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IC should be remembered that closed basins created during mining should be '1 balanced against existing noncontributing areas, when estimating resulting - streamflow depletion. For example, Historically glaciated areas of many North Dakota mines are internally drained; while 85 percent of the permit area of the East Gillete mine in Wyoming is comprised of closed basins, resulting from Historic coal burns. Also to be considered are existing Stack ponds and internally draining, previously mined areas that will be reclaimed to discharging areas by current operations. Increased infiltration This is an abstraction from runoff above premining conditions resulting from the regulatory requirements to reestablish infiltration rates. Because compliance with this requirement must be demonstrated, there should be estimates available comparing premining and postmining infiltration rates. Althougn differences in infiltration may be slight, runoff from the _ " entire reclamation surface could constitute a definable abstraction from streamflow, assuming higher postmining infiltration. It is recommended that premining and postmining infiltration rates be compared and, if significantly different, that runoff effects be estimated possibly on trie basis of the resulting change in annual unit runoff for the mine area. Aquifer interruption This is disruption of aquifers that are tributary to surface flows and, as such, eliminates from consideration deep aquifers that are hydraulically isolated from surface flows. Disruption of alluvial aquifers which are not AVF's, and, hence, do not have to be restored constitutes the most direct effect on streamflow. However, disruption of aquifers wnicn subcrop beneath alluvial aquifers, as discussed for underground mines, may also affect streamflow. Because downstream flows .nay be affected, in most cases estimates of changes in alluvia] underflow resulting from mining should be available for estimating streamflow depletions. It is recommended that depletions from streamflow resulting from disruptions of mine-area alluvial aquifers be estimated in most cases. However, because streamflow effects resulting from disruption to aquifers , subcropping beneath alluvial aquifers are indirect and difficult to estimate, in such cases it is recommended that only clearly-demonstrated and quantifiable effects be considered in estimating streamflow depletion. Mine water rights See discussion under Underground Mines. Well pumpage cell pumpage at mining operations usually represents potable water supplies from good quality, deep aquifers which are Hydraulically isolated frorn surface flows. Therefore, it is recommended that only well pumpage from alluvial wells for uses such as oust control or coal processing be considered as streamflow depletions. -8-