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RULE 4 PERFORMANCE STANDARDS <br /> In accordance with Rule 4.05.9(13), the permittee may retain impoundments to be permanent to <br /> support the post-mine land use. The Gulch A Pond has been requested by the surface landowner <br /> (please see Volume 213, Exhibit I B) to remain as a permanent impoundment. Inlcuded with this <br /> request and part of the Gulch A watershed the surface landowner also requested that the East Side <br /> Collection Ditch remain as permanent structures. The Gulch A Pond in it's current configuration <br /> (which will also be the post-mine condition) meets the requirments of Rules 4.05.9(13)(a) — (f). <br /> The Gulch A Pond has not exhibited any water quality issues with any discharges from the pond. <br /> The normal water level in the pond is typically well below the primary discharge elevation. The <br /> surface landowner has adequate access via a road from State Highway 13 to the pond, and the size <br /> of the Gulch A Pond is adequate for livestock watering which is the intended post-mine use. <br /> 4.05.10 Underground Mine Entry and Access Discharges <br /> Colowyo currently conducts surface coal mining exclusively. <br /> 4.05.11 Ground Water Protection <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 /> 4.05.12 Protection of Groundwater Recharge Capacity <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 /> The history of the ground water monitoring plan is further documented in 4.05.13. The mine has <br /> not established Point of Compliance locations for ground water monitoring because of a lack of <br /> ground water. The following discussion is provided to document this: <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 /> Rule 4 Performance Standards 4-15 Revision Date: 4/29/19 <br /> Revision No.: MR-201 <br />