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historic ranges. Water levels at Well YW30 are the lowest on record. • <br />Well YW7 has been dry since June 2005. <br />- Wadge Underburden. Four wells; YWU16, 28, 29, and 30; monitor the <br />Wadge underburden. Well YWU28 exists in the Annand Draw basin, all <br />others exist in the Sage Creek basin. Most of these wells do not exhibit <br />any significant seasonal variation, although some variation from year- <br />to-year is evident. Well YWU28 (downgradient of the 1996/99 mine pit in <br />Annand Draw) had experienced a significant increase (66 feet) in October <br />2002, followed by a significant drop (67 feet) in October 2003. Well <br />YWU28 exhibited water levels this year within its historic range. In the <br />Sage Creek basin, Well YWU29 had experienced a decrease in water levels <br />from May 1999 to October 2005, but have increased since then. Well YWU16 <br />is often dry, but had water in June 2006. Well YWU30 displayed it lowest <br />water level ever in October 2004, but water levels have been on the rise <br />since then. <br />- Wolf Creek Coal and Underburden. Wells YWC31 and YWCU31 were abandoned <br />on October 26, 2001. They were about to be buried in spoils. Wells YWC33 <br />and YWCU33 were completed in August 2002 to replace those wells. Both <br />wells exhibit water levels within their historic ranges. <br />Ground Water Quality. Table 4 shows the ground water parameter list <br />used for all well water samples. Appendix C provides all ground water <br />quality data collected during the past two years, along with sampling <br />remarks. This is followed by a plot of TDS versus time for the entire <br />period of record. The regression line on this plot is generated by a <br />method known as LOWESS (Locally Weighted Scatter plot Smoothing). Unless <br />otherwise noted, smoothness factor (SF) of 1 (on a scale of 0 to 1) was <br />used, which gives maximum smoothing. This plot is followed by a table <br />listing historic TDS values and percent milliequivalents for major ions. <br />Finally, a statistical report representing baseline (i.e., premining) <br />data for each well (when available) is presented in Appendix C1. On this <br />statistics report, "censored data" refers to analytical values that were <br />below the detection limit, which were censored from the min/max/mean • <br />4 <br />