U.S. Department of the Interior

U.S. Geological Survey

Open-File Report 2010–1058

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

Preliminary Investigation of Paleochannels and 

Groundwater Specific Conductance using Direct-Current 

Resistivity and Surface-Wave Seismic Geophysical 

Surveys at the Standard Chlorine of Delaware, Inc., 

Superfund Site, Delaware City, Delaware, 2008
Cover. Three-dimensional view of direct-current resistivity cross sections and wells, looking from the northeast to the southwest, 

Standard Chlorine of Delaware Inc., Superfund Site, Delaware City, Delaware.
Preliminary Investigation of Paleochannels 

and Groundwater Specific Conductance using 

Direct-Current Resistivity and Surface-Wave 

Seismic Geophysical Surveys at the Standard 

Chlorine of Delaware, Inc., Superfund Site, 

Delaware City, Delaware, 2008

By James R. Degnan and Michael J. Brayton

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

Open-File Report 2010–1058

U.S. Department of the Interior

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

KEN SALAZAR, Secretary

U.S. Geological Survey

Marcia K. McNutt, Director

U.S. Geological Survey, Reston, Virginia: 2010

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reproduce any copyrighted materials contained within this report.

Suggested citation:

Degnan, J.R., and Brayton, M.J., 2010, Preliminary investigation of paleochannels and groundwater specific 

conductance using direct-current resistivity and surface-wave seismic geophysical surveys at the Standard 

Chlorine of Delaware, Inc., Superfund Site, Delaware City, Delaware, 2008: U.S. Geological Survey Open-File 

Report 2010–1058, 27 p., at http://pubs.usgs.gov/of/2010/1058/.
iii

Acknowledgments

The authors of this report would like to recognize the work and dedication of Bernice Pasquini 

(1962–2009) of the U.S. Environmental Protection Agency. Bernice was instrumental in providing 

background and perspective for a variety of technical and regulatory issues related to the 

Standard Chlorine of Delaware, Inc., Superfund Site. Her recommendations and knowledge 

of the site hydrology and geology have served as a foundation for ongoing investigations of 

contaminant transport and cross-aquifer interaction. 

Logistical support, data, and explanations of site history and hydrogeology from Hilary Thornton 

and Bernice Pasquini, U.S. Environmental Protection Agency (USEPA), Region III; Todd Keyser, 

Delaware Department of Natural Resources and Environmental Control (DNREC); and Chris 

Wolfe, HydroGeoLogic, Inc., were essential in the planning of this investigation and the analysis 

of the results of these surveys. Data collection would not have been possible without field 

assistance from Todd Keyser, John Cargill, John Barndt, and Doug Rambo, all of DNREC, and 

Jessica Teunis, Noel Stroik, Jeffrey Raffensperger, Luke Myers, and Brandon Fleming, all of 

the U.S. Geological Survey (USGS) MD-DE-DC Water Science Center. Equipment and technical 

advice provided by John Lane and Carole Johnson of the USGS Branch of Geophysics, and Wade 

Kress and Andrew Teeple of the USGS West Texas Program Office, made high-quality data 

collection possible. Site visits, sharing of results, and discussions of regional and neighboring 

site geology with Thomas E. McKenna, Delaware Geological Survey, John Jengo, Suzanne Eckel, 

and Bryn Welker from MWH (engineering firm), and Stephen J. Zahniser from URS Corporation 

(engineering firm) helped the authors conceptualize the hydrogeologic system.
iv

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v

Contents

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

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

Introduction.....................................................................................................................................................1

Site Description.....................................................................................................................................3

Purpose and Scope ..............................................................................................................................3

Hydrogeologic Setting .........................................................................................................................3

Methods of Surface Geophysical Data Collection and Analysis...........................................................5

Direct-Current Resistivity ....................................................................................................................5

Multi-Channel Analysis of Surface Waves.......................................................................................6

Paleochannels and Groundwater Specific Conductance .............................................................6

Results of Geophysical Surveys, Paleochannels and Relation to Groundwater Specific 

Conductance.....................................................................................................................................7

Direct-Current Resistivity ....................................................................................................................7

Multi-Channel Analysis of Surface Waves.......................................................................................7

Paleochannels and Groundwater Specific Conductance ...........................................................12

Summary........................................................................................................................................................17

References Cited..........................................................................................................................................18

Appendix 1. Direct-Current Resistivity Cross Sections with nearby Well Water Levels, 

Screened Intervals, and Specific Conductance Values ..........................................................21

Figures

1. (A) Map showing site location in the State of Delaware and (B) generalized geologic 

cross section, Standard Chlorine of Delaware, Inc., Superfund Site, 

Delaware City, Delaware.............................................................................................................2

2. Map showing locations of geophysical-survey lines and wells, Standard Chlorine of 

Delaware, Inc., Superfund Site, Delaware City, Delaware....................................................4

3. Cross sections showing direct-current resistivity results from (A) line 1, (B) line 2, 

(C) line 13, (D) line 3, (E) line 9, and (F) line 25, Standard Chlorine of Delaware, Inc., 

Superfund Site, Delaware City, Delaware................................................................................8

4. Cross sections showing direct-current resistivity results from (A) line 4, (B) line 5, 

(C) line 20, and (D) line 11, Standard Chlorine of Delaware, Inc., Superfund Site, 

Delaware City, Delaware.............................................................................................................9

5. Cross sections showing direct-current resistivity results from (A) line 8, (B) line 6, 

(C) line 10, and (D) line 12, Standard Chlorine of Delaware, Inc., Superfund Site, 

Delaware City, Delaware...........................................................................................................10

6. Cross sections showing direct-current resistivity results from (A) line 24, (B) line 21, 

and (C) line 7, Standard Chlorine of Delaware, Inc., Superfund Site, 

Delaware City, Delaware...........................................................................................................11
vi

7. Cross sections showing multi-channel analysis of surface waves (MASW) results 

from (A) line 15, (B) line 14, and (C) line 16, Standard Chlorine of Delaware, Inc., 

Superfund Site, Delaware City, Delaware..............................................................................12

8. Cross sections showing multi-channel analysis of surface waves (MASW) results 

from (A) line 17, (B) line 18, and (C) line 19, Standard Chlorine of Delaware, Inc., 

Superfund Site, Delaware City, Delaware..............................................................................13

9. Cross section showing co-located surface geophysical results from (A) line 17 

multi-channel analysis of surface waves (MASW) with stiff layer interpretation 

in black and (B) line 20 direct-current resistivity with MASW projected 

interpretation, Standard Chlorine of Delaware, Inc., Superfund Site, 

Delaware City, Delaware...........................................................................................................14

10. Cross section showing co-located surface geophysical results from (A) line 18 

multi-channel analysis of surface waves (MASW) with stiff layer interpretation in 

black, and (B) line 4 direct-current resistivity with MASW projected interpretation, 

Standard Chlorine of Delaware, Inc., Superfund Site, Delaware City, Delaware............15

11. Cross section showing co-located surface geophysical results from (A) lines 14 

(left) and 15 (right) multi-channel analysis of surface waves (MASW) with stiff 

layer interpretation in black, and (B) line 24 direct-current resistivity with MASW 

projected interpretation, Standard Chlorine of Delaware, Inc., 

Superfund Site, Delaware City, Delaware..............................................................................16

12. Graph showing relation between specific-conductance measurements from wells 

and resistivity values at screened-interval depths from adjacent cross sections, 

Standard Chlorine of Delaware, Inc., Superfund Site, Delaware City, Delaware............17

Tables

1. Relative response of direct-current resistivity and multi-channel analysis of surface 

waves to material, unsaturated sand, and specific conductance of groundwater...........7
vii

Conversion Factors, Datums, and Acronyms

Multiply By To obtain

Length

meter (m) 3.281 foot (ft) 

meter (m) 1.094 yard (yd) 

kilometer (km) 0.6214 mile (mi)

Flow rate

meter per second (m/s) 3.281 foot per second (ft/s) 

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)

Horizontal coordinate information is referenced to the North American Datum of 1983 (NAD 83)

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

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

25°C).

Resistivity is given in Ohm meters.

ACRONYMS USED IN REPORT

USEPA U.S. Environmental Protection Agency

USGS U.S. Geological Survey

DNAPL Dense Non-Aqueous Phase Liquid

SCD Standard Chlorine of Delaware, Inc.

SC Specific conductance

DC Direct current

MASW Multi-channel analysis of surface waves
viii

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Preliminary Investigation of Paleochannels and 

Groundwater Specific Conductance using Direct-Current 

Resistivity and Surface-Wave Seismic Geophysical 

Surveys at the Standard Chlorine of Delaware, Inc., 

Superfund Site, Delaware City, Delaware, 2008

By James R. Degnan and Michael J. Brayton

Abstract

The U.S. Geological Survey (USGS), in cooperation 

with Region III of the U.S. Environmental Protection Agency 

(USEPA) and the State of Delaware, is conducting an ongoing 

study of the water-quality and hydrogeologic properties of the 

Columbia and Potomac aquifers and the extent of cross-aquifer contamination with benzene; chlorobenzene; 1,2-dichlorobenzene; 1,4-dichlorobenzene; and hydrogen chloride (hydrochloric acid when dissolved in water) in the vicinity of the 

Standard Chlorine of Delaware, Inc. (SCD), Superfund Site, 

Delaware City, Delaware. Surface geophysical surveys and 

well data were used to identify and correlate low-permeability 

units (clays) across the site and to search for sand and gravel 

filled paleochannels that are potential conduits and receptors 

of contaminated groundwater and (or) Dense Non-Aqueous 

Phase Liquid (DNAPL) contaminants. The combined surveys and well data were also used to characterize areas of the 

site that have groundwater with elevated (greater than 1,000 

microsiemens per centimeter) specific conductance (SC) as a 

result of contamination.

The most electrically conductive features measured with 

direct-current (DC) resistivity at the SCD site are relatively 

impermeable clays and permeable sediment that are associated with elevated SC in groundwater. Many of the resistive features include paleochannel deposits consisting of 

coarse-grained sediments that are unsaturated, have low (less 

than 200 microsiemens per centimeter) SC pore water, or 

are cemented. Groundwater in uncontaminated parts of the 

Columbia aquifer and of the Potomac aquifer has a low SC. 

Specific-conductance data from monitoring wells at the site 

were used to corroborate the DC-resistivity survey results. 

For comparison with DC-resistivity surveys, multi-channel 

analysis of surface wave (MASW) surveys were used and 

were able to penetrate deep enough to measure the Columbia aquifer, which is known to have elevated SC in some 

places. MASW survey results respond to solid material 

stiffness; clays and cemented sediments will have a higher 

velocity than silts, sands, and gravels (in order of increasing 

hydraulic conductivity).

Geophysical surveys detected elevated SC associated with contamination of the surficial Columbia aquifer. 

Groundwater with elevated SC over ambient (by an order of 

magnitude) produced a decrease in measured resistivity at the 

SCD site. Where SC data are not available from wells, it is not 

known if a low resistivity value measured with DC resistivity alone results from the geologic material (clay) or elevated 

SC in groundwater (in sand or gravel). Seismic surface waves 

used as part of the MASW technique are not affected by water 

content or quality and are used herein to distinguish between 

sand and clay when SC is high. Through concurrent interpretation of MASW and DC-resistivity surveys, information was 

gained about water quality and lithology over large areas at the 

SCD site.

Introduction

The U.S. Geological Survey (USGS), in cooperation 

with Region III of the U.S. Environmental Protection Agency 

(USEPA), is involved in an ongoing study to define the hydrogeologic properties of the Columbia and Potomac aquifers 

in the vicinity of the former Standard Chlorine of Delaware, 

Inc. (SCD), Superfund Site near Delaware City, Delaware 

(fig. 1A). The aquifer in the Columbia Formation (also 

referred to herein as the Columbia aquifer) is discontinuous 

and infrequently used for small domestic water supplies. Parts 

of the Potomac Formation, however, form large continuous 
2 Preliminary Investigation of Paleochannels and Groundwater Specific Conductance, Delaware City, Delaware, 2008

Figure 1. (A) Site location in the State of Delaware and (B) generalized geologic cross section, Standard Chlorine of Delaware, Inc., 

Superfund Site, Delaware City, Delaware.

!

!

!

!

New Jersey

Delaware

Maryland

Pennsylvania

New Jersey

Dover

Newark

Wilmington

Delaware

City

Delaware River

75°30' 75° 74°30'

39°30'

39°

38°30'

Standard Chlorine of 

Delaware, Inc., Superfund Site

0 0.25 MILE

0 0.25 KILOMETER

Red Lion Creek

0 10 20 MILES

0 10 20 KILOMETERS

Land surface

Columbia Formation

Merchantville Formation

Potomac Formation

NOT TO SCALE

A

B
Introduction 3

aquifers used as a public and industrial water supply throughout the region. The Potomac Formation (also referred to herein 

as the Potomac aquifer) is stratigraphically below the Columbia Formation (fig. 1B). 

Site Description

The SCD site is in an industrial area north of Delaware 

City, just south of Red Lion Creek. The SCD site was listed on 

the USEPA National Priorities List in 1987 and has been the 

subject of continuing subsurface investigations and site remediation. Investigations are designed to determine the nature 

and extent of contamination (U.S. Environmental Protection 

Agency, 2009) by chemicals released on site including benzene; hydrogen chloride (hydrochloric acid when dissolved in 

water); chlorobenzene; 1,2-dichlorobenzene; and 1,4-dichlorobenzene (Agency for Toxic Substances and Disease Registry, 

2008). Remediation has included the removal of contaminants 

and industrial equipment on site and installation of a subsurface barrier wall keyed into exiting clay layers that consists of 

a slurry of clay, bentonite, and sand. A pump-and-treat system 

has been installed within the barrier wall to help prevent the 

spread of contamination by reversing groundwater gradients 

and to remove contaminants from groundwater.

Extensive groundwater contamination by over 

500,000 gallons of products that were spilled at SCD was 

identified in the surficial (unconfined) Columbia aquifer 

(Roy F. Weston, Inc., 1992; Black and Veatch Special Project 

Corp., 2005). The Merchantville Formation clay, stratigraphically beneath the Columbia aquifer, was initially thought to 

be a nearly continuous impermeable layer that helped prevent 

contamination from migrating deeper at the site. However, 

recent detection of benzene; chlorobenzene; 1,2-dichlorobenzene; and 1,4-dichlorobenzene contaminants in the upper 

layers of the confined Potomac aquifer (U.S. Environmental 

Protection Agency, 2004, 2006) suggests that the clay may be 

discontinuous, or that holes may have been eroded through 

the clay by paleochannels prior to and during the deposition 

of the Columbia Formation. Contamination has been detected 

at monitoring wells screened in the upper Potomac Formation 

southeast of the site (fig. 2) (U.S. Environmental Protection 

Agency, 2004). A better understanding of subsurface features 

associated with paleochannels in the Columbia and Potomac 

aquifers would assist in defining potential groundwaterflow and transport properties of the aquifers at the SCD site. 

A preliminary assessment of groundwater specific conductance 

(SC) would help define areas of the underlying aquifers that 

may contain contaminants.

Purpose and Scope

The purpose of this report is to present preliminary geophysical survey data and analyses that are being used to help 

define the extents of the aquifer (sand and gravel) and clay 

paleochannel materials, and to identify areas of the aquifers 

that contain SC levels above natural background conditions 

due to contaminant transport at the SCD site. These data and 

analyses can be used to help refine a conceptual model of 

groundwater flow at this site. Concurrent ongoing investigations to determine the directions and rate (vertically and 

horizontally) of groundwater flow and potentially Dense NonAqueous Phase Liquid (DNAPL) contaminant migration (flux) 

into the Potomac aquifer will utilize the information presented 

in this report.

Hydrogeologic Setting

The Quaternary Columbia Formation forms the uppermost unconfined aquifer at the SCD site (Ramsey, 2005). 

Locally, it is 12 to 23 m thick (Roy F. Weston, Inc., 1992) and 

is composed of sand with some coarse sand, gravel, and stringers of silt and clay. The Cretaceous Merchantville Formation 

underlies the Columbia Formation and is a discontinuous layer 

of marine clay and silty/sandy clay forming a leaky confining 

unit (Woodruff, 1986). Underlying the Merchantville Formation is the Cretaceous Potomac Formation, which is composed 

of sand and gravel in a matrix of silt and clay nonmarine 

fluvial sediments. These sediments are generally deeper than 

12 m below land surface and continue down to the crystalline 

bedrock at approximately 210 m. Individually, the aquifers in 

the Columbia and Potomac Formations have a complex heterogeneous set of hydraulic properties. Complexity is greatly 

enhanced by the discontinuous Merchantville confining layer, 

local pumping from multiple supply wells, and various braided 

and meandering fluvial system deposits within the formations.

Thicker sections of the Columbia Formation fill 

paleochannels that cut into the Merchantville and (or) Potomac 

Formations and form areas of increased groundwater flow 

having higher than average yields (Woodruff, 1986). Though 

they are separated by an erosional unconformity, clays of the 

Potomac and Merchantville Formations act together to form a 

confining layer of varying thickness (Woodruff, 1988). Roy F. 

Weston, Inc. (1992) found several locations where the 

Merchantville Formation is thin or non-existent, predominantly in the north-central portion of the site. The absence 

of the Merchantville Formation is a result of an increased 

gradient and fluvial erosion from the lowering of sea level 

during Pleistocene time (Phillips, 1987), which was followed by the fluvial and likely braided deposition of the 

Columbia Formation.

Within a meandering river system, such as that which 

formed the Potomac Formation, coarser material found in bed, 

bar, and levee deposits may form substantial groundwater-flow 

paths, and fine grained flood-plain material will form barriers 

to flow. The Delaware Geological Survey (DGS) has subdivided the Potomac Formation into five facies (environments), 

of which the first three, amalgamated and isolated channel 

sands and crevasse splay and proximal levee sands, have good 

to variable permeability (McKenna and others, 2004). The 

facies alternate with each other sequentially on the basis of 
4 Preliminary Investigation of Paleochannels and Groundwater Specific Conductance, Delaware City, Delaware, 2008

Figure 3

Figure 4

Figure 5 Figure 6

Figure 7

Figure 8

9

4

11

20

6

2

7

10

12

1

25

13

24

8

21

3

5

18

19

16

17

15

14

DP-9

DP-8

DP-7

EM-6D

EM-2D

MW-36

MW-8 MW-5

PW-5S

PW-5D

MW-37

MW-25

MW-24 MW-23

MW-22 MW-21

MW-20

0 500 1,000 FEET

0 125 250 METERS

EXPLANATION

Boundary of area shown in figures 3–8

Barrier wall

Multi-channel analysis of surface-waves

survey and identification number

Direct-current resistivity survey

and identification number

Drivepoint location and identifier

Location and identifier of well screened in:

 Potomac Formation

 Columbia Formation

10

16

DP-9

MW-5

PW-5D

Figure 2. Locations of geophysical-survey lines and wells, Standard Chlorine of Delaware, Inc., Superfund Site, Delaware City, 

Delaware.
Methods of Surface Geophysical Data Collection and Analysis 5

the depositional environment and all potentially have some 

permeable sand or potential to provide aquifer leakage with 

limited connections. In addition to these features identified 

in drilling cores, other meandering river fluvial deposits may 

affect groundwater flow in the Potomac Formation. Clayfilled abandoned channels (oxbow lakes) can form barriers to 

flow, while sand and gravel bars can form flow paths, though 

they are difficult to correlate with borehole data (Freeze and 

Cheery, 1979). Benson (2006) describes the lateral variations 

of the different facies within the Potomac Formation that make 

it a heterogeneous and complex hydrogeologic system. A zone 

of complex faulting in the crystalline basement with offsets of 

5 m or more and undetermined propagation into the Potomac 

Formation is located under and around the site (Woodruff, 

1986; Spoljaric, 1973) and has the potential to affect groundwater flow.

In recent years, consistently downward vertical gradients 

from the Columbia aquifer to the Potomac aquifer at the SCD 

site are evident on the basis of observed water-level measurements (M.J. Brayton, U.S. Geological Survey, written commun., 2007). Groundwater flow within the Columbia aquifer 

is generally north towards Red Lion Creek, which is the local 

groundwater discharge point. In the Potomac aquifer, groundwater flow is generally from northwest to southeast towards 

the Delaware River, except where locally influenced by 

pumping (Phillips, 1987). Confining units between these two 

aquifers tend to limit aquifer interaction; however, some aquifer interaction has taken place on the basis of contamination 

detected at monitoring wells screened in the upper Potomac 

Formation (U.S. Environmental Protection Agency, 2004). 

The location and extent of gaps in confining layers between 

aquifers is part of an ongoing investigation to further define 

site hydrogeology. 

Methods of Surface Geophysical Data 

Collection and Analysis

Surface geophysical survey methods are useful in waterresource investigations of unconsolidated aquifers (Haeni, 

1995); the use of techniques that measure different physical 

properties along the same survey line strengthens interpretations of hydrogeologic properties (Johnson and others, 

2006). Sediment grain size, mineral content, groundwater 

saturation, groundwater chemistry, and surface topography 

affect geophysical properties. Variations in aquifer electrical 

properties result from different materials, pore-water chemistry, porosity, and degree of saturation. Direct-current (DC) 

resistivity geophysical surveys are used to measure electrical contrasts between different types of aquifer material and 

variations in groundwater chemistry. Water with a high SC 

will produce a decrease in resistivity measured by electrical 

geophysical methods (Urish, 1983). Contamination in the 

Columbia aquifer at the SCD site is commonly associated with 

groundwater having SC greater than 200 μS/cm, though the 

known Potomac aquifer contaminants are not associated with 

elevated SC (M.J. Brayton, U.S. Geological Survey, written 

commun., 2008). 

Seismic methods, such as the multi-channel analysis 

of surface wave (MASW) technique, are complementary to 

electrical methods, because the chemistry of the water does 

not affect the propagation and velocities of the surface seismic 

wave. In areas of the SCD study site where SC varies over 

several orders of magnitude, MASW is essential to making 

lithologic interpretations from DC-resistivity data. Both the 

DC resistivity and MASW geophysical techniques were used 

at the SCD site. Line locations were chosen to avoid interference from metal fences and utilities and to maximize depth 

and detail of the survey. The DC and MASW surveys were 

located throughout the northern and eastern areas of the SCD 

site to investigate areas of the Columbia and Potomac Formations known to be contaminated (fig. 2). The western area 

of the site was avoided because of a lack of land access at 

the time of the surveys; in addition, this area is thought to be 

upgradient of groundwater contamination.

Direct-Current Resistivity

DC-resistivity surveys measure the electrical resistivity of the subsurface materials and can be a valuable tool to 

help characterize lithologic materials, including paleochannel features, and water quality of contaminated sites. For 

example, under ambient groundwater-quality conditions at 

the SCD site, clay will have a much lower resistivity response 

than sand, which will be less resistive than gravel. Saturated 

sand or gravel will be less resistive than unsaturated sand or 

gravel (Zohdy and others, 1974; Kearey and Brooks, 1991). If 

the pore water of a sand or gravel is altered by contaminated, 

conductive groundwater, gravel may appear less resistive than 

clay because of elevated SC of the water. 

Direct current is induced in the ground using two current electrodes, while the voltage is measured across two 

potential electrodes; larger surveys use up to 10 electrode 

pairs at once to improve survey efficiency. Apparent resistivity is calculated from the resistance value measured and 

geometric factors, which are based on electrode spacing and 

array type (arrangement of current and potential electrodes 

in relation to each other). Dipole-dipole and Schlumberger 

array (Zohdy and others, 1974) survey configurations were 

used, and reverse dipole-dipole and reciprocal Schlumberger 

surveys served as quality-check surveys for this study. Results 

of the Dipole-dipole array have the greatest lateral resolution and are interpreted and presented in this report. DCresistivity data were processed using RES2DINV version 3.55 

(Loke, 1999) to produce inverted resistivity sections from the 

apparent resistivity data. Data are inverted to convert apparent values that are averages corresponding to a half-sphere 

depth into estimates of values at a specific depth; however, 

results are slightly less reliable at the ends of survey lines. 
6 Preliminary Investigation of Paleochannels and Groundwater Specific Conductance, Delaware City, Delaware, 2008

The quality-check survey inversion results were compared to 

ensure that the same general interpretations could be made.

Cultural features such as buried pipes, well casings, and 

fences can interfere with the DC-resistivity surveys, and were 

avoided, where possible, in this study. Several metal chainlink fences and a large buried metal waste pipe on the southeast side of the site outside the barrier wall (fig. 2) limited 

data collection in this area. Survey line locations were chosen 

to maximize length, which corresponds to depth of DCresistivity investigations.

Multi-Channel Analysis of Surface Waves

MASW surveys take advantage of the strongest part of 

the seismic signal, the surface (S) wave, which is also known 

as ground roll. Data collection using a towable land streamer 

with 24 skid-mounted geophones receiving data at each measuring point (center of land streamer) allows for a dispersion 

curve analysis (Park and others, 1998, 2001). A higher-energy 

sound seismic source helps to create a low-frequency signal; 

a hitch-mounted 40 km accelerated weight drop was used in 

this study. Though data collection through coupling to the 

ground with spikes is ideal, reliable results can be obtained 

with skid-mounted geophones because the method utilizes 

the lower frequency portion of the seismic signal (J. Ivanov, 

Kansas Geological Survey, written commun., 2006). Nearcontinuous data collection is possible with a towable land 

streamer (Lane and others, 2008) equipped with skid-plate 

mounted geophones.

Dispersion-curve results are inverted (Xia and others, 

1999) to interpolate S-wave velocity with depth in SurfSeis2 

(Park, 2006). S-wave velocities are roughly equivalent to 

shear-wave velocities. Unlike compression-wave velocities 

used in seismic reflection and refraction (Zohdy and others, 

1974), S-wave velocities are unaffected by water content. 

MASW velocity results indicate rigidity of solid material; 

therefore, waves traveling through clay, cemented sediment, 

and bedrock will have a higher velocity than those traveling 

through unconsolidated silt, sand, and gravel. Because the 

surface-wave propagation velocity is not affected by water 

content or water conductivity, MASW is especially useful in 

contaminated-site settings. In these settings, the conductivity 

of the pore water may be higher in some areas because of contaminants. Use of only DC resistivity would make it difficult 

to distinguish between conductive pore-water and a conductive geologic material.

Interpretations of surface geophysical surveys are made 

in the context of water-level and SC data from monitoring 

wells at the SCD site. Because of the depth limit of MASW 

signal penetration (21 m maximum at this site), it is best suited 

for imaging the Columbia and Merchantville Formations, 

though in lower-elevation parts of the site, the upper Potomac 

Formation silts and clays are shallow enough to be imaged.

Paleochannels and Groundwater Specific 

Conductance

In areas where SC is low and constant, DC resistivity 

alone can be used to identify electrically resistive, hydraulically conductive paleochannel features within electrically 

conductive silts and clays. In places at the site where SC 

varies or is elevated (greater than 1,000 μS/cm), different 

and complementary physical properties measured with DC 

resistivity and MASW (electrical versus seismic) are needed 

for interpretations. A more detailed and accurate interpretation of paleochannel features and elevated groundwater SC is 

made when the surveys cover the same area and are plotted at 

the same scale. Slight differences in the line locations (fig. 2) 

occur because of the physical layout of each tool. Combined 

interpretations in this study are facilitated by sketching 

an interpreted layer on MASW results and overlaying the 

sketched layer on resistivity cross sections at the same depth 

and location. A velocity of approximately 250 m/s was chosen 

as a value to guide the sketching of a layer and aid in interpretations because it is approximately the halfway point in the 

range of velocities measured. This helped to delineate major 

differences in lithology. This sketched pattern was projected 

from the MASW cross sections onto the resistivity cross sections to aid in interpretations.

One range of resistivity values can represent one or more 

types of material, degrees of saturation, and groundwater SC. 

Because the data from MASW surveys are not affected by the 

presence of water or its electrical properties, results can be 

used to narrow the range of materials that can be interpreted 

from a resistivity survey (table 1). Sand interpretations in 

MASW (slow velocity) that correspond with low resistivity 

indicate areas of increased SC in the pore water. Low velocity in MASW results and high-resistivity values are likely 

unconsolidated sand or gravel and may indicate incised areas 

in low-resistivity, high-velocity clay layers.

A three-dimensional data set was constructed to facilitate 

an analysis of DC-resistivity results and nearby groundwater 

SC values from wells at the site. Field SC values with sample 

dates as close as possible to the DC-resistivity survey dates 

were chosen (J. Cannon, HydroGeoLogic, and M.J. Brayton, 

U.S. Geological Survey, written commun., 2009) Field measurements were made when parameters stabilized in a flowthrough cell under low-flow pumping conditions.
Results of Geophysical Surveys, Paleochannels and Relation to Groundwater Specific Conductance 7

Results of Geophysical Surveys, 

Paleochannels and Relation to 

Groundwater Specific Conductance

In general, the low-velocity layers identified with MASW 

correspond to hydraulically conductive silts, sands, and possibly gravels (in order of increasing hydraulic conductivity); 

the more rigid, stiffest, highest-velocity layers represent clays, 

sandy silty clays, or cemented layers of coarser sediments. 

DC-resistivity results provide thickness and extent information 

on these near-surface materials in addition to deeper hydraulically conductive sand or gravel within the Potomac Formation. 

The most electrically conductive features at the site are impermeable clays and sediment with high SC groundwater. Resistive features include unsaturated sediments, sands, and gravels 

with low SC pore water and cemented sediments. Sands and 

gravels are more likely associated with paleochannel, or near 

channel features, where silts and clays would be a part of a 

paleo-flood plain, cut-off oxbow infilling, or marine deposit. 

Direct-Current Resistivity

Unsaturated gravels, sands, and silts of the Columbia 

Formation and saturated sands and gravels with low SC (less 

than 200 μS/cm) groundwater in sands of the Columbia and 

Potomac Formations have relatively high resistivity values (resistive), in contrast to clays of the Merchantville and 

Potomac Formations. High SC (over 1,000 μS/cm) groundwater in the Columbia Formation has relatively lower resistivity 

values (conductive).

Results from lines 1 and 2 show a thick (about 20 m) 

resistive sequence on top of a more conductive feature at 

about -10 m elevation (figs. 3A and B). Wells near lines 13 and 

3 (figs. 3C and D) contain water with high SC in the Columbia Formation. This, in addition to close proximity to metal 

well casings and metal fence posts, make results from these 

lines difficult to interpret. There is a thick conductive layer 

in lines 9 and 25 from approximately -3 to -23 m elevation. 

The conductive feature is thinner and discontinuous from 

220 to 275 m along line 9. There is a highly resistive zone 

at depth from 100 to 150 m along line 9 and around 100 m 

along line 25 (figs. 3E and F).

Results from lines 4, 20, and 11 (figs. 4A, C, and D) 

show a very thin and inconsistent conductive layer below 

-4 m elevation with a thin resistive layer on top. The edge of a 

conductive layer is identified on the bottom east edge of line 5 

(fig. 4B) at -20 m elevation, and there is a thin (3 m thick), 

slightly conductive layer at the surface. A deep very resistive 

feature is identified centered at -50 m elevation from 200 to 

250 m along line 20. Moderately resistive features of different 

sizes are identified in lines 20 and 11 (figs. 4C and D) beneath 

the conductive layer. The barrier wall within the SCD site is 

imaged as a vertical conductive feature at 27 m along line 11.

A thin, moderately conductive layer extends from 0 to 

around 50 m at -1 m elevation along line 8 (fig. 5A); most of 

the rest of the material along this line is resistive. The thick 

conductive layer in lines 6 (fig. 5B) and 12 thins to the north 

and west in lines 8 and 10. Results from line 10 indicate large 

and small resistive features beneath a thin discontinuous conductive layer (fig. 5C). There is a resistive feature below the 

thick conductive layer (described above) from -40 m elevation through the bottom of the section extending from 100 to 

155 m along line 12.

Conductive features are thin and discontinuous along 

line 24 (fig. 6A). The conductive anomaly at the surface on 

the east end of line 24 is because of high SC groundwater, and 

there are some resistive features beneath the conductive layers 

on the west end of the line. Along line 21, a thick conductive 

feature extends from 0 to 105 m, and a similar conductive 

feature extends from about 40 m to the east end along line 7 

(figs. 6B and C).

Multi-Channel Analysis of Surface Waves

MASW surveys provided results from just below the 

surface to a depth of 13 to 21 m below the ground surface. 

The higher-quality data with clear dispersion curve images 

provided more reliable lateral resolution, and when lower-frequency signals could be generated, they allowed for the deeper 

investigations. Higher-velocity materials are rigid and likely 

correspond to semi-permeable or impermeable silts, clays, or 

cemented layers at the SCD site. A high-velocity layer appears 

Table 1. Relative response of direct-current resistivity and 

multi-channel analysis of surface waves to material, unsaturated 

sand, and specific conductance of groundwater.

[SC, specific conductance; DC, direct current; MASW, multi-channel analysis of surface waves]

Material

Relative response

DC Resistivity MASW

Low High Slow Fast

Unsaturated sand x x

Cemented sand x x

Sand with high SC 

groundwater x x

Sand with low SC 

groundwater x x

Clay x x
8 Preliminary Investigation of Paleochannels and Groundwater Specific Conductance, Delaware City, Delaware, 2008

9

2

1

25

13 3

19

0 125 METERS0 500 FEET

NE

W E SW

W

E

W

E

W

E

W

E

A

B

C

D

E

F

EXPLANATION

Multi-channel analysis of surface-waves survey and identification numberDirect-current resistivity survey and identification number 9

19

RESISTIVITY, IN OHM METERS

25 40 55 75 100 185 400 780 1,605

Figure 3. Direct-current resistivity results from (

A) line 1, (

B) line 2, (

C) line 13, (

D) line 3, (

E) line 9, and (

F) line 25, Standard Chlorine of Delaware, Inc., Superfund Site, Delaware 

City, Delaware.
Results of Geophysical Surveys, Paleochannels and Relation to Groundwater Specific Conductance 9

N

S

A

NW SE

C

NW SE

D

NW SE

B

0 125 METERS0 500 FEET

4

11

20

7

24

21

5

18

17

15

14

EXPLANATION

Multi-channel analysis of surface-waves survey and identification numberDirect-current resistivity survey and identification number

1821

RESISTIVITY, IN OHM METERS

25 40 55 75 100 185 400 780 1,605

Barrier wall

Figure 4. Direct-current resistivity results from (

A) line 4, (

B) line 5, (

C) line 20, and (

D) line 11, Standard Chlorine of Delaware, Inc., Superfund Site, Delaware City, Delaware.
10 Preliminary Investigation of Paleochannels and Groundwater Specific Conductance, Delaware City, Delaware, 2008 NW SE

A

N

S

B

SW NE

C

SW NE

D

6

10

12

8

16

0 125 METERS0 500 FEET

EXPLANATION

Multi-channel analysis of surface-waves survey and identification numberDirect-current resistivity survey and identification number

1610

RESISTIVITY, IN OHM METERS

25 40 55 75 100 185 400 780 1,605

Barrier wall

Figure 5. Direct-current resistivity results from (

A) line 8, (

B) line 6, (

C) line 10, and (

D) line 12, Standard Chlorine of Delaware, Inc., Superfund Site, Delaware City, Delaware.
Results of Geophysical Surveys, Paleochannels and Relation to Groundwater Specific Conductance 11 Figure 6. Direct-current resistivity results from (

A) line 24, (

B) line 21, and (

C) line 7, Standard Chlorine of Delaware, Inc., Superfund Site, Delaware City, Delaware.

W

E

A

NW SE

B

W

E

C

6

7

20

24

11

21

12

16

15

14

17

0 125 METERS0 500 FEET

EXPLANATION

Multi-channel analysis of surface-waves survey and identification numberDirect-current resistivity survey and identification number

1610

RESISTIVITY, IN OHM METERS

25 40 55 75 100 185 400 780 1,605

Barrier wall
12 Preliminary Investigation of Paleochannels and Groundwater Specific Conductance, Delaware City, Delaware, 2008

to be continuous below about -18 m in elevation along line 14 

(fig. 7A). Results from line 15 indicate areas where holes or 

thin spots in the clay may be present in the vicinity of 5, 40, 

and 80 m along the line. There is also a thin layer of highervelocity material that is discontinuous along line 15 from 0 to 

-5 m in elevation (fig. 7B).

Data quality from the line 16 survey is poor, lacking consistency and low-frequency returns (resulting in a shallower 

investigation depth of 14 m), likely because of inconsistent 

and poorly compacted fill material beneath the road and (or) 

poor coupling of the skid plates on the rough surface. Results 

show some high-velocity material at the start of the line but 

are unreliable past 30 m distance (fig. 7C). Lines 17 and 18 

indicate thin spots and holes in high-velocity layers (figs. 8A 

and B). Though data from line 19 did not have many low-frequency returns, which resulted in a shallow penetration depth, 

the returns were of good quality, enabling an interpretation of 

a thin, high-velocity zone near the surface from 70 to 140 m. A 

discontinuous high-velocity layer around 0 m elevation is also 

seen in the results from line 19 (fig. 8C), which was surveyed 

through pavement.

Paleochannels and Groundwater Specific 

Conductance

Electrically resistive paleochannel features were interpreted with DC-resistivity data alone where SC was low; 

where SC was high, MASW was needed to help interpret 

paleochannels. Paleochannels in the Columbia Formation 

have been interpreted that incise through the Merchantville 

Formation and into the Potomac Formation. Paleochannels in 

the Potomac Formation are often found in a matrix of more 

conductive material, likely clay or silt. Potomac Formation 

paleochannel features that contain abundant sand and are 

electrically resistive could be part of facies identified by 

McKenna and others (2004), including amalgamated and 

isolated channels (and bars) and crevasse splay and proximal 

levee sands.

Resistive features identified in DC-resistivity lines 5, 

8, and 9 (figs. 4B, 5A, and 3E) are interpreted as Columbia 

Formation material in paleochannels that have eroded through 

the Merchantville or Potomac Formation clay. A similar 

E W

A

E W

B

N S

C

6

7

24

21

20

11

16

15

14

0 125 METERS

0 500 FEET

EXPLANATION

Multi-channel analysis of surface-waves

survey and identification number

Direct-current resistivity survey

and identification number 24

16

SURFACE-WAVE VELOCITY, IN METERS PER SECOND

150 190 210 235 260 290 335 405

Figure 7. Multi-channel analysis of surface waves (MASW) results from (A) line 15, (B) line 14, and (C) line 16, Standard Chlorine of 

Delaware, Inc., Superfund Site, Delaware City, Delaware.
Results of Geophysical Surveys, Paleochannels and Relation to Groundwater Specific Conductance 13

Figure 8. Multi-channel analysis of surface waves (MASW) results from (A) line 17, (B) line 18, and (C) line 19, Standard Chlorine of 

Delaware, Inc., Superfund Site, Delaware City, Delaware.

W E

A

N S

B

S N

C

4

11

2

1

13

20

3

18

19

17

0 125 METERS

0 500 FEET

EXPLANATION

Multi-channel analysis 

of surface-waves survey 

and identification number

Direct-current resistivity 

survey and identification 

number

3

18

SURFACE-WAVE VELOCITY, IN METERS PER SECOND SURFACE-WAVE VELOCITY, IN METERS PER SECOND

150 190 210 235 260 290 335 405

deep-cutting feature is seen in line 13 (fig. 3C), though it is 

not known if the low-resistivity features are clay or high SC 

water. Deeper paleochannel features formed during the deposition of the Potomac Formation consist of resistive (greater 

than 150 ohm m) material at -10 m elevation or deeper that 

is within a matrix of silt and clay are seen in lines 4, 5, 6, 9, 

10, 11, 12, 13, 20, 24, and 25 (figs. 3C, 3E, 3F, 4A, 4C, 4D, 

5A, 5C, 5D, and 6A). Ongoing DC-resistivity measurements 

of core and SC measurements at wells will help further define 

these features. 

Combined DC-resistivity and MASW results from lines 

17 and 20 indicate continuous thin clays around -8 m elevation with sand having elevated SC pore water on top from 200 

to 250 m along the line. Shallower, discontinuous, cemented 

layers are indicated throughout the combined section as well 

(figs. 9A and B). Results from lines 4 and 18 indicate thin 

spots, discontinuous clay, and potentially elevated SC at the 

northern end (figs. 10A and B). Outcroppings of cemented 

sediment and loose sand along the south and center areas 

of these lines provided evidence for interpretations. Results 

from lines 14, 15, and 24 indicate small amounts of thin clay, 

cemented sediments, and sand with slightly higher SC in the 

pore water on the east side (figs. 11A and B).

Information on well water SC and MASW results are 

used to determine where groundwater SC is elevated (above 

1,000 μS/cm). Wells, the potentiometric surface, and screened 

intervals plotted on resistivity sections for analysis are shown 

in appendix 1. Resistivity values measured during DC-resistivity surveys nearest to screen intervals where groundwater 

SC was measured have been selected from these views. In 

general, when SC was higher, resistivity values were lower. 

When SC was lower, resistivity was higher and had a wider 

range of values because it is controlled more by varying geologic materials (fig. 12). Because SC likely changes with time, 

groundwater levels and flow, dates of the measurements, and 

DC-resistivity data collection are listed in the figure captions 

in appendix 1.

SC was low (below 200 μS/cm) and resistivity was high 

at wells near line 5 where there were not any site-related 

contaminants (appendix 1, fig. 1–1). Groundwater SC was 

considered ambient here. Groundwater with elevated specific 

conductance SC over ambient levels (by an order of magnitude) produced a decrease in measured resistivity. SC was very 

high (3,800 μS/cm) at EM-2D and resistivity was low (appendix 1, fig. 1–2). Along line 24, SC increased to the east and 

resistivity dropped (appendix 1, fig. 1–6).
14 Preliminary Investigation of Paleochannels and Groundwater Specific Conductance, Delaware City, Delaware, 2008

Figure 9. Co-located surface geophysical results from (

A) line 17 multi-channel analysis of surface waves (MASW) with stiff layer interpretation in black and (

B) line 20 directcurrent resistivity with MASW projected interpretation, Standard Chlorine of Delaware, Inc., Superfund Site, Delaware City, Delaware.

Land surface

B)

A)

High specificconductancegroundwater

Cemented layers

Thin clay or silt

W

E

Land surface 0

-50

-100

50

VERTICAL SCALE, IN METERS

DISTANCE, IN METERS

B) Direct-Current Resistivity Line 20

A) Multi-Channel Analysis of Surface Waves Line 17

SURFACE-WAVE VELOCITY, IN METERS PER SECOND

RESISTIVITY, IN OHM METERS

SURFACE-WAVE VELOCITY, IN METERS PER SECOND

150 190 210 235 260 290 335 405

RESISTIVITY, IN OHM METERS

25 40 55 75 100 185 400 780 1,605
Results of Geophysical Surveys, Paleochannels and Relation to Groundwater Specific Conductance 15 Figure 10. Co-located surface geophysical results from (

A) line 18 multi-channel analysis of surface waves (MASW) with stiff layer interpretation in black, and (

B) line 4 directcurrent resistivity with MASW projected interpretation, Standard Chlorine of Delaware, Inc., Superfund Site, Delaware City, Delaware. 

Cementedlayer

Holes in silt or clay High specific

conductanceground water

S

N

Land surface

Land surface

0

-50

-100

50

VERTICAL SCALE, IN METERS

DISTANCE, IN METERS

B) Direct-Current Resistivity Line 4

A) Multi-Channel Analysis of Surface Waves Line 18

SURFACE-WAVE VELOCITY, IN METERS PER SECOND

150 190 210 235 260 290 335 405

RESISTIVITY, IN OHM METERS

25 40 55 75 100 185 400 780 1,605
16 Preliminary Investigation of Paleochannels and Groundwater Specific Conductance, Delaware City, Delaware, 2008Figure 11. Co-located surface geophysical results from (

A) lines 14 (left) and 15 (right) multi-channel analysis of surface waves (MASW) with stiff layer interpretation in black, 

and (

B) line 24 direct-current resistivity with MASW projected interpretation, Standard Chlorine of Delaware, Inc., Superfund Site, Delaware City, Delaware.

W

E

Land surface

Cemented layers Clay or silt

Land surface

High specificconductanceground water

0

-50

-100

50

VERTICAL SCALE, IN METERS

DISTANCE, IN METERS

C) Direct-Current Resistivity Line 24

B) Multi-Channel Analysis of Surface Waves Line 14 A) Multi-Channel Analysis of Surface Waves Line 15

SURFACE-WAVE VELOCITY, IN METERS PER SECOND

150 190 210 235 260 290 335 405

RESISTIVITY, IN OHM METERS

25 40 55 75 100 185 400 780 1,605
Summary 17

Summary

The USGS is cooperating with Region III of the USEPA 

in an ongoing study to define the hydrogeologic properties 

of the Columbia and Potomac aquifers in the vicinity of the 

Standard Chlorine of Delaware, Inc. (SCD), Superfund Site 

near Delaware City, Delaware. The SCD site was listed on 

the USEPA National Priorities List in 1987 and has been the 

subject of continuing investigations to determine the nature 

and extent of dissolved phase and DNAPL contamination. 

Results from this preliminary investigation on the occurrence 

of paleochannels and areas of elevated groundwater specific 

conductance at the SCD site may be useful for remedial planning and operations.

Electrically resistive units measured with DC-resistivity 

surveys correspond to unsaturated gravel and sand of the 

Columbia Formation or saturated sand and gravel with low 

SC groundwater in the Columbia and Potomac Formations. Electrically conductive clays of the Merchantville and 

Potomac Formations and high SC groundwater in the Columbia Formation were identified with DC-resistivity surveys. 

MASW surveys detected higher velocity, rigid materials 

that are interpreted as semi-permeable or impermeable silts, 

clays, or cemented layers; lower-velocity materials correspond to unconsolidated sand or gravel. MASW surveys are 

not affected by groundwater or its electrical properties, and 

DC-resistivity results are not strongly affected by the degree 

of cementation of sediment.

Through combining interpretations from the MASW and 

DC-resistivity surveys, more detailed and specific materials 

were identified. Lower-velocity MASW results associated with 

sand that corresponds with areas of low resistivity indicate 

areas of increased SC groundwater. Low-velocity MASW 

results in conjunction with high resistivity values represent unconsolidated sand or gravel and can indicate gaps or 

paleochannel incision in the low-resistivity, high-velocity clay 

layers. Sand-filled paleochannels identified in the Columbia 

Formation have incised through the Merchantville and into 

the Potomac Formation. Sand-filled paleochannels were also 

identified within the Potomac Formation at the SCD site, as 

part of a more conductive clay or silt matrix.

Variations in groundwater SC affect the results of DCresistivity surveys at this site. For example, when SC values 

were lower, resistivity survey result values were controlled 

more by differences in geologic material than groundwater 

quality on the west side of the site and on the north side of Red 

Lion Creek. When pore water had a low SC, lower resistivity 

values indicated silt and clay; higher resistivity values correspond with higher hydraulic conductivity sands or gravels. 

Elevated SC, confirmed by well data and the combination of 

DC-resistivity and MASW, was detected along the northern 

edge of the SCD site (southern edge of Red Lion Creek) in the 

Columbia Formation. 

Figure 12. Relation between specificconductance measurements from wells 

and resistivity values at screened-interval 

depths from adjacent cross sections, 

Standard Chlorine of Delaware, Inc., 

Superfund Site, Delaware City, Delaware.

10

100

1,000

10,000 1,000 100

RESISTIVITY, IN OHM METERS

SPECIFIC CONDUCTANCE, IN MICROSIEMENS

PER CENTIMETER AT 25 DEGREES CELSIUS
18 Preliminary Investigation of Paleochannels and Groundwater Specific Conductance, Delaware City, Delaware, 2008

References Cited

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Public health assessment: Metachem Products, LLC 

(a/k/a Standard Chlorine of Delaware, Incorporated) New 

Castle, New Castle County, Delaware, accessed February 

4, 2008, at http://www.atsdr.cdc.gov/HAC/PHA/metachem/

met_p1.htm1, 24 p.

Benson, R.N., 2006, Internal stratigraphic correlation of 

the subsurface Potomac Formation, New Castle County, 

Delaware, and adjacent areas in Maryland and New Jersey: 

Delaware Geological Survey Report of Investigations 

No. 71, 15 p., 3 pls.

Black and Veatch Special Project Corp., 2005, Technical 

Memorandum to Hilary Thronton, USEPA Region III from 

Dane Pehrman and Aaron Epstein, dated February 16, 2005, 

Re: Relationships and Contaminant Migration between the 

Columbia and Potomac Aquifers at the Standard Chlorine 

Site, Delaware City, Delaware: 11 p. 

Freeze, R.A., and Cherry, J.A., 1979, Groundwater: Englewood Cliffs, N.J., Prentice-Hall, Inc., 604 p.

Haeni, F.P., 1995, Application of surface-geophysical methods 

to investigations of sand and gravel aquifers in the glaciated 

northeastern United States: U.S. Geological Survey Professional Paper 1415–A, 70 p. 

Johnson, C.D., White, E.A., Ivanov, J., and Lane, J.W., Jr., 

2006, Use of electrical resistivity and surface-wave seismic 

imaging methods to characterize the geologic framework of 

the NAWC site, West Trenton, New Jersey [abs.]: Geological Society of America Abstracts with Programs, v. 38, 

no. 7, p. 528, Paper no. 219–9.

Kearey, Philip, and Brooks, Michael, 1991, An introduction to 

geophysical exploration (2d ed.): Cambridge, Mass., Blackwell Scientific Publications, 254 p.

Lane, J.W., Jr., Ivanov, J., Day-Lewis, F.D., Clemens, D., 

Patev, R., and Miller, R.D., 2008, Levee evaluation using 

MASW—Preliminary findings from the Citrus Lakefront 

Levee, New Orleans, Louisiana in Symposium on the 

Application of Geophysics to Engineering and Environmental Problems, April 6–10, 2008, Philadelphia, Pennsylvania, 

Proceedings: Denver, Colo., Environmental and Engineering Geophysical Society, 10 p.

Loke, M.H., 1999, Electrical imaging surveys for environmental and engineering studies, A practical guide to 2-D and 

3-D Surveys: Penang, Malaysia, 57 p., accessed October 2, 

2009, at http://www.agiusa.com/literature.shtml. 

McKenna, T.E., McLaughlin, P.P., and Benson, R.N., 2004, 

Characterization of the Potomac Aquifer, an extremely 

heterogeneous fluvial system in the Atlantic Coastal Plain 

of Delaware: Delaware Geological Survey Open-File 

Report 45, 1 p., 3 sheets.

Park, C.B., 2006, SurfSeis Active and Passive MASW Seismic Processing Software (Supplementary), User’s Manual 

v 2.0 (Beta): Kansas Geological Survey, May 2006, 40 p.

Park, C.B., Miller, R.D., and Xia, J., 1998, Imaging dispersion curves of surface waves on multi-channel record 

[Expanded Abstract]: Journal of the Society of Exploration 

Geophysicists, p. 1377–1380 (PAR-98-03).

Park, C.B., Miller, R.D., and Xia, J., 2001, Higher modes of 

surface waves over unconsolidated sediments: Proceedings 

of the 5th International Symposium on Recent Advances 

in Exploration Geophysics (RAEG2001), Kyoto, p. 9–17 

(PAR-01-01).

Phillips, S.W., 1987, Hydrogeology, degradation of groundwater quality, and simulation of infiltration from the Delaware River into the Potomac aquifers, Northern Delaware: 

U.S. Geological Survey Water-Resources Investigations 

Report 87–4185, 86 p.

Ramsey, K.W., 2005, Geologic map of New Castle County, 

Delaware: Delaware Geological Survey, Geologic Map 

Series No. 13, 1 pl. 

Roy F. Weston, Inc., 1992, Remedial investigation report for 

the Standard Chlorine of Delaware, Inc. Site, Delaware 

City, Delaware: v. 2, variously paged.

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the northern coastal plain, Delaware: Geological Society 

of America Bulletin, August 1973, v. 84, p. 2781–2784. 

Urish, D.W., 1983, The practical application of surface 

electrical resistivity to detection of groundwater pollution: Ground Water, March–April 1983, v. 21, no. 2, 

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18, 2009, at http://www.epa.gov/reg3hscd/super/sites/

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Woodruff, K.D., 1986, Geohydrology of the Chesapeake and 

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dspace/bitstream/19716/3085/2/Hydro6%2csht1.pdf.

Woodruff, K.D., 1988, Geohydrology of the Chesapeake and 

Delaware Canal Area, Delaware: Delaware Geological 

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Xia, J., Miller, R.D., and Park, C.B., 1999, Estimation of 

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20 Preliminary Investigation of Paleochannels and Groundwater Specific Conductance, Delaware City, Delaware, 2008

THIS PAGE INTENTIONALLY LEFT BLANK
Appendix 1 21

Appendix 1. Direct-Current Resistivity Cross 

Sections with nearby Well Water Levels, 

Screened Intervals, and Specific Conductance 

Values
22 Preliminary Investigation of Paleochannels and Groundwater Specific Conductance, Delaware City, Delaware, 2008

Figure 1–1. Direct-current resistivity cross section with nearby wells (MW-37 and PW-5S) projected showing screened intervals, 

water levels, and specific conductance values (measured August 29 and 30, 2007). Results from line 5 (collected November 13, 2007) 

viewed looking to the north from the south with a 2X vertical exaggeration. For locations, distance, and depth scales refer to figures 2 

and 6, Standard Chlorine of Delaware, Inc., Superfund Site, Delaware City, Delaware.

EXPLANATION

163

MW-37 Well location and identifier

Screened interval and specific conductance

at screened interval, in microsiemens per

centimeter at 25 degrees Celsius

RESISTIVITY, IN OHM METERS

25 40 55 75 100 185 400 780 1,605

Estimated water table

Land surface

PW-5S, MW-37

163

130
Appendix 1 23

Figure 1–2. Direct-current resistivity cross section with nearby well (EM-2D) projected showing screened intervals, water levels, and 

specific conductance values (measured June 12, 2008). Results from line 20 (collected July 9, 2008) viewed looking to the south from the 

north with a 2X vertical exaggeration. For locations, distance, and depth scales refer to figures 2 and 6, Standard Chlorine of Delaware, 

Inc., Superfund Site, Delaware City, Delaware.

Estimated water table

Land surface

RESISTIVITY, IN OHM METERS

25 40 55 75 100 185 400 780 1,605

EXPLANATION

3,800

EM-2D Well location and identifier

Screened interval and specific conductance

at screened interval, in microsiemens per

centimeter at 25 degrees Celsius

EM-2D

3,800
24 Preliminary Investigation of Paleochannels and Groundwater Specific Conductance, Delaware City, Delaware, 2008

Figure 1–3. Direct-current resistivity cross section with nearby well (MW-5) projected showing screened interval, water level, and 

specific conductance value (measured December 15, 2008). Results from line 11 (April 23, 2008) are viewed looking to the north from the 

south with a 2X vertical exaggeration. For locations, distance, and depth scales refer to figures 2 and 6, Standard Chlorine of Delaware, 

Inc., Superfund Site, Delaware City, Delaware.

EXPLANATION

370

MW-5 Well location and identifier

Screened interval and specific

conductance, in microsiemens per

centimeter at 25 degrees Celsius

RESISTIVITY, IN OHM METERS

25 40 55 75 100 185 400 780 1,605

Estimated water table

MW-5 Land surface

370
Appendix 1 25

Figure 1–4. Direct-current resistivity cross section with nearby wells (MW-25 and MW-24) projected showing screened intervals, 

water levels, and specific conductance values (measured December 12 and 15, 2008). Results from lines 6, 10 (sections with wells, 

collected January 25, 2008, and April, 22, 2008), and 8 (on right side, coming out of page) are viewed looking to the east from the west 

with a 2X vertical exaggeration. For locations, distance, and depth scales refer to figures 2 and 7, Standard Chlorine of Delaware, Inc., 

Superfund Site, Delaware City, Delaware.

EXPLANATION

511

MW-24 Well location and identifier

Screened interval and specific conductance

at screened interval, in microsiemens per

centimeter at 25 degrees Celsius

RESISTIVITY, IN OHM METERS

25 40 55 75 100 185 400 780 1,605

Estimated water table

Land surface

MW-25

627

MW-24

511
26 Preliminary Investigation of Paleochannels and Groundwater Specific Conductance, Delaware City, Delaware, 2008

Figure 1–5. Direct-current resistivity cross section with nearby wells (MW-37 and PW-5S) projected showing screened intervals, 

water levels, and specific conductance values (measured August 29 and 30, 2007). Results from lines 6, 8 (coming out of page, left 

side), and 12 (section with wells, collected April, 23, 2008) viewed looking to the east from the west with a 2X vertical exaggeration. 

For locations, distance, and depth scales refer to figures 2 and 7, Standard Chlorine of Delaware, Inc., Superfund Site, Delaware City, 

Delaware.

EXPLANATION

372

MW-8 Well location and identifier

Screened interval and specific conductance

at screened interval, in microsiemens per

centimeter at 25 degrees Celsius

RESISTIVITY, IN OHM METERS

25 40 55 75 100 185 400 780 1,605

Estimated water table

Land surface

MW-20

193

MW-8

372
Appendix 1 27

Figure 1–6. Direct-current resistivity cross section with nearby wells (MW-22, MW-23, MW-21, and EM-6D) projected showing 

screened intervals, water levels, and specific conductance values (measured December 12, 12, and 15, 2008, and September 16, 2008). 

Results from line 24 (collected July 10, 2008) viewed looking to the north from the south with a 2X vertical exaggeration. For locations, 

distance, and depth scales refer to figures 2 and 8, Standard Chlorine of Delaware, Inc., Superfund Site, Delaware City, Delaware.

EXPLANATION

1,093

MW-23 Well location and identifier

Screened interval and specific conductance

at screened interval, in microsiemens per

centimeter at 25 degrees Celsius

RESISTIVITY, IN OHM METERS

25 40 55 75 100 185 400 780 1,605

Estimated water table

Land surface

MW-21

442

MW-22

236

MW-23

1,093

EM-6D

1,520

Prepared by the West Trenton Publishing Service Center.

For more information concerning this report, contact:

Director

U.S. Geological Survey

New Hampshire-Vermont Water Science Center

331 Commerce Way, Suite 2

Pembroke, NH 03275

dc_nh@usgs.gov

or visit our Web site at:

http://nh.water.usgs.gov
Degnan, J.R. and Brayton, M.J.—Preliminary Investigation of Paleochannels and Groundwater Specific Conductance, Delaware City, Delaware, 2008—Open-File Report 2010–1058