2011-08-29_REVISION - M1986015 (11)

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• • • Projected Phase 7 ground water level impacts were estimated based upon observed ground water impacts during Phase 1 mining and a best -fit using the Dupuis equation. Starting in January 2002, TMOP implemented a ground water level monitoring program using a network of monitoring wells surrounding the Phase 1 mining area. Well water levels were measured on a monthly basis throughout Phase I mining which was largely completed in June 2007. Following Phase I mining, additional dewatering was completed in the Phase II mining area. The location of the monitoring wells, Phase 1 and Phase 11 mining areas are shown in Figure G -1. Water level hydrographs for the monitoring wells are shown in Figure G -2. Total water level decline between January 2002, when Phase 1 mining began, and July 2007, when Phase I mining was completed, was plotted against distance from the Phase I permit boundary to evaluate the relationship between ground water level decline and distance from dewatering. As expected, the relationship is nearly linear and closely fits the Dupuit ground water flow equation, as shown in Figure G -3. The Dupuit ground water flow equation for an unconfined aquifer was used to estimate water level impacts from Phase 7 mining using an average saturated thickness of 25 feet and a distance to zero drawdown of 3, 400 feet. Actual water level impacts may be less than projected due to natural recharge, the buffering effects of the Arkansas River and the distance to zero drawdown is probably less than 3, 400 feet. Ground water level impacts are not projected south of the Arkansas River, which provides aquifer recharge and buffers water level drawdowns. As a result, projected ground water level impacts near the Arkansas River are probably overstated due to recharge from the River. (c) Inventory of Local Water Supply Wells To complete the well inventory, the State's database of well permits was queried to identify wells that may be located within affected areas. TMOP conducted field visits to all identifiable wells and water users that may be affected by Phase 7 dewatering. Well owners were interviewed regarding water use practices and the location of wells were recorded using a hand -held GPS. Wells identified in TMOP's well inventory are presented in Figure G -1. Not all of the permitted wells in the State's database were identified in the field, which is common due to lacking detail and errors in the State's database, such as mis- located wells or wells that have been abandoned and no longer exist. TMOP will coordinate with affected well owners to mitigate changes in well 3