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The site encompassed ~2500 acres in eastern Pennsylvania. Four buildings at the site were supplied with water from three wells. A fourth well supplied water to a pond. In 1998, the client filed plans to build another facility on the mountain, near existing structures. In part, the plan called for the construction of a new well to supply water to that facility.

The client commissioned Hazlett-Kincaid, Inc. to construct a local-scale groundwater flow model in order to determine the potential impact to groundwater levels in a mountainous setting (Figure 1) caused by pumping at four existing wells and a proposed well. MODFLOW software , as part of the GMS package, was applied.

Results of the modeling study indicated that, under normal environmental conditions and average pumping rates, pumping at the existing and proposed wells was sustainable and would not cause groundwater levels to drop below the well bottom elevations. Small groundwater level declines were predicted to propagate across the modeled area and down the mountain. Normal conditions corresponded to those measured during the summer of 1999. Average pumping rates were defined as high as 500 gpd and as low as 200 gpd at various wells.

The region expected to experience the most significant impact was localized around the wells near the ridge-line and extended toward the northwest corner of the site (Figure 2). Predictive scenarios indicated that increased pumping rates (2 x normal rates in all wells or 5 x the normal rate at the highest production well alone) would likely result in a localized reduction in groundwater levels sufficient to dry out the highest elevation well

The conceptual model of the site hydrogeology consisted of one unconfined aquifer with inflow limited to recharge due to precipitation. The aquifer was comprised of two geologic formations that dipped steeply across the modeled region and were cut by a northeast striking high-angle reverse fault. A quartzite formation underlaid the steep, higher elevation ridges to the north and south. A limestone-shale formation underlaid the lower angle slopes in the eastern part of the modeled area and much of the topographic saddle between the north and south ridges. Recharge was concentrated over the upper elevations of the mountain and averaged approximately 25% of precipitation over the entire modeled region. Two of the wells were completed in the quartzite and within the fault zone. The other wells were completed in the limestone-shale formation.

As a direct consequence of the modeling, the client adopted recommended groundwater use and budgeting guidelines and is currently in the process of implementing them. Future modeling work at the site may include a site-wide, comprehensive, water-budget model, hydrologic database, and groundwater flow model. This system would be used to quantitatively assess withdrawal or environmental impact scenarios in relation to the aquifer and site sensitive receptors.