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to be observed following spring runoff, but these discharges would be less significant due to the fact that much higher flows in the creek also occur at this time. Actual backfill discharges, as estimated from average low-flow .period (September) flows from Ponds A, D, and F during 1994, 1995, and 1996, have been higher than anticipated at approximately 660 gpm The major concern of increases in Foidel Creek solute concentration as a result ofmine-related discharges is the possibilih~ of material damage to downstream alluvial valley floor (AVF) areas. Irrigation of these AVF areas is from direct diversion of creek waters. Direct Diversion of Foidel Creek water is no[ presently practiced, nor has it ever been historically practiced. The first diversion of surface waters that could potentially be affected by tnitte- related discharges to Foidel Creek is at the Jefferson Ditch on Trout Creek downstream from the confluence with Middle Creek. A salt-loading analysis was perfontted in 1986 for "worst-case" conditions dusing low-flow periods for the Trout Creek drainage as part of the report entitled, Bucl~l! Hydrologic E'valuarion, Eckman Pnrk Mares. The results of the initial analysis are shown in Permit Renewal Table 1 I, Trout Creek Salt-Load Analysis, taken from the report. The results indicated that backfill discharge at Eckman Park and Mine # 1 might eventually cause an increase in TDS in Trout Creek of about 122 mg/I. This represented an increase of about 22% over baseline conditions. The • projected solute contributions from backfill discharge at the operation constituted about 16% of the total salt load in Trout Creek downstream from Middle Creek The salt-loading analysis was revisited and updated in January 1997, utilizing data compiled from [he 1994, 1995, and 1996 water years. The results of this analysis are shown in Permit Renewal Table 1 I A. The 1997 evaluation utilized the same assumptions as the 1986 study to characterize the "worst-case" scenario. No attenuating flows from Foidel Creek, Middle Creek, or Fislt Creek were considered. Average September monthly flow values from the preceding three-year period for monitoring stations 69 (Trout Creek, Upstream), I I~ (Foidel Creek, Mine Discharge). 39, 84, and 87 (Ponds A, D, and F -used to estimate backfill discharge flow) were utilized in the calculations. An additional 0.5 cfs flow was added to the backfill discharge from Pond A to account for withdrawals from this system currently utilized by Twentymile Coal Company. Average TDS concentrations for the same period and same monitoring stations were utilized with aflow-weighted TDS concentration calculated for the backfill discharge contribution. The results of the 1997 evaluation indicate that backfill discharge at Eckman Park and Mine # I might eventually • cause an increase in TDS in Trout Creek of about 655 mg/I, constituting approximately 62% of the salt load in Trout Creek Downstream from Middle Creek under the "worst-case" criteria defined. This represents an increase 1996 Permit Ren. Permit Renewal 780-144-26 Revised 3/18/97