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4.8.3 Probable Hydrologic Consequences <br />This section discusses the probable hydrologic consequences for the surface and groundwater systems <br />at 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- <br />mine 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. <br />As the materials settle and consolidate, infiltration rates are expected to approximate pre-disturbance <br />levels. The increased infiltration rate prevailing during this initial period may be offset by a commensurate <br />lack of vegetative cover that could act to decrease retention of precipitation and, therefore, increase <br />runoff. The quantity of surface-water runoff will vary substantially for different conditions. It is likely that <br />the quantity of surface water runoff occurring following the establishment of stabilized post-mine <br />conditions will be similar 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 decline. <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. <br />High total iron concentrations were observed before mining (see Table 2.7-18) and are expected to occur <br />after mining as well. The post-mine values of pH in surface water runoff are not expected to be <br />significantly lower or higher than present or pre-mine levels. Manganese concentrations are likely to <br />continue to be 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 />4-234