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Foidel Creek, C- 1982 -056 <br />PR -09 <br />Groundwater Review, 10/12/2012 <br />The Foidel Creek mine is largely confined to the Twentymile Park groundwater basin ( TPGWB), which is <br />itself mostly within the Trout Creek surface water basin. The groundwater and surface water hydrology <br />of the area within and around these basins has undoubtedly been affected by mining activity, including <br />activity at the Foidel Creek mine. The complex mining history and the paucity of baseline data makes <br />precise attribution of effect to cause very challenging. <br />For the purposes of the Foidel Creek mine permit, the groundwater and surface water basins are <br />defined on Map 4, Proposed Hydrologic Area Boundaries. The hydraulic gradient within the TPGWB is <br />generally towards the centre of the basin and to the North East. There are two regionally significant <br />aquifers in the TPGWB, the Twentymile sandstone and the Trout Creek sandstone, which sandwich the <br />interval containing the Wadge seam from which coal is mined. The recharge zone of each aquifer is up- <br />gradient from the mine. The stratigraphy of the area is such that each aquifer unit may be considered <br />hydrologically isolated from the mine workings by thick shales of low permeability; each aquifer is <br />confined down - gradient from its outcrop, and significant artesian pressures exist in the central part of <br />the basin. <br />The Wadge coal seam is overlain by a mixed sequence of siltstones, shales, coals and sandstones, up to <br />100' thick. Although this interval contains water bearing zones, they are discontinuous and the yield and <br />quality are low; the Wadge overburden is not considered an aquifer (page 2.04 -19). <br />The Division's review of the Foidel Creek mine Annual Hydrology Reports (AHRs), finds that current <br />monitoring of groundwater is sufficient to ensure that basic standards for groundwater are upheld, and <br />that adverse impacts to groundwater systems outside the permit area are prevented. The question is: <br />"Will the proposed extension to the permit area and underground workings have a negative impact on <br />groundwater beyond the impact that has already occurred and been approved ?" My opinion is that any <br />additional impact is likely to be relatively insignificant and, given the current level of monitoring, likely to <br />be difficult to detect. The possibility remains, however, that the increased extent of mining activity could <br />have an impact on groundwater quantity and quality in either of the regional aquifer units if mining <br />disturbs an area where these units are hydrologically connected. A fault has been identified in the area <br />discussed in this revision, but is currently poorly characterized. At present TCC have not acknowledged <br />this possibility in their PAP, and consequently have no monitoring or mitigation plan. <br />My recommendations are as follows: <br />• Section 2.05.6(3) of the permit must be amended to reflect the probable hydrologic <br />consequences of the proposed extension. <br />• In addition to the generic consequences which must be expected such as the extended cone of <br />depression within the Wadge overburden, consideration should be given to the uncertainty <br />