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permit application demonstrates the pond is an efficient sediment control structure, <br />although less than 24 hours of detention is provided given the principal spillway design. <br />The pond receives inflow from up slope spoils aquifers which have developed in the old <br />Wadge spoils. Surface runoff detained in the pond is considered to dilute the <br />concentrations of total dissolved solids (TDS) in spoils inflow and may serve to <br />improve water quality in general. This pond is in compliance with the requirements of <br />Rule 4.05.6 and continues to meet National Pollution Discharge Elimination System <br />(NPDES) effluent limitations. Since the pond does not provide at least 24 hours <br />detention time, the following finding is in order; <br />Alternative design criteria have been approved for use in sediment pond design and/or <br />construction. This decision is based on a thorough analytical demonstration by a <br />qualified professional engineer that the resulting pond will be as environmentally sound <br />and structurally stable taking into consideration physical, climatological and other <br />chazacteristics of the site. (4.05.6(11)). <br />Northwest Impoundment (003) A second pond is located in the Grassy Creek basin and <br />serves to control runoff and sediment from the shop and office azea. The Northwest <br />Impoundment was permitted as a permanent impoundment which drains an area of 30.5 <br />acres and has a permanent pool of 5.1 acre-feet. This pond also receives dischazge from <br />a truck washing facility after the water has been treated. An increase of total dissolved <br />solids on the order of 1500 mg/I (from 1500 to 3000) was observed between 1983 and <br />1991 in the effluent from this pond. This increase is attributable to the truck-wash <br />facility. A review of the pond performance indicated a reduction in the size of the <br />principal spillway to a 6 inch orifice was necessary to provide sufficient detention time <br />to increase sedimentation within the pond and produce effluent within NPDES <br />limitations. The orifice was reconstructed in 1987. With this revised design, the pond <br />was in compliance with the design standards of Rule 4.05.6 and continues to meet <br />NPDES permit requirements. <br />Pond 004 Pond 004 was constructed in 1982 when mining progressed into the Fish <br />Creek basin in the southeast part ofthe permit azea. Pond 004 is located on Cow Camp <br />Creek and drains an area of 393 azeas. The pond has a permanent pool of 10 acre-feet. <br />Pond 004 is permitted as a permanent impoundment. <br />Pond 008 Pond 008 was constructed in the Fish Creek drainage basin in a tributary <br />referred to as Bond Creek. NPDES discharge site 008 replaced 007, which was mined <br />through. Pond 008 drains an area of 247 acres of which 226 acres is disturbed. The <br />pond is designed to provide storage fora 10-yeaz, 24-hour precipitation event with <br />2.1 acre-feet of runoff and has a capacity of 16.4 acre-feet. Pond 008 is permitted as a <br />permanent impoundment. <br />PeCoCo Impoundment The PeCoCo impoundment was constructed in 1987 in a <br />watershed that is tributary to Little Grassy Creek. The embankment was constructed to <br />control the water level and dischazge of the impoundment. The watershed was <br />15 <br />