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iis: nti <br /> t <br /> completely weathered, they lie mostly below the water table, and they serve as a more or less <br /> homogeneous substrate. I won't discuss this feature much further. <br /> Most of the metals are present in low abundances, so except for zinc and copper, 1 did not conduct <br /> more than a cursory exam. As I believe this memo will indicate, you should be able to make a <br /> semi-quantitative determination of the effects of the tailings on the hydrologic setting with this <br /> information. <br /> OBSERVATIONS: <br /> Groundwater: gene ral. <br /> Included with this memo are contour maps for TDS, SO„ and pH, and highlighted maps for Zn. <br /> It is evident from the 1985 and 1986 contour maps that there are significant trends which indicate <br /> either groundwater courses, high sulfate and acid load points, a leaky liner, or all of the above. The <br /> metals concentrations are highest along these particular trends, which leads me to believe that they <br /> are all related. The following discussion focuses on a comparison of the 1985 and 1986 ground and <br /> surface water trends. <br /> All of the 1985 surface and groundwater samples were collected within a few days of one another <br /> in September and October. The 1986 groundwater samples were collected in July whereas the <br /> surface waters were collected in September. <br /> Although I cannot know from the limited data whether it makes a difference in this case, sampling <br /> during different seasons can yield significant differences in concentrations. <br /> SO,. <br /> Sulfate is a good indicator of pyrite weathering in this environment. The native geology and the <br /> mineralogy of the ores are generally void of readily soluble sulfates, so the great majority of sulfate <br /> measured in the waters derives from the weathering of sulfides, most of which are iron sulfides <br /> (pyrite, and lesser amounts of marcasite and pyrrhotite). <br /> On the 1985 sulfate map there is an area of high values that trends eastward from well 9, through <br /> wells 6 and 3A, then northward beside well 17 to well 13. With only minor exception, this trend <br /> appears in all of the maps. <br /> The 1986 sulfate map has a trend of elevated sulfate values similar to the 1985 map. However, the <br /> 1986 concentrations in 9, 6 and 3A are lower. These trends, and the direction and magnitude of <br /> change in concentration, are also seen in nearly all of the 1986 maps. <br /> Wells 1B and 2A had significantly higher concentrations in 1986 than in 1985; welt 13 sulfate <br /> concentration also increased. Apparently, the lower pond became a source of Sulfate after 1985, as <br /> did something in the northeastern sector of the tailings area. <br /> 2 <br />