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overburden volume. Studies conducted by the federal government show that up to 20 percent of <br />potentially toxic material in a truck-and-shovel operation would be diluted to acceptable levels. <br />Twenty-three of the samples exceeded the Montana guidelines suspect levels for molybdenum. <br />Wyoming does not have a suspect level for molybdenum. Studies indicate that a field <br />occurrence of toxicity does not exist with respect to molybdenum. All surface water and <br />groundwater samples evaluated by the mine are below the detection limit. <br />Sodium Adsorption Ratio (SAR) values in 38.6 percent of the samples were above the suspect <br />level of 15 described in the Wyoming guidelines. The weighted average value is 8.74. Many of <br />the samples were contaminated with drilling mud, drilling foam, or other drilling fluid. Kerr <br />Coal Company cited a study that showed that drilling fluids dramatically increase SAR values <br />above samples taken from a highwall or drilled with air. None of the drill holes were drilled <br />using air; therefore, all samples were deemed contaminated, and their value for determining SAR <br />found questionable. Acid-Base Potential analysis did not indicate a potential problem with acid- <br />forming material. Overall, the interpretation of the overburden analysis showed that only nickel <br />and selenium were found at levels that were of any concern and that the mixing of the <br />overburden during haulage would dilute the few samples that were in the suspect range. A <br />discussion of the analysis and interpretation can be found on page 779-16a of the permit <br />application packet. <br />Groundwater <br />There are predominantly three aquifers of interest in the Marr permit area: the Sudduth coal <br />aquifer, upland terrace deposits, and alluvial deposits. The coal aquifer has moderately poor <br />yields, except where it is faulted. The water is slightly alkaline and total dissolved solids <br />concentrations average 500 mg/l. The water is acceptable for stock and limited domestic use. <br />For discussion of upland terrace deposits, see the April 15, 1993 addendum to the December 9, <br />1992 Findings of Compliance for Permit Renewal. <br />Alluvium is found sporadically along all draws draining the mine site, next to the Canadian <br />River, and adjacent to the Illinois River near the loadout. Monitoring has been performed along <br />the draw and adjacent to the loadout on the Illinois River. The discontinuous alluvium within the <br />draws draining the Marr permit area is predominantly composed of clay with isolated sand and <br />gravel lenses. However, the permeability of the alluvium adjacent to the Illinois River is much <br />higher and is estimated to be 2,500 gallons per day per square foot (gpd/ft2). <br />Surface Water <br />The surface water hydrology of the general area, including the mine plan area, consists of the <br />high altitude, semi-arid environment found in the upland parks of the Central Colorado Rocky <br />Mountains. The average annual rainfall for the area is 11 inches. The major soil moisture <br />9