Aquifer and aquifer-isolation test results in and around North Penn Area 6 Superfund site, Lansdale, Montgomery County, Pennsylvania are reviewed to provide estimated aquifer properties for use in a numerical model of ground-water flow. This review is in support of remedial action investigations by U.S. Environmental Protection Agency (USEPA), Region III, Philadelphia. Data are from files of the U.S. Geological Survey, USEPA, and water companies, and from unpublished consultant reports for USEPA and corporations in the Lansdale area. Tested wells are in fractured sedimentary rocks of the Brunswick Formation, which are Triassic-aged, dipping shales and sandstones. Review procedures include, in some cases, new analyses of drawdown during pumping and recovery using analytical models of flow to wells. Estimated aquifer transmissivities (T) range from zero to about 1,300 m2/d (meters squared per day), with most tests indicating T between 10 and 100 m2/d. Aquifer-isolation testing results indicate that most flow enters wells at a few discrete zones, probably fractures or bedding plane openings. The vertical connection between the zones in a single borehole with multiple producing zones often is negligible. This suggests that the formation is vertically anisotropic; the hydraulic conductivity is much larger in the horizontal direction than in the vertical direction. Some evidence of well-field-scale horizontal anisotropy exists, with maximum transmissivity aligned with the regional northeast strike of bedding, but this evidence is weak because of the small number of observation wells, particularly wells screened in isolated depth intervals. Analysis of recovery data after constant-pumping-rate aquifer tests and of drawdown during step tests suggests that a significant fraction, perhaps as much as 85 percent, of the drawdown in some production wells is due to well loss or skin effects in or very near the pumped well and is not caused by resistance to flow in the surrounding formations.
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USGS Numbered Series
Review of aquifer test results for the Lansdale area, Montgomery County, Pennsylvania, 1980-95