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spring to early summer declining to low volume base flows later in the year, with short duration elevation of base flow in response to localized thunderstorm events. The geology of the area is an important factor relative to both subsidence projections and evaluation of subsidence effects. The study area is located on the southwestern flank of the locally significant Twentymile Park syncline. The Wadge coal seam and overlying units are part of a sequence of coalbearing strata forming the base of the Williams Fork Formation. This sequence contains, in order of deposition the Wolf Creek seams, Wadge seam and Lennox seam interbedded with shales claystones, siltstones and sandstones. The Wadge seam along with certain units within the immediately overlying sequence may have sufficient permeability and continuity to function as local groundwater aquifers. The overlying member is a marine shale, referred to in Maleki, 1987, as "Tongue of Lewis Shale", averaging 600 feet in thickness. Except in areas where faults may affect groundwater movement, this shale sequence effectively acts as an aquiclude minimizing hydraulic communication between the underlying coalbearing sequence and other potential aquifers higher in the stratigraphic sequence. The Twentymile Sandstone, a massive, white to cream-colored, well cemented, cross-bedded sandstone approximately 200-250 feet thick overlies the Lewis shale and serves as a key mapping unit. Given it's thickness, competency, lateral extent and physical separation from the Wadge seam in the sequence, the Twentymile Sandstone may significantly influence the nature and extent of mining related subsidence. The Twentymile Sandstone is overlain by several hundred feet of interbedded sandstones, siltstones and mudstones. These units, along with limited deposits of geologically recent alluvial/colluvial materials form the surficial geologic units in the study area. The following activities were completed to evaluate potential subsidence affects within the designated Fish Creek AVF area due to proposed longwall mining: • Review existing available data • Conduct literature review • Evaluate existing available information • Develop and implement data collection plan for required supplemental information • Project anticipated mining related subsidence • Evaluate effects on designated Fish Creek AVF area based on subsidence projections • Develop and implement monitoring plan to verify assumptions and determine effects The information presented in the technical revision represents the completion of the above activities, except for the installation of the proposed monitoring systems. The hydrologic monitoring system