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The trend of decreasing recharge va figures are more representative of material has consolidated vegetation Most of the recharge occurs during which usually occurs from mid-April piration is low. lues indicates that the lower • recharge after the backfill has become more established. the spring snowmelt period to mid-June when evapotrans- Discharge rate information from the Pond F Spring and the Area 2 is available from CYCC from June 1985 to April 1986. Discharge from the spring is entirely from groundwater. Discharge rate information from the Area 2 Pit is available from June and July of 1986 and during this period almost all discharge from the pit is derived from groundwater. The discharge rate data from June to October 1985 used in this report have been corrected for measurement error. Future monitoring of flow rates, as part of the overall spoil monitoring program, will serve to establish the validity of the model of ground water flow in the spoil proposed in this report. Structure data for the base of the mined Wadge coal seam and reclaimed land surface elevation data were available from CYCC to generate contour maps and geologic cross-sections. GEOLOGIC SETTING • The topographic surface in the vicinity of the Eckman Park operations is strongly controlled by the structure of the more resistant geologic units in the Twentymile Park Basin. Mining of the Wadge coal seam at the Eckman Park operations has occurred on the dip slope between Foidel Creek and the southern rim of the topographic divide formed by the Trout Creek sandstone outcrop. Removal of the coal and replacement of overburden material has resulted in a backfill aquifer approximately 100 feet thick and dipping to the north at about 6-10 degrees (Figures 2 and 3). The backfill material is underlain by an interbedded shale/silt- stone/sandstone unit that probably forms a reasonably effective lower aquitard. The permeability of the unmined Wadge coal and shale/sandstone overburden sequence to the north of the backfilled area has an average permeability ranging from 10~10yft/sec, based on pumping tests run by CYCC. These values are several orders of magnitude lower than the average backfill permeability. It is therefore reasonable to assume that groundwater flow into the undisturbed area from the backfilled area would be limited. Recharge to the backfill is primarily from snowmelt during the period which usually occurs from mid-April to mid-June. This recharge would infiltrate through the unsaturated zone of the backfill and tend to build up a zone of saturation at the base of the material above the underlying aquitard. Groundwater flow in the saturated • backfill material would tend to follow the structural dip of the underlying aquitard. Due to the low permeability 3