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• <br />By minimizing the extent of surface disturbance, EFCI effectively limits <br />potential changes in existing surface drainages. Because the Southfield <br />operation is an underground mine, associated surface disturbance is <br />limited relative to the total permit area. Mith a permit area of <br />approximately 2,800 acres including both mine and loadout areas and a <br />total surface disturbance of approximately 100 acres, surface disturbance <br />constitutes less than four (4) percent of the permitted area. <br />During mine development and facility installation, Dorchester constructed <br />a diversion to route the Magpie Creek drainage around the disturbance <br />area. This diversion is designed to minimize potential mining related <br />impacts on Magpie Creek and -was designed and constructed as a permanent <br />diversion to minimize erosion and additional contributions of suspended <br />solids to drainage flows. While it was originally designed as a permanent <br />structure, the original design criteria for Magpie Creek only met <br />subsequent regulatory standards for temporary diversions. In order to <br />comply with current regulatory provisions for permanent diversions, EFCI <br />plans to make appropriate modifications to the Magpie Creek diversion in <br />conjunction with site reclamation. <br />Vegetation and topsoil are removed from all mine facilities areas prior <br />to disturbance. This practice, while necessary to preserve topsail <br />resources, exposes underlying materials to potential erosion and <br />consequent material Ions. In order to minimize erosion and prevent lass <br />of surficial materials, which can result in increases in TSS in the runoff <br />water, EFCI routes undisturbed drainage around disturbance areas, grades <br />disturbed areas to provide for effective drainage control, has established <br />a drainage and sediment control network to collect and retain disturbed <br />area runoff, reclaims disturbance areas as soon as operationally <br />practical, and utilizes other specific localized drainage and erosion <br />control methods as necessary. <br />EFCI has constructed and maintains both temporary and permanent diversion <br />ditches to intercept and route drainage from disturbed areas around the <br />area of surface disturbance. Temporary diversions are designed to pass <br />peak flows resulting from at least a 10-year, 24-hour storm event with a <br />2.05.6-16 <br />