e., rainfall <br />volume, duration, and distribution). Hydrographs are developed for each watershed (or <br />subwatershed) based on the watershed area, time of concentration, Curve Number, and a <br />dimensionless storm-type hydrograph shape. Calculated run-off is routed to various structures <br />included in the model with the use of Muskingum routing parameters. <br />Inputs to the hydrology component of the SEDCAD4 computer model include: <br />• Storm Type <br />• Design Storm <br />• Rainfall Depth <br />