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• between recharge and discharge to the backfill presumably flows into the undisturbed overburden downdip for the backfill area. Based on the available water balance data and the much lower permeability of the undisturbed bedrock dipdown from the backfil- led areas it is projected that less than 5 percent of the total recharge to the eastern backfill infiltrates into the bedrock. Storage At any given instant in time the difference between recharge rate and discharge rate in the backfill system will probably vary quite appreciably through the year. The difference between the two values is taken into account for by a change in groundwater storage within the backfill. During active recharge periods, the recharge rate exceeds the discharge rate and the excess leads to an increase in groundwater storage (an increase in water levels.) During most of the year discharge will exceed recharge so that the deficit will be taken out of groundwater storage leading to a decrease in water levels. The net change in storage over the year will be close to zero if the system has reached stabiliza- tion. The fluctuation in water levels described above is illustr- ated in the data from spoil wells in the western backfill area. • Water level data from the SP-1 spoil well shows a significant rise of about 45 feet following the start of snowmelt in mid- April 1985 (Figure 4). The water level in this well peaks about the end of May and then drops about 25 feet to a base level by about the end of July 1985. It is assumed that the SP-1 annual water level fluctuation is representative of the north-central part of the backfilled area, at a distance of several hundred feet from discharge areas. The absolute value of fluctuation would be expected to be related to the amount of recharge in any given year. The difference in water levels in January 1985 and December 1984 is an indication that "steady state" conditions do not exist in the western backfill area. The water level data from the SP-2 well is also shown in Figure 4. This well is located at the downdip end of the western backfill area and consequently is close to the area of ground water discharge. As would be expected, the seasonal water level fluctuation in this well is not as pronounced as in the SP-1 as the potentiometzic level in this part of the backfill is influ- enced by the elevation of the discharge areas. An increase in water level of about 5 feet during the snowmelt period is indicated by the SP-2 data. The SP-3 well did not encounter any water during drilling and has remained dry since its installation in late 1984. This well is located in the central part of the western backfill area. it is • reasonable to assume, based on the data from the SP-3 well, that the updip part of the backfill does not build up any significant groundwater storage. This could indicate that recharge to this 8