2013-09-03_HYDROLOGY - M1988112 - Laserfiche WebLink

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concentrations above their respective analytical reporting limits. Manganese has not been shown to be present above the laboratory reporting limit since April 2011. Reporting limits for iron, manganese, and WAD cyanide are all below the permit concentration values at the M -14 point of compliance. Sulfate concentrations have remained relatively consistent over the last 5 years and are greater than one order of magnitude below the 250 mg/L permit concentration value. The pH found in M -14 has remained within the permit range. Review of the historic TDS concentrations in M -14 shows that TDS concentrations were frequently greater than 400 mg/L even at the time of establishing the permit concentration of 500 mg/L. Since late 2007, the variability in TDS results between sampling events, has increased when compared to previous years. In addition to the permit condition parameters, BMRI has also monitored a number of additional parameters at M -14 which may contribute to an increased TDS concentration and these parameters have not shown any significant concentration increase. A review of water quality parameters in nearby monitoring wells and the downgradient point of compliance monitoring well M -9 did not show any concentrations above the Permit Condition Values and concentrations of other analytes in these wells were consistent with historical results, including the concentrations for TDS. Based upon the review, there was no indication that there has been a change in the water chemistry that would result in the elevated TDS at M -14. During interviews with site personnel and a review of the sampling logbooks for monitoring well M -14, it was found that this well had a dedicated pump up until late 2008 at which time it was removed due to problems with the pump. Since this time, sampling at M -14 has been performed utilizing a portable pump. TR -32 allows for the use of dedicated or portable pumps and sampling can be performed by standard purge or micro purge techniques. While both techniques are acceptable for groundwater sampling, standard purge techniques generally stress the aquifer more than micro purge techniques and may potentially lead to differences in turbidity and TDS. Based upon the review of the historic analytical results, field logbooks, and interviews with site personnel, it is not fully understood why there has been an increased variability of the reported TDS concentrations or if the TDS actually has increased from historical results in monitoring well M -14. It appears that the increased TDS variability in M -14 may be associated with the removal of the dedicated pump in 2008. BMRI would propose as the initial response plan to collect additional water quality samples at monitoring well M -14. BMRI proposes that samples be collected from M -14 on a bi- monthly basis for a period of ninety (90) days utilizing the micro purge sampling technique. The micro purge technique will be conducted as to place minimal stress on the aquifer and minimize impacts of well recovery on the sample collection. The pump intake will be located at or slightly above the middle of the screened interval and drawn directly from the formation with little mixing of casing water or disturbance to the sampling zone. During sampling, pump flow and drawdown will be monitored and minimized to preclude the entrainment of sediment in the water collected for analyses. Water quality indicator parameters including flow, pH, specific conductance, dissolved oxygen, temperature and turbidity will be used to determine purging adequacy. Samples will be analyzed on a bi- monthly basis for TDS and on a monthly basis for the on -site ground water well quality parameters listed in Table 2 -4 of TR -32. Analytical results from this response plan will be compared to the historical analytical results and to verify if the TDS concentrations have stabilized utilizing the micro purge sampling method. BMRI will provide Colorado Department of Reclamation, Mining and Safety ( CDRMS) a monthly summary report of the final laboratory analytical results received for all samples collected under this response plan for the previous thirty (30) day period. Additionally, BMRI will prepare a final report summarizing the findings of this response plan and submit this report to CDRMS within thirty (30) days after receiving the final analytical results from the laboratory.