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could be when the primary or emergency spillways become blocked with debris during <br />intense precipitation events. <br />It should be noted that Colowyo's ponds are designed not to contain the 10-year, 24- <br />hourevent, but rather to treat it. These ponds are, for the most part, designed to have <br />a permanent pool of water within the pond up to the elevation of the pond's primary <br />spillway inlet. The ponds are further required to have the capacity to pass the l0-year, <br />24-hour event even when the pond is filled with water to the elevation of the primary <br />spillway inlet. Dewatering a pond to "regain capacity" should therefore only have to be <br />done so that a pond's water level is reduced down to the elevation of a pond's primary <br />spillway inlet, not so that a pond's water level is near the base of the pond. We believe <br />that if Colowyo elects to manually discharge a pond's water through the pond's <br />dewatering gate valves, rather than allowing the pond to self dewater by discharging <br />through the primary spillway inlet, Colowyo will need to demonstrate that the manually <br />discharged water is in compliance with primary effluent limitations. <br />7. With regard to language in the permit regarding water pumped from coal production <br />pits, please find enclosed a copy of an April 17, 1996 memorandum from CDPHE to <br />DMG (2 pages) regarding this matter. <br />8. It is stated in the Permit (page 11, seventh paragraph) that "samples and measurements <br />taken as required herein shall be representative of the volume and nature of the <br />monitored discharge". DMG suggests Colowyo's permit contain language requiring the <br />permittee to sample and analyze each manually-controlled discharge, to demonstrate <br />compliance with the language in the CDPS permit (page 5, second paragraph) that states <br />"All manual dewatering of ponds that are equipped with automatic dewatering systems <br />must meet TSS and total iron limitations". <br />9. The Division suggests the CDPS permit also contain language requiring the dewatering <br />of sediment ponds "be achieved in accordance with applicable State laws". This <br />language is found in our "Regulations of the Colorado Mined Land Reclamation Board <br />for Coal Mining" at Section 4.05.6(3)(c). This is impottant because in "Synopsis of <br />Colorado Water Laws" (May, 1991) published by the Colorado Division of Water <br />Resources, it is stated that "Erosion control reservoirs may be constructed with a <br />capacity in excess of two acre-feet if an ungated twelve inch minimum diameter outlet <br />tube is installed and the outlet is large enough to allow for draining within athirty-six <br />hour period any amount of water in excess of two acre-feet." <br />l0. With regard to Part I.A.3. of the Permit (page 5, third paragraph), DMG would <br />appreciate being informed of any proposed modification to this individual permit. The <br />Division requests this especially if the limitations may be modified as a result of mined <br />land reclamation activities. <br />I I. Assume a scenario wherein the volume of water (non-pumped, non-vehicle-washwater) <br />enters a pond during one 24-hour period, and [hat the volume of water was less than the <br />