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I. 7.2 Criteria To qualify as a Small Area Exemption (SAE), runoff from disturbed ground must not exceed effluent limitations during a 10-year 24-hour storm event of 0.5 milliliters/liter (tnl/1) of peak settleable concentration (SSp) of sediment (reference Rule 4.05.2, Division of Minerals and Geology). The diversions around surface developments need to pass the 2-year, 24-hour storm event [Rule 4.05.3(2)]. This analysis designs these diversions to pass the 10-yeaz, 24-hour storm event. A portion of Ditch D-1 is partially located above the development waste pile (the subject of a separate 5AE) that requires protection from a 100-year, 24-hour precipitation event (Rules 4.10.3(2) and 4.09.2(7). The circumvential ditches around the Topsoil Storage Pile need to pass the 2-year, 24-hour storm event [Rule 4.05.3(2)]. This analysis designs these ditches to pass the 10-year, 24-hour storm event. A 0.3 foot of freeboard for diversion ditches is required by the Division of Minerals and Geology [Rule 4.05.3(7)(b)]. 1.3 Project Description • The project consists of three parts (SAE facilities): a Fan Bench, a Staging Area, and a Topsoil Storage Pile. 1.3.1 Location Locations are shown on Drawing LPG-103F, 7/29/94, Lone Pine Gulch Fan/Portal Bench Design. 1.3.2 Configuration Enclosure 1 (modified S Sep 95) is a map (1' = 200') which portrays the three SAE elements. Enclosure 2 is a map (1" = 2,000', an extract of the Somerset, CO, 1:24,000 USGS Topographic Map Quadrangle) that indicates the general outlines of four watersheds that extended beyond the limits of the larger scale map and Watershed 1. The drainage system is described by a number of watersheds, ditches, culverts, and vegetative debris filters. Characteristics of the features are presented in Enclosure 3. The Topsoil Storage Pile is located immediately below an existing road. The road ditch (Ditch D-1) protects the Topsoil Storage Pile (and the Development Waste Pile) from runoff from • (Lone Pine Gulch SAES Demonstration, 12 October 95, Page 2 of 13)