Dames & Moore, 1999 - USDA Forest Service

higher than water levels in the alluvial/reworked till unit. Therefore, groundwater flow between the units, if
it occurred, was downward from the tailings and into the alluviallreworked till unit. At the PZ-l location
(Figure 4.4-12) and the PZ-4 location (Figure 4.4-14), water levels in the alluviaVreworked till unit were
higher than those in the tailings in May 1997. By June 1997, water levels in the alluvial/reworked till unit
had dropped and were lower than water levels in the tailings. This condition was maintained throughout the
rest of the monitoring period, ending in ~e~tember 1997. Therefore, water may have flowed from the
alluviallreworked till unit upward into the tailings in the spring, and then reversed from the tailings back
downward into the alluviaVreworked till from June through September. Water level data from well clusters
throughout tailings piles 2 and 3 indicate the trends shown on Figures 4.4-12 through 4.4-14.
The relationship of water levels, and hence the direction of potential groundwater flow, for wells screened in
the tailings and the alluviaVreworked till units is shown for cross-sections through tailings pile 2 on Figures
4.4-2 and 4.4-4 and for tailings pile 3 on Figures 4.4-3 and 4.4-5.
Groundwater Flow in Western Portion of Site
Groundwater flow in the western portion of the Site (west of tailings pile 1) appears to take place through
the soil and fill material and potentially within the alluviurn/reworked till and dense till layers that
presumably underlie the soivfill. Groundwater in the western portion of the Site appears to be recharged by
snowmelt and rainfall on the slopes to the north and south of the Site, and on the western portion of the Site
itself. This includes the mill building area and the waste rock piles. Seep flow from the waste rock piles is
collected at the base of the piles and transported via ditches to the lagoon south of Railroad Creek.
Infiltration into the western waste rock pile also likely contributes to seep SP-15W, located at the break in
slope south of the lagoon area (see Figure 4.3-8). Surface water loss from the ditches or pond also appears
to recharge groundwater in this portion of the Site. A loss of water from the portal drainage (P-1 to P-5) has
been demonstrated. The water is assumed to infiltrate to the alluviaVreworked till and ultimately exit into
Railroad Creek.
Results from the electromagnetic (EM) terrain conductivity survey (Appendix A), which investigated to a
depth of approximately 18 to 20 feet, show relatively high resistivity from the vicinity of the mill building
toward ail road Creek, indicating the presence of shallow groundwater. The survey shows that the water
flows in relatively narrow pathways based on the spikes on the EM survey which are narrow rather than
broad peaks, which would indicate diffuse flow. Several of the EM "spikes" were coincident with the portal
drainage and seep SP-23. '
Groundwater Flow - Honeymoon Heights Area
Snowmelt and rainfall are assumed to enter fractures and faults in the bedrock in the Honeymoon Heights
area and move downward into stopes associated with the underground mining (Figures 4.2-6% 4.2-14, and
4.2- 15). This water is assumed to travel downward to the 1500-foot level and becomes part of the mine pool
before emerging at the 1500-level main portal. A dye test was conducted during the RI to assess the surface
waterlgroundwater flow path of an intermittent drainage in the Honeymoon Heights area as it potentially
relates to mine infiltration and seepage flow at seeps SP-12 and SP-23; however, the results were
inconclusive.
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