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• Horizon 2 mining area. See Attachment 2.04.7-11 (Peabody Appendix 7-9). <br />For both seasons, the water type at Site SW-N101 was a calcium magnesium sulfate. The mean <br />milliequivalent values for each major ion increased during periods of non-irrigation. <br />Average pH measured at SW-N101 was less during periods of no irrigation (7.64) compared to the <br />mean pH representative of the irrigation season (7.82). However, the pH range was larger (7.23 <br />- 8.05) during the non-irrigation months than when irrigation was occurring (7.44 - 7.98). <br />Average TDS dramatically increased at SW-N101 when irrigation.shut down, being almost three <br />times the mean (2,942 mg/I) determined at this site when irrigation occurred (1,026 mg/I). <br />Increases in the major ions occurred after irrigation stops greatly influenced increase in TDS, while <br />the relative proportions (percent milliequivalents) of each ion remained fairly constant. <br />Based on the period of record, TSS, FeT and Feo all averaged greater (71.3 mg/I, 1.79 mg/I and <br />.48 mg/I, respectively) during the irrigation season than the non-irrigation period (28.3 mg/I, 1.12 <br />• mg/I, and .15 mg/I, respectively). The opposite was true for MnT, averaging 1.43 mg/I when <br />irrigation ceased (mid-Octoberthrough mid-April) compared to a mean of .40 mg/I during irrigation. <br />Site SW-N102 was located on the lower end of a small return ditch that flows into Calamity Draw <br />approximately one quarter mile downstream of Site SW-N101. When flowing, water quality <br />samples were collected at this site since July of 1986 (Attachment 2.04.7-11 (Peabody Appendix <br />7-9)). <br />The water type at SW-N102 during the two seasons was a calcium sulfate. Even as levels of each <br />major ion increased after the irrigation season ended, the relative proportions of each ion remained <br />consistent (Attachment2.04.7-10 (PeabodyAppendix7-8)). ThemeanvalueofpHduringirrigation <br />was 7.7, while averaging slightly lower during periods of no irrigation (7.39). <br />Mean TDS also increased after the irrigation season ended, averaging 1900 mg/I during this period <br />in comparison to a mean TDS of 1,176 mg/I during the irrigation season. <br />• After the irrigation season ended, TSS, FeT and Fep all averaged slightly higher (12.5 mg/1, .88 <br />REVISED JULY 2006 2.04.7-33 <br />