Prepared in cooperation with the U.S. Environmental Protection Agency

Investigations of the Groundwater System and Simulation 

of Regional Groundwater Flow for North Penn Area 7 

Superfund Site, Montgomery County, Pennsylvania

75°20' 75°15' 

40°15'

40°10'

EXPLANATION

Selected cells of model—

Stream in layer 1 and

pumping well in 

underlying layer

Pumping well

Stream

Model boundary

North Penn Area 7

boundary Discharge to stream

0 1 2 KILOMETERS

0 1 2 MILES

Scientific Investigations Report 2013–5045

U.S. Department of the Interior

U.S. Geological Survey
Front cover. Model boundary, streams cells, and pumped well cells for model of North Penn Area 7 Superfund site, Upper Gwynedd 

Township and vicinity, Montgomery County, Pennsylvania.

Back cover. Cross section in the dip direction of model grid for North Penn Area 7 Superfund site, Upper Gwynedd Township and 

vicinity, Montgomery County, Pennsylvania. (See figure 33 for location of line of section.)
Investigations of the Groundwater System 

and Simulation of Regional Groundwater 

Flow for North Penn Area 7 Superfund Site, 

Montgomery County, Pennsylvania

By Lisa A. Senior and Daniel J. Goode

Prepared in cooperation with the U.S. Environmental Protection Agency

Scientific Investigations Report 2013–5045

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

KEN SALAZAR, Secretary

U.S. Geological Survey

Suzette M. Kimball, Acting Director

U.S. Geological Survey, Reston, Virginia: 2013

For more information on the USGS—the Federal source for science about the Earth, its natural and living 

resources, natural hazards, and the environment, visit http://www.usgs.gov or call 1–888–ASK–USGS.

For an overview of USGS information products, including maps, imagery, and publications, 

visit http://www.usgs.gov/pubprod

To order this and other USGS information products, visit http://store.usgs.gov

Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the 

U.S. Government.

Although this information product, for the most part, is in the public domain, it also may contain copyrighted materials 

as noted in the text. Permission to reproduce copyrighted items must be secured from the copyright owner.

Suggested citation:

Senior, L.A., and Goode, D.J., 2013, Investigations of groundwater system and simulation of regional groundwater 

flow for North Penn Area 7 Superfund site, Montgomery County, Pennsylvania: U.S. Geological Survey Scientific 

Investigations Report 2013–5045, 95 p.
iii

Acknowledgments

The authors wish to thank the U.S. Geological Survey personnel who contributed 

substantially to this report. Philip H. Bird conducted borehole video logging, and Allan J. 

Ruddy and Leif E. Olson conducted water-level and streamflow measurements. Peter J. Cinotto, 

Leif E. Olson, and Robert Rosman 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. 
iv

Contents

Acknowledgements......................................................................................................................................iii

Abstract...........................................................................................................................................................1

Introduction.....................................................................................................................................................2

Purpose and scope...............................................................................................................................4

Previous Investigations........................................................................................................................4

Well-Identification System..................................................................................................................5

Geologic and Hydrogeologic Setting..........................................................................................................5

Geologic Setting....................................................................................................................................5

Hydrogeologic Setting .........................................................................................................................8

Summary of Field Investigations of Groundwater System at North Penn Area 7.............................11

Geophysical Logs................................................................................................................................11

Aquifer Tests........................................................................................................................................16

Single-Well Packer Tests .........................................................................................................16

Multiple-Well Aquifer Tests .....................................................................................................22

Groundwater Levels ...........................................................................................................................26

Streamflow Measurements and Groundwater/Surface-Water Relations ................................28

Groundwater Quality at North Penn Area 7 ...................................................................................30

Groundwater Quality in Isolated Intervals ............................................................................30

Groundwater Quality in Existing and New Monitor Wells ..................................................31

Volatile Organic Compounds and Metals .....................................................................33

Selected Inorganic Constituents ...................................................................................33

Chloride .....................................................................................................................33

Sulfate........................................................................................................................33

Silica ..........................................................................................................................36

Boron .........................................................................................................................36

Bromide .....................................................................................................................36

Inorganic Constituents as Tracers or Indicator of Lithology.....................................43

Simulation of Regional Groundwater Flow..............................................................................................43

Estimation of Regional-Scale Aquifer Hydraulic Properties ......................................................43

Numerical Simulation of Regional Groundwater Flow .................................................................43

Conceptual Model .....................................................................................................................44

Model Structure and Boundary Conditions...........................................................................44

Calibration Methods..................................................................................................................48

Recharge and Discharge..........................................................................................................49

Measured and Simulated Water Levels in Wells .................................................................51

Estimated Aquifer Hydraulic Properties and Recharge Rates...........................................58

Regional Groundwater-Flow Paths..................................................................................................61

Simulated Flow Paths, Contributing Areas, and Uncertainty ......................................................61

Groundwater-Flow Paths in 1990 .....................................................................................................63

Groundwater-Flow Paths in 1996 .....................................................................................................66

Groundwater-Flow Paths in 2000 .....................................................................................................66
v

Groundwater-Flow Paths in 2005 .....................................................................................................71

Groundwater/Surface-Water Interactions.....................................................................................71

Simulated Shutdown of Well MG-202..............................................................................................71

Relation Between Water Quality and Groundwater Flow............................................................76

Inferred Flow Paths from Distribution of Measured Contaminants .................................76

Inferred Flow Paths from Observed Inorganic Constituent Distribution ..........................82

Limitations and Uncertainties in Predictive Simulations .............................................................85

Summary and Conclusions.........................................................................................................................85

References Cited..........................................................................................................................................87

Figures

1. Map showing location of the North Penn Area 7 Superfund site and selected wells, 

Upper Gwynedd Township and vicinity, Montgomery County, Pennsylvania.....................3

2. Map showing physiographic provinces in southeastern Pennsylvania .............................6

3. Map showing units of bedrock underlying North Penn Area 7 Superfund site and 

model boundary for North Penn Area 6 , Upper Gwynedd Township and vicinity, 

Montgomery County, Pennsylvania...........................................................................................7

4. Map showing preliminary revised lithologic mapping of bedrock geology at and 

near North Penn Area 7 Superfund site, Upper Gwynedd Township and vicinity, 

Montgomery County, Pennsylvania...........................................................................................9

5. A, cross section showing conceptual groundwater-flow system in dipping-bed 

fractured sedimentary rock aquifer and B, schematic cross section showing 

numerical simulation of groundwater flow in conceptual dipping-bed sedimentary 

rock aquifer with layered units of high and low permeability.............................................10

6. Map showing location of existing and new monitor wells with geophysical logs 

and packer tests conducted by U.S. Geological Survey at and near the North Penn 

Area 7 Superfund site, Upper Gwynedd Township and vicinity, Montgomery County, 

Pennsylvania, 2000–2005 ...........................................................................................................14

7. Map showing direction of vertical gradients measured in boreholes and (or) 

determined from water levels in well clusters at and near North Penn Area 7 

Superfund site, Upper Gwynedd Township and vicinity, Montgomery County, 

Pennsylvania, 2001–2005 ...........................................................................................................15

8. Natural gamma-ray logs indicating beds of elevated natural gamma-ray activity 

that can be correlated among boreholes/wells in the western part of North Penn 

Area 7 Superfund site, Upper Gwynedd Township and vicinity, Montgomery County, 

Pennsylvania ...............................................................................................................................17

9. Interpreted correlation of natural gamma-ray activity and single-point resistance 

logs for monitor well clusters in the A, western (RI-15 cluster) and B, eastern (RI-8 

cluster) parts of North Penn Area 7 Superfund site, Upper Gwynedd and vicinity, 

Montgomery County, Pennsylvania.........................................................................................18

10. Graph showing water levels in the isolated interval of 193 to 215 ft below land 

surface and adjacent intervals in well MG-2131 (RI-15DD) during the single-well 

packer tests, North Penn Area 7 Superfund site, Upper Gwynedd Township and 

vicinity, Montgomery County, Pennsylvania, June 10, 2005 ................................................20
vi

11. Boxplots showing A, calculated transmissivities and B, hydraulic conductivities 

in relation to a range of depths for water-bearing intervals isolated by packers in 

15 wells of similar depths, North Penn Area 7 Superfund site, Upper Gwynedd 

Township and vicinity, Montgomery County, Pennsylvania, March 2004 through 

August 2005..................................................................................................................................21

12. Section A–A’ with transmissivity of tested zones in selected wells that are projected 

onto a line approximately parallel to estimated dip of 10 degrees, North Penn Area 

7 Superfund site, Upper Gwynedd Township and vicinity, Montgomery County, 

Pennsylvania ...............................................................................................................................21

13. Boxplots showing A, calculated transmissivities and B, hydraulic conductivities, by 

mapped geologic unit, for water-bearing intervals isolated by packers in 15 wells of 

similar depths, North Penn Area 7 Superfund site, Upper Gwynedd Township and 

vicinity, Montgomery County, Pennsylvania, March 2004 through August 2005..............22

14. Map showing location of pumped production and observation wells used for 

multiple well aquifer tests, and lines of section A–A’ and B–B’, at North Penn Area 

7 Superfund site, Upper Gwynedd Township and vicinity, Montgomery County, 

Pennsylvania, 2002–2005 ...........................................................................................................23

15.A, section A–A’ with production well MG-202 (L-22) and 15 observation wells 

monitored during shutdown and after restart of pumping in well MG-202 in 

March 2002 and B, section B–B’ with production well MG-202, 14 observation wells 

monitored during shutdown and restart of pumping in well MG-202 in December 

2004, well MG-175 at the Spra-Fin property, and mapped geologic units at and near 

North Penn Area 7, Upper Gwynedd Township and vicinity, Montgomery County, 

Pennsylvania ...............................................................................................................................24

16. Water-level responses to pumping of isolated intervals in well MG-2131 (RI-15DD) 

in June 2005, North Penn Area 7 Superfund site, Upper Gwynedd Township 

and vicinity, Montgomery County, Pennsylvania...................................................................25

17. Graphs showing water levels measured in A, wells MG-2085 (RI-3I) and MG-2084 

(RI-3D) and B, MG-2092 (RI-5S), MG-2091 (RI-5I), MG-2090 (RI-5D), and MG-2126 

(RI-13D) during the packer test of well RI-15DD (MG-2131), June 9–13, 2005, 

North Penn Area 7 Superfund site, Upper Gwynedd Township and vicinity, 

Montgomery County, Pennsylvania.........................................................................................27

18. Graph showing water levels in long-term observation wells BK-929 and BK-1020 

and in well MG-68, North Penn Area 7, Upper Gwynedd Township and vicinity, 

Montgomery County, Pennsylvania, 1996–2006.....................................................................28

19. Map showing location of pumped wells with pumping rates, observation wells, 

and streamflow-measurement sites for the June 2003 seepage investigation on 

Wissahickon Creek and lithology at and near North Penn Area 7, Upper Gwynedd 

Township and vicinity, Montgomery County, Pennsylvania.................................................29

20. Graph showing measured groundwater levels (shown as altitudes) in wells 

MG-72, MG-1145, and MG-1146 and estimated altitudes of the streambed 

of Wissahickon Creek near the wells, at and near North Penn Area 7 Superfund 

site, Upper Gwynedd Township and vicinity, Montgomery County, Pennsylvania, 

December 2000–November 2006..............................................................................................30

21. Graphs showing specific conductance, acid neutralizing capacity as estimate 

of alkalinity, pH, and concentrations of dissolved oxygen, nitrate, and sulfate 

measured in the field in water samples from isolated zones in 15 deep monitor 

wells, North Penn Area 7 Superfund site, Upper Gwynedd Township and vicinity, 

Montgomery County, Pennsylvania, March 2004 through August 2005 ............................32
vii

22. Map showing chloride concentrations in samples collected in spring 2006 from 

monitor well clusters and open-hole wells and line of section A–A’, North Penn 

Area 7 Superfund site, Upper Gwynedd Township and vicinity, Montgomery County, 

Pennsylvania ...............................................................................................................................34

23. Locations of monitor wells projected onto a line parallel to dip and chloride 

concentrations in samples collected from the monitor wells in spring 2006, 

North Penn Area 7 Superfund site, Upper Gwynedd Township and vicinity, 

Montgomery County, Pennsylvania.........................................................................................35

24. Map showing silica concentrations in samples collected in fall 2005 from monitor 

well clusters and open-hole wells, and line of section A–A’, North Penn Area 7 

Superfund site, Upper Gwynedd Township and vicinity, Montgomery County, 

Pennsylvania ...............................................................................................................................37

25. Graph showing locations of monitor wells projected onto a line parallel to dip 

and silica concentrations in samples collected from the monitor wells in fall 2005, 

North Penn Area 7 Superfund site, Upper Gwynedd Township and vicinity, 

Montgomery County, Pennsylvania.........................................................................................38

26. Map showing boron concentrations in samples collected in spring 2006 from 

monitor well clusters and open-hole wells, and line of section A–A’, North Penn 

Area 7 Superfund site, Upper Gwynedd Township and vicinity, Montgomery County, 

Pennsylvania ...............................................................................................................................39

27. Graph showing locations of monitor wells projected onto a line parallel to dip 

and boron concentrations in samples collected from the monitor wells in 

spring 2006, North Penn Area 7 Superfund site, Upper Gwynedd Township 

and vicinity, Montgomery County, Pennsylvania...................................................................40

28. Graph showing chloride/bromide mass ratio in relation to chloride concentration 

in water samples collected in March 2006 from monitor wells at and near North 

Penn Area 7 Superfund site, Upper Gwynedd Township and vicinity, Montgomery 

County, Pennsylvania.................................................................................................................41

29. Map showing spatial distribution of chloride/bromide mass ratios in water collected 

in March 2006 from monitor and existing open-hole wells, at and near North Penn 

Area 7 Superfund site, Upper Gwynedd Township and vicinity, Montgomery County, 

Pennsylvania ...............................................................................................................................42

30. Map showing model boundary, streams cells, and pumped well cells for model 

of North Penn Area 7 Superfund site, Upper Gwynedd Township and vicinity, 

Montgomery County, Pennsylvania.........................................................................................45

31. Cross section in the dip direction of model grid for North Penn Area 7 Superfund 

site, Upper Gwynedd Township and vicinity, Montgomery County, Pennsylvania..........47

32. Cross section in the strike direction of model grid for North Penn Area 7 Superfund 

site, Upper Gwynedd Township and vicinity, Montgomery County, Pennsylvania..........47

33. Screen capture of model preprocessor showing structural contours for top of bed 

B4 (projected), layer 10 thickness for the model, and lines of section, North Penn 

Area 7 Superfund site, Upper Gwynedd Township and vicinity, Montgomery County, 

Pennsylvania ...............................................................................................................................48

34. Screen capture of model preprocessor showing locations of streamflow 

measurements, land-surface elevations at streams, and locations of pumped wells 

for the numerical model for North Penn Area 7 Superfund site, Upper Gwynedd 

Township and vicinity, Montgomery County, Pennsylvania.................................................50

35. Map showing simulated water-table altitudes and location of observation wells 

showing simulated water levels minus measured water levels in A, 1996, B, 2000, 

and C, 2005 for the model for North Penn Area 7 Superfund site, Upper Gwynedd 

Township and vicinity, Montgomery County, Pennsylvania.................................................55
viii

36. Graph showing relation of measured groundwater-level altitudes to groundwaterlevel altitudes simulated by the numerical model for North Penn Area 7 Superfund 

site, Upper Gwynedd Township and vicinity, Montgomery County, Pennsylvania..........58

37. Graph showing sensitivity of model calibration to model parameters for 

groundwater-flow simulation of North Penn Area 7 Superfund site and vicinity, 

Upper Gwynedd Township and vicinity, Montgomery County, Pennsylvania...................60

38. Map showing simulated groundwater-flow paths extending from contaminant 

source areas to pumped wells for pumping conditions in 1990 for North Penn 

Area 7 Superfund site, Upper Gwynedd Township and vicinity, Montgomery County, 

Pennsylvania ...............................................................................................................................64

39. Map showing simulated area contributing recharge to well MG-202 (L-22) 

for pumping conditions in 1990 for North Penn Area 7 Superfund site, 

Upper Gwynedd Township and vicinity, Montgomery County, Pennsylvania...................65

40. Map showing simulated groundwater-flow paths extending from contaminant 

source areas to pumped wells for pumping conditions in 1996 for North 

Penn Area 7 Superfund site, Upper Gwynedd Township and vicinity, 

Montgomery County, Pennsylvania.........................................................................................67

41. Map showing simulated area contributing recharge to well MG-202 (L-22) 

for pumping conditions in 1996 for North Penn Area 7 Superfund site, 

Upper Gwynedd Township and vicinity, Montgomery County, Pennsylvania...................68

42. Map showing simulated groundwater-flow paths extending from contaminant 

source areas to pumped wells for pumping conditions in 2000 for North Penn 

Area 7 Superfund site, Upper Gwynedd Township and vicinity, 

Montgomery County, Pennsylvania.........................................................................................69

43. Map showing simulated area contributing recharge to well MG-202 (L-22) 

for pumping conditions in 2000 for North Penn Area 7 Superfund site, 

Upper Gwynedd Township and vicinity, Montgomery County, Pennsylvania...................70

44. Map showing simulated groundwater-flow paths extending from contaminant 

source areas to pumped wells for pumping conditions in 2005 for North Penn 

Area 7 Superfund site, Upper Gwynedd Township and vicinity, 

Montgomery County, Pennsylvania.........................................................................................72

45. Map showing simulated area contributing recharge to well MG-202 (L-22) 

for pumping conditions in 2005 for North Penn Area 7 Superfund site, 

Upper Gwynedd Township and vicinity, Montgomery County, Pennsylvania...................73

46. Map showing simulated stream loss and stream gain for the Upper Wissahickon 

Creek and other streams, and pumping rates for selected wells, in 2005, 

for the model for North Penn Area 7 Superfund site, Upper Gwynedd Township 

and vicinity, Montgomery County, Pennsylvania...................................................................74

47. Map showing simulated area contributing recharge to well MG-76 (L-17) 

for pumping conditions in 2005 for North Penn Area 7 Superfund site, 

Upper Gwynedd Township and vicinity, Montgomery County, Pennsylvania...................75

48. Maps showing measured water-level changes in observation wells at 1,000 minutes 

after shutdown of well MG-202 (L-22) in 2004 and simulated water-level recovery 

contours in the respective middle sub-layers of model layers after shutdown of well 

MG-202 (L-22): A, model layer 8 at at 1 day (1,440 minutes), B, model layer 8 at 7 days, 

and C, model layer 7 at 7 days, North Penn Area 7, Upper Gwynedd Township and 

vicinity, Montgomery County, Pennsylvania ..........................................................................77
ix

49. Maps showing simulated groundwater-flow paths for conditions in A, 2005 and 

B, 1990, and measured TCE concentrations in samples collected from observation 

wells in fall 2005, North Penn Area 7 Superfund site, Upper Gwynedd Township 

and vicinity, Montgomery County, Pennsylvania...................................................................80

50. Maps showing simulated groundwater-flow paths for conditions in 2005 and 

measured concentrations of A, CFC-11 and B, CFC-113 in samples collected 

from observation wells in fall 2005, North Penn Area 7 Superfund site, 

Upper Gwynedd Township and vicinity, Montgomery County, Pennsylvania...................83

Tables

1. Characteristics of wells with geophysical logs collected and aquifer-intervalisolation (packer) tests conducted by the U.S. Geological Survey at and near 

North Penn Area 7 Superfund site, Upper Gwynedd Township and vicinity, 

Montgomery County, Pennsylvania, 2000–2005.....................................................................12

2. Summary statistics of physical and chemical characteristics measured in the 

field of unfiltered water samples collected from isolated zones in 15 deep monitor 

wells, North Penn Area 7 Superfund site, Upper Gwynedd Township and vicinity, 

Montgomery County, Pennsylvania, March 2004 through August 2005 ............................31

3. Hydrostratigraphy used in the groundwater model for North Penn Area 7 

Superfund site, Upper Gwynedd Township and vicinity, Montgomery County, 

Pennsylvania ...............................................................................................................................46

4. Measured and simulated groundwater discharge to stream reaches for the 

calibrated numerical model of groundwater flow in the North Penn Area 7 

Superfund site, Upper Gwynedd Township and vicinity, Montgomery County, 

Pennsylvania ...............................................................................................................................52

5. Pumping well identification, locations and pumping rates for North Penn Area 

7 Superfund site, Upper Gwynedd Township and vicinity, Montgomery County, 

Pennsylvania ...............................................................................................................................53

6. Water levels in wells used for calibration of the groundwater-flow model for North 

Penn Area 7 Superfund site, Upper Gwynedd Township and vicinity, 

Montgomery County, Pennsylvania.........................................................................................91

7. Optimum and approximate, individual, 95-percent confidence-interval values 

for parameters estimated through calibration of the groundwater-flow model 

for North Penn Area 7 Superfund site, Upper Gwynedd Township and vicinity, 

Montgomery County, Pennsylvania.........................................................................................59

8. Simulated water budgets for calibration periods 1996, 2000, and 2005 for model 

area and North Penn Area 7 Superfund site, Upper Gwynedd Township and 

vicinity, Montgomery County, Pennsylvania ..........................................................................61

9. Correlation and variance/covariance matrices for generation of probabilistic 

parameters...................................................................................................................................62
x

Conversion Factors and Datums

Inch/Pound to SI

Multiply By To obtain

Length

inch (in) 2.54 centimeter (cm)

inch (in) 25.4 millimeter (mm)

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

Area

acre 0.4047 hectare (ha)

acre 0.004047 square kilometer (km2)

square foot (ft2) 929.0 square centimeter (cm2)

square foot (ft2) 0.09290 square meter (m2)

square mile (mi2) 259.0 hectare (ha)

square mile (mi2) 2.590 square kilometer (km2) 

Volume

gallon (gal) 3.785 liter (L) 

gallon (gal) 0.003785 cubic meter (m3) 

gallon (gal) 3.785 cubic decimeter (dm3) 

million gallons (Mgal) 3,785 cubic meter (m3)

cubic foot (ft3) 28.32 cubic decimeter (dm3) 

cubic foot (ft3) 0.02832 cubic meter (m3) 

Flow rate

foot per day (ft/d) 0.3048 meter per day (m/d)

cubic foot per second (ft3/s) 0.02832 cubic meter per second (m3/s)

cubic foot per second per square

mile [(ft3/s)/mi2]

 0.01093 cubic meter per second per square

kilometer [(m3/s)/km2]

cubic foot per day (ft3/d) 0.02832 cubic meter per day (m3/d)

gallon per minute (gal/min) 0.06309 liter per second (L/s)

gallon per day (gal/d) 0.003785 cubic meter per day (m3/d)

gallon per day per square mile

 [(gal/d)/mi2]

 0.001461 cubic meter per day per square

kilometer [(m3/d)/km2]

million gallons per day (Mgal/d) 0.04381 cubic meter per second (m3/s)

inch per year (in/yr) 25.4 millimeter per year (mm/yr)

Specific capacity

gallon per minute per foot 

[(gal/min)/ft)]

 0.2070 liter per second per meter [(L/s)/m]

Hydraulic conductivity

foot per day (ft/d) 0.3048 meter per day (m/d)

Hydraulic gradient

foot per mile (ft/mi) 0.1894 meter per kilometer (m/km)

Transmissivity*

foot squared per day (ft2/d) 0.09290 meter squared per day (m2/d) 

Leakance

foot per day per foot [(ft/d)/ft] 1 meter per day per meter

inch per year per foot [(in/yr)/ft] 83.33 millimeter per year per meter

[(mm/yr)/m]
xi

Temperature in degrees Celsius (°C) may be converted to degrees Fahrenheit (°F) as follows:

°F=(1.8×°C)+32

Temperature in degrees Fahrenheit (°F) may be converted to degrees Celsius (°C) as follows:

°C=(°F-32)/1.8

Vertical coordinate information is referenced to the North American Vertical Datum of 1988 

(NAVD 88) for data shown in feet, unless specified otherwise. Model input and output shown in 

meters are referenced to the National Geodetic Vertical Datum of 1929 (NGVD 29).

Horizontal coordinate information is referenced to the North American Datum on 1927 (NAD 27) 

for model input and output. Other data, unless otherwise specified, are referenced to the North 

American Datum of 1983 (NAD 83).

Altitude, as used in this report, refers to distance above the vertical datum.

*Transmissivity: The standard unit for transmissivity is cubic foot per day per square foot times 

foot of aquifer thickness [(ft3/d)/ft2]ft. In this report, the mathematically reduced form, foot 

squared per day (ft2/d), is used for convenience.

Specific conductance is given in microsiemens per centimeter at 25 degrees Celsius (μS/cm at 

25 °C).

Concentrations of chemical constituents in water are given either in milligrams per liter (mg/L) 

or micrograms per liter (μg/L).

NOTE TO USGS USERS: Use of hectare (ha) as an alternative name for square hectometer 

(hm2) is restricted to the measurement of small land or water areas. Use of liter (L) as a special 

name for cubic decimeter (dm3) is restricted to the measurement of liquids and gases. No prefix 

other than milli should be used with liter. Metric ton (t) as a name for megagram (Mg) should be 

restricted to commercial usage, and no prefixes should be used with it.
xii
Investigations of the Groundwater System and Simulation 

of Regional Groundwater Flow for North Penn Area 7 

Superfund Site, Montgomery County, Pennsylvania

By Lisa A. Senior and Daniel J. Goode 

Abstract

Groundwater in the vicinity of several industrial facilities in Upper Gwynedd Township and vicinity, Montgomery 

County, in southeast Pennsylvania has been shown to be 

contaminated with volatile organic compounds (VOCs), 

the most common of which is the solvent trichloroethylene 

(TCE). 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, and water-level monitoring, 

and measured streamflows in and near North Penn Area 7 

from fall 2000 through fall 2006 in a technical assistance 

study for the USEPA to develop an understanding of the 

hydrogeologic framework in the area as part of the USEPA 

Remedial Investigation. In addition, the USGS developed a 

groundwater-flow computer model based on the hydrogeologic framework to simulate regional groundwater flow and 

to estimate directions of groundwater flow and pathways of 

groundwater contaminants.

The study area is underlain by Triassic- and Jurassic-age 

sandstones and shales of the Lockatong Formation and Brunswick Group in the Mesozoic Newark Basin. 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 layers of differing 

permeabilities. Depth to competent bedrock typically is less 

than 20 ft below land surface. The aquifer layers are recharged 

locally by precipitation and discharge locally to streams. The 

general configuration of the potentiometric surface in the aquifer is similar to topography, except in areas affected by pumping. The headwaters of Wissahickon Creek are nearby, and the 

stream flows southwest, parallel to strike, to bisect North Penn 

Area 7. Groundwater is pumped in the vicinity of North Penn 

Area 7 for industrial use, public supply, and residential supply.

Results of field investigations by USGS at the site and 

results from other studies support, and are consistent with, a 

conceptual model of a layered leaky aquifer where the dip of 

the beds has a strong control on hydraulic connections in the 

groundwater system. Connections within and (or) parallel to 

bedding tend to be greater than across bedding. 

Transmissivities of aquifer intervals isolated by packers ranged over three orders of magnitude [from about 2.8 to 

2,290 square feet per day (ft2/d) or 0.26 to 213 square meters 

per day (m2/d)], did not appear to differ much by mapped 

geologic unit, but showed some relation to depth being 

relatively smaller in the shallowest and deepest intervals (0 to 

50 ft and more than 250 ft below land surface, respectively) 

compared to the intermediate depth intervals (50 to 250 ft 

below land surface) tested. Transmissivities estimated from 

multiple-observation well aquifer tests ranged from about 700 

to 2,300 ft2/d (65 to 214 m2/d). Results of chemical analyses 

of water from isolated intervals or monitoring wells open to 

short sections of the aquifer show vertical differences in concentrations; chloride and silica concentrations generally were 

greater in shallow intervals than in deeper intervals. Chloride 

concentrations greater than 100 milligrams per liter (mg/L), 

combined with distinctive chloride/bromide ratios, indicate a 

different source of chloride in the western part of North Penn 

Area 7 than elsewhere in the site.

Groundwater flow at a regional scale under steady-state 

conditions was simulated by use of a numerical model (MODFLOW-2000) for North Penn Area 7 with different layers 

representing saprolite/highly weathered rock near the surface 

and unweathered competent bedrock. The sedimentary formations that underlie the study area were modeled using dipping 

model layers for intermediate and deep zones of unweathered, 

fractured rock. Horizontal cell model size was 100 meters (m) 

by 100 meters (328 ft by 328 ft), and model layer thickness 

ranged from 6 m (19.7 ft) representing shallow weathered 

rock and saprolite up to 200 m (656 ft) representing deeper 

dipping bedrock. The model did not include detailed structure 

to account for local-scale differences in hydraulic properties, 

with the result that local-scale groundwater flow may not be 

well simulated. Additional detailed multi-well aquifer tests 

would be needed to establish the extent of interconnection 
2 Groundwater System and Simulation of Flow for North Penn Area 7 Superfund Site, Montgomery County, Pennsylvania

between intervals at the local scale to address remediation of 

contamination at each source area. 

This regional groundwater-flow model was calibrated 

against measured groundwater levels (1996, 2000, and 2005) 

and base flow estimated from selected streamflow measurements by use of nonlinear-regression parameter-estimation 

algorithms to determine hydraulic conductivity and anisotropy 

of hydraulic conductivity, streambed hydraulic conductivity, and recharge during calibration periods. Results of the 

simulation using the calibrated regional model indicate that the 

aquifer appears to be anisotropic where hydraulic conductivity 

is greatest parallel to the orientation of bedding of the formations underlying the area and least in the cross-bed direction. 

The maximum hydraulic conductivity is aligned with the average regional strike of the formations, which is “subhorizontal” 

in the model because the altitudes of the beds and model cells 

vary in the strike, as well as dip, direction. Estimated subhorizontal hydraulic conductivities (in strike direction parallel to 

dipping beds) range from 0.001 to 1.67 meters per day (0.0032 

to 5.5 feet per day). The ratio of minimum (dip direction) to 

maximum (strike direction) subhorizontal hydraulic conductivity ranges from 1/3.1 to 1/8.6, and the ratio of vertical to 

horizontal hydraulic conductivity ranges from 1/1 to 1/478. 

However, limited available field data precluded rigorous calibration of vertical anisotropy in the model. Estimated recharge 

rates corresponding to calibration periods in 1996, 2000, and 

2005 are 150, 109, and 124 millimeters per year (5.9, 4.3, and 

4.9 inches per year), respectively. 

The calibrated groundwater-flow model was used to 

simulate groundwater flow under steady-state conditions during periods of relatively high withdrawals (pumpage) (1990) 

and relatively low withdrawals (2000 and 2005). Groundwater-flow paths originating from recharge areas near known 

areas of soil contamination (sources) were simulated. Pumped 

industrial and production wells captured more groundwater 

from several of these sources during 1990 than after 1990 

when pumping declined or ceased and greater amounts of contaminated groundwater moved away from North Penn Area 7 

Superfund site to surrounding areas. Uncertainty in simulated 

groundwater-flow paths from contaminant sources and contributing areas, resulting from uncertainty in estimated hydraulic properties of the model, was illustrated through Monte 

Carlo simulations. The effect of uncertainty in the vertical 

anisotropy was not included in the Monte Carlo simulations. 

Contributing areas indicating the general configuration 

of groundwater flow towards production well MG-202 (L-22) 

in the study area also were simulated for the different time 

periods; as simulated, the flow paths do not pass through any 

identified contaminant source in North Penn Area 7. However, contributing areas to wells, such as MG-202, located 

near many pumped wells are particularly complex and, in 

some cases, include areas that contribute flow to streams that 

subsequently recharge the aquifer through stream loss. In these 

cases, water-quality constituents, including contaminants that 

are present in surface water may be drawn into the aquifer to 

nearby pumped wells. Results of a simulated shutdown of well 

MG-202 under steady-state 2005 conditions showed that the 

area contributing recharge for nearby production well MG-76 

(L-17), when MG-202 is not pumping, shifts downstream and 

is similar to the area contributing recharge for MG-202 when 

both wells are pumping. 

Concentrations of constituents in groundwater samples 

collected in fall 2005 or spring 2006 were compared to simulated groundwater-flow paths for the year 2005 to provide a 

qualitative assessment of model results. The observed spatial 

distribution of selected constituents, including TCE, CFC-11, 

and CFC-113 in groundwater in 2005 and the chloride/bromide 

mass ratios in 2006, generally were consistent with the model 

results of the simulated 2005 groundwater-flow paths at North 

Penn Area 7, indicating the presence of several separate sources 

of contaminants within North Penn Area 7.

Introduction

Groundwater in and around Lansdale Borough and Upper 

Gwynedd Township, Montgomery County, Pennsylvania, 

was found to be contaminated with organic chemicals, such 

as trichloroethylene (TCE) and tetrachloroethylene (PCE), in 

1979. The contamination was discovered by the North Penn 

Water Authority (NPWA), which at that time relied entirely on 

groundwater to supply public drinking water. The U.S. Environmental Protection Agency (USEPA) investigated sources of 

soil and groundwater contamination in the vicinity of Lansdale 

and subdivided the areas of contamination into groups of properties. The group of contaminated properties in the vicinity of 

production well L-22 (MG-202) in Upper Gwynedd Township, 

southeast of Lansdale and northwest of North Wales, was designated North Penn Area 7 and covers about 2 square miles (mi2

)

(fig. 1). Well L-22 (MG-202) is one of several production wells 

near the headwaters of Wissahickon Creek located in an area 

shown as the Wissahickon well field on figure 1. The USEPA 

began its investigation at North Penn Area 7 in June 1986, 

and the site was placed on the National Priorities List (NPL) 

on March 31, 1989 (CH2M Hill, 1992). North Penn Area 7 is 

southeast from and nearly adjacent to the NPL (also known as 

Superfund) site North Penn Area 6 centered in Lansdale (fig. 1).

The North Penn Area 7 Superfund site encompasses 

six industrial facilities (fig. 1) reported to have used volatile 

organic compounds (VOCs). The most commonly used VOCs 

were the solvents TCE, PCE, 1,1,1-trichloroethane (1,1,1-

TCA), methylene chloride (MC), trichloromonofluoromethane 

(Freon-11 or CFC-11), and dichlorofluoromethane (Freon-21) 

(CH2M-Hill, Inc., 1992, p. 2-1 to 2-6). Contaminants of concern detected in groundwater in the vicinity of the site include 

TCE, PCE, 1,1,1-TCA, 1,1-dichloroethylene (1,1-DCE), 

1,2-dichloroethylene (1,2-DCE), cis-1,2,-DCE, trans-1,2-DCE, 

vinyl chloride (VC), and carbon tetrachloride. Similar contamination also was detected in soils on at least six properties 

(CH2M-Hill, 1992).
Introduction 3

PENNSYLVANIA

STUDY AREA

G-202

-

(MG-56)

(MG-203)

Approximate area of

Wissahickon well field

0 0.5 KILOMETER

0 0.5 MILE

75°17'30"

40°13'45"

40°12'30"

75°16'30"

(MG-56)

L-22 (MG-202)

Approximate area of

Wissahickon well field

(MG-203)

-

Base from U.S. Geological Survey

Lansdale 1983, 1:24,000

Universal Transverse Mercator, zone 18

North American Datum of 1927

EXPLANATION

L-22 (MG-202)

Approximate preliminary boundary

of North Penn Area 7 in 1986

Well and Identifier (U.S. Geological 

Survey identifier)

Figure 1. Location of the North Penn Area 7 Superfund site and selected wells, Upper Gwynedd Township 

and vicinity, Montgomery County, Pennsylvania.
4 Groundwater System and Simulation of Flow for North Penn Area 7 Superfund Site, Montgomery County, Pennsylvania

Groundwater in the vicinity of North Penn Area 7 has 

been used and continues to be used for industrial, public, and 

private supply. Although some wells were abandoned after 

contamination was discovered, other wells remain active, 

in some cases such as well L-22 (MG-202), equipped with 

air strippers to remove VOCs. Abandoned wells include two 

contaminated North Wales Water Authority (NWWA) production wells just south of North Penn Area 7 (MG-56, MG-203) 

and five industrial wells at the former FERCO property in the 

northern part of the site (fig. 1). As of fall 2006, groundwater pumping in the vicinity (within 0.5 miles) of North Penn 

Area 7 continued in NPWA wells along Wissahickon Creek 

near well L-22 (MG-202) to the northeast of the site, wells 

at Precision Tube near the center of the site, and wells at the 

West Point facility of Merck & Co., Inc., southwest of the 

North Penn Area 7 (fig. 1).

The USEPA requested technical assistance from the 

U.S. Geological Survey (USGS) to provide hydrogeologic 

data and interpretation of the data to be used in the Remedial 

Investigation (RI) for the North Penn Area 7 Superfund site. 

In fall 2000, the USGS, in cooperation with USEPA and in 

coordination with USEPA’s contractor CDM Federal Programs 

Corporation (CDM in this report; renamed CDMSmith in late 

2011), began to collect data as part of the technical assistance. 

The data were used to describe the groundwater system and 

to provide a basis for the simulation of groundwater flow. The 

first phase of work, completed in September 2002, included 

geophysical logging of existing wells, aquifer tests of isolated intervals in existing wells, streamflow measurements, 

and groundwater-level mapping and monitoring (Senior and 

others, 2005; Senior and Ruddy, 2004). The second phase of 

work from October 2002 through December 2006 included 

geophysical logging of existing production and monitor wells 

and new monitor wells drilled for the RI, aquifer tests of 

isolated intervals in previously constructed and new monitor wells, streamflow measurements, and groundwater-level 

monitoring (Senior and others, 2008). In addition to collection 

and interpretation of data, the USGS also developed a computer model, described in this report, to simulate groundwater 

flow at and near North Penn Area 7. The groundwater-flow 

simulation is used to evaluate the effect of pumping on the 

directions of groundwater flow and transport of contaminants 

in groundwater.

Purpose and scope

This report describes the hydrogeologic setting and 

groundwater system on the basis of previous studies and findings from two phases of data collection and investigations 

by the USGS at the North Penn Area 7 Superfund site and 

vicinity. In addition, a computer-based numerical model that 

was constructed to simulate regional-scale groundwater flow is 

described. This model was used to estimate values for aquifer 

properties and simulate groundwater-flow directions under 

different conditions.

Data collected by USGS during the two phases—December 2000 through September 2002 and October 2002 through 

September 2006—to help describe the hydrogeologic system 

at and near the site are summarized. These data include results 

of geophysical logs of existing production wells and existing 

and new monitor wells, aquifer characteristics determined 

from pumping tests of aquifer intervals isolated by packers (packer tests) in selected existing and new wells, results 

of water-quality analyses of groundwater samples from 

the packer tests, results of aquifer tests involving multiple 

observation wells, streamflow measurements, continuous 

groundwater levels in selected observation wells, and sets 

of synoptic measurements of groundwater levels in wells at 

and near the site. In addition, inorganic water-quality constituents in groundwater samples collected by CDM during 

October 2005 and March 2006 are discussed in relation to the 

hydrogeologic system.

Aquifer properties of transmissivity, hydraulic conductivity, and (or) storage were estimated when possible from 

the field data at the local scale (aquifer tests) and from a 

computer-based numerical simulation of groundwater flow at 

the regional scale. The basis of the numerical simulation of 

regional groundwater flow is described, including the conceptual model, model structure and boundaries, and calibration 

using regression-based parameter estimation (optimization) 

techniques. Data used for calibration include sets of synoptic 

groundwater levels and streamflow measurements from 1996 

to 2005.

The calibrated model is used to simulate groundwaterflow paths from known and suspected sources of contamination for selected periods from 1990 to 2005 that correspond 

to various industrial and water-supply pumping rates and 

locations (scenarios). The uncertainty associated with model 

simulation of flow paths determined using a Monte Carlo 

approach is shown with the flow paths simulated using optimized parameters. Similarly, the area contributing recharge 

to a contaminated production well and associated uncertainty of that area are simulated for the same periods. Simulated groundwater-flow paths from contaminant sources are 

compared to measured concentrations of selected VOCs in 

well-water samples collected in 2005 for qualitative assessment of model results. In addition, the distribution of selected 

inorganic constituents (boron, bromide, chloride, sulfate, and 

silica) analyzed in samples collected in fall 2005 and spring 

2006 are discussed in relation to the hydrogeologic framework 

and groundwater-flow paths.

Previous Investigations

Groundwater studies in and near Lansdale Borough and 

Upper Gwynedd Township have been prompted by concern 

about limited groundwater availability during periods of 

drought, by discovery of contaminated drinking water from 

production wells, and by interest in commercial and industrial 

uses of the groundwater. Rima (1955), Longwill and Wood 
Geologic and Hydrogeologic Setting 5

(1965), and Newport (1971) provide well-characteristic and 

groundwater-quality data and describe groundwater resources 

in Montgomery County, Pa., including the Lansdale and 

Upper Gwynedd Township area. Longwill and Wood (1965) 

compiled a geologic map, which in the Lansdale area was 

based almost entirely on unpublished manuscripts by Dean 

B. McLaughlin of the Pennsylvania Geological Survey. Lyttle 

and Epstein (1987) compiled a geologic map of the Newark 

1° x 2° Quadrangle that updates and revises the geologic 

nomenclature for the area. Biesecker and others (1968) 

describe the water resources of the Schuylkill River Basin, 

which drains part of the study area. Barton and others (2003) 

describe a case study to determine contributing area for a production well in Lansdale that is near North Penn Area 7.

Investigations of groundwater contamination after 1979 

by the USEPA and others are summarized in a report to the 

USEPA by CH2MHill (1992). An evaluation of groundwater 

withdrawals at the Merck & Co., Inc., (hereinafter “Merck”) 

West Point plant was done by Geraghty & Miller, Inc. (1993). 

Investigations of groundwater quality at the Ford Electronics 

and Refrigeration Corporation (FERCO) facility in North Penn 

Area 7 are described by Converse Consultants East (1994). 

Sources of groundwater contamination in the nearby North 

Penn Area 6 site also are identified in other reports to the 

USEPA by Black & Veatch Waste Science, Inc. (1994; 1999). 

Investigations since 2000 further delineated soils contaminated 

with TCE and other VOCs at Spra-Fin (CDM Federal Programs Corporation, 2003), former FERCO (Golder Associates, 

Inc. 2003), and Teleflex (Turner, 2006) properties.

A map of groundwater levels in 1996 in the vicinity 

of Lansdale that includes groundwater levels within North 

Penn Area 7 was done by Senior and others (1998) to support 

groundwater investigations at the nearby North Penn Area 

6 site (fig. 1). Goode and Senior (1998) present a review of 

aquifer tests done in the Lansdale area from 1980 through 

1995, including tests done in industrial supply wells at manufacturing facilities in and near North Penn Area 7. Senior and 

Goode (1999) describe the groundwater system and simulation of groundwater flow for the North Penn Area 6 site and 

vicinity. The model domain for previous North Penn Area 6 

(shown later in report on fig. 3) groundwater-flow simulations 

(Senior and Goode, 1999; Goode and Senior, 2000) extended 

into North Penn Area 7 and was bounded by Wissahickon 

Creek. Studies (Senior and Goode,1999; Goode and Senior, 

2000) that investigated the control on groundwater flow by the 

hydrogeologic structure of dipping sedimentary beds through 

field studies and flow modeling for North Penn Area 6 provide 

a basic framework for subsequent USGS work in the Lansdale 

area, including North Penn Area 7.

The study discussed in this report included two phases 

of data collection. Data collected during phase 1 (December 

2000–September 2002) were published by Senior and others 

(2005), including a map showing groundwater levels in and 

near North Penn Area 7 in December 2000 (Senior and Ruddy, 

2004). Data collected during phase 2 (October 2002–September 2006) were published by Senior and others (2008).

Well-Identification System

This report uses the USGS local well number as the 

primary well identification and the owner-assigned well 

number as the secondary well identification. The USGS local 

well number consists of a two-letter county-abbreviation 

prefix followed by a sequentially assigned number. The prefix 

MG denotes a well in Montgomery County. The USGS also 

assigns each well a unique 15-digit site number based on 

latitude and longitude in degrees, minutes, and seconds and 

a 2-digit sequence number. The 15-digit site number is the 

primary identifier in the USGS databases. Some wells have 

other names or numbers assigned by owners or used in the 

CH2M-Hill report (1992). The owner assigned well number 

commonly has a prefix consisting of a letter or letters followed 

by a sequentially assigned number; the new monitor wells 

drilled by USEPA in clusters for the remedial investigation 

(RI) use the prefix RI and a number for the cluster and are 

further identified as shallow (S), intermediate (I), deep (D), or 

extra-deep (DD). Listings of USGS local well and site numbers and owner-assigned well numbers for most wells cited in 

this report are given in tables 67, 79, and 22, at the end of the 

two previous data reports for North Penn Area 7 (Senior and 

others, 2005; 2008) and a report for North Penn Area 6 (Senior 

and Goode, 1999). 

Geologic and Hydrogeologic Setting

The composition and structure of bedrock underlying 

North Penn Area 7 and surrounding areas is a controlling factor that affects topography, character of the groundwater system, and stream network. The general geologic and hydrogeologic setting of the study area described below is based mostly 

on previous work by others and on work done by USGS at 

North Penn Area 7 and nearby North Penn Area 6 Superfund 

sites. Nomenclature (code) assigned to geologic units used in 

the simulation of regional groundwater flow presented in this 

report is described. Detailed investigations of the groundwater 

system at the local or borehole-scale that were done at and 

near North Penn Area 7 from December 2000 through September 2006 are summarized in a separate section of this report 

and presented completely in two previous reports (Senior and 

others, 2005; 2008). 

Geologic Setting

The study area in and near Lansdale and Upper Gwynedd 

Township is in the Gettysburg–Newark Lowlands section of 

the Piedmont Physiographic Province (Berg and others, 1989; 

fig. 2). The area is underlain by sedimentary rocks of the 

Lockatong Formation and lower beds of the Brunswick Group 

of the Newark Supergroup (Lyttle and Epstein, 1987; fig. 3). 

Sediments of the Newark Supergroup were deposited in a rift 

basin during the Triassic and Jurassic ages (about 260 million 
6 Groundwater System and Simulation of Flow for North Penn Area 7 Superfund Site, Montgomery County, Pennsylvania

PENNSYLVANIA

NEW YORK

NEW

JERSEY

MARYLAND DELAWARE

77° 76° 75°

40°

41°

42°

Newark Basin

Valley and Ridge

Physiographic Province

Piedmont Physiographic Province

Appalachian Plateaus

Physiographic Province

Reading Prong of 

the New England

Physiographic Province

Atlantic Coastal Plain

Physiographic Province

Reading Prong of 

the New England

Physiographic

Province

Gettysburg Basin

BK-929

BK-1020

1

2

3

4 5

Study

area

PENNSYLVANIA

STUDY AREA

(Gettysburg-Newark

Lowland Section)

(Piedmont Section)

0 20 40 60 MILES

0 20 40 60 KILOMETERS

Base from Pennsylvania Bureau of Topographic and Geologic Survey Physiographic provinces from Sevon (2000)

Physiographic Provinces, 1995, 1:100,000-scale digital data

Universal Transverse Mercator, zone 18

Observation well and U.S. Geological Survey 

identifier

 

1 - Sellersville 

2 - Bucksville 

3 - Conshohocken 

4 - Graterford 

5 - Neshaminy Falls 

EXPLANATION

1

BK-929

National Oceanic and Atmospheric 

Administration precipitation station 

and identifier 

Figure 2. Physiographic Provinces in southeastern Pennsylvania.
Geologic and Hydrogeologic Setting 7

Wissahickon Creek

Stony Creek

Neshaminy Creek

Towamencin Creek

917

01473900

Trs

Trl

Trb

Trl

Cl

Trb

Cch

Trb

Cch

Trl Trs

Trb

Trl

Trb

Trl Trl

Trl Trb Trl

Trb

Trl

Trl

Hatfield

Montgomery

Towamencin

Upper Gwynedd

New Britain

Franconia

Warrington

Lansdale

Lower Salford

Hilltown

Hatfield

New Britain

North Wales

Doylestown

Whitpain

Worcester

Horsham

Upper Dublin

Lower Gwynedd

East Norriton

Whitemarsh

Plymouth

Norristown

Ambler

West Norriton

Springfield

Chalfont

EXPLANATION

Municipal boundary

Stream

Well and U.S. Geological Survey identifier (MG- prefix omitted)

Streamflow-measurement station and U.S. Geological Survey

station identification number 

68

01473900

Geologic unit Boundary for North Penn Area 6 model (Senior and Goode, 1999)

Brunswick Group

Chickies Formation

Ledger Formation

Lockatong Formation

Trs Stockton Formation

Trl

Cl

Cch

Trb

0 1 2 MILES

0 1 2 KILOMETERS

Approximate boundary

of North Penn Area 7

Boundary for North Penn Area 6 

model (Senior and Goode, 1999)

Area of figure 4

Geology from Berg and others (1980)

based on Longwill and Wood (1965)

75°20' 75°15'

40°10'

40°15'

68

202

Base from Pennsylvania Geological Survey

Bedrock Geology of Pennsylvania, 2001

Universal Transverse Mercator, zone 18

North American Datum of 1927

Figure 3. Units of bedrock underlying North Penn Area 7 Superfund site and model boundary for North Penn 

Area 6 , Upper Gwynedd Township and vicinity, Montgomery County, Pennsylvania.
8 Groundwater System and Simulation of Flow for North Penn Area 7 Superfund Site, Montgomery County, Pennsylvania

years ago). Following deposition, sediments in the Newark 

Basin were buried, lithified, tilted, and faulted. The oldest 

sediments in the Newark Basin compose the Stockton Formation, mainly sandstones with some shale deposited along the 

southern margin on Paleozoic and older rocks. Overlying the 

Stockton Formation are the generally finer-grained Lockatong 

Formation and Brunswick Group rocks, which underlie the 

study area. The Lockatong Formation typically is relatively 

resistant to erosion and tends to form ridges that rise above 

flat or rolling topography. This flat or rolling topography 

is underlain by sedimentary rocks of the Brunswick Group 

that are younger than and may be interfingered with the 

Lockatong Formation. 

The Lockatong Formation consists of detrital sequences 

(cycles) of gray to black calcareous shale and siltstone, with 

some pyrite, and chemical sequences (cycles) of gray to black 

dolomitic siltstone and marlstone with lenses of pyritic limestone, overlain by massive gray to red siltstone with anacline 

(Van Houten, 1962; Lyttle and Epstein, 1987). Interbeds of 

reddish-brown, sandy siltstone have been mapped in the Lockatong Formation south of Lansdale (Lyttle and Epstein, 1987). 

Contacts between the Lockatong Formation and the overlying 

Brunswick Group are conformable and gradational, and the 

two formations may interfinger (Lyttle and Epstein, 1987). 

The lower beds of the Brunswick Group consist predominantly of homogeneous, soft, red to reddish-brown and gray to 

greenish-gray mudstones and clay- and mud-shales, with some 

fine-grained sandstones and siltstones. Bedding is irregular 

and wavy. Some beds are micaceous. Interbedded silt-shales 

and siltstones are moderately well sorted. Mud cracks, ripple 

marks, crossbeds, and worm burrows are common in all the 

beds. The Brunswick Group rocks contain detrital cycles of 

medium- to dark-gray and olive- to greenish-gray, thin-bedded 

and evenly bedded shale and siltstone, similar to those of the 

underlying Lockatong Formation.

Unpublished lithologic maps (Joseph Smoot, U.S. Geological Survey, written commun., 2005) indicate that deltaic 

and fluvial sequences are present in the geologic units mapped 

in the study area (fig. 4). This preliminary lithologic mapping retains geologic contacts presented in earlier mapping 

(Longwill and Wood, 1965) (fig. 3) but adds a new contact 

delimiting the extent of deltaic sequences in the lower part of 

the Brunswick Group rocks. The lithologic mapping identified 

interbedded fluvial to deltaic sandstone and conglomerate and 

lacustrine cyclic siltstone and shale that are predominantly red 

(TrS/Sic) or predominantly gray (TrS/ Sicg) (fig. 4). For the 

purposes of this report, these bedding units are assigned codes: 

B4, B6, B8, and B10 refer to units with the predominantly red 

lithology labeled TrS/Sic; L5, L7, and L9 refer to units with 

the predominantly gray lithology labeled TrS/Sicg; B refers 

to the predominantly red non-deltaic lower Brunswick Group 

rocks labeled TrSic [equivalent to Trb of Longwill and Wood 

(1965)]; and L refers to the predominantly gray non-deltaic 

Lockatong Formation rocks labeled TrSicg [equivalent to the 

Trl of Longwill and Wood (1965)]. Prior to the unpublished 

mapping by Smoot, Lyttle and Epstein (1987) had reclassified 

the predominantly gray beds mapped by Longwill and Wood 

(1965) as interfingered Lockatong Formation within the 

Brunswick Group (fig. 3) as part of the lower Brunwick Group 

(see units labeled Trblg in fig. 4) and the predominantly red 

beds mapped as interfingered Brunswick Group with the 

Lockatong Formation (fig. 3) as part of the Lockatong Formation (see unit labeled Trlr in fig. 4).

Bedding in the Newark Basin regionally strikes northeast and dips to the northwest. The regional homoclinal dip 

has been cut by normal and strike-slip faults and warped by 

transverse folds (Schlische, 1992). Many faults with small 

displacements have not been mapped. Locally, the beds of the 

Brunswick Group and Lockatong Formation generally strike 

northeast and dip shallowly to the northwest in the vicinity of 

the North Penn Area 7 site with a gradual shift in strike from 

northeast in central Lansdale to east-northeast in the area south 

of Lansdale near North Wales (fig. 3) (Longwill and Wood, 

1965). Thin shale marker beds in the Brunswick Group identified by elevated natural gamma-ray activity on geophysical 

logs can be correlated in wells and boreholes over distances of 

1,000 ft or more. High natural gamma-ray activity typically is 

associated with thin dark gray or black shale beds. Correlation 

of natural gamma-ray activity in well and borehole logs collected by USGS in and near Lansdale shows that these shale 

beds strike N. 48° to 60° E. and dip 6° to 30° NW. with an 

average dip of about 11° (Conger, 1999). In the western part 

of the North Penn Area 7 site, a strike of N. 57° E. with dip of 

9° to 10° NW. was determined from correlation of beds with 

elevated natural gamma-ray activity among wells and boreholes (Senior and others, 2008). 

Hydrogeologic Setting

The conceptual model of the groundwater system in 

the study area consists of dipping, layered fractured rocks 

with groundwater flow occurring within openings developed 

primarily along or in the orientation of bedding planes (Senior 

and Goode, 1999). These openings are either low-angle 

bedding-plane partings or high-angle fractures and joint sets 

orthogonal to bedding that form a network parallel to bedding. High-angle or nearly vertical fractures generally do not 

cut extensively across beds but may provide local routes of 

groundwater flow or leakage between beds. 

Groundwater to depths of probably about 1,000 ft below 

land surface in the rocks underlying the North Penn Area 7 site 

originates from infiltration of local precipitation. After infiltrating through soil and saprolite (extensively weathered rock), 

groundwater moves through near-vertical and bedding-plane 

fractures in the shale and siltstone bedrock (fig. 5A). Depth to 

competent bedrock commonly is less than 20 ft below land 

surface. The soil, saprolite, and individual beds of the sedimentary bedrock form a layered aquifer, with varying degrees 

of hydraulic connection between the layers. Hydraulic properties of the soil, saprolite, and fracture networks in individual 

beds of the underlying sedimentary bedrock differ. Primary 
Geologic and Hydrogeologic Setting 9

TrSic

TrS/Sic

TrS/Sicg

TrS/Sic

TrS/Sic

TrS/Sic

TrS/Sicg

TrS/Sicg

TrSicg

(JTrb)

(JTrb)

(JTrblg)

(JTrb)

(Trl)

(Trl)

(Trlr)

(JTrb)

(JTrblg)

Tr

B

B4

L5

B6

L7

B8

L9

B10

L

Wissahickon Creek

Approximate boundary

of North Penn Area 7

 Towamencin Creek

75°18'0" 75°17'0" 75°16'0"

40°13'0"

40°14'0"

Geology from Berg and others (1980) with nomenclature

from Lyttle and Epstein (1987) and additional mapping and

lithologic classification from Smoot (unpublished)

0 200 400 800 METERS

0 500 1,000 2,000 3,000 FEET

Base from U.S. Geological Survey

Lansdale 1983, 1:24,000

Universal Transverse Mercator, zone 18

North American Datum of 1927

72

202

1146

1145

68

69

76

EXPLANATION

Lithology

Brunswick Group (non-deltaic)

Gray beds predominant (deltaic)

Contact in Brunswick

Group with deltaic units

Stream Red beds predominant (deltaic)

TrSic

TrS/Sic

TrS/Sicg

TrSicg Lockatong Formation (non-deltaic)

JTrb

Trl

JTrblg, Trl

B

B4, B6, B8, B10

L5, L7, L9

L

Nomenclature

Smoot

(unpublished)

Bed code,

this report

Lyttle and Epstein

(1987)

JTrb, Trlr

Well and U.S. Geological 

Survey identifier

(MG- prefix omitted)

72

Figure 4. Preliminary revised lithologic mapping of bedrock geology at and near North Penn Area 7 Superfund site, 

Upper Gwynedd Township and vicinity, Montgomery County, Pennsylvania.
10 Groundwater System and Simulation of Flow for North Penn Area 7 Superfund Site, Montgomery County, Pennsylvania

STREAM

NW SW

Stream

NOT TO SCALE

High-permability beds

Low-permeability beds

Groundwater-flow path

B

Groundwater gradient

between high-permeability 

beds

Stream

VERTICAL EXAGGERATION

NOT TO SCALE

Potentiometric contour

Direction of flow

EXPLANATION

NW SE

A

Deep flow

path

Shallow flow

path

Soil and saprolite

Vertical

fracture Bedding plane

Fractured bedrock

(shales, siltstones,

sandstones)

Weathered rock

Figure 5. A, Conceptual groundwater-flow system in dipping-bed fractured sedimentary rock aquifer 

(from Senior and Goode, 1999) and B, schematic cross section showing numerical simulation of 

groundwater flow in conceptual dipping-bed sedimentary rock aquifer with layered units of high and 

low permeability (modified from Risser and Bird, 2003).
Summary of Field Investigations of Groundwater System at North Penn Area 7 11

porosity, permeability, and storage in the Triassic to Jurassic 

age sedimentary bedrock are very low.

Groundwater in the shallowest part of the sedimentaryrock aquifer may be under unconfined (water-table) or partially confined conditions; the unconfined part of the aquifer 

probably is thin and is difficult to delineate. In some areas, 

perched water is present at shallow depths (less than 50 ft). 

Groundwater in the deeper part of the aquifer generally is confined or partially confined, resulting in artesian conditions. 

Shallow and deep groundwater-flow paths may be present 

at the site. Generally, groundwater flows in a direction similar 

to the topographic gradient, although flow paths may be complex, as illustrated by a numerical simulation of the conceptual 

hydrogeologic setting (fig. 5B). The conceptual simulation 

shows that, in settings west of the stream, groundwater can 

flow updip in high permeability layers to discharge to the 

stream, but in settings east of the stream, groundwater generally flows downdip in high permeability layers to discharge to 

the stream. Water from the shallow part of the system likely 

discharges locally to streams or leaks downward to the deeper 

part of the groundwater-flow system. Deep groundwater discharges to streams or to pumped wells with the natural direction of shallow to deep groundwater flow altered by pumping. 

Pumping from deep zones may induce downward flow from 

shallow zones. Cones of depression caused by pumping have 

been observed to extend preferentially along strike of bedding 

planes or in the direction of fracture orientation in the Triassic 

to Jurassic age sedimentary rocks of the Brunswick Group and 

the Lockatong Formation (Longwill and Wood, 1965). A similar cone of depression associated with pumping at an industrial 

property (Merck & Co.) southwest of, and adjacent to, North 

Penn Area 7 is described by Geraghty & Miller, Inc. (1993) 

and Goode and Senior (1998).

The North Penn Area 7 site is on relatively flat terrain 

that is bisected by Wissahickon Creek. The site extends past 

the surface-water divide between the Wissahickon Creek 

Basin and the Towamencin Creek Basin to the west (fig. 3). 

Church Road (fig. 4) runs along the approximate location 

of this surface-water divide. The location of the associated groundwater divide, estimated from a map of regional 

groundwater levels measured in open-hole wells in the vicinity 

of North Penn Area 7 in December 2000 (Senior and Ruddy, 

2004) probably is near the surface-water divide between the 

Towamencin Creek and Wissahickon Creek Basins. 

Summary of Field Investigations of 

Groundwater System at North Penn 

Area 7

Information about the local-scale groundwater system at 

selected locations at and near North Penn Area 7 was obtained 

through collection of data in field investigations by USGS 

and others. Borehole geophysical logging provided data on 

the distribution of water-bearing zones, vertical gradients, and 

lithology. Packer tests provided data on the transmissivity and 

water chemistry of isolated water-bearing intervals, extent of 

hydraulic connection between isolated aquifer intervals, and 

vertical gradients. Water levels measured in wells provided 

data that could be used to determine depth to water from land 

surface, to evaluate vertical and horizontal gradients, to evaluate relations between groundwater levels and stream gain or 

loss, and to calibrate the groundwater-flow model. Measurements of streamflow under base-flow conditions provided data 

to evaluate groundwater/surface-water relations (including 

identification of gaining and losing reaches of Wissahickon 

Creek) and to calibrate the groundwater-flow model. Results 

of each type of data collection effort are summarized in the 

following sections.

Geophysical Logs

Geophysical logs were collected in wells at and near 

North Penn Area 7 to determine the location of water-bearing 

fractures, direction of vertical borehole flow (and, therefore, 

presence of vertical hydraulic gradients), and orientation of 

beds. From 2001 through 2005, USGS collected borehole 

geophysical logs in 19 existing production and monitor wells 

and 39 new monitor wells drilled for the RI (table 1; fig. 6) 

(Senior and others, 2005; 2008). The depths of existing boreholes, including 12 relatively shallow (less than 90-ft deep) 

monitor wells, 1 deep monitor well, and 6 deep current and 

former production wells, range from 37.5 to 623 ft. depth. The 

39 new monitor wells drilled for the RI from 2003 through 

2005 were installed in 15 well clusters on the basis of waterbearing zones identified by logs of the first and deepest well in 

each cluster. The deepest monitor well was initially drilled to 

a depth of about 300 ft in 11 of the 15 clusters and to depths 

ranging from 246 to 290 ft in the other four clusters. Shallower 

wells in the clusters subsequently were drilled to depths ranging from 40 to 230 ft. After logging and other testing, all new 

monitor wells were reconstructed with 20- to 40-ft screens to 

isolate water-bearing zones. The number of new monitor wells 

at each cluster are as follows: one well (2 locations); two wells 

(2 locations); two wells and reconstruction of an existing well 

(1 location); three wells (9 locations); and four wells (1 location) (table 1; fig. 6).

Results of geophysical logging show active water-bearing 

zones occur throughout the aquifer from depths of about 20 

to at least 370 ft below land surface (in well MG-151, former 

Ford 5). Measured directions of vertical borehole flow tended 

to be upward east of Wissahickon Creek and downward west 

of Wissahickon Creek or near areas of active pumping. The 

distribution of vertical gradients indicated by borehole-flow 

directions was confirmed by water levels measured in isolated 

zones in packer tests and in well clusters (fig. 7); the distribution of vertical gradients probably is related to the dippingbed structure, except in areas of pumping. Higher heads in 

deep water-bearing zones than in shallower water-bearing 

zones can been inferred from a numerical simulation of 
12 Groundwater System and Simulation of Flow for North Penn Area 7 Superfund Site, Montgomery County, Pennsylvania

Table 1. Characteristics of wells with geophysical logs collected and aquifer-interval-isolation (packer) tests conducted by the 

U.S. Geological Survey at and near North Penn Area 7 Superfund site, Upper Gwynedd Township and vicinity, Montgomery County, 

Pennsylvania, 2000–2005.—Continued

[USGS, U.S. Geological Survey; ft, feet; ft bls, feet below land surface; T, transmissivity; ft2/d, feet squared per day; ft/d, feet per day; --, not available]

USGS 

well 

identifier1

Well name 

or number

Logged 

well 

depth 

(ft)

Logged 

casing 

length 

(ft)

Casing 

diameter 

(inches)

Date 

logged

Depth to 

water on 

date of 

logging 

(ft bls)

Start date 

for packer 

tests

Depth to 

water in 

shallowest 

interval 

in packer 

tests 

(ft bls)

Number of 

isolated 

intervals 

tested

Total T for 

all isolated 

intervals 

(ft2/d)

Total T/ 

length of 

saturated 

open 

borehole 

(ft/d)

Phase 1

174 Clearline 2 160 73 6 12/12/00 34.93 9/17/01 31.50 6 154 1.20

175 Spra-Fin 1 103 14 6 3/29/02 38.83 4/22/02 36.37 3 531 7.97

202 L-22 623 40 12 12/13/01 53.32 12/19/01 45.28 4 650 1.13

1144 T-13 84 18.5 6 10/12/01 31.35 11/29/01 36.09 4 1,063 22.19

1145 T-14 83 19 6 10/12/01 26.80 12/5/01 33.81 3 306 6.22

1146 T-4 84.5 18.5 6 10/1/01 37.33 11/27/01 42.62 2 48 1.15

1147 T-11 83.5 18 6 8/30/01 39.19 11/15/01 48.19 2 56 1.59

1148 T-12 84 19 6 10/11/01 52.48 -- -- -- -- --

1149 T-10 84 18.5 6 10/11/01 51.13 -- -- -- -- --

1505 RW- 83.2 16 6 10/26/01 25.94 -- -- -- -- --

1842 T-15 86 18 6 10/10/01 41.18 11/14/01 44.90 2 908 22.09

1843 T-6 37.5 18 6 10/11/01 30.30 -- -- -- -- --

1844 -- 51.2 15 6 10/30/01 43.98 -- -- -- -- --

1845 -- 54.6 19 6 10/30/01 44.92 -- -- -- -- --

1846 -- 55.9 21 6 10/30/01 46.19 -- -- -- -- --

1897 Clearline 3 288 44 10 10/24/01 24.28 11/7/01 27.70 4 120 0.46

Phase 2

151 Ford #5 477 86 8 3/26/04 25.22 3/30/04 24.81 8 1,012 2.24

1841 Spra-Fin 2 104 17 6 1/24/06 23.57 -- -- -- -- --

1920 Ford MW-1 125 47 6 4/1/04 39.42 4/21/04 40.39 3 47 0.56

2080 RI-1D 299 18 8 5/24/05 36.85 6/1/05 36.50 6 707 2.69

2081 RI-2D 300 18 8 7/12/04 ~34 7/15/04 12.35 8 2,699 9.38

2082 RI-2I 188 18 6 8/16/04 13.04 -- -- -- -- --

2083 RI-2S 61 17.5 6 9/2/2004 9.25 -- -- -- -- --

2084 RI-3D 300 15 8 2/13/04 38.16 3/5/04 38.04 10 1,779 6.79

2085 RI-3I 137 18 6 7/24/04 42.23 -- -- -- -- --

2086 RI-3S 65 18.5 6 7/24/04 0.68 -- -- -- -- --

2087 RI-4D 300 25 8 2/20/04 24.06 4/26/04 22.91 7 3,094 11.17

2088 RI-4I 137 18 6 7/23/04 28.07 -- -- -- -- --

2089 RI-4S 70 19 6 8/3/04 ~69 -- -- -- -- --

2090 RI-5D 300 19 8 2/27/04 21.16 5/17/04 20.18 9 1,908 6.82
Summary of Field Investigations of Groundwater System at North Penn Area 7 13

Table 1. Characteristics of wells with geophysical logs collected and aquifer-interval-isolation (packer) tests conducted by the 

U.S. Geological Survey at and near North Penn Area 7 Superfund site, Upper Gwynedd Township and vicinity, Montgomery County, 

Pennsylvania, 2000–2005.—Continued

[USGS, U.S. Geological Survey; ft, feet; ft bls, feet below land surface; T, transmissivity; ft2/d, feet squared per day; ft/d, feet per day; --, not available]

USGS 

well 

identifier1

Well name 

or number

Logged 

well 

depth 

(ft)

Logged 

casing 

length 

(ft)

Casing 

diameter 

(inches)

Date 

logged

Depth to 

water on 

date of 

logging 

(ft bls)

Start date 

for packer 

tests

Depth to 

water in 

shallowest 

interval 

in packer 

tests 

(ft bls)

Number of 

isolated 

intervals 

tested

Total T for 

all isolated 

intervals 

(ft2/d)

Total T/ 

length of 

saturated 

open 

borehole 

(ft/d)

Phase 2—Continued

2091 RI-5I 98 18 6 7/23/04 23.68 -- -- -- -- --

2092 RI-5S 60 18 6 8/4/04 21.47 -- -- -- -- --

2093 RI-6D 300 22 8 5/18/04 11.57 5/24/04 9.79 9 1,518 5.23

2094 RI-6S 62 18.5 6 7/28/04 8.13 -- -- -- -- --

2095 RI-7D 246 19 8 2/4/04 23.58 3/1/04 24.12 6 2,505 11.29

2096 RI-7S 72 18 6 8/3/04 24.95 -- -- -- -- --

2097 RI-8D 300 18 8 7/20/04 9.22 8/2/04 5.87 9 4,835 16.44

2098 RI-8I 81 18 6 9/1/04 12.25 -- -- -- -- --

2099 RI-8S 40 19 6 9/1/04 12.58 -- -- -- -- --

2100 RI-9D 286 19 8 7/16/04 54.14 7/26/04 28.29 8 3,682 14.29

2101 RI-9I 188 19 6 9/1/04 ~61.4 -- -- -- -- --

2102 RI-9S 105 18 6 9/8/04 ~67.7 -- -- -- -- --

2119 RI-10D 289 19 8 3/12/04 39.33 3/23/04 39.19 7 3,312 13.26

2120 RI-10I 140 18.5 6 7/29/04 42.93 -- -- -- -- --

2121 RI-10S 90 19 6 8/11/04 41.68 -- -- -- -- --

2122 RI-11D 299 25 8 7/6/04 21.62 7/9/04 24.10 6 601 2.19

2123 RI-11I 100 18.5 6 8/10/04 ~21 -- -- -- -- --

2124 RI-11S 60 19 6 9/3/04 23.94 -- -- -- -- --

2125 RI-12D 300 20 8 3/3/04 43.68 4/6/04 41.41 8 515 1.99

2126 RI-13D 279 20 8 5/25/04 24.61 6/8/04 25.72 7 6,081 24.01

2127 RI-13I 138 19 6 9/3/04 27.28 -- -- -- -- --

2128 RI-13S 75 18 6 8/12/04 27.75 -- -- -- -- --

2129 RI-14D 299 54 8 6/1/05 43.51 6/16/05 43.52 4 757 2.96

2130 RI-14S 118 56 6 7/20/05 46.01 -- -- -- -- --

2131 RI-15DD 299 18 8 5/25/05 39.34 6/9/05 39.75 7 1,109 4.28

2132 RI-15DD 220 17 6 7/14/05 41.94 -- -- -- -- --

2133 RI-15I 130 18 6 7/14/05 41.09 -- -- -- -- --

2134 RI-15S 100 18 6 7/20/05 40.53 -- -- -- -- --

1

MG- prefix omitted.
14 Groundwater System and Simulation of Flow for North Penn Area 7 Superfund Site, Montgomery County, Pennsylvania

B4

L5

B6

L7

B8 L9

Leeds and Northrup

75°17'30" 75°17' 75°16'30W

40°14'

40°13'30"

40°13'

Wissahickon Creek

Zenith

Teleflex

FERCO

Spra-Fin

Geology from Berg and others (1980) with nomenclature

from Lyttle and Epstein (1987) and additional mapping and

lithologic classification from Smoot (unpublished)

Base from U.S. Geological Survey

Lansdale 1983, 1:24,000

Universal Transverse Mercator, zone 18

North American Datum of 1927

175

2134

2133

2132

2131

2130

2129

2128

2127

2126

2125

2124

2123

2122

2121

2120

2119

2102

2101

2100

2099

2098

2097

2096

2095

2094

2093

2092

2091

2090

2089

2088

2087

2086

2085

2084

2083

2082

2081

2080

RI-9

RI-8

RI-7

RI-11

RI-2

RI-10

RI-13

RI-5

RI-4

RI-3

RI-15

RI-12

RI-1

RI-14

RI-6

202

174

1897

1846

1845

1844

1843

1842

1841

1505

1149

1148

1146

1145

1144

1147

151

1920

76

72

0 500 1,000 2,000 FEET

0 150 300 600 METERS

2095

1897

76

Existing well, 2001–06

New monitor well and cluster, 2004–05

Existing well, 1995–96

Well and U.S. Geological Survey identifier (MG- prefix omitted),

well cluster identifier (RI-), and dates of logging for—

EXPLANATION

Lithology

Red beds predominant

Gray beds predominant

B, B4-B8

L5-L9

Bed code,

this report 

RI-7

Figure 6. Location of existing and new monitor wells with geophysical logs and packer tests conducted by U.S. 

Geological Survey at and near the North Penn Area 7 Superfund site, Upper Gwynedd Township and vicinity, 

Montgomery County, Pennsylvania, 2000–2005. (See table 1 for list of wells with packer tests.)
Summary of Field Investigations of Groundwater System at North Penn Area 7 15

B4

L5

B6

L7

B8 L9

75°17'30" 75°17' 75°16'30W

40°14'

40°13'30"

40°13'

Wissahickon Creek

Geology from Berg and others (1980) with nomenclature

from Lyttle and Epstein (1987) and additional mapping and

lithologic classification from Smoot (unpublished)

Base from U.S. Geological Survey

Lansdale 1983, 1:24,000

Universal Transverse Mercator, zone 18

North American Datum of 1927

0 500 1,000 2,000 FEET

0 150 300 600 METERS

2129 2130

2125

2080

RI-12

RI-1

RI-14

202

151

1920

76

72

2133 2134

2132 2131

2128 2127

2126

2121 2120

2119

2092 2091

2090

2088

2086 2085

2084

RI-10

RI-13

RI-5

RI-3

RI-15

1842

1149

1148

175

2123 2124

2122

2096

2095

2094

2093

2089

2087

RI-7

RI-11

RI-4 RI-6

174

1846

1845

1844

1843

1841

1505

1146

1147

2102

2101 2100

2099 2098 2097

2082 2083

2081

RI-9

RI-8

RI-2

1897

1145

1144

2095

1897

76

Existing well, 2001–06

New monitor well and cluster, 2004–05

Existing well, 1995–96

Well and U.S. Geological Survey identifier (MG- prefix omitted),

well cluster identifier (RI-), and dates of logging for—

EXPLANATION

Lithology

Red beds predominant

Gray beds predominant

B, B4-B8

L5-L9

Bed code 

RI-7

Predominant direction 

of vertical gradient

or borehole flow

Down Up

Figure 7. Direction of vertical gradients measured in boreholes and (or) determined from water levels in well 

clusters at and near North Penn Area 7 Superfund site, Upper Gwynedd Township and vicinity, Montgomery County, 

Pennsylvania, 2001–2005.
16 Groundwater System and Simulation of Flow for North Penn Area 7 Superfund Site, Montgomery County, Pennsylvania

groundwater-flow paths in a conceptual model of the geologic 

setting (fig. 5B)

The borehole geophysical logs show the presence of 

relatively thin (less than 15-ft thick) zones with elevated natural gamma-ray activity that can be correlated between wells 

and that can be used to estimate sedimentary bed orientation 

(Senior and others, 2005; 2008). Bedding generally strikes 

northeast and dips about 10 degrees to the northwest in the 

vicinity of North Penn Area 7, although the dip angle may not 

be uniform throughout the area as a result of minor faulting. Reported estimates of the dip angle range from about 6 

to 12 degrees at and near the location of North Penn Area 7 

(Longwill and Wood, 1965; Conger, 1999; Senior and others, 2005; 2008). The relatively thin zones of elevated natural 

gamma-ray activity commonly are associated with dark gray 

to black sedimentary layers in the central and western part 

of North Penn Area 7 site (fig. 8), which probably are lake 

deposits that are laterally continuous over several thousands 

of feet. Although zones of elevated natural gamma-ray activity 

were measured in wells logged in the eastern part of North 

Penn Area 7 (east from Wissahickon Creek), these zones could 

be correlated to similar zones on logs in nearby wells, such 

as in well clusters that were less than 100 ft apart, but did not 

appear to correlate between logs of wells more than about 

300 ft apart. The apparent lack of correlation of zones with 

elevated natural gamma-ray activity between wells more than 

a few hundred ft apart in the eastern part of North Penn Area 7 

may be related to changes in the sedimentary environment that 

either limited or disrupted lateral continuity. In addition, lithologic differences across the site are inferred from an apparent 

greater abundance of coarser bedded material, as indicated 

by single-point resistance logs, in wells in the eastern part of 

the study area than in wells in the western part of the study 

area. The lithologic characteristics in the eastern part of the 

study area may be attributed to the presence of deltaic deposits 

mapped by Smoot (Joseph P. Smoot, U.S. Geological Survey, 

written commun., 2005).

Single-point resistance logs for deep (300 ft) wells separated by hundreds to thousands of feet were correlated in the 

western part of North Penn Area 7, as was done with the natural gamma-ray logs. Correlations of elevated resistance among 

well logs indicate laterally continuous deposits of probable 

relatively coarser-grained sediments (siltstone or sandstone). 

In the central to eastern part of the study area, only a few 

thick zones of high resistivity that are probably indicative of 

sandstone beds could be correlated among wells (Senior and 

others, 2005); the zones do not appear to be laterally continuous over distances of more than a few hundred feet.

In the monitor well clusters throughout the study area, 

correlation of natural gamma-ray and single-point resistance 

logs indicate that bedding is laterally continuous over the 

small horizontal distances (typically less than 30 ft) between 

the deep, intermediate, and shallow wells. Examples of logs 

showing interpreted lithologic correlations in monitor-well 

clusters in the western (RI-15 cluster) and eastern (RI-8 cluster) parts of North Penn Area 7 are shown in figure 9.

Aquifer Tests

Packer tests of single wells provided information about 

local-scale hydraulic properties and water chemistry of isolated intervals of the aquifer. Aquifer tests involving a pumping well with multiple observation wells provided information 

about hydraulic properties over a larger area around the tested 

well than the single-well packer tests.

Single-Well Packer Tests

Packer tests were conducted by USGS in wells at and 

near North Penn Area 7 to obtain hydraulic and water-quality 

data in isolated intervals of the aquifer. During these singlewell tests, individual water-bearing zones, consisting of one 

or more fractures, were isolated by use of straddle packers to 

obtain hydraulic information, such as the extent of hydraulic connection between isolated intervals and transmissivity 

and hydraulic heads in isolated zones, and to obtain water 

samples to estimate the vertical distribution of contaminants 

and water-quality characteristics. Tests were conducted on a 

total of 152 intervals in 26 wells ranging in depth from 85 to 

622 ft (9 wells in phase 1 and 17 wells in phase 2 of field 

investigations) (Senior and others, 2005; 2008). Water-quality 

data for zones isolated by packers are discussed in the section “Groundwater Quality in Isolated Intervals” farther on in 

this report. 

Methods used for single-well packer tests done at North 

Penn Area 7 by USGS are explained in previous reports 

(Senior and others, 2005; 2008). Water-bearing intervals 

selected for testing typically were isolated by packers placed 

about 20 to 30 ft apart. The transmissivity of each interval was 

calculated from pumping and drawdown data. The transmissivity (T) values when divided by the thickness of the isolated 

interval can be converted to hydraulic conductivity (K). 

Results of packer tests revealed that isolated intervals had 

little to no vertical hydraulic connection to adjacent intervals, 

as indicated by differences in hydraulic heads in isolated intervals after packer inflation and little water-level response in 

adjacent isolated intervals to pumping of the isolated interval. 

For example, water-level responses in the isolated interval of 

193 to 215 ft below land surface and adjacent intervals in well 

MG-2131 (RI-15DD; fig. 10) were typical of many isolated 

zones tested in most wells. The differences in hydraulic heads 

after packer inflation under static conditions generally confirmed the direction of vertical gradients indicated by borehole 

flow measured during logging. These findings support the conceptual model of a leaky layered aquifer where water-bearing 

layers, typically less than 20 ft in thickness, are separated by 

low-permeability layers that vary in thickness. 

Because of similarity in depth and diameter, the hydraulic 

properties from 15 deep monitor wells were could be compared without bias for those characteristics across North Penn 

Area 7. Transmissivity values calculated from pumping rates 

and drawdown in the isolated intervals in the 15 deepest new 

monitor wells ranged over three orders of magnitude (2.8 to 
Summary of Field Investigations of Groundwater System at North Penn Area 7 17 RI-12D MG-2125 RI-13D MG-2126 RI-5D MG-2090 RI-10D MG-2119 RI-1D MG-2080 RI-15D MG-2131 MG-1920 RI-14D MG-2129

10 100 1,000 10,000

Natural gamma-ray activity,

in counts per second

10 100 1,000 10,000

Natural gamma-ray activity,

in counts per second

10 100 1,000 10,000

Natural gamma-ray activity,

in counts per second

10 100 1,000 10,000

Natural gamma-ray activity,

in counts per second 10 100 1,000 10,000

Natural gamma-ray activity,

in counts per second

10 100 1,000 10,000

Natural gamma-ray activity,

in counts per second

10 100 1,000 10,000

Natural gamma-ray activity,

in counts per second

10 100 1,000 10,000

Natural gamma-ray activity,

in counts per second

50

370

90807060

360350340330320310300290280270260250240230220210200190180170160150140130120110100

50

370

90807060

360350340330320310300290280270260250240230220210200190180170160150140130120110100

Altitude, in feet above NAVD 88

50

370

90807060

360350340330320310300290280270260250240230220210200190180170160150140130120110100

50

370

90807060

360350340330320310300290280270260250240230220210200190180170160150140130120110100

50

370

90807060

360350340330320310300290280270260250240230220210200190180170160150140130120110100

380370

90807060

360350340330320310300290280270260250240230220210200190180170160150140130120110100

380370

90807060

360350340330320310300290280270260250240230220210200190180170160150140130120110100

380370360350340330320310300290280270260250240230220

EXPLANATION

Line showing log correlation

Figure 8. Natural gamma-ray logs indicating beds of elevated natural gamma-ray activity that can be correlated among boreholes/wells in the western part of North Penn Area 7 Superfund site, Upper Gwynedd Township and vicinity, Montgomery County, Pennsylvania (Locations of wells are shown in fig. 6.) 
18 Groundwater System and Simulation of Flow for North Penn Area 7 Superfund Site, Montgomery County, Pennsylvania

Depth, in feet below land surface

Well

Natural gamma-ray activity, in counts per second, and single-point resistance, in ohm-meters

Single-pointresistance log

Naturalgammaray log

Log correlation

0 500 1,000 1,500 0 500 1,000 1,500 0 500 1,000 1,500 0 500 1,000 1,500

0

50

100150200250300

MG-2132 (RI-15D) MG-2133 (RI-15I) MG-2134 (RI-15S) MG-2131 (RI-15DD)

0 500 1,000 1,500 0 500 1,000 1,500 0 500 1,000 1,500 0 500 1,000 1,500

0

50

100150200

0

50

100150200

0

50

200

250300

250300

100150250300

A

Figure 9. Interpreted correlation of natural gamma-ray activity and single-point resistance logs for monitor well clusters in the, 

A, western (RI-15 cluster) and 

B, 

eastern (RI-8 cluster) parts of North Penn Area 7 Superfund site, Upper Gwynedd and vicinity, Montgomery County, Pennsylvania. (Locations of wells are shown in figure 6.)
Summary of Field Investigations of Groundwater System at North Penn Area 7 19 0 200 400 600 800 1,000 0 200 400 600 800 1,000 0 200 400 600 800 1,000

Depth, in feet below land surface

MG-2097 (RI-8D) MG-2098 (RI-8I)

Well

MG-2099 (RI-8S)

0 200 400 600 800 1,000

0

50

100150200250300

0 200 400 600 800 1,000 0 200 400 600 800 1,000

0

50

100150200250300

0

50

100150200250300

Natural gamma-ray activity, in counts per second, and single-point resistance, in ohm-meters

Single-pointresistance log

Naturalgammaray log

Log correlation

B

Figure 9. Interpreted correlation of natural gamma-ray activity and single-point resistance logs for monitor well clusters in the A, western (RI-15 cluster) and B, 

eastern (RI-8 cluster) parts of North Penn Area 7 Superfund site, Upper Gwynedd and vicinity, Montgomery County, Pennsylvania.—Continued (Locations of wells are shown in figure 6.)
20 Groundwater System and Simulation of Flow for North Penn Area 7 Superfund Site, Montgomery County, Pennsylvania

EXPLANATION

Water level above isolated interval

Water level in isolated interval

Water level below isolated interval

Depth to water, in feet below land surface

45

44

43

42

41

40

39

Time elapsed since test began, in minutes

0 40 80 120 160 200 240 280

Inflate upper packer

Pump on

Inflate

lower

packer

Pump off

Deflate

lower

packer

Deflate upper packer

MG-2131 (RI-15DD) Zone 5 (193–215 feet below land surface)

Figure 10. Water levels in the isolated interval of 193 to 215 ft below land surface and 

adjacent intervals in well MG-2131 (RI-15DD) during the single-well packer tests, North 

Penn Area 7 Superfund site, Upper Gwynedd Township and vicinity, Montgomery County, 

Pennsylvania, June 10, 2005.

2,290 ft2/d) (Senior and others, 2008). These transmissivity 

values, however, showed some relation to depth over the range 

of depths tested, although the full range of transmissivities was 

measured throughout the 300-ft thickness of the aquifer. When 

transmissivities of tested intervals were grouped by depth in 

ranges of 50 ft (fig. 11A), the transmissivities of the shallowest 

zones and deepest zones tested (interval midpoints of 0 to 50 

and 251 to 300 ft below land surface, respectively) were statistically significantly different (smaller) from transmissivities 

of intermediate depths, as determined by the non-parametric 

Kruskall-Wallis test using a p-value of 0.05 (statistically significant at a 95-percent confidence level). Transmissivities of 

tested zones at intermediate depths (interval midpoints ranging 

from 51 to 250 ft below land surface) were statistically similar 

to each other. The hydraulic conductivity of tested intervals, 

calculated by dividing transmissivity by the length of the 

tested interval, shows the same relation to depth as transmissivity (fig. 11B). Results of the evaluation of differences in 

transmissivity with depth suggests that weathering may reduce 

the permeability of the shallowest interval tested (0 to 50 ft 

below land surface) and that the frequency of high-permeability zones decreases with depth below 250 ft. The transmissivities of water-bearing zones in the existing production and 

monitor wells tested mostly during phase 1 of field activities 

(Senior and others, 2005) ranged from 1.2 to 795 ft2

/d (0.11 to 

146 m2/d) and were similar to those determined for the 15 new 

deep monitor wells. Transmissivities of tested zones for deep 

monitor and existing production wells are shown in a crosssection (fig. 12) where well locations have been projected onto 

the section line oriented in the dip direction. 

Transmissivities and associated hydraulic conductivities of individual tested zones did not differ statistically by 

geologic unit (fig. 13A), as determined by the non-parametric 

Kruskall-Wallis test using a p-value of 0.05. These hydraulic 

properties ranged over the same three orders of magnitude 

for the four geologic units with more than four water-bearing 

zones tested. Mean and median values of hydraulic conductivity determined in packer tests of individual isolated zones in 

geologic units ranged from 5.7 to 18.4 ft/d (1.7 to 5.6 m/d) and 

3.0 to 5.1 ft/d (0.9 to 1.6 m/d), respectively (fig. 13B). Estimates of bulk or average hydraulic conductivity for geologic 

units calculated by dividing the total transmissivity of waterbearing zones by the total open interval of the geologic unit 

intersected by a borehole were slightly less than average of 

the hydraulic conductivities determined for individual zones 

because the bulk calculation included very low permeability sections of the aquifer that were not tested with packers. 

For data collected from the 15 new deep monitor wells, bulk 

hydraulic conductivity ranged from 0.1 to 26.4 ft/d (0.03 to 

8.0 m/d), and average estimates of bulk conductivity for 

geologic units L5, B6, L7, B8, L9 were 3.7, 8.8, 7.6, 5.2, and 

9.4 ft/d (1.1, 2.7, 2.3, 1.6, and 2.9 m/d), respectively.
Summary of Field Investigations of Groundwater System at North Penn Area 7 21

75th percentile

Number of values

Outside value—Values are more than

 1.0 times the interquartile range

 from the top to bottom of the box

Far-out value—Values are more than

 1.5 times the interquartile range

 from the top to bottom of the box

50th percentile (median)

Mean

25th percentile

Interquartile

range

EXPLANATION

(31)

A B

Transmisivity, in square feet per day

Hydraulic conductivity, in feet per day

1

2

5

10

20

50

100

200

500

1,000

2,000

5,000

10,000

0.01

0.02

0.05

0.1

0.2

0.5

1

2

5

10

20

50

100

200

500

1,000

(31) (19)

(17) (15) (13) (10)

Range of depths tested, midpoint, 

in feet below land surface

0–50 51–100 101–150 151–200 201–250 251–300

(31) (19)

(17) (15) (13)

(10)

Range of depths tested, midpoint, 

in feet below land surface

0–50 51–100 101–150 151–200 201–250 251–300

Figure 11. A, calculated transmissivities and B, hydraulic conductivities in relation to a range of depths for water-bearing intervals 

isolated by packers in 15 wells of similar depths, North Penn Area 7 Superfund site, Upper Gwynedd Township and vicinity, Montgomery 

County, Pennsylvania, March 2004 through August 2005. Wells ranging in depth from 246 to 300 feet (new monitor wells RI-1D to 

RI-15DD) were initially drilled as the deepest borehole in a monitor-well cluster.

MG-2125

RI-12D MG-2081

RI-2D

MG-151

Ford #5

A A'

B8

L7

B6

L5

L9

EXPLANATION

MG-202

L-22

0–24

21–100

101–300

301–1,000

1,001–2,290

Transmissivity of isolated 

interval, in square feet 

per day

Well bottom

L7

Mapped geologic unit

and bed code (see figure 6

for bed codes)

Land surface at well head. 

U.S. Geological Survey 

well identifer (MG-)

and cluster number (RI-) 

or other identifier

-300

-200

-100

0

100

200

300

400

500

0 1,000 2,000 3,000 4,000 5,000 6,000

Elevation, in feet above NAVD88

Distance from origin of transect, in feet

Land surface along transect

MG-2126

RI-13D

MG-2090

RI-5D

MG-2119

RI-10D

MG-2080

RI-1D MG-1920

MG-2131

RI-15DD

MG-2129

RI-14D MG-2084

RI-3D

MG-2087

RI-4D

MG-202

L-22

MG-1897

CL-3

MG-2095

RI-7D MG-2097

RI-8D

MG-2122

RI-11D

MG-2093

RI-6D

MG-2100

RI-9D

Figure 12. Section A–A’ with transmissivity of tested zones in selected wells that are projected onto a line approximately parallel 

to estimated dip of 10 degrees, North Penn Area 7 Superfund site, Upper Gwynedd Township and vicinity, Montgomery County, 

Pennsylvania. (See figure 6 for explanation of bed codes and figure 14 for location of section line.)
22 Groundwater System and Simulation of Flow for North Penn Area 7 Superfund Site, Montgomery County, Pennsylvania

75th percentile

Number of values

Outside value—Values are more than

 1.0 times the interquartile range

 from the top to bottom of the box

Far-out value—Values are more than

 1.5 times the interquartile range

 from the top to bottom of the box

50th percentile (median)

Mean

25th percentile

Interquartile

range

EXPLANATION

(31)

1

2

5

10

20

50

100

200

500

1,000

2,000

5,000

10,000

0.01

0.02

0.05

0.1

0.2

0.5

1

2

5

10

20

50

100

200

500

1,000

Transmisivity of isolated aquifer interval,

in square feet per day 

Hydraulic conductivity of isolated aquifer interval,

in feet per day

Geologic unit bed code Geologic unit bed code

L5 B6 L7 B8 L9 L5 B6 L7 B8 L9

(4)

(31)

(26) (24) (21)

(4)

(31) (26)

(24) (21)

A B

Figure 13. A, calculated transmissivities and B, hydraulic conductivities, by mapped geologic unit, for water-bearing intervals isolated 

by packers in 15 wells of similar depths, North Penn Area 7 Superfund site, Upper Gwynedd Township and vicinity, Montgomery County, 

Pennsylvania, March 2004 through August 2005. Wells ranging in depth from 246 to 300 feet (RI-1D to RI-15DD) were initially drilled as 

the deepest boreholes in monitor-well clusters. (See figures 4 and 6 for explanation of geologic unit bed codes.)

Multiple-Well Aquifer Tests

In 2002 and 2004, the production well MG-202 (L-22) 

(fig. 2) was shut down for periods of a few days, providing an 

opportunity to measure water-level response in nearby wells to 

the shutdown and restart of pumping. Data collected for these 

shutdown tests at multiple observation wells are presented 

in detail by Senior and others (2005) and Senior and others 

(2008). Locations of pumped and observation wells used for 

these tests are shown in figure 14. The 623-ft deep production 

well MG-202 (L-22) was pumped at rates from about 75 to 

125 gallons per minute (gal/min) during routine operation. The 

primary purpose of the tests was to determine the spatial distribution of hydraulic responses rather than to estimate aquifer 

properties of transmissivity and storage. However, drawdown 

and recovery data for observation wells obtained during the 

two tests were analyzed by use of Theis (1935) solution for 

confined aquifers, a method that is not strictly appropriate 

for these dipping-bed fractured-rock leaky aquifers but was 

considered useful as a first approximation and to evaluate 

the extent of deviation from the Theis solution. This analysis 

yielded estimates of transmissivity that ranged from 712 to 

2,286 ft2

/d (66 to 212 m2/d) and of storage that ranged from 

0.00003 to 0.0071 (Senior and others, 2005; 2008). 

Wells that responded to changes in pumping of well 

MG-202 (L-22) generally were along strike or open to the 

projected dip of the thickness of aquifer intersected by waterproducing zones in well MG-202 (L-22). Water levels in 

wells that were open to the structurally projected thickness of 

the main producing interval of well MG-202 (L-22), located 

from 53 to 260 ft below land surface with the main producing zone at about 150 ft below land surface, reflected changes 

in pumping at well MG-202 (L-22), whereas water levels in 

wells that were not open to the structurally projected thickness of the main producing interval in well MG-202 (L-22) 

did not reflect changes during the 2002 or the 2004 shutdown 

tests (fig. 15). The changes in water levels shown on figure 15 

were not corrected for changes in background water levels, 

which were +0.10 ft (rise) and -0.44 ft (decline), respectively, 

for the March 2002 and December 2004 tests in background 

well MG-68. The schematic cross-sections (fig. 15) assume a 

dip angle of 10 degrees to the northwest and depict the general 

pattern of wells that respond to pumping in well MG-202 

(L-22). However, the dip angle may not be uniform throughout 

the area as a result of minor faulting. Previous estimates of the 

dip angle determined from log correlation range from about 

6 to 10 degrees in the area (Conger, 1999; Senior and others, 

2005; 2008); therefore, actual bedding planes of geologic units 

may differ from those shown in this schematic and other cross 

sections presented in this report. 

A pattern of water-level responses, indicating similar 

structural/stratigraphic controls on hydraulic connections, was 

observed in nearby wells during the June 2005 packer test of 

the deep well MG-2131 (RI-15DD) when water-levels were 

monitored in wells MG-2085 (RI-3I) , MG-2084 (RI-3D), 

MG-2092 (RI-5S), MG-2091 (RI-5I), MG-2090 (RI-5D), 

and MG-2126 (RI-13D) (fig. 16). These data, which are not 

presented in previous reports, show that only well MG-2090 

(RI-5D), which is open downdip from the tested isolated 

interval at 193 to 215 ft below land surface in well MG-2131 
Summary of Field Investigations of Groundwater System at North Penn Area 7 23

0.0–1.0

1.1–10.0

10.1–40.0

40.1–80.0

80.1–141.8

Stream

Observation well and U.S. Geological Survey (USGS) 

well identifier(s) (MG- prefix omitted) monitored 

in December 2004 and(or) in March 2002

Observation well and USGS well identifier(s) 

(MG- prefix omitted) monitored in March 2002 

 Pumping well and USGS well identifier(s) 

2101

175

202

Pumping rate in well

in December 2004,

in gallons per minute

B8 L9

B4

L5

B6

L7

75°17'30" 75°17' 75°16'30"

40°14'

40°13'30"

40°13'

Wissahickon Creek

Geology from Berg and others (1980) with nomenclature

from Lyttle and Epstein (1987) and additional mapping and

lithologic classification from Smoot (unpublished)

Base from U.S. Geological Survey

Lansdale 1983, 1:24,000

Universal Transverse Mercator, zone 18

North American Datum of 1927

2101

2087

2084

1146

204

1841

171

135 (Ford 3)

147 (Ford 4)

175

2094

2093

2082

1897

1145

72

77

76

202

174

2124 2123 2122

1848 1849

2083

B

A

B'

A'

0 500 1,000 2,000 FEET

0 150 300 600 METERS

EXPLANATION

Lithology

Red beds predominant

Gray beds predominant

B4, B6, B8

L5, L7, L9

Bed code,

this report 

Nomenclature A A' Section line

Figure 14. Location of pumped production and observation wells used for multiple well aquifer tests, and lines of 

section A–A’ and B–B’, at North Penn Area 7 Superfund site, Upper Gwynedd Township and vicinity, Montgomery 

County, Pennsylvania, 2002–2005. Cross sections for A–A’ and B–B’ lines shown in figure 15.
24 Groundwater System and Simulation of Flow for North Penn Area 7 Superfund Site, Montgomery County, Pennsylvania Altitude, in feet above NAVD 88 400

300

200

100

0

-200

-300

-100

0 1,000 2,000 3,000 4,000 5,000 6,000

A A’

L5

B6

L7

B8

L9

RI-3D

RI-4D

MG-1146 MG-1145

RI-2I

RI-2D

MG-72

MG-202

MG-1897

RI-9I

RI-6D

RI-6S RI-11S

RI-11I

RI-11D

MG-175

TELEFLEX Spra-Fin

Vertical exaggeration x 5

(-106)

(-1.45)

(-1.62)

(-0.63) (-0.58)

(-2.0)

(-1.31)

(-0.03)

(-2.15)

(-1.48)

(-0.29) (-0.28)

(-0.31)

(0.10)

(-0.27)

Most productive water-bearing zone

in well MG-202 projected along dip

Elevation of land surface

at well head

MG-175

MG-174

MG-202

MG-72

MG-76

MG-1897

MG-1848 MG-1849 MG-1146

Ford 4.4

Ford 4.3

Ford 4.2

Ford 4.1

Ford 3.2

Ford 3.3

Ford 3.4

Major producing zone

in well MG-202

Interval of greatest

producing zones 

in well MG-202 projected

in direction of local dip

(-1.6)

(-1.09)

(-0.11)

(-6.86)

(0.26)

(0.32)

(-0.02) (0.07)

(-3.95)

(0.25)

(0.28)

(0.27)

(0.20)

(no data)

Distance along transect, in feet from origin A

MG-2084

MG-2087 MG-2082

MG-2081

MG-2094 MG-2124

MG-2123

RI-11D

MG-2122

(0.10) Other well identifier

Change in water level, 

in feet, after 1,000 

minutes of pumping 

well MG-202, restarted 

on December 3, 2004

Top of open interval

EXPLANATION

Bottom of open interval

MG-2093

MG-2101

MG-2122

U.S. Geological Survey 

well identifier

EXPLANATION

Top of open interval

Bottom of open interval

Water-bearing zone

Land-surface altitude at wellhead

Well identifer and change in water 

level, in feet, after 1,000 minutes 

of pumping well MG-202, 

restarted on March 5, 2002; 

italized if showing relatively 

large drawdown

MG-1848

(0.07)

L7

Mapped geologic unit 

and bed code (see 

figure 6 for bed codes)

400

-300

-200

-100

0

100

200

300

Altitude, in feet above NGVD 29

005-000,1-005,1- 0 000,1005 1,500

Distance from well MG-202 in dip direction of N. 50 degrees W. (Dip angle 10 degrees), in feet

000,2-

NW SE

B B’

B

A

Figure 15. A, section B–B’ with production well MG-202 (L-22) and 15 observation wells monitored during shutdown and after restart 

of pumping in well MG-202 in March 2002 and B, section A–A’ with production well MG-202, 14 observation wells monitored during 

shutdown and restart of pumping in well MG-202 in December 2004, well MG-175 at the Spra-Fin property, and mapped geologic units at 

and near North Penn Area 7, Upper Gwynedd Township and vicinity, Montgomery County, Pennsylvania. Well open interval is depicted 

with measured change in water levels 1,000 minutes after restart of pumping in well MG-202 on March 5, 2002, and December 3, 2004. 

Changes in water levels in wells shown on figure are not corrected for changes in background water levels, which were +0.10 feet (rise) 

and -0.44 feet (decline), respectively, for the March 2002 and December 2004 tests in background well MG-68. (Figures modified from 

A, Senior and others (2005) and B, Senior and others (2008). Lines of sections are shown in figure 14. Mapped geologic units in 15A are 

shown in figure 6.)
Summary of Field Investigations of Groundwater System at North Penn Area 7 25

MG-2125

RI-12D

MG-2128,2127,2126

RI-13S,13I,13D

MG-2092, 2091,2090

RI-5S,5I,5D

MG-2080 MG-1920 RI-1D

MG-2121,2120,2119

RI-10S,10I,10D

MG-2131

RI-15DD

MG-2130,2129

RI-14I,14D

MG-2083,2082,2081

RI-2S,2I,2D

MG-202

L-22

MG-2089,2088,2087

RI-4S,4I,4D

A A'

B8

L7

B6

L5

L9

0–25

51–75

76–100

No apparent waterlevel response

to tests

Water-level response

No data

Transmissivity of 

isolated interval, 

in square feet per day

Wells monitored during 

aquifer-interval isolation 

tests in well MG-2131 

(RI-15DD)

EXPLANATION

L7

MG-202

L-22

Zone number

Mapped geologic unit 

and bed code (see 

figure 6 for bed codes)

Land surface at well head. 

U.S. Geological Survey 

well identifer (MG-)

and cluster number (RI-) 

or other identifier

z1

-300

-200

-100

0

100

200

300

400

500

0 1,000 2,000 3,000 4,000 5,000 6,000

Altitude, in feet above NAVD 88

Distance from origin of transect, in feet

Land surface along transect

Plane through

isolated interval

projected along dip

z2

z1

z4

z5

z6

z7

z3

MG-1897

CL-3

MG-2102,2101,2100

RI-9S,9I,9D

MG-2094,2093

RI-6S,6D

MG-2124,2123,2122

RI-11S,11I,11D

MG-2099,2098,2097

RI-8S,8I,8D

MG-2096,175,2095

RI-7S,7I,7D

MG-2086, 2085,2084

RI-3S,3I,3D

Figure 16. Water-level responses to pumping of isolated intervals in well MG-2131 (RI-15DD) in June 2005, North Penn Area 7 

Superfund site, Upper Gwynedd Township and vicinity, Montgomery County, Pennsylvania. (Locations of wells are shown in figure 6, and 

measured water levels are shown in figure 17. Line of section is shown in figure 14.) 
26 Groundwater System and Simulation of Flow for North Penn Area 7 Superfund Site, Montgomery County, Pennsylvania

(RI-15DD) (zone 5 in Senior and others, 2008), responds 

measurably to pumping (fig. 17). The water-level responses 

in MG-2090 (RI-5D) track water-level changes resulting from 

both pumping and packer inflation in any interval in MG-2131 

(RI-15DD) that included fractures at 193 to 215 ft below land 

surface. Thus, the two wells were connected through the fractures at 193 to 215 ft below land surface while well MG-2131 

(RI-15DD) was an open borehole during the packer testing 

and before reconstruction. Wells located nearby but not open 

updip or downdip from the 193 to 215 ft interval and other 

tested intervals in well MG-2131 (RI-15DD) did not respond. 

Long open sections of boreholes can act as short circuits to 

connect fractures in layers of the aquifer that under natural 

conditions are separated. 

The spatial distribution and magnitude of hydraulic connections of water-bearing fractures will vary at the local scale 

from site to site and are likely to be specific to each site at 

the local scale. Additional multi-well aquifer tests would be 

needed to establish extent of interconnection between intervals at the local scale to address remediation or migration of 

contamination at each source area.

Groundwater Levels

 Water levels were measured by USGS in existing and 

new monitor wells in synoptic rounds in 2000, 2005, and 2006 

to provide information on horizontal and vertical gradients 

and depth to water throughout North Penn Area 7. Data on 

the synoptic water levels, water levels measured by USGS in 

1996, and water levels measured and reported by Merck & Co. 

in 2000 and 2005 for about 40 observation wells on and near 

the Merck facility in West Point, Pa., were used in the calibration of the groundwater-flow model. Also, water levels in 

four wells were measured continuously by USGS for various 

long-term periods from 2000 through 2006 to provide information about groundwater conditions during the RI. Three of 

the four wells (MG-72, MG-1145, MG-1146) are within the 

boundary of the North Penn Area 7 (fig. 4) or within about 

1,000 ft of the boundary, and the fourth well (MG-68) is about 

3,500 ft to the northwest (figs. 3 and 4). Well MG-68 provided 

background water-level data because the well did not appear 

to be directly affected by pumping in the area after early 2000 

when a nearby production well (MG-69, fig. 4) in Lansdale 

was shutdown.

 Depths to static water levels in wells in North Penn 

Area 7 from December 2000 through September 2006 ranged 

from about 6 to 83 ft below land surface, generally were least 

in shallow wells near streams or springs, and were greatest in 

wells affected by nearby pumping or on hilltops. Water levels 

fluctuated seasonally in response to changes in recharge and 

were lowest during dry periods in 2001 and 2002. Regionally, 

groundwater levels, as mapped in 2000 (Senior and Ruddy, 

2004) and measured in the synoptic rounds from 2000 through 

2005, indicate a potentiometric surface similar to the topography, except in areas affected by relatively large amounts 

of pumping.

In the December 2000 synoptic round, water levels were 

measured by USGS in 56 existing non-pumping residential, 

production, and monitor wells; those water levels combined 

with water levels reported by Merck & Co. in 40 observation 

wells on or near their West Point facility were used to estimate 

the altitude and configuration of the regional potentiometric 

surface at and near North Penn Area 7 (Senior and Ruddy, 

2004). These existing mostly, open-hole wells range in depth 

from less than 50 ft to more than 400 ft, although most wells 

(about 70 percent) range in depth from 50 to 200 ft. Wells for 

residential, industrial, and water supply typically are constructed as open holes (surface casing only) in competent bedrock aquifers and frequently have more than one water-bearing 

zone; therefore, measured water levels in these wells typically 

represent composite heads. Cones of depression are indicated 

in an area at and near the Merck facility where numerous wells 

pump a total of about 1 million gallons per day (Mgal/d). 

The regional potentiometric surface estimated from measured 

water levels appears relatively flat at North Penn Area 7 with 

water-level altitudes within the approximate site boundary 

(fig. 4) ranging from 301 to 323 ft above NAVD 88 in 2000.

Comparison of water levels measured in the same wells 

in August 1996, December 2000, and June 2005 indicates that 

levels generally were 1 to 15 ft higher in 1996 and 2005 than 

in 2000, except in some areas where water levels were locally 

affected by nearby pumping that appeared to vary over time. 

For example, differences in water levels between measurement 

periods were as large as 69 ft at the Merck facility, probably 

because of different rates of nearby pumping at the time of 

measurement. Evaluation of water-level records for the nearest 

USGS observation wells completed in similar geologic units 

(BK-929 and BK-1020 in Bucks County, fig. 2) shows levels 

were close to long-term annual mean water levels in August 

1996 but about 2 to 3 ft lower than the long-term annual 

means in December 2000 (fig. 18). These long-term records 

indicate that regional water levels were below average for fallto-winter periods during 2000–02 and fall 2005 and generally 

above average from early 2003 to mid-2005 and 2006. 

 Several additional rounds of synoptic water-level measurements were made in new monitor and existing wells in the 

immediate vicinity of North Penn Area 7 from late fall 2004 

through spring of 2006. Water levels in 76 wells were measured during December 2004, 82 wells during June 2005, 83 

wells during September 2005, 49 wells during October 2005, 

and 90 wells during March 2006. Water levels measured in 

December 2004, June 2005, and March 2006 when compared 

to long-term data (wells BK-929 and BK-1020) were slightly 

higher than or close to long-term annual means. Water levels 

typically exhibit seasonal fluctuations and are lowest in the 

fall, but water levels measured in September and October 2005 

were lower than long-term seasonal and long-term annual 

means. Although 2005 overall was a relatively normal year in 

terms of annual precipitation, precipitation was below normal 

from April to October, and water levels in wells declined by 

as much as 15 ft during this relatively dry period. As part of 

the RI, groundwater samples were collected by CDM for the 
Summary of Field Investigations of Groundwater System at North Penn Area 7 27

MG-2092 (RI-5S)

MG-2090 (RI-5D)

MG-2126 (RI-13D)

MG-2084 (RI-3D)

MG-2085 (RI-3I)

MG-2091 (RI-5I)

Time of tests of isolated zones 

in well MG-2134 (RI-15)

EXPLANATION

333

Groundwater-level altitude, in feet above NAVD 88

329

328

327

332

331

330

Groundwater-level altitude, in feet above NAVD 88

329

328

327

331

330

Date

6/9/05 6/10/05 6/11/05 6/12/05 6/13/05 6/14/05 6/15/05 Zone 1 Zone 2 Zone 3 Zone 4 Zone 5 Zone 6

Figure 17. Water levels measured in A, wells MG-2085 (RI-3I) and MG-2084 (RI-3D) and B, MG-2092 

(RI-5S), MG-2091 (RI-5I), MG-2090 (RI-5D), and MG-2126 (RI-13D) during the packer test of well 

RI-15DD (MG-2131), June 9–13, 2005, North Penn Area 7 Superfund site, Upper Gwynedd Township 

and vicinity, Montgomery County, Pennsylvania. (Open intervals of wells and isolated zones in well 

MG-2131 (RI-15DD) are shown in figure 16.)
28 Groundwater System and Simulation of Flow for North Penn Area 7 Superfund Site, Montgomery County, Pennsylvania

401415075175101 MG-68 

402643075150501 BK-929 Bucks County observation well 

401157075032001 BK-1020 Bucks County observation well 

15

20

25

30

35

40

45

50

55

60

Daily mean depth to water, in feet below land surface

Long-term (1984–2010) annual 

mean of 43.16 feet for BK-929

Long-term (1975–2010) annual mean

of 32.68 feet for BK-1020

EXPLANATION

August 1996 December 2000 June 2005

Year

1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006

Figure 18. Water levels in long-term observation wells BK-929 and BK-1020 and in well MG-68, North Penn Area 7, Upper 

Gwynedd Township and vicinity, Montgomery County, Pennsylvania, 1996–2006. (Locations of wells BK-929 and BK-1020 are 

shown in figure 2 and location of well MG-68 in figure 3.)

USEPA in October 2005, a dry period when water levels were 

low, and in March 2006 when groundwater levels were on 

average about 6 to 7 ft higher than in October 2005.

Synoptic water-level measurements for the monitor well 

clusters showed the presence of vertical gradients, which were 

predominantly downward west of Wissahickon Creek and 

predominantly upward, except where affected by pumping, 

east of Wissahickon Creek (Senior and others, 2008; fig. 7). 

Although water levels in all wells fluctuated from one synoptic 

round of measurements to the next, vertical gradients were 

relatively similar for wells in clusters for all synoptic measurement rounds (table 78, p. 157–158 in Senior and others, 

2008), except for wells in the RI-2 and RI-9 clusters (fig. 6). 

In these two clusters, vertical gradients increased substantially from December 2004 to periods in 2005 and 2006, and 

these changes appear to be independent of the drought in 

late summer and fall 2005. For the RI-2 cluster, water levels 

in the intermediate and deeper wells [MG-2082 (RI-2I) and 

MG-2081 (RI-2D)] declined much more (greater than 30 

ft) than levels in the shallow well [MG-2083 (RI-2S)]. For 

the RI-9 cluster, water levels in the shallow and intermediate wells [MG-2102 (RI-9S) and MG-2101 (RI-9I)] declined 

much more (greater than 30 ft) than levels in the deep well 

[MG-2100 (RI-9D)]. The wells that had the largest declines 

have intervals open to the hydrogeologic unit most affected 

by pumping along the Wisshahickon Creek and at the Merck 

facility (see unit coded B8 in figures 4, 6, and 16). 

Streamflow Measurements and Groundwater/

Surface-Water Relations

Streamflow under base-flow conditions was measured at 

selected locations (fig. 19) along Wissahickon Creek to evaluate groundwater/surface-water relations periodically from 

December 2000 to September 2005. The periodic streamflow 

measurements show that the stream lost water in the reach 

from station 01473808 at Wissahickon Avenue to 01473809 at 

Sumneytown Pike in 2001, 2002, most of 2003, summer 2005, 

and fall 2005 when groundwater levels were low and gained 

water in winter and spring 2004 and 2005 when groundwater levels were relatively high (fig. 20). The stream was dry 

(had no measureable base flow) at station 01473809 (fig. 19) 

in December 2000, summer and fall 2001, spring through 

summer 2002, and the summers of 2003, 2004, and 2005. A 

seepage study to investigate gains and losses from stream to 
Summary of Field Investigations of Groundwater System at North Penn Area 7 29

0 400 800 METERS 200

0 1,000 2,000 3,000 FEET 500

Wissahickon Creek

Geology from Berg and others (1980) with nomenclature

from Lyttle and Epstein (1987) and additional mapping and

lithologic classification from Smoot (unpublished)

Base from U.S. Geological Survey

Lansdale 1983, 1:24,000

Universal Transverse Mercator, zone 18

North American Datum of 1927

5B

4A

9

7

2

1

1A

3A

72

68

202

1146

1145

01473809

01473808

01473807

01473806

75°17' 75°16'

40°13'

40°14'

EXPLANATION

Lithology—

Red beds predominant

Gray beds predominant

Lower Brunswick contact with deltaic units

Stream

Well and U.S. Geological Survey identifier (MG- prefix omitted)

01473806 Streamflow-measurement site and identifier

Pumping rate in well in June 2003, 

in gallons per minute

0.0–0.1

0.1–20.0

20.1–50.0

50.1–100.0

100.1–131.9

1145

Mainstem streamflow gain measured at site on June 30, 2003

Mainstem streamflow loss measured at site on June 30, 2003

7 Seepage study streamflow-measurement site and identifier

Figure 19. Location of pumped wells with pumping rates, observation wells, and streamflowmeasurement sites for the June 2003 seepage investigation on Wissahickon Creek and 

lithology at and near North Penn Area 7, Upper Gwynedd Township and vicinity, Montgomery 

County, Pennsylvania.
30 Groundwater System and Simulation of Flow for North Penn Area 7 Superfund Site, Montgomery County, Pennsylvania

MG-1146

Water-level altitude, in feet above NAVD 88

MG-72

Estimated altitude of streambed near well MG-72

350

340

330

320

310

300

290

MG-1145

Year

Estimated altitude of streambed near 

wells MG-1145 and MG-1146

2001 2002 2003 2004 2005 2006

Figure 20. Measured groundwater levels (shown as altitudes) in wells MG-72, MG-1145, and MG-1146 and estimated altitudes 

of the streambed of Wissahickon Creek near the wells, at and near North Penn Area 7 Superfund site, Upper Gwynedd Township 

and vicinity, Montgomery County, Pennsylvania, December 2000–November 2006.

groundwater was conducted in late June 2003. Synoptic measurements of streamflow on June 30 and July 3, 2003 (Senior 

and others, 2005), indicate loss of streamflow in reaches with 

production wells near Wissahickon Creek (between sites 1 

and 2 and between sites 01473806 and 01473807 in fig. 19). 

The June 2003 seepage study indicated a gain in streamflow 

between sites 2 and 01473806, the latter being very near well 

MG-72. Streamflow measurements are described in detail in 

reports by Senior and others (2005; 2008).

Groundwater Quality at North Penn Area 7

Data on groundwater quality at and near North Penn 

Area 7 were collected by USGS for isolated intervals of the 

aquifer during packer tests of existing wells and new deep 

monitor wells during 2001–05 (Senior and others, 2005; 

Senior and others, 2008); CDM sampled existing open-hole 

production, supply, and monitor wells and screened intervals of new monitor wells during 2001–06 (CDM Federal 

Programs Corporation 2011). Analyses for concentrations of 

volatile organic compounds (VOCs) and other contaminants 

in all groundwater samples were conducted by laboratories 

under contract to CDM and USEPA; complete results for 

these analyses are reported and interpreted in CDM (2011) 

and only briefly discussed in this report. Concentrations of 

VOCs in water samples collected from intervals isolated during packer tests were used to investigate the vertical extent of 

contamination in groundwater and to guide completion depths 

of nested wells in clusters. The spatial extent of VOCs and 

other contaminants at North Penn Area 7 were determined 

by CDM through sampling rounds in 2001, 2005, and spring 

2006. Contaminant concentrations in groundwater generally 

were greatest for TCE and PCE at the site, but numerous other 

VOCs were detected, including 1,1,1-trichloroethane (TCA), 

1,1-diochloroethene (DCE), 1,2-DCE, cis-1,2,-DCE, trans1,2-DCE, vinyl chloride (VC), carbon tetrachloride, and the 

chlorofluorocarbons CFC-11 and CFC-113.

Groundwater Quality in Isolated Intervals 

Water samples were collected from the isolated intervals 

in the fractured-rock aquifer for use as screening values only 

because the samples potentially were affected by the condition 

of open boreholes. In open boreholes, water from producing 

fractures may travel in the borehole to exit in receiving fractures, and thus, water samples collected from the interval with 

receiving fractures may represent a mixture of water from that 

interval and other producing intervals in the open borehole. At 
Summary of Field Investigations of Groundwater System at North Penn Area 7 31

North Penn Area 7, packer tests were done in boreholes that 

had been open for periods ranging from a few weeks for some 

recently drilled monitor wells to decades for some previously 

existing current and former production wells. Nevertheless, 

water chemistry of samples from the isolated intervals showed 

some distinct differences, which are supported by results of 

subsequent sampling by CDM in 2005 and 2006 of monitor 

well clusters, that provide evidence for a conceptual model of 

discrete flow paths through the layered aquifer. 

Concentrations of TCE and some other VOCs tended to 

be, but were not always, greatest in the samples from shallow 

isolated intervals of wells at known contaminant source areas. 

Maximum concentrations of frequently detected VOCs in 

samples from isolated intervals were 640 micrograms per liter 

(μg/L) for TCE, 37 μg/L for PCE, 680 μg/L for cis-1,2,-DCE, 

59 μgL for 1,1,1-TCA, 33 μg/L for 1,1-DCE, 55 μg/L for 

CFC-11, and 71 μg/L for CFC-113. Maximum concentrations 

of some infrequently detected VOCs were 14 μg/L for vinyl 

chloride (VC) and 33 μg/L for carbon tetrachloride.

In addition to collection of water samples from isolated 

zones for VOC analysis, field measurements were made by 

USGS of pH, temperature, specific conductance, dissolved 

oxygen concentration, acid neutralizing capacity (ANC) which 

often is similar or equivalent to alkalinity, nitrate, sulfate, 

sulfide, total iron, and ferrous iron in unfiltered samples by 

methods described in Senior and others (2005; 2008). Summary statistics describing these measurements are listed in 

table 2, and graphs showing the distribution of selected waterquality characteristics of, and constituents in, water from 

isolated zones in each well are presented in figure 21. Generally, water samples had near neutral to slightly alkaline pH; 

low to moderate concentrations of dissolved oxygen, nitrate, 

and sulfate; mostly low concentrations of total and ferrous 

iron; and moderate to high specific conductance (table 2). 

Comparison of water quality between wells indicates some 

general differences. Specific conductance is much higher 

[greater than 700 and up to 2,700 microsiemens per centimeter (μS/cm)] in water samples from isolated intervals in wells 

MG-2125, MG-2126, and MG-2090 (open boreholes later 

reconstructed as RI-12D, RI-13D, and RI-5D, respectively), 

in the western part of the study area than elsewhere. Alkalinity 

(as estimated by ANC) is also elevated (250 to 350 mg/L as 

CaCO3) in one of these wells [MG-2125 (later reconstructed 

as RI-12D)]. Sulfate concentrations in water samples from 

isolated intervals differ more among wells than among zones 

in an individual well.

Groundwater Quality in Existing and New 

Monitor Wells

Groundwater samples were collected by CDM from 

existing and new monitor wells during three rounds of sampling during 2001–06 as part of the RI to assess the extent of 

groundwater contamination at North Penn Area 7. Only existing wells were sampled during the first round in 2001–02, and 

both existing and new monitor wells were sampled during the 

second and third rounds in fall 2005 and spring 2006. The first 

round of groundwater samples was analyzed for VOCs, semivolatile organic compounds, pesticides, and selected major 

ions and metals. The second and third rounds of groundwater 

samples were analyzed for VOCS, selected major ions and 

metals, and a few additional inorganic constituents suggested 

by USGS, including chloride, sulfate, and silica in the second 

round samples and chloride, bromide, and boron in the third 

round samples.

Table 2. Summary statistics of physical and chemical characteristics measured in the field of unfiltered water samples collected 

from isolated zones in 15 deep monitor wells, North Penn Area 7 Superfund site, Upper Gwynedd Township and vicinity, 

Montgomery County, Pennsylvania, March 2004 through August 2005.

[°C, degrees Celsius; mg/L, milligrams per liter; μS/cm, microsiemens per centimeter at 25 °C; ANC, acid neutralizing capacity; mg/L as CaCO3, milligrams 

per liter as calcium carbonate; mg/L as N, milligrams per liter as nitrogen; <, less than]

Characteristic Units Number of 

zones

Minimum 10th percentile Median 90th percentile Maximum

pH pH units 106 6.34 7.03 7.49 7.83 8.09

Temperature °C 105 11.7 13.1 14.5 17.6 19.1

Dissolved oxygen mg/L 106 0.10 0.16 1.40 4.33 9.00

Specific conductance μS/cm 105 362 390 578 1,026 2,742

ANC (alkalinity) mg/L as CaCO3 106 25 133 159 201 354

Sulfide mg/L 102 <0.001 <0.001 0.003 0.016 0.070

Ferrous iron (Fe2+) mg/L 103 <0.01 <0.01 0.03 0.12 1.47

Iron, total mg/L 103 <0.01 0.07 0.17 0.43 2.02

Sulfate mg/L 103 9 18 30 42 59

Nitrate mg/L as N 103 <0.1 0.1 0.8 1.5 3.1
32 Groundwater System and Simulation of Flow for North Penn Area 7 Superfund Site, Montgomery County, Pennsylvania

0

100

50

150

200

250

300

350

400

Alkalinity, in milligrams per liter

as calcium carbonate

0

1

2

3

4

5

6

7

8

9

RI- 12 13 5 10 1 15 14 4 3 2 9 6 11 8 7

Dissolved oxygen,

in milligrams per liter 

Dissolved Oxygen

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

RI- 12 13 5 10 1 15 14 4 3 2 9 6 11 8 7

Nitrate, in milligrams per liter

as nitrogen

Nitrate

0

500

1,000

1,500

2,000

2,500

3,000

RI- 12 13 5 10 1 15 14 4 3 2 9 6 11 8 7

Specific conductance, in microsiemens

per centimeter at 25 degrees Celsius

Specific Conductance

6.0

6.5

7.0

7.5

8.0

8.5

9.0

RI- 12 13 5 10 1 15 14 4 3 2 9 6 11 8 7

pH, in pH units

pH

0

10

20

30

40

50

60

70

RI- 12 13 5 10 1 15 14 4 3 2 9 6 11 8 7

Sulfate, in milligrams per liter

Deepest monitor well, as open well, in each cluster

(suffixes not shown)

Deepest monitor well, as open well, in each cluster

(suffixes not shown)

Sulfate

RI- 12 13 5 10 1 15 14 4 3 2 9 6 11 8 7

Alkalinity

Figure 21. Specific conductance, acid neutralizing capacity as estimate of alkalinity, pH, and concentrations of dissolved oxygen, 

nitrate, and sulfate measured in the field in water samples from isolated zones in 15 deep monitor wells, North Penn Area 7 Superfund 

site, Upper Gwynedd Township and vicinity, Montgomery County, Pennsylvania, March 2004 through August 2005. Results are plotted in 

order of wells projected onto line parallel to dip. 
Summary of Field Investigations of Groundwater System at North Penn Area 7 33

Volatile Organic Compounds and Metals

The main contaminants identified in groundwater from 

the three rounds of sampling are VOCs, of which TCE was 

the VOC most frequently detected and measured at the highest concentrations [up to 650 μg/L in monitor well RI-11S 

(MG-2124)] (CDM Federal Programs Corporation, 2011). 

Other VOCs detected include, but are not limited to, PCE, 

cis-1,2-DCE, 1,1,1-TCA, 1,1-DCE, VC, CFC-11, and CFC113. The highest VOC concentration measured from 2001 to 

2006 was 1,700 μg/L for cis-1,2-DCE in one sample from well 

MG-1841 (SF-1) in 2001, although concentrations of cis-1,2-

DCE were less than 330 μg/L for all other samples (CDM Federal Programs Corporation, 2011). Arsenic, chromium, iron, 

lead, manganese, and mercury are the metals most frequently 

measured in concentrations greater than health-screening levels, as reported by CDM (2011). The occurrence and distribution of VOCs and metals are described and discussed in detail 

in the RI report prepared by CDM (2011). 

Selected Inorganic Constituents 

As part of the assessment of the spatial distribution of 

contaminants in groundwater in wells at and near North Penn 

Area 7, water samples collected by CDM in fall 2005 (second round) and spring 2006 (third round) were also analyzed 

for one or more selected inorganic constituents, including 

chloride, boron, bromide, silica, and sulfate. These inorganic 

constituents were thought to be potentially useful in understanding the groundwater-flow system and (or) determining 

potential contaminant sources and pathways. In addition, 

chloride and sulfate were analyzed to identify the ions causing 

the high specific conductance, determined through geophysical logging of some wells, as concentrations of these anions 

commonly are elevated in water that has high specific conductance. Acid neutralizing capacity (ANC), a field measure 

that is approximately equivalent to alkalinity (and of the 

bicarbonate ion), was determined by USGS during packer tests 

during 2002–04 and, in general, was not found to differ much 

between wells, ranging mostly from about 130 to 200 mg/L as 

CaCO3 with and without high fluid conductance identified during logging. The exceptions are samples from well MG-2125 

(RI-12), which had the highest ANC (alkalinity) values of up 

to 354 mg/L as CaCO3 (fig. 14). In fall 2005, samples from 

all reconstructed monitor wells were analyzed for chloride, 

silica, and sulfate. In spring 2006, samples were analyzed for 

chloride, boron, and bromide.

Evaluation of chloride, nitrate, and sulfate concentrations 

and other data not collected during the RI, such as hydrogen 

or ethane concentrations, may be helpful in understanding 

the extent of possible PCE or TCE degradation at North Penn 

Area 7. A detailed assessment of the potential for degradation 

of PCE and TCE is beyond the scope of this report. 

Chloride

Chloride is a naturally occurring constituent in the 

environment but also can be artificially introduced by various 

human activities. Once dissolved, chloride is a relatively 

conservative anion (not degraded, readily adsorbed, or precipitated) and may be used as a tracer in groundwater and 

surface-water flow. At North Penn Area 7, chloride concentrations greater than natural background levels could originate 

from several sources. In urban and suburban areas, a common source of chloride released on the land surface is road 

salt used for de-icing. Sodium chloride is the most common 

component of road salt, but other compounds, such as calcium 

chloride, are used. Chloride may also be released into groundwater as part of degradation processes of halogenated organic 

compounds, such as TCE. 

Most chloride concentrations measured during fall 2005 

and spring 2006 rounds of sampling by CDM at North Penn 

Area 7 did not differ much between sampling rounds and were 

within the range of 10 to 50 mg/L in about half of the samples, 

slightly to moderately elevated above natural background 

concentrations in southeastern Pennsylvania, estimated to be 

about 10 mg/L or less (Senior and other, 1997). Across the 

site at North Penn Area 7, chloride concentrations generally 

decreased with depth of water samples from monitor well 

clusters, indicating near-surface or surface sources of chloride 

(figs. 22, 23). 

Samples from some monitor wells had substantially 

elevated chloride concentrations—greater than 100 mg/L to as 

high as 350 mg/L. The highest chloride concentrations were in 

samples from shallow- and intermediate-depth monitor wells 

[MG-2092 (RI-5S), MG-2091 (RI-5I), MG-2128 (RI-13S), 

MG-2127 (RI-13I), MG-2121 (RI-10S), MG-2120 (RI-10I)] 

west of Church Road on the former Zenith and adjacentproperties, one shallow monitor well [MG-2086 (RI-3S)] on 

the former Ford property (figs. 22 and 23), and two shallow 

open-hole wells (MG-1844, MG-1845) at an industrial facility 

along North Wales Road (fig. 22). Sources of the substantially 

elevated chloride concentrations in groundwater are unknown, 

but road salt is a likely source for wells near North Wales 

Road and a possible contributing source for the wells west 

of Church Road, as these latter wells are near parking lots. 

However, water from other wells near roads and parking lots 

elsewhere at North Penn Area 7 typically do not have such 

high chloride concentrations, suggesting an additional source 

of chloride for the wells west of Church Road.

Sulfate

Sulfate concentrations were used to identify the source 

of elevated specific conductance and to assess the potential for, and extent of, anaerobic degradation of chlorinated 

solvents, such as TCE, in groundwater. Sulfate concentrations in samples collected from reconstructed monitor wells 

in North Penn Area 7 ranged from 10 to 68.6 mg/L, were 

between 20 and 35 mg/L in samples from most wells, generally were not elevated above background levels estimated 

from regional studies (Sloto and Schreffler, 1994; Durlin and 

Schaffstall, 2000, p. 599), and showed no strong pattern in 

relation to depth or spatial distribution. The reported sulfate 

concentrations in the samples collected in fall 2005 confirmed 
34 Groundwater System and Simulation of Flow for North Penn Area 7 Superfund Site, Montgomery County, Pennsylvania

B4

L5

B6

L7

B8 L9

75°17'30" 75°17' 75°16'30"

40°14'

40°13'30"

40°13'

Wissahickon Creek

Geology from Berg and others (1980) with nomenclature

from Lyttle and Epstein (1987) and additional mapping and

lithologic classification from Smoot (unpublished)

Base from U.S. Geological Survey

Lansdale 1983, 1:24,000

Universal Transverse Mercator, zone 18

North American Datum of 1927

A

A'

MG-202

RI-12D 

RI-1D 

RI-6 cluster

RI-3 cluster

RI-2 cluster

RI-14 cluster

RI-7 cluster

RI-11 cluster

RI-5 cluster

RI-13 cluster

RI-15 cluster

Church Road

RI-10 cluster

RI-4 cluster

RI-8 cluster

RI-9 cluster

MG-1844

MG-1845

0 500 1,000 2,000 FEET

0 150 300 600 METERS

EXPLANATION

Lithology

Red beds predominant

Gray beds predominant

B4, B6, B8

L5, L7, L9

Bed code,

this report 

A A' Section line

11.7–25.0

25.1–50.0

50.1–75.0

75.1–100.0

100.1–304.0

Chloride concentrations in 

groundwater samples (2006),

in micrograms per liter

Shallow monitor

Intermediate monitor

Deep monitor

Open-hole existing well

Type of well—Label is 

well (MG-) or cluster (RI-) 

identifier

Nomenclature

Figure 22. Chloride concentrations in samples collected in spring 2006 from monitor well clusters and open-hole wells 

and line of section A–A’, North Penn Area 7 Superfund site, Upper Gwynedd Township and vicinity, Montgomery County, 

Pennsylvania. (Section A–A’ is shown in figure 23.)
Summary of Field Investigations of Groundwater System at North Penn Area 7 35

A A'

Land surface along transect

B8

L7

B6

L5

L9

Whole-well sample concentration

11–25

26–50

51–75

76–100

100–304

Chloride concentration 

in 2006 groundwater 

sample, in micrograms 

per liter 

EXPLANATION

L7

MG-202

L-22

Mapped geologic unit 

and bed code (see 

figure 6 for bed codes)

Land surface at well head. 

U.S. Geological Survey 

well identifer (MG-)

and cluster number (RI-) 

or other identifier

-300

-200

-100

0

100

200

300

400

500

0 1,000 2,000 3,000 4,000 5,000 6,000

Altitude, in feet above NAVD 88

Distance from origin of transect, in feet

MG-2128,2127,2126

RI-13S,13I,13D

MG-2092,2091,2090

RI-5S,5I,5D

MG-2080

RI-1D

MG-2121,2120,2119

RI-10S,10I,10D MG-2134,2133,2132,2131

RI-15S,15I,15D,15DD

MG-2130,2129

RI-14I,14D

MG-2102,2101,2100

RI-9S,9I,9D

MG-2083,2082,2081

RI-2S,2I,2D

MG-202

L-22 MG-2094,2093

RI-6S,6D

MG-2124,2123,2122

RI-11S,11I,11D MG-2096,175,2095

RI-7S,7I,7D MG-1897

CL-3

MG-2125

RI-12D

MG-2099,2098,2097

RI-8S,8I,8D

MG-2089,2088,2087

RI-4S,4I,4D

MG-2086,2085,2084

RI-3S,3I,3D

Figure 23. Locations of monitor wells projected onto a line parallel to dip and chloride concentrations in samples collected from 

the monitor wells in spring 2006, North Penn Area 7 Superfund site, Upper Gwynedd Township and vicinity, Montgomery County, 

Pennsylvania. (See figure 22 for location of line of section.)
36 Groundwater System and Simulation of Flow for North Penn Area 7 Superfund Site, Montgomery County, Pennsylvania

concentrations previously estimated using a field spectrophotometer for analysis of samples from packer tests (Senior 

and others, 2008). The moderate sulfate concentrations and 

alkalinity indicate chloride is the main anion associated with 

high specific conductance measured in some wells at North 

Penn Area 7.

During anaerobic degradation under sulfate-reducing 

conditions of VOCs, sulfate concentrations may decrease 

and sulfide concentrations concurrently increase (Chapelle 

and Bradley, 1998), although sulfide may precipitate out of 

solution if iron is present (Kennedy and others, 1998). Sulfide 

concentrations measured in samples collected during packer 

tests using a field spectrophotometer were less than 0.06 mg/L 

(Senior and others, 2005; 2008); these low concentrations 

indicate some, but relatively little, reduction of sulfate and 

associated concurrent degradation of chlorinated solvents. At 

concentrations greater than 20 mg/L, sulfate may compete 

with the reductive pathway for degradation of VOCs (Wiedemeier and others, 1998). Heimann and others (2005) report 

that sulfate concentrations greater than 2.5 millimolar (mM) 

(or 240 mg/L) may limit microbial dechlorination of TCE 

and other chlorinated solvents. At North Penn Area 7, sulfate 

concentrations in groundwater were frequently in the range of 

20 to 35 mg/L and as high as to 69 mg/L and, therefore, could 

be, but not necessarily are, limiting for anaerobic degradation 

of VOCs.

Many zones tested during packer tests at North Penn 

Area 7 (Senior and others, 2005; 2008) had low concentrations (less than 1 mg/L) of dissolved oxygen and nitrate, and 

a few had elevated concentrations (1 to 2 mg/L) of ferrous 

iron, consistent with reducing conditions that may be associated with degradation of chlorinated ethenes. The detection 

of PCE and TCE degradation products in groundwater, such 

as cis-1,2-DCE across the site and VC detected at Spra-Fin 

property, indicate that degradation occurs in the areas sampled 

but that sulfate reduction does not appear to be a main part of 

the process. 

Silica

Silica may accumulate in groundwater as a product of 

mineral weathering, and concentrations have sometimes been 

found to correlate with residence time (Burns and others, 

2003). Silica concentrations in samples from the monitor well 

clusters ranged from about 14.7 to 26.4 mg/L and tended to be 

higher in samples from the shallow or intermediate well than 

from the deep well in each cluster (figs. 24, 25). This finding 

indicates the following possible explanation. Shallow groundwater follows different flow paths than deeper groundwater, 

and water reacts more extensively with minerals because of 

greater surface area and more reactive geochemical environment in the shallow weathered zone and less extensively with 

minerals in fractures at depth. Also, groundwater may travel 

more slowly in the shallow weathered zone with relatively 

higher porosity than in fracture networks at depth. Some 

water at depth may be recharged relatively rapidly through 

preferential paths, reducing transit time through the shallow 

weathered zone; however, variability in groundwater chemistry (such as pH) and mineral composition of aquifer materials 

will affect, and may alternatively explain, the distribution of 

dissolved silica in groundwater. From limited analyses of the 

chemical data, it is unclear whether or not silica concentrations 

reflect residence time in the hydrogeologic setting at North 

Penn Area 7.

Boron

Boron is a naturally occurring trace element that occurs 

in elevated concentrations (up to about 5,000 μg/L) in mineralized areas of the Newark Basin (Senior and Sloto, 2006), 

but natural background concentrations typically are less than 

40 μg/L in non-mineralized areas. Elevated boron concentrations in groundwater of as much as 24,700 μg/L were found to 

be associated with the Salford Quarry site, located about 10 mi 

northwest of North Penn Area 7 and used by several industries 

including the former American Olean Tile of Lansdale for 

waste disposal (U.S. Environmental Protection Agency, 2010). 

Boron was selected for analysis as a possible indicator of 

industrial waste after broken waste tile from American Olean 

was observed in disturbed fill on the former Clearline property 

(between wells MG-174 and MG-1897, fig. 6) in North Penn 

Area 7. 

Boron concentrations in water samples from wells at 

North Penn Area 7 ranged from less than 20 to 220 μg/L 

and were highest in the RI-6 well cluster and wells along 

the strike from that cluster (figs. 26, 27). Boron concentrations were greater than or about equal to 100 μg/L in water 

from five wells, four of which are along the strike in the same 

geologic unit, denoted as B8, [181 μg/L in well MG-2094 

(RI-6S); 220 μg/L in well MG-2093 (RI-6D); 122 μg/L in well 

MG-2081 (RI-2D); and 94 μg/L in well MG-1541 (N5)] and 

one of which is in a separate unit, denoted as L7, [110 μg/L in 

well MG-2090 (RI-5D)] (figs. 26, 27). The highest boron concentrations were near, but not at, wells on the former Clearline 

property (MG-174 and MG-1897), and thus, the data do not 

clearly support an association of elevated boron in groundwater with the occurrence of waste tile in disturbed soil. The 

source of slightly elevated boron concentrations in groundwater (greater than the estimated background of about 40 μg/L) 

is unknown. The spatial distribution of the slightly elevated 

boron concentrations may be related to a natural occurrence in 

the geologic formation that follows geologic structure (bedding orientation) or may follow groundwater transport partly 

controlled by geologic structure from a natural or anthropogenic source (such as one related to waste-disposal activities). 

Bromide

Bromide is a relatively soluble halide anion, like chloride. Chloride/bromide molar or mass ratios have been used 

to distinguish sources of salinity (Edmunds, 1996; Davis and 

others, 1998; Vengosh and Pankratov, 1998; Davis and others 

2004) and were selected by USGS for analysis to possibly 
Summary of Field Investigations of Groundwater System at North Penn Area 7 37

B4

L5

B6

L7

B8 L9

75°17'30" 75°17' 75°16'30"

40°14'

40°13'30"

40°13'

Wissahickon Creek

Geology from Berg and others (1980) with nomenclature

from Lyttle and Epstein (1987) and additional mapping and

lithologic classification from Smoot (unpublished)

Base from U.S. Geological Survey

Lansdale 1983, 1:24,000

Universal Transverse Mercator, zone 18

North American Datum of 1927

A

A'

MG-202

RI-12D 

RI-1D 

RI-6 cluster

RI-3 cluster

RI-2 cluster

RI-14 cluster

RI-7 cluster

RI-11 cluster

Clearline

RI-5 cluster

RI-13 cluster

RI-15 cluster

Church Road

RI-10 cluster

RI-4 cluster

RI-8 cluster

RI-9 cluster

0 500 1,000 2,000 FEET

0 150 300 600 METERS

EXPLANATION

Lithology

Red beds predominant

Gray beds predominant

B4, B6, B8

L5, L7, L9

Bed code,

this report 

A A' Section line

14.7–16.0

16.1–18.0

18.1–20.0

20.1–22.0

22.1–25.2

Silica concentrations in

groundwater samples (2005),

in micrograms per liter

Shallow monitor

Intermediate monitor

Deep monitor

Open-hole existing well

Type of well—Label is 

well (MG-) or cluster (RI-) 

identifier

Nomenclature

Figure 24. Silica concentrations in samples collected in fall 2005 from monitor well clusters and open-hole wells, 

and line of section A–A’, North Penn Area 7 Superfund site, Upper Gwynedd Township and vicinity, Montgomery 

County, Pennsylvania. (Section A–A’ is shown in figure 25.)
38 Groundwater System and Simulation of Flow for North Penn Area 7 Superfund Site, Montgomery County, Pennsylvania

A A'

Land surface along transect

B8

L7

B6

L5

L9

Whole-well sample concentration

No data

14–16

16.1–18

18.1–20

20.1–22

22.1–26

Silica concentration 

in 2005 groundwater 

sample, in micrograms 

per liter 

EXPLANATION

L7

MG-202

L-22

Mapped geologic 

unit and bed code 

(see figure 6 for 

bed codes)

Land surface at well head. 

U.S. Geological Survey 

well identifer (MG-)

and cluster number (RI-) 

or other identifier

-300

-200

-100

0

100

200

300

400

500

0 1,000 2,000 3,000 4,000 5,000 6,000

Altitude, in feet above NAVD 88

Distance from origin of transect, in feet

MG-2128,2127,2126

RI-13S,13I,13D

MG-2092,2091,2090

RI-5S,5I,5D

MG-2080

RI-1D

MG-2121,2120,2119

RI-10S,10I,10D

MG-2134,2133,2132,2131

RI-15S,15I,15D,15DD

MG-2130,2129

RI-14I,14D

MG-2102,2101,2100

RI-9S,9I,9D

MG-2083,2082,2081

RI-2S,2I,2D

MG-202

L-22 MG-2094,2093

RI-6S,6D

MG-2124,2123,2122

RI-11S,11I,11D

MG-2096,175,2095

RI-7S,7I,7D

MG-1897

CL-3

MG-2125

RI-12D

MG-2099,2098,2097

RI-8S,8I,8D

MG-2089,2088,2087

RI-4S,4I,4D

MG-2086,2085,2084

RI-3S,3I,3D

Figure 25. Locations of monitor wells projected onto a line parallel to dip and silica concentrations in samples collected from the 

monitor wells in fall 2005, North Penn Area 7 Superfund site, Upper Gwynedd Township and vicinity, Montgomery County, Pennsylvania. 

(See figure 24 for line of section A–A’.)
Summary of Field Investigations of Groundwater System at North Penn Area 7 39

B4

L5

B6

L7

B8 L9

75°17'30" 75°17' 75°16'30"

40°14'

40°13'30"

40°13'

Wissahickon Creek

Geology from Berg and others (1980) with nomenclature

from Lyttle and Epstein (1987) and additional mapping and

lithologic classification from Smoot (unpublished)

Base from U.S. Geological Survey

Lansdale 1983, 1:24,000

Universal Transverse Mercator, zone 18

North American Datum of 1927

A

A'

MG-202

RI-12D 

RI-1D 

RI-6 cluster

RI-3 cluster

RI-2 cluster

RI-14 cluster

RI-7 cluster

RI-11 cluster

Clearline

RI-5 cluster

RI-13 cluster

RI-15 cluster

Church Road

RI-10 cluster

RI-4 cluster

RI-8 cluster

RI-9 cluster

0 500 1,000 2,000 FEET

0 150 300 600 METERS

EXPLANATION

Lithology

Red beds predominant

Gray beds predominant

B4, B6, B8

L5, L7, L9

Bed code,

this report

A A' Section line

0–20

21–40

41–60

61–80

81–100

101–150

151–230

Boron concentrations in

groundwater samples (2006),

in micrograms per liter

Shallow monitor

Intermediate monitor

Deep monitor

Open-hole existing well

Type of well—Label is 

well (MG-) or cluster (RI-) 

identifier

Nomenclature

Figure 26. Boron concentrations in samples collected in spring 2006 from monitor well clusters and openhole wells, and line of section A–A’, North Penn Area 7 Superfund site, Upper Gwynedd Township and vicinity, 

Montgomery County, Pennsylvania.
40 Groundwater System and Simulation of Flow for North Penn Area 7 Superfund Site, Montgomery County, Pennsylvania

A A'

Land surface along transect

B8

L7

B6

L5

L9

Whole-well sample concentration

Less than 20

21–40

41–60

61–80

81–100

101–150

151–229

Boron concentration 

in 2006 groundwater 

sample, in micrograms 

per liter

EXPLANATION

L7

MG-202

L-22

Mapped geologic unit 

and bed code (see 

figure 6 for bed codes)

Land surface at well head. 

U.S. Geological Survey 

well identifer (MG-)

and cluster number (RI-) 

or other identifier

-300

-200

-100

0

100

200

300

400

500

0 1,000 2,000 3,000 4,000 5,000 6,000

Altitude, in feet above NAVD 88

Distance from origin of transect, in feet

MG-2128,2127,2126

RI-13S,13I,13D

MG-2092,2091,2090

RI-5S,5I,5D

MG-2080

RI-1D

MG-2121,2120,2119

RI-10S,10I,10D MG-2134,2133,2132,2131

RI-15S,15I,15D,15DD

MG-2130,2129

RI-14I,14D

MG-2102,2101,2100

RI-9S,9I,9D

MG-2083,2082,2081

RI-2S,2I,2D

MG-202

L-22 MG-2094,2093

RI-6S,6D

MG-2124,2123,2122

RI-11S,11I,11D

MG-2096,175,2095

RI-7S,7I,7D

MG-1897

CL-3

MG-2125

RI-12D

MG-2099,2098,2097

RI-8S,8I,8D

MG-2089,2088,2087

RI-4S,4I,4D

MG-2086,2085,2084

RI-3S,3I,3D

Figure 27. Locations of monitor wells projected onto a line parallel to dip and boron concentrations in samples collected from 

the monitor wells in spring 2006, North Penn Area 7 Superfund site, Upper Gwynedd Township and vicinity, Montgomery County, 

Pennsylvania. (See figure 26 for location of line of section.)
Summary of Field Investigations of Groundwater System at North Penn Area 7 41

identify different sources of elevated chloride at North Penn 

Area 7. Davis and others (1998) state that chloride/bromide 

mass ratios generally range from 50 to 150 in atmospheric 

precipitation, from 100 to 200 in shallow ground water, from 

300 to 600 in domestic sewage, from 1,000 to 10,000 in water 

affected by dissolution of halite, and from 10 to 100 in summer runoff from urban streets.

In water samples collected from 70 wells at North Penn 

Area 7 in 2006, bromide concentrations were quantified in 

samples from 60 wells, ranging from 0.075 to 1.59 mg/L, and 

concentrations were less than detection levels in samples from 

10 wells (less than 0.075 mg/L in samples from 8 wells and 

less than 0.1 mg/L in samples 2 wells). In samples that had 

bromide concentrations reported at greater than the detection 

level, the 2006 chloride/bromide mass ratios ranged from 144 

to 1,386 in two main groups of samples—those in which the 

chloride/bromide mass ratios increased almost linearly in relation to chloride concentrations and those in which chloride/

bromide mass ratios were relatively constant and (or) were 

independent of chloride concentration (fig. 28). The group 

for which the chloride/bromide mass ratios were independent 

of chloride concentration include shallow- and intermediatedepth monitor wells west of Church Road [MG-2092 (RI-5S), 

MG-2091 (RI-5I), MG-2121 (RI-10S), MG-2120 (RI-10I), 

MG-2128 (RI-13S), and MG-2127 (RI-13I)] and shallow 

open-hole wells along, but east of, Church Road at the Teleflex 

facility [MG-1149 (T-10), MG-1148 (T-12),] (figs. 28, 29). 

The spatial clustering of these wells indicates similar sources 

of chloride. Other groundwater samples with chloride/bromide mass ratios that appear relatively less strongly related to 

chloride concentrations were from several shallow wells at the 

Teleflex facility [MG-1146 (T-4), MG-1147 (T-11), MG-1842 

(T-15), MG-1843 (T-6), and MG-2089 (RI-4S)], three nearby 

shallow wells [MG-2086 (RI-3S), MG-1847, and MG-2134 

(RI-15S)], one well to the southwest of the RI-10 well cluster 

[MG-1537 (N1)], and two shallow wells east of Wissahickon 

Creek [MG-2099 (RI-8S) and MG-2102 (RI-9S) (figs. 28, 29). 

The spatial distribution of these other wells indicates (1) some 

RI-13I

RI-10S

RI-10I and duplicate

RI-5I

RI-5S

RI-3S

RI-13S

RI-13D

RI-12D

RI-9S

RI-4S RI-3I

RI-11I

RI-15D

RI-15I

RI-1D, RI-6D

RI-8I, RI-7I

RI-14S

RI-14I

RI-2I

RI-9I

RI-4D RI-7S

RI-10D

RI-3D

RI-8S

RI-15S, RI-4I

T10

T12

T14

N5

T13

MG-1848

T15

N1

T15 duplicate

MG-1847

T6

T4

T11

N3

MG-1849

L-17

L-22

MG-1846

MG-1845

MG-1844

PT-2

R-27

PT1 R-18

R-21

SF-2

R-24

N19

Wells with high chloride concentrations 

and similar chloride/bromide mass ratios

EXPLANATION

RI-9I

RI-15I

East - monitor well in cluster and identifier

Mid - monitor well in cluster and identifier

West - monitor well in cluster and identifier

East - open well and identifier

Mid and west - open well and identifier

Location on North Penn Area 7 site, relative to Wissahickon Creek with Mid near but slightly west 

of Wissackon Creek, and type of well, defined as monitor if reconstructed with a short-screened 

interval and open if borehole is left open in competent rock—

T13

L-22

RI-13I

0

200

400

600

800

1,000

1,200

1,400

1,600

0 50 100 150 200 250 300 350

Chloride/bromide mass ratio

Chloride, in milligrams per liter

Figure 28. Chloride/bromide mass ratio in relation to chloride concentration in water samples collected in March 2006 

from monitor wells at and near North Penn Area 7 Superfund site, Upper Gwynedd Township and vicinity, Montgomery 

County, Pennsylvania. (See figure 29 for location of wells.)
42 Groundwater System and Simulation of Flow for North Penn Area 7 Superfund Site, Montgomery County, Pennsylvania

B4

L5

B6

B8 L9

L7

Wissahickon Creek

75°17'30" 75°17' 75°16'30"

40°14'

40°13'30"

40°13'

Towamencin Creek

0 500 1,000 2,000 FEET

0 150 300 600 METERS

Geology from Berg and others (1980) with nomenclature

from Lyttle and Epstein (1987) and additional mapping and

lithologic classification from Smoot (unpublished)

Base from U.S. Geological Survey

Lansdale 1983, 1:24,000

Universal Transverse Mercator, zone 18

North American Datum of 1927

MG-1148 (T-12)

MG-1149 (T-10)

MG-1847

MG-1843 (T-6)

MG-1537 (N1)

MG-1541 (N5)

MG-1539 (N3)

MG-1553 (N19)

MG-2134 (RI-15S)

MG-2089 (RI-4S)

MG-2092 (RI-5S)

MG-2091 (RI-5I)

MG-2121 (RI-10S)

MG-2120 (RI-10I)

MG-2128 (RI-13S)

MG-2127 (RI-13I)

MG-2099 (RI-8S)

MG-2102 (RI-9S)

MG-2086 (RI-3S)

MG-2080 (RI-1D)

MG-2125 (RI-12D)

MG-202 (L-22)

MG-76

(L-17)

MG-1846

MG-1844

MG-1845

MG-171 (PT-2)

MG-1848

MG-1849

MG-1144 (T-13)

MG-1146 (T-4)

MG-1145 (T-14)

MG-1841 (SF-2)

MG-1147 (T-11)

MG-1842 (T-15)

MG-1505 (R-18)

MG-174

MG-2130 (RI-14I)

MG-2129 (RI-14D)

MG-2090 (RI-5D)

MG-2126 (RI-13D)

MG-2119 (RI-10D)

MG-2133 (RI-151)

MG-2132 (RI-15D)

MG-213! (RI-15DD)

MG-2088 (RI-4I)

MG-2087 (RI-4D)

MG-2085 (RI-3I)

MG-2084 (RI-3D)

MG-2083 (RI-2S)

MG-2082 (RI-2I)

MG-2081 (RI-2D)

MG-2096 (RI-7S)

MG-175 (RI-7I)

MG-2095 (RI-7D)

MG-2098 (RI-8I)

MG-2097 (RI-8D)

MG-2101 (RI-9I)

MG-2100 (RI-9D)

MG-204 (PT-1)

MG-1652 (R-27)

MG-204 (PT-1)

MG-691 (R-24)

MG-2124 (RI-11S)

MG-2123 (RI-11I)

MG-2122 (RI-11D)

MG-2094 (RI-6S)

MG-2093 (RI-6D)

MG-1897

MG-1836

EXPLANATION

Lithology

Red beds predominant

Gray beds predominant

B4, B6, B8

L5, L7, L9

Bed code,

this report 

Chloride/bromide mass ratios

in groundwater samples (2006)

Shallow monitor

Intermediate monitor

Deep monitor

Open-hole existing well

Type of well—Label is 

well (MG-) or cluster (RI-) 

or other identifier

Nomenclature

Less than 0.1 or no data

0.1–550

550.1–700

700.1–850

850.1–1,390 Shaded area shows selected wells 

with high chloride concentrations 

and similar chloride/bromide mass 

ratios shown on figure 28.

Figure 29. Spatial distribution of chloride/bromide mass ratios in water collected in March 2006 from monitor and 

existing open-hole wells, at and near North Penn Area 7 Superfund site, Upper Gwynedd Township and vicinity, 

Montgomery County, Pennsylvania.
Simulation of Regional Groundwater Flow 43

mixing of chloride sources occurs at and near the Teleflex 

facility, (2) unique sources of chloride are near MG-2086 (RI3S) and MG-2099 (RI-8S); and (3) groundwater flow is from 

shallow sources near the RI-5, RI-10, and RI-13 well clusters 

toward the southwest near well MG-1537 (N1). The remaining 

wells belong to the group for which chloride/bromide mass 

ratios increased almost linearly in relation to chloride concentrations, likely reflecting the introduction of bromide-poor salt, 

such as road salt or halite (sodium chloride), to the groundwater that has a natural background chloride/bromide mass ratio 

in the range of 100 to 150.

Inorganic Constituents as Tracers or Indicator of Lithology

The 2005 and 2006 water samples from discrete isolated 

zones represented by the monitor well clusters at North Penn 

Area 7 showed that silica concentrations generally decreased 

with depth, indicating the presence of mechanisms for rapid 

recharge and (or) more reactive surfaces in shallower materials. Differences in silica concentrations across the site may be 

attributable to lithology to some extent, concentrations being 

higher overall in one of the predominantly red beds. 

Like silica, chloride concentrations generally were higher 

in shallow zones. Chloride concentrations greater than the estimated natural background of about 10 mg/L were measured 

in most deep zones, indicating transport of recharge affected 

by surface applications of chloride (such as road salt or septic 

systems) to depths. The presence of chloride from surface 

sources may be used as a tracer and (or) surrogate for organic 

compounds or other constituents at the surface. Chloride/

bromide mass ratios indicate that sources of chloride in water 

from wells west of and along Church Road appear to differ 

from sources at other locations at North Penn Area 7 and probably include substances other than road salt. 

Elevated boron concentrations (greater than 100 μg/L and 

up to 220 μg/L in RI-6D cluster) may be associated with flow 

paths from a source area or be associated with the lithology of 

beds that occur along Wissahickon Creek. The spatial distribution of boron concentrations in well-water samples appears to 

be related to the geologic structure, with the highest concentrations measured in samples from wells completed in units L7 

and B8 (fig. 27), although it is unknown whether controls on 

the distribution are lithologic or hydrologic.

Simulation of Regional Groundwater 

Flow

A model using numerical simulation of regional groundwater flow at North Penn Area 7 was developed to (1) estimate regional-scale aquifer properties to better understand 

and describe the groundwater system and (2) provide a tool 

to estimate directions of groundwater flow (and contaminants 

transported in groundwater) under various historical and predictive scenarios.

Estimation of Regional-Scale Aquifer Hydraulic 

Properties 

Hydraulic conductivity and storage are aquifer properties that may vary spatially because of geologic heterogeneity. 

Transmissivity, the hydraulic conductivity multiplied by the 

saturated thickness of the aquifer, represents a vertical average 

of hydraulic conductivities that may vary with depth. Estimation of these properties allows a quantitative prediction of the 

hydraulic response of the aquifer to recharge, pumping, and 

other hydrologic changes. Storage coefficients are important 

for understanding hydraulic response to transient stresses on 

aquifers. These properties can be estimated on a local scale by 

analysis of data from aquifer tests, such as single-well or multiple-well aquifer tests or on a regional scale by a numerical 

simulation of groundwater flow by use of a computer-based 

model. The local scale ranges from tens of feet to hundreds of 

feet. The regional scale is characterized by lengths of hundreds 

to thousands of feet. 

Most of the analytical techniques used to estimate the 

hydraulic properties of aquifers were developed for porous 

media, such as unconsolidated sediments. These techniques 

may provide reasonable estimates of hydraulic properties in 

fractured rocks when the hydraulic response of the fracturedrock aquifers approximates porous media at the scale of 

interest. Previous application of this approach near the North 

Penn Area 7 Superfund site by Senior and Goode (1999) 

demonstrates that regional groundwater-flow properties can be 

estimated using porous media methods. 

The regional-scale groundwater-flow model for North 

Penn Area 7 and vicinity described in this report assumes 

steady-state conditions and, therefore, can be used to estimate regional-scale hydraulic conductivities but not storage 

properties. Once hydraulic properties have been estimated, 

groundwater flow (and inferred advective transport of contaminants in groundwater) may be simulated to help describe 

and determine effects of pumping on the spatial distribution of 

contaminants in groundwater.

In the following section describing the model, both 

metric units and inch/pound units are given for convenience. 

Metric units were used for model input and output. However, 

all data used to construct and calibrate the model, except 

elevations from the digital elevation model (DEM), originally 

were collected, and in some cases presented elsewhere in this 

and previous reports, in inch/pound units.

Numerical Simulation of Regional Groundwater 

Flow

A three-dimensional finite-difference numerical model, 

MODFLOW-2000 (Harbaugh and others, 2000), was used to 

simulate regional steady-state flow. Model data were prepared 

using the Argus-ONE preprocessor (Agrus Interware, 1997) 

with a customized interface for preparing input files for and 

displaying model results from MODFLOW (Winston, 2000). 
44 Groundwater System and Simulation of Flow for North Penn Area 7 Superfund Site, Montgomery County, Pennsylvania

The model was calibrated using automatic, nonlinear regression-based parameter estimation (optimization) and sensitivity 

algorithms incorporated in MODFLOW-2000 (Hill and others, 

2000). Model parameters were adjusted to reduce the model 

error, which was computed from the differences between 

measured and simulated water levels and streamflow. MODPATH (Pollock, 1994) was used to calculate groundwater-flow 

paths and to plot the groundwater-flow paths on maps. S-Plus 

statistical software (Insightful Corporation, 2008) was used for 

Monte Carlo simulation using procedures developed by Starn 

and others (2010). ArcGIS (ESRI, 2006) was used to prepare 

maps of simulation results. 

Conceptual Model

The model structure is based on a simplified conceptualization of the groundwater-flow system as understood from 

field investigations at North Penn Area 7 and previous studies. 

The weathered and fractured-rock formations are modeled 

as equivalent porous media, such as unconsolidated granular deposits. Thus, it is assumed that groundwater flow can 

be described using a three-dimensional flow equation based 

on Darcy’s Law. In this approach, the hydraulic conductivities used in the model represent the bulk properties of the 

fractured-rock formations. Water flux, which may pass through 

only a small fraction of the rock mass occupied by fractures, 

is simulated as if it were distributed throughout all parts of 

the formations. 

The regional-scale model presented here incorporates 

the effect of bed-oriented anisotropy, with generally lower 

hydraulic conductivity perpendicular to beds, by modeling the 

dipping stratigraphic beds (such as shown in fig. 15) with dipping model layers, as described by Goode and Senior (2000). 

Anisotropy refers to a dependence of hydraulic conductivity on direction. In contrast, under isotropic conditions, the 

hydraulic conductivity does not depend on direction. On the 

basis of field testing described in the previous section, the 

vertical hydraulic conductivity that is normal to the plane of 

bedding or “cross bed” is expected to be less than the subhorizontal hydraulic conductivity, which is oriented in the bedding 

plane. In addition, subhorizontal hydraulic conductivity anisotropy with different hydraulic conductivities in the dip and 

strike directions was incorporated for some parts of the model. 

As shown by Senior and Goode (1999), use of horizontal 

anisotropy approximates some features of groundwater flow in 

dipping sedimentary formations. The entire thickness of rock 

represented by each model layer is assumed to be saturated. 

This approximation means that the transmissivity, the product 

of the hydraulic conductivity and the saturated thickness, of 

the top model layer is assumed to be independent of the computed hydraulic head. In fact, the transmissivity of the shallow 

weathered zone is proportional to the saturated thickness of 

this unit. However, the model results are relatively insensitive 

to minor changes in the transmissivity of the weathered zone 

because most flow is in the deeper parts of the groundwater 

system. Where not affected by pumping, the depth to water in 

wells in the study area typically was less than 15 meters (m; 

50 ft) and was less than 9 m (30 ft) in about half of the wells 

measured in August 1996 (Senior and others, 1998).

As used here, MODFLOW-2000 calculates optimum 

values of model parameters, such as recharge rate and hydraulic conductivity, for a particular model structure on the basis 

of overall differences between simulated and observed water 

levels and streamflow. The model structure includes all quantitative information that establishes the functional relation 

between model parameters and simulated water levels and 

streamflow. Although properties of model cells can be specified individually, the approach used here was to group cells 

with similar properties into zones with uniform parameters. 

This approach significantly reduced the number of model 

parameters and improved the reliability of parameter estimates, although it generally reduced the model fit (Hill and 

Tiedeman, 2007). Zones, in this case primarily model layers, were delineated on the basis of hydrogeologic information, namely the regional bedrock geology as mapped at land 

surface, and the estimated regional dip angles for the rock 

formations. During model calibration, further grouping of 

model layers which are expected on the basis of hydrogeologic information to be similar and which are less sensitive to 

the observations, reduced the number of separate parameters. 

In addition, some model parameters that are shown to be 

very insensitive to the observations were removed from the 

automatic optimization for final calibration and sensitivity 

calculations. Thus, although the model in general calculates 

the optimum parameter values for each simulation, significant 

hydrogeologic judgment was used during the model construction and calibration to guide and control the calibration 

Model Structure and Boundary Conditions

The model grid is aligned parallel to the regional strike 

of the dipping sedimentary beds (45 degrees NE) and corresponds to the assumed major axis of anisotropy of horizontal 

hydraulic conductivity (figs. 3 and 30). The assumed minor 

axis of anisotropy, therefore, is oriented generally in the dip 

direction. Cell dimensions of the horizontal model grid are 

100 m × 100 m (328 ft × 328 ft). Lateral boundaries of the 

model are defined as zero-flux (no flow) cells that include 

streams (discharge boundaries) and topographic divides that 

are assumed to be groundwater divides (fig. 30). Definition of 

the lateral boundaries is based, in part, on maps of water levels 

in the area (Senior and others, 1998; Senior and Ruddy, 2004). 

The altitude of the top surface of the model is derived 

from 30-m digital-elevation-model (DEM) data with 30-m 

(100-ft) grid spacing. The top of the model is defined as a 

constant flux boundary, where the flux into the model domain 

equals the recharge rate. The top two hydrogeologic units 

are conceptualized as a soil or colluvium unit and a highly 

weathered rock unit. These units have uniform thicknesses of 

6 m (19.7 ft). 

Beneath the subhorizontal soil and highly weathered 

rock units, the regional-scale model has a vertical structure 
Simulation of Regional Groundwater Flow 45

75°20' 75°15' 

40°15'

40°10'

0 1 2 KILOMETERS

0 1 2 MILES

Base from U.S. Geological Survey

Reading, Pennsylvania-New Jersey 1984, 1:100,000

EXPLANATION

Selected cells of model—

Stream in layer 1 and

pumping well in 

underlying layer

Pumping well

Stream

Model boundary

Boundary of North Penn Area 7 

for model water budget Discharge to stream

Figure 30. Model boundary, streams cells, and pumped well cells for model of North Penn Area 7 Superfund site, 

Upper Gwynedd Township and vicinity, Montgomery County, Pennsylvania. 
46 Groundwater System and Simulation of Flow for North Penn Area 7 Superfund Site, Montgomery County, Pennsylvania

that mimics the dipping stratigraphy of the geologic units, 

as defined by geologic mapping in the area and by correlations between borehole logs (Senior and others, 2008). The 

model preprocessor computes appropriate layer elevations and 

thicknesses and assigns the corresponding model parameters. 

The geologic structure is simulated using contours of elevation on the top of the uppermost (to the NW) dipping bed, B4, 

corresponding to model layer 4 (table 3). The contour lines 

were digitized from the surface geology map of Smoot (Joseph 

P. Smoot, written communication, 2006). Starting from the 

contact contour of the top of bed B4, which is at the elevation 

of the land surface, the assumed regional dip of 10 degrees to 

the NW was used to extrapolate the elevation of the top of bed 

B4 throughout the model domain, updip and downdip from the 

contact contour. Note that in updip areas parts or all of this bed 

have been eroded. Approximate bed thicknesses were calculated geometrically for each bed from the geologic-contact 

contour horizontal spacings. These thicknesses were used to 

compute the structural contour elevations for the top of the 

each bed.

Using the depth of the weathered zone and the assumed 

lower boundary of the model, the model layers representing 

the beds are truncated at the top and bottom (figs. 31, 32). 

The upper truncation occurs where each bed represented by a 

model layer subcrops below the subhorizontal highly weathered rock layer or 12 m (39.4 ft) below the land surface. At 

this interface, truncated bedrock layers are assigned a thickness of 0.01 m (0.033 ft), and the hydraulic properties are 

those of the overlying highly weathered rock layer. In areas 

where model layers representing beds are truncated near 

the surface, the thickness of the overlying highly weathered 

rock unit is thus slightly increased, but the increase does 

not significantly affect the estimation of aquifer properties 

or regional flow results. The lower truncation is at the bottom of the model, 200 m (656 ft) beneath the bottom of the 

highly weathered rock layer, or 212 m (695 ft) below the land 

surface. Model cells truncated at the bottom are inactive cells 

and are not included in the simulation. The bottom layer of the 

model is defined as a no-flow boundary. 

In summary, the model structure is similar to the 

regional-scale model of Senior and Goode (1999) but with 

dipping model layers to represent mapped dipping sedimentary units. Computations of model layer top and bottom elevations and specification of model cell properties are performed 

Table 3. Hydrostratigraphy used in the groundwater model for North Penn Area 7 Superfund site, Upper Gwynedd Township and 

vicinity, Montgomery County, Pennsylvania.

[m, meters]

Geologic unit Bed code 

for model

Geologic 

map 

symbol1

Lithologic 

map 

symbol2

Model 

layer

Thickness3

(m)

Hydraulic conductivity parameters

Value in 

strike 

direction

Horizontal 

anisotropy4

Vertical 

anisotropy5

Subhorizontal units (uniform thickness)

Overburden 1 6 KW 1 1

Highly-weathered rock 2 6 KW 1 1

Dipping units (varying thickness) 

Brunswick Group - undifferentiated B JTrb TrSic 3 200 KB HANI VANI

Red beds predominant - deltaic B4 JTrb TrS/Sic 4 80 KB46 HANIBED VANIBED

Gray beds predominant - deltaic L5 JTrblg TrS/Sicg 5 83 KL5 HANIBED VANIBED

Red beds predominant - deltaic B6 JTrb TrS/Sic 6 140 KB46 HANIBED VANIBED

Gray beds predominant - deltaic L7 JTrblg TrS/Sicg 7 57 KL7 HANIBED VANI7

Red beds predominant - deltaic B8 JTrb TrS/Sic 8 74 KB8 HANIBED VANI8

Gray beds predominant - deltaic L9 Trl TrS/Sicg 9 233 KL9 HANIBED VANIBED

Red beds predominant - deltaic B10 Trlr TrS/Sic 10 47 KB10 HANIBED VANIBED

Lockatong Formation - undifferentiated L Trl TrSicg 11 200 KL HANI VANI

1

Lyttle and Epstein, 1987.

2

Joseph Smoot, U.S. Geological Survey, unpublished mapping, 2005.

3

Thickness used in model for layers 3–11 depends on location with respect to dipping beds. Maximum stratigraphic thickness of layer listed. Total thickness 

of layers 3–11 is limited to 200 m.

4

Hydraulic conductivity in the dip direction divided by the value in the strike direction.

5

Hydraulic conductivity in the strike direction divided by the value in the vertical direction.
Simulation of Regional Groundwater Flow 47

1

2

4

3

5 6

11

10 9

8 7

Model grid cell containing a pumped well

NORTHWEST

SOUTHEAST

EXPLANATION

VERTICAL EXAGGERATION x 1.0

0 1,000 METERS

0 5,000 FEET

VERTICAL EXAGGERATION x 10.0

0 1,000 METERS

0 5,000 FEET

1 Model grid layer number

Figure 31. Cross section in the dip direction of model grid for North Penn Area 7 Superfund site, Upper Gwynedd 

Township and vicinity, Montgomery County, Pennsylvania. (See figure 33 for location of lines of section.)

EXPLANATION

1

2

4

3

5

6

11 10

9

8

7

Model grid cell containing a pumped well

SOUTHWEST

NORTHEAST 7

VERTICAL EXAGGERATION x 1.0

VERTICAL EXAGGERATION x 10.0

0 1,000 METERS

0 5,000 FEET

0 1,000 METERS

0 5,000 FEET

1 Model grid layer number

Figure 32. Cross section in the strike direction of model grid for North Penn Area 7 Superfund site, Upper Gwynedd 

Township and vicinity, Montgomery County, Pennsylvania. (See figure 33 for lines of section.)
48 Groundwater System and Simulation of Flow for North Penn Area 7 Superfund Site, Montgomery County, Pennsylvania

by a preprocessor using a programmed geographic information 

system (GIS) (Winston, 2000). This approach yields dipping model layers whose geometry conforms to the mapped 

geologic units in the study area (fig. 33) and are pinched out 

where these beds have been eroded or subcrop within the 

weathered zone. 

This model is constructed to simulate regional features of 

groundwater flow in the study area and is not designed to simulate features of groundwater flow observed during local-scale 

testing. In contrast to the model of Goode and Senior (2000), 

in which thin dipping layers a couple of meters thick represent 

individual bed-oriented flow features, the present model has 

dipping layers that represent larger hydyrostratigraphic units 

and do not represent individual high-transmissivity zones. The 

thinnest model layer (representing fractured-bedrock units) 

used here is 47 m thick, whereas field testing indicates that 

high-transmissivity features in boreholes are generally less 

than 1 m thick.

Calibration Methods

The numerical model is calibrated by use of parameterestimation components of MODFLOW-2000 (Hill and others, 

2000) that minimize model error through a linearized gradient 

method. During parameter estimation, an iterative procedure 

is used to adjust aquifer hydraulic properties in the model 

Contours of altitude of top of

bed B4 (projected), in meters

after map of Smoot (unpublished).

Interval is variable.

-385

-190

0

80

163

303

360

434

667

714

926

1138

Contacts of surficial

outcrop of bed B10,

after map of 

Smoot (unpublished)

Thickness of model layer 10, 

representing bed B10:

color scale 0 to 50 meters 

in 5-meter increments

(uncolored less than 0.1 meter)

Thickness of model layer

10, representing bed B10

Locations of 

cross sections

Northwest

Northeast

Southeast

Southwest

Figure 33. Model preprocessor showing structural contours for top of bed B4 (projected), layer 10 thickness for the model, and lines 

of section, North Penn Area 7 Superfund site, Upper Gwynedd Township and vicinity, Montgomery County, Pennsylvania. Cross sections 

for depicted section lines shown on figure 31.
Simulation of Regional Groundwater Flow 49

in such a way as to minimize an overall model error. Model 

error is defined as the sum of squared, weighted residuals, 

where residuals are the differences between measured and 

simulated hydraulic head (water level) and streamflow. These 

residuals are weighted to account for differences in units, for 

example between units of meters for water-level measurements and units of cubic meters per day (m3

/d) for streamflow. 

The weight for all water-level measurements is 1.0 (in units 

of 1/m), and the weight for all streamflow residuals is 0.058 

[in units of days per cubic meter (d/m3)] (Senior and Goode, 

1999, p. 76). 

The model was calibrated using measured groundwater 

levels (317 values), measured streamflows (10 values), and 

specified pumping rates for three time periods. The calibration procedure computes the total model error as the sum of 

the errors for each simulation period and uses a consistent 

set of hydraulic parameters for all simulations. The time 

periods used for model calibration were August 1996 (Senior 

and others, 1998; Senior & Goode, 1999), December 2000 

(Senior and Ruddy, 2004), and June 2005 (Senior and others, 2008). Although water levels fluctuate seasonally and 

typically are lowest in late summer/early fall and highest in 

spring, the pattern of rainfall prior to each set of synoptic 

measurements evened out the differences related to seasonal 

timing of measurements. The regional groundwater levels in 

each set of synoptic measurements were near long-term (30-

year) annual averages (fig. 19). Compared to the long-term 

(30-year) precipitation normals, the hydrologic conditions 

during these periods were relatively wet prior to August 1996 

and near the long-term average prior to December 2000 and 

June 2005 (Senior and others, 2008). During calibration, the 

recharge during the three time periods (1996, 2000, and 2005) 

was specified as three independent model parameters. The 

conductivity of the streambed, which controls the head gradient between the aquifer and the stream, provided the stream is 

flowing, was an estimated model parameter.

External procedures were used to guide and control 

the parameter estimation process. During initial calibration, 

several model parameters were identified that were relatively insensitive to the observations. That is, large changes 

in the model parameter value had relatively small effects on 

the overall model error. For example, the limited observations (14 monitor well clusters) of the vertical head gradient 

limits the sensitivity of the model error to vertical anisotropy. 

Hydrogeologic judgment was used to remove such parameters 

from the automatic calibration. In several cases, initial calibrations were used to identify a model parameter value that was 

reasonable on the basis of hydrogeologic judgment and field 

observations and that yielded a low model error. Subsequently, 

these parameter values were fixed and removed from the 

calibration process. Parameters estimated using this procedure 

also were not used in Monte Carlo simulations. The estimates 

of these parameters are considered to have high uncertainty. 

Final parameter values were estimated using a combination of manual and automatic optimization procedures. Automatic calibration successfully reduced the overall model error 

by adjusting parameters from their initial values. However, 

near the optimum, the gradient search method failed to converge. There may be several aspects of this particular application that cause this, including numerous and sometimes poorly 

constrained parameters and nonlinear behavior of the groundwater-flow model and optimization. Separate optimizations 

were conducted with many different sets of parameters fixed, 

and in some cases, all but one parameter was fixed. However, 

even in this case the overall model error increased during 

the automatic calibration when starting close to the optimum 

value. The final parameter values presented here were eventually identified by picking, by hand, the model parameter set 

that produced the lowest overall model error from among the 

trials conducted near the optimum. Although these values are 

not guaranteed to be the absolute optimum parameter values 

possible, the parameter values identified are considered close 

enough to the true optimum to be used for reasonably accurate 

simulation. This uncertainty is considered acceptable given 

the other uncertainties in the model. It may be possible to use 

alterative optimization procedures beyond the gradient search 

method that may yield slightly different optimum parameter 

values, but the application presented here is limited to the 

procedures in MODFLOW-2000 (Hill and others, 2000). 

Recharge and Discharge

The components of the water budget for the saturated 

zone that are included in the model are (1) uniform recharge 

to the water table, (2) discharge to pumped wells, and (3) 

discharge to, and infiltration from, streams. The steady-state 

assumption implies that these fluxes are in equilibrium and 

that hydraulic head is not changing in time. In reality, these 

fluxes, particularly pumping rates and recharge, are changing in time, and hydraulic head changes in response to these 

fluctuations. The steady-state model corresponds to the 

average flow conditions for the time period of interest and 

approximates the average fluxes and hydraulic head during 

that period. Thus, the steady-state model does not and cannot 

simulate instantaneous flow conditions. 

Recharge to the saturated zone is assumed to be spatially 

uniform because detailed spatial information on factors affecting infiltration is not available for the study area. On average, 

recharge to the water table is precipitation minus surface runoff and evapotranspiration. Areal recharge enters through the 

top model layer, and the magnitude of recharge is determined 

from calibration. An average, the annual recharge rate of 

210.8 millimeters per year (mm/yr; 8.3 inches per year (in/yr)) 

estimated by Senior and Goode (1999) for the Lansdale area, 

was used as an initial estimate in this model. Recharge was not 

varied spatially according to differences in land use or topography. Three separate parameters were used for the recharge 

in 1996, 2000, and 2005, named Rech1996, Rech2000, and 

Rech2005, respectively. 

Streams are simulated in the model by use of the stream 

package (Prudic, 1989) as modified for MODFLOW–2000. 

Streams are in the shallow top layer of the model, and the 
50 Groundwater System and Simulation of Flow for North Penn Area 7 Superfund Site, Montgomery County, Pennsylvania

aquifer discharges to the stream if the hydraulic head in a 

model cell is higher than the hydraulic head of the stream 

in that cell. The stream package allows simulated streams 

to gain or lose water and accounts for the flow in each 

stream cell so that losses cannot exceed the simulated base 

flow of the stream. Land-surface elevations from the 10-m 

digital elevation model (DEM) were interpolated to points 

along each stream. Stream stage was assigned an altitude 

1 m lower than the interpolated land-surface elevation. The 

thickness of the streambed was assumed to be 2 m (6.6 ft). 

Stream width was assumed to be 3 m (9.8 ft). The location of 

streams in the model domain and interpolated land-surface 

elevation at streams are shown in figure 34. The uniform 

streambed conductivity parameter (STR) was estimated 

during calibration.

Values for aquifer discharge to streams are derived from 

25 measurements of base flow made at five locations from 

May 1995 through November 1996 (Senior and Goode, 1999, 

table 4) and from measurements made at several locations 

on Wissahickon Creek from June 2000 to September 2005 

(Senior and others, 2005, table 65; Senior and others, 2008, 

tables 74 and 75) (fig. 20). Base-flow measurements used to 

estimate groundwater discharge to the stream at various time 

periods of the simulation were available at several streams for 

the 1996 calibration period but only at Wissahickon Creek for 

the 2000 and 2005 calibration period (table 4). Comparison of 

SW-17 01473806 

SW-21

01473808 

01473809 

SW-3

SW-10 

Land-surface altitude, 

color scale 40 to 140 meters

in 10-meter increments

Pumping wells 

Locations and

station numbers

of streamflow 

measurements 

Streams in model layer 1

and land-surface altitude

Figure 34. Model preprocessor showing locations of streamflow measurements, land-surface elevations at streams, and locations 

of pumped wells for the numerical model for North Penn Area 7 Superfund site, Upper Gwynedd Township and vicinity, Montgomery 

County, Pennsylvania.
Simulation of Regional Groundwater Flow 51

measured and simulated streamflow for 1996, 2000, and 2005 

simulation periods is shown in table 4, which lists the measured and simulated incremental change in streamflow, that is 

the net discharge from the aquifer to the stream (gain) or flow 

from the stream to the aquifer (loss) for a given stream reach. 

Measured streamflows were relatively well-simulated by the 

model in 1996 for streams other than Wissahickon Creek. 

Residuals (simulated-measured) for Wissahickon Creek in all 

calibration periods (1996, 2000, and 2005) were larger than 

those in 1996 for other streams (table 4).

Groundwater withdrawals from wells are represented 

by a constant flux of water removed from the model using 

the multi-node well (MNW) package in MODFLOW–2000. 

Withdrawals from each well are computed for all model layers representing beds to which the well is open. An iterative 

procedure ensures that the sum of the layer fluxes for a given 

well is equal to the well pumping rate, within a user-specified 

tolerance. Locations of pumped wells used in model simulations are shown in figure 34. Well information and pumping 

rates for calibration periods are shown in table 5. 

The pumping rates used in the model represent annual 

average rates (Pennsylvania Department of Environmental 

Protection, State Water Plan Division, written commun., 

1995), except for some NPWA wells (table 5). NPWA wells 

were assigned the average pumping rate for the month of 

interest, if monthly data were available. 

Measured and Simulated Water Levels in Wells

A total of 317 measured water levels in 215 wells within 

the model domain were available for three different time 

periods (table 6, at end of report). The periods used for model 

calibration are August 1996 (Senior and others, 1998; Senior 

and Goode, 1999), December 2000 (Senior and Ruddy, 2004), 

and June 2005 (Senior and others, 2008). Water-level data 

consist of one measurement per well for each period. The 

water-level data were distributed over a larger area for the 

1996 calibration (139 wells) than for the 2000 calibration 

(95 wells) and the 2005 calibration (84 wells); data for the 

2000 and 2005 calibration periods were spatially centered 

on North Penn Area 7 and vicinity. A simultaneous calibration was performed using steady-state models for each of the 

periods. On the basis of specified altitudes of the top and bottom of the open interval of each well, the model preprocessor 

determined the corresponding model layers for each well and, 

if needed, thickness-proportional layer weights. In the latter 

case, the measured water level was compared to a weighted 

vertical average of the simulated water levels in the model 

layers that intersect the open interval of the well. 

Maps of simulated water-table altitudes (water levels 

in top layer of model representing the weathered zone) are 

shown for the three calibration periods, 1996, 2000, and 2005 

(fig. 35). The simulated water-table contours are similar 

to potentiometric-surface maps prepared from measured 

water levels in wells completed at various depths (Senior 

and Goode, 1999; Senior and Ruddy, 2004; Senior and 

others, 2008).

Groundwater-level residuals (simulated water level minus 

the measured water level) for wells with measurements also 

are shown on these maps for the three calibration periods, 

1996, 2000, and 2005 (fig. 35). The root mean square residuals for the 1996, 2000, and 2005 calibration periods are 5.53, 

4.86, and 4.54 m (18.1, 16.0 and 14.9 ft), respectively. The 

residuals show that many simulated groundwater levels are 

close in value to measured levels and indicate that there are 

some clusters of over-simulated and under-simulated groundwater levels. The groundwater levels at several locations in 

the northern part of the modeled area are under-simulated for 

1996 by the model (fig. 35). This northern area is far from 

the contamination in the North Penn Area 7 and is modeled 

as a single hydrogeologic unit of the Brunswick Group, after 

Senior and Goode (1999). Additional effort to add heterogeneity and parameters in this part of the model was not attempted 

in the present study but could be attempted in future model 

applications to reduce model error for that area. Simulated 

water levels for several wells in the vicinity of the Merck 

facility are too high by more than 5 m (16.4 ft) for all three 

time periods and too low by more than 5 m (16.4 ft) for 2005, 

which may be due to higher or lower than average pumping 

rates, respectively, at the time of the water-level measurement. In addition, the local-scale heterogeneity that has been 

observed during aquifer tests at the Merck facility (Goode and 

Senior, 1998) and in Lansdale (Goode and Senior, 2000) was 

not incorporated in the present regional-scale model. 

The relation of simulated groundwater levels to measured 

groundwater levels indicates that the groundwater-flow model 

generally captures the regional characteristics of groundwater 

flow (fig. 36). The overall root-mean-square water-level residual is 5.02 m (16.5 ft) for the three calibration periods, which 

is small in comparison to the range of measured water level 

altitudes as great as 115 m (377 ft). However, the residuals 

at individual wells range from -21.6 m (-70.8 ft) to +16.7 m 

(+54.8 ft), indicating that the simulation error at individual 

well locations may be large. Residuals (or model errors) are 

among the largest for water levels in wells affected by pumping, such as those at the Merck facility or in the RI-2 and RI-9 

well clusters, indicating that, locally, the model sometimes did 

not closely simulate the observed vertical gradient determined 

using measured water levels in well clusters. The direction, 

but not the magnitude, of the vertical gradients generally were 

correctly simulated in the areas affected by pumping. This 

result is due, in part, to two factors—(1) inaccurate pumping 

rates, annual or monthly average pumping rates were used in 

the steady-state simulation, but measured water levels reflect 

possibly different daily or hourly rates and (2) the model structure in which occasionally more than one well in a cluster, 

each with its own water level, may be in the same model cell, 

making accurate simulation of water levels impossible. For 

example, in 2005, the measured water levels were about 10 m 

(33 ft) lower in the intermediate well [MG-2101 (RI-9I)] than 

the deep well [MG-2100 (RI-9D)] of the RI-9 cluster because 
52 Groundwater System and Simulation of Flow for North Penn Area 7 Superfund Site, Montgomery County, Pennsylvania Table 4. Measured and simulated groundwater discharge to stream reaches for the calibrated numerical model of groundwater flow in the North Penn Area 7 Superfund site, Upper Gwynedd Township and vicinity, Montgomery County, Pennsylvania. [See figure 34 for location of stream-measurement sites. USGS, U.S. Geological Survey; m3/d, cubic meters per day; m, meters] USGS station number Site number Stream site location Measurement dates Model calibration year Base-flow measurement type1 Groundwater discharge to stream reach ending at measurement site (m3/d) Weighted residual4 Measured gain or loss2 Simulated gain or loss2 Residual (simulated minus measured) Normalized residual3 Streams other than Wissahickon Creek SW-21 Tributary to Towamencin Creek at Troxell Rd. May 1995–November 1996 1996 Estimated from 5 measurements 245 333 87.7 0.3 5.08 SW-3 Tributary to W. Branch Neshaminy Creek at Cowpath Rd near Kulp Rd May 1995–November 1997 1996 Estimated from 5 measurements -832 -723 109 0.14 6.35 SW-10 Tributary to W. Branch Neshaminy Creek near Line & Cowpath Rd May 1995–November 1998 1996 Estimated from 5 measurements 0 0 0 0 0 SW-17 Towamencin Creek at Sumneytown Pike May 1995–November 2000 1996 Estimated from 5 measurements 685 817 132 0.18 7.66 Wissahickon Creek 01473806 (and 01473808) SW-13 (and SW-13A) Wissahickon Creek at Hancock St. (and at Wissahickon Ave.) May 1995–November 1999 1996 Estimated from 5 measurements5 98 31 -67 -1.04 -3.89 01473806 Wissahickon Creek at Hancock St. June 2003–September 2005 2005 Estimated from 7 measurements 0 131 131 2 7.58 01473808 Wissahickon Creek at Wissahickon Ave. December 11, 2000 2000 1 measurement 51.8 0 -51.8 -2 -3 01473808 Wissahickon Creek at Wissahickon Ave. December 2002–September 2005 2005 Estimated from 9 measurements 0 -15.4 -15.4 -2 -0.9 01473809 Wissahickon Creek at Sumneytown Pike December 11, 2000 2000 1 measurement -95.4 -43.6 51.8 0.75 3 01473809 Wissahickon Creek at Sumneytown Pike December 2002–September 2006 2005 Estimated from 9 measurements -43.6 -24.5 19.1 0.56 1.11

1Measurements from Senior and Goode (1999) and Senior and others (2007).2(+) indicates gain of groundwater discharge to stream; (-) indicates stream loss to groundwater.3Calculated as residual/[|(measured+simulated)|/2].4All streamflow residuals are weighted by 0.058 (day / m3) and thus are dimensionless.5First two measurements were at site 01473806 and remainder were at 01473808.
Simulation of Regional Groundwater Flow 53

Table 5. Pumping well identification, locations and pumping rates for North Penn Area 7 Superfund site, Upper Gwynedd Township and 

vicinity, Montgomery County, Pennsylvania.—Continued

[USGS, U.S. Geological Survey; m avd, meters above vertical datum NGVD 29; m3/d, cubic meters per day; gal/min, gallons per minute]

USGS 

well 

identifier1

Owner’s well 

name or number

Altitude of open 

interval (m avd) Model 

layer

Pumping rate (gal/min) Pumping rate (m3/d)

Top Bottom 1990 1996 December 

2000

June 

2005 1990 1996 December 2000

June 

2005

52 NW-4 93.574 0 9 35 0 0.0 0.0 190.76 0.00 0.00 0.00

55 NW-5 76.505 8.534 9 60 0 0.0 0.0 327.02 0.00 0.00 0.00

59 PW3 84.430 37.186 4 37.9 37.9 30.5 21.4 206.57 6.95 5.60 3.93

66 L-7 101.498 -0.610 8 39.8 0 0.0 0.0 216.93 0.00 0.00 0.00

67 L-8 86.350 10.455 3 60 0 0.0 0.0 327.02 0.00 0.00 0.00

68 L-9 85.222 -54.346 3 2.3 0 0.0 0.0 12.54 0.00 0.00 0.00

69 L-10 87.691 20.025 3 68.8 34.9 0.0 0.0 374.99 6.40 0.00 0.00

71 L-12 110.947 37.186 8 41.3 0 0.0 0.0 225.10 0.00 0.00 0.00

73 L-14 99.487 14.143 8 71.1 78.2 70.4 0.0 387.52 14.35 12.92 0.00

75 L-16 102.718 -6.096 8 34.8 84.5 0.0 0.0 189.67 15.50 0.00 0.00

76 L-17 93.574 -11.582 8 87.2 81 75.0 66.7 475.27 14.86 13.76 12.24

77 L-18 94.732 -15.301 8 125.6 136 133.9 0.0 684.57 24.95 24.57 0.00

78 L-19 101.194 -16.764 8 68.1 71.8 50.0 138.2 371.17 13.17 9.17 25.36

124 PW1 87.173 8.839 9 94.1 2 74.0 99.2 512.88 0.37 13.58 18.20

125 PW2 97.231 18.898 8 42.5 40 45.0 35.4 231.64 7.34 8.26 6.49

126 PW3 89.916 -24.994 9 94.1 86 69.0 80.6 512.88 15.78 12.66 14.79

128 PW5 94.183 -26.822 8 0 0 53.0 72.5 0.00 0.00 9.72 13.30

130 PW7 90.221 11.887 8 88.7 85 66.0 29.9 483.45 15.60 12.11 5.49

134 Kendick Rubber 84.430 71.628 3 2.4 2.4 2.4 2.4 13.08 0.44 0.44 0.44

135 Ford-3 99.670 -39.624 8 48.2 0 0.0 0.0 262.71 0.00 0.00 0.00

140 PW4 70.714 11.582 4 78.9 78.9 59.3 47.1 430.04 14.48 10.88 8.64

143 L-21 76.810 -32.004 3 72.5 0 0.0 0.0 395.15 0.00 0.00 0.00

147 Ford-4 99.670 -39.624 7 74.4 0 0.0 0.0 405.51 0.00 0.00 0.00

151 Ford-5 87.478 -41.148 7 86.3 0 0.0 0.0 470.37 0.00 0.00 0.00

153 PW-2 96.012 -12.802 4 19.6 0 0.0 0.0 106.83 0.00 0.00 0.00

167 PW1 L&N 88.392 21.946 9 14.6 14.6 0.0 0.0 79.58 2.68 0.00 0.00

171 PW1 90.678 -40.996 8 4.6 4.6 4.6 4.6 25.07 0.84 0.84 0.84

202 L-22 92.354 -84.26 8 81.8 83.1 72.1 107.1 445.84 15.25 13.23 19.65

203 NW-7 82.906 -41.148 9 46.2 0 0.0 0.0 251.81 0.00 0.00 0.00

204 PW2 89.002 -43.282 8 4.6 4.6 4.6 4.6 25.07 0.84 0.84 0.84

223 PW2 L&N 88.087 -5.486 9 15.8 15.8 0.0 0.0 86.12 2.90 0.00 0.00

498 L-23 77.267 -65.989 3 27.5 0 24.5 20.8 149.89 0.00 4.50 3.82

566 PW-5 71.628 -15.24 4 55 55 60.6 79.0 299.77 10.09 11.12 14.49

593 L-25 75.377 -51.420 3 64.9 0 0.0 0.0 353.73 0.00 0.00 0.00

620 PW-3 74.371 -12.192 4 10.6 0 0.0 0.0 57.77 0.00 0.00 0.00

621 PW-4 80.833 -21.885 3 10 0 0.0 0.0 54.50 0.00 0.00 0.00

625 Rex-1 83.698 -24.811 3 35.4 35.4 35.4 35.4 192.94 6.49 6.49 6.49

704 L-26 71.415 -25.207 3 39.7 0 0.0 0.0 216.38 0.00 0.00 0.00

875 NW-17 82.296 -51.816 5 69.3 69.3 5.2 5.2 377.71 12.71 0.94 0.94
54 Groundwater System and Simulation of Flow for North Penn Area 7 Superfund Site, Montgomery County, Pennsylvania

Table 5. Pumping well identification, locations and pumping rates for North Penn Area 7 Superfund site, Upper Gwynedd Township and 

vicinity, Montgomery County, Pennsylvania.—Continued

[USGS, U.S. Geological Survey; m avd, meters above vertical datum NGVD 29; m3/d, cubic meters per day; gal/min, gallons per minute]

USGS 

well 

identifier1

Owner’s well 

name or number

Altitude of open 

interval (m avd) Model 

layer

Pumping rate (gal/min) Pumping rate (m3/d)

Top Bottom 1990 1996 December 

2000

June 

2005 1990 1996 December 2000

June 

2005

914 NP-12 78.334 -97.536 5 99.6 57.6 0.0 0.0 542.86 10.57 0.00 0.00

919 NP-17 37.795 -109.728 3 258.4 86.9 118.9 172.1 1408.38 15.94 21.81 31.58

991 PW8 96.622 -76.2 8 98.2 123 48.0 108.6 535.23 22.57 8.81 19.93

1028 NP34 56.693 -32.004 9 80 70.8 76.4 71.5 436.03 12.99 14.02 13.12

1045 PW5 87.417 2.987 3 13.4 0 0.0 0.0 73.04 0.00 0.00 0.00

1050 NW-21 78.334 -60.96 9 139.8 103 65.5 65.5 761.97 18.90 12.02 12.02

1051 NW-22 81.382 -57.912 5 121.9 121.9 9.7 9.7 664.40 22.37 1.79 1.79

1052 NW-23 67.056 -85.344 8 52.2 39.1 52.1 52.1 284.51 7.17 9.56 9.56

1125 NP-61 87.792 -21.022 5 40.4 121 72.8 79.4 220.20 22.20 13.36 14.57

1198 PW9 91.135 12.802 7,8 50.6 50 7.0 23.1 275.79 9.17 1.28 4.24

1199 PW11 95.098 15.850 8 41.7 51 68.0 101.7 227.28 9.36 12.48 18.66

1336 Allied Conc. 86.868 69.494 9 4.4 4.4 4.4 4.4 23.98 0.81 0.81 0.81

1418 Ziegler 86.563 50.902 4 2.5 2.5 2.5 0.0 13.63 0.46 0.46 0.00

1423 PW12 84.734 -28.042 8 0 74 11.0 35.3 0.00 13.58 2.02 6.48

1424 PW13 79.858 -32.918 8,9 0 94 51.0 88.1 0.00 17.25 9.36 16.16

1484 Trotter Pretzel 72.786 -33.894 3 0.32 0 0.0 0.0 1.74 0.00 0.00 0.00

1641 Rex-2S 81.875 79.742 3 0 0 5.0 5.0 0.00 0.00 0.92 0.92

1653 Trotter Pretzel 1 80.772 63.398 3 0.06 0 0.0 0.0 0.33 0.00 0.00 0.00

1667 Royal Cleaners 94.488 -3.658 4 2 2 2.0 0.0 10.90 0.37 0.37 0.00

1701 PW14 89.916 21.031 8 0 0 15.0 13.6 0.00 0.00 2.75 2.50

1702 PW15 84.734 6.401 9 0 0 75.0 113.1 0.00 0.00 13.76 20.75

1841 SpraFin 97.103 79.730 9 4.5 4.5 4.5 4.5 24.53 0.83 0.83 0.83

1905 Keystone 7 86.344 49.158 3 0 0 0 20 0.00 0.00 0.00 3.67

1938 Royal 2 95.341 71.872 4 0 0 0 15 0.00 0.00 0.00 2.75

Special cases—wells on model border were assigned half pumping rates

924 NP-21 70.104 -67.056 5 148.1 90.7 129.3 0.0 807.20 16.64 23.72 0.00

2

1014 H-10 73.762 -1.524 9 57.3 0 0.0 0.0 312.31 0.00 0.00 0.00

1486 Baum’ Meat 91.14 28.042 3 2.3 2.3 0.0 0 12.54 0.42 0.00 0.00

1

MG- prefix omitted.

2

H-10 was artificially moved so that the well is inside the model grid.
Simulation of Regional Groundwater Flow 55

EXPLANATION

Model domain boundaryStream

-21.58 – -5.00-4.99 – -1.00-0.99 – 1.001.01 – 5.005.01 – 10.01

Simulated water-table 

contour. Contour interval is 5 meters

Observation/monitor well

showing simulated water level minus measured water level, in meters

60

45

60

A. 1996

65 60 55 50

808590 100 105 110

45

115 120

110115 120

125

155

150

145

75

80

70

80

85

90 95 105 105

80 80

85

95

95

90

85

80

70

75

90

85

100

130

135

140

80

70

125

120

130 110

75°15' 75°20'

40°15'40°10'

0 1 2 MILES

0 1 2 KILOMETERS

Base from Pennsylvania Department of TransportationMajor Rivers, 1995Universal Transverse Mercator, zone 18North American Datum of 1927

Figure 35. Simulated water-table altitudes and location of observation wells showing simulated water levels minus measured water levels in A, 1996, B, 2000, 

and C, 2005 for the model for North Penn Area 7 Superfund site, Upper Gwynedd Township and vicinity, Montgomery County, Pennsylvania.
56 Groundwater System and Simulation of Flow for North Penn Area 7 Superfund Site, Montgomery County, Pennsylvania EXPLANATION Model domain boundary Stream-18.48 – -5.00 -4.99 – -1.00 -0.99 – 1.00 1.01 – 5.00 5.01 – 16.49 Simulated water-table contour. Contour interval is 5 meters Observation/monitor well showing simulated water level minus measured water level, in meters 60 B. 2000

80

70

45

110

65

60

55

50

75

80

70

80

80

85

90

100

105

110

110

115

120

125

130

145 140

85

90

95

100

45

90

85

80

75

70

135

125 120

130

115

90

85

95

95

80

75

75°15' 75°20'

40°15'40°10'

Base from Pennsylvania Department of TransportationMajor Rivers, 1995Universal Transverse Mercator, zone 18North American Datum of 1927

0 1 2 MILES

0 1 2 KILOMETERS

Figure 35. Simulated water-table altitudes and location of observation wells showing simulated water levels minus measured water levels in 

A, 1996, 

B, 2000, 

and 

C, 2005 for the model for North Penn Area 7 Superfund site, Upper Gwynedd Township and vicinity, Montgomery County, Pennsylvania.—Continued
Simulation of Regional Groundwater Flow 57

EXPLANATION

Model domain boundaryStream

-10.55 – -5.00-4.99 – -1.00-0.99 – 1.001.01 – 5.005.01 – 11.73

Simulated water-table 

contour. Contour interval is 5 meters

Observation/monitor well

showing simulated water level minus measured water level, in meters

60

C. 2005

80

70

110

65 60 55 50

75

80

70

80

85 90 100 105

110

110

115

120125 135

150

145

859095 100

90

85 80

75

70

140

130

125

130 115

90

85

95

95

80 75

75°15' 75°20'

40°15'40°10'

130

Base from Pennsylvania Department of TransportationMajor Rivers, 1995Universal Transverse Mercator, zone 18North American Datum of 1927

0 1 2 MILES

0 1 2 KILOMETERS

Figure 35. Simulated water-table altitudes and location of observation wells showing simulated water levels minus measured water levels in A, 1996, B, 2000, 

and C, 2005 for the model for North Penn Area 7 Superfund site, Upper Gwynedd Township and vicinity, Montgomery County, Pennsylvania.—Continued
58 Groundwater System and Simulation of Flow for North Penn Area 7 Superfund Site, Montgomery County, Pennsylvania

of nearby pumping (Senior, 2008, table 78), but the structure 

of the model placed the intermediate and deep well in the 

same model cell. Residuals for 2005 measurements in and 

near the North Penn Area 7 Superfund site range from -10.5 m 

(-34.4 ft) to +11.7 m (+38.4 ft), but except for selected wells in 

the RI-2 and RI-9 clusters, the residuals are smaller within the 

boundary of North Penn Area 7, ranging from -3.9 m (-13.0 ft) 

to 4.1 m (+13.4 ft). Two of the three wells in the RI-2 and RI-9 

clusters are affected by pumping, resulting in large vertical 

gradients not well simulated by the model, and residuals in 

these clusters range from -0.9 to 9.8 m (-3.0 to 32 ft). The 

highly heterogeneous fractured-rock aquifer is simulated only 

approximately by this regional-scale model; however, it is 

judged that the model accuracy is adequate for simulation of 

overall regional patterns in groundwater flow and for simulation of flow paths at the regional scale. 

Estimated Aquifer Hydraulic Properties and 

Recharge Rates

 The hydraulic properties and other features of the 

groundwater-flow system were represented by parameters of 

the calibrated numerical model (table 7) that were determined 

by parameter estimation, a process in which the parameters 

are adjusted until the simulated water levels and groundwater 

discharge to streams reasonably match the measured water 

levels and groundwater discharge to streams. In this way, the 

numerical model mimics features of the real groundwatersystem, as characterized by the measurements, and the model 

parameters are considered estimates of the regional-scale 

hydraulic properties of the groundwater-flow system. As 

described above, model parameters were assigned by layers, 

and further grouped during calibration. Some trial parameters, 

such as vertical anisotropy ratios for individual layers, could 

not be estimated because the parameter value had no effect on 

the model error. Some of these parameters were assumed to be 

equal to other similar parameters, such as the vertical anisotropy of another layer in this example. Even with this reduced 

set, some parameters could not be estimated by the automatic 

algorithm and were manually adjusted, as discussed in previous sections. 

The top two layers of the model are assumed to be 

isotropic in all cases because extensive fracture features 

are less likely to be important in highly weathered rock and 

saprolite and because preliminary model evaluation indicated 

the simulated water levels in underlying layers, where water 

levels have been measured, are not sensitive to the anisotropy 

of model layers 1 and 2. The model parameter describing the 

horizontal anisotropy is designated HANI for layers 3 and 11, 

and HANIBED for layers 4 to 10. Model layers 3 and 11 

represent bulk properties of the various beds to the northwest 

(layer 3) and southeast (layer 11), whereas layers 4 to 10 are 

dipping layers representing individual mapped hydrostratigraphic units. The parameter is the hydraulic conductivity in 

the dip direction (northwest direction in model) divided by 

EXPLANATION

1996

2000

2005

60 70 80 90 100 110 120 130 140

Measured groundwater-level altitude, in meters

60

70

80

90

100

110

120

130

140

Simulated groundwater-level altitude, in meters

Figure 36. Relation of measured groundwater-level altitudes to 

groundwater-level altitudes simulated by the numerical model for 

North Penn Area 7 Superfund site, Upper Gwynedd Township and 

vicinity, Montgomery County, Pennsylvania.

the hydraulic conductivity in the strike direction (northeast 

direction in model) (or HANI = Kdip/Kstrike). In anisotropic 

cases, the hydraulic conductivity parameters listed in table 7 

for model layers 3 to 11 are the hydraulic conductivities in 

the strike direction; therefore, for example, the Brunswick 

Group parameter KB = KBstrike, and the Lockatong Formation parameter KL = KLstrike. The hydraulic conductivity in 

the dip direction is the value in the strike direction multiplied 

by HANI. 

The vertical anisotropy is parameterized in a similar, but 

different, manner in MODFLOW-2000. The vertical anisotropy parameter, designated VANI, is the ratio of the vertical 

hydraulic conductivity to the hydraulic conductivity in the 

strike direction; VANI = Kstrike/Kvertical. Thus, to compute 

the vertical hydraulic conductivity, the hydraulic conductivity 

in the strike direction is divided by the ratio VANI. 

Other model parameters include the vertical hydraulic 

conductivity of streambeds, STR, which controls the conductance between layer 1 of the model and the stream. The 

simplified approach here is to assume that all streams have 

uniform width (3 m) and uniform streambed thickness (2 m) 

and that the hydraulic conductivity of the streambed is also 

uniform. Another model parameter estimated by calibration is 

the uniform recharge rate, designated RECH, which is specified separately for the three different calibration time periods 

(table 7).

The optimum parameter values and approximate individual 95-percent confidence intervals are shown in table 7. 
Simulation of Regional Groundwater Flow 59

Table 7. Optimum and approximate, individual, 95-percent confidence-interval values for parameters estimated through calibration of the groundwater-flow model for North Penn Area 7 Superfund site, Upper Gwynedd Township and vicinity, Montgomery County, Pennsylvania.[m/d, meters per day; mm/yr, millimeters per year; ft/d, feet per day; in./yr, inches per year]

Layers Parameter

Metric units English units

Units Optimum value Approximate, individual, 95-percent confidence interval Units Optimum value Approximate, individual, 95-percent confidence interval

Lower Upper Lower Upper

Hydraulic conductivity

Weathered rock and overburden 1, 2 KW m/d 0.162 0.095 0.275 ft/d 0.531 0.313 0.902Brunswick Group (non-deltaic) 3 KB m/d 1.673 1.492 1.876 ft/d 5.487 4.894 6.153Lockatong Formation (non-deltaic) 11 KL m/d 0.040Red beds predominant 4, 6 KB46 m/d 0.004Gray beds predominant 5 KL5 m/d 0.791 0.436 1.435 ft/d 2.594 1.429 4.707Gray beds predominant 7 KL7 m/d 0.250 0.088 0.706 ft/d 0.820 0.290 2.317Red beds predominant 8 KB8 m/d 1.135 0.753 1.710 ft/d 3.723 2.471 5.610Gray beds predominant 9 KL9 m/d 0.426 0.233 0.777 ft/d 1.397 0.766 2.549Red beds predominant 10 KB10 m/d 0.001Streambed Streamcells 

in 1

STR m/d 30.033 29.811 30.257 ft/d 98.533 97.805 99.268

Horizontal anisotropy

Brunswick & Lockatong 3, 11 HANI (-) 0.319 0.159 0.643Deltaic beds 4–10 HANIBED (-) 0.117 0.088 0.155

Vertical anisotropy

Brunswick & Lockatong 3, 11 VANI (-) 1Deltaic beds 4, 5, 6, 9, 10 VANIBED (-) 1Gray beds predominant 7 VANI7 (-) 48.3Red beds predominant 8 VANI8 (-) 478.5

Recharge

1996 1 RECH1 m/d 4.061E-4 3.80E-4 4.42E-4Dec-00 1 RECH2 m/d 2.990E-4 2.85E-4 3.12E-4Jun-05 1 RECH3 m/d 3.395E-4 3.17E-4 3.64E-41996 1 RECH1 mm/yr 148 in./yr 5.8 5.5 6.4Dec-00 1 RECH2 mm/yr 109 in./yr 4.3 4.1 4.5Jun-05 1 RECH3 mm/yr 124 in./yr 4.9 4.6 5.2
60 Groundwater System and Simulation of Flow for North Penn Area 7 Superfund Site, Montgomery County, Pennsylvania

All but the top two model layers representing weathered rock/

saprolite are anisotropic with respect to subhorizontal hydraulic conductivity. The optimum value for hydraulic conductivity 

listed in table 7 for model layers 3–10, representing dipping 

bedrock units, is subhorizontal and in the strike direction. In 

the set of optimum parameters, the ratio of minimum (dip 

direction) to maximum (strike direction) subhorizontal hydraulic conductivity ranges from 1/3.1 to 1/8.6 (horizontal anisotropy of 0.319 to 0.117). The ratio of vertical to horizontal 

hydraulic conductivity ranges from 1/1 (manually set during 

calibration for some model layers) to the optimized value of 

1/478 (table 7).

The optimum parameter values yield the minimum 

model error for the model structure, boundary conditions, and 

observations used. The approximate confidence intervals are 

estimated from a linear statistical model with the calibrated 

model and assumed error variances of the observations (Hill 

and Tiedeman, 2007). Confidence intervals are shown only 

for parameters that are included in the final calibration. Model 

adjustments focused on parameters that, when changed, 

caused the greatest proportional change in simulated water 

levels and flow, which are indicated by their composite scaled 

sensitivities (fig. 37). The composite scaled sensitivity is the 

rate of change in the parameter-estimation optimization objective function for incremental changes in the parameter value, 

normalized by the optimum parameter value. Thus, the overall 

model error changes the most for (proportional) changes in 

parameters with the highest composite scaled sensitivities 

(Hill and others, 2000; Hill and Tiedeman, 2007). Changes 

to the values of parameters that have low composite scaled 

sensitivity will cause small changes in the model error. Compared to other parameters, the vertical hydraulic conductivity 

model parameters are less constrained by the measured water 

levels, which are relatively well distributed in horizontal space 

but less well distributed in vertical space and thus, provide 

less information about vertical head gradients to constrain 

the model than they do about horizontal gradients. Values for 

which confidence intervals are not shown in table 7 are to be 

considered more uncertain. During calibration, the optimization process tended to yield values for vertical anisotropy 

(VANI) that were less than 1 for some beds; however, values 

of VANI less than 1 are not consistent with the low hydraulic 

connections across beds observed during local-scale packer 

tests. The model, as structured, was not sensitive to changes 

in values for the parameter VANI, and therefore, the estimated 

value of 1 was set for the parameter VANI for beds 3 to 6 and 

9 to 11 (table 7) to minimize model error and maintain some 

consistency with observed hydraulic properties of the aquifer.

Estimated hydraulic conductivity is comparable to previous estimates made using aquifer-test results and regional 

flow models. Senior and Goode (1999) estimated hydraulic 

conductivities of the weathered zone (0.05 m/d or 0.16 ft/d), 

Lockatong Formation (0.34 m/d or 1.1 ft/d in strike), and the 

Brunswick Group (1.6 m/d or 5.2 ft/d in strike) by calibration of a steady-state regional-scale model that included the 

current model area west of Wissahickon Creek using water 

Automatic calibration

Manual calibration

Type of parameter calibration 

EXPLANATION

10 3

10 2

101

10 0

10-1

10-2

Composite scaled sensitivity

STR

RECH2RECH1

KB8

KB

RECH3

VANI8

KL5KL9

KW

KL7

HANI

HANIBED

KL

VANI

VANI7

VANIBED

KB46KB10

Model parameter

Figure 37. Sensitivity of model calibration to model parameters 

for groundwater-flow simulation of North Penn Area 7 Superfund 

site and vicinity, Upper Gwynedd Township and vicinity, 

Montgomery County, Pennsylvania. (Model parameters are 

described in table 7.)

levels during 1996. The optimum hydraulic conductivity for 

the weathered zone (KW) is 0.16 m/d (0.53 ft/d), about 3 

times higher than the results from Senior and Goode (1999). 

The optimum hydraulic conductivities for the (non-deltaic) 

Lockatong Formation (KL) and Brunswick Group (KB) for 

the present study are 0.040 and 1.67 m/d (0.13 and 5.5 ft/d) in 

strike, respectively. For the present study, the area for which 

the bulk Lockatong Formation hydraulic conductivity (KL) 

was estimated is to the south and east of the area considered 

by Senior and Goode (1999) and is an area for which few 

water-level measurements are available. The predominantly 

gray beds farthest north in the present model have an optimum 

hydraulic conductivity (KL5) of 0.79 m/d (2.6 ft/d) in strike, 

which is slightly larger than the Lockatong Formation value 

estimated by Senior and Goode (1999) for rocks in the same 

geographic location. Hydraulic conductivities estimated using 

the numerical groundwater-flow model are within the range 

of those estimated from results of the packer tests for isolated 

aquifer intervals at North Penn Area 7 (Senior and others, 

2008). Estimates of bulk hydraulic conductivties from packer 

tests calculated by dividing the total transmissivity of waterbearing zones by the total open interval of the geologic unit 

intersected by a borehole ranged from about 0.03 to 8.0 m/d 

(0.1 to 26.4 ft/d). Mean and median values of hydraulic conductivity for discrete aquifer intervals determined in packer 

tests of individual isolated zones in geologic units ranged 

from 1.7 to 5.6 m/d (5.7 to 18.4 ft/d) and 0.9 to 1.6 m/d (3.0 to 

5.1 ft/d), respectively (fig. 13B). However, hydraulic conductivities estimated from local-scale packer tests do not appear 

to differ as much by geologic unit as those regional values 

estimated from the numerical groundwater-flow model. 

Recharge rates estimated for the three simulation periods 

range from 109 to 148 mm/yr (4.3 to 5.9 in/yr) in 2000 and 

1996, respectively (table 7). The higher recharge values correspond to general features of the water levels in the study area: 
Simulation of Regional Groundwater Flow 61

compared to the long-term average, water levels were similar 

or slightly higher in 1996 and slightly lower in December 

2000 and June 2005 (fig. 19). The assumption of steady-state 

flow also has some effect on the estimated recharge values 

(Halford, 1999). The natural flow system is not at steady state 

for any of the time periods because of variations in time of 

recharge, pumping rates, and evapotranspiration. Halford 

(1999) found that the long-term average recharge rate was 

bracketed by “effective” recharge rates determined from the 

calibration of steady-state flow models using synoptic water 

levels and streamflow. In the present case, the variability of 

the effective recharge rate is enhanced by the low storage 

of the fractured-rock aquifer system. The range of recharge 

rates estimated in this study is similar to but about 25 percent 

smaller than the value of 208 mm/yr (8.2 in/yr) estimated from 

a different steady-state regional-flow model calibration for 

1996 conditions (Senior and Goode, 1999) for a model area 

that included a portion of current model area west of Wissahickon Creek (see North Penn Area 6 model boundary, fig. 3). 

The lower value identified here may reflect that the geology 

underlying the current model is less dominated by the Brunswick Group and more affected by properties of the Lockatong 

Formation. The Lockatong Formation generally has lower permeability and, hence, may have less recharge. A single value 

of recharge is assumed to be representative of the entire model 

area for this study. Recharge rates may be estimated from, and 

compared to, stream base flow. White and Sloto (1990) used 

1959 to 1972 streamflow records for two streams overlying 

Triassic sedimentary rocks in southeastern Pennsylvania and 

estimated average annual base flows of 148 and 201 mm/yr 

(5.8 and 7.9 in/yr). 

The water budgets are different for each calibration 

period of the North Penn Area 7 model (table 8). Withdrawals 

from and recharge to the entire modeled area vary similarly, 

with highest rates in 1996 and lowest rates in 2000. Local 

withdrawals in the immediate vicinity of North Penn Area 7 

(area shown by dashed boundary in figure 30) change in a 

similar manner.

Regional Groundwater-Flow Paths

The groundwater-flow model can be used to evaluate 

groundwater-flow paths under different hydrologic conditions 

and recharge/discharge relations. Groundwater-flow paths 

were simulated under conditions representative of different periods when industries using water or those identified 

as probable contaminant source areas were and (or) still are 

active in the vicinity of North Penn Area 7. The changes in 

hydrologic conditions considered in this report are (1) changes 

in pumping rates at wells and (2) changes in recharge rates, 

during calibration periods. For hydrologic conditions in 

1990, the average of the recharge values determined for the 

three calibration periods (1996, 2000, and 2005), 128 mm/yr 

(5.0 in./yr), is used. 

Table 8. Simulated water budgets for calibration periods 1996, 

2000, and 2005 for model area and North Penn Area 7 Superfund 

site, Upper Gwynedd Township and vicinity, Montgomery 

County, Pennsylvania. Area for water-budget calculation 

delineated by North Penn Area 7 boundary as shown in 

figure 30.

[m3/d, cubic meters per day]

Units Simulation period

1996 2000 2005

Entire model

Inflows

Recharge m3

/d 41,642 30,256 34,508

Stream loss m3

/d 2,361 2,904 2,863

Outflows

Withdrawal by pumping wells m3

/d 11,743 9,207 9,991

Stream gain m3

/d 32,259 23,953 27,380

North Penn Area 7 (immediate vicinity)

Inflows

Recharge m3

/d 1,178 856 976

Stream loss m3

/d 26 44 101

Ground-water inflow m3

/d 1,432 1,297 1,901

Outflows

Withdrawal by pumping wells m3

/d 693 468 658

Stream gain m3

/d 107 0 31

Ground-water outflow m3

/d 1,836 1,729 2,289

The model was used to evaluate groundwater-flow 

paths and areas contributing recharge to wells under several 

steady-state scenarios corresponding to historic and current 

hydrologic conditions of recharge and withdrawals in 1990, 

1996, 2000, and 2005. Results from historic groundwaterflow path simulations were compared to selected measured 

constituent concentrations in water samples from monitor and 

pumped wells that may be used to infer possible contaminant 

migration pathways.

Simulated Flow Paths, Contributing Areas, and 

Uncertainty

Model simulations were conducted under steady-state 

conditions to estimate groundwater-flow paths and contributing areas. Steady-state simulations give results that represent 

the average position of groundwater-flow paths and contributing areas on the basis of the values of average groundwater 

recharge and withdrawals assigned to the model. Changes 

caused by seasonal variations in recharge or operational variability of withdrawals were not simulated.
62 Groundwater System and Simulation of Flow for North Penn Area 7 Superfund Site, Montgomery County, Pennsylvania

A probabilistic method is used to approximate uncertainty in simulated regional groundwater-flow paths because 

of model hydraulic-parameter uncertainty (Starn and others, 

2010). Deterministic groundwater-flow paths are simulated 

using the optimal calibrated values for all model parameters. 

However, these parameters are not exactly known. The amount 

of uncertainty in parameter values is estimated during the 

automatic calibration procedure, and these results can be carried through the groundwater-flow path simulation to produce 

probabilistic groundwater-flow paths. A Monte Carlo procedure developed by Starn and others (2010) is used in which 

1,000 realizations of different parameter sets are produced, 

based on the probabilistic model of the parameters and their 

uncertainty. This method incorporates the individual parameter 

uncertainty and the correlation between estimated parameters. 

This method was recently applied by Lindsey (2005) to a 

carbonate fractured-rock aquifer in Pennsylvania. 

Although recharge values for 1996, 2000, and 2005, and 

their respective estimation variances, were estimated, these 

parameters are considered exactly known for the analysis 

here. Thus, this analysis illustrates the uncertainty that is due 

to selected hydraulic properties alone. A variance/covariance 

matrix for this uncertainty analysis is generated by the sensitivity calculations with all model parameters at their respective 

optimal values and with the recharge values considered known 

and removed from the sensitivity calculation. The resulting 

variance/covariance of the selected hydraulic parameters alone 

(table 9) is used to generate realizations of model parameters 

that sample the assumed lognormal parameter distribution 

and that preserve the estimated covariances between parameters. Many assumptions underlie the probabilistic theory for 

this method (Neupauer and Wilson, 2004; Starn and others, 

2010), and this model may not meet all those assumptions. 

For example, only 1,000 realizations were simulated for 

each case, and more realizations may be necessary to accurately represent low-frequency features. Nonetheless, this 

systematic approach does allow illustration of the effect that 

uncertainty in the model-selected hydraulic parameters has 

on model predictions, in this case regional groundwater-flow 

paths (Starn and others, 2010). 

Groundwater-flow paths are presented on areal maps 

showing both deterministic and probabilistic results. The 

deterministic results are obtained by simulating groundwaterflow paths using the optimal parameter values identified 

during calibration. Deterministic groundwater-flow paths 

from probable contaminant sources in North Penn Area 7 

are shown as gray dashed lines (for example, see figure 38 

farther on in this report). Contributing areas for the pumped 

production well MG-202 (L-22) (fig. 4) are shown as black 

dots indicating model cells from which recharge flows to the 

pumped well (for example, see figure 39 farther on in this 

report).

For probabilistic results, model cell color indicates 

frequency, which is expressed as a fraction ranging from 0 to 

1.0. For contributing areas of water for pumped well MG-202 

(L-22), the colors correspond to the frequency of simulations 

for which recharge from the indicated model cell at the top of 

the saturated zone flowed to the pumped well. For example, 

if 800 of the 1,000 simulations resulted in flow to the pumped 

well from a particular cell, then that cell would be the color 

corresponding to a frequency of 0.8. For the groundwaterflow-path simulations, the color map indicates the frequency 

at which particles from source locations flowed through 

the area covered by the model cell. This result is vertically 

integrated in that groundwater-flow paths through the cell 

area are counted regardless of which vertical model layer the 

Table 9. Correlation and variance/covariance matrices for generation of probabilistic parameters.

[Correlations are in shaded part of table. Both matrices are symmetric, so the upper or lower diagonal of either matrix is the transpose of the part of the 

matrix shown. Correlations of parameters with themselves are equal to 1.0 and are not shown. The logarithm of the parameter value is used in the regression 

for all parameters. These covariances and correlations are for the parameters in the regression space]

Parameter HANIBED KB KW STR KB46 KL5 HANI KB8 KL7 KL9

HANIBED 1.75E-2 6.76E-4 6.43E-3 -9.69E-5 -1.27E-2 -1.14E-2 1.16E-2 -3.57E-3 1.93E-3 -5.89E-3

KB 0.14 1.25E-3 -4.80E-3 -4.52E-5 3.62E-3 -2.09E-3 4.02E-3 -2.04E-3 3.67E-3 -8.39E-4

KW 0.19 -0.54 6.32E-2 2.60E-4 -4.88E-2 -2.68E-3 -1.22E-2 1.37E-2 -3.82E-2 -4.99E-3

STR -0.27 -0.48 0.39 7.19E-6 -4.26E-4 3.78E-4 -5.64E-4 3.57E-4 -3.16E-4 2.87E-4

KB46 -0.12 0.13 -0.24 -0.20 6.38E-1 -1.09E-1 7.11E-2 7.40E-3 -1.08E-1 -5.31E-2

KL5 -0.33 -0.22 -0.04 0.54 -0.52 6.93E-2 -4.18E-2 6.20E-3 -1.31E-2 2.83E-2

HANI 0.33 0.43 -0.18 -0.80 0.34 -0.60 7.00E-2 -2.35E-2 7.67E-3 -2.86E-2

KB8 -0.16 -0.34 0.32 0.78 0.05 0.14 -0.52 2.90E-2 -5.09E-2 1.06E-2

KL7 0.03 0.20 -0.30 -0.23 -0.26 -0.10 0.06 -0.59 2.60E-1 1.05E-2

KL9 -0.30 -0.16 -0.13 0.73 -0.45 0.73 -0.73 0.42 0.14 2.17E-2
Simulation of Regional Groundwater Flow 63

groundwater-flow path occurs in. For example, if 400 of the 

1,000 simulations resulted in at least one groundwater-flow 

path from any of the sources passing through any layer at a 

model cell location, then that color of the cell corresponds to a 

frequency of 0.4. 

In general, the probabilistic groundwater-flow-path 

results resemble a diffuse cloud around the deterministic 

groundwater-flow paths. Simulations of contributing area to 

a pumped well have high frequencies in the middle of the 

deterministic contributing area and close to the pumped well. 

Frequencies are lower at greater distances from the pumped 

well and at the edges of the contributing area. Similar features 

occur for groundwater-flow-path results where frequencies are 

high near source locations; however, the features may occur 

far from the source location near large pumped wells as a 

result of the convergence of groundwater-flow paths near the 

large well or well field.

In the following sections, deterministic groundwaterflow paths and contributing areas simulated using optimal 

model parameters are discussed for each period. Uncertainty 

associated with flow paths estimated using the Monte Carlo 

method is shown in figures with results of the deterministic 

simulations for each time period but is not discussed at length. 

In general, probabilistic groundwater-flow paths simulated 

using uncertain model parameters (Monte Carlo method) pass 

through similar, but expanded, areas around deterministic flow 

paths simulated using optimal model parameters.

Groundwater-Flow Paths in 1990

Groundwater withdrawals in the study area were relatively high in 1990, and more wells in the vicinity of North 

Penn Area 7 were pumped for industrial and public supply 

than in subsequent periods. Using optimal model parameters, 

simulated deterministic groundwater-flow paths from contaminant sources in North Penn Area 7 ultimately reach local wells 

at the industrial facilities, with the exception of groundwaterflow paths from the source at Leeds & Northrup and some of 

the groundwater-flow paths from the source at Spra-Fin, which 

discharge to wells such as well MG-130 at the Merck facility 

immediately southwest of North Penn Area 7 (fig. 38). Probabilistic simulations also show most groundwater-flow paths 

extend from contaminant sources towards local pumped wells 

in the vicinity of North Penn Area 7. Simulated deterministic 

groundwater-flow paths from sources at the Zenith, Teleflex, 

and Ford facilities discharge to pumped wells at Ford. The 

frequencies of probabilistic groundwater-flow paths extending 

from contaminant sources to areas at and near Ford are higher 

than 0.75. Simulated groundwater-flow paths from the source 

at Spra-Fin travel beneath the upper Wissahickon Creek and 

discharge to industrial wells at other properties in the vicinity 

of North Penn Area 7, including pumped wells at Ford and 

well MG-130 at Merck. Groundwater flow from the source 

at the Rogers facility (a named contaminant source in NPL 

site North Penn Area 6) is generally southwest, away from 

North Penn Area 7, towards pumped production wells MG-59, 

MG-566, and MG-140. Some probabilistic simulations result 

in groundwater-flow paths extending east from the Rogers 

facility to nearby pumped wells MG-66 and MG-71, although 

the frequencies are less than 0.25. 

The production well MG-202 (L-22) does not capture any 

groundwater-flow paths from identified contaminant sources at 

North Penn Area 7 in the deterministic simulation using optimal model parameters (fig. 38). For the probabilistic simulations, the frequency of groundwater-flow paths extending from 

contaminant sources to areas near well MG-202 ranges from 

0.05 to 0.25. 

Modeled contaminant source locations do not appear 

likely to be in the contributing area of recharge flowing to 

well MG-202 under conditions in 1990 (fig. 39). The frequency of probabilistic simulations for which recharge from 

modeled contaminant source cells flows to MG-202 is less 

than 0.05. The deterministic simulated contributing area for 

water pumped from MG-202 is east of the pumped well. For 

probabilistic simulations, the frequency of recharge flowpaths 

discharging to well MG-202 (L-22) decreases with distance 

away from the well to the east. Under simulated steadystate conditions, some water flowing to the well is recharged 

beyond the contributing area for nearby well MG-76 (L-17). 

The contributing area for well MG-76 (L-17) is surrounded by 

areas that contribute flow to MG-202 (L-22). 

The complex shape of the contributing area to MG-202 

(L-22) is caused by the juxtaposition of contributing areas 

of other nearby wells and the complex groundwater/surfacewater interaction in the headwaters of the Wissahickon Creek. 

In addition to capturing groundwater recharge through the 

aquifer, well MG-202 (L-22) also captures flow from the Wissahickon Creek. This flow originates as recharge to groundwater near the stream, discharges to the stream, and then returns 

to the aquifer near well MG-202 (L-22). Thus, both groundwater and surface water contribute flow to this well. Contaminant 

sources in areas that discharge to Wissahickon Creek could 

be sources of contamination to well MG-202 (L-22), provided that the discharge to the stream occurs upstream from 

the area where the stream loses water to the aquifer near well 

MG-202 (L-22). 

Although the deterministic groundwater-flow paths 

indicate that a thin ring of surface area contributes recharge to 

the well, the probabilistic plume indicates that a much larger 

area could potentially contribute recharge to the well, but the 

frequency for any particular spot as a contaminant source is 

relatively low. In general, these probabilistic results do not 

incorporate all uncertainty in the predictive methods used for 

groundwater-flow simulations, but only the uncertainty associated with specific parameter values for the specific regionalscale model developed for North Penn Area 7 and described in 

this report.
64 Groundwater System and Simulation of Flow for North Penn Area 7 Superfund Site, Montgomery County, Pennsylvania 78 76 59 77 73 69 55 71 66 52 68 566 128 140 125 130 171 223 151 143 593 203 1702 1423 1198 1841 991 126 167 1199 1424 1050 1052 1701 1336 202 124 75°16' 75°17' 75°18' 75°19' 75°20' 40°14' 40°13' 40°12' JTrb, B6 JTRb, B4 JTrblg, L5 JTrblg, L7 JTrb, B8 Trl, L9 Trlr, B10 JTrb, B Trl, L Zenith Ford2 Ford1Rogers Teleflex SpraFin LeedsNorthrup 204

Wissahickon Creek

Towamencin Creek

Base from U.S. Geological SurveyNational Hydrography Dataset, 1999Universal Transverse Mercator, zone 18North American Datum of 1927

EXPLANATION

Contaminant sourceStream

>1,000>300–1,000>100–300>30–1000–30

RoadGeologic contactGeologic formation and

layer identifier

0.05–0.25>0.25–0.5>0.5–0.75>0.75–1.0

Well, by pumping rate in 1990,

in cubic meters per day 

202

Fraction of Monte Carlo simulations

for which pathlines from sourcespass through model cell

U.S. Geological Survey well 

identifier (MG- prefix omitted)

Pathline from source

(optimal-parameter simulation)

Trlr, B10

0

0 0.5 1 KILOMETER

0.5 1 MILE

Figure 38. Simulated groundwater-flow paths extending from contaminant source areas to pumped wells for pumping conditions in 1990 for North Penn Area 7 Superfund site, Upper Gwynedd Township and vicinity, Montgomery County, Pennsylvania. (>, greater than)
Simulation of Regional Groundwater Flow 65

75°15' 75°16' 75°17' 75°18'

40°15'

40°14' 40°13'

JTrb, B6

JTRb, B4

JTrblg, L5

JTrblg, L7

JTrb, B8

Trl, L9

Trlr, B10

JTrb, B

Trl, L

Zenith

Ford2

Rogers

Ford1

Teleflex

SpraFin

LeedsNorthrup

Wissahickon Creek

78

73

75

71

66

69

67

68

153

1125

1905

1938

498

143

593

76

59

55

991

124

126

566 140

128

125

130

171

204

223

167

151

203

1702 1424

1423

1198

1701

1841

1336

77

Base from U.S. Geological SurveyNational Hydrography Dataset, 1999Universal Transverse Mercator, zone 18North American Datum of 1927

Model cell that recharges

well 202 (optimal-parameter simulation)

EXPLANATION

Contaminant sourceStream

>1,000>300–1,000>100–300>30–1000–30

RoadGeologic contactGeologic formation and

layer identifier

0.05–0.25>0.25–0.5>0.5–0.75>0.75–1.0

Well, by pumping rate in 1990,

in cubic meters per day 

202

Fraction of Monte Carlo simulations

for which model cell rechargeswell 202

U.S. Geological Survey well 

identifier (MG- prefix omitted)

Trlr, B10

0

0 0.5 1 KILOMETER

0.5 1 MILE

52

202

Figure 39. Simulated area contributing recharge to well MG-202 (L-22) for pumping conditions in 1990 for North Penn Area 7 Superfund site, Upper Gwynedd Township and vicinity, Montgomery County, Pennsylvania. (>, greater than)
66 Groundwater System and Simulation of Flow for North Penn Area 7 Superfund Site, Montgomery County, Pennsylvania

Groundwater-Flow Paths in 1996

Groundwater pumping rates in the vicinity of North Penn 

Area 7 in 1996 (a model calibration period) were lower than 

in 1990 (table 5), and fewer wells were operating. Simulated 

deterministic groundwater-flow paths (fig. 40) are generally 

longer in 1996 than in 1990, with nearly all groundwater-flow 

paths leaving the immediate area of the contaminant sources 

and discharging to pumped wells southwest and west of North 

Penn Area 7. Industrial wells at Ford that captured simulated 

groundwater-flow paths from contaminant sources in the 

1990 simulation were no longer pumping in 1996. Simulated 

deterministic and probabilistic groundwater-flow paths extend 

from the contaminant source at the Zenith facility to Merck 

facility wells (including wells MG-1198 and MG-1199) to 

the southwest and to well MG-140 to the west of North Penn 

Area 7 (fig. 40). For probabilistic simulations, the frequencies 

of flow paths extending from all North Penn Area 7 contaminant-source areas to pass near or arrive at Merck wells are 

greater than 0.75. The deterministic groundwater-flow paths 

from the Rogers facility source are similar to those in 1990. 

The shutdown of the two pumped wells northeast of Rogers (MG-66 and MG-71) results in very low frequency of the 

probabilistic groundwater-flow paths passing through the area 

east of Rogers (fig. 40). 

Production well MG-202 (L-22) does not capture any 

deterministic groundwater-flow paths from identified contaminant sources in North Penn Area 7 in the 1996 simulation 

(fig. 40). The frequency of probabilistic simulations that indicate groundwater-flow paths extend from contaminant sources 

to areas near well MG-202 (L-22) is less than 0.05. 

In the simulation of contributing area, modeled source 

locations do not appear to contribute recharge to well MG-202 

(L-22) under conditions in 1996 (fig. 41). The frequency of 

probabilistic simulations for which recharge from identified 

contaminant sources in North Penn Area 7 flows to MG-202 

(L-22) is less than 0.05. The deterministic contributing area 

simulated using optimal model parameters for withdrawals 

from well MG-202 (L-22) is located east of the well; a thin 

and discontinuous contributing area extends to the northeast. The probabilistic contributing area also extends to the 

northeast, but the frequencies are low, less than 0.25 at any 

particular location. As in the 1990 simulation, the probabilistic 

contributing area to MG-202 has a complex shape caused by 

nearby pumped wells and surface-water/groundwater interaction in the headwaters of the Wissahickon Creek. Under 

simulated steady-state conditions, some water flowing to 

well MG-202 (L-22) is recharged beyond the contributing 

areas for nearby wells in the Wissahickon well field [MG-76 

(L-17), MG-77 (L-18), MG-73 (L-14), MG-78 (L-19), and 

MG-75 (L-16)]. The contributing areas for other wells in the 

well field are surrounded by areas that contribute flow to well 

MG-202 (L-22). 

Groundwater-Flow Paths in 2000

Groundwater pumping rates in the study area were relatively low (table 5), and fewer wells were pumping in 2000 

(a calibration period) than in the other time periods. Simulated 

deterministic and probabilistic groundwater-flow paths from 

contaminant sources in North Penn Area 7 (fig. 42) are similar 

to, but slightly different than, those in 1996. For 2000, simulated groundwater-flow paths from all contaminant sources 

converge towards nearby pumped wells west and southwest 

of North Penn Area 7. More of the deterministic groundwaterflow paths from the source at the Zenith facility discharge to 

the area that contributes to Merck wells (MG-128, MG-1198, 

and MG-1199) and fewer discharge to the areas contributing to production well MG-140 in the 2000 simulation (fig. 

42) than in the 1996 simulation (fig. 40). The frequencies for 

probabilistic flow paths from all North Penn Area 7 contaminant sources to pass near or arrive at Merck wells are higher 

than 0.75. 

As in the 1990 and 1996 simulations, production well 

MG-202 (L-22) does not capture any deterministic groundwater-flow paths from identified contaminant sources in North 

Penn Area 7 (fig. 42). The frequency of probabilistic simulations that indicates groundwater-flow paths extend from North 

Penn Area 7 contaminant sources to areas near well MG-202 

is less than 0.05. 

In the simulation of contributing area, modeled contaminant source locations do not appear likely to contribute 

recharge to well MG-202 (L-22) under conditions in 2000 

(fig. 43). The frequency of probabilistic simulations for which 

recharge from identified contamination sources in North Penn 

Area 7 flows to MG-202 (L-22) is less than 0.05. The deterministic contributing area for water pumped from MG-202 

(L-22) is east of the well; a thin and discontinuous contributing area extends to the northeast. The probabilistic contributing area also extends to the northeast, but the frequencies are 

low, less than 0.25 at any particular location. As in the 1990 

and 1996 simulations, the contributing area to MG-202 (L-22) 

has a complex shape caused by nearby pumped wells and 

groundwater/surface-water interaction in the headwaters of 

the Wissahickon Creek. Under simulated steady-state conditions, some water flowing to well MG-202 (L-22) is recharged 

beyond the contributing areas for nearby wells in the Wissahickon well field. [MG-76 (L-17), MG-77 (L-18), MG-73 

(l-14), and MG-78 (L-19) were pumping, but MG-75 (L-16) 

was not pumping in December 2000.] The contributing areas 

for other wells in the well field are surrounded by areas that 

contribute flow to well MG-202 (L-22). 
Simulation of Regional Groundwater Flow 67

75°17' 75°18' 75°19' 75°20'

40°14'

40°13' 40°12'

JTrb, B6

JTRb, B4 JTrblg, L5

JTrblg, L7

JTrb, B8

Trl, L9 Trlr, B10

JTrb, B

Trl, L

Zenith

Ford2

Ford1

Rogers

Teleflex

SpraFin

LeedsNorthrup

Towamencin Creek

W si sah ci kon Creek

76

59

77

68

991

202

124

126

566

128

140

130

171 204

167

151

203

1702 1199 1424

1050

1052

1423

1198

1701

1336

125

55

52

223

1841

1028

69

71

66

143

919

Base from U.S. Geological SurveyNational Hydrography Dataset, 1999Universal Transverse Mercator, zone 18North American Datum of 1927

EXPLANATION

Contaminant sourceStream

>1,000>300–1,000>100–300>30–1000–30

RoadGeologic contactGeologic formation and

layer identifier

0.05–0.25>0.25–0.5>0.5–0.75>0.75–1.0

Well, by pumping rate in 1996,

in cubic meters per day 

202

Fraction of Monte Carlo simulations

for which pathlines from sourcespass through model cell

U.S. Geological Survey well 

identifier (MG- prefix omitted)

Pathline from source

(optimal-parameter simulation)

Trlr, B10

0

0 0.5 1 KILOMETER

0.5 1 MILE

Figure 40. Simulated groundwater-flow paths extending from contaminant source areas to pumped wells for pumping conditions in 1996 for North Penn Area 7 Superfund site, Upper Gwynedd Township and vicinity, Montgomery County, Pennsylvania. (>, greater than)
68 Groundwater System and Simulation of Flow for North Penn Area 7 Superfund Site, Montgomery County, Pennsylvania 75°15' 75°14' 75°16' 75°17' 75°18' 40°15' 40°14' 40°13' JTrb, B6 JTRb, B4 JTrblg, L5 JTrblg, L7 JTrb, B8 Trl, L9 Trlr, B10 JTrb, B Trl, L Rogers 223 6968 625 498 875 134 153 620 621 1125 1905 1938 1418 1045 202 78 76 59 77 73 75 202 140 171 151 1841 52 Zenith Ford2 Ford1 Teleflex SpraFin LeedsNorthrup 71 66 223 167 203 1702 55 52 124126 128 125 130 1424 1701 67 204

i W s as h ci kon Creek

Base from U.S. Geological SurveyNational Hydrography Dataset, 1999Universal Transverse Mercator, zone 18North American Datum of 1927

Model cell that recharges

well 202 (optimal-parameter simulation)

EXPLANATION

Contaminant sourceStream

>1,000>300–1,000>100–300>30–1000–30

RoadGeologic contactGeologic formation and

layer identifier

0.05–0.25>0.25–0.5>0.5–0.75>0.75–1.0

Well, by pumping rate in 1996,

in cubic meters per day 

202

Fraction of Monte Carlo simulations

for which model cell rechargeswell 202

U.S. Geological Survey well 

identifier (MG- prefix omitted)

Trlr, B10

0

0 0.5 1 KILOMETER

0.5 1 MILE

Figure 41. Simulated area contributing recharge to well MG-202 (L-22) for pumping conditions in 1996 for North Penn Area 7 Superfund site, Upper Gwynedd Township and vicinity, Montgomery County, Pennsylvania. (>, greater than)
Simulation of Regional Groundwater Flow 69

75°17' 75°18' 75°19' 75°20'

40°14'

40°13' 40°12'

Towamencin Creek

W si sah ci kon Creek

Base from U.S. Geological SurveyNational Hydrography Dataset, 1999Universal Transverse Mercator, zone 18North American Datum of 1927

Zenith

Ford1

Rogers

SpraFin

LeedsNorthrup

76

59

77

69

55

71

66

52

68

566

128

140

171 204

223

167

151

143

593

1050

1423

1198

1841

Trlr, B10

JTrb, B

Trl, L

Ford2

Teleflex 202

124

126

130

203

1702

1028

1052

1336

JTrb, B6

JTRb, B4 JTrblg, L5

JTrblg, L7

JTrb, B8

Trl, L9

991

125 1199

1424

1701

EXPLANATION

Contaminant sourceStream

>1,000>300–1,000>100–300>30–1000–30

RoadGeologic contactGeologic formation and

layer identifier

0.05–0.25>0.25–0.5>0.5–0.75>0.75–1.0

Well, by pumping rate in 2000,

in cubic meters per day 

202

Fraction of Monte Carlo simulations

for which pathlines from sourcespass through model cell

U.S. Geological Survey well 

identifier (MG- prefix omitted)

Pathline from source

(optimal-parameter simulation)

Trlr, B10

0

0 0.5 1 KILOMETER

0.5 1 MILE

Figure 42. Simulated groundwater-flow paths extending from contaminant source areas to pumped wells for pumping conditions in 2000 for North Penn Area 7 Superfund site, Upper Gwynedd Township and vicinity, Montgomery County, Pennsylvania. (>, greater than)
70 Groundwater System and Simulation of Flow for North Penn Area 7 Superfund Site, Montgomery County, Pennsylvania 75°15' 75°14' 75°16' 75°17' 75°18' 40°15' 40°14' 40°13'

i W s as h ci kon Creek

78

76

77

73

75

69

55

67

71

66

52

68

625

498

875

134

167

593

153

620

621

1125 1905

1938

1841

1418

1045

JTrb, B8

Trl, L9 Trl, L Trlr, B10

Ford2

Rogers

Ford1

Teleflex

SpraFin

LeedsNorthrup

59

202

124

566

128

140

125

130

171

204

223

151

203

1702

1424

1423

1701

JTrb, B6

JTRb, B4

JTrblg, L5

JTrblg, L7

JTrb, B

Zenith

126

Base from U.S. Geological SurveyNational Hydrography Dataset, 1999Universal Transverse Mercator, zone 18North American Datum of 1927

Model cell that recharges

well 202 (optimal-parameter simulation)

EXPLANATION

Contaminant sourceStream

>1,000>300–1,000>100–300>30–1000–30

RoadGeologic contactGeologic formation and

layer identifier

0.05–0.25>0.25–0.5>0.5–0.75>0.75–1.0

Well, by pumping rate in 2000,

in cubic meters per day 

202

Fraction of Monte Carlo simulations

for which model cell rechargeswell 202

U.S. Geological Survey well 

identifier (MG- prefix omitted)

Trlr, B10

0

0 0.5 1 KILOMETER

0.5 1 MILE

Figure 43. Simulated area contributing recharge to well MG-202 (L-22) for pumping conditions in 2000 for North Penn Area 7 Superfund site, Upper Gwynedd Township and vicinity, Montgomery County, Pennsylvania. (>, greater than)
Simulation of Regional Groundwater Flow 71

Groundwater-Flow Paths in 2005

Pumping rates in the vicinity of North Penn Area 7, and 

in the model domain as a whole, were somewhat higher in 

2005 (a calibration period) than in 2000, although 2005 rates 

were lower than 1990 and 1996 rates. Simulated deterministic 

and probabilistic groundwater-flow paths from contaminant 

sources in North Penn Area 7 discharge to the contributing 

area of Merck wells (including MG-125, MG-128, MG-991, 

MG-1198, MG-1199, and MG-1423), except for the source 

area at the Rogers facility (North Penn Area 6), which discharges to the area contributing to pumped production wells 

MG-59, MG-140, and MG-566 (fig. 44). Simulated deterministic and probabilistic groundwater-flow paths from Leeds 

& Northrup and Spra-Fin sources do not flow beneath Wissahickon Creek but flow more directly to the southwest and 

discharge to wells at Merck. The frequencies for probabilistic 

flow paths from all North Penn Area 7 source areas to pass 

near or arrive at Merck wells are higher than 0.75. 

As in the 1990, 1996, and 2000 simulations, production well MG-202 (L-22) does not capture any deterministic 

groundwater-flow paths from identified sources in North 

Penn Area 7 (fig. 44). The frequency for probabilistic flow 

paths that extend from contaminant sources to areas near well 

MG-202 (L-22) is less than 0.05. 

In the simulation of contributing area, modeled source 

locations do not appear likely to contribute recharge to well 

MG-202 (L-22) under conditions in 2005 (fig. 45), as was the 

case for 1990, 1996, and 2000 simulations. The frequency of 

probabilistic simulations for which recharge from identified 

contaminant sources in North Penn Area 7 flows to MG-202 

(L-22) is less than 0.05. The deterministic contributing area 

simulated using optimal model parameters for withdrawals 

from MG-202 (L-22) is east of the pumped well; a thin and 

discontinuous contributing area extends to the northeast. The 

probabilistic contributing area also extends to the far northeast, but the frequencies are low, less than 0.25 at any particular location. As in the 1990, 1996, and 2000 simulations, 

the probabilistic contributing area to MG-202 (L-22) has a 

complex shape caused by nearby pumped wells and surfacewater/groundwater interaction in the headwaters of the Wissahickon Creek. The probabilistic contributing area is larger 

than in previous simulations, apparently as a result, in part, 

of the change in the number (decreased to three in 2005) of 

large pumped wells that affect the complex flow field. Under 

simulated steady-state conditions, some water flowing to well 

MG-202 (L-22) is recharged beyond the contributing areas 

for nearby pumped wells MG-76 (L-17) and MG-78 (L-19) in 

the Wissahickon well field. The contributing areas for wells 

MG-76 (L-17) and MG-78 (L-19) are separated by a thin strip 

that contributes flow to well MG-202 (L-22). 

Groundwater/Surface-Water Interactions

Analysis of computed groundwater discharge to streams 

shows the complex flow patterns in the headwaters area of 

Wissahickon Creek in the vicinity of North Penn Area 7 

where groundwater withdrawals are a large part of the water 

budget (table 8). Streamflow gain, or discharge from the 

groundwater to surface water, occurs in the model where the 

aquifer hydraulic head is higher than the specified hydraulic 

head in the stream (Prudic 1989). In contrast, if the simulated 

aquifer hydraulic head is lower than the specified hydraulic 

head in the stream, then streamflow loss, or recharge of the 

groundwater by surface water, occurs. Under 2005 hydrologic conditions, the Wissahickon Creek has both gaining and 

losing reaches in the vicinity of North Penn Area 7 (fig. 46). 

Away from pumping wells, the streams generally gain water; 

this also occurs in sections of Wissahickon Creek upstream 

from pumped wells. Stream loss, in some cases, results in 

total depletion of the streamflow. Sections of the Wissahickon 

Creek, near and upstream and downstream from Sumneytown Pike (approximate southern boundary of the North Penn 

Area 7) are dry in the simulation because of large groundwater 

withdrawals in this area. These results are consistent with 

observed streamflow in the study area in previous studies 

(Senior and Goode, 1999) and are reported in the section 

“Streamflow Measurements and Groundwater/Surface-Water 

Relations.” Most of the groundwater removed by pumping 

is eventually discharged to surface water at wastewatertreatment-plant discharge points on the Wissahickon Creek 

or other nearby streams. Downstream from these discharge 

points, measured base flow may be relatively high, whereas 

the stream may be dry during low-flow conditions upstream 

from the discharge points. 

Simulated Shutdown of Well MG-202

Well MG-202 (L-22) produces water contaminated with 

VOCs, as documented since the 1980s (Martin, 1981; CH2M 

Hill, 1992), yet water from the nearby production well MG-76 

(L-17) has rarely contained contaminants in detectable concentrations. Anecdotal accounts indicate that the pumping of 

well MG-202 (L-22) effectively “protects” well MG-76 (L-17) 

from drawing in contaminated water. A hypothetical simulation was run using the calibrated groundwater-flow model 

for North Penn Area 7 under 2005 conditions to estimate the 

contributing area for MG-76 (L-17) with and without MG-202 

(L-22) pumping. A transient simulation of recovery following 

the shutdown of MG-202 (L-22) was conducted using 2005 

pumping and recharge rates; results were compared with the 

recovery measured in December 2004.

Results of the simulated shutdown of MG-202 (L-22) 

under steady-state 2005 conditions show that the area contributing recharge for well MG-76 (L-17) when well MG-202 

(L-22) is not pumping shifts downstream (fig. 47), overlapping, and similar in shape to, the area contributing recharge for 

well MG-202 (L-22) when both wells are pumping (fig. 45). 

This result is consistent with the anecdotal account that the 

pumping of well MG-202 (L-22) “protects” well MG-76 

(L-17) from drawing in contaminated water if the contaminant 

source is in the overlapping area that contributes recharge 
72 Groundwater System and Simulation of Flow for North Penn Area 7 Superfund Site, Montgomery County, Pennsylvania 75°17' 75°17' 75°18' 75°19' 75°20' 40°14' 40°13' 40°12'

Towamencin Creek

W si sah ci kon Creek

Zenith

JTrb, B6

JTRb, B4

JTrblg, L5

JTrblg, L7

JTrb, B8

Trl, L9

Trlr, B10

JTrb, B

76

77

73

69

55

71

66

52

68

124

143

593

1052

1336

Ford2

Ford1

Rogers

Teleflex

59

202

126

566

140

128

125

130

171 204

223

167

151

203

1702

1424

1423

1198

1701

1841

SpraFin

LeedsNorthrup

991

1199

Trl, L

1050

Base from U.S. Geological SurveyNational Hydrography Dataset, 1999Universal Transverse Mercator, zone 18North American Datum of 1927

EXPLANATION

Contaminant sourceStream

>1,000>300–1,000>100–300>30–1000–30

RoadGeologic contactGeologic formation and

layer identifier

0.05–0.25>0.25–0.5>0.5–0.75>0.75–1.0

Well, by pumping rate in 2005,

in cubic meters per day 

202

Fraction of Monte Carlo simulations

for which pathlines from sourcespass through model cell

U.S. Geological Survey well 

identifier (MG- prefix omitted)

Pathline from source

(optimal-parameter simulation)

Trlr, B10

0

0 0.5 1 KILOMETER

0.5 1 MILE

Figure 44. Simulated groundwater-flow paths extending from contaminant source areas to pumped wells for pumping conditions in 2005 for North Penn Area 7 Superfund site, Upper Gwynedd Township and vicinity, Montgomery County, Pennsylvania. (>, greater than)
Simulation of Regional Groundwater Flow 73

75°15' 75°14' 75°16' 75°17'

40°15'

40°14' 40°13'

i W ssah ci kon Creek JTrb, B6

JTRb, B4

JTrblg, L5

JTrblg, L7

JTrb, B8 Trl, L9

JTrb, B

Trl, L Trlr, B10

Zenith

Ford2

Ford1

Rogers

Teleflex

SpraFin

LeedsNorthrup

78

76

75

55

67

71

66

52

68

202

126

625

130

875

171 204

134

223

167

151

203

153

620

621

1702

1125 1905

1938

1841

1418 1045

77

73

Base from U.S. Geological SurveyNational Hydrography Dataset, 1999Universal Transverse Mercator, zone 18North American Datum of 1927

Model cell that recharges

well 202 (optimal-parameter simulation)

EXPLANATION

Contaminant sourceStream

>1,000>300–1,000>100–300>30–1000–30

RoadGeologic contactGeologic formation and

layer identifier

0.05–0.25>0.25–0.5>0.5–0.75>0.75–1.0

Well, by pumping rate in 2005,

in cubic meters per day 

202

Fraction of Monte Carlo simulations

for which model cell rechargeswell 202

U.S. Geological Survey well 

identifier (MG- prefix omitted)

Trlr, B10

0

0 0.5 1 KILOMETER

0.5 1 MILE

Figure 45. Simulated area contributing recharge to well MG-202 (L-22) for pumping conditions in 2005 for North Penn Area 7 Superfund site, Upper Gwynedd Township and vicinity, Montgomery County, Pennsylvania. (>, greater than)
74 Groundwater System and Simulation of Flow for North Penn Area 7 Superfund Site, Montgomery County, Pennsylvania 75°17' 75°16' 75°18' 75°19' 40°14' 40°13' Zenith Ford2 Ford1 Rogers 59 566 140 171 204

Sumneytown Pike

Measured no flow in stream, May 31, 2005

Measured no flow in stream, May 31, 2005

Measured loss of flow in stream, May 31, 2005

Industrial discharge of about 4.7 m

Teleflex

SpraFin

LeedsNorthrup

78

76

202

126

128

125

130

1702

1424

1423

1198 1841

Wissahickon Creek

Industrial discharge 

991

124

1199

1052

1701

1336

Sewage discharge 

3/d (0.017 ft /s) 3

Base from U.S. Geological SurveyNational Hydrography Dataset, 1999Universal Transverse Mercator, zone 18North American Datum of 1927

EXPLANATION

Contaminant sourceStreams

>300 to 938>100 to 300>30 to 10013 to 30

Roads

0 to 3>3 to 10>10 to 30>30 to 100>100 to 205

Well, by pumping rate in 2005,

in cubic meters per day 

78

Stream loss, in cubic 

meters per day 

U.S. Geological Survey well 

identifier (MG- prefix omitted)

>100 to 192>30 to 100>10 to 30>3 to 10

0 to 3

Stream gain, in cubic 

meters per day 

0

0 0.5 1 KILOMETER

0.5 1 MILE

Figure 46. Simulated stream loss and stream gain for the Upper Wissahickon Creek and other streams, and pumping rates for selected wells, in 2005, for the model for North Penn Area 7 Superfund site, Upper Gwynedd Township and vicinity, Montgomery County, Pennsylvania. (>, greater than; ft3/s, cubic feet per second; m3/d, cubic meters per day)
Simulation of Regional Groundwater Flow 75

75°15' 75°16' 75°17' 75°18'

40°15'

40°14' 40°13'

202

Zenith

Ford2

Ford1

Rogers

Teleflex

SpraFin

LeedsNorthrup

78

76

59

75

69

55

71

66

52

68

991

202

124

126

566

128

140

125

130

498

171

204

167

151

143

593

203

153

1702

1199

1424

1125

1423

1198

1938

1701

1841

1336

JTrb, B6

JTRb, B4

JTrblg, L5

JTrblg, L7

JTrb, B8

Trl, L9

JTrb, B

Trl, L Trlr, B10

77

73

223

1905

67

i W ssah ci kon Creek

Base from U.S. Geological SurveyNational Hydrography Dataset, 1999Universal Transverse Mercator, zone 18North American Datum of 1927

Model cell that recharges

well 202 (optimal-parameter simulation)

EXPLANATION

Contaminant sourceStream

>1,000>300–1,000>100–300>30–1000–30

RoadGeologic contactGeologic formation and

layer identifier

0.05–0.25>0.25–0.5>0.5–0.75>0.75–1.0

Well, by pumping rate in 1990,

in cubic meters per day 

76

Fraction of Monte Carlo simulations

for which model cell rechargeswell 76

U.S. Geological Survey well 

identifier (MG- prefix omitted)

Trlr, B10

0

0 0.5 1 KILOMETER

0.5 1 MILE

Figure 47. Simulated area contributing recharge to well MG-76 (L-17) for pumping conditions in 2005 for North Penn Area 7 Superfund site, Upper Gwynedd Township and vicinity, Montgomery County, Pennsylvania. (>, greater than)
76 Groundwater System and Simulation of Flow for North Penn Area 7 Superfund Site, Montgomery County, Pennsylvania

captured by the wells. However, this area (figs. 45 and 47) 

does not include known contaminant sources, indicating the 

presence of an unknown or unidentified contaminant source. 

The shutdown of well MG-202 (L-22) was also simulated under transient conditions using 2005 pumping and 

recharge to allow comparison of the groundwater-model 

results to measurements made in observation wells during the 

December 2004 shutdown, described earlier in this report. 

The initial conditions for this simulation were the steadystate potentiometric heads corresponding to 2005 pumping 

and recharge rates. For the transient simulation, the specific 

yield was set equal to 0.2, and specific storage was set equal 

to 0.00001. These values of aquifer storage parameters were 

not calibrated, but were selected from the literature to approximately represent local conditions. A specific yield of 0.2 was 

reported by Johnson (1967) for silt loess. For comparison, in 

other simulations of groundwater-flow in fractured rock in the 

Newark Basin in New Jersey, Lewis-Brown and Rice (2002) 

used a specific yield value of 0.15 for overburden overlying 

the Lockatong Formation, and Tiedeman and others (2010) 

used a specific storage value of 0.00001 for weathered and 

unweathered fractured rock of the Lockatong Formation. 

The model layers representing mapped geologic units were 

subdivided into three sub-layers for the transient simulation. 

The pumped well MG-202 (L-22) intersects layers 8 and 9 

but withdraws water primarily from layer 8. The simulated 

recovery from the shutdown of well MG-202 (L-22) generally is consistent with measurements made during shutdown 

tests of that well in 2002 and 2004, which are described by 

Senior and others (2005; 2008) and previously in this report. 

The recovery in water levels after 1 day (1,440 minutes) in the 

middle sub-layer of model layer 8 is depicted in figure 48A, 

which shows that the distribution of changes in water levels 

is elongated in the strike direction but extends downdip to the 

northwest. For some wells, such as MG-72 (L-13), the simulated recovery is similar in magnitude to the actual measured 

changes in water levels during shutdown tests in 2002 and 

2004 (fig. 15), and overall, the general shape and magnitude 

of simulated recovery is consistent with measured water-level 

changes. Little to no recovery in water levels was simulated 

near Spra-Fin, which is consistent with measured water levels 

in well MG-175 during the 2002 shutdown test. The recovery 

in layer 8 is much larger (at least one order of magnitude) than 

in the overlying layer 7, as indicated by simulated changes 

in water levels in the middle sub-layer of model layers 7 and 

8 after 7 days (figs. 48B and 48C). Thus, the regional-scale 

groundwater-flow model, in general, is able to simulate aquifer 

response at the scale of the MG-202 aquifer test, although the 

model does not include sufficient detail to accurately simulate 

all measured water-level changes. 

Transmissivity values estimated from measured waterlevel changes in response to shutdown and restart of pumping in well MG-202 (L-22) using the Theis (1935) analytical method ranged from about 700 to 2,300 ft2

/d (65 to 

214 m2/d) in the 2004 test (Senior and others, 2008) and 770 

to 1,625 ft2/d (72 to 151 m2/d) in the 2002 test (Senior and 

others, 2005). Although the application of the Theis method 

to the fractured-rock setting does not account for anisotropy 

or heterogeneity, transmissivity values determined using 

this analytical approach may be considered rough estimates 

and are similar in magnitude to the transmissivity of about 

904 ft2/d (84 m2/d) in the strike direction [optimum K of 

3.72 ft/d (1.135 m/d) multiplied by maximum layer thickness 

of 243 ft (74 m)] estimated using the computer model for 

layer 8 (table 7). 

Relation Between Water Quality and 

Groundwater Flow

Soluble chemical constituents may be transported in 

groundwater and can act as tracers of groundwater-flow paths. 

Chemical constituents that are introduced at the land surface by human activities may enter the groundwater system 

in recharge through soils and unsaturated aquifer materials. 

A constituent that is relatively conservative (not degradable, readily adsorbed, or precipitated to solid phases), such 

as the dissolved inorganic anion chloride, usually will trace 

advective groundwater flow more closely than other constituents, such as metals or organic compounds that are more 

chemically reactive.

Concentrations of constituents in groundwater samples 

collected by CDM Programs Corporation in fall 2005 are 

evaluated in relation to results of groundwater-flow simulations for the year 2005 to provide a qualitative assessment of 

model results, acknowledging that a snapshot of groundwater 

quality may not exactly match steady-state flow paths. Flow 

paths change over time because of differences in recharge and 

pumping rates. Constituents, including contaminants, may be 

transported to one area and then to another area as groundwater-flow directions change. The observed spatial distribution 

of selected constituents in groundwater in 2005 generally was 

supportive of, or consistent with, the model results of the 2005 

groundwater-flow simulation at North Penn Area 7. 

Inferred Flow Paths from Distribution of 

Measured Contaminants 

The most common contaminant in groundwater at North 

Penn Area 7 is TCE. The spatial distribution of TCE in fall 

2005 shows that highest TCE concentrations were in or near 

groundwater-flow paths simulated under steady-state conditions in 2005 (fig. 49A). Notably, TCE was not detected in 

water samples from most wells that were not in or near flow 

paths from identified contamination sources; the exception is well MG-202 (L-22) and possibly wells MG-174 and 

MG-1897 at the former Clearline property. As discussed previously, the simulated contributing area for well MG-202 (L-22) 

does not include any identified contamination source in North 

Penn Area 7; therefore, the model results suggest the presence 

of an unidentified contaminant source of TCE for MG-202 

(L-22).
Simulation of Regional Groundwater Flow 77

Base from U.S. Geological Survey

Lansdale 1983, 1:24,000

Universal Transverse Mercator, zone 18

North American Datum of 1927

75°17'30" 75°17' 75°16'30"

40°14'

40°13'30"

40°13'

Towamencin Creek

B4

L5

B6

L7

B8

L9

Wissahickon Creek

0 500 1,000 2,000 FEET

0 150 300 600 METERS

Geology from Berg and others (1980) with nomenclature

from Lyttle and Epstein (1987) and additional mapping and

lithologic classification from Smoot (unpublished)

(Not measured in 2004

but was ~0 in 2002 test)

(1.62)

(2.0)

2101 (RI-9I)

2083 (RI-2I)

2082 (RI-2D) 1145 (T-14)

1146 (T-4)

2087 (RI-4D)

2084 (RI-3D)

202

(0.28)

(0.29)

(0.27)

(0.31)

(2.15)

(0.58) (0.03)

(-0.10)

175

2122 (RI-11D)

2123 (RI-11I) 2124 (RI-11S)

76

72

(1.31)

(1.48)

(0.63) (Not measured in 2004

but was ~0 in 2002 test)

(Not measured in 2004

but was ~1.5 in 2002 test)

2094 (RI-6S)

2093 (RI-6D)

1897 (CL-3)

1849

1848

174 CL-2)

(1.45)

EXPLANATION

Lithology

Red beds predominant

Gray beds predominant

B4, B6, B8

L5, L7, L9

Bed code, 

this report 

Nomenclature

(1.31)

(0.28)

1146 (T-4)

2101 (RI-9I)

Contours, in feet, for layer 8 on 

day 1 of simulated recovery 

from MG-202 shutdown—

1.0–1.9

7.0–8.0

6.0–6.9

5.0–5.9

4.0–4.9

3.0–3.9

2.0–2.9

Observation wells in layer 8—Upper number 

and (string) are well identifiers and (lower 

number) is measured change in water levels, 

in feet after 1,000 minutes

Observation wells in layer 7—Upper number 

and (string) are well identifiers and (lower 

number) is measured change in water levels, 

in feet after 1,000 minutes

L7 Model layer

A

Figure 48. Measured water-level changes in observation wells at 1,000 minutes after shutdown of well MG-202 (L-22) in 2004 and 

simulated water-level recovery contours in the respective middle sub-layers of model layers after shutdown of well MG-202 (L-22): 

A, model layer 8 at at 1 day (1,440 minutes), B, model layer 8 at 7 days, and C, model layer 7 at 7 days, North Penn Area 7, Upper 

Gwynedd Township and vicinity, Montgomery County, Pennsylvania. [See figure 15 for cross-section showing changes in water levels 

measured in observation wells in 2004 shutdown test of well MG-202 (L-22).]
78 Groundwater System and Simulation of Flow for North Penn Area 7 Superfund Site, Montgomery County, Pennsylvania

75°17'30" 75°17' 75°16'30"

40°14'

40°13'30"

40°13'

Towamencin Creek

B4

L5

B6

L7

B8

L9

Wissahickon Creek

0 500 1,000 2,000 FEET

0 150 300 600 METERS

Geology from Berg and others, (1980) with nomenclature

from Lyttle and Epstein (1987) and additional mapping and

lithologic classification from Smoot (unpublished)

Base from U.S. Geological Survey

Lansdale 1983, 1:24,000

Universal Transverse Mercator, zone 18

North American Datum of 1927

(Not measured in 2004

but was ~0 in 2002 test)

(1.62)

(2.0)

2101 (RI-9I)

2083 (RI-2I)

2082 (RI-2D) 1145 (T-14)

1146 (T-4)

2087 (RI-4D)

2084 (RI-3D)

202

(0.28)

(0.29)

(0.27)

(0.31)

(2.15)

(0.58) (0.03)

(-0.10)

175

2122 (RI-11D)

2123 (RI-11I) 2124 (RI-11S)

76

72

(1.31)

(1.48)

(0.63) (Not measured in 2004

but was ~0 in 2002 test)

(Not measured in 2004

but was ~1.5 in 2002 test)

2094 (RI-6S)

2093 (RI-6D)

1897 (CL-3)

1849

1848

174 CL-2)

(1.45)

1.0–1.9

7.0–7.9

6.0–6.9

5.0–5.9

4.0–4.9

3.0–3.9

2.0–2.9

8.0–8.9

9.0–10.0

EXPLANATION

Lithology

Red beds predominant

Gray beds predominant

B4, B6, B8

L5, L7, L9

Bed code, 

this report 

Nomenclature

(1.31)

(0.28)

1146 (T-4)

2101 (RI-9I)

Contours, in feet, for layer 8 on 

day 7 of simulated recovery 

from MG-202 shutdown— Observation wells in layer 8—Upper number 

and (string) are well identifiers and (lower 

number) is measured change in water levels, 

in feet after 1,000 minutes

Observation wells in layer 7—Upper number 

and (string) are well identifiers and (lower 

number) is measured change in water levels, 

in feet after 1,000 minutes

L7 Model layer

B

Figure 48. Measured water-level changes in observation wells at 1,000 minutes after shutdown of well MG-202 (L-22) in 2004 and 

simulated water-level recovery contours in the respective middle sub-layers of model layers after shutdown of well MG-202 (L-22): 

A, model layer 8 at at 1 day (1,440 minutes), B, model layer 8 at 7 days, and C, model layer 7 at 7 days, North Penn Area 7, Upper 

Gwynedd Township and vicinity, Montgomery County, Pennsylvania.—Continued [See figure 15 for cross-section showing changes in 

water levels measured in observation wells in 2004 shutdown test of well MG-202 (L-22).]
Simulation of Regional Groundwater Flow 79

75°17'30" 75°17' 75°16'30"

40°14'

40°13'30"

40°13'

Towamencin Creek

B4

L5

B6

L7

B8

L9

Wissahickon Creek

0 500 1,000 2,000 FEET

0 150 300 600 METERS

Simulated recovery here is artifact

of model layer 7, present but very 

thin in model updip of outcrop under 

model layers 1 and 2

Base from U.S. Geological Survey

Lansdale 1983, 1:24,000

Universal Transverse Mercator, zone 18

North American Datum of 1927

Geology from Berg and others (1980) with nomenclature

from Lyttle and Epstein (1987) and additional mapping and

lithologic classification from Smoot (unpublished)

(Not measured in 2004

but was ~0 in 2002 test)

(1.62)

(2.0)

2101 (RI-9I)

2083 (RI-2I)

2082 (RI-2D) 1145 (T-14)

1146 (T-4)

2087 (RI-4D)

2084 (RI-3D)

202

(0.28)

(0.29)

(0.27)

(0.31)

(2.15)

(0.58) (0.03)

(-0.10)

175

2122 (RI-11D)

2123 (RI-11I) 2124 (RI-11S)

76

72

(1.31)

(1.48)

(0.63)

but was ~0 in 2002 test)

(Not measured in 2004

but was ~1.5 in 2002 test)

2094 (RI-6S)

2093 (RI-6D)

1897 (CL-3)

1849

1848

174 CL-2)

(1.45)

(Not measured in 2004

EXPLANATION

Lithology

Red beds predominant

Gray beds predominant

B4, B6, B8

L5, L7, L9

Bed code, 

this report 

Nomenclature

(1.31)

(0.28)

1146 (T-4)

2101 (RI-9I)

Contours, in feet, for layer 7 on 

day 7 of simulated recovery 

from MG-202 shutdown—

0.10–0.19

0.70–0.80

0.60–0.69

0.50–0.59

0.40–0.49

0.30–0.39

0.20–0.29

Observation wells in layer 8—Upper number 

and (string) are well identifiers and (lower 

number) is measured change in water levels, 

in feet after 1,000 minutes

Observation wells in layer 7—Upper number 

and (string) are well identifiers and (lower 

number) is measured change in water levels, 

in feet after 1,000 minutes

L7 Model layer

C

Figure 48. Measured water-level changes in observation wells at 1,000 minutes after shutdown of well MG-202 (L-22) in 2004 and 

simulated water-level recovery contours in the respective middle sub-layers of model layers after shutdown of well MG-202 (L-22): 

A, model layer 8 at at 1 day (1,440 minutes), B, model layer 8 at 7 days, and C, model layer 7 at 7 days, North Penn Area 7, Upper 

Gwynedd Township and vicinity, Montgomery County, Pennsylvania.—Continued [See figure 15 for cross-section showing changes in 

water levels measured in observation wells in 2004 shutdown test of well MG-202 (L-22).]
80 Groundwater System and Simulation of Flow for North Penn Area 7 Superfund Site, Montgomery County, Pennsylvania 75°17' 75°18' 40°14' 40°13'

Wissahickon Creek

Ford2

LeedsNorthrup

2129

2125

2122

2100 2097

2095

2093

2087

2084

2080

2101

2098

2088

2085

2099

2094

2086

76

202

174

1897

1849 1848

1847

1846

1844

1845

1842

1146

1145

1144

Church Road

Zenith

Ford1

Teleflex

SpraFin

2126

2119

2090

2081

175

2127

2123

2120

2091

2092

2082

2128

2124

2121

2102

2089

2083

171

1505

1149

1148

Sumneytown Road

Towamencin Creek

Rogers

2131

2134

2132

2133

Base from U.S. Geological Survey National Hydrography Dataset, 1999Universal Transverse Mercator, zone 18North American Datum of 1927

EXPLANATION

Contaminant source StreamRoad

Ford1Ford2Leeds NorthrupRogersSpraFinTeleflexZenith

Simulated groundwater-flow 

paths in 2005 from contaminantsource areas

A

Open hole0.0–2.02.1–5.05.1–20.020.1–50.050.1–410.0

Type of well—

Shallow monitor wellIntermediate monitor wellDeep monitor well

TCE concentration,

in micrograms per liter—

TCE concentration in 2005

from screened wells with different depths and for open holes and well number (MG- prefix omitted)

1848

2097

2098

2099

0 0.5 KILOMETER

0 0.5 MILE

Figure 49. Simulated groundwater-flow paths for conditions in 

A, 2005 and 

B, 1990, and measured TCE concentrations in samples collected from 

observation wells in fall 2005, North Penn Area 7 Superfund site, Upper Gwynedd Township and vicinity, Montgomery County, Pennsylvania.
Simulation of Regional Groundwater Flow 81

75°17' 75°18'

40°14'40°13'

Wissahickon Creek

Ford2

LeedsNorthrup

2131

2129

2125

2122

2100 2097

2095

2093

2087

2084

2080

2101 2098

2088

2085 2134

2099

2094

2086

76

202

174

1,897

1849

1848

1847

1846

1844

1845

1842

1146

1145

1144

Church Road

Zenith

Ford1

Teleflex

SpraFin

2132

2119

2081

175

2133

2123

2120

2082

2124

2121

2102

2089

2083

171

1505

1149

1148

Sumneytown Road

Towamencin Creek

Rogers

2090 2091 2092

2126

2127

2128

Base from U.S. Geological Survey National Hydrography Dataset, 1999Universal Transverse Mercator, zone 18North American Datum of 1927

EXPLANATION

Contaminant source StreamRoad

Ford1Ford2Leeds NorthrupRogersSpraFinTeleflexZenith

Simulated groundwater-flow 

paths in 1990 from contaminantsource areas

B

Open hole0.0–2.02.1–5.05.1–20.020.1–50.050.1–410.0

Type of well—

Shallow monitor wellIntermediate monitor wellDeep monitor well

TCE concentration,

in micrograms per liter—

TCE concentration in 2005

from screened wells with different depths and for open holes and well number (MG- prefix omitted)

1848

2097

2098

2099

0 0.5 KILOMETER

0 0.5 MILE

Figure 49. Simulated groundwater-flow paths for conditions in 

A, 2005 and 

B, 1990, and measured TCE concentrations in samples collected from 

observation wells in fall 2005, North Penn Area 7 Superfund site, Upper Gwynedd Township and vicinity, Montgomery County, Pennsylvania.—Continued
82 Groundwater System and Simulation of Flow for North Penn Area 7 Superfund Site, Montgomery County, Pennsylvania

The effects of differences in aquifer stresses on directions 

of flow paths are depicted in figure 49B where TCE concentrations in fall 2005 are shown with flow paths simulated for 

1990 steady-state conditions when more wells were pumping and pumping rates were higher than in 2005. The TCE 

concentrations in 2005 samples from well clusters west of 

Church Road [wells MG-2119 (RI-10D), MG-2120 (RI-10I), 

MG-2121 (RI-10S) of the RI-10 cluster] and near the southern 

extent of Dickerson Road [wells MG-2100 (RI-9D), MG-2101 

(RI-9I), MG-2102 (RI-9S) of the RI-9 cluster] are not in or 

near simulated deterministic 1990 flow paths (and not along 

high-frequency probabilistic flow paths; fig. 38), indicating 

that flow paths from known sources were different in 1990 

than in 2005. The 1990 simulated flow paths are similar to 

those for 2005 in that the simulated 1990 flow paths from 

identified contaminant sources do not pass near well MG-202, 

which nevertheless yields water with TCE at concentrations 

of concern, indicating contamination from an unknown or 

unidentified source.

In addition to TCE, other VOCs were detected in samples 

from wells in North Penn Area 7. The fall 2005 spatial distribution of CFC-11 and CFC-113 (fig. 50 A and B), two VOCs 

present in relatively low to moderate concentrations (up to 230 

and 79 μg/L, respectively) in selected groundwater samples, 

indicate different source areas for these compounds. The 

distribution of CFC-11 and CFC-113 in groundwater samples 

generally agrees with the 2005 simulated path lines. CFC-11 

primarily was detected in samples from wells west of Church 

Road (well clusters RI-5, RI-13, and RI-10), two wells in the 

RI-15 cluster just east of Church Road [MG-2133 (RI-15I), 

MG-2134 (RI-15S)], and the shallow well [MG-2099 (RI8S)] of the RI-8 cluster east of Wissahickon Creek (fig. 50A). 

CFC-113 primarily was detected at concentrations higher 

than those for CFC-11 in samples from wells east of Church 

Road on the Teleflex property and the shallow well of the RI-8 

cluster [well MG-2099 (RI-8S)] east of Wissahickon Creek 

and at relatively lower concentrations in samples from wells at 

the Precision Tube facility (MG-171 and MG-204) and former 

FERCO facility (RI-15 and RI-3 clusters) along strike from 

Teleflex (fig. 50B). Samples from wells in the RI-8 and RI-15 

well clusters contained detectable concentrations of CFC-11 

and CFC-113. Analyses of 2006 well samples indicated that 

CFC-11 and CFC-113 were present in concentrations similar 

to, or higher than, those reported for 2005 samples, indicating 

that the spatial distribution pattern of these compounds was 

persistent over that time period.

The 2005 observed concentrations and 2005 simulated 

path lines indicate (1) a source of CFC-11 near the RI-5 cluster 

west of Church Road, (2) a source of CFC-113 on the Teleflex 

property east of Church Road, and (3) a source of CFC-11 and 

CFC-113 near RI-8 cluster on the former Leeds & Northrup 

property east of Wissahickon Creek. The presence of CFC-113 

in samples from wells at the Precision Tube and former 

FERCO facilities may be a result of previous and current 

pumping drawing the compound from the Telefex facility, or 

the CFC-113 could come from independent sources. 

CFC-11 and CFC-113 measured in 2005 samples from 

the shallow and intermediate wells (MG-2099, MG-2098) 

of the RI-8 cluster near a contaminant source at the Leeds & 

Northrup facility east of Wissahickon Creek were not detected 

in 2005 samples collected downgradient, possibly because of 

limited data. Simulated 2005 groundwater-flow paths from 

this source do not pass directly through areas where wells 

were sampled for CFC-11 and CFC-113 analysis, although the 

flow paths pass near the RI-9 well cluster. Neither CFC-11 nor 

CFC-113 was detected in 2005 samples from wells in the RI-9 

well cluster, but low concentrations (less than 1 μg/L) of both 

compounds were measured in 2006 samples from the shallow 

well [MG-2102 (RI-9S)] in the RI-9 cluster. 

Inferred Flow Paths from Observed Inorganic 

Constituent Distribution

As discussed previously, elevated concentrations of chloride coupled with distinct chloride/bromide mass ratios were 

measured in samples from well clusters RI-5, R-13, and RI-10 

west of Church Road (figs. 22, 28, and 29). The distribution 

of these inorganic chemical characteristics (figs. 22 and 29) is 

similar to the spatial distribution of CFC-11 (fig. 50A), indicating a similar source location and (or) similar flow paths for 

the elevated chloride and CFC-11 in that part of North Penn 

Area 7.

Boron is another inorganic constituent that appears to 

occur in a distinct spatial distribution. Boron was detected in 

elevated concentrations above estimated background concentrations of about 40 μg/L in the 2006 samples from selected 

wells only. The highest boron concentrations (up to 229 μg/L) 

were measured in samples from wells in the RI-6 cluster 

southeast, updip, and across the Wissahickon Creek from 

production well MG-202 (L-22) (fig. 26). Relatively elevated 

boron concentrations also were measured in samples from 

wells generally downgradient and along strike from the RI-6 

cluster. The spatial distribution of the elevated boron may be 

related to natural geologic occurrence (composition of certain 

beds) and (or) to groundwater flow through the aquifer from 

a natural or anthropogenic source near the RI-6 cluster. If the 

elevated boron were from a source, the spatial distribution 

would be consistent with the general direction of groundwater 

flow. The RI-6 well cluster is at the edge of the 2005 simulated 

contributing area for well MG-202, and therefore, pumping 

at MG-202 may not capture all groundwater originating as 

recharge in the vicinity of the RI-6 cluster. The boron concentration of 50 μg/L, slightly higher than estimated natural 

background, in the 2006 water sample from well MG-202 

(L-22) indicates that the source of elevated boron is relatively 

small or, if geologically controlled, does not extend far along 

strike to the northeast of the RI-6 cluster. Boron in MG-202 

(L-22) well water also could be a mixture of some water with 

high boron concentrations from near RI-6 and other water 

with lower boron concentrations. Analysis for boron isotopes 

in groundwater might be useful in identifying boron sources 
Simulation of Regional Groundwater Flow 83

75°17' 75°18'

40°14'40°13'

Wissahickon Creek

Ford2

LeedsNorthrup

2129

2125

2122

2100 2097

2095

2093

2087

2084

2080

2101

2098

2088

2085

2099

2094

2086

76

202

174

1897

1849 1848

1847

1846

1844

1845

1842

1146

1145

1144

Church Road

Zenith

Ford1

Teleflex

SpraFin

2119

2081

175

2123

2120

2082

2124

2121

2102

2089

2083

171

1505

1149

1148

Sumneytown Road

Towamencin Creek

Rogers

2131

2134

2132

2133

2090 2091 2092

2126

2127

2128

Base from U.S. Geological Survey National Hydrography Dataset, 1999Universal Transverse Mercator, zone 18North American Datum of 1927

EXPLANATION

Contaminant source StreamRoad

Ford1Ford2Leeds NorthrupRogersSpraFinTeleflexZenith

Simulated groundwater-flow 

paths in 2005 from contaminantsource areas

A

Open hole0.0–2.02.1–5.05.1–20.020.1–50.050.1–230.0

Type of well—

Shallow monitor wellIntermediate monitor wellDeep monitor well

CFC-11 concentration,

in micrograms per liter—

CFC-11 concentration in 2005

from screened wells with different depths and for open holes and well number (MG- prefix omitted)

1848

2097

2098

2099

0 0.5 KILOMETER

0 0.5 MILE

, CFC-113 in samples collected from 

, Pennsylvania.

B , CFC-11 and -flow paths for conditions in 2005 and measured concentrations of 

A

, Montgomery County

Simulated groundwater Figure 50.

observation wells in fall 2005, North Penn Area 7 Superfund site, Upper Gwynedd Township and vicinity
84 Groundwater System and Simulation of Flow for North Penn Area 7 Superfund Site, Montgomery County, Pennsylvania 75°17' 75°18' 40°14' 40°13'

Wissahickon Creek

Ford2

LeedsNorthrup

2129

2125

2122

2100 2097

2095

2093 2087

2084

2080

2101

2098

2088

2085

2099

2094

2086

76

202

174

1,897

1849

1848

1847

1846

1844

1845

1842

1146

1145

1144

Church Road

Zenith

Ford1

Teleflex

SpraFin

2119

2081

175

2123

2120

2082

2124

2121

2102

2089

2083

171

1505

1149

1148

Sumneytown Road

Towamencin Creek

Rogers

2131

2134

2132

2133

2090 2091 2092

2126

2127

2128

Base from U.S. Geological Survey National Hydrography Dataset, 1999Universal Transverse Mercator, zone 18North American Datum of 1927

EXPLANATION

Contaminant source StreamRoad

Ford1Ford2Leeds NorthrupRogersSpraFinTeleflexZenith

Simulated groundwater-flow 

paths in 2005 from contaminantsource areas

B

Open hole0.0–2.02.1–5.05.1–20.020.1–50.050.1–79.0

Type of well—

Shallow monitor wellIntermediate monitor wellDeep monitor well

CFC-113 concentration,

in micrograms per liter—

CFC-113 concentration in 2005

from screened wells with different depths and for open holes and well number (MG- prefix omitted)

1848

2097

2098

2099

0 0.5 KILOMETER

0 0.5 MILE

, CFC-113 in samples collected from 

, Pennsylvania.—Continued

B , CFC-11 and -flow paths for conditions in 2005 and measured concentrations of 

A

, Montgomery County

Simulated groundwater Figure 50.

observation wells in fall 2005, North Penn Area 7 Superfund site, Upper Gwynedd Township and vicinity
Summary and Conclusions 85

in the area and their relative contribution to water withdrawn 

from well MG-202 (L-22) and, thus, could be potentially helpful in identifying the location of the unknown source of TCE 

contamination affecting well MG-202 (L-22). 

Limitations and Uncertainties in Predictive 

Simulations

Regional groundwater-flow paths in the study area are 

approximated by the predictive simulations in this report. 

Although the calibrated regional model reasonably matches 

overall regional water-level trends, the measurements are 

not precisely reproduced by the models, partly as the result 

of the model structure and availability of data. The actual 

groundwater-flow paths are likely to be more complex than 

those shown here because of the highly heterogeneous characteristics of the fractured-rock aquifers, and the groundwaterflow paths are likely to change in time because of changing 

recharge and pumping conditions. Nevertheless, the model 

and results here can be used to compare the potential effects of 

alternative groundwater-management methods and to indicate 

general characteristics of contributing areas for wells in the 

study area. The uncertainties in the predictive simulations of 

regional groundwater flow could be reduced by more detailed 

field studies and longer-term aquifer and tracer tests, which 

are beyond the scope of this study. Similar additional data 

also would be needed to simulate groundwater flow at the 

local scale. The probabilistic groundwater-flow paths indicate 

that the area that may have contributed recharge to individual 

pumped wells is larger than that shown for deterministic 

groundwater-flow paths. Vertical anisotropy of some layers of 

the model could not be calibrated with the observations available, and these parameters were fixed, rather than calibrated. 

The effect of uncertainty in the vertical anisotropy was not 

included in the Monte Carlo simulations. 

Summary and Conclusions

Groundwater in an area near Lansdale and Upper Gwynedd Township in southeastern Pennsylvania is contaminated 

with organic solvents, and on the basis of investigations in the 

1980s that identified several probable industrial sources, the 

U.S. Environmental Protection Agency (USEPA) placed the 

area on the National Priority List in 1989 as the North Penn 

Area 7 Superfund site. Groundwater in and near North Penn 

Area 7 has been and currently (2012) is withdrawn for water 

supply. Contaminant migration is of concern as pumping patterns in the area change. In 2000, the U.S. Geological Survey 

(USGS) and the USEPA began a cooperative study, in which 

the USGS provided technical assistance for the Remedial 

Investigation (RI) at the North Penn Area 7 Superfund site. 

This assistance included describing the groundwater system 

and simulating groundwater flow on a regional scale. 

The study area is underlain by Triassic and Jurassic age 

sandstones and shales of the Lockatong Formation and Brunswick Group in the Mesozoic Newark Basin. 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 layers of differing 

permeabilities. The aquifer layers are recharged locally by precipitation through thin soils and discharge locally to streams. 

Depth to the top of competent bedrock typically is less than 

20 ft below land surface. The Wissahickon Creek begins less 

than 1 mile northeast of the study area and flows southwest, 

parallel to strike, to bisect North Penn Area 7. 

Results of field investigations conducted by USGS at 

North Penn Area 7, including geophysical logging, singlewell testing of isolated aquifer intervals (packer testing), and 

aquifer tests with multiple observation wells, support the 

conceptual model of a layered aquifer with low hydraulic connection across beds and higher hydraulic connection parallel to 

bedding. Correlation of natural gamma-ray activity in borehole 

logs for the western part of North Penn Area 7 is possible over 

distance of hundreds to thousands of feet, indicating lateral 

continuity of beds that dip about 9 to 10 degrees northwest. 

Correlation of natural gamma-ray-activity logs appears possible only over smaller distances (less than 1,000 ft) in the eastern part of the study area and may reflect different depositional 

environments for sedimentary rocks than in the western part 

of the study area. Vertical hydraulic gradients vary throughout 

the area, as indicated by measurements of borehole flow in 

open wells, by different water levels in vertically nested wells, 

and by different water levels in zones isolated by packers in 

open wells. Vertical gradients are predominantly upward east 

of Wissahickon Creek, except where affected by pumping, and 

downward west of Wissahickon Creek. 

Depths to static water levels in wells at North Penn 

Area 7 from December 2000 through September 2006 ranged 

from about 6 to 83 ft below land surface and generally were 

least in shallow wells near streams and greatest in wells 

affected by nearby pumping or located on hilltops. Water 

levels fluctuated seasonally in response to changes in recharge 

and were lowest during dry periods in 2001 and 2002. 

Regional groundwater levels mapped by USGS in 2000 and 

measured in several synoptic rounds from 2000 through 2005 

indicate a potentiometric surface similar to topography, except 

in areas affected by relatively high pumping rates. Periodic 

base-flow stream measurements at selected sites on Wissahickon Creek from December 2000 through September 2005 

show that the stream lost water between two sites on a reach in 

the study area when groundwater levels were low and gained 

water when groundwater levels were relatively high. The 

stream frequently was dry (no measureable base flow) at the 

most downstream site on Wissahickon Creek (at Sumneytown 

Road) that was measured for the North Penn Area 7 study.

Transmissivity values calculated from pumping rates and 

drawdown in isolated intervals in 11 existing wells and the 

15 deepest new monitor wells drilled for the RI ranged over 

three orders of magnitude (2.8 to 2,290 square feet per day). 
86 Groundwater System and Simulation of Flow for North Penn Area 7 Superfund Site, Montgomery County, Pennsylvania

Transmissivity values showed some relation to depth over the 

range of depths tested; the full range of transmissivities was 

measured throughout the 300-ft thickness of the aquifer penetrated by the new deep monitor wells. When the transmissivities of tested intervals in the 15 deepest monitor wells, which 

are of similar depths, were grouped by depth in ranges of 50 ft, 

the transmissivities of the shallowest zones and deepest zones 

tested (interval midpoints of 0 to 50 and 251 to 300 ft below 

land surface, respectively) were statistically significantly different (smaller) than transmissivities of intermediate depths, as 

determined by the non-parametric Kruskall-Wallis test using 

a p-value of 0.05. Possible explanations for the apparent differences in transmissivity with depth are that weathering may 

reduce the permeability of the shallowest intervals and that 

the frequency of high-permeability zones decreases with depth 

below 250 ft below land surface. 

 The structure of dipping beds appears to control hydraulic connections in the fractured-rock aquifer, as determined 

from water-level responses in observation wells to the 

shutdown and restart of pumping in production well MG-202 

(L-22). Water-level changes measured in nearby monitor wells 

during packer testing of well MG-2131 (RI-15DD) show similar structural/stratigraphic controls on hydraulic connections; 

water-level changes also show that long open sections of boreholes can act as short circuits to connect fractures in layers of 

the aquifer that under natural conditions are separated. 

Groundwater samples collected by CDM from existing 

and new monitor wells during three rounds of sampling during 

2001–06 as part of the RI to assess the extent of groundwater 

contamination at North Penn Area 7 were analyzed for VOCs 

in all rounds and for selected major ions, metals, inorganic 

constituents, semi-volatile organic compounds, and (or) pesticides in one or more rounds. The main contaminants identified in groundwater from the three rounds of sampling are 

VOCs; trichloroethylene (TCE) is the VOC most frequently 

detected and measured at the highest concentration (up to 

650 μg/L in monitor well MG-2124 (RI-11S). Other detected 

VOCs include (but are not limited to) tetrachloroethylene, 

cis-1,2-DCE, 1,1,1-TCA, 1,1-DCE, vinyl chloride, CFC-11, 

and CFC-113. 

Water samples were analyzed for the additional inorganic 

constituents, including chloride, bromide, boron, sulfate, 

and silica, to determine the ions causing the high specific 

conductance in water from some wells identified through 

geophysical logging and packer tests and to potentially aid in 

the understanding of the groundwater-flow system and (or) 

determine potential contaminant sources and (or) pathways. 

Chloride concentrations were elevated above the estimated 

natural background of 10 milligrams per liter (mg/L) in most 

groundwater samples, generally decreased with depth, and 

were highly elevated (100 to 350 mg/L) in water samples from 

wells with high specific conductance in the western part of 

North Penn Area 7, indicating dissolved salts are the probable 

cause of the high conductance there. Chloride/bromide mass 

ratios indicate that sources of chloride in water from wells 

west of and along Church Road appear to differ from other 

locations at North Penn Area 7 and probably include substances other than road salt. Sulfate concentrations in samples 

ranged from 10 to 68.6 mg/L, were not elevated above 

background levels estimated from regional studies, showed no 

strong pattern in relation to depth or spatial distribution, and 

were not high enough to limit anaerobic degradation of VOCs. 

Silica concentrations, a possible surrogate for residence time, 

generally decreased with depth like chloride, indicating possible rapid recharge through preferential pathways to deep 

groundwater. Silica concentrations also indicate that shallow 

groundwater may follow different, slower flow paths than 

deeper groundwater. Boron concentrations in water samples 

from wells at North Penn Area 7 ranged from less than 20 

to 220 micrograms per liter (μg/L) and were highest in the 

RI-6 well cluster and wells along strike from that cluster. 

The spatial distribution of the slightly to moderately elevated 

boron concentrations (greater than 40 μg/L) may be related 

to a natural occurrence of boron in the geologic formation 

that follows geologic structure (bedding orientation) or may 

trace groundwater transport partly controlled by geologic 

structure from a natural or anthropogenic source (such as 

waste-disposal facilities). 

Groundwater flow in and near North Penn Area 7 under 

steady-state conditions was simulated by use of a numerical 

model (MODFLOW-2000). The model, intended to simulate 

groundwater flow at a regional scale, was oriented parallel to 

regional strike and consisted of multiple layers. The top two 

layers represent saprolite and highly weathered rock near the 

surface. The dipping sedimentary formations that underlie 

the study area were modeled using dipping model layers for 

intermediate and deep zones of unweathered, fractured rock. 

The beds and their geometry were identified on the basis of 

geologic mapping of the Lockatong Formation and Brunswick Group and transitional beds (maps of the beds are not 

published). The model does not include detailed structure to 

account for local-scale differences in hydraulic properties, 

with the result that local-scale groundwater flow may not be 

well simulated. Additional detailed multi-well aquifer tests 

would be needed to establish the extent of interconnection 

between intervals at the local scale to address remediation of 

contamination at each source area. 

The regional groundwater-flow model was calibrated 

to measured water levels (1996, 2000, and 2005) and base 

flow estimated from selected streamflow measurements by 

use of nonlinear-regression parameter-estimation algorithms. 

Estimated model parameters include hydraulic conductivity 

(subhorizontal and vertical), anisotropy of hydraulic conductivity, streambed hydraulic conductivity, and recharge during 

calibration periods. Vertical anisotropy of some layers of the 

model could not be calibrated with the observations available and, consequently, was fixed for these layers. Estimated 

hydraulic conductivity ranges from 0.001 to 1.67 meters per 

day (m/d) (0.0032 to 5.5 ft/d). The calibrated regional model 

indicates that the aquifer appears to be anisotropic; hydraulic 

conductivity is greatest parallel to the strike of bedding of 

the dipping sedimentary formations underlying the area and 
References Cited 87

smallest in the cross-bed (dip) direction. The ratio of minimum 

to maximum subhorizontal hydraulic conductivity ranges from 

1/1 to 1/8.5, and the ratio of vertical to (sub)horizontal hydraulic conductivity ranges from 1/1 to 1/478. Estimated recharge 

rates corresponding to calibration periods in 1996, 2000, and 

2005 are 148, 109, and 124 millimeters per year (mm/yr) (5.8, 

4.3, and 4.9 in/yr), respectively. 

The calibrated groundwater-flow model was used to 

simulate groundwater flow during periods of relatively high 

withdrawals (pumpage) (1990) and relatively low withdrawals 

(2000 and 2005). Groundwater-flow paths originating from 

recharge near known source areas of soil contamination were 

simulated. Pumped industrial wells captured groundwater 

from several of these sources. Because pumping at some of 

these wells ceased or decreased after 1990, groundwater from 

those sources was no longer captured at those wells. Greater 

amounts of contaminated groundwater moved away from 

North Penn Area 7 Superfund site to surrounding areas under 

pumping conditions in 1996, 2000, and 2005 than in 1990. 

Changes in the hydraulic properties of the model result in 

changes in the simulated flow paths of groundwater from contaminant source areas to pumped wells, and this uncertainty 

in the groundwater-flow paths was illustrated through Monte 

Carlo simulations. The effect of uncertainty in the vertical 

anisotropy was not included in the Monte Carlo simulations 

because limited available field data precluded calibration of 

vertical anisotropy in the model. The probabilistic simulations 

show that the groundwater-flow paths from potential areas of 

contaminant sources are generally consistent with deterministic paths but that uncertainty in the aquifer properties leads 

to uncertainty in the paths, such that contaminated water may 

have moved through a much larger part of the formations in 

the study area. The uncertainty in these paths could potentially 

be reduced by further field studies, such as tracer tests, that 

characterize flow paths directly. 

Simulated contributing areas indicate the general configuration of groundwater flow towards production well MG-202 

(L-22) in the study area, and as simulated, contributing areas 

likely do not include any identified contaminant source in 

North Penn Area 7. Recharge to wells generally comes from 

infiltration near the well and over an area that extends upgradient from the well. The contributing area is more complex at 

groundwater divides, can extend in more than one direction, 

and can capture recharge from thousands of feet away. Contributing areas to wells in areas with many wells are particularly complex and, in some cases, include areas that contribute 

flow to streams that subsequently recharge the aquifer through 

stream loss. In these cases, water-quality constituents in the 

surface water may be drawn into nearby pumped wells. 

The groundwater-flow model was used to determine the 

contributing area for well MG-76 (L-17) when production well 

MG-202 was shutdown. Results of the simulated shutdown of 

well MG-202 (L-22) under steady-state 2005 conditions show 

that the area contributing recharge to well MG-76 (L-17) when 

MG-202 (L-22) is not pumping shifts downstream and is similar to the area contributing recharge to MG-202 (L-22) when 

both wells are pumped. This result is consistent with the anecdotal account that pumped well MG-202 (L-22) “protects” 

well MG-76 (L-17) from drawing in contaminated water if the 

contaminant source is in the overlapping area that contributes 

recharge to both wells. Simulation of the MG-202 (L-22) 

shutdown under transient conditions shows that the regionalscale groundwater-flow model is, in general, able to simulate 

observed aquifer response at the scale of the MG-202 (L-22) 

aquifer test, although the model does not include sufficient 

detail to accurately simulate all measured water-level changes. 

Concentrations of constituents in groundwater samples 

collected by CDM in fall 2005 are compared with groundwater-flow simulations for the year 2005 to provide a qualitative 

assessment of model results, acknowledging that a snapshot 

of groundwater quality may not exactly match steady-state 

flow paths. The observed spatial distribution of selected constituents, including TCE, CFC-11, CFC-113 in groundwater in 

2005 and the chloride/bromide mass ratios for 2006, generally 

were supportive of, or consistent with, the model results of the 

2005 groundwater-flow simulation at North Penn Area 7.

References Cited

Argus Interware, Inc., 1997, User’s Guide Argus ONETM, 

Argus Open Numerical Environments—A GIS Modeling System, Version 4.0: Jericho, N.Y., Argus Holdings, 

Limited, 506 p.

Barton, G.J., Risser, D.W., Galeone, D.G., and Goode, D.J., 

2003, Case study for delineating a contributing area to 

a well in a fractured siliciclastic-bedrock aquifer near 

Lansdale, Pennsylvania: U.S. Geological Survey WaterResources Investigations Report 02–4271, 46 p.

Berg, T.M., Edmunds, W.E., Geyer, A.R., and others, comps., 

1980, Geologic map of Pennsylvania: Pennsylvania 

Geological Survey, 4th Series, Map 1, 2nd edition, scale 

1:250,000, 2 sheets.

Berg, T.M., Barnes, J.H., Sevon, W.D., Skema, V.W., Wilshusen, J.P., and Yannacucci, D.S., 1989, Physiographic Provinces of Pennsylvania: Pennsylvania Geological Survey, 

4th ser., map 13, scale 1:2,000,000.

Biesecker, J.E., Lescinsky, J.B., and Wood, C.R., 1968, Water 

resources of the Schuylkill River Basin: Pennsylvania 

Department of Environmental Protection Water Resources 

Bulletin, no. 3, 198 p.

Black & Veatch Waste Science, Inc., 1994, Remedial Investigation Feasibility Study Report North Penn Area 6 Site 

Source Control Operable Unit, Lansdale, Pennsylvania, 

Work assignment no. 91-19-3LW9, contract no. 68-W8-

0091: Prepared for the U.S. Environmental Protection 

Agency, December 20, 1994.
88 Groundwater System and Simulation of Flow for North Penn Area 7 Superfund Site, Montgomery County, Pennsylvania

Black & Veatch Waste Science, Inc., 1999, Remedial Investigation Feasibility Study Report North Penn Area 6 Site 

Groundwater Operable Unit (OU3), Lansdale, Pennsylvania.Work assignment no. 004-RICO03W9, contract no. 

68-S8-3002. Prepared for the U.S. Environmental Protection Agency, August 1999

Burns, D.A., Plummer, L.N., McDonnell, J.J., Busenberg, 

Eurybiades, Casile, G.C., Kendall, Carol, Hooper, R.P., 

Freer, J.E., Peters, N.E., Beven, Keith, and Schlosser, Pete, 

2003, The geochemical evolution of riparian ground water 

in a forested Piedmont catchment: Ground Water, v. 41, 

no. 7, p. 913–925.

Chapelle, F.H, and Bradley, P.M, 1998, Selecting remediation goals by assessing the natural attenuation capacity of 

groundwater systems: Bioremediation Journal, v. 2, no. 3–4, 

p. 227–238. 

CDM Federal Programs Corporation, 2003, Revised final 

remedial investigation report for North Penn Operable Unit 

2 Spra-Fin property, North Wales, volume 1: U.S. Environmental Protection Agency work assignment no. 015-RICO03X1 document no. 3232-015-RT-RIRT-01570, June 23, 

2003, accessed December 3, 2010, at http://loggerhead.epa.

gov/arweb/public/pdf/464104.pdf.

CDM Federal Programs Corporation, 2011, Final remedial 

investigation report for North Penn Area 7 Superfund Site, 

Operable Unit 3, Montgomery County, Pennsylvania: U.S. 

Environmental Protection Agency contract no. EP-S3-07-

06, work assignment no. 024-RICO-03X1 document control 

no. 3330-024-RT-RIRT-01543, April 28, 2011.

CH2M-Hill, Inc., 1992, North Penn Area 7 Phase II RI/FS 

Work Plan. Work assignment no. 05-3LX1.0, contract 

no. 68-W8-0090: Prepared for the U.S. Environmental Protection Agency, February 1992.

Conger, R.W., 1999, Evaluation of geophysical logs at North 

Penn Area 6 Superfund Site, Lansdale, Montgomery 

County, Pennsylvania: U.S. Geological Survey Open-File 

Report 99–271A, 149 p.

Converse Consultants East, 1994, Report: Task 2—Investigation of regional and site groundwater quality Ford Electronics and Refrigeration Corporation (FERCO)—Church Road 

facility, Lansdale, Pennsylvania, Project No. 91-37322-07: 

Parsippany, N.J., Sept. 20, 1994, 2 vols.

Davis, S.N, Whittemore, D.O., Fabryka-Martin, 1998, Uses of 

chloride/bromide ratios in studies of potable water: Ground 

Water, v. 36, no. 2, p. 338–350.

Davis, S.N., Fabryka-Martin, J.T., and Wolfsberg, L.E., 2004, 

Variations of bromide in potable ground water in the United 

States: Ground Water, v. 42, no. 6, p. 902–909.

Durlin, R.R., and Schaffstall, W.P., 2000, Ground water in the 

clastic bedrock within the Triassic lowlands section of the 

Piedmont Physiographic Province, in Water resources data 

for Pennsylvania, water year 1999, volume 1, Delaware 

River Basin: U.S. Geological Survey Water-Data Report 

PA-00-1, p. 1–24, accessed December 3, 2010, at http://

pa.water.usgs.gov/infodata/surfacewater/annual_rpt/wy00/

pdfs/nawqa-piedmont.pdf.

Edmunds, W.M., 1996, Bromine geochemistry of British 

groundwaters: Mineralogical Magazine, v. 60, p. 275–284.

ESRI, 2006, ArcGIS 9.2, Using ArcGIS Desktop: Redlands, 

Calif., ESRI Inc., 452 p.

Geraghty & Miller, Inc., 1993, Evaluation of groundwater 

pumpage and containment at the Merck & Co., Inc., West 

Point, Pennsylvania, plant: Reston, Virginia, Dec. 3, 1993.

Golder and Associates, Inc., 2003, RI sampling data review, 

1190 Church Road, North Penn Area 7 Superfund site, letter 

dated October 28, 2003, to U.S. Environmental Protection 

Agency, accessed December 3, 2010, at http://loggerhead.

epa.gov/arweb/public/pdf/2037767.pdf.

Goode, D.J., and Senior, L.A., 1998, Review of aquifer test 

results for the Lansdale area, Montgomery County, Pennsylvania, 1980-95: U.S. Geological Survey Open-File Report 

98–294, 70 p.

Goode, D.J., and Senior, L.A., 2000, Simulation of aquifer tests 

and ground-water flow paths at the local scale in fractured 

shales and sandstones of the Brunswick Group and Lockatong Formation, Lansdale, Montgomery County, Pennsylvania: U.S. Geological Survey Open-File Report 00–97, 46 p.

Halford, K.J., 1999, Effects of steady-state assumption on 

hydraulic conductivity and recharge estimates in a surficial 

aquifer system: Ground Water, v. 37, no. 1, p. 70–79.

Harbaugh, A.W., Banta, E.R., Hill, M.C., and McDonald, 

M.G., 2000, MODFLOW-2000, The U.S. Geological Survey 

modular ground-water model—User’s guide to modularization concepts and the ground-water flow process: U.S. 

Geological Survey Open-File Report 00–92, 191 p.

Heimann, A.C., Friis, A.K, and Jakobsen, Rasmus, 2005, 

Effects of sulfate on anaerobic chloroethene degradation by 

an enriched culture under transient and steady-state hydrogen supply: Water Research, v. 39, no. 15, September 2005, 

p. 3579–3586.

Hill, M.C., Banta, E.R., Harbaugh, A.W., and Anderman, 

E.R., 2000, MODFLOW-2000, The U.S. Geological Survey 

modular ground-water model—User’s guide to the observation, sensitivity, and parameter-estimation processes and 

three post-processing programs: U.S. Geological Survey 

Open-File Report 00–184, 220 p.
References Cited 89

Hill, M.C., and Tiedeman, C.R, 2007, Effective groundwater model calibration: With analysis of data, sensitivities, 

predictions, and uncertainty: Hoboken, N.J., John Wiley & 

Sons, 455 p.

Insightful Corporation, 2008, S-Plus 7 for Windows statistical 

software documentation, accessed June 2, 2008, at http://

www.insightful.com/support/doc_splus_win.asp.

Johnson, A.I., 1967, Specific yield—compilation of specific 

yields for various materials: U.S. Geological Survey Water 

Supply Paper 1662-D, 74 p.

Kennedy, L.G., Everett, J.W., Ware, K.J., Parsons, Robert, 

and Green, Valerie, 1998, Iron and sulfur mineral analysis 

methods for natural attenuation assessments: Bioremediation Journal, v. 2, no. 3, p. 259–276.

Lewis-Brown, J.D., and Rice, D.E., 2002, Simulated groundwater flow, Naval Air Warfare Center, West Trenton, New 

Jersey: U.S. Geological Survey Water-Resources Investigations Report 02–4019, 44 p.

Lindsey, B.D., 2005, Hydrogeology and simulation of source 

areas of water to production wells in a colluvium-mantled 

carbonate-bedrock aquifer near Shippensburg, Cumberland, and Franklin Counties, Pennsylvania: U.S. Geological 

Survey Scientific Investigations Report 2005–5195, 49 p.

Longwill, S.M., and Wood, C.R., 1965, Ground-water 

resources of the Brunswick Formation in Montgomery and 

Berks Counties, Pennsylvania: Pennsylvania Geological 

Survey, 4th ser., Water Resource Report W22, 59 p.

Lyttle, P.T., and Epstein, J.B., 1987, Geologic map of the 

Newark 1° x 2° Quadrangle, New Jersey, Pennsylvania and 

New York: U.S. Geological Survey Miscellaneous Investigations Map I-1715, scale 1:250,000.

Martin, L.M, 1981, Source identification of TCE and other 

chlorinated organic groundwater pollutants in the upper 

Wissahickon watershed—phase II: Report prepared for the 

Wissahickon Valley Watershed Association in cooperation 

with the North Penn Water Authority, November 1981, 

141 p.

Neupauer, R.M., and J.L. Wilson, 2004, Numerical implementation of a backward probabilistic model of ground 

water contamination: Ground Water, v. 42, no. 2, 

p. 179–189.

Newport, T.G., 1971, Groundwater resources of Montgomery 

County, Pennsylvania: Pennsylvania Geological Survey, 

4th ser., Water Resource Report W29, 83 p.

Pollock, D.W., 1994, User’s Guide for MODPATH/MODPATH-PLOT, Version 3: A particle tracking post-processing 

package for MODFLOW, the U.S. Geological Survey 

finite-difference ground-water flow model: U.S. Geological 

Survey Open-File Report 94–464, 6 chap.

Prudic, D.E., 1989, Documentation of a computer program to 

simulate stream-aquifer relations using a modular, finite-difference, ground-water flow model: U.S. Geological Survey 

Open-File Report 88–729, 113 p.

Rima, D.R., 1955, Ground water resources of the Lansdale 

area, Pennsylvania: Pennsylvania Geological Survey, 4th 

ser., Prog. Report 146, 24 p.

Risser, D.W., and Bird, P.H., 2003, Aquifer tests and simulation of ground-water flow in Triassic sedimentary rocks near 

Colmar, Bucks and Montgomery Counties, Pennsylvania: 

U.S. Geological Survey Water-Resources Investigations 

Report 03–4159, 73 p.

Schlische, R.W., 1992, Structural and stratigraphic development of the Newark extensional basin, eastern North 

America—Evidence for growth of the basin and its bounding structures: Geological Society of America Bulletin, 

v. 104, p. 1246–1263.

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 Survey Scientific Investigations Report 2005–5069, 

129 p.

Senior, L.A., Conger, R.W., and Bird, P.H., 2008, 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, 2002–06: 

U.S. Geological Survey Scientific Investigations Report 

2008–5154, 277 p.

Senior, L.A., and Goode, D.J., 1999, Ground-water system, 

estimation of aquifer hydraulic properties, and effects of 

pumping on ground-water flow in Triassic sedimentary rocks 

in and near Lansdale, Pennsylvania: U.S. Geological Survey 

Water-Resources Investigations Report 99–4228, 112 p.

Senior, L.A., Rowland, C.A., and Prieto, D.A., 1998, Altitude 

and configuration of the potentiometric surface in Lansdale 

and vicinity, Montgomery County, Pennsylvania, August 

22–23, 1996: U.S. Geological Survey Open-File Report 

98–253, 1 plate, scale 1:24,000.
90 Groundwater System and Simulation of Flow for North Penn Area 7 Superfund Site, Montgomery County, Pennsylvania

Senior, L.A., and Ruddy, A.J., 2004, Altitude and configuration of the water-level surface in Mesozoic sedimentary 

rocks at and near the North Penn Area 7 Superfund site, 

Upper Gwynedd Township, Montgomery County, Pennsylvania, December 4–6, 2000: U.S. Geological Survey OpenFile Report 2004–1006, 1 pl., scale 1:24,000.

Senior, L.A., Sloto, R.A., and Reif, A.G., 1997, Hydrogeology 

and water quality of the West Valley Creek Basin, Chester 

County, Pennsylvania: U.S. Geological Survey WaterResources Investigations Report 94–4137, 160 p.

Senior, L.A., and Sloto, R.A., 2006, Arsenic, boron, and 

fluoride concentrations in ground water in and near diabase 

intrusions, Newark Basin, Southeastern Pennsylvania: U.S. 

Geological Survey Scientific Investigations Report 2006–

5261, 105 p. 

Sevon, W.D., comp., 2000, Physiographic provinces of Pennsylvania: Pennsylvania Geological Survey, 4th ser., map 13, 

scale 1:2,000,000.

Sloto, R.A., and Schreffler, C.L., 1994, Hydrogeology and 

ground-water quality of northern Bucks County, Pennsylvania: U.S. Geological Survey Water-Resources Investigations 

Report 94–4109, 85 p.

Starn, J.J., Bagtzoglou, A.C., and Robbins, G.A., 2010, Using 

atmospheric tracers to reduce uncertainty in groundwater 

recharge areas: Ground Water, v. 48, no. 6, p. 858–868.

Theis, C.V., 1935, The relation between the lowering of the 

piezometric surface and the rate and duration of discharge 

of a well using groundwater storage: Transactions American 

Geophysical Union, v. 16, p. 519–524.

Tiedeman, C. R., Lacombe, P. J. and Goode, D. J., 2010, Multiple well-shutdown tests and site-scale flow simulation in 

fractured rocks: Ground Water, v. 48, no. 3, p. 401–415.

Turner, D.P., 2006, Draft soil sampling summary tables, 

figures and the soil data validation narratives for the North 

Penn Area 7 Superfund Site, 205 Church Rd property, 

memorandum dated June 26, 2006, to site file: U.S. Environmental Protection Agency, accessed December 3, 2010, 

at http://loggerhead.epa.gov/arweb/public/pdf/2062825.pdf.

U.S. Environmental Protection Agency, 2010, NPL Site Narrative for Salford Quarry, accessed October 1, 2010, at: http://

www.epa.gov/superfund/sites/npl/nar1490.htm

VanHouten, F.B., 1962, Cyclic sedimentation and the origin of 

analcime-rich Upper Triassic Lockatong Formation, westcentral New Jersey and adjacent Pennsylvania: American 

Journal of Science, v. 260 no. 8, p. 561–576.

Vengosh, Avner, and Pankratov, Irena, 1998, Chloride/bromide 

and chloride/fluoride ratios of domestic sewage effluents 

and associated contaminated ground water: Ground Water, 

v. 36, no. 5, p. 815–824.

White, K.E., and Sloto, R.A., 1990, Base-flow frequency characteristics of selected Pennsylvania streams: U.S. Geological Survey Water-Resources Investigations Report 90–4169, 

67 p.

Wiedemeier, T.H., Swanson, M.A., Moutoux, D.E., Gordon, 

E.K., Wilson, J.T., Wilson, B.H., Kampbell, D.H., Haas, 

P.E., Miller, R.N., Hansen, J.E., and Chapelle, F.H., 1998, 

Technical protocol for evaluating natural attenuation of 

chlorinated solvents in ground water: U.S. Environmental 

Protection Agency report EPA/600/R-98/128, accessed 

February 14, 2012, at http://www.epa.gov/superfund/health/

conmedia/gwdocs/protocol.htm.

Winston, R.B., 2000, Graphical user interface for MODFLOW, version 4: U.S. Geological Survey Open-File 

Report 00–315, 27 p.
Table 6 91

Table 6. Water levels in wells used for calibration of the groundwater-flow model for North Penn Area 7 Superfund site, Upper 

Gwynedd Township and vicinity, Montgomery County, Pennsylvania.—Continued

[USGS, U.S. Geological Survey; UTM-18, Universal Transverse Mercator, zone 18; NAD 27, North American Datum of 1927; --. no data; altitude in meters 

above North American Vertical Datum of 1929; GPS, Global Positioning System]

USGS 

well 

identifier1

Owner’s 

well 

name or 

number

UTM-18/NAD 27 

coordinates 

(meters)

Altitude of open 

interval

(meters) 

Altitude of measured water levels

(meters) Data 

source2

Location 

method

USGS site 

identifier

Easting Northing Top of 

interval

Bottom of 

interval

1996 

calibration 

head

2000 

calibration 

head

2005 

calibration 

head

62 L-3 476031.6 4454323.5 102.14 -6.07 -- 98.94 -- c Surveyed 401428075165501

67 L-8 475198.3 4455205.6 93.39 10.18 95.75 -- -- b Surveyed 401456075173001

68 L-9 474698.3 4453930.4 95.59 -41.87 86.22 87.02 87.80 a Surveyed 401415075175101

69 L-10 474614.6 4454327.8 88.33 19.75 87.31 -- -- a Surveyed 401427075175401

72 L-13 476650.6 4452806.2 94.82 14.97 97.71 94.19 102.78 c Surveyed 401338075162801

80 475084.2 4455217.8 57.30 1.83 95.63 -- -- a Surveyed 401454075173401

81 LB6 475550.4 4454741.5 94.49 -2.13 92.90 -- -- a Surveyed 401442075171501

82 LB5 475426.0 4456017.1 89.12 -19.69 91.14 -- -- a Surveyed 401523075171801

90 Ford 2 475894.6 4452773.9 94.34 21.79 -- 94.68 -- c Map 401337075170001

135 Ford 3 475752.0 4452590.1 66.60 -18.14 -- 94.15 -- c Map 401331075170601

138 475996.3 4453934.4 108.69 -13.84 102.49 100.19 -- a Surveyed 401415075165601

143 L-21 473750.5 4454693.4 80.77 -32.00 88.18 -- -- a Map 401439075183101

147 Ford 4 476035.8 4452743.4 92.35 -5.18 -- 95.52 -- c Map 401336075165401

152 AO1 476207.0 4455360.7 101.22 46.06 93.38 -- -- a Surveyed 401503075164301

154 475829.7 4454932.1 99.21 49.53 93.39 -- -- a Surveyed 401447075170301

157 475245.5 4455567.4 82.88 10.33 95.43 -- -- a Surveyed 401507075173001

163 474854.8 4455113.3 94.24 11.64 95.79 -- -- b Surveyed 401453075174401

164 474925.4 4454959.8 94.52 -19.78 95.10 -- -- a Surveyed 401448075174101

174 CL-2 476163.2 4452060.5 95.59 62.07 -- 95.92 -- c Map 401315075164901

175 RI-7I3 476252.0 4451808.6 104.32 61.65 -- 98.54 -- c Map 401306075164401

498 L-23 474203.9 4455370.7 76.99 -66.26 97.94 -- -- a Surveyed 401501075181201

618 476496.1 4455538.2 96.86 6.79 93.14 -- -- a Surveyed 401506075163501

621 AO4 476096.5 4456005.3 80.56 -22.16 94.70 -- -- a Surveyed 401521075164901

623 L-24 474841.5 4456444.2 70.41 -54.56 93.52 -- -- a Surveyed 401536075174101

624 475310.0 4456197.7 69.22 -92.32 91.83 -- -- a Surveyed 401527075172601

630 471391.9 4455841.9 82.30 48.77 70.64 -- -- b Map 401516075201101

704 L-26 475650.3 4456241.4 71.14 -25.48 91.17 -- -- a Surveyed 401532075170801

930 472916.8 4452846.1 66.45 42.06 72.80 -- -- a Map 401339075190601

1045 AO5 476490.5 4455882.0 87.14 2.71 93.18 -- -- a Surveyed 401518075163501

1124 476838.8 4455203.7 95.75 -13.98 97.40 98.9 -- a Surveyed 401504075161501

1126 477147.5 4455626.7 93.99 5.30 96.00 -- -- d GPS 401516075155901

1128 473375.2 4455579.7 83.00 -65.75 80.95 -- -- a Surveyed 401508075184801

1144 475513.6 4452035.9 96.41 76.60 -- 93.56 -- c Map 401314075171801

1145 T-14 475608.0 4452004.5 94.96 75.15 -- 93.69 97.64 c Map 401314075171401

1146 T-4 475632.5 4452219.7 98.97 79.16 -- 94.62 98.30 c Map 401318075171101

1147 T-11 475611.8 4452323.5 100.25 80.44 -- 94.67 98.86 c Map 401322075171201

1148 T-12 475538.6 4452374.3 104.12 84.31 -- 94.61 98.78 c Map 401324075171601

1149 T-10 475490.6 4452282.3 103.30 83.48 -- 94.30 98.43 c Map 401321075171701

1169 475871.5 4453021.1 106.68 91.74 101.42 -- -- a Map 401345075170101

1179 473808.4 4457899.9 97.84 -62.48 76.22 -- -- b Map 401623075182901

1270 477157.9 4455334.6 97.99 6.25 98.15 99.58 -- a Surveyed 401506075160001

1284 476764.6 4459000.1 68.58 -42.98 90.73 -- -- b Map 401659075162401

1440 475649.9 4455672.1 100.68 38.65 95.25 -- -- a Surveyed 401511075171101

1441 474508.8 4453321.5 89.37 40.87 80.46 -- -- a Surveyed 401354075175901

1442 475621.7 4454801.2 100.28 79.86 93.26 -- -- a Surveyed 401443075171201
92 Groundwater System and Simulation of Flow for North Penn Area 7 Superfund Site, Montgomery County, Pennsylvania

Table 6. Water levels in wells used for calibration of the groundwater-flow model for North Penn Area 7 Superfund site, Upper 

Gwynedd Township and vicinity, Montgomery County, Pennsylvania.—Continued

[USGS, U.S. Geological Survey; UTM-18, Universal Transverse Mercator, zone 18; NAD 27, North American Datum of 1927; --. no data; altitude in meters 

above North American Vertical Datum of 1929; GPS, Global Positioning System]

USGS 

well 

identifier1

Owner’s 

well 

name or 

number

UTM-18/NAD 27 

coordinates 

(meters)

Altitude of open 

interval

(meters) 

Altitude of measured water levels

(meters) Data 

source2

Location 

method

USGS site 

identifier

Easting Northing Top of 

interval

Bottom of 

interval

1996 

calibration 

head

2000 

calibration 

head

2005 

calibration 

head

1443 476118.5 4455278.1 103.97 34.17 94.17 -- -- a Surveyed 401457075165301

1444 475670.8 4453694.1 106.38 22.25 95.93 93.99 -- a Surveyed 401407075165901

1445 476366.6 4455754.2 99.15 43.37 93.47 -- -- a Surveyed 401513075163901

1446 476361.7 4455514.7 103.30 65.20 93.18 -- -- a Surveyed 401504075164101

1447 476305.4 4455674.1 100.77 62.36 93.29 -- -- a Surveyed 401508075164401

1448 474190.7 4452163.3 95.40 79.55 90.50 -- -- a Map 401317075181201

1449 472202.6 4454955.4 71.63 45.87 77.46 -- 77.35 d GPS 401446075193701

1450 474644.7 4453641.7 96.93 72.54 86.90 -- -- a Map 401406075175501

1451 473034.3 4452537.1 79.25 50.29 76.49 75.23 -- c Map 401329075190101

1452 473865.7 4453860.2 94.49 -24.38 91.40 -- -- a Map 401412075182601

1453 472949.9 4455466.7 77.72 17.68 81.11 -- -- b Map 401504075190501

1454 473022.2 4455867.2 84.73 83.58 86.65 -- -- b Map 401517075190201

1455 474428.7 4452778.7 93.27 34.44 91.70 92.14 -- a Map 401337075180201

1456 471577.4 4454885.9 73.15 1.83 89.24 -- -- b Map 401445075200301

1457 471973.7 4453435.4 79.55 55.17 73.08 -- -- b Map 401358075194601

1458 471617.8 4453066.7 75.90 55.29 66.47 -- -- b Map 401346075200101

1459 471976.0 4454052.0 77.72 53.34 68.90 -- -- a Map 401418075194601

1460 476819.6 4456115.2 92.26 30.39 92.54 -- -- a Surveyed 401527075162301

1461 477585.1 4457085.6 81.69 14.94 88.10 -- -- a Map 401557075154901

1462 478097.9 4454709.5 126.19 101.80 122.80 121.09 -- a Map 401440075152701

1463 476076.1 4457294.7 75.04 29.02 87.17 -- -- a Surveyed 401604075165001

1464 473382.5 4457561.7 87.63 16.46 65.55 -- -- b Map 401612075184701

1465 474824.8 4458050.1 76.50 -21.03 91.50 -- -- b Map 401628075174601

1466 475862.2 4457491.7 82.91 59.44 85.85 -- -- b Map 401610075170201

1467 475523.1 4456746.3 86.75 79.74 88.30 -- -- a Surveyed 401547075171501

1468 476616.3 4456934.4 84.43 54.86 83.73 -- -- a Map 401552075163001

1469 476047.4 4456319.5 92.96 68.58 93.30 -- -- a Map 401532075165401

1470 472476.5 4455221.8 81.08 80.89 84.78 -- -- b Map 401456075192501

1471 472512.3 4452076.8 68.28 15.54 79.14 -- -- b Map 401314075192301

1472 471947.6 4452788.0 75.59 51.21 71.74 -- -- b Map 401337075194701

1473 471894.5 4451247.1 91.44 67.06 93.92 93.23 -- c Map 401247075194901

1474 472739.3 4456053.3 87.78 55.47 87.63 -- -- b Map 401523075191401

1475 473316.2 4452135.4 84.73 60.35 86.75 85.83 -- c Map 401316075184901

1476 472655.2 4452415.3 67.97 54.25 74.28 74.59 -- c Map 401325075191701

1477 474619.0 4452932.3 92.96 50.29 92.45 90.06 -- a Map 401342075175401

1478 474291.6 4454043.7 90.83 29.87 86.71 -- -- a Map 401418075180801

1479 472397.5 4453002.1 80.16 55.78 75.34 -- -- b Map 401344075192801

1480 478028.5 4455234.4 116.43 92.05 115.95 -- -- a Map 401457075153001

1481 473391.1 4453306.9 84.43 -0.91 82.46 -- -- a Map 401354075184601

1482 472819.4 4451951.8 91.74 63.09 82.87 81.87 -- c Map 401309075190901

1483 474476.3 4456106.4 100.00 75.62 94.19 -- -- a Surveyed 401526075180101

1484 475245.4 4456461.0 72.51 -34.17 83.88 -- -- b Surveyed 401537075172701

1485 473161.5 4455188.4 81.38 57.00 78.30 -- -- a Map 401455075185601

1487 474273.1 4455554.6 97.54 73.15 92.00 -- -- a Map 401507075180901

1488 470326.7 4455260.7 66.45 -14.02 61.55 -- -- b Map 401457075205601
Table 6 93

Table 6. Water levels in wells used for calibration of the groundwater-flow model for North Penn Area 7 Superfund site, Upper 

Gwynedd Township and vicinity, Montgomery County, Pennsylvania.—Continued

[USGS, U.S. Geological Survey; UTM-18, Universal Transverse Mercator, zone 18; NAD 27, North American Datum of 1927; --. no data; altitude in meters 

above North American Vertical Datum of 1929; GPS, Global Positioning System]

USGS 

well 

identifier1

Owner’s 

well 

name or 

number

UTM-18/NAD 27 

coordinates 

(meters)

Altitude of open 

interval

(meters) 

Altitude of measured water levels

(meters) Data 

source2

Location 

method

USGS site 

identifier

Easting Northing Top of 

interval

Bottom of 

interval

1996 

calibration 

head

2000 

calibration 

head

2005 

calibration 

head

1489 472332.6 4454636.5 72.73 42.67 67.70 -- -- a Map 401437075193101

1490 473277.1 4454478.9 89.31 55.78 85.32 -- -- a Map 401432075185101

1491 473706.3 4455587.3 58.83 56.69 89.04 -- -- a Map 401508075183301

1492 471317.9 4454979.4 88.70 64.31 85.67 -- -- b Map 401448075201401

1493 471269.0 4454548.0 79.25 54.86 82.70 -- -- b Map 401434075201601

1494 474085.2 4455863.5 93.88 69.49 91.54 -- -- a Map 401517075181701

1495 474182.3 4449727.7 101.50 63.40 95.57 -- -- b Map 401158075181201

1496 473426.6 4449915.2 85.95 55.47 89.83 89.34 -- c Map 401204075184401

1497 475258.1 4453238.8 100.22 68.21 95.22 93.03 -- a Map 401352075172701

1498 477295.7 4454959.4 110.34 85.95 109.95 109.61 -- a Map 401448075160101

1499 475155.4 4456528.3 81.84 68.43 92.00 -- -- a Surveyed 401539075173201

1500 477091.9 4458012.0 85.04 60.66 86.24 -- -- b Map 401627075161001

1501 478074.9 4455018.2 124.97 100.58 125.01 123.88 -- a Map 401450075152801

1502 477114.4 4457642.0 82.91 67.06 84.21 -- -- b Map 401615075160901

1503 476899.3 4456810.2 90.83 86.26 95.40 -- -- a Map 401548075161801

1504 473358.8 4450964.3 98.15 99.36 103.78 103.58 -- c Map 401238075184701

1505 476033.1 4451911.0 100.04 79.56 98.13 97.77 -- c Map 401309075165401

1506 477574.3 4455348.0 107.96 83.58 111.45 -- -- a Surveyed 401502075155201

1507 472697.1 4450812.4 95.40 58.83 91.96 92.55 -- c Map 401233075191501

1508 476809.8 4458413.7 91.44 67.06 88.88 -- -- b Map 401640075162201

1509 477280.0 4457734.0 85.95 64.62 87.78 -- -- b Map 401618075160201

1510 476005.0 4457830.4 87.48 63.09 85.70 -- -- b Map 401621075165601

1511 478638.9 4453845.6 122.53 75.29 124.89 124.89 -- c Map 401412075150401

1533 476174.3 4455314.9 101.29 76.90 93.48 -- -- a Surveyed 401459075164701

1537 N1 474711.0 4452222.8 87.32 84.27 92.32 88.96 89.65 a Map 401319075175001

1538 N2 474781.0 4452038.3 90.39 87.34 96.84 94.73 98.56 a Map 401313075174701

1539 N30 475181.6 4451728.4 74.98 71.93 94.20 91.85 95.45 a Map 401303075173001

1540 N4 475489.8 4452035.9 79.75 76.70 96.90 93.88 97.68 a Map 401313075171701

1541 N5 475062.3 4451420.2 64.04 60.99 78.78 72.46 72.53 a Map 401253075173501

1542 N6 474800.9 4450835.0 72.85 69.80 91.45 -- -- a Map 401234075174601

1543 N7 474967.2 4451205.2 63.11 60.07 81.46 71.34 70.71 a Map 401246075173901

1544 N8 474493.2 4450712.9 73.24 70.20 92.33 90.74 92.01 c Map 401230075175901

1545 N9 473900.8 4450437.4 78.03 71.94 88.35 87.58 88.81 c Map 401221075182401

1546 N10 474232.5 4450621.6 72.54 69.49 86.87 85.61 88.93 c Map 401227075181001

1547 N11 474304.9 4450898.9 77.93 74.89 85.65 81.92 88.06 c Map 401236075180701

1548 N12 473217.2 4450871.6 75.81 72.76 84.19 78.45 78.45 c Map 401235075185301

1549 N12D 473217.2 4450871.6 8.42 -0.73 81.60 78.64 78.72 c Map 401235075185302

1550 N13 473406.9 4451087.3 77.85 74.80 83.10 77.83 -- c Map 401242075184501

1551 N16 473810.6 4451670.9 72.25 69.20 87.54 84.46 85.49 a Map 401301075182801

1552 N17 474000.3 4451886.6 83.84 80.79 90.57 86.92 88.00 a Map 401308075182001

1553 N19 474569.4 4452347.5 77.23 74.18 92.52 88.57 89.69 a Map 401323075175601

1554 N20 474190.6 4452071.3 85.80 79.71 91.49 87.38 89.04 a Map 401314075181201

1555 N20D 474213.6 4452071.3 23.56 17.47 90.13 75.58 -- c Map 401314075181101

1556 N21 474567.8 4451884.7 78.46 75.42 91.29 91.14 95.70 a Map 401308075175601

1557 N22 474804.0 4451760.7 81.08 78.03 92.93 91.29 95.41 a Map 401304075174601
94 Groundwater System and Simulation of Flow for North Penn Area 7 Superfund Site, Montgomery County, Pennsylvania

Table 6. Water levels in wells used for calibration of the groundwater-flow model for North Penn Area 7 Superfund site, Upper 

Gwynedd Township and vicinity, Montgomery County, Pennsylvania.—Continued

[USGS, U.S. Geological Survey; UTM-18, Universal Transverse Mercator, zone 18; NAD 27, North American Datum of 1927; --. no data; altitude in meters 

above North American Vertical Datum of 1929; GPS, Global Positioning System]

USGS 

well 

identifier1

Owner’s 

well 

name or 

number

UTM-18/NAD 27 

coordinates 

(meters)

Altitude of open 

interval

(meters) 

Altitude of measured water levels

(meters) Data 

source2

Location 

method

USGS site 

identifier

Easting Northing Top of 

interval

Bottom of 

interval

1996 

calibration 

head

2000 

calibration 

head

2005 

calibration 

head

1558 N22D 474803.9 4451760.7 9.70 -2.49 89.36 85.81 90.30 c Map 401304075174602

1559 N23 474921.9 4451667.1 77.11 74.07 93.50 -- -- a Map 401301075174101

1560 N24 474733.0 4451667.7 81.99 78.94 91.79 -- -- a Map 401301075174901

1561 N25 474589.1 4451144.3 70.43 67.39 87.57 84.85 87.80 a Map 401244075175501

1562 N26 473644.5 4451364.0 80.22 77.18 84.03 74.92 75.11 c Map 401251075183501

1563 N28 473739.6 4451547.9 73.00 69.95 85.22 80.40 80.66 a Map 401257075183101

1564 N29 473999.7 4451732.4 80.64 77.59 89.56 85.63 86.49 a Map 401303075182001

1565 N30 473905.0 4451640.6 69.74 66.69 88.24 69.21 84.72 a Map 401300075182401

1566 3-85 474379.4 4452039.6 77.28 74.23 89.87 85.97 86.92 a Map 401313075180401

1567 4-85 474896.6 4451236.5 63.40 60.35 79.20 -- 70.37 a Map 401247075174201

1568 6-85 474045.6 4451208.3 93.78 71.84 75.67 77.39 84.78 c Map 401246075181801

1569 7-85 474872.2 4451051.2 91.44 73.46 83.80 -- 88.18 a Map 401241075174301

1570 9-85 473975.9 4451486.0 75.90 72.85 78.30 -- 75.66 a Map 401255075182101

1571 10-85 474756.4 4451791.9 88.24 85.19 91.64 89.39 93.86 a Map 401305075174801

1572 11-85 474139.4 4451022.6 76.57 73.52 83.60 80.67 87.26 c Map 401240075181401

1600 Rog 3I 475689.6 4453755.5 71.52 65.42 -- 96.37 98.98 c Surveyed 401409075170701

1601 Rog 3S 475692.2 4453758.1 106.20 80.81 -- 91.87 94.41 c Surveyed 401409075170702

1602 Rog 2I 475720.0 4453665.0 81.67 75.57 -- 95.91 98.45 c Surveyed 401406075170601

1603 Rog 2S 475721.9 4453667.5 110.32 85.02 -- -- 94.14 Surveyed

1822 477919.2 4451619.7 133.50 35.05 -- 129.74 -- d GPS 401300075153301

1823 475772.5 4449852.2 86.87 64.01 -- 91.54 -- d GPS 401203075170301

1824 474833.5 4450306.3 88.39 88.39 -- 89.41 -- d GPS 401217075174301

1825 477592.7 4451598.4 129.84 129.84 -- 134.26 -- d GPS 401259075154701

1827 476742.3 4450246.3 104.24 11.89 -- 105.88 -- d GPS 401215075162201

1828 473751.1 4449861.7 91.44 68.58 -- 92.17 -- d GPS 401203075182901

1829 473715.7 4449461.0 94.49 57.30 -- 93.88 -- d GPS 401150075183001

1830 475875.0 4449525.4 102.11 77.72 -- 93.26 -- c Map 401152075165901

1831 476369.7 4448960.8 99.36 19.20 -- 100.92 -- d GPS 401134075163801

1832 478156.1 4453403.3 124.36 99.97 -- 108.61 -- c Map 401358075152301

1833 474724.7 4449294.2 111.25 77.72 -- 99.70 -- c Map 401144075174901

1834 475787.6 4450132.1 103.02 78.64 -- 97.69 -- d GPS 401212075170301

1835 475453.1 4449624.8 90.83 28.35 -- 87.54 -- d GPS 401155075171701

1836 475948.6 4451109.9 99.06 63.09 -- 97.53 -- d GPS 401243075165601

1837 474867.7 4449153.1 111.25 62.48 -- 105.62 -- d GPS 401140075174201

1838 474789.2 4452531.0 102.11 78.33 -- 90.08 -- d GPS 401329075174501

1839 472972.6 4451389.7 94.49 70.10 -- 91.00 -- d GPS 401252075190201

1840 476867.2 4452712.4 106.68 42.98 -- 99.79 -- d GPS 401335075161701

1841 SF-2 476256.6 4451862.7 110.21 79.73 -- 98.53 102.11 d GPS 401308075165401

1842 T-15 475647.0 4452280.3 100.87 80.45 -- 94.38 98.46 c Surveyed 401323075171201

1843 475688.4 4452231.1 98.09 92.30 -- 95.27 -- d GPS 401320075171101

1844 476519.4 4451658.7 108.87 97.74 -- 100.21 103.53 c Surveyed 401302075163301

1845 476520.2 4451640.3 107.94 97.27 -- 99.77 103.53 c Surveyed 401300075163401

1846 476465.7 4451764.3 107.04 96.37 -- 99.29 103.26 d Surveyed 401305075163601

1847 475973.3 4452512.8 98.17 90.55 -- 95.46 99.76 d Surveyed 401329075165701

1848 475998.9 4452322.1 94.57 90.00 -- 95.51 99.75 d Surveyed 401323075165601
Table 6 95

Table 6. Water levels in wells used for calibration of the groundwater-flow model for North Penn Area 7 Superfund site, Upper 

Gwynedd Township and vicinity, Montgomery County, Pennsylvania.—Continued

[USGS, U.S. Geological Survey; UTM-18, Universal Transverse Mercator, zone 18; NAD 27, North American Datum of 1927; --. no data; altitude in meters 

above North American Vertical Datum of 1929; GPS, Global Positioning System]

USGS 

well 

identifier1

Owner’s 

well 

name or 

number

UTM-18/NAD 27 

coordinates 

(meters)

Altitude of open 

interval

(meters) 

Altitude of measured water levels

(meters) Data 

source2

Location 

method

USGS site 

identifier

Easting Northing Top of 

interval

Bottom of 

interval

1996 

calibration 

head

2000 

calibration 

head

2005 

calibration 

head

1849 476042.8 4452349.9 95.69 91.11 -- 96.10 100.58 d Surveyed 401324075165401

1897 CL-3 476091.4 4452155.2 89.33 14.96 -- 96.52 99.44 d GPS 401317075165201

2080 RI-1D 475961.0 4452977.6 69.98 63.88 -- -- 102.25 e Surveyed 401344075165601

2081 RI-2D 475737.0 4452030.8 16.53 10.44 -- -- 84.02 e Surveyed 401313075170501

2082 RI-2I 475735.1 4452030.4 46.94 43.89 -- -- 85.37 e Surveyed 401313075170502

2083 RI-2S 475733.2 4452029.9 87.00 82.23 -- -- 97.05 e Surveyed 401313075170503

2084 RI-3D 475903.3 4452567.4 58.03 51.93 -- -- 99.22 e Surveyed 401331075165801

2085 RI-3I 475902.9 4452565.6 77.63 71.54 -- -- 99.62 e Surveyed 401331075165802

2086 RI-3S 475902.5 4452564.1 98.29 92.20 -- -- 99.55 e Surveyed 401331075165803

2087 RI-4D 475613.7 4452288.9 48.07 41.97 -- -- 98.41 e Surveyed 401322075171001

2088 RI-4I 475615.6 4452288.1 82.73 79.68 -- -- 98.44 e Surveyed 401322075171002

2089 RI-4S 475617.4 4452286.9 88.82 85.77 -- -- 98.77 e Surveyed 401322075171003

2090 RI-5D 475603.9 4452826.5 22.23 16.13 -- -- 100.49 e Surveyed 401339075171101

2091 RI-5I 475601.7 4452826.2 84.36 78.27 -- -- 101.36 e Surveyed 401339075171102

2092 RI-5S 475602.2 4452828.1 95.34 89.24 -- -- 101.65 e Surveyed 401339075171103

2093 RI-6D 476355.7 4452304.4 53.68 47.58 -- -- 100.81 e Surveyed 401322075163901

2094 RI-6S 476354.4 4452305.4 92.90 86.81 -- -- 101.73 e Surveyed 401322075163902

2095 RI-7D 476255.6 4451811.1 57.17 51.08 -- -- 103.40 e Surveyed 401306075164301

2096 RI-7S 476253.7 4451809.8 94.64 88.55 -- -- 102.22 e Surveyed 401306075164302

2097 RI-8D 475990.2 4451576.1 32.23 26.13 -- -- 103.13 e Surveyed 401259075165401

2098 RI-8I 475988.2 4451575.5 90.10 80.96 -- -- 101.45 e Surveyed 401259075165402

2099 RI-8S 475985.8 4451574.7 99.23 93.14 -- -- 101.45 e Surveyed 401259075165403

2100 RI-9D 475451.0 4451457.3 26.27 20.17 -- -- 92.49 e Surveyed 401255075171701

2101 RI-9I 475449.2 4451455.8 51.95 45.86 -- -- 83.74 e Surveyed 401255075171702

2102 RI-9S 475447.0 4451454.0 78.27 72.17 -- -- 81.99 e Surveyed 401255075171703

2119 RI-10D 475228.5 4452361.5 47.68 41.59 -- -- 98.47 e Surveyed 401324075172601

2120 RI-10I 475229.9 4452359.9 78.29 72.19 -- -- 99.56 e Surveyed 401324075172602

2121 RI-10S 475231.3 4452358.0 91.44 85.34 -- -- 99.66 e Surveyed 401324075172603

2122 RI-11D 476193.1 4451941.2 32.47 26.38 -- -- 103.31 e Surveyed 401310075164601

2123 RI-11I 476190.9 4451940.8 84.09 77.99 -- -- 101.40 e Surveyed 401310075164602

2124 RI-11S 476189.0 4451940.2 96.14 90.05 -- -- 100.89 e Surveyed 401310075164603

2125 RI-12D 475557.5 4453168.5 58.15 52.05 -- -- 95.30 e Surveyed 401350075171301

2126 RI-13D 475461.5 4452734.5 44.64 38.54 -- -- 100.27 e Surveyed 401336075171701

2127 RI-13I 475460.1 4452732.6 73.31 67.21 -- -- 101.07 e Surveyed 401336075171702

2128 RI-13S 475458.8 4452731.0 92.79 86.69 -- -- 100.96 e Surveyed 401336075171703

1

MG- prefix omitted.

2

Data sources:

a, 1996 data used in 1999 North Penn Area 6 model (except at wells 498, 618, and 624, which were probably in error)

b, 1996 data not used in 1999 North Penn Area 6 model

 c, 2000 data

d, 2000 data for wells first measured for 2000 water-level map

e, 2005 data from new monitor wells at North Penn Area 7

3

Well MG-175 orginally drilled as production well for Spra-Fin and later converted to screened monittor well RI-7I in 2004.

For additional information:

Director

U.S. Geological Survey

215 Limekiln Road

New Cumberland, PA 17070

http://pa.water.usgs.gov/

Document prepared by the West Trenton Publishing Service Center
Senior and Goode—Groundwater System and Simulation of Flow for North Penn Area 7 Superfund Site, Montgomery County, Pa.—Scientific Investigations Report 2013–5045

Cell containing

pumped well NORTHWEST SOUTHEAST

Layer 1 Layer 2 Layer 3

Layer 4

Layer 5

Layer 6

Layer 10

Layer 11

Layer 7

Layer 8

Layer 9

VERTICAL EXAGGERATION x 10.0

0 1,000 METERS 0 5,000 FEET