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37 <br /> shown graphically in Figure 11 . This figure shows the similarity of compo- <br /> sition of the mine discharges. The major difference in relative composition <br /> of the stream waters as compared to the mine discharges is a lower concen- <br /> tration of sodium. Otherwise the compositions are quite similar. The <br /> combined concentration of dissolved salts in the mine discharges are greater <br /> than in the stream, however. <br /> Table 6 is a comparison of the chemical analyses (Appendix E, Table E2) <br /> of waters taken from the three bedrock wells established as part of this <br /> study with the means from the Maxwell Mine discharge. The data for well <br /> LA 221A is believed to be representative of the quality of the undisturbed <br /> waters in the coal seam. The differences observed between the water quality <br /> in LA 221A and of the mine discharge is attributable to activities within <br /> i the mine and, to some extent, to sample and analytic variability. The large <br /> j concentrations of total iron and manganese are attributed to the steel casing <br /> and the elevated total zinc is due to the galvanized iron discharge pipe <br /> used in the pumping system. The concentrations of dissolved iron, manganese <br /> and zinc are meaningful , but the total concentrations of these elements are <br /> not. <br /> Water pumped from LA 264 is believed to be produced from a thin fractur- <br /> ed zone at a depth of about 72 ft. as discussed previously. Even though the <br /> water sample from this well represents a zone high in the overburden, the <br /> composition and total concentrations are very similar to the corresponding <br /> parameters from LA 221A. This observation suggests a uniform water quality <br /> throughout the profile. <br /> The sample from well LA 218A is not representative of the coal seam <br /> waters. Because the productivity of the well was small , a volume of water <br /> sufficient to displace the water standing in the well bore was not pumped, <br /> j and the sample is believed to be contaminated with cement which would ac- <br /> count for the high pH and large concentration of carbonate. <br /> 1 <br /> The change in the quality of waters in the Purgatoire River as a <br /> result of mine discharge is an item of particular concern. The estimated <br /> change in selected parameters due to the Maxwell Mine discharge are present- <br /> ed in Table 7. The mass balance-mixing model : <br />