2012-12-10_REVISION - M2004009 (9)

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1.0 WATER QUALITY 1.1 BACKGROUND The reclamation plan calls for the placement of shale backfill material into CeII 2. The shale backfill material was previously excavated from the pit floor of CeII 1. Due to the low permeability of the shale backfill material, it is possible that up- gradient groundwater levels could increase (mounding) and down - gradient groundwater levels could decrease (shadow). For the purpose of evaluating the extent of mounding /shadowing, installation of observation and monitoring wells shall be completed as discussed below. The DRMS had commented that there is the possibility of impacts to groundwater quality due to the backfilling of shale material within the alluvial aquifer. Impacts to groundwater are predicted to be unlikely due to the very low permeability of the backfilled shale material. The shale backfill material is classified as lean clay with a plasticity index of 22 as determined by a geotechnical analysis of the same shale bedrock material which was used to construct the reservoir liner in CeII 1 (see Appendix A). The backfilling process will likely result in compaction to 80- 90% of maximum dry density, which combined with the high clay content, will yield very low permeability as achieved by the weight of and compaction by heavy equipment placing the material. This plan will however, gather ambient water quality data and, in the event that water is in fact observed to flow through the backfilled shale, a water quality sampling program has been specified. In order to determine if any groundwater flow occurs through the backfilled shale material, observation wells shall be constructed within the backfilled shale area. In accordance with Section 3.1.7(b) of the Construction Materials Rule, the following information is provided concerning groundwater monitoring: 1.2 MAP The map given in Figure 1 accurately locates all proposed groundwater sample points (monitor wells) and observation wells. 1.3 METHOD OF MONITORING WELL COMPLETION Monitor wells (MW -1, MW -2) shall be completed at the locations shown in Figure 1. Wells shall be completed to the depth of bedrock and screened within the sand and gravel layer. A typical well completion diagram is given in Figure 2. Observation wells shall be completed within 2ft of the bottom of the shale backfill area at locations shown in Figure 1. Observation wells may be constructed of plain PVC pipe with a 5 ft screen interval at the bottom of the string. The annulus may be backfilled with onsite sand and followed by 2ft of shale for a surface plug. Observation wells are designed for water level measurement and not water quality sampling. 1.4 METHOD OF SAMPLING, FREQUENCY OF SAMPLING AND REPORTING TO THE OFFICE; Rule 3.1.7 (4) b states "If there is a reasonable potential to exceed groundwater quality standards promulgated by the WQCC, the Operator shall modify the Page 1 of 6