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-8- viz. Alluvial yallev Floors (2.06.8, 6.24) Identification: The initial application did not include a discussion of the presence or absence of an alluvial valley floor. The Division therefore recuired that the applicant conduct an investigation to affirmatively demonstrate the absence of AZZuvial Valley Floors in the 'affected' area. The applicant responded by submitting an investicative study that demonstrates no Alluvial Valley Floors exist within the mininc or adjacent affected area. To define the 'affected' area the applicant first considered the maximum extent of drawdown which is 0.5 miles for the life-cf-the-mine. However, t~is assumption would only hold true if the transmissivity of the backfilled area was identical to the pzemining overburden. Since it is uni:no»n what the actual post-mining transmissivity will be, the applicant assumed twe worst-case conditions: I) That the post-mining permeability is zero and 2J that the permeability is infinite. Usino an equation by tdcWhorter (Md+'horter, et al. 1979. Surface and Subsurface Water Quality Hydrology in Surface Mined D;atersheds, EPA-600/ i-79), the applicant predicted a worst-case affected distance of 3.2 miles. Since no changes in water cuaIity could be felt Greater than this distance, the applicant used ttis distance as the maximum probable affected area. No stream laid deposits holding streams were found within this study area. Since the Division agrees with the applicants results trat show no Alluvial Valley Floors within the affected area, the folio»dng findings required by section 1.06.8(5) of the regulations and 36-33-114(2)(e)(I) of the Act can be ' made. Findings: 1. The proposed surface coal mining operations would net interrupt, discontinue, or preclude farming on an alluvial valley floor. (2.06.8(5)) 2. The proposed surface coal mining operations would not materially damaoe the quantity and quality of water in surface and underground water systems that supply alluvial valley floors or portions of alluvial valley floors. 3. The proposed operations will be conducted in accordance with section 4.24 and all other applicable requirements of the Act and these rules. 9. Any change in land use of the Lands covered by. the proposed permit area and adjacent area, from its post-mining use in or adjacent to alluvial valley floors will not interfere with or preclude the reestablishment of the essential hydrologic functions of the alluvial valley floor. VIII Water Rights and Replacement (2.06.7(3), 2.05.6(3), 2.07.6, 4.05.15) The opera lion is being conducted in the South Platte River Basin which is over appropriated, therefore any new use of tributary ground water would be very junior and could only occur if a plan of augmentation has been approved by the Water Court or the State Engineer in emergency situations. Although the applicant states that replacement water would be replaced if a "call" exists, the replacement of water must be included in a formal Plan of Augumenta- tion. Informal or verbal agreement to do so is unacceptable to the Division and Lhe Colorado Division of Water Resources.