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pH 7 and pH 10 buffer solutions, since the pH of most waters sampled at the Nucla Mine <br />ranges between 7 and 9 pH units. However, the lower buffer solution (pH 4) is used for <br />two point calibrations prior to measuring water historically known to exhibit pH values <br />less than 7 pH units. One -point calibrations involve using the pH 7 buffer solution. <br />Table 3 presents the list of parameters used to analyze water quality samples obtained at <br />surface water monitoring sites established at the Nucla Mine during the 1991 water year. <br />This parameter list will be used for analyzing surface water quality samples collected <br />during the 1992 water year. <br />Surface Water Quality. Water quality data for Nucla Mine surface water monitoring sites <br />are given in Appendix C. Laboratory chemical analyses for surface water sites monitored <br />during the 1991 water year were compared with those obtained during 1990 and with previous <br />data (1980- 1989). Table 4 gives a listing of those chemical parameters whose historic <br />maximums were exceeded during 1991. Regarding this table, there does not appear to be a <br />direct cause for elevated zinc levels at monitoring Sites SW -N1 and SW -N3. Record sodium <br />levels at monitoring Sites SW -N3 and NPDES 001 are coupled with high sulfate and magnesium <br />levels at both locations, and are possibly related to lower than average flow rates during <br />sampling (189 gpm and 23 gpm, respectively). It is possible that at sufficiently low flow <br />rates, contribution of relatively high TDS water from the spoil surrounding NPDES 001 pond <br />could produce increased concentrations of these constituents at both the NPDES 001 outfall <br />and at monitoring Site SW -N3. <br />Record levels of ten different chemical parameters at monitoring Site SW -N7 are related to <br />both high suspended solids content (164 mg /t), and extreme low flow conditions (3.45 gpm). <br />It is interesting to note that while this site is located upgradient of all past mining <br />activity, and hence should reflect local non - mining surface water conditions, it <br />apparently recorded the greatest increases in select parameter levels of any site <br />monitored. It should be pointed out, however, that all exceedences of historic levels of <br />chemical water quality during 1991 occurred during the April (non- irrigation) sampling <br />period when all surface sites were at or near their lowest discharge levels. <br />Ground Water <br />Cessation Monitoring Programs at Nucla Mine. Monitoring of wells associated with the <br />7 <br />