Laserfiche WebLink
Coal down -dip of and adjacent to the Seneca mine, but farther north and downgradient of <br />• SW19, shows a seasonal pattern like that of YW28, but with less than one foot of annual <br />fluctuation. Water levels in underburden wells YWU28 and SWU11 also exhibit the <br />pattern of seasonal highs in late spring and summer and seasonal lows in late fall and <br />winter, with recent annual fluctuations of less than two feet. The water level SWUI I has <br />shown an upward trend since 1983 and is about 40 feet higher now than in 1983. Water <br />levels in the more shallow alluvium and spoils units (Figure 2.04.7 -F4) are monitored for <br />the Seneca II mine and have a longer period of record. Water levels in those wells were <br />highest in the late spring and early summer, suggesting that recharge occurs seasonally <br />during and shortly after snowmelt. <br />Vertical hydraulic gradients indicated by the water levels vary between the two locations <br />where closely- spaced wells are completed in the three units. In the west - central part of <br />the permit area, at wells COV23, CW23, and CWU23, the vertical gradient is toward the <br />Wadge coal from both above and below. The maximum observed vertical gradients are <br />relatively small, however, from the overburden to the coal: about 12 feet; from the <br />underburden to the coal: about 14 feet; and from the overburden to the underburden: about <br />6 feet. Immediately southwest of the permit area, at wells YOV28, YW28, and YWU28, <br />the hydraulic gradient is downward. The water -level difference from the overburden to <br />the coal is less than ten feet, but the water level elevations in the underburden are about <br />150 feet lower than in the coal or overburden. The location of these wells near the Yoast <br />mine may have affected vertical gradients in the vicinity. From 1996 to 2002, water levels <br />in the overburden and coal wells YOV28 and YW28 dropped about 58 feet, while during <br />• the same period the water levels in underburden well YWU28 rose about 5 feet. <br />Water level elevations in the monitoring wells were used to draw potentiometric surface <br />elevation maps representing conditions in the overburden, Wadge Coal and underburden <br />units (Figures 2.04.7 -F5, 2.04.7 -F6 and 2.04.7 -F7, respectively). <br />The groundwater flow patterns interpreted from the potentiometric surface elevation <br />contours for the overburden and Wadge Coal indicate that groundwater flow is generally <br />down -dip and toward the northeast and north in the central portion of the permit area and <br />to the west in the eastern portion of the permit area. This pattern is in general agreement <br />with the regional flow conditions depicted by Robson and Stewart (1990, Figure 33). The <br />pattern suggests strong influence by the geologic structure in the area, principally the <br />Hayden syncline. Recharge in the structurally high area southwest of the permit area also <br />may influence the flow. The structural influence of the Hayden syncline, which plunges <br />to the north, would be expected to result in groundwater flow to the north or north - <br />northwest as interpreted from the contoured data shown on Figures 2.04.7 -F5 and 2.04.7 - <br />F6. <br />The groundwater flow pattern interpreted from the underburden unit potentiometric <br />surface differs from that of the Wadge coal and overburden units. Figure 2.04.7 -F7 <br />suggests underburden unit groundwater flow to the northeast off the structurally high <br />YWU28 area and toward the Hayden syncline axis, but the relatively low potentiometric <br />• surface elevation at CWU14 suggests that flow is toward that area from the west, east and <br />north. <br />PSCM Permit App. 2.04 -42 Revision 12/17/09 <br />