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<br /> <br />These are assumed values, since no measurements were made of dispersiviry in <br />the field. In fact, dispersivity is often es[irnated, since it i.r quite difficult to <br />e~ectivety measure. However, the values used here appear inappropriately high, <br />especially if used for evaluating contaminate plumes between the monitor wells <br />and collection potul. <br />RESPONSE: In the first paragraph of Mr. Mefford's comments, he ignores dispersion in the <br />aquifer in stating that "none of the wells appear particularly well suited to identify <br />contamination, which may originate from the collection pond, or center of rite <br />tailings embankment". While he acknowledges the effects of dispersion in the <br />second paragraph, it doesn't seem to affect his conclusion. Additidnally, the use <br />of "reverse flow lines" to support the contention that the monitoring wells are not <br />adequate is tenuous at best, given the equipotential lines were drawn from only <br />three data points. These equipotential lines could have a sligllrtly different <br />orientation, which would give a different answer based on "reverse flow line" <br />methodology. Also, we expect that there could be seasonal swings in the <br />direction of the gradient of 15 to 30 degrees, again rendering a "reverse flow <br />line" methodology incorrect under those circumstances. <br />Based on the foregoing, BMR disagrees with Mr. Mefford's comment that <br />contaminants can't be detected by the existing monitoring well cyst@m, and BMR <br />believes that the existing monitoring wells can adequately identify contamination <br />that hypothetically may emanate from any location within rite tailings facility <br />and/or collection pond (see sensitivity analysis results). <br />4. (partial) [IJt seeuts that monitor/recovery wells located immediately down. gradient <br />of d:e center of dre tailings embanktncnt, mrd innncdiately down gradient of the <br />collection potrd would be best sinmted to ideru~ and potentially remediate arty <br />contanrina[ion reaching tl:e groundwater. We reconrrncnd dte installation of wells <br />at these locations. <br />RESPONSE: The current ground water monitoring system (sans M-12 and M-13) was approved <br />by the CDMG as part of the permit to operate this mine. That approval was <br />based on the known geology and hydrogeology of the area. The drilling and <br />completion of wells M-12 and M-13 has only served to confirm the geologic and <br />hydrogeologic interpretation that was known when the monitoring system was <br />approved by CDMG. Thereafter, additional monitoring of the local ground water <br />table has been provided by BMR (through the installation of M-lp and M-13), <br />without any new facts coming to light regarding the geologic and hydrogeologic <br />interpretations in this area. Because of this, BMR believes drat rite original, <br />approved monitoring system was adequate, and the expanded rnoniloring system <br />is also adequate. <br />-8- <br />