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Table 3 documents the source of data used to calculate predicted salinity <br />impacts from mining, Salinity changes were predicted under five different <br />flow regimes for three different scenarios. The five flow regimes which were <br />used included baseline data collected in April of 1987, baseline data <br />collected in October of 1987, mean flow data collected from a variety of data <br />sources and historical records, low flow data of the irrigation season and low <br />flow data of the non-irrigation season. The low flow records were collected <br />from varying time periods of the historical records. A Q7_10 analysis was <br />used on historical United States Geological Survey (USGS) low flow data from <br />the San Miguel River sampling station at Naturita. The Division utilized this <br />statistically-derived low flow analysis of historical data as a standard for <br />comparing development scenarios on major waterways. The three scenarios <br />included operational impacts from the existing Nucla Mine, the combined Nucla <br />and Nucla East Mines while active, and the combined post-mining spoils <br />discharges. <br />The flow and salinity data were acquired from a variety of sources. The site <br />specific monitoring locations have a shorter period of record than the USGS <br />sites on the San Miguel River at Naturita. However, data were utilized <br />despite the statistical time inequity between sample sites since they were the <br />best available data. <br />The data collected in 1987 is most representative of actual hydrologic <br />conditions since same day data were available from all of the monitoring <br />sites. The Peabody sampling site located on the San Miguel River above <br />Calamity Draw is considered to be similar to the USGS site on the San Miguel <br />River at Naturita for this discussion. The spoils discharge and pit inflow <br />data are compared to chronologically similar periods. Flows during the 1987 <br />water year were slightly higher than the mean flow. The mean flow data were <br />collected site specifically during a variety of time frames. Data from <br />Calamity Draw has been collected eighteen times over a year-and-a-half period <br />starting in late 1986 and continuing through early 1988. There were 89 data <br />points collected at the Tuttle Draw sites monthly between 1980 and 1988. A <br />Q7-10 low flow was determined for USGS Site 09175500, on the San Miguel <br />River at Naturita, based on daily flows recorded between 1961 and 1981. These <br />data were coupled with the lowest flow of record at sites on Calamity Draw and <br />Tuttle Draw, again from eighteen data points on the former and 89 data points <br />on the latter. <br />The Q7_lp on the San Miguel River was utilized for the low flow case because <br />it is a statistically derived standard unit of low flow. Once every ten <br />years, the San Miguel River at Naturita will have an average flow of <br />6.48 cfs over a period of seven days. There is a 0,2~ chance of this <br />happening in any year. Water quantity would be so low, that it is speculative <br />that any irrigation water would return to Tuttle or Calamity Draws. <br />Consequently the mines would contribute nothing to the salinity of the <br />drainage basin. In addition, low flow of record for other sites were used for <br />the calculated predictions. <br />-23- <br />