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NORTHFIELD PROJECT <br />DRAINAGE AND SEDIMENT CONTROL PLAN <br />PREFACE <br />This drainage and sediment control plan has been prepared as a revision to the previously accepted <br />Northfield Project Drainage and Sediment Control Plan (latest revision May 2007) prepared by Applegate <br />Group, Inc. (Denver, Colorado). Hydrologic, topographic, and soil information from the original plan <br />was used in combination with new facility and site information to produce updated drainage and <br />sedimentation information for this revised report. The design information provided in this report is based <br />on the best and most recent site information available during report preparation. <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 19 South, Range 70 West of the 6th Principle Meridian. The proposed facilities will be <br />constructed adjacent to Chandler Creek and entirely within the Chandler Creek drainage basin. To <br />control stormwater run -off from disturbed areas, diversion structures, collection ditches, and a sediment <br />pond will be used to manage site drainage. A haul road will be constructed from Fremont County <br />Road 79 and across Chandler Creek to access the facilities. <br />Drainage and sediment control evaluations and design for the mining activities have been conducted to <br />address Section 4.05; Hydrologic Balance, and Section 4.09; Disposal of Excess Spoil, of the Regulations <br />of the Colorado Mined Reclamation Board for Coal Mining (Revised September 14, 2005). Once mining <br />and use of the facilities is complete, the reclamation plan proposes returning the majority of the disturbed <br />area to the approximate original topography. In general, drainage structures included in this report are not <br />anticipated to remain following reclamation. Only the South Run -on Diversion Ditch upgradient of the <br />mine waste stockpile is expected to remain following final reclamation of the site. <br />Design of the sediment pond and ditches was performed utilizing the SEDCAD4 computer model <br />program developed by Civil Software Design (September 2008). The SEDCAD4 model performs <br />hydrologic, hydraulic, and sedimentation calculations to provide run -off flow and sediment quantity <br />estimates. The model also provides sizing information for the design of drainage and sediment control <br />structures. <br />2.0 HYDROLOGIC CALCULATIONS <br />SEDCAD4 is a comprehensive, computer -based model used to evaluate stormwater run -off, erosion, and <br />sediment control management techniques. The SEDCAD4 model calculates run -off and peak flow with a <br />numerical modeling technique based on user inputs of a design storm event (i.e., rainfall volume, <br />duration, and distribution). Hydrographs are developed for each watershed (or subwatershed) based on <br />the watershed area, time of concentration, Curve Number, and a dimensionless storm -type hydrograph <br />shape. Calculated run -off is routed to various structures included in the model with the use of <br />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 />