Laserfiche WebLink
Response to DRMS Comments <br />Environmental Protection Plan, <br />Denison Sunday Mines Group <br />Response Denison continues to collect quarterly groundwater samples from these <br />monitoring wells. Following five quarters of monitoring, the <br />groundwater data and assessment will be provided to DRMS for review. <br />Denison anticipates submittal of this information in June 2010. <br />Comment 8 Proposed "compliance" monitoring wells. The Division agrees with Densson's <br />choices for the proposed well locations and geologic strata to be intercepted, <br />being hydrologically downgradient from the underground mine workings. The <br />groundwater quality compliance levels that Denison proposes to be defined <br />statistically on the ambient water quality levels that are established in the <br />existing underground well nest, appear to satisfactorily meet the Division's <br />requirements, as long as the wells generate enough data for valid analyses. At <br />this time, Denison appears to have satisfactorily demonstrated through modeling <br />and analyses that there is minimum probability of offsite migration and impact. <br />However, to ensure validity, continuity and acceptability of the baseline <br />sampling, the Division wishes to see dewatering continue throughout the period <br />of collecting baseline data. Denison must perform the quarterly monitoring for <br />the full suite of analytes that are listed under applicable CDPHE regulations. <br />The Division may later approve that the set of analytes be abbreviated if certain <br />ones return non-detectable or if other justification is provided by Denison. The <br />Division will require that the samples be taken quarterly and reported timely to <br />this office. Before the wells are drilled, however, please provide the proposed <br />specifications and preparatory steps taken prior to the commencement of <br />sampling (e.g., casing, screens, purging, etc.). Also, please provide the plans for <br />sealing and closure of the wells. (Please be reminded that review and approval <br />of these wells may be required from BLM.) <br />Response Standard well installation methods will be used and detailed <br />specifications and well diagrams will be submitted to DRMS for review <br />and approval prior to well construction. The groundwater sample <br />analyte list has been revised to be consistent with the DRMS' approved <br />groundwater characterization data collection work plan (see <br />Attachment N of the EPP). The EPP has been revised to provide <br />additional information regarding groundwater monitoring (see revised <br />Section 11 of the EPP; Section 11 replacement pages are attached). <br />Comment 9 Post-mining mine pool. There is a history of standing water in the mine, but the <br />potential for the existence of and impacts from a post-mining mine pool have not <br />been adequately discussed. This office feels that if there is an offsite impact from <br />a mine pool, it will probably be a direct result of leaching of toxic forming <br />material. There are numerous questions that should be identified and, as much <br />as possible at this point, addressed by Denison, such as: Does Denison anticipate <br />that there will be standing water in any workings post-mining? If so, what is the <br />anticipated water quality (are there any water quality data from the mine pool <br />before the current dewatering program)? What is the potential for migration of <br />the mine pool offsite and subsequent potential for offsite groundwater <br />degradation? Besides the proposed compliance wells, how does Denison plan to <br />monitor these possibilities? Is there a mitigation plan in the event of offsite <br />impacts? The baseline to be created by sampling of the "compliance wells" will <br />Final RTC Sunday Mines EPP.doc