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through their period of record is presented in Appendix 7-2. <br /> <br />Cround water monitor well installation began et Yoest in 1980 when the USGS completed e <br />total of 40 wells in portions of the Vedge coal sequence (overburden, coal, underburden), <br />Lennox coal sequence (coal end overburden only), and Sege Creek alluvium. Table 7-2 <br />presents general well completion information for all Yoast monitoring wells. The USGS <br />wells were drilled as part of a premining hydrologic study one in association with <br />development of the Seneee II-V Mine. Due fo well completion problems, failed annular <br />seals, and sediment infilling, at least one-third of these wells ere no longer suitable <br />for hydrologic monitoring purposes. All USGS bedrock monitor wells in the Vedge coal <br />sequence (except YY14 and YOV15) are slated for removal by mining. The four Lennox coal <br />sequence wells will be removed by constructing impoundment Pond 012, and will be abandoned <br />according to established abandonment procedures (see Teb 18, Hydrologic Reclamation Plan). <br />The Sage Creek alluvial wells ere expected to be retained es part of Peabody~s operational <br />Hydrologic Monitoring Program for the Yoast Mine. <br />In 1990, Peebody installed a total of 16 monitor wells in portions of the Yadge coal <br />sequence, Volf Creek coal sequence (coal and underburden only), end Grassy Creek and • <br />Annand Draw alluvial systems (Table 7-2). These monitoring wells ere intended to remain <br />viable throughout the life of the mining operation. TebLe 7-3 presents a compilation of <br />time periods during which water levels collected from all Yoast monitoring wells ere <br />considered valid, and this information is referenced where necessary in the following <br />sections. <br />Seasonality. In order to analyze end discuss seasonal variability of baseline hydrologic <br />data collected at monitoring sites (surface end ground water) established at the Yoest <br />Mine, four date ranges were selected to define each season: 1) spring (03/15 to 07/01); <br />2) summer (07/02 to 09/15); 3) fall (09/16 to 11/15); end 4) winter (11/16 to 03/14). The <br />spring season date range encompasses the period in which snowmelt runoff Largely <br />influences increases in stream discharges end recharge to shallow end rapidly responding <br />geologic units. The summer date range corresponds to periods of lower precipitation, when <br />stream baseflows attenuate end lowering water tables are exhibited. The fell date range <br />usually coincides with the cessation of evapotranspiration, and the winter date range <br />includes the majority of colder weather end associated snowfall. These date ranges and <br />associated seasons will be used throughout this tab to describe variability of the various • <br />hydrologic data collected et Toast during the baseline period. <br />6 <br />