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Fred R. Banta, Director August 10, 1990 <br /> MLRD, Denver, CO 80203 Page 5 <br /> a sediment pond shall not relieve the person from <br /> compliance with applicable effluent limitations. . . <br /> To analyze the problems that occurred Mid-Continent <br /> employed a hydrologist, Edward E. Rovey, P.E. , Denver, Colorado, an <br /> independent consultant. Based on analysis of the inflow to the <br /> ponds from the mine, Mr. Rovey calculated that the ponds would have <br /> some 800 days after pond cleaning before the sediment storage <br /> volume was occupied and pond cleaning would again be required.' <br /> Mr. Rovey analyzed published National Weather Service (NWS) <br /> and Coal Basin weather data for the period. He noted that from <br /> December 1, 1988 until February 12, 1989, the average daily <br /> temperature at the Coal Basin operations never rose above freezing. <br /> He concluded that the extended period of cold weather had caused <br /> development of a thick layer of surface ice. <br /> In addition, he believed that the ponds froze from the <br /> bottom and sides upward as well from the top downward. This is a <br /> condition, known as "anchor ice, " that occurs in Arctic <br /> environments comparable to the alpine and sub-alpine conditions in <br /> Coal Basin. Mr. Rovey concluded that the extreme weather <br /> conditions caused the ponds to freeze from the top, sides and <br /> bottom inward. The ever accumulating ice occupied otherwise <br /> available treatment space in the ponds and reduced the detention <br /> time of water discharged from the mine and resultant sediment <br /> deposition. <br /> J. Scott Jones, a Professional Engineer and a Mid-Continent <br /> employee, observed the cleaning of the 016 ponds. He saw the <br /> dragline removing large slabs of ice from the ponds confirming Mr. <br /> Rovey's conclusion. <br /> Absent the unusually severe weather conditions, the <br /> consequent malfunctioning of the Outfall No. 016 ponds would not <br /> have occurred even with increased water and/or sediment loading. <br /> Confronted with the problem of malfunctioning ponds in the dead of <br /> winter, Mid-Continent made, as acknowledged in the Justification <br /> 1 Mr. Rovey's calculation was based on a sediment inflow rate <br /> of two tons per day and a storage volume of 1.5 acres feet in the <br /> ponds, or a calculated 65, 000 cubic feet of available sediment <br /> storage capacity. <br />