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to 110 mg/1 on Upper Center Creek during the same snowmelt runoff sampling. No runoff from the disturbed area is expected during dry periods or during minor precipitation and snowmelt events, due to high surface infiltration rates, evaporation and interception of minor runoff by sediment ponds. There is very little contribution of flow to Naturita Creek from the permit area drainage. While flow in Naturita Creek does increase from above the permit area to its confluence with the San Miguel, that increase appears to be due primarily to irrigation return flow and minor subsurface flow. Except during significant snowmelt and storm events, there appears to be insufficient runoff to allow flow in the draws across the proposed permit area. In those rare instances where runoff does develop, little water actually reaches Naturita Creek. For example, an October 2-3, 1988 storm event contributed to flow in all draws across the permit area, yet there was no flow in lower Hamilton Creek at its confluence with Naturita Creek, below where it received water from the proposed permit area. This indicates that either the flow event was extremely short-lived, or that flow infiltrated prior to reaching the confluence with Naturita Creek. Except during infrequent high precipitaiton events, surface runoff within the permit area is insufficient to routineiy mobilize constituents and transport them to receiving waters. During an average year, runoff from the site is calculated to contribute between 13 and 69 tons/day dissolved constituents as TDS which may not, however, actually enter Naturita Creek or the San Miguel River. Infiltration, evaporation, and evapotranspiration will reduce runoff, sometimes to nothing. As an extreme example, in the low flow year 1977, when the San Miguel River at Naturita had a total flow of 1.6 cfs, it is possible that there was no flow from most or ail of the drainages into Naturita Creek, nor from Naturita Creek itself for an extended period of time. In the case of a high precipitation event, the amount of dissolved constituents carried from the site is expected to increase and the concentrations decrease as a direct result of the increased volume of water after an initial flushing effect. Runoff volumes of the area being worked during mining activities are expected to increase somewhat due to compaction by equipment and exposure of materials with higher clay and silt content than that currently at the surface. This effect is expected to be offset by low precipitation, minor ponding of precipitation in the working area, retention of runoff in the sediment ponds, evaporation and infiltration. Pit dewatering is not anticipated. TDS and other constituents of concern, sulfate in particular, are expected to have minimal or insignificant effect on the water ~.. ~.. Y -21-