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continue under the variance of Rule 4.05.6 granted previously by the Division <br />as provided for by Rule 4,05.5(2). The design of Pond 001, the largest pond <br />located at the base of disturbed area on Tuttle Draw, has been modified and <br />the revised design meets the requirements of Rule 4.05.6. <br />The ditches and culverts which route runoff on the mine site were reviewed and <br />were determined to meet design requirements. A variance from the culvert <br />spacing requirements was granted by the Division at the time of initial permit <br />approval in 1983. This variance is no longer required based on a change of <br />Rule 4.03.1 (4)(e)(vi) effective June 26, 1985. A reexamination of the culvert <br />specifications in the revised drainage system indicates that same culverts <br />will pass the design flow with a head of water, Based on information <br />submitted in the application, it was determined this condition specified in <br />tie regulations would not cause increases in erosion, Therefore, a variance <br />from the headwater design requirements as provided by Rule 4.03.1 (4 )(e)(vi) <br />can be approved by the Division. <br />Surface water quality conditions prior to mining could not be determined at <br />the Nuc1a Mine as mining occurred prior to arty water quality monitoring <br />requirements. Surface water data collection was initiated in 1975 and is <br />planned to continue throughout the life of the mine. These long-term data <br />records will identify any pattern of water quality change. A comparison of <br />recently collected data (1986) to data available from 1979 has indicated no <br />significant change in dissolved constituent concentrations during this period <br />of time. Total Dissolved Solids (TDS) has been identified as the water <br />quality condition of primary concern of the Nucla Mine. TDS concentration at <br />the downstream monitoring station has remained the same during this period at <br />similar flow conditions in Tuttle Draw. A further discussion of water quality <br />is presented in the probable hydrologic consequences and cumulative hydrologic <br />impact section of this document (Section IX). <br />With the acceptance of the stipulation, the operation is in compliance with <br />the requirements of this section. <br />VI. Ground Water I{ydrology - Rules 2.04.5, 2.04.7, 2.05,6(3} and 4.05 <br />Information pertaining to the occurrence and quality of ground water may be <br />found in Tab 7, Volumes 3 through 6 of the permit application. <br />Peabody has conducted an extensive investigation to determine the quality and <br />quantity of ground water in the vicinity of the Nucla Mine. Currently, <br />thirteen wells at the site monitor the underburden, coal, overburden, and <br />spoils. Ten of these wells were in existence prior to 1980 while three were <br />completed in 1986. The ten pre-1980 wells indicate that ground water <br />occurrence within the Dakota Sandstone in the vicinity of the mine is <br />limited, In general, ground water occurs in small, laterally discontinuous <br />aquifers within the overburden, as well as alluvial/colluvial materials along <br />Tuttle Draw. <br />Information obtained from monitoring Melts at the site indicate that leakage <br />from upgradient irrigation ditches supply the ground water recharge to the <br />mine site. As such, almost all of the monitoring Melts reflect a seasonal <br />variability which coincides with flow in the irrigation ditch. <br />-12- May 6, 1988 <br />