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Scientific Investigations Report 2005–5069

Interpretation of Geophysical Logs, Aquifer Tests, and Water Levels in Wells in and Near the North Penn Area 7 Superfund Site, Upper Gwynedd Township, Montgomery County, Pennsylvania, 2000-02

By Lisa A. Senior, Peter J. Cinotto, Randall W. Conger, Philip H. Bird, and Karl A. Pracht

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Abstract

Ground water in the vicinity of various industrial facilities in Upper Gwynedd Township and Lansdale Borough, Montgomery County, Pa., is contaminated with various volatile organic compounds (VOCs). The 2-square-mile area was placed on the National Priorities List as the North Penn Area 7 Superfund site by the U.S. Environmental Protection Agency (USEPA) in 1989. The U.S. Geological Survey (USGS) conducted geophysical logging, aquifer testing, water-level monitoring, and streamflow measurements in the vicinity of North Penn Area 7 beginning autumn 2000 to assist the USEPA in developing an understanding of the hydrogeologic framework in the area as part of the USEPA Remedial Investigation.

The study area is underlain by Triassic and Jurassic-age sandstones, siltstones, and shales of the Lockatong Formation and the Brunswick Group. Regionally, these rocks strike northeast and dip to the northwest. The sequence of rocks form a fractured-sedimentary-rock aquifer that acts as a set of confined to partially confined layered aquifers of differing permeabilities. The aquifers are recharged by precipitation and discharge to streams and wells. The Wissahickon Creek headwaters are less than 1 mile northeast of the study area, and this stream flows southwest to bisect North Penn Area 7. Ground water is pumped in the vicinity of North Penn Area 7 for industrial use and public supply.

The USGS collected geophysical logs for 16 wells that ranged in depth from 50 to 623 feet. Aquifer-interval-isolation testing was done in 9 of the 16 wells, for a total of 30 zones tested. A multiple-well aquifer test was conducted by monitoring the response of 14 wells to pumping a 600-ft deep production well in February and March 2002. In addition, water levels were monitored continuously in three wells in the area and streamflow was measured quarterly at two sites on Wissahickon Creek from December 2000 through September 2002.

Geophysical logging identified water-bearing zones associated with high-angle fractures and bedding-plane openings throughout the depth of the boreholes. Heatpulse-flowmeter measurements under nonpumping, ambient conditions indicated that borehole flow, where detected, was in the upward direction in three of the eight wells and in the downward direction in three wells. In two wells, both upward and downward flow were measured. Heatpulse-flowmeter measurements under pumping conditions were used to identify the most productive intervals in wells. Correlation of natural-gamma-ray and single-point-resistance logs indicated that bedding in the area probably strikes about 40 degrees northeast and dips from 6 to 7 degrees northwest.

Aquifer intervals isolated by inflatable packers in wells were pumped to test productivity and to collect samples to determine chemical quality of water produced from the interval. Interval-isolation testing confirmed the presence of vertical hydraulic gradients indicated by heatpulse-flowmeter measurements. The specific capacities of isolated intervals ranged over two orders of magnitude, from 0.02 to more than 3.6 gallons per minute per foot. Intervals adjacent to isolated pumped intervals showed little response to pumping the isolated zone. The presence of vertical hydraulic gradients and lack of adjacent-interval response to pumping in isolated intervals indicate a limited degree of vertical hydraulic connection between the aquifer intervals tested. Concentrations of most VOC contaminants generally were highest in well-water samples from the shallowest isolated intervals, with some exceptions. Trichloroethylene, cis-1,2-dichloroethylene, and toluene were the most frequently detected VOCs, with maximum concentrations of greater than 340, 680, and greater than 590 micrograms per liter, respectively.

Results of the aquifer test with multiple observation wells showed that water levels in 4 of the 14 wells declined in response to pumping. The four wells that responded to pumping are either along strike or within the up-dip or down-dip projection of the producing zones of the pumped well. The spatial distribution of the four responding wells indicates that geologic structure has some affect over hydraulic connections in the aquifer.

Water-level monitoring in three wells from December 2000 through September 2002 shows the seasonal rise and decline of levels for the period. Water levels in two wells near Wissahickon Creek were evaluated in relation to streamflow on dates of quarterly streamflow measurements. The Wissahickon Creek was a losing stream between the two measurement sites and ground-water levels were lower than the stream channel bottom for most dates. Water levels measured in a 16-square-mile area around and including North Penn Area 7 during December 2002 indicated that the ground-water level surface is relatively flat in the immediate vicinity of the North Penn Area 7 site (as compared to surrounding areas) and generally is similar to topography except in areas affected by large amounts of ground-water withdrawal.

Revised June 2012

First posted September 2005

For additional information contact:
Director
USGS Pennsylvania Water Science Center
215 Limekiln Road
New Cumberland, Pennsylvania 17070
Telephone: 717–730–6900
Fax: 717–730–6997
or access the USGS Water Resources of Pennsylvania Home page at:
http://pa.water.usgs.gov/.

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Suggested citation:

Senior, L.A., Cinotto, P.J., Conger, R.W., Bird, P.H., and Pracht, K.A., 2005, Interpretation of geophysical logs, aquifer tests, and water levels in wells in and near the North Penn Area 7 Superfund Site, Upper Gwynedd Township, Montgomery County, Pennsylvania, 2000-02: U.S. Geological Scientific Investigations Report 2005–5069, 129 p., available only at http://pubs.usgs.gov/sir/2005/5069.



Contents

Abstract

Introduction

Purpose and Scope

Physical and Hydrogeologic Setting

Well-Identification System

Previous Investigations

Geophysical Logs

Interpretation of Individual Well Logs

Well MG-174 (Clearline 2)

Well MG-175 (Spra-Fin 1)

Well MG-202 (L-22)

Well MG-1144 (Teleflex T-13)

Well MG-1145 (Teleflex T-14)

Well MG-1146 (Teleflex T-4)

Well MG-1147 (Teleflex T-11)

Well MG-1148 (Teleflex T-12)

Well MG-1149 (Teleflex T-10)

Well MG-1505 (Huey)

Well MG-1842 (Teleflex T-15)

Well MG-1843 (Teleflex T-6)

Well MG-1844 (Fitzpatrick Container)

Well MG-1845 (Fitzpatrick Container)

Well MG-1846 (Fitzpatrick Container)

Well MG-1897 (Clearline 3)

Correlation of Well Logs

Borehole-Deviation Logs

Acoustic-Televiewer Logs

Aquifer Tests

Single-Well, Interval-Isolation Tests

Well MG-174 (Clearline 2)

Well MG-175 (Spra-Fin 1)

Well MG-202 (L-22)

Well MG-1144 (Teleflex T-13)

Well MG-1145 (Teleflex T-14)

Well MG-1146 (Teleflex T-4)

Well MG-1147 (Teleflex T-11)

Well MG-1842 (Teleflex T-15)

Well MG-1897 (Clearline 3)

Discussion of Single-Well, Aquifer-Interval-Isolation-Test Results

Multiple-Well Test

Water Levels

Fluctuations

Relation to Streamflow

Regional Potentiometric Surface

Vertical Gradients

Summary

Acknowledgments

References Cited


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