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• result of significant increases in erosion and dissolution of mineral <br />constituents from granitic and related mafic materials in headwaters areas <br />or scour and dissolution of residual mineral precipitates deposited in <br />lowland channel areas where surface water pools and infiltrates through <br />the relatively porous streambed materials to the groundwater system. <br />In lowland areas, ephemeral drainages commonly flow only in response to <br />snowmelt and major thunderstorm events. With limited vegetative cover in <br />these areas there is significant potential for erosion and TSS levels from <br />undisturbed areas are commonly well over 9,000 parts per million. The <br />single measured flow event for Magpie Creek on July 6, 1981, resulted in <br />a TSS level of 48,500 parts per million and a TDS level of 1,130 with <br />elevated concentrations of several metals. This physical data indicates <br />the susceptibility of both undisturbed land areas and stream channels to <br />significant erosion and sediment loss during major storm events. In <br />conjunction with flow modeling for the GEC, Mine Simons Li also evaluated <br />• potential sedimentation for mine and adjacent areas. Modeling resulted <br />in calculated TSS levels of approximately 20,000 parts per million as a <br />result of the 10-year, 24-hour storm event for both Magpie and Newlin <br />Creeks. <br />In order to evaluate chemical type for mine area surface water resources, <br />EFCI used the same information utilized to develop Table 16, Newlin Creek <br />Water Quality, converted average analysis values for major chemical <br />species to milliequivalents per litre, and plotted the resulting <br />information on Figure 10, Trilinear Diagram - Newlin Creek. As <br />illustrated by this figure, mine area surface waters can be characterized <br />as a relatively strong calcium carbonate chemical type. Surface water <br />chemistry appears to be a reflection of the dominant sedimentary units in <br />the lower Newlin Creek drainage basin with limited influence from mafic <br />materials exposed in the Wet Mountain uplift to the west. <br />Loadout Area. Water quality for the loadout area is represented by Table <br />• 17, Oak Creek Water Quality. This table summarizes available monitoring <br />information collected to date and includes minimum, maximum and mean <br />values for major chemical constituents and analysis parameters. Surface <br />water in the loadout area can be characterized as being slightly alkaline <br />2.04.7-39 <br />