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RULE 4 PERFORMANCE STANDARDS <br /> <br />Rule 4 Performance Standards 4-15 Revision Date: 8/21/24 <br /> Revision No.: MR-259 <br />of the Streeter Pond [Rule 4.05.9(13)(d)]. The post-mine land use for Colowyo is Rangeland and <br />Wildlife habitat. Given this, the Streeter Pond provides an exceptional water source for livestock <br />and wildlife which will support both of those post-mine land uses for the Streeter Pond [Rule <br />4.05.9(13)(e)]. <br /> <br />4.05.10 Underground Mine Entry and Access Discharges <br /> <br />Colowyo currently conducts surface coal mining exclusively. <br /> <br />4.05.11 Ground Water Protection <br /> <br />There are no aquifers or continuous sources of ground water within the stratigraphic section from <br />which the Colowyo Mine mines coal using surface mining techniques. This is also noted in Section <br />2.04.7. In addition, there are no continuous aquifers of regional extent within the entire Williams <br />Fork Formation in the location of the Colowyo Mine. Occasionally, a minimal amount of water <br />is found under perched conditions in noncontiguous lenticular sandstones and in fractured coal <br />under the sandstones. No toxic concentrations of acid forming materials have been found in the <br />overburden, reclaimed slopes or surface and ground water system associated with the Colowyo <br />Mine. No adverse effects on groundwater quality are expected to occur due to mine excavations <br />or backfilling. <br /> <br />4.05.12 Protection of Groundwater Recharge Capacity <br /> <br />The reclamation plan as described in 2.05.4 will return the disturbed lands to approximately the <br />pre-mining condition; therefore, ground water recharge capacity is expected to approximate the <br />premining condition. Also, because of the minimal existence of ground water in the mining area, <br />the mining operation and subsequent reclamation should have no adverse effect on the existing <br />ground water recharge capacities. <br /> <br />The ground water monitoring plan is further documented in 4.05.13. The mine has established <br />Point of Compliance locations for alluvial and valley fill aquifers. Please refer to Volume 2C, <br />Exhibit 7, Item 19 for a description of the alluvial aquifer investigation report and the points of <br />compliance wells for Goodspring, Taylor, and Wilson Creeks. There are not established points of <br />compliance for any regional aquifers because of a lack of ground water. The following is provided <br />to document this: <br /> <br />The aspect of monitoring ground water is dependent on whether or not there is a <br />continuous, non-perched ground water layer/zone to monitor. Since active mining at <br />Colowyo Mine began 30 years ago, the mining zone in both the East and West Pits have <br />not encountered any significant ground water, except for perched ground water. Therefore, <br />the following is presented to clarify the ground water conditions at the Colowyo Mine. <br /> <br />Geology/Topography <br /> <br />The Colowyo Mine is located in the Williams Fork Formation of the Cretaceous Mesaverde <br />Group. The Williams Fork Formation is comprised of discordant beds/units of sandstone,