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Monitoring Frequencies. Water quality monitoring at surface water sites is performed generally • during the months of March through October. Heavy snowfall and/or extended winter weather conditions may delay the monthly monitoring and field season sampling start-up until April or May. Continuous flow monitoring at surface water sites is not maintained during the December to March period because surface discharge is very small and weather conditions cause the stilling well float to freeze and thaw. The resolution of actual flow data monitored during the winter is so small, it is masked by the freezing and thawing action recorded by the monitor. Thus, the flow data is suspect and continuous recorders are not maintained during the winter months. However, during the spring snowmelt event from March to May and subsequent precipitation events thereafter through October, continuous flow monitoring at surface water sites is maintained. Monitoring of surface water for flow and chemistry on a tri-annual basis (March-October) provides hydrologic data during seasons of existing and potential surface water usage in the Seneca II-W area. Moreover, the significant hydrologic changes in flow and chemistry that occur in the surface water system Isee Tab 7, Hydrologic Description) take place during March through October when continuous flow monitoring, monthly field water chemistry measurements, end triannual water sampling are ongoing. Historic Surface Water Monitoring Program. The Historic Surface Water Monitoring Program is described in Appendix 15-1. Historic surface water monitoring sites are shown in Exhibit 7-1, Tab 7, Hydrologic Description. Table 15-1 contains a summary of historical and descriptive • information at Seneca II-W surface water monitoring sites. Surface water monitoring at Seneca II-W began in 1979 through a cooperative effort between Peabody Coal Company and the U.S. Geological Survey IUSGS). Peabody and the USGS established continuous recording stream gaging stations near the mouths of Hubberson and Watering Trough Gulch drainage basins IFG1 and FG2, respectively) in order to collect data that would be useful in the determination of surface water impacts induced by the Seneca II-W operation. Six additional stream monitoring sites were established by Peabody in 1979 at various locations nearby the Seneca II-W Mine: SG1, CG1, SG3, and SG4 in the Sage Creek drainage basin; and SG2 and CG2 in the Watering Trough Gulch drainage basin. Three more sites added in the early 1980's include SG5 in the Dry Creek drainage basin and Sites SG6 and SG7 in the Hubberson Gulch drainage basin. Prior to 1986, water quality monitoring at surface water sites consisted of quarterly long list analyses and monthly short list analyses. After December 1985, water quality monitoring at surface sites consisted of triannual water quality sampling according to the • 3 Revised 9/98