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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 Phase III bond released 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 1999, 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 1999 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 1999 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, like most others monitored, exhibited lower levels in the spring and therefore through out the water year than have been observed for a period of several years . 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; 1999 average approximately 2000) were again noted to be higher than the upgradient site 009-S-10 (see Figure 15; 1999 average approximately 1275). Moving downgradient, field conductivities at well 008-AV-2 are averaging approximately 1600. Conductivity values at well 009-S-10 fluctuated within previously established ranges during 1999. 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 continue to bee seen in the 1999 data. CYCC will continue to monitor the direction of this trend. At well 009-S-10 (Table 9), new maximum values for hardness and bicarbonate was noted in November, 1998. At Well 001-S-5 (Table 8), a new maximum value was recorded for molybdenum in March, 1999. At Well 008-AV-2 (Table 10), a new minimum vale was recorded for hardness and a new maximum value was recorded for ammonium-total in November, 1998 and a new maximum value was recorded for ammonia-free in August, 1999. All other measured parameters at these sites returned values within the previously established ranges throughout the monitoring year. cycc99 02/14/00 3