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Page 4 <br />The elevation of water in a Trout Creek Sandstone monitoring well (TCS-1), west of the permit <br />area, is 7174 feet above sea level 20 The recharge outcrop, east of the permit area, is at an <br />elevation of 7600 feet. The elevation of some spoil springs (see backfill groundwater following) <br />in cross-section between these two elevations is 7125. <br />Backfill Groundwater <br />The Edna coal mine was a strip (open-pit) operation.21 The pits were excavated and then <br />backfilled to approximate original contour.22 Backfill depths varied, but were up to sixty feet. <br />The original stratification of geologic units is not reconstructed during this backfill process. <br />Placed backfill materials are not as dense (materials were back-cast by shovel, dragline, end- <br />dumped from trucks) as in situ geologic formations. They have more voids, are more permeable, <br />and generally have higher transmissivity values (up to 39 ft2/day)23. In addition, the backfill <br />section becomes a more homogenous section. As precipitation permeates these areas, it becomes <br />(spoil) ground water. <br />Alluvial Groundwater <br />Alluvial groundwater is located at shallow depths in the floodplain terrace of Trout Creek24, the <br />alluvial valley floor. Trout Creek is a perennial stream. Flows appear to be greater at the lower <br />end of the permit area than at the upper end, and quality of groundwater in wells TR-125 and TR- <br />Z26 suggests that alluvial groundwater flows are toward the stream27 (gaining stream). Well TR-1 <br />was located on the east side of Trout Creek near the up-stream limits of mining. Well TR-2 was <br />located near the center of the west boundary of the permit area, on the west side of Trout Creek. <br />A third well, TR-3 is located on the east side of Trout Creek at the lower boundary of the permit <br />area. A fourth well, TR-4 is located on the east side of Trout Creek, approximately a mile <br />downstream from the permit boundary. Alluvial well TR-3 is probably the best indicator of the <br />base line quality of alluvial waters that have a potential for being affected by mining.28 <br />The arithmetic mean of TDS (mg/1) base line monitoring for TR-1 is ] 414.3, and for TR-2 is <br />1982.3. These two wells were near areas that had been mined for up to thirty years. TR-2 was in <br />the vicinity of return (west side of Trout Creek, opposite the mining activity to the east of Trout <br />Creek) irrigation flows.29 TR-3 is located on the east side of Trout Creek, nearly opposite <br />(approximately 700 feet downstream) of the most northerly advance of mining. TR-4 well is <br />located neazly a mile downstream of any mining activity. The arithmetic mean of TDS baseline <br />20 PAP Exhibit 4.6-26 and CDWR Permit 84607 <br />21 PAP Page 1.0-4 <br />zz PAP Page L0-4 <br />Z' PAP Page 2.5-51 <br />Z4 PAP page2.5-62 <br />29 A predecessor of, and located in near vicinity of, TR-1.5 <br />zb A baseline monitoring well, not included in the operational monitoring plan <br />Z' PAP page 2.5-75 <br />za PAP page 2.5-75 <br />29 PAP page 2.5-97 <br />