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-to- Creek Tipple. The areal extent of the isolated alluvial unit is approximately 6 acres. The 6 acre area of alluvium upon which the tipple was constructed does not qualify as an alluvial valley floor due to the size of the farmable unit. Office of Surface Mining Guidelines have recommended that alluvial bodies of less than 10 acres in areal extent be excluded from consideration as AVF's due to constraints with respect to farming operations. Information provided by the Soil Conservation Service and contained in the application supports the negative determination. Since the area was less than 10 acres, a regional practices study was not required. Areas of unconsolidated streamlaid deposits along Fish Creek, located geographically adjacent to the tipple facilities, could potentially be affected. The applicant's discussion of probable hydrologic consequences indicates that discharge from the tipple sediment pond is expected to increase the dissolved salt load of Fish Creek until final reclamation. Since water from the Fish Creek stream/alluvial systems drains to Trout Creek, both these areas must be considered in the alluvial valley floor determination. Alluvial Vallev Floor Determination Map 7 of the permit application shows that the capability for flood irrigation exists within and adjacent to the proposed permit area. The Boettler Ditch derives water from Fish Creek upstream from the proposed permit area and has been used to irrigate the Fish Creek flood plain. Several irrigation systems exist on the Trout Creek flood plain upstream of the confluence of Fish Creek and Trout Creek. As part of the permit application, no flood irrigation has been identified immediately downstream. However, Trout Creek is a perennial stream with stream flow water yields and water quality capable of supporting flood irrigation as evidenced by the upstream flow water yields and water quality capable of supporting flood irrigation as evidenced by the upstream flood irrigation systems. Also visual observations by Division personnel verify the use of flood irrigation on the Trout Creek flood plain downstream. In order to evaluate the potential for subirrigation within the proposed permit and adjacent area, the applicant conducted a study on subirrigation capability in the flood plain of Fish Creek. Based on this study, the applicant found that subirrigation does not occur. The study was conducted in October, 1980. The Division does not feel that the study is representative of S~ the entire growing season. Therefore, the results of this study reported in J the permit application are not sufficent for the Division to conclude that (~ subirrigation does not occur during a major portion of the growing season. J l~ ~~ Furthermore, since base flow in Fish Creek is sustained by ground water it can be inferred that there is a potential for subirrigation within the proposed permit and adjacent area. Based on available information, the unconsolidated streamlaid deposits of Fish and Trout Creeks are found to be alluvial valley floors because of the current or historical existence of flood irrigation and the presumed capability of these areas to support subirrigation during a portion of the growing season. A described previously, a 6 acre parcel of the Fish Creek alluvium west of the Railroad tracks within the permit area is excluded.