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• ALLUVIUM Alluvial sediments are monitored in the Foidel Creek valley upstream and downstream of Mine 1 and Eckman Park and in the Fish Creek valley upstream and downstream of Mine 2. Three wells completed in the Foidel Creek alluvium are monitored (001-S-5, 009-S-10, and 008-AV- 2). Three wells completed in the Fish Creek alluvium are also monitored (006-AY-1, 006-AZ-3, and 006-AW-2). Foidel Creek Alluvial Groundwater: During 1998, three Foidel Creek alluvial wells (009-S-10, 001-S-5, and 008-AV-2) required monitoring for water levels and field parameters on a monthly basis, and water quality sampling on a quarterly basis. All monitoring requirements were met at these sites. Tables 8 through 10 provide summaries of the 1998 Water Year data collected at each site. Tables 8a through 10a provide period of record statistical summaries of collected data at each site. Figures 12 through 17 provide graphical representations of water levels and TDS concentrations recorded at each site. Water levels during 1998 remained generally consistent with established ranges and patterns and showed the typical seasonal variability of elevated water levels in the spring. Well 009-S- 10 provides data for the alluvial aquifer downgradient from the Eckman Park mine (Figure 14). This well exhibited relatively high water levels in the spring due to the early and rapid melt of the snowpack. Well 001-S-5 is located downgradient from Mine 1 and below the Twentymile Coal Company mine portals and is monitored in conjunction with surface water monitoring site 8. Figure 12 is indicative of the general relationship between the alluvial groundwater elevations and surface water elevations at these two sites. Wells 008-AV-1 and 008-AV-2 are monitored in conjunction with surface water site 304 at a point on Foidel Creek approximately 1000 feet upstream of the confluence of Foidel and Middle Creeks. Water levels in these wells • and the stream show the typical seasonal interrelationship of relatively rapid increases and declines associated with spring runoff (Figure 16). The longer term trends in water levels at these sites generally parallel the fluctuations observed in annual streamflows. Field conductivity measurements in general at well 001-S-5 (see Figure 13; 1998 average approximately 2000) were again noted to be higher than the upgradient site 009-S-10 (see Figure 15; 1998 average approximately 1275). Moving downgradient, field conductivities at well 008-AV-2 are averaging approximately 1625. Conductivity values at well 009-S-10 fluctuated within previously established ranges during 1998. Field conductivity measurements at wells 001-S-5 and 008-AV-2 also occurred within previously established ranges for these sites. The generally increasing field conductivity trend previously noted for wells 001-S-5 and 008-AV-2 appears to be leveling off in the 1998 data. CYCC will continue to monitor the direction of this trend. At well 009-S-10 (Table 9), new maximum values for manganese and ammonia was noted in November, 1997. Then in August, new maximum values for nitrite was noted. All other measured parameters at well 009-S-10 returned values within the previously established ranges throughout the monitoring year. At Well 001-S-5 (Table 8) and Well 008-AV-2 (Table 10), all 1998 values were documented to occur within previously established ranges at this site. Fish Creek Alluvial Groundwater: During 1998, three Fish Creek alluvial wells (006-AY-1, 006- AZ-3, and 006-AW-2) required monitoring for water levels and field parameters on a monthly basis, and water quality sampling on a quarterly basis. Tables 11 through 13 provide • summaries of the 1998 Water Year data collected at each site. Tables 11 a through 13a cycc98 06/11/99 3