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_„_ The present pattern of surface drainage on the teas to b.• miucd w~.ll b~• rnodifiad as a result of mining. No major effects of the rnor)iti.cation arc an ticipatod. A:pending upon the final configuration of the regraded spoils, there may be a tendency toward greater detention time and, therefore, yreater maximum potential retention on the Ploffat area. The effect of this change will be to reduce surface runoff and to increase subsurface runoff somewhat. The maynituclc of such a change will be small and beyond the resolution and reliability of a wilable prey/i cti ve procedures. Re- grading and topsoiling of the [Jest Rirlge, now occupier) by old spoils, will probably have the effect of reducing suhanrfacc nu~~~~ll~ h~~r~aar:- ~~ ~lecn~asr.~rl pr,t•:•~tin; retention and increased evapotranspiration. Post-Ffi Wing fJa to Bolan cr. Mining will have no effect on ground water recharge that may occur outside of the permit area. A small affect on the partitioning of total runoff into surface and subsurface components is the only anticipated effect of mining on the oi•erall water balance. It is expected that the post-min.inq contribution to flows in Trout and Oak Creeks From the permit area will he unchanged from that which now exists. The post-mining landscape on the ~~foffat area will be a regraded and topsoiled area with the same general topography as now exists. It is expected that the mean slope and infiltration capacity of the area will eventually be veru similar to the pre- mining conditions. A somewhat increased potential maximum retention is expected, but not of the magnitude that will affect the surface c;~ater balance significantly. Therefore, about the same partitioning of precipitation into overland runoff and infiltration is expected to occur in the Host-mining phasn_ as now exists. Between the time that mining occurs and the time that full revegetation has been accomplished, evapotranspiration may be re ducerl somewhat, relative to the current water use by vegetation. A corresponding increase in subsurface runoff will occur. However, the decrease in evapotranspiration will not be as great as one might expect, considering only the reduced vegetation. Current water use by plants is limited by water availability as shown by the subsurface water balance in Table 2.5-24 in the permit application. This makes it possible for the rec?uction ~n dater use caused by reduced vegetation to he _'ess than propostional to the reduced vegetation. Zt is anticipated that reclamation will eventuall~~ cr.tnl,li~h a plant cover with a water demand very similar to that which now exists. Possibly the most significant factor that could substantially affect the post-mining water balance is a change in the effective rooting depth and the total available water-holding capacity of the root zone. Again, such a chance is difficult to predict rluantitatively. The inter- face between the topsoil and the spoil may serve to reduce downward movement of water and cause the available water-holding capacity to be yreater than in the undisturbed state. Changes in the evapotranspiration and the partitioning of runoff into surface and subsurface components due to the factors discussed above are expected to be small on the Moffat area and beyond the resolution and reliability of predictive techniques. Therefore, the post-mining water balance is estimated to be unchanged from that which now exists.