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April2021 MNGW-I pH Memo♦4 <br /> 3.0 GROUNDWATER FLOW <br /> 3.1 GROUNDWATER ELEVATIONS AND FLOW DIRECTION <br /> Water levels collected between 2014 and 2020 from MNGW-3 and MNGW-4 were evaluated <br /> along with concurrent data from POC well MNGW-1.Additionally,Henderson conducted an <br /> elevation survey of No Name Gulch in the area of the three monitoring wells. The survey <br /> elevations of No Name Gulch were compared with seasonal water level data for the <br /> monitoring wells to assess whether the gulch is a gaining or losing (recharging) stream in the <br /> area. These data were used to assess groundwater flow directions in the shallow aquifer east <br /> of the Henderson Mine surface facilities. <br /> Measured depths to water and groundwater elevations for the three monitor wells and <br /> streambed elevations for No Name Gulch are presented in Table 1. Figure 3 presents <br /> hydrographs of the three wells.Depths to water between September 2014 and December 2020 <br /> ranged between 2.46 and 17.77 feet below top of casing(ft btoc),with the highest and lowest <br /> water levels in June 2015 and February 2019,respectively. <br /> Figures 4 and 5 present groundwater elevation contours in December and June 2020. <br /> Groundwater in the colluvial sediments generally flows from the southwest to the northeast, <br /> towards the West Fork of Clear Creek. An easterly shift in groundwater flow direction (from <br /> approximately N40°E to N65°E) occurs during the drier fall and winter months of year as <br /> indicated on Figure 6. The hydraulic gradient varies between approximately 0.065 feet/foot <br /> (ft/ft)in the winter months and 0.125 ft/ft in the summer months. Survey elevation data from <br /> No Name Gulch shows the elevation of the gulch stream bed to be above the water table <br /> indicated by water level data in adjacent wells (see Figure 5), indicating that when No Name <br /> Gulch is flowing (i.e., during spring and summer months), the gulch is a losing stream in the <br /> vicinity of the monitoring wells, and is a potential source of groundwater recharge to the <br /> shallow aquifer. <br />