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Cresson Project Hvdroaeochemistry AdrianBrown <br />3.3.5.1 Average Water Quality <br />The average water quality in the Carlton Tunnel in the period 1988 to the present is functionally <br />indistinguishable from the quality of the water that is produced by neutralizing effluent from the <br />humidity cell tests with natural calcite, as shown in Table 6. This result verifies that carbonate <br />neutralization is occurring in the Diatreme, and that the neutralization process in the Diatreme is <br />protective of the quality of the regional ground water exiting the Diatreme to the Carlton Tunnel <br />3.3.5.2 Chemistry History <br />The chemistry of the Carlton Tunnel water has been monitored since 1988. A selection of the parameters <br />measured is presented in Plate 17 for that period. The following is noted: <br />1. pH. The pH has remained between 7 and 8.5 for the entire history. The value declined slightly <br />after surface mining began in 1993, but has become less variable and higher since 1996. There is <br />evidence that the process(es) controlling pH are strengthening slightly as mining proceeds, <br />consistent with a reducing input of acidic water from all sources. <br />2. Conductivity. The electrical conductivity is a gross measure of total dissolved solids. The value <br />has increased slightly since the inception of monitoring, but has been essentially constant since <br />1996 The results indicate great and increasing stability in chemical composition over the <br />surface mining period. <br />3. Zinc. Zinc is present at low concentrations (below 1 mg/L) over the history of the monitoring. <br />Peaks formerly occurred during upset periods of high infiltration, particularly in the summer of <br />1995, 1998, 1999, and 2001. Since that time flow has stabilized, and the peaks have been <br />attenuated to less than 0.1 mg/L elevation of zinc. Surface mining has reduced and stabilized the <br />zinc peaks, and this trend continues to strengthen to the present. <br />Taken together, the chemical data indicate chemical stability over the long term, and improving <br />chemical conditions at the Carlton Tunnel portal as a result of the Cresson Project surface mining <br />activities. <br />3.4 Conclusion <br />Potential impacts to water quality as a result of the implementation of the proposed MLE2 mining <br />and processing activities are as follows: <br />1. No potentially deleterious change in the average regional ground water quality has <br />occurred due to recent surface mining (1993- 2011). <br />2. No potentially deleterious change in the average regional ground water quality will ever <br />occur due all surface mining operations to the end of MLE2. <br />8 There are two periods since 1996 when the conductivity suddenly changed: 2002 -3 and 2010. It is suspected that these represent periods <br />when the calibration of the conductivity probe was slightly in error. <br />1385L.20120125 20 <br />