2009-05-19_REVISION - M1981021 (36)

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11.0 Water Quality Monitoring Plan Water quality monitoring requirements at the Sunday Mines Group currently include the monitoring requirements set forth in the existing CDPS General Stormwater Permit. Denison proposes to increase the existing water quality monitoring program to include continued monitoring of the underground monitoring well nest to establish ambient quality, and installation and future monitoring of groundwater at two wells located south and west of the Sunday Mines Group. Denison proposes that the two new monitoring wells would be groundwater quality compliance points for the DRMS permits, and thus the compliance limit be based on the ambient groundwater condition. The proposed location for these two wells is shown in Figure 11-1. The revised Sunday Mines Group water quality monitoring plan would include the following components: ¦ Surface water monitoring as set forth in the existing CDPS general stormwater permit; ¦ Groundwater monitoring at the underground monitoring well nest and two downgradient monitoring wells. The existing surface water monitoring program is considered adequate and appropriate for the Sunday Mines Group, because perennial or intermittent surface water bodies are not present in the affected areas of the mines, because existing stormwater BMPs are in place, and because an existing permit is in place that addresses surface water. Denison proposes to continue maintaining compliance with the existing CDPS General Stormwater Permit, and to report the performance monitoring data to CDPHE as specified in the existing permit. A groundwater quality monitoring program has not previously been in place at the Sunday Mines Group. Therefore, Denison proposes to establish a groundwater monitoring program at the Sunday Mines Group through the DRMS mine permits in accordance with this EPP. The monitoring program would include the following components: ¦ Continued quarterly monitoring of the subsurface monitoring well nest until a period of at least five quarters of data are available to determine ambient groundwater conditions; ¦ Monitoring of the two compliance wells on a quarterly basis until at least five quarters of data are obtained and on an annual basis after that time, until final reclamation liability for the Sunday Mines Group is released by the Board. It is proposed that groundwater compliance points be established at the two compliance wells based on the ambient groundwater quality determined from the subsurface monitoring well nest. The compliance limit at the groundwater compliance points is proposed to be the 95th confidence interval of the mean, as defined by the 11-1 TA64986-Denison Mines\Task Order 4- EPP Sunday Mines GroupTINAL EPPTINAL - Environmental Protection Plan Sunday Mines.doc