07/25/2007 Env Bd Packet - Laserfiche WebLink

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• • • be limited to the horizontal areas subject to prolonged wetting; and (c) A minimum of three feet of separation from the seasonal high water table. (ii) Permanent sedimentation and water quality ponds must be designed to provide: (a) Water quality features consistent with NURP criteria and District wet pond criteria; (b) A permanent wet pool with dead storage at least equal to the runoff from a 2.5 -inch rainfall over the area tributary to the pond; and (c) An outlet structure capable of preventing migration of floating debris and oils for at least the one -year storm. (iii) Detention basins must be designed to provide: (a) An outlet structure to control the two -year & 100 -year frequency events to pre - settlement peak runoff sites; and (b) An identified overflow spillway sufficiently stabilized to convey flows greater than the 100 -year critical storm event. (iv) An outfall structure discharging to a wetland, public water or public water wetland must incorporate a stilling- basin, surge- basin, energy dissipater, placement of ungrouted natural rock riprap or other feature to minimize disturbance and erosion of natural shoreline and bed resulting from stormwater discharges. (v) All new residential, commercial, industrial and other habitable or non - habitable structures, and all stormwater basins, must be constructed so that the lowest floor and lowest entry elevations comply with the following table: Within a landlocked basin, lowest floor elevations must be at least one foot above the surveyed basin overflow elevation. Where a structure is proposed below the runout elevation of a land - locked basin, the low -floor elevation will be a minimum of two feet above the high water level as determined from an estimate of high water levels determined from the highest of either the 100 -year, ten -day runoff event or back -to -back 100 -year, 24 -hour rainfalls. Aerial photos, vegetation, soils, and DRAFT DOCUMENT 13 Regional Elevations Local Detention Basins & Wetlands Infiltration Basins Mottled Soils 100 -yr EOF 100 -yr EOF Bottom 100 -yr EOF per borings Low Floor 2 -ft 1 -ft 0 -ft NA 0 -ft NA NA 3 -ft Low Entry NA NA 2 -ft 1 -ft NA 2 -ft 1 -ft NA Within a landlocked basin, lowest floor elevations must be at least one foot above the surveyed basin overflow elevation. Where a structure is proposed below the runout elevation of a land - locked basin, the low -floor elevation will be a minimum of two feet above the high water level as determined from an estimate of high water levels determined from the highest of either the 100 -year, ten -day runoff event or back -to -back 100 -year, 24 -hour rainfalls. Aerial photos, vegetation, soils, and DRAFT DOCUMENT 13