Investigations of groundwater system and simulation of regional groundwater flow for North Penn Area 7 Superfund site, Montgomery County, Pennsylvania

Abstract

conducted aquifer-interval isolation (packer) testing. Randall W. Conger conducted geophysical logging. J. Jeffrey Starn provided guidance on probabilistic modeling, and Richard B. Winston provided guidance on model preprocessing. The authors gratefully acknowledge the assistance of U.S. Environmental Protection Agency (USEPA) project managers Deanna Moultrie-Jackson and David Turner, the guidance of USEPA hydrogeologist Kathy Davies, and the cooperation of CDM Federal Programs Corporation (USEPA contractor) consultants Andrew Hopton, Aaron Frantz, and Andrea Soo. Property and well owners in the study area are thanked for giving permission to access sampling locations.

Effects of changes in pumping on regional groundwater-flow paths, 2005 and 2010, and areas contributing recharge to discharging wells, 1990–2010, in the vicinity of North Penn Area 7 Superfund site, Montgomery County, Pennsylvania

“…Simulated groundwater-flow paths under 2005 conditions (Senior and Goode, 2013) from known sources of soil contamination were consistent with the distribution of contaminants in groundwater determined from the autumn 2005 sampling, including apparent separate plumes of CFC-11 and CFC-113. In 2010, the EPA collected another round of groundwater samples in the western part of North Penn Area 7 that showed large decreases in contaminant concentrations compared to 2005-06 results (CDM Federal Programs Corporation, 2011a, b;David Turner, EPA, written commun., 2014).…”

“…From 2000 to 2005, USGS collected groundwater-level, geophysical, and aquifer-test data to describe the groundwater system and to provide a basis for the simulation of groundwater flow (Senior and Ruddy, 2004;others, 2005, 2008). Simulations of steady-state regional groundwater flow for periods of different pumping conditions (1990,1996,2000,2005) showed that directions of groundwater flow changed in response to changes in pumping (Senior and Goode, 2013). Senior and Goode (2013) also showed that the observed spatial distribution of contaminants was generally consistent with advective transport by groundwater flow from known source areas.…”

“…Simulations of steady-state regional groundwater flow for periods of different pumping conditions (1990,1996,2000,2005) showed that directions of groundwater flow changed in response to changes in pumping (Senior and Goode, 2013). Senior and Goode (2013) also showed that the observed spatial distribution of contaminants was generally consistent with advective transport by groundwater flow from known source areas.…”

“…This report describes the results of simulations of groundwater flow using a previously developed calibrated groundwater-flow model for North Penn Area 7 (Senior and Goode, 2013). The model was used to simulate groundwater flow (1) under 1990, 2000, 2005, 2010, and No Pumping (representing natural background or cessation of pumping) conditions to quantify the amount of recharge discharging to wells and streams and delineate the areas contributing recharge to discharging wells and streams in and near North Penn Area 7, and (2) under 2005 and 2010 conditions to evaluate the effects of changes in pumping between those time periods on groundwater-flow directions and potential distribution of contaminants in groundwater.…”

“…Subsequently, to further assist the EPA in understanding how pumping may have affected groundwater-flow directions and, specifically, whether 2005 to 2010 decreases in TCE concentrations could be related to changes in pumping, the USGS conducted simulations using the previously developed regional groundwater-flow model (Senior and Goode, 2013). Changes in pumping may also result in changes in the amount of contaminated groundwater discharging to wells or to streams and (or) changes in plume configuration and control.…”