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• 4.13.3 Probable Hvdrolooic Consequences <br />This section discusses the probable hydrologic consequences for the surface and groundwater systems at <br />Trapper. Included are discussions of projected impacts to both water quantity and quality. Impacts to <br />groundwater flows from springs and seeps are addressed in each section as appropriate. <br />4.8.3.1 Surface Water Impacts <br />The probable hydrologic consequences to surface water are presented in this section. The section <br />presents the predicted post-mine conditions for surface water quantity followed by the predicted post-mine <br />conditions for surface water quality. <br />Post-mine Surface Water Quantity <br />Following reclamation, relatively looser surface materials will act to increase infiltration for a few years. As <br />the materials settle and consolidate, infiltration rates are expected to approximate pre-disturbance levels. <br />The increased infiltration rate prevailing during this initial period may be offset by a commensurate lack of <br />• vegetative cover that could act to decrease retention of precipitation and, therefore, increase runoff. The <br />quantity of surface-water runoff will vary substantially for different conditions. It is likely that the quantity of <br />surface water runoff occurring following the establishment of stabilized post-mine conditions will lie similar <br />to pre-mine surface water runoff quantity. <br />Post-mine Surface Water Quality <br />Higher total suspended solids (TSS) levels are expected in the surface water runoff for a few years after <br />mining. As vegetation and ground cover become permanently established, TSS values will deGine. <br />Evaluations of sediment production and yield from reclaimed areas have concluded that equivalent or <br />lesser amounts of sediment can be expected from reclaimed areas relative to pre-mining conditions. High <br />total iron concentrations were observed before mining (see Table 2.7-18) and are expected to occur after <br />mining as well. The post-mine values of pH in surface water runoff are not expected to be significantly <br />lower or higher than present or pre-mine levels. Manganese concentrations are likely to continue to be <br />relatively high at times, as they have been during the pre-mine and operational monitoring. <br />During base flow conditions for surface water runoff, some water quality constituents may exhibit elevated <br />concentrations in areas where backfill aquifers contribute to surface water flows through spoil springs. <br />• Where elevated total dissolved solids (TDS) levels exist in the backfill aquifer, elevated TDS levels will be <br />exhibited in base flows derived from the backfill aquifer. To date, Johnson Gulch is the only surface water <br />drainage that definitety shows mining effects on TDS during base flow conditions. The higher TDS base <br />flow concentrations in Johnson Gulch are expected to gradually decline with time as the TDS Revisl~~ ~,~ _~y <br />a Zia ,gpprovedOCT 2 3 2000 <br />