GEOLOGY, HYDROGEOLOGY, AND POTENTIAL OF 

INTRINSIC BIOREMEDIATION AT THE NATIONAL 

PARK SERVICE DOCKSIDE II SITE AND 

ADJACENT AREAS, CHARLESTON, 

SOUTH CAROLINA, 1993-94

By Bruce G. Campbell, Matthew D. Petkewich, James E. Landmeyer, and 

Francis H. Chapelle

U.S. GEOLOGICAL SURVEY 

Water-Resources Investigations Report 96-4170

Prepared in cooperation with the 

NATIONAL PARK SERVICE

Columbia, South Carolina 

1996
U.S. DEPARTMENT OF THE INTERIOR 

BRUCE BABBITT, Secretary

U.S. GEOLOGICAL SURVEY 

Gordon P. Eaton, Director

The use of firm, trade, and brand names in this report is for identification purposes 

only and does not constitute endorsement by the U.S. Government.

For additional information write to:

District Chief 

U.S. Geological Survey 

Stephenson Center-Suite 129 

720 Gracern Road 

Columbia, SC 29210-7651

Copies of this report can be purchased 

from:

U.S. Geological Survey 

Branch of Information Services 

Box 25286 

Denver, CO 80225-0286
Errata Sheet 

Water-Resources Investigations Report 96-4170

Geology, Hydrogeology, and Potential of Intrinsic Bioremediation at the National Park Service 

Dockside II Site and Adjacent areas, Charleston, South Carolina, 1993-94.

Please replace page 32 with the attached corrected page 32. Equation 1 on this page has been 

corrected.
CONTENTS

Page

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

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

Purpose and scope .................................................... 3

Previous investigations ................................................ 5

Acknowledgments .................................................... 6

Geology.................................................................... 6

Regional geology...................................................... 6

Late Cretaceous deposits ........................................ 9

Tertiary deposits ................................................ 9

Quaternary deposits ........................................... 10

Site geology ......................................................... 11

Hydrogeology ............................................................. 13

Aquifers and confining units .......................................... 13

Surficial aquifer system ......................................... 17

Santee Limestone/Black Mingo confining unit..................... 17

Santee Limestone/Black Mingo aquifer ........................... 22

Black Creek aquifer and overlying confining unit .................. 22

Middendorf aquifer and overlying confining unit .................. 22

Cape Fear aquifer and overlying confining unit .................... 22

Ground water ....................................................... 23

Ground-water flow............................................. 23

Ground-water recharge ......................................... 23

Hydraulic characteristics........................................ 24

Ground-water use ................................................... 29

Intrinsic-bioremediation potential ............................................ 29

Solute-transport model inputs ......................................... 33

Solute-transport simulations .......................................... 36

Model conclusions ................................................... 56

Summary ................................................................. 59

References................................................................. 63

Appendix I. Description of boring logs for wells drilled on the National

Park Service property, Charleston, S.C., November 1993 ..................... 66

Appendix II. Well identification, test dates, hydraulic conductivity values, 

and method of water displacement for aquifer tests conducted in the 

surficial aquifers beneath the National Park Service property, 

Charleston, S.C., 1993.................................................... 68
ILLUSTRATIONS

Page

Figure 1. Map showing study area and locations of observation wells 

on National Park Service property and adjacent properties, 

Charleston, S.C. .................................................4

2. Map showing generalized areas of outcrop of Atlantic Coastal

Plain aquifers in South Carolina ..................................7

3. Schematic showing lithostratigraphic units and geologic ages of

Coastal Plain sediments in the Charleston, S.C., area ................8

4. Map showing Pleistocene terraces in the Charleston, S.C., area .........12

5. Map showing locations of geologic sections A-A', B-B', C-C', 

and D-D' on the National Park Service property and adjacent 

properties, Charleston, S.C. ......................................14

6. Geologic sections A-A', B-B', C-C', and D-D' across the National Park

Service property and adjacent properties, Charleston, S.C. ...........15

7. Schematic showing general geologic, hydrologic, and lithologic 

logs of the subsurface Coastal Plain environment at the 

National Park Service Dockside II site, Charleston, S.C...............16

8-13. Map showing:

8. Thickness of the upper surficial aquifer beneath the National

Park Service property, Charleston, S.C. .........................18

9. Thickness of the upper confining unit beneath the National

Park Service property, Charleston, S.C. .........................19

10. Depth to the top of the lower surficial aquifer beneath the

National Park Service property, Charleston, S.C. .................20

11. Thickness of the lower surficial aquifer beneath the

National Park Service property, Charleston, S.C. ................21

12. Water-table surface of the upper surficial aquifer, National Park

Service property, Charleston, S.C., September 14,1994 ............25

13. Lateral hydraulic conductivity values measured in surficial 

aquifers located on the National Park Service property, 

Charleston, S.C., 1993 ........................................26

14. Hydrographs of wells screened in the upper and lower surficial 

aquifers on the National Park Service property and National 

Weather Service rainfall data, Customs House rain gage, 

Charleston, S.C., January 1994 to November 1994 ...................28

15. Map showing wells located within 1 and 3 miles of the

National Park Service property, Charleston, S.C. ....................30

IV
ILLUSTRATIONS-Continued

Page

16. Graph showing adsorption isotherms for toluene and naphthalene 

on upper surficial aquifer sediments beneath the National Park 

Service property, Charleston, S.C. ................................35

17. Graph showing mineralization rate of uniformly ring-labeled 

14C-toluene and 14C-naphthalene under aerobic and anaerobic 

aquifer conditions in sediment samples collected from the 

upper surficial aquifer, National Park Service property, 

Charleston, S.C. ................................................37

18-32. Maps showing:

18. Model boundaries for the study area, Charleston, S.C. .............39

19. Toluene and naphthalene concentrations measured in upper 

surficial aquifer wells on the National Park Service property 

and adjacent properties, Charleston, S.C., January 1994 ...........40

20. Simulated water-table elevations of the upper surficial aquifer

using a rate of 50 gallons per day draining through the brick-lined 

drainage archway, National Park Service property and adjacent 

properties, Charleston, S.C., January 8,1994.....................42

21. Simulated water-table elevations of the upper surficial aquifer

using a rate of 500 gallons per day draining through the brick-lined 

drainage archway, National Park Service property and adjacent 

properties, Charleston, S.C., January 8,1994 ....................43

22. Simulated water-table elevations of the upper surficial aquifer

using a rate of 5,000 gallons per day draining through the brick-lined 

drainage archway, National Park Service property and adjacent 

properties, Charleston, S.C., January 8,1994 ....................44

23. January 1994 distribution of toluene in the upper surficial aquifer

simulated by the standard model ..............................46

24. Year 2144 distribution of toluene in the upper surficial aquifer 

simulated by the standard model and assuming conservative 

transport ...................................................47

25. Year 2144 distribution of toluene in the upper surficial aquifer

simulated using the standard model with high andlow estimates of 

aquifer hydraulic conductivities ...............................49

26. Year 2144 distribution of toluene in the upper surficial aquifer

simulated using the standard model with high and low estimates 

of microbial degradation......................................50

27. Year 2144 distribution of toluene in the upper surficial aquifer

simulated using the standard model with high and low estimates 

of adsorption................................................51
ILLUSTRATIONS-Continued

Page

28. January 1994 distribution of naphthalene in the upper

surficial aquifer simulated by the standard model ...............53

29. Year 2144 distribution of naphthalene in the upper surficial 

aquifer simulated by the standard model and assuming 

conservative transport .......................................54

30. Year 2144 distribution of naphthalene in the upper

surficial aquifer simulated using the standard model with high

and low estimates of aquifer hydraulic conductivities ............55

31. Year 2144 distribution of naphthalene in the upper

surficial aquifer simulated using the standard model with

high and low estimates of microbial degradation ................57

32. Year 2144 distribution of naphthalene in the upper surficial

aquifer simulated using the standard model with high and low 

estmates of adsorption .......................................58

TABLES

Table 1. Vertical hydraulic gradients measured during the low-tide

cycle in well pairs located on the National Park Service property, 

Charleston, S.C. .............................................29

2. Estimates of lateral hydraulic conductivity, and microbialdegradation rates and adsorption coefficients of toluene for site 

conditions at the National Park Service property and adjacent 

properties, Charleston, S.C., 1994 ..............................36

3. Estimates of lateral hydraulic conductivity, and microbialdegradation rates and adsorption coefficients of naphthalene 

for site conditions at the National Park Service property and 

adjacent properties, Charleston, S.C., 1994 ......................38

VI
CONVERSION FACTORS, VERTICAL DATUM, ABBREVIATIONS, AND ACRONYMS

Multiply__________________By___________To obtain_______

inch (in.) 2.54 centimeter

inch per year (in./yr) 2.54 centimeter per year

foot (ft) 0.3048 meter

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

foot per day (ft/d) 0.0003528 centimeter per second

foot per foot (ft/ft) 1.0 meter per meter

square foot per day (ft2 /d) 0.09290 square meter per day

acre 4,047 square meter

mile (mi) 1.609 kilometer

gallon per day (gal/d) 3.785 liter per day

gallon per day per foot [(gal/d)/ft] 12.42 liter per day per meter

cubic foot (ft3) 0.02832 cubic meter

Water temperature in degrees Celsius (°C) can be converted to degrees Fahrenheit (°F) 

by using the following equation:

°F = 1.8(°C) + 32

Sea level: In this report "sea level" refers to the National Geodetic Vertical Datum 

of 1929 a geodetic datum derived from a general adjustment of the first-order level 

nets of the United States and Canada, formerly called Sea Level Datum of 1929.

The use of trade, product, industry, or firm names in this report is for identification 

or location purposes only, and does not constitute endorsement of products by the U.S. 

Government, nor impute responsibility for any present or potential effects on the natural 

resources.

VII
CONVERSION FACTORS, VERTICAL DATUM, ABBREVIATIONS, AND ACRONYMS-Continued

Additional abbreviations

Kad = adsorption coefficient

bis = below land surface

bsl = below sea level

Kbio = biodegradation coefficient

cm/s = centimeter per second

ft3 /mg = cubic feet per milligram

DPM = disintegrations per minute

g = grams

K = hydraulic conductivity

oq = longitudinal dispersivity

mCi/mmol = milliCuries per millimole

mg = milligram

mg/L = milligram per liter

mL = milliliter

mM = millimolar = millimoles per liter

Ma = million years before present

M = molar = moles per liter

d"1 = one per day

8 = porosity

ka = thousand years before present

at = transverse dispersivity

yr = year

Acronyms

BTEX - benzene, toluene, ethylbenzene, and xylene

MGP - manufactured-gas plant(s)

MODFLOW - modular ground-water-flow model

NFS - National Park Service

PAH - polynuclear aromatic hydrocarbon

PCB - polychlorinated biphenyl

PVC - polyvinyl chloride

SCDHEC - South Carolina Department of Health and

Environmental Control

SUTRA - Saturated and Unsaturated TRAnsport 

TAL - Target analyte list 

TCL - Target compound list 

USGS - U.S. Geological Survey

VIII
GEOLOGY, HYDROGEOLOGY, AND POTENTIAL OF INTRINSIC

BIOREMEDIATION AT THE NATIONAL PARK SERVICE

DOCKSIDE II SITE AND ADJACENT AREAS,

CHARLESTON, SOUTH CAROLINA,

1993-94

By

Bruce G. Campbell, Matthew D. Petkewich, 

James E. Landmeyer, and Francis H. Chapelle

ABSTRACT

A long history of industrial and commercial use of the National Park Service 

property and adjacent properties located in downtown Charleston, South Carolina, has 

caused extensive contamination of the shallow subsurface soils and water-table aquifer. 

The National Park Service property is located adjacent to a former manufactured-gas 

plant site, which is the major source of the contamination. Contamination of this 

shallow water-table aquifer is of concern because shallow ground water discharges to 

the Cooper River and contains contaminants, which may affect adjacent wildlife or 

human populations.

The geology of the National Park Service property above the Ashley Formation of 

the Cooper Group consists of two Quaternary lithostratigraphic marine units, the 

Wando Formation and Holocene deposits, overlain by artificial fill. The Wando 

Formation overlies the Ashley Formation, a sandy calcareous clay, and consists of soft, 

organic clay overlain by gray sand. The Holocene deposits are composed of clayey to 

silty sand and soft organic-rich clay. The artificial fill, which was placed at the site to 

create dry land where salt marsh existed previously, is composed of sand, silt, and 

various scrap materials.

The shallow hydrogeology of the National Park Service property overlying the 

Ashley Formation can be subdivided into two sandy aquifers separated by a leaky, 

black, organic-rich clay. The unconfined upper surficial aquifer is primarily artificial fill. 

The lower surficial aquifer consists of the Wando sand unit and is confined by the leaky 

organic-rich clay. Aquifer tests performed on the wells screened in these aquifers 

resulted in hydraulic conductivities from 0.1 to 10 feet per day for the upper surficial 

aquifer, and 16 feet per day for the lower surficial aquifer. Vertical hydraulic gradients 

at the site are typically low. A downward gradient from the upper surficial aquifer to 

the lower surficial aquifer occurs throughout most of the year. A brick-lined storm-
water-drainage archway located in the study area is a conduit for the overflow of 

seawater into the surficial aquifer during exceptionally high tides.

The efficiency of intrinsic bioremediation to reduce contaminant migration in the 

upper surficial aquifer at the National Park Service site was assessed to determine if, and 

at what concentrations, contaminants are being transported to the Cooper River. This 

assessment required incorporating hydrologic, geochemical, microbiologic, and 

demographic information into a predictive solute-transport model to determine rates of 

contaminant transport to the Cooper River. The transport of toluene and naphthalene 

was modeled as a surrogate for the transport of aromatic and other hydrocarbon 

compounds at the study area.

Laboratory estimates of the adsorption coefficients for sediments of the upper 

surficial aquifer suggest preferential adsorption of naphthalene over toluene. The 

adsorption coefficient of naphthalene is at least two orders of magnitude greater than 

that determined for toluene. Laboratory microbial-biodegradation experiments indicate 

that microorganisms present in the shallow aquifer have the potential to degrade 

toluene under anaerobic and aerobic conditions, and naphthalene primarily under 

aerobic conditions. Rates of microbial biodegradation are similar for both compounds 

under aerobic conditions.

Flow-model calibration to the January 1994 water-table surface of the upper 

surficial aquifer was achieved by specifying appropriate hydrogeologic boundary 

conditions and using hydraulic conductivity values determined in the field. The bricklined storm-water drainage archway located in the study area was modeled to account 

for ground-water discharge through this drain.

An exploratory modeling approach was used to evaluate the range of possible 

solutions that approximate the transport of contaminants to the observed distributions. 

Approximate toluene solute-transport conditions for January 1994 were estimated using 

velocity distributions simulated by the calibrated ground-water-flow model and 

simulating a constant source located on the former manufactured-gas plant property. 

Predictive solute-transport results indicate that toluene will probably not reach the 

Cooper River within 150 years under the current conditions observed in the field. 

Additional solute-transport results indicate that ground water containing naphthalene 

at concentrations ranging from 0.0 to greater than 5.0 milligrams per liter will discharge 

to the Cooper River over the next 150 years.

INTRODUCTION

In 1989, the National Park Service (NPS) acquired an 8-acre site, 4 of which are 

submerged, adjacent to the Cooper River in downtown Charleston, S.C., for future use 

as a tour-boat dock facility for Fort Sumter National Monument. During geotechnical 

testing for the tour boat dock-facility pile construction, contamination in the subsurface 

soil was detected. Since then, extensive testing has documented environmental 

contamination on the NPS property and adjacent areas.
The NPS site and the adjacent area is filled marsh and has a long history of 

commercial and industrial use dating back to the late 1700's. The northern part of the 

area (fig. 1) is currently the Charlotte Street electrical substation. A manufactured-gas 

plant (MGP) was operational in the area of the substation from approximately 1855 to 

1910. The plant was modified and operated as a carbureted-gas plant between 1910 and 

1957. Potential wastes produced by these types of plants include coal tar, various 

sludges, and iron oxides (South Carolina Department of Health and Environmental 

Control, 1992). Extensive contamination of the type associated with MGP has been 

found at and in the vicinity of the NPS site.

Calhoun Park, a city playground located south of the substation (fig. 1), was closed 

because of polynuclear aromatic hydrocarbon (PAH) contamination detected in the park 

soils in 1989. A chemical company was located on Calhoun Park property in the late 

1800's, where coal-tar distillation was used to manufacture various products. Soil 

contamination, similar to that found at the substation, has been documented (Davis and 

Floyd, 1989).

The southern part of the study area includes city of Charleston public housing that 

was built in the 1940's (fig. 1). From the 1850's to the 1930% this area was used for the 

storage of lumber, scrap metal, and rosin.

Calhoun St. (fig. 1) is underlain by a brick-lined storm-water-drainage system that 

discharges into a concrete-box culvert, which underlies the NPS property. The box 

culvert, in turn, discharges directly into the Cooper River. This drainage system is 

tidally influenced and saltwater overflows from the drain into low-lying parts of the 

area during exceptionally high tides.

The NPS plans to build the tour-boat dock facility on its property (fig. 1). Extensive 

soil and ground-water contamination has been documented on the proposed dockfacility site (General Engineering Laboratories, Inc., 1992).

The industrial use of the area produced numerous by-products and wastes, 

including PAH's; benzene, toluene, ethylbenzene, and xylene (BTEX); phenols; cyanide; 

hydrogen sulfide; ammonia; and heavy metals. Previous investigations in the study area 

(General Engineering Laboratories, Inc., 1992; South Carolina Department of Health and 

Environmental Control, 1992) indicated soil and ground-water contamination by PAH's, 

cyanide, polychlorinated biphenyls (PCB's), lead, chromium, and various other 

synthetic organic compounds.

In 1993, the U.S. Geological Survey (USGS) in cooperation with the NPS, initiated a 

study to define the NPS site geology and hydrogeology, and to determine the potential 

of intrinsic bioremediation to mitigate ground-water contamination. Field studies were 

conducted from August 1993 to January 1995. The information collected at the study 

area is part of a environmental assessment to be used by the NPS and local officials to 

evaluate site-remediation strategies.

Purpose and Scope

This report describes the results of a study initiated to describe the geology, 

hydrogeology, water use, intrinsic-bioremediation potential, and solute transport in the
f Location of Study Site

\ Private 

Business Location of U.S. Customs House

XI Former 

Manufacture_d

Gas Plant 

f [(Electrical Substation)

 I National

[Park Service

JProoertv

JPrivate 

[Property

ICondominiums

EXPLANATION

 OBSERVATION WELL

Figure 1 . Study area and locations of observation wells on National Park Service property and

adjacent properties, Charleston, S.C.
study area. This report presents the results of water-level measurements, soil sampling, 

aquifer tests, and an evaluation of the potential for intrinsic bioremediation as part of an 

overall remediation strategy. This evaluation is based largely on the analyses of 

laboratory- and field-derived data and solute-transport simulations.

The scope of the study included the installation of four ground-water-monitoring 

wells in the surficial aquifers. Soil samples collected during the drilling and groundwater samples obtained from the installed wells were analyzed for all constituents on 

the U.S. Environmental Protection Agency Target Compound List (TCL) and Target 

Analyte List (TAL), which include inorganic constituents, and volatile organic, semivolatile organic, and pesticide compounds (U.S. Environmental Protection Agency, 

1994a and b). Continuous water-level recording equipment was installed in two wells 

and recorded data from January 1994 to February 1995. Aquifer hydraulic 

characteristics were determined and used to simulate the transport of PAH and BTEX 

compounds in the surficial aquifer.

Previous Investigations

Holmes (1849) gives a general description of the Charleston area, specifically the 

filled tidal creeks on the Charleston peninsula, and a description of the shallow groundwater resources of the area. He describes white and gray sands that extend to 20-ft 

below land surface (bis) where "pump-water" was obtained by the residents. He also 

describes a sand at the top of the "great marl-bed," the Ashley Formation of the Cooper 

Group. This sand unit corresponds to the lower sand found at some locations in the 

Calhoun Park area (Chester Environmental, Inc., 1994).

Lynch and others (1881) describe the shallow ground-water resources of the city of 

Charleston along with a history of the potable-water sources used since the founding of 

the city in 1678. Of particular interest is a description of a flowing well drilled by Dr. 

Joseph Johnson in tenements he owned on Washington Street, between Boundary Street 

(now Calhoun) and Inspection Street (fig. 1). The well was 109-ft deep and terminated in 

the Ashley Formation. The source of water in the well was probably the lower surficial 

aquifer in the Wando Formation.

Stephenson (1914) gives a description of a 2,007-ft deep well located on the 

substation property. It was drilled in 1911 to provide water for boilers at the former 

MGP. The well was completed in 90 days using hydraulic rotary methods, and 

provided 617,000 gal/d through artesian flow. The well is double cased with a 14-in.- 

diameter steel casing set to 86-ft bis within the Ashley Formation and a 6 5/8 in.- 

diameter steel casing set from land surface to a depth of 1,875-ft bis. An open hole was 

extended to 2,007-ft bis through the Middendorf Formation. A lithologic log and 

descriptions of fossils found in cuttings from the well are also included in Stephenson's 

work (1914). The USGS collected borehole-geophysical logs from the well in 1990 and 

found the depth to be 1,865-ft bis. The open-hole part of the well had collapsed and 

filled the bottom 10 ft of the casing. The well functions as a piezometer for the top sand 

of the Middendorf aquifer (Gohn and Campbell, 1992) with water levels being 

continuously recorded since April 1990.
McCartan and others (1984) mapped the geology of the area between Charleston 

and Orangeburg including the study area. Park (1985) described the ground-water 

resources of Charleston, Berkeley, and Dorchester Counties (fig. 2). Weems and Lemon 

(1993) mapped the surficial geology of the Charleston quadrangle at 1:24,000 scale.

Acknowledgments

The authors thank John Tucker and Carl Wang of the NPS for support throughout 

the project. Mike Shakespear, Rhodes/Dahl, provided field support and background 

information on the site. Walter Irwin, South Carolina Electric and Gas Company, 

through Diane Roote, Chester Environmental, Inc. (now known as Groundwater 

Technology, Inc.), provided geologic samples, hydrologic information, and analytical 

data for the Calhoun Park area. Laura Cabiness, City of Charleston, provided access to 

the city storm-sewer system for flow measurements. Gerry Ebeling, City of Charleston, 

provided assistance in the search for a 400-ft deep well at Calhoun Park.

GEOLOGY

The NPS property is located in the Atlantic Coastal Plain Province in southeastern 

South Carolina (fig. 2). Geologic units at the site range in age from Late Cretaceous to 

Holocene and are composed of stratified gravel, sand, silt, clay, and limestone. The 

thickness of the Coastal Plain sediments ranges from a few feet at the Fall Line to 

approximately 3,600 ft in the southernmost part of South Carolina (fig. 2).

Regional Geology

The geologic units in the South Carolina Coastal Plain underlying the Charleston 

area include several nearshore-marine to fluvial deposits of the Late Cretaceous and 

Tertiary age that overlie pre-Cretaceous crystalline rock (fig. 3). Geologic units are, from 

oldest to youngest, the Beech Hill, Clubhouse, Cape Fear, Middendorf, Shepherd Grove, 

and Caddin Formations; the Cane Acre, Coachman, Bladen, and Donoho Creek 

Formations of the Black Creek Group; the Peedee Formation; the Rhems and 

Williamsburg Formations of the Black Mingo Group; the Santee Limestone; and the 

Cross Formation. In the shallow subsurface of the Charleston area, there are eleven 

sedimentary depositional units that record high stands of sea level during the last 40 

million years before present (Ma) (Weems and Lemon, 1993). These units are bounded 

by unconformities and are, for the most part, fossiliferous. The deposits are marine, 

marginal marine, and fluvial/estuarine in origin, and range in age from Eocene to 

Holocene. From oldest to youngest, these deposits are the Harleyville, Parkers Ferry, 

and Ashley Formations of the Cooper Group; the Chandler Bridge, Edisto, and Marks 

Head Formations; the Goose Creek Limestone, the Daniel Island beds, the Penholoway 

Formation, the Ten Mile Hill beds, the Wando Formation, and various late Pleistocene 

and Holocene alluvium, artificial fill, barrier-island sands, and estuarine deposits.
83

Blue 

Ridge

0

SOUTH>GAROLINA

y-^tiNION I , -Qk Y

. yv-i!uV *

Piedmont

EXPLANATION 

MIDDENDORF AQUIFER OUTCROP 

BLACK CREEK AQUIFER OUTCROP 

TERTIARY SAND AQUIFER OUTCROP

SURFICIAL AQUIFER OUTCROP 

CAPE FEAR AQUIFER DOES NOT CROP OUT IN SOUTH CAROLINA

33°

ATLANTIC OCEAN

20 40 60 80 MILES

0 20 40 60 80 KILOMETERS

Hilton Head Island

Figure 2. Generalized areas of outcrop of Atlantic Coastal Plain aquifers in South Carolina. (Modified from Aucott, 1988).
SYSTEM

Quaternary

fc*

03 " c

CD

Cretaceous

SERIES

Holocene

Pleistocene

Pliocene

Miocene

Oligocene

Eocene

Paleocene

CD 

Q. 

Q.

z>

LITHOLOGIC UNIT

Holocene Deposits

Wando Formation

Ten Mile Hill beds

Penholoway Formation

Daniel Island beds

Goose Creek Limestone

Marks Head Formation

Edisto Formation

Chandler Bridge Formation

Ashley Formation

CD °

Parkers Ferry Formation §" o 

°<5

Harleyville Formation °

Cross Formation

Santee Limestone

Williamsburg Formation -g §,§-

 CO C O

Rhems Formation CD ^ o

Peedee Formation

Donoho Creek Formation ^

05

CD o

Bladen Formation ^5 3

 2 

Coachman Formation "oo CO

Cane Acre Formation m

Caddin Formation

Shepherd Grove Formation

Middendorf Formation

Cape Fear Formation

Clubhouse Formation

Beech Hill Formation

AGE

8-0 ka

1 30-70 ka

240-200 ka

1 ,250-730 ka

1 ,600-730 ka

3.5 Ma

18 Ma

24 Ma

28 Ma

36-28 Ma

46-37 Ma

65-55 Ma

70-65 Ma

81 -72 Ma

83-81 Ma

84-83 Ma

86-84 Ma

89-86 Ma

95-93 Ma

98-95 Ma

ka-thpusand years before present 

Ma-million years

NOT TO SCALE

Figure 3. Lithostratigraphic units and geologic ages of Costal Plain sediments

in the Charleston B.C., area.(Modified from Weems and Lemon,

1993 and Gohn Campbell, 1992)
Late Cretaceous Deposits

Eleven formations comprise the Late Cretaceous deposits in the study area (Gohn 

and Campbell, 1992). The Beech Hill Formation is the basal Coastal Plain unit and 

overlies pre-Cretaceous crystalline rock in the Charleston area. This unit consists of 

brownish, non-calcareous clays and clayey sands. The fluvial and colluvial materials of 

this formation are interpreted as being deposited in a subaerial environment. The age of 

this formation is questionable due to the lack of fossils. The Clubhouse Formation is 

described as fossiliferous silts and sands interlayered with dark silty clays. The Cape 

Fear Formation consists of oxidized, tan to light-gray sands and gravelly sands 

interlayered with yellow-gray, red, and brown clays. The planktic fossils present in this 

formation suggest a marginal-marine to marine depositional environment. The 

Middendorf Formation overlies the Cape Fear Formation and consists of fine to coarse 

sands and lignitic clays. The uppermost sand in this formation is composed of fine- to 

medium-fossiliferous sand. This formation appears to have been deposited in 

flu vial/estuarine and nearshore-marine environments. Light olive-gray to medium 

light-gray, calcareous silty clay, clayey silt, and fine sand comprise the Shepherd Grove 

Formation. The marine fossils, fine grain size, and heavy bioturbation suggest 

deposition in a marine, subtidal environment. The Caddin Formation consists of light 

olive-gray to greenish-gray, clayey, calcareous, fine glauconite and quartz sand. This 

unit represents a fully marine environment.

The Black Creek Group consists of four units in the Charleston area, which includes 

the Cane Acre, Coachman, Bladen, and Donoho Creek Formations. These units 

represent cycles of transgressive-regressive marine to nearshore deposits that are 

separated by basal phosphatic, glauconitic, and (or) shelly lag deposits (Gohn and 

Campbell, 1992).

The Peedee Formation consists of two sections, the lower of which is composed of 

gray, calcareous, clayey and silty, fine to medium sand (Gohn and Campbell, 1992). This 

section also contains sand-sized glauconite and coarse to very coarse quartz sand. This 

lower section is overlain by a gray-green, calcareous, massive clayey silt. Both sections 

contain common microfossils and phosphate.

Tertiary Deposits

The Tertiary Black Mingo Group is composed of two Upper Paleocene formations: 

the Williamsburg Formation and the underlying Rhems Formation (Sloan, 1908). The 

dominant lithology of the Black Mingo Group consists of interbedded sequences of 

greenish-gray mudstones and dark-gray to black laminated clays. This unit is 

fossiliferous and was deposited in inner-shelf and marginal-marine environments 

(Park, 1985).

The Santee Limestone is a creamy-white to gray, fossiliferous and slightly 

glauconitic calcilutite to calcirudite. It was formed in an open-marine-shelf 

environment.
The middle to upper Eocene Cross Formation is a white, dense, partially silicified 

calcilutite containing abundant foraminifera, echinoid spines, and ostracods 

(Fronabarger and others, 1995). Total thickness of the Cross Formation at the site is 

approximately 50 ft. The sediments were deposited in an outer-continental-shelf 

environment 46-37 Ma.

Tuomey (1848) named the relatively unconsolidated, greenish-yellow limestones 

that comprise what is now known as the Cooper Group. Ward and others (1979) 

subdivided the original Cooper Formation into three members (the Harleyville, Parkers 

Ferry, and Ashley) based on the presence of basal unconformities represented by 

phosphatic or glauconitic lag deposits. Weems and Lemon (1984) raised the original 

Cooper Formation to Group rank and the attendant members to Formation rank. The 

Parkers Ferry and Ashley Formations are the most widespread of the shallowsubsurface formations in the Charleston area. The Harleyville Formation is a compact, 

phosphatic, calcareous clay and clayey calcarenite. The Parkers Ferry Formation is 

described as a dense, sticky, moderate yellowish-green to light blue-green calcilutite. It 

was formed in a open-marine-shelf environment approximately 36-28 Ma. The Ashley 

Formation is a tough, light olive-brown, weakly cemented, phosphatic and quartzose 

calcarenite. It was formed in a open-marine-shelf environment about 36-28 Ma.

Sanders and others (1982) named the medium-gray to dusky-green quartz and 

phosphatic sands of the Chandler Bridge Formation. These sediments accumulated in 

lagoonal to shallow-marine environments about 28 Ma. Deposits of the Chandler Bridge 

Formation are patchy, because they formed in dispersed, topographically low areas on 

the top of the Ashley Formation.

Sloan (1908) named the Edisto Formation. It is an olive-gray to greenish-gray, 

phosphatic, shelly, calcareous sand that was deposited approximately 24 Ma. This 

formation is thought to be the parent lithology for the phosphate that was extensively 

mined in the Charleston area in the early 1900's.

Abbott and Huddleston (1980) defined the Marks Head Formation as olive-gray to 

moderate olive-brown quartz phosphate beds and attapulgite-rich clays. The unit was 

formed in shallow, brackish-water lagoons about 18 Ma.

Weems and others (1982) described the white to very pale-orange quartzose and 

phosphatic calcarenite of the Goose Creek Limestone. The Goose Creek Limestone was 

deposited in a open-shelf, shallow-marine environment that received little clastic influx 

from land between 3 and 4 Ma.

Quaternary Deposits

Quaternary deposits form five terrace complexes in the lower South Carolina 

Coastal Plain. These deposits, which formed during interglacial ages, represent partially 

filled-backbarrier, barrier-island, and shallow-marine-shelf deposits (Weems and 

Lemon, 1993). Each barrier island deposit represents the position of the Atlantic 

shoreline at the time it was formed. These deposits are similar to the ones forming along 

the present-day shoreline. The terrace deposits record successive transgressive and

10
regressive shoreline movements caused by sea-level changes superposed on vertical 

tectonic uplift.

The Daniel Island beds are an informal subsurface unit consisting of layers of dark 

bluish-gray to dark-gray clay, mud, and sandy clay, which formed approximately 1.2 

Ma. These beds are inshore deposits of an extensive paleoestuary system that is 

preserved in deeply cut estuaries that were not scoured during later transgressions.

McCartan and others (1984) defined the Penholoway Formation as a sand, clayey 

sand, and clay deposited in shallow-marine to marginal-marine environments 

approximately 970 thousand years before present (ka). The only sediments of the 

Penholoway Formation found in the Charleston area occur in the 82- to 83-ft interval bis 

at a Middendorf aquifer well located 3,500 ft southwest of the NFS property (location 

not shown).

Weems and Lemon (1993) designated the clays and clayey sands that underlie the 

Cainhoy barrier as an informal unit called the Ten Mile Hill beds. These sediments were 

deposited in marginal-marine and lagoonal environments adjacent to a barrier beach.

McCartan and others (1980) defined the slightly weathered beds of sand, clayey 

sand, and clay underlying the Pamlico and Princess Ann terraces as the Wando 

Formation (fig. 4). The Wando Formation is characterized by an extensive outcrop area 

extending from Georgetown to Hilton Head parallel to the present-day coastline. The 

outcrop belt is typically 7-mi wide and 74-mi long. The unit varies in thickness from 3 to 

about 82 ft. The maximum elevation of the formation is 32-ft above sea level. The 

formation is composed of six distinct facies deposited during three late Pleistocene high 

sea-level stands. Weems and Lemon (1993) report that in many places in the Charleston 

area, the high sea-level, transgressive-sand deposits are separated by clay beds 

deposited in lagoonal environments during minor regressions. The oldest Wando 

Formation facies was deposited when sea level was about 25 ft above its present level in 

the Charleston area. The third facies was deposited when sea level was about 15 ft above 

its present level. No terrace level from the second facies was preserved as it was 

probably overridden by the transgression that produced the third facies. A coral found 

in the Wando Formation along the Wando River has been dated at 130 +/-10 ka by 

Szabo (1985). Other corals found in the formation have yielded dates of 80 to 90 ka.

Recent deposits of tidal marsh, peat and muck, and recent alluvium of 

Wisconsinian and Holocene age are not formally named in the Charleston area. These 

deposits are found in and around the Cooper and Wando Rivers and Carolina Bays.

Site Geology

The NPS site is located west of the Cooper River on the Charleston Peninsula and is 

underlain by pre-Cretaceous crystalline rock, and Cretaceous, Tertiary, and Quaternary 

sediments (fig. 3). Geologic units overlying the Ashley Formation consist of two 

Quaternary lithostratigraphic marine units and surficial, artificially emplaced fill. The 

two marine units are the Wando Formation and Holocene deposits. Several geologic 

cross sections were completed using boring information collected from wells drilled on

11
WILLIAMSBURG 

CO.

ORANGEBURG 

^ CO.

COLLETON 

CO. CHARLESTON

5 10 15 20 25 MILES 

I I f I

l l I l I 

0 5 10 15 20 25 KILOMETERS

EXPLANATION

APPROXIMATE SEAWARD LIMIT OF TERRACES

Figure 4. Pleistocene terraces in the Charleston, S.C area (modified from Weems and Lemon, 1993).

12
the NFS site and adjacent properties (figs. 5 and 6). Boring logs for the four NFS wells 

drilled in November 1993 are listed in Appendix I (fig. 5).

The Wando deposits overlie the Ashley Formation starting at depths between 25- to 

80-ft bsl. These deposits consist of a clay layer overlain by sand, both of which represent 

a fossiliferous, marine-depositional environment. The upper deposits, gray sand with 

variable amounts of clay and shell, may represent an open-shelf, marine-depositional 

environment. The lower deposits consist of soft-organic and stiff-inorganic clays with a 

slight sand and shell content. These sediments may have been deposited in an 

embayment environment similar to present-day Charleston Harbor (R. E. Weems, U.S. 

Geological Survey, written commun., 1993).

Above the Wando Formation, the Holocene deposits vary in thickness and extend 

from sea level to depths of 60-ft bsl. These sediments are composed of mostly clayey to 

silty sand and clay, and probably represent a back barrier, flat-depositional 

environment. The Holocene clay units tend to be organic-rich, soft, and non-compacted 

(McCartan and others, 1990).

The surficial material on the NFS site consists of artificial fill, which was deposited 

along the Cooper River over the past 300 years. This fill consists of sand, silt, wood, 

sawdust, concrete, bricks, cinders, and metallic debris (nuts and bolts) and varies in 

thickness from 5 to 26 ft (General Engineering, Inc., 1992; Soil Consultants, 1989). The 

origin of this fill material is questionable, and may have been deposited from the various 

industries that occupied the NFS site and adjacent property since the 1700's (South 

Carolina Department of Health and Environmental Control, 1992).

HYDROGEOLOGY

The hydrogeological evaluation completed for the NFS site included a description 

of the aquifers and confining units, a general description of ground-water flow in the 

area, and a compilation of ground-water use information for wells located near the 

study area. The hydrogeologic units described range in age from Recent to Late 

Cretaceous.

Aquifers and Confining Units

The NFS property is underlain by a series of aquifers and confining units of the 

Atlantic Coastal Plain sediments that extend from the land surface to approximately 

2,500-ft bis. The units are distinguished on the basis of their relative permeabilities. The 

units, in descending order from the land surface, are: upper surficial aquifer, lower 

surficial aquifer confining unit, lower surficial aquifer, Santee Limestone/Black Mingo 

confining unit, Santee Limestone/Black Mingo aquifer, Black Creek confining unit, 

Black Creek aquifer, Middendorf confining unit, Middendorf aquifer, Cape Fear 

confining unit, and Cape Fear aquifer (fig. 7).

13
EXPLANATION

TRACE OF GEOLOGIC SECTION

OBSERVATION WELL LOCATIONAND WELL INDENTIFICATION NUMBER

SOIL BORING LOCATION AND 

IDENTIFICATION NUMBER

Cooper 

River

SITE 

REFERENCE

Private 

Business

USGMS Property ,**\ r ^*

USGS-2 .*** Jfc' USGS-1 B'

Former

Manufactured 

Gas Plant Private 

Property

Calhoun 

Park

Condominiums

00

100 200

50

300

100

400 FEET

METERS

Figure 5. Locations of geologic sections A-A1 , B-B', C-C1 , and D-D1 on the National Park Service property and adjacent properties, Charleston, S.C.
A-A1 B-B'

S6 S7 S2

A'

S1

SEA LEVEL-

 10-

 20  30- 40- 50- 80  70  80- 90-

 100- 110 

HOLOCENE DEPOSITS (CLAY) 

~~-______^

WANDO FORMATION (SmS)

WANDO FORMATION (CLAY)

ASHLEY FORMATION

 120-

- SEA LEVEL- -10

- -20- -30- -40- -50

- -90- -100

- -110 

-120

b s0 wF Q o zUJ UJ If) CO

FEET B B' FEET

10-]

S EA LEVEL - 10-

-20--30--60- 70--80--90-

-100-

S5 S4 S3

=;-Ji

ARTIFICAL FILL

j^> HOLOCENE DEPOSITS (CLAY)'^^~~^- - _ WANDO FORMATION (SAND)

- .

WANDO FORMATION (CLAY)

'

- 

HOLOCENE DEPOSITS (CLAY)

~~~ ~-_ -$- HOLOCENE DEPOSITS (SAND)

^~~--^

^^

ASHLEY FORMATION

-_ -^_

f

±:

r1 -=

-10- SEA LEVEL

--10--20--30--60--70--80

 90-100

0 50 FEET0 I'D METERS

ON

C-C' D-D'

EXPLANATION

SAND FACIES [-'^-"J CLAY FACIES

SANDY CLAY or CLAYEY SAND FACIES b4xd SANDY LIMESTONE

Figure 6. Geologic sections A-A', B-B', C-C', and D-D' across the National Park Service property and adjacent properties, Charleston, S.C.
Quaternary

^

D

t 

(D

Cretaceous

Holocene

Pleistocene

Oligocene

Eocene

Paleocene

Upper

Artificial fill

Estuarine deposits

Wando Formation

Ashley Formation

Parkers Ferry 

Formation

Harteyville 

Formation

1%o o

O ffi (jCD

Cross Formation

Santee Limestone

Williamsburg 

Formation

Rhems 

Formation

^OQ. oo>3

DC O

m^O

Peedee 

Formation

Donoho 

Creek 

Formation

Bladen 

Formation

Coachman 

Formation

Cane Acre 

Formation

Q. 

O

0 

_^

(D 

(D

U 

.^

O 

O 

CO

Caddin 

Formation

Shepherd Grove 

Formation

Middendorf 

Formation

Cape Fear 

Formation

Clubhouse 

Formation

Beech Hill

Formation

Upper surficial aquifer

Lower surficial 

aquifer confining unit

Lower surficial aquifer

Santee Limestone/ 

Black Mingo 

confining unit 

(Cooper Marl)

Santee Limestone/ 

Black Mlngo aquifer

Black Creek 

confining unit

Black Creek 

aquifer

Middendorf 

confining 

unit

Middendorf 

aquifer

Cape Fear 

confining unit

Cape Fear aquifer

Confining unit

Sand, silt, clay, cinders, 

bricks, tar, wood

Dark, organicrich clay

Gray, fine-grained 

quartz sand

Greenish-yellow 

sandy calcareous 

clay

White fossiliferous calcilutite

Light-gray sandy 

fossiliferous 

limestone

Gray to black 

micaeous, calcareous 

clay; calcareous, silty 

clay; clayey sand

Macrofossiliferous 

clayey, fine to 

medium sand.

Gray, calcareous, 

silty, sandy clay.

Macrofossiliferous 

medium to coarse 

sand; dark, lignitic 

clay interbeds.

Olive to gray 

silty clay.

Well-sorted 

silty, fine to 

medium sand.

Brown, medium 

silty clay.

20'

20'

25'

280'

120'

340'

570'

200'

250'

200'

240'

126'

Figure 7. General geologic, hydrologic, and lithologic logs of the subsurface Coastal Plain

environment at the National Park Service Dockside II site, Charleston, S.C.

(modified from Gohn and Campbell, 1992).

16
Surficial Aquifer System

The surficial aquifer system underlying the NFS property can be subdivided into 

an unconfined upper surficial aquifer comprised largely of artificial fill at the site and a 

partially to fully confined lower surficial aquifer comprised of the sands of the Wando 

Formation. The two units are separated by a leaky confining unit of black organic-rich 

Holocene clay.

The upper surficial aquifer is found in artificial fill placed at the site to create dry 

land where salt marsh had once been (Reynolds, 1987). This aquifer varies in thickness 

across the NFS property, but tends to thicken toward the northeast part of the site as 

shown in figure 8. Hydraulic conductivities of 13 ft/d are reported for the surficial 

aquifer in the Charleston area (Park, 1985).

The clay separating the upper and lower surficial aquifers is part of the old salt 

marsh on which the artificial fill was emplaced (fig. 9). The clay varies in thickness 

across the NFS property (fig. 9). The lower surficial aquifer, unlike the upper surficial 

aquifer, consists of naturally deposited sediments of the Wando Formation that vary 

from 17- to 59-ft bis (fig. 10). This aquifer tends to thicken toward the northern part of 

the property (fig. 11). These sands and clays are characterized by distinctive textures, 

colors, and sedimentary structures, unlike the heterogeneous fill that comprises the 

upper surficial aquifer. The lower surficial aquifer is composed of the barrier-sand facies 

and possibly the fossiliferous shelf-sand facies of the Wando Formation (Weems and 

Lemon, 1993). This aquifer is extensive across the entire Charleston peninsula and is 

described in Lynch and others (1881) as the "60-foot sand/'

Santee Limestone/Black Mingo Confining Unit

The Santee Limestone/Black Mingo aquifer is confined by dense, low permeability 

sediments of the Cooper Group and Cross Formation (fig. 7). These calcarenites are 

approximately 280-ft thick beneath the NFS site and comprise a highly effective 

confining unit. Few vertical hydraulic conductivity measurements are available for the 

Cooper Group sediments. Chester Environmental, Inc. (1994) reports laboratoryderived vertical hydraulic conductivities of 1.5 X 10'7 to 2.0 X 10-7cm/s (4.3 X 10'4 to 

5.7 X 10~4 ft/d, respectively) for Ashley Formation sediments of the Cooper Group in the 

Calhoun Park area (fig. 1). A qualitative measure of the low permeability of the Ashley 

Formation sediments is presented by Gibson (1942) from observations made during the 

construction of the water-supply tunnel from the Edisto River to Charleston in 1936-37. 

Observed infiltration rates into the tunnel during construction were 0.5 (gal/d)/ft of 

length of the 7-ft-diameter tunnel.

17
Cooper 

River

100 200 300 400 FEET

100 METERS

EXPLANATION

, 15 ... L| NE OF EQUAL THICKNESS OF THE 

UPPER SURFICIAL AQUIFER-Dashed 

where approximately located. Interval 5 feet.

,13 DATA POINT--Number is thickness of the 

upper surficial aquifer, in feet.

14 OBSERVATION WELL--Number is thickness 

of the upper surficial aquifer, in feet.

Figure 8. Thickness of the upper surficial aquifer beneath the National Park Service

property, Charleston, S.C.

18
\

Copper 

River

X National 

Park Service 

Prdpprty

100 200 300 400 FEET

100 METERS

13

L AN ATION

LINE OF EQUAL THICKNESS OF 

THE UPPER CONFINING UNIT-- 

Dashed where approximately 

located. Interval 10 feet.

DATA POINT-Number is thickness 

of the upper confining unit, in feet.

Figure 9. Thickness of the upper confining unit beneath the National Park 

Service property, Charleston, S.C.

19
Copper 

River

National

Park Service

Property

EXPLANATION

100 200 300 400 FEET

100 METERS

33

- TOP OF AQUIFER CONTOUR-- Shows 

depth to the top of the lower surficial 

aquifer. Dashed where approximately 

located. Contour interval 10 feet. 

Datum is land surface.

DATA POINT-Number is depth to the 

top of the lower surficial aquifer, in feet 

below land surface.

Figure 10. Depth to the top of the lower surficial aquifer beneath the 

National Park Service property, Charleston, S.C.

20
\

Cooper 

River

""-. National /

ParPcSemcej/15

Property f

XPLANATION

- LINE OF EQUAL THICKNESS OF 

THE LOWER SURFICIAL AQUIFER 

Dashed where approximately 

located. Interval 5 feet.

0 13 DATA POI NT-Number is thickness 

of the lower surficial aquifer, in feet.

200 300

100 METERS

Figure 11. Thickness of the lower surficial aquifer beneath 

the National Park Service property, Charleston, S.C.

21
Santee Limestone/Black Mingo Aquifer

The Eocene-age Santee Limestone is the northern extension of the Floridan aquifer, 

one of the most extensive limestone aquifers in the United States. The Santee Formation 

is described by Cooke (1936) as a white to creamy-yellow, fossiliferous, glauconitic 

limestone. The section at well CHN-14, located on the electrical substation property 

described by Stephenson (1914) (fig. 1), is 20-ft thick with alternating hard and soft, lightgray, sandy, fossiliferous limestone (fig. 7).

The underlying Black Mingo sediments are usually hydraulically connected to the 

Santee Limestone and form a single aquifer (fig. 7). The Black Mingo sediments are 

described as dark- to light-gray, sandy, micaeous, calcareous clays and loose, darkgreen, glauconitic sand. The aquifer is effectively confined by the overlying Cooper 

Group sediments. Water levels in wells completed in the Santee Limestone/Black 

Mingo aquifer near the NFS property average approximately 30-ft bis. The aquifer is an 

important source of potable water in the Charleston, Berkeley, and Dorchester County 

area (fig. 2).

Black Creek Aquifer and Overlying Confining Unit

The Black Creek aquifer is the uppermost regionally extensive aquifer of 

Cretaceous-age in the southern South Carolina Coastal Plain and is composed of sands 

of the Black Creek Group, and locally, sands of the overlying Peedee Formation (Aucott 

and Speiran, 1985) (fig. 7). The overlying Peedee Formation and lower part of the Black 

Mingo Formation effectively confine the Black Creek aquifer at the regional scale. The 

Black Creek aquifer thickens from its outcrop area to the present-day shoreline.

Middendorf Aquifer and Overlying Confining Unit

The Middendorf aquifer, in the Charleston area, is composed of late Cretaceous-age 

sands of the Middendorf Formation, and locally, sands of the overlying Shepard Grove 

Formation and the underlying Cape Fear Formation (Aucott and Speiran, 1985) (fig. 7). 

In outcrop, the Middendorf Formation is an interbedded clay and sand sequence 

deposited in environments ranging from delta plain to fluvial. In the Charleston area, 

the Middendorf aquifer is composed of well-sorted, coarse-grained sands and 

interbedded dark, lignitic clays deposited in marginal-marine environments. The 

Middendorf aquifer is confined at the top by low-permeability sediments of the Cane 

Acre and Caddin Formations.

Cape Fear Aquifer and Overlying Confining Unit

The Cape Fear aquifer is the lower-most, late Cretaceous-age Coastal Plain aquifer 

(Aucott and Speiran, 1985) (fig. 7). This aquifer is composed of thick, red clays with

22
immature, poorly sorted quartz and feldspar. In the Charleston area, thick sand units 

are present in the lower part of the Cape Fear Formation. These sands form the Cape 

Fear aquifer, which is confined by low permeability clay in the upper part of the Cape 

Fear Formation.

Ground Water

All of the Coastal Plain geologic materials underlying the NFS site are saturated 

with ground water. These materials are divided into aquifers and confining units based 

on their relative permeability.

Ground-Water Flow

The surficial aquifers underlying the NFS site are saturated with ground water. 

Ground water in the surficial aquifer at the NFS site moves from higher elevations (at 

the topographic divide along the center axis of the Charleston peninsula) toward the 

Cooper River (fig. 1). The primary direction of the hydraulic gradient of the ground 

water in the surficial aquifer is toward the Cooper River; however, local gradients 

caused by topographic highs (such as the fill material located on the electrical substation 

property) or underground drainage structures (such as the brick archways) may cause 

variations in this overall flow direction. Ultimately, all of the water flowing in these 

surficial aquifers discharges to the Cooper River, unless it is removed by pumping or 

evapotranspiration.

Ground-Water Recharge

Although this area of South Carolina receives approximately 48 in. of precipitation 

per year, probably only a small percentage of the total rainfall recharges the water-table 

aquifer; largely as a result of land use, surface runoff, and evapotranspiration. An 

estimate of net recharge to the surficial aquifer using the USGS modular ground-waterflow model MODFLOW (McDonald and Harbaugh, 1988) indicates a net recharge rate 

to the surficial aquifer of approximately 0.2 in/yr.

This small estimated net-recharge rate may be explained by the nature of trie land 

use in Charleston, a warm, humid climate characterized by high rates of 

evapotranspiration, and the presence of brick drainage archways beneath the streets. 

Land within the city of Charleston is highly developed and has very few open areas 

where precipitation can infiltrate to permeable surfaces. This results in an abundance of 

runoff during and following precipitation. Areas of Charleston that are undeveloped 

and where infiltration of rain water can potentially occur usually are populated with 

trees, shrubs, and grasses, which in conjuction with evaporation, remove potential 

recharge water through transpiration. Finally, the brick-lined drainage archways 

beneath the city streets, which were not simulated by the MODFLOW model, act as a 

sink by receiving ground-water flow from the shallow aquifer. This sink tends to

23
decrease the overall elevation of the water-table surface. The net recharge value of 0.2 

in./yr is considered a minimum value. Krause and Randolph (1989) suggested an 

approximate net recharge rate of 4 in./yr for this area. However, the Krause and 

Randolph investigation was a regional study that did not differentiate between 

developed and rural areas; thus, net recharge was possibly overestimated for the 

Charleston peninsula.

The water-table potential distribution for the upper surficial aquifer on the NFS site 

(September 14,1994) indicates that radial flow occurs away from a recharge mound in 

the center of the NFS site (fig. 12). Such recharge mounds are present in open areas, such 

as the NFS site, where man-made structures are absent. Water-table elevations also 

indicate that ground-water flow in areas outside the NFS property also is affected by the 

brick-lined archway located beneath Calhoun Street (Chester Environmental, Inc., 1994).

Hydraulic Characteristics

To determine the lateral hydraulic conductivity of the sediments on the NFS 

property, aquifer tests were conducted in several of the wells on site. The lateral 

hydraulic conductivity of an aquifer is a measure of the rate at which water of a specific 

density and viscosity can flow through the aquifer medium. A slug test is a type of 

aquifer test that estimates the lateral hydraulic conductivity of the aquifer directly 

surrounding the screened part or open section of the well being tested. Slug tests consist 

of measuring the change in the water level in a well, over time, after instantaneously 

displacing a certain volume of water in the well. Displacement can occur by physically 

adding or removing a submergible object or a volume of water (the slug) to or from the 

well (Lohman, 1972). Displacement may also occur by pushing water out of the 

screened or open section of the well by the introduction of compressed air (J.H. Doss, 

U.S. Geological Survey, written commun., 1993). The results of the water-level recovery 

data are analyzed using methods specifically developed for the aquifer characteristics 

and test methodology (Bouwer and Rice, 1976).

The September 1993 slug tests were all completed using an air compressor to 

displace the water in the wells. This methodology was chosen to eliminate the need for 

decontamination of slug-test equipment that would come into contact with the 

contaminated ground water. Tests completed in December 1993 consisted of positiveand negative-displacement-slug tests. Well identification, test dates, and test 

methodology and analysis are listed in appendix II.

Test results for wells screened in the unconfined upper surficial aquifer were 

analyzed using the Bouwer and Rice Method for partially or fully penetrating wells 

(Bouwer and Rice, 1976; Bouwer, 1989). Test results for wells screened in the confined 

lower surficial aquifer were analyzed using the Cooper method (Cooper and others, 

1967). Calculated lateral hydraulic conductivity values for the upper surficial aquifer 

range from 0.1 to 10 ft/d (fig. 13). A lateral hydraulic conductivity value of 16 ft/d was 

determined for the lower surficial aquifer.

24
ational

Service 

Property

Cooper 

River

EXPLANATION

3.5- - - WATER TABLE CONTOUR-- Shows 

elevation of water table, September 14, 

1994. Dashed where approximately located. 

Contour interval 0.5 feet. 

Datum is sea level.

3.26 OBSERVATION WELL-Number is altitude 

of water level, in feet, above mean sea level,

Figure 12. Water-table surface of the upper surficial aquifer, National 

Park Service property, Charleston, S.C., September 14, 1994.

25
Cooper 

River

National

Service 

Property

100 200 300 400 FEET

100 METERS

EXPLANATION

MW-4 OBSERVATION WELL LOCATION, WELL 

 0.4 IDENTIFICATION, AND HYDRAULIC CONDUCTIVITY 

VALUE, IN FEET PER DAY, FOR WELLS SCREENED 

IN THE UPPER SURFICIAL AQUIFER.

USCS-2 OBSERVATION WELL LOCATION, WELL

Ol 6 IDENTIFICATION, AND HYDRAULIC CONDUCTIVITY 

VALUE, IN FEET PER DAY, FOR WELLS SCREENED 

IN THE LOWER SURFICIAL AQUIFER.

NM HYDRAULIC CONDUCTIVITY NOT MEASURED.

Figure 13. Lateral hydraulic conductivity values measured in surficial aquifers 

located on the National Park Service property, Charleston, S.C., 1993.

26
Four monitoring wells were installed for this investigation. A well pair (USGS-2 

and USGS-2S) was installed at the site and fitted with continuous water-level recording 

equipment (fig. 13). Well USGS-2S was screened in the upper surficial aquifer, and 

USGS-2 was double cased and screened in the lower surficial aquifer. The wells are 

located approximately 6 ft apart. Wells USGS-1 and USGS-3 were screened in the lower 

surficial aquifer adjacent to pre-existing upper surficial aquifer wells, thus making two 

additional well pairs.

The water levels in the upper surficial aquifer fluctuate due to several stresses. In 

the winter months, when there is little growing vegetation and reduced 

evapotranspiration, rainfall events produce marked rises in water levels in the aquifer. 

On January 28,1994, for example, 0.43 in. of rain was recorded between 8 and 

10 a.m. at the National Weather Service rain gage located approximately 4,000 ft south of 

the NFS property. The water level in the upper surficial aquifer well USGS-2S 

responded by rising from 3.85 ft at 8 a.m. to 5.26 ft at 2 p.m., a total rise of 1.41 ft in 6 

hours (fig. 14). Water levels in the upper surficial aquifer react similarly during the rainy 

season of summer months when the soil is highly saturated with ground water. 

However, during the extended low-rainfall period between March and May 1994, 

isolated events had little influence on the water levels of the upper surficial aquifer. A 

0.95 in. rainfall on April 22,1994, from 5 p.m. to 11 p.m., raised the water level in 

USGS-2S by 0.01 ft, from 2.29 ft to 2.30 ft (fig. 14). The controlling influence on the 

upper surficial aquifer water levels appears to be the soil-moisture content and 

evapotranspiration rates. Water levels in this aquifer also are influenced by the semidiurnal tides that occur in Charleston Harbor, responding a few hundredths of a foot 

due to the tidal loading.

Water levels in the confined lower surficial aquifer are influenced by the Cooper 

River due to tidal loading. As the stage of the Cooper River increases during the hightide cycle, the increased volume of water in the river basin exerts an increasing amount 

of pressure on the confining unit and lower surficial aquifer where these units are in 

contact with the river. This increased pressure is dissipated during the low-tide cycle. 

During the period of January 1994 to August 1994, continuous water levels recorded 

little variation at USGS-2 (fig. 14).

Continuous water-level measurements in the upper surficial aquifer (well 

USGS-2S) and the lower surficial aquifer (well USGS-2) illustrate the changing 

vertical hydraulic gradients between these aquifers throughout the year (fig. 14). 

Vertical hydraulic gradients for the three well pairs located on the NFS property 

(fig. 13) are listed in table 1. The vertical flow component between the upper and lower 

surficial aquifers at the site typically is downward. This is evident by predominantly 

higher water levels in USGS-2S compared to water levels in USGS-2 (fig. 14). However, 

an upward vertical hydraulic gradient was observed in May and June 1994 following a 

relatively dry period that began in March. The downward vertical hydraulic gradient 

returned on June 10 following a 1.4 in. rainfall and continued throughout the remainder 

of the year. A vertical hydraulic gradient reversal between the upper and lower surficial 

aquifers was observed in the USGS-3/MW-4 well pair for high- and low-tide water-level 

measurements made on January 8,1994 (Chester Environmental, Inc., 1994). This 

reversal was not observed in the other two well pairs located on the NFS property.

27
^s

Z UJ> oUJ -J^J UJUJ CQ> o

2 - -1

a 

O 

aUJa.

CO 

UJO

u.Z

RAINFALL AT THE CUSTOMS HOUSE, 

CHARLESTON, SOUTH CAROLINA

II I

1 994

Figure 14. Hydrograph of wells screened in the upper (USGS-2S) and lower (USGS-2) surficial aquifers on the National Park Service property and National Weather Service Rainfall Data, Customs House rain gage

Charleston, S.C., January 1994 to November 1994.
Table 1.-- Vertical hydraulic gradients measured during the low-tide cycle in well pairs 

located on the National Park Service property, Charleston, S.C.

[ft/ft, foot per foot; USGS, U.S. Geological Survey; MW, monitoring well; 

[-, vertical gradient downward]

Well Pair 

(fig. 15)

USGS-1

MW-9

USGS-2

USGS-2S

USGS-3

MW-4

January 8, 1994 

(ft/ft)

-0.03

-.08

.01

September 14, 1994 

(ft/ft)

-0.03

-.07

-.07

Ground-Water Use

Locations of wells within 1- and 3-mi radii surrounding the NFS site are shown in 

figure 15 (Ted Millings, S.C. Department of Natural Resources, Water Resources 

Division, written commun., 1994). The wells within the 1-mi radius include two watersupply wells, one recreational well, one well of unknown use, and several monitoring 

wells. These monitoring wells are associated with a previous investigation of the study 

area and are screened in the upper and lower surficial aquifers. The water-supply wells 

are screened in the Middendorf aquifer (fig. 7). Wells located within a 3-mi radius are 

either unused, used as water-supply wells for the cities of Charleston and Mount 

Pleasant, or used for recreation, irrigation, domestic use, or for monitoring purposes.

INTRINSIC-BIOREMEDIATION POTENTIAL

The efficiency of intrinsic bioremediation (natural attenuation) to contain 

contaminant migration in ground-water systems can be assessed by quantitatively 

comparing rates of contaminant transport to rates of biodegradation. If rates of 

transport by ground water are fast relative to rates of biodegradation, then contaminants 

may migrate more freely with ground water and possibly reach points of contact with 

human or wildlife populations. Conversely, if transport rates are slow relative to

29
79'55" 79'50" 79'45"

32'55'

32'50" - North Charleston Charleston Harbor ivans Island

EXPLANATION

WELL LOCATION 0 6,000 12,000 FEET James Island

Figure 15. Wells located within 1 and 3 miles of the National Park Service Property, Charleston, S.C.
biodegradation rates, contaminant migration will be more confined and be less likely to 

reach points of contact. In either case, the efficiency of intrinsic bioremediation can be 

assessed at a particular site by evaluating the presence or absence of contaminant 

transport to pre-determined points of contact. This assessment included hydrologic 

(rates of ground-water flow), geochemical (adsorption properties of the aquifer 

material), microbiologic (rates of degradation), and demographic (point of contact) 

considerations.

The USGS has developed a framework for assessing the efficiency of intrinsic 

bioremediation that is based on integration of hydrologic, geochemical, and 

microbiologic data using a digital solute-transport model to determine rates of 

contaminant transport from a source area to pre-defined points of contact (such as 

adjacent surface-water bodies) (Chapelle and others, 1996). This framework is consistent 

with recent guidance documents prepared by the South Carolina Department of Health 

and Environmental Control (SCDHEC) and is designed for application at sites where 

ground-water contamination is the principle issue of concern.

Two approaches commonly used to examine the transport of contaminants in the 

subsurface are consolidative and exploratory modeling. The objective of consolidative 

modeling is to find the unique solution to a problem by simulating the "exact" 

conditions at the site. This effort involves reproducing the potentiometric surface and 

contaminant plume observed in the field by calibrating the model using hydrologic, 

chemical, and biologic parameters such as hydraulic conductivity, dispersivity, porosity, 

adsorption, and biodegradation. Each of these parameters can be determined for 

specific locations in the field; however, these parameters can be highly variable, spatially 

and temporally. Measuring the variability of these parameters in the field and 

reproducing them in a model is a very cumbersome and expensive task, so much so that 

most studies do not try to characterize the variability, but instead try to determine and 

model average values of these parameters. Field data are seldom sufficient to 

adequately describe the spatial variability of these parameters and, as a result, 

consolidative modeling is generally less appropriate than exploratory modeling as a 

method to investigate subsurface contamination transport. Exploratory modeling 

efforts focus on determining the range of possible solutions that adequately represent 

the conditions observed in the field. This is accomplished by varying model parameters, 

within reasonable ranges, in order to determine appropriate limits for each parameter.

The exploratory modeling approach was used to simulate the conditions at the NFS 

site and adjacent properties. This approach was used to determine under what 

conditions, if any, would contaminants reach points of contact, and if so, at what 

concentrations. The USGS two-dimensional model SUTRA (Saturated and Unsaturated 

TRAnsport) was chosen for this study because it simulates ground-water flow and 

transport of a single reactive or non-reactive solute within the subsurface environment 

(Voss, 1984). SUTRA also accounts for the reactive processes of adsorption and 

biodegradation of contaminant in the model area. Knowledge of the rates of these two 

processes is critical to determining the rate of transport of organic contaminants in the 

subsurface environment.

31
The processes of advection, mechanical dispersion, adsorption, and microbial 

degradation can be described by the one-dimensional mass-balance equation (Freeze 

and Cherry, 1979):

- SCn - kC, (1) at ex2 ax

where

C is solute concentration, in milligrams per liter;

t is time, in days;

D is the coefficient of hydrodynamic dispersion, in square feet per day;

x is distance, in feet;

v is ground-water-flow velocity, in feet per day;

S is adsorption isotherm parameter, in feet cubed per milligram;

n is adsorption isotherm parameter, unitless; and,

k is a first-order microbial degradation rate constant, in one per day.

Although SUTRA is a two-dimensional model, a one-dimensional equation was 

described for simplicity.

The primary hydrologic factors that affect solute transport are advection and 

mechanical dispersion. Advection is the general physical transport of dissolved solute 

with average ground-water flow. Mechanical dispersion is the mixing or spreading of 

solute within ground water due to the heterogeneities of the physical properties that 

constitute the subsurface environment. Mechanical dispersion is related to the 

coefficient of hydrodynamic dispersion (eq. 1) by the one-dimensional equation (Freeze 

and Cherry, 1979):

D = av + D*, (2)

where

D is the coefficient of hydrodynamic dispersion, in square feet per day; 

a is dispersivity, in feet;

v is the average linear ground-water velocity, in feet per day; and 

D* is the coefficient of molecular diffusion, in square feet per day.

At high ground-water velocities, mechanical dispersion (represented in equation 2 as 

av) is the dominant dispersive process and molecular diffusion can be ignored.

The two-dimensional model SUTRA requires two values of dispersivity to simulate 

dispersion both parallel and perpendicular to the general ground-water-flow direction. 

Dispersion along the ground-water-flow path is controlled by the longitudinal 

dispersivity (04); whereas, dispersion perpendicular to the ground-water-flow path is 

controlled by the transverse dispersivity (0^). The transverse dispersivity is typically 

smaller than the longitudinal dispersivity (Freeze and Cherry, 1979).

32
The primary geochemical and biological processes that affect the transport of 

soluble petroleum hydrocarbons in ground water are sorption and microbial 

degradation. Sorption is the process in which hydrocarbon solute adheres to sediment 

grains as the solute plume migrates through the subsurface matrix. This process tends 

to retard the overall plume movement in relation to the average ground-water flow. 

Microbial degradation is an important biological process that removes hydrocarbons 

from ground water.

Solute-Transport Model inputs

Hydrologic, geochemical, and microbiological data were used to determine the 

solute-transport conditions of the NFS property and adjacent areas. Water-level 

measurements were made in all monitoring wells located on the NFS site and adjacent 

properties to determine the general gradient of the water-table surface of the upper 

surficial aquifer. Field samples were collected and analyzed to document the extent of 

contamination in the area. Laboratory experiments were performed to determine the 

adsorption potential of the aquifer material to remove model BTEX and PAH 

compounds from the ground water, and to estimate rates of microbial degradation of 

these same compounds under in situ conditions. These hydrologic, geochemical, and 

microbiological parameters were then incorporated into SUTRA to determine if 

contaminant transport to the Cooper River is occurring or could occur in the future at 

the NFS site.

Field sampling of existing monitoring wells on the NFS property and adjacent 

properties was done between November 1993 and January 1994. During the installation 

of four new wells on the NFS property in November 1993, soil and ground-water 

samples were collected by Professional Services Industries, Inc. (1994), for soil- and 

water-chemistry analyses, including toluene and naphthalene. During November 1993 

through January 1994, soil, ground-water, and surface-water samples were collected 

from the study area (fig. 1) during the installation of the monitoring wells, drilling of 

several soil borings, and subsequent sampling of all monitoring wells and local surface 

water, such as the Cooper River, by Chester Environmental, Inc. (1994). Several soil 

samples were collected during these investigations for the purpose of determining 

adsorption (Kad) coefficients and microbial degradation (Kbio) rates. Chester 

Environmental, Inc. also conducted a synoptic water-level survey in all of the existing 

monitoring wells on January 8,1994.

Adsorption coefficients were determined using a modification of the method 

described in Schwarzenbach and Westall (1981). Approximately 5 g of dried, sterilized 

(to avoid potential microbial degradation effects) aquifer material collected during 

installation of wells USGS-1 and USGS-3 (fig. 13), were placed in separate septated 

serum vials and amended with aqueous solutions of toluene or naphthalene. All vials 

were equilibrated by shaking on a vibrating table overnight. Samples of the liquid 

fraction were then analyzed for the above compounds using ultra-violet detection highpressure liquid chromatography. The amount of adsorbed compound was estimated as 

the difference between the amount added and the amount present in the liquid fraction

33
after equilibration. Adsorbed concentrations of toluene and naphthalene were regressed 

against dissolved concentrations to obtain a linear adsorption coefficient.

Adsorption coefficients describe the potential for an organic hydrocarbon to be 

partitioned between an aqueous phase (ground water) and a solid phase (aquifer 

material). The higher the potential of hydrocarbon adsorption onto aquifer material, the 

higher the Kad value. This relation can be approximated using a linear model of 

adsorption. Values of Kad determined for toluene and naphthalene in contact with the 

fine-grained, sedimentary, organic-rich sand at the site were 3.32 X 10'8 and 4.84 X 

10'6 ftYmg, respectively, and were obtained by regressing the adsorption data with 

concentration data (fig. 16). These values suggest substantial adsorption of naphthalene 

and much less adsorption of toluene onto the aquifer material. The movement of both 

compounds will be retarded to some degree relative to ground-water flow.

The microbial degradation of a model BTEX compound was determined by 

evaluating the production rate of radiolabeled carbon-14 dioxide (14CO2). The rate is 

calculated from a known amount of radiolabel added to three microcosms containing 

NFS-site aquifer sediment. The three sediment samples were obtained from soil borings 

from wells USGS-1 and USGS-3 (fig. 13). Approximately 428,000 DPM of uniformly 

ring-labeled 14C-toluene (specific activity of 9.7 mCi/mmol) was added to triplicate 

40-mL glass microcosms containing 5 mL of a sediment/ground-water slurry collected 

from each sample location and 2.5 mL of ground water collected from adjacent wells. 

For both aerobic and anaerobic treatments, dead controls for estimating abiotic 

evolution of 14CO2 were prepared by sterilizing the microcosms by autoclaving at 121 °C 

for 1 hour, and adding 8 mM HgCl2. Aerobic treatments for evaluating degradation 

rates of toluene were implemented without further modification. Anaerobic 

degradation rates were estimated using vials prepared as above but made anaerobic by 

purging the vials with helium for 3 minutes prior to capping. At specified intervals, 

aerobic and anaerobic vials were sacrificed by acidification with 45 percent H3PO4. The 

evolved 14CO2 was then captured in a 3 M solution of KOH suspended in the microcosm 

in a plastic bucket assembly, and the 14C activity was measured through liquid 

scintillation counting using a 1600TR liquid scintillation counter (Packard Instrument 

Corp.). The 14C activity data were corrected using dead-control, background-radiation, 

activity at time = 0, and counting-efficiency data. Activities are reported as a percentage 

of the added radiolabel recovered as 14CO2. The microbial degradation of a PAH 

compound was determined through similar procedures using uniformly ring-labeled 

naphthalene as the model compound.

To assess the microbial degradation of toluene and naphthalene in the upper 

surficial aquifer at the NPS site, a series of degradation experiments involving

radiolabeled 14C-toluene and 14C-naphthalene in laboratory microcosms was utilized. 

Microcosm conditions were arranged to provide rates of degradation under appropriate 

field conditions, namely aerobic (with dissolved oxygen) and anaerobic (without 

dissolved oxygen). This approach allows for interpretations to be made under the 

conditions at the site.

34
180

(A)

20 40 60 80 100 120 140 160 180 

DISSOLVED CONCENTRATION, 

IN MILLIGRAMS PER LITER

(B)

100

h- DC 

Z HI 60 

HI CL 

O ,o

o 

o

CD 

DC 

O 

C/} 

Q 

<

40

20

NAPHTHALENE

0.0 0.1 0.2 0.3 0.4 0.5 0.6 

DISSOLVED CONCENTRATION, 

IN MILLIGRAMS PER LITER

0.7

Figure 16. Adsorption isotherms for toluene (A) and naphthalene (B)

on upper surficial aquifer sediments beneath the National

Park Service property, Charleston, S.C.

35
The results of the radiolabel experiments suggest an active microbial population at 

the site that can readily degrade toluene and naphthalene. Upper surficial aquifer 

material collected near monitoring well USGS-1 (fig. 13) produced aerobic, first-order 

degradation rates of 0.84 and 0.88 d'1 for toluene and naphthalene, respectively. 

Anaerobic, first-order degradation rates were 0.0020 and 4.6 X 10~5 d~' for toluene and 

naphthalene, respectively. Microbial-degradation rates for toluene and naphthalene 

were estimated from initial linear rates of 14CO2 production (fig. 17).

Solute-Transport Simulations

A range of lateral hydraulic conductivities, adsorption coefficients, and microbial 

degradation rates determined for toluene and naphthalene at the NFS site were used to 

calibrate a model of the NFS site and adjacent areas that approximates the 1994 

hydrologic conditions and contaminant distribution (tables 2 and 3). After development 

of this model, henceforth called the standard model, the variability of contaminant 

distribution and transport rates was tested by model simulation using a reasonable 

range of input parameter values. Thus, the possibility of contaminant transport to 

points of contact was determined for a range of input parameter values that represent 

the uncertainty inherent when hydrologic environments are evaluated spatially by 

extrapolation from point data. Reference to or discussions of hydraulic conductivity 

used herein in conjunction with model simulations indicate lateral hydraulic 

conductivity.

Table 2.-Estimates of lateral hydraulic conductivity, and microbial-degradation rates and adsorption 

coefficients of toluene for site conditions at the National Park Service property and adjacent 

properties, Charleston, S.C., 1994

[ft/d, feet per day; d" 1 , one per day; ft3/mg, cubic feet per milligram]

Best estimate

Model Parameter High estimate Low estimate (standard

model)

Range of lateral hydraulic 16; 1.6 1; 0.1 4; 0.4

conductivity 1

(ft/d)

Microbial degradation .84 0 9.0 X10'5 

(d- 1 )

Adsorption 2.2 X10'7 2.2 X 10'9 2.2 X 10'8

(ft3/mg)_____________________________________________

Hydraulic conductivity rates represent the zones modeled (fig. 18).

36
LLI 

O 

CC 

LLI 

Q.

70

60

50

(A)

o

LU 

CC 

LU

>

O

o

LLI 

CC

CM

O

o

i- 60

0

0

0

^40 

S30

i i 

_ Enlarged origin -

200 400 600 800 1,000

0 10 20 

hours

200 400 600 800 1,000

HOURS

Figure 17. Mineralization rate of uniformly ring-labeled 14C-tpluene (A) and 14C-naphthalene (B)

under aerobic and anaerobic aquifer conditions in sediment samples collected from

the upper surficial aquifer, National Park Service Property, Charleston, S.C.

37
Table 3.--Estimates of lateral hydraulic conductivity, and microbial-degradation rates and adsorption 

coefficients of naphthalene for site conditions at the National Park Service property and adjacent 

properties, Charleston, S.C., 1994

[ft/d, feet per day; d" 1 , one per day; ftVrng, cubic feet per milligram; > greater than]

Best estimate

Model Parameter High estimate Low estimate (standard

model)

Range of lateral hydraulic 16; 1.6 1;0.1 4; 0.4

conductivity

(ft/d)

Microbial degradation .88 4.6 X 10'5 6.9 X 10'5 

(d- 1 )

Adsorption 4.84 X 10'8 0 4.84 X 10-" 

(ftVmg)_____________________________________________

Hydraulic conductivity rates represent the zones modeled (fig. 18).

The model was calibrated to represent the conditions observed in the field in 

January 1994 using estimates for hydrologic, geochemical, and microbiological 

parameters determined from field and laboratory work. This model was not created to 

exactly reproduce the water-table surface or the concentration of contaminants in the 

ground water at the site; it was created, however, to approximate these conditions and to 

simulate similar flow paths and contaminant distributions.

An areal grid of the upper surficial aquifer was created and directionally aligned 

with the Cooper River (fig. 18). The model grid consisted of 2,025 nodes evenly spaced 

across the modeled domain to simulate an area of 1,320 ft by 1,320 ft. Discretization of 

the model in this manner created 1,936 square elements (each 30 ft by 30 ft). The upper 

surficial aquifer was simulated to be 15-ft thick in the model, a representative value 

determined from boring logs in the area (Chester Environmental, Inc., 1994; General 

Engineering Laboratories, Inc., 1992; Professional Service Industries Inc., 1994; and Soil 

Consultants, Inc., 1989). The eastern boundary along the Cooper River was assigned 

constant-head values (H = 0.0 to 2.95 ft). The western, southern, and northern 

boundaries were also simulated as constant-head boundaries based on interpretations of 

available water-level data. The Holocene clay was considered the base of the simulated 

flow system. No water was allowed to flow into or out of this model boundary.

The standard model was calibrated for the water-table surface measured on 

January 8,1994 (Chester Environmental, Inc., 1994), and for toluene and naphthalene 

concentrations measured in ground-water samples collected in January 1994 (fig. 19).

38
Hydraulic Conductivity

y - ^T-T-rn-rrrr i

-Natidn^I , Park Servic^

Prpperty

EXPLANATION

 MODEL BOUNDARY 

OBSERVATION WELL

Figure 18. Model boundaries for the study area, Charleston, S.C.

39
(A) (B)

EXPLANATION

OBSERVATION WELL

; 6 TOLUENE CONCENTRATION, 

IN MILLIGRAMS PER LITER.

'-. -: NATIONAL \ ....-

* SERVYbE .. 

S'' 9 PROPERTY .,,-"'..>

EXPLANATION

OBSERVATION WELL

0.28 NAPHTHALENE CONCENTRATION, 

IN MILLIGRAMS PER LITER.

. 0.065 . '

,',* !'''.6.097 ON A L \ \ \\ ^i'x"""" 

\ \ \\\ ,--"..c^ - "\

^ S" \\ \-> ^ \ \ \

Figure 19. Toluene (A) and naphthalene (B) concentrations measured in upper surficial aquifer wells on the National 

Park Service property and adjacent properties, Charleston, S.C., January 1994.
The simulated source area was the tank area located on the former MGP site (fig. 18). A 

former employee for the MGP described this as an area of multiple spills (S.C. 

Department of Health and Environmental Control, 1992).

Two of the main assumptions applied to the standard model involved the location 

of the source area and the shape of the water-table surface. This model assumes only 

one source area located on the MGP property. Several other industries that operated in 

the model area could have contributed to the contamination, such as the chemical 

company formerly located on the Calhoun Park property; however, it was assumed that 

most of the toluene and naphthalene contaminants originated at the former MGP. The 

second major assumption was that the water-table surface in the model area is constant 

and approximates that measured on January 8,1994. Although this surface has and will 

fluctuate over time, especially throughout the seasons of the year, it was assumed that 

the January water-table surface represents average annual conditions.

In order to approximate the water-table surface observed in the field on January 8, 

1994, two zones of hydraulic conductivity were used in the standard model (fig. 18). A 

zone of higher hydraulic conductivity (K = 4 ft/d) was assigned west of Concord Street, 

with a zone of lower hydraulic conductivity (K = 0.4 ft/d) located east of Concord Street. 

The hydraulic conductivity value of K = 0.4 ft/d was determined by averaging all the 

hydraulic conductivity values determined for the upper surficial aquifer on the NPS 

property with the exception of a value of K = 10 ft/d at well MW-2 (fig. 13). This value 

was at least an order of magnitude greater than all of the other hydraulic conductivity 

values and was considered to be not representative of the aquifer. Although no slug 

tests were completed on wells outside the NPS property during this investigation, the 

use of the high zone of hydraulic conductivity was supported by hydraulic conductivity 

values determined in other investigations (Chester Environmental Inc., 1994).

The toluene and naphthalene plume simulations were constructed by simulating a 

constant source (free product at 50 and 15 mg/L, respectively) in the tank area on the 

former MGP property (fig. 18) for 150 years. The biodegradation and adsorption values 

were determined from soil samples collected for laboratory analysis as described 

previously. Values of porosity (e = 0.30) and mechanical dispersivity (cq - 30 ft and at = 

15 ft) for sandy sediments were chosen from the literature as reasonable estimates for the 

model (Freeze and Cherry, 1979).

To account for ground-water discharge into the brick-lined drainage archway 

beneath Calhoun Street, several sink nodes (points of ground-water removal) were 

included in the model (fig. 18). Because the quantity of ground water discharged to this 

drain is unknown, several simulations were completed to evaluate the influence of this 

ground-water sink on controlling ground-water flow in the area. Three steady-state 

simulations utilizing drainage rates of 50; 500; and 5,000 gal/d were modeled 

(figs. 20-22). Water-level data (Chester Environmental Inc., 1994) measured in wells 

screened in the upper surficial aquifer on January 8,1994 are included in the figures. 

The drainage rates were chosen arbitrarily, but are believed to encompass realistic 

discharge rates occurring at the study area. Model results indicate that ground-water 

flow into this drain using the 50 gal/d rate had little effect on the water-table surface of 

the upper surficial aquifer. The simulation using the 5,000 gal/d drainage rate depicted

41
Cooper 

River

3.5

2.92

EXPLANATION

SIMULATED WATER-LEVEL CONTOUR-Shows 

elevation of water level. Contour interval is 0.5 feet. 

Datum is sea level.

OBSERVATION WELL AND WATER-TABLE ELEVATION, 

IN FEET ABOVE SEA LEVEL 100 200 300 400 FEET 

METERS

Figure 20. Simulated water-table elevation in the upper surficial aquifer using a rate of 50 gallons per day 

draining through the brick-lined drainage archway, National Park Service property and adjacent

properties, Charleston, S.C., January Q, 1994.

42
N

Model Boundary

Cooper 

River

3.5

2.92

EXPLANATION

SIMULATED WATER-LEVEL CONTOUR-Shows 

elevation of water level. Contour interval is 0.5 feet. 

Datum is sea level.

OBSERVATION WELL AND WATER-TABLE ELEVATION, 

IN FEET ABOVE SEA LEVEL. 0 100 200 300 400 FEET I ' ' < , '

0 100 METERS

Figure 21. Simulated water-table elevation in the upper surficial aquifer using a rate of 500 gallons per day 

draining through the brick-lined drainage archway, National Park Service property and adjacent

properties, Charleston, S.C., January 8, 1994.

43
Cooper 

River

3.5

2.92

EXPLANATION

SIMULATED WATER-LEVEL CONTOUR-Shows elevation 

of water level. Contour interval is 0.5 feet. Datum is sea level.

OBSERVATION WELL AND WATER-TABLE ELEVATION, 

IN FEET ABOVE SEA LEVEL. 0 100 200 300 400 FEET I ' >-

100 METERS

Figure 22. Simulated water-table elevation in the upper surficial aquifer using a rate of 5,000 gallons per 

day draining through the brick-lined drainage archway, National Park Service property and adjacent

properties, Charleston, S.C., January 8, 1994.

44
a water-table surface that was strongly influenced by the drain. Because the drain does 

not have much effect on the ground-water-flow regime of the study area, the 500 gal/d 

drainage rate was used in the standard model and in all the subsequent simulations to 

account for any flow to the drain. The simulated January 8,1994, water-table surface is 

illustrated in figure 21 (Chester Environmental, Inc., 1994).

The 'best estimate7 model parameters listed in table 2 were used to calibrate the 

toluene model. This model simulated the 150-year travel time that corresponds to initial 

MGP operations through 1994 using the steady-state ground-water-flow field and 2.5-yr 

time steps for solute-transport calculations. The resultant toluene distribution 

represents the best approximation of the extent of toluene contamination observed in the 

study area in January 1994 (fig. 23). Because the January 1994 distribution of toluene 

was discontinuous in the study area, the goal of this simulation was to match the extent 

of contamination as best as possible. Because the well with the 0.043 mg/L toluene 

concentration was located south of the drainage archway (fig. 23) and probably 

represents a secondary source of contamination, simulation of contamination in this area 

was not attempted for the January 1994 toluene plume simulation. Instead, simulation 

of a 0.01 mg/L contour that encompassed the toluene plume north of the drainage 

archway was achieved and considered the best approximation. The 0.05 mg/L contour 

was simulated to intersect the distance between the two wells with January 1994 toluene 

concentrations of 0.037 and 0.078 mg/L. A solute transport simulation using 

1-yr time steps produced a January 1994 toluene plume almost identical to the 2.5-yr 

time step simulation, indicating that 2.5-yr time steps adequately simulate the changes in 

concentration with time. This calibrated model was then used to evaluate the extent of 

the toluene contamination 150 years in the future. A toluene transport simulation using 

the same model parameters as the calibrated model produced a year 2144 plume with a 

0.01 mg/L toluene concentration that was simulated 300 ft from the point of contact (fig. 

24). Because of the uncertainty of the model input parameters, the results related to 

high and low input values need to be evaluated to determine if contaminants would 

possibly reach the point of contact.

Simulations of toluene transport using a conservative or 'worst-case' scenario of no 

adsorption or microbial degradation and high estimates of hydraulic conductivity 

indicate a discharge of toluene contaminated ground water into the Cooper River after 

150 years of transport (fig. 24). The simulated toluene concentration of this discharge is 

less than 1.0 mg/L. Although this simulation is unrealistic, based on non-zero 

laboratory values obtained for Kad and Kbio for this compound at the NFS site, it indicates 

an upper limit of the distribution and concentration of contamination in the next 150 

years future, and by comparison with standard model simulations, depicts the influence 

of microbial activity as a limiting process for contaminant transport.

To assess the effect of hydraulic conductivity on the transport of toluene to the 

Cooper River, two simulations were completed using high and low estimates of 

hydraulic conductivity (K). All other input parameters used in these simulations were 

equal to standard model values. The two zones of different hydraulic conductivity were 

modeled for both simulations (high K's and low K's) as in the calibrated model (fig. 18). 

The high estimates of hydraulic conductivity were 16 and 1.6 ft/d, whereas the low 

estimates were 1 and 0.1 ft/d. Both sets of estimates represent a four-fold difference

45
Model Parameters

K =4,0.4 ft/d 

Kbio =9.0xlO-5 c|- 1 

= 2.2xlCT8 ft3/mg

Model Bound_ajT

V

0.01

0. 19

Cooper 

River

EXPLANATION

LINE OF EQUAL TOLUENE CONCENTRATION,

IN MILLIGRAMS PER LITER. INTERVAL IS VARIABLE.

TOLUENE CONCENTRATION, IN MILLIGRAMS PER LITER 

OBSERVATION WELL 0 100 200 300 400 FEET 

0 100 METERS

Figure 23. January 1994 distribution of toluene in the upper surficial aquifer 

simulated by the standard model.

46
(A) (B)

Model Parameters!

K =4,0.4ft/d Kbio =9.0xlO-5 d- 1 

Kad = 2.2xlO-8 ft3/mg

Model Boundor

Cooper 

River

EXPLANATION

LINE OF EQUAL TOLUENE CONCENTRATION,

IN MILLIGRAMS PER LITER. INTERVAL IS VARIABLE.

OBSERVATION WELL 0 100 200 300 400 FEET

|Model Parameters]

K ="16, 1.6 ft/d Kblo = 0 d' 1 

Kad = 0 ft3/mg

EXPLANATION

LINE OF EQUAL TOLUENE CONCENTRATION,

IN MILLIGRAMS PER LITER. INTERVAL IS VARIABLE.

OBSERVATION WELL 0 100 200 300 400 FEET

Figure 24. Year 2144 distribution of toluene in the upper surficial aquifer simulated by the standard model (A)

and assuming conservative transport (B).
from the average hydraulic conductivity values used in the standard model. 

Simulations of toluene distribution utilizing the high estimates of K's (fig. 25) predicted 

a plume more dispersed than the standard model after 150 years of transport. Simulated 

ground-water discharge to the Cooper River occurs with a toluene concentration 

ranging from about 0.1 and 0.5 mg/L. Toluene transport simulations using the low 

estimates of K's produced a year 2144 plume more confined than the distribution of 

toluene simulated by the standard model (fig. 25). The smaller plume was the result of 

lower ground-water velocities, which allowed less contaminant migration by advection 

than the standard model in the same amount of time. The inverse conditions are true for 

simulations produced using the higher values of hydraulic conductivity.

The microbial degradation coefficients for toluene determined from aerobic and 

anaerobic laboratory experiments were 0.84 and 0.0020 d'1 , respectively. Simulation 

results that best approximated conditions observed in January 1994 used a degradation 

coefficient of 9.0 X10'5 . This rate was used in the standard model but is much lower than 

the aerobic and anaerobic rates determined by laboratory experiment. The difference 

between model and laboratory rates may be explained by variable field conditions. 

Chester Environmental, Inc. (1994) reported scattered aerobic and anaerobic conditions 

in the shallow-subsurface environment during the January 1994 sampling period. Such 

variability was accounted for by simulating the microbial degradation of toluene using 

high and low estimates of Kbio (table 2). Using the higher value of Kbio simulates an 

environment in which all of the toluene that was released from the source area was 

rapidly degraded. This approach results in a simulated contaminant plume restricted to 

an area near the source (fig. 26). Using the lower value of Kbio produced a simulated 

toluene plume that traveled farther than the plume simulated using the standard model 

(fig. 26). A 0.01 mg/L toluene concentration was simulated 280 ft from the point of 

contact.

The estimate used in the standard model for toluene adsorption onto aquifer 

sediments was 2.2 X 10'8 ft3 /rng (table 2). A higher adsorption value of Kad = 2.2 X 10~7 

ftYmg produced a more confined toluene plume than the standard model after 150 

years of transport (fig. 27). This plume, in fact, is only slightly larger than the plume 

simulated for January 1994. Use of a lower adsorption value of Kad = 2.2 X 10~9 ftYmg, 

produced a year 2144 toluene plume that traveled farther than the plume simulated by 

the standard model with a 0.01 mg/L concentration 40 ft from the point of contact 

(fig. 27).

The hydrologic, geochemical, and microbiological values listed in table 3 were used 

to develop a standard model for naphthalene transport. Simulations of naphthalene 

transport using the adsorption coefficient determined in the laboratory (4.84 X 10~6 

ftYmg) invariably resulted in small immobile plumes. The high adsorption rate so 

constrained the naphthalene plume such that no appropriate simulations of January 

1994 plume conditions could be attained, regardless of the combinations of input 

parameters applied to the model.

48
(A)

I Model Parameters"1

K =16,1.6 ft/cf Kbio =9.0x10-5 d- 1 Kad = 2.2x10-8 ft3/mg

'ModeJ Parameters

K =l,0.1ft/d Kbio =9.0x10-5 d- 1

Kad =2.2x10-8 ft3/mg

LINE OF EQUAL TOLUENE CONCENTRATION,

IN MILLIGRAMS PER LITER. INTERVAL IS VARIABLE.

OBSERVATION WELL 0 100 200 300 400 FEE!

LINE OF EQUAL TOLUENE CONCENTRATION,

IN MILLIGRAMS PER LITER. INTERVAL IS VARIABLE.

OBSERVATION WELL 0 100 200 300 400 FEET

Figure 25. Year 2144 distribution of toluene in the upper surficial aquifer simulated using the standard model with high (A) and low (B) estimates of aquifer hydraulic conductivities.
(A)

Ulo

'Model Parameters"

K =4,0.4 ft/d Kbio=0,84d-' Kad =

Mnrlel Boundary

MpdeLParqmeters j 

K = 4,04 ft/d

i 'A ', ^ \ ., 1 '/ \ \ te wflJih ', ', !V, <u_ - . -''--- 

', ' ,'v l_ - ---'.i i t L -'-'' \ _ ^-i r \ . i i \ ""i 1 i i -.

EXPLANATION

0,01 LINE OF EQUAL TOLUENE CONCENTRATION, 

IN MILLIGRAMS PER LITER. INTERVAL IS VARIABLE.

OBSERVATION WELL

\ \ ^r^~~\ \ \ ,^ / \ y-~

^* / ^ '

0 100 200 300 400 FEET0 100 METERS

; \\ JP : Ji

EXPLANATION

0.01 LINE OF EQUAL TOLUENE CONCENTRATION, 

IN MILLIGRAMS PER LITER. INTERVAL IS VARIABLE.

OBSERVATION WELL

\ -^ \\ .-' -'/ ^>" /

f

0 100 200 300 400 FEET0 100 METERS

Figure 26. Year 2144 distribution of toluene in the upper surficial aquifer simulated using the standard model with high (A) and low (B) estimates of microbial degradation.
(A) (B)

[Model Parameters I

K = 4,0.4 ft/d Kbio =9.0xlO-5 d- 1 Kad = 2.2xlO-7 ft3/mg

lode/ Boundary

Cooper 

River

EXPLANATION

LINE OF EQUAL TOLUENE CONCENTRATION,IN MILLIGRAMS PER LITER. INTERVAL IS VARIABLE.

OBSERVATION WELL 0 100 200 300 400 FEET

1 Model Parameters!

K = 4,0.4 ft/d Kbio =9.0xlO-5 d- 1

Kad =2.2xlO-'ft3/mg

Model 6 o u n d o_r

EXPLANATION

LINE OF EQUAL TOLUENE CONCENTRATION,

IN MILLIGRAMS PER LITER. INTERVAL IS VARIABLE.

OBSERVATION WELL

Figure 27. Year 2144 distribution of toluene in the upper surficial

and low (B) estimates

aquifer simulated using the standard model with high (A) 

of adsorption.
The fact that the naphthalene plume was observed at greater distances from the 

assumed source than could be simulated can be explained by several lines of reasoning. 

First, the model simulates naphthalene transport using an adsorption coefficient 

determined from a single sediment core. Because of heterogeneities in the shallow 

aquifer system, adsorption rates determined from a single core may not represent the 

general sediment types present. Second, because of the lack of definitive information 

regarding contaminant source areas and volumes of contaminant released, only one 

source area was modeled. More than one source area may have existed in the past. 

Also, much of the upper surficial aquifer is composed of fill along the river. Some of this 

fill material may have come from the contaminated gas-plant site or other contaminated 

properties in the area (South Carolina Department of Health and Environmental 

Control, 1992). Such activities would have spread the contamination and also created 

other potential source areas. Finally, light-non-aqueous-phase liquids that contain 

naphthalene are present in the area and could be moving across the water table. Thus 

naphthalene can dissolve into the adjacent ground water from water-table sources. If 

this free-product source existed since the initial operations of the MGP, may have spread 

throughout this area during the previous 150 years.

Although the January 1994 naphthalene plume could not be simulated using the 

adsorption coefficient measured in the laboratory, a reasonable plume was simulated 

using a much smaller adsorption coefficient (Kad = 4.8 X 10' 11 ftYmg) and the 'best 

estimate7 parameters listed in table 3 (fig. 28). This adsorption coefficient is considered 

appropriate because any higher value would restrict the naphthalene plume to a smaller 

area than that observed in January 1994. Although more than one source area or a 

moving naphthalene source zone could have been simulated to produce the plume 

observed in January 1994, the lack of information regarding these field conditions 

prohibited any justifiable attempt. The results of this simulation produced a January 

1994 naphthalene plume with a 0.01 mg/L concentration 40 ft from the point of contact. 

The primary goal of this simulation was to circumscribe the wells that had January 1994 

naphthalene concentrations greater than 1.0 mg/L with a simulated 1.0 mg/L contour. 

The results of this simulation is considered the best approximation of the January 1994 

naphthalene distribution. Using this simulation as a basis, the standard model could 

then be used to evaluate the future transport of naphthalene. Standard model 

simulations for the year 2144 indicated that ground water with naphthalene 

concentrations between 0.01 and 0.05 mg/L will reach the point of contact (fig. 29).

Predictive simulations of 150 years of naphthalene transport using a conservative 

model (no adsorption or microbial biodegradation and high estimates of hydraulic 

conductivities) indicated that ground-water discharge into the Cooper River would 

contain naphthalene at a concentration greater than 5.0 mg/L in year 2144 (fig. 29). 

Although this simulation is unrealistic, based on non-zero laboratory values obtained for 

Kad and Kbio for this compound at the NFS site, it indicates an upper limit of the 

distribution and concentration of contamination for the next 150 years.

To assess the effect of hydraulic conductivity on the transport of naphthalene to the 

Cooper River in the future, two simulations were completed using reasonable high (16 

and 1.6 ft/d) and low (1.0 and 0.1 ft/d) values of hydraulic conductivity (fig. 30). A

52
I Model Parameters

K = 4,0.4 ft/d

Kbio =6.9xlO-5 d- 1

Kad = 4.84xlO- 11 ft3/mg

Model Boundary

Cooper 

River

- 0.01-

0.077

EXPLANATION

LINE OF EQUAL NAPHTHALENE CONCENTRATION, 

IN MILLIGRAMS PER LITER. INTERVAL IS VARIABLE.

NAPHTHALENE CONCENTRATION, IN MILLIGRAMS 

PER LITER.

OBSERVATION WELL 0 100 200 I ' ' 300 400 FEET

100 METERS

Figure 28. January 1994 distribution of naphthalene in the upper surficial aquifer

simulated by the standard model.

53
[Model Parameters

K =4,0. Kbio =6,9xlCr0 d

= 4.84xlO-"ft3/mg

[Model Parameters I

K = 16, 1.6 ft/d M o cle/6ojjndCL

EXPLANATION EXPLANATION

LINE OF EQUAL NAPHTHALENE CONCENTRATION, 

IN MILLIGRAMS PER LITER. INTERVAL IS VARIABLE

LINE OF EQUAL NAPHTHALENE CONCENTRATION, 

IN MILLIGRAMS PER LITER. INTERVAL IS VARIABLE.

OBSERVATION WELL OBSERVATION WELL

Figure 29. Year 2144 distribution of naphthalene in the upper surficial aquifer simulated by the standard model (A)

and (B) assuming conservative transport.
[Model Parameters

K = 16, 1,6 ft/d Mode I Boundary

4,84xlCr 11 ft3 /mg

Cooper 

River

',',"« I '^', . t-> FS

>, wMl

EXPLANATION

LINE OF EQUAL NAPHTHALENE CONCENTRATION, 

IN MILLIGRAMS PER LITER. INTERVAL IS VARIABLE.

OBSERVATION WELL

(B)

[Model Parameters

K =16,1.6 ft/dKj = 0 ft3/mg

Cooper 

River

EXPLANATION

LINE OF EQUAL NAPHTHALENE CONCENTRATION, IN MILLIGRAMS PER LITER. INTERVAL IS VARIABLE.

OBSERVATION WELL 100 200 300 400 FEET 

100 METERS

Figure 30. Year 2144 distribution of naphthalene in the upper surficial aquifer simulated using the standard model with high (A) and low (B) estimates of aquifer hydraulic conductivities.
simulation of the year 2144 distribution of naphthalene using the high estimates of K's 

predicted ground-water discharge to the Cooper River with naphthalene concentrations 

ranging between 1.0 and 5.0 mg/L. A simulation utilizing the low values of K's 

produced year 2144 distributions of naphthalene more confined than that simulated by 

the standard model for January 1994. This reduced transport rate allowed the 

degradation of naphthalene that was already in place when the simulation started.

The microbial degradation coefficients for naphthalene determined from aerobic 

and anaerobic laboratory experiments were 0.88 and 4.6 X 10'5 d' 1 , respectively. 

Simulation of year 2144 naphthalene distributions utilizing the higher value of Kbio 

produced a contaminant plume that was restricted to an area near the source (fig. 31). 

This high value allowed the degradation of naphthalene that was already in place when 

the simulation was started. Simulation of the naphthalene plume using the lower value 

of Kblo predicted that ground water containing naphthalene concentrations between 0.1 

and 0.5 mg/L will reach the point of contact by the year 2144 (fig 31).

The standard model simulation of naphthalene required an adsorption of 

coefficient equal to 4.84 X 10~ n ft3 /mg to calibrate the model to the January 1994 data. 

Simulations using a high estimate of adsorption (Kad = 4.84 X 10'8 ftVmg) produced a 

year 2144 naphthalene plume (fig. 32) that was slightly smaller than the standard model 

for the year 2144. Reducing the adsorption coefficient to 0 ftYmg produced model 

results equal to that of the standard model for the year 2144 (fig. 32).

Model Conclusions

By incorporating field- and laboratory-derived hydrologic, geochemical, and 

microbiological parameters into the solute-transport model SUTRA, a toluene plume 

was simulated that approximated the January 1994 plume. Using these results as initial 

conditions for predictive simulations and testing the variability of the model input 

parameters produced a majority of toluene transport simulations that did not reach the 

point of contact within 150 years. Predictive toluene transport simulations indicate that 

this model is most sensitive to the high estimates of aquifer hydraulic conductivity (1.6 

and 16 ft/d).

Naphthalene adsorption coefficients determined for upper surficial aquifer 

sediments were equal to or greater than 4.84 X 10'6 ft3 /mg. Using this high adsorption 

coefficient, simulation of the January 1994 naphthalene plume was not possible for a 

model with only one source located near the former tank locations on the MGP property. 

Possible explanations for the size of the naphthalene plume observed in the field are the 

variability of adsorption in the upper surficial aquifer, the existence of more than one 

source area, man-made deposition of contaminated fill material, or naphthalene 

dissolving from a mobile free-product surface on site. To determine the mobility of this 

plume, several predictive simulations were completed using a model with initial 

naphthalene concentrations approximately equal to that measured in January 1994. 

Predictive model results indicate that the size of the naphthalene plume may increase in 

the next 150 years with concentrations ranging from 0.0 to greater than 5.0 mg/L 

discharging to the Cooper River.

56
(A) (B)

QMpdel Parameters |

K" =4,0.4ft/d

Kbio = 0.88 d' 1Kad = 4.84xlO-n ft3/mg|

Mode/ Boundary

Cooper 

River

EXPLANATION

LINE OF EQUAL NAPHTHALENE CONCENTRATION, IN MILLIGRAMS PER LITER. INTERVAL IS VARIABLE.

OBSERVATION WELL

'Model Parameters ,

K =4,04ft/dKbio =4,6x 10-5 d''Kad = 4.84xlO-"ft3/mg

Model

Cooper 

River

EXPLANATION

LINE OF EQUAL NAPHTHALENE CONCENTRATION, 

IN MILLIGRAMS PER LITER. INTERVAL IS VARIABLE.

OBSERVATION WELL 100 200 300 100 FEET 

100 METERS

Figure 31. Year 2144 distribution of naphthalene in the upper surficial aquifer simulated using the standard model with high (A)

and low(B) estimates of microbial degradation.
(A) (B)

Model Parameters 1 K =4, 0.4 ft/cf 

Kbto = d.PxlO^d' 1 Kad = 4.84x 10'8 ft3/mg

Model Boundary

Cooper 

River

EXPLANATION

LINE OF EQUAL NAPHTHALENE CONCENTRATION, 

IN MILLIGRAMS PER LITER. INTERVAL IS VARIABLE.

OBSERVATION WELL

Model Parameters

K =4, 0.4 ft/d Kbio =6.9xlO-5 d-' 

Kad = 0ft3/mg

tjinrtei Bound of.

Cooper 

River

EXPLANATION

LINE OF EQUAL NAPHTHALENE CONCENTRATION, IN MILLIGRAMS PER LITER. INTERVAL IS VARIABLE.

OBSERVATION WELL 100 200 300 400 FEEI

Figure 32. Year 2144 distribution of naphthalene in the upper surficial aquifer simulated using the standard model with high (A) and low (B) estimates of adsorption.
Solute-transport models were developed using the assumption that all of the 

toluene and naphthalene in the study area soils originated from a single source located 

on the former MGP. It is possible and highly probable that more than one source area 

exists for both of these compounds, but due to lack of information, a single reasonable 

source area was assumed.

SUMMARY

In 1989, the NPS acquired an 8-acre site adjacent to the Cooper River in downtown 

Charleston, S.C., for future use as a tour-boat dock facility for Fort Sumter National 

Monument. During geotechnical testing (1989) for the tour-boat dock-facility pile 

construction, contamination in the subsurface soil was detected. Since then, extensive 

testing has documented environmental contamination on the NFS property and adjacent 

properties owned by the city of Charleston and a state-wide power company.

The NFS site and the adjacent area is filled marsh and has a long history of 

commercial and industrial use dating back to the late 1700's. The Charlotte Street 

electrical substation was the former location of a manufactured coal gasification plant 

that operated from 1855 to 1910, and a carbureted-gas plant that operated from 1910 to 

1957. A chemical company was located on a part of the adjacent Calhoun Park property 

in the late 1800's. Adjacent city of Charleston public housing property was previously 

used for storage of lumber, scrap metal, and rosin from the 1850's to the 1930's. The 

industrial use of these properties produced numerous by-products and wastes, 

including PAH's; BTEX; phenols; cyanide; hydrogen sulfide; ammonia; and heavy 

metals.

In 1993, the USGS, in cooperation with the NPS, initiated a study to define the site 

geology and hydrogeology, and determine the potential of intrinsic bioremediation as 

part of an environmental assessment of the site contamination. This investigation 

involved a combination of field and laboratory work. Field studies, which included the 

installation of four ground-water monitcring wells, water-level measurements, soil and 

ground- water sampling, and aquifer tests, were conducted from August 1993 to January 

1995. Laboratory analyses performed during this study included an estimation of 

adsorption coefficients and microbial degradation rates for toluene and naphthalene in 

site soils. A determination of the ground-water-flow characteristics and solute transport 

of toluene and naphthalene also was made. The information collected at the study area 

can be used by the NPS and local officials to evaluate remediation strategies at the site.

Sediments at the NPS site range in age from Late Cretaceous to Holocene, and are 

composed of stratified gravel, sand, silt, clay, and limestone. The deep geologic units in 

the South Carolina Coastal Plain consist of several marine, nearshore, to fluvial deposits 

of the Late Cretaceous and Tertiary age. These units overlie a pre-Cretaceous crystalline 

rock and, from oldest to youngest, are the Beech Hill, Clubhouse, Cape Fear, 

Middendorf, Shepherd Grove, and Caddin Formations; the Cane Acre, Coachman, 

Bladen, and Donoho Creek Formations of the Black Creek Group; the Peedee Formation; 

the Rhems and Williamsburg Formations of the Black Mingo Group; and the Santee 

Limestone. The shallow units range in age from Eocene to Holocene and consist of the

59
Cross Formation; the Harleyville, Parkers Ferry, and Ashley Formations of the Cooper 

Group; the Chandler Bridge, Edisto, and Marks Head Formations; the Goose Creek 

Limestone, the Daniel Island beds, the Penholoway Formation, the Ten Mile Hill beds, 

the Wando Formation, and various Holocene and late Pleistocene alluvium, artificial fill, 

barrier-island sands, and estuarine deposits.

Tertiary deposits at the site represent high stands of sea level during the last 40 Ma 

and are of marine, marginal-marine, and flu vial/estuarine origin. The Harleyville 

formation is composed of compact, phosphatic, calcareous clay, and clayey calcarenite. 

The Parkers Ferry Formation is a dense, sticky, moderate yellowish-green to light bluegreen calcilutite. The Ashley Formation is a tough, light olive-brown, weakly cemented, 

phosphatic and quartzose calcarenite. Chandler Bridge Formation sediments are 

composed of medium-gray to dusky-green quartz and phosphatic sands. These deposits 

are patchy, forming in topographically low areas on the top of the Ashley Formation. 

Olive-gray to greenish-gray, phosphatic, shelly, calcareous sand comprise the Edisto 

Formation. The Marks Head Formation is composed of olive-gray to moderate olivebrown quartz phosphate beds and attapulgite-rich clays. The Goose Creek Limestone is 

described as white to very pale-orange quartzose and phosphatic calcarenite.

Quaternary deposits form five terrace complexes in the lower South Carolina 

Coastal Plain that were formed during interglacial ages. These deposits represent 

partially filled backbarrier, barrier-island, and shallow-marine-shelf deposits. The 

Daniel Island beds are an informal subsurface unit consisting of layers of dark bluishgray to dark-gray clay, mud, and sandy clay. Penholoway Formation sediments consist 

of sand, clayey sand, and clay. Ten Mile Hill beds are composed of clays and clayey 

sands. The Wando Formation is made up of slightly weathered beds of sand, clayey 

sand, and clay.

Recent deposits of tidal marsh, peat, and recent alluvium are not formally named in 

the Charleston area. These deposits are found in and around the Cooper and Wando 

Rivers and Carolina Bays.

The NPS site is underlain by a series of aquifers and confining units of the Atlantic 

Coastal Plain sediments from the land surface to approximately 2,500-ft bis. These units, 

in descending order from the land surface are: upper surficial aquifer, lower surficial 

aquifer confining unit, lower surficial aquifer, Santee Limestone/Black Mingo confining 

unit, Santee Limestone/Black Mingo aquifer, Black Creek confining unit, Black Creek 

aquifer, Middendorf confining unit, Middendorf aquifer, Cape Fear confining unit, and 

Cape Fear aquifer.

The upper surficial aquifer on the NPS property is composed of artificial fill and 

unconsolidated sands and clays. The fill material was deposited at the site to create dry 

land where salt marsh had existed previously, and is a mixture of sand and silt with 

various amounts of debris such as wood, sawdust, concrete, bricks, cinders, and nuts 

and bolts.

The lower surficial aquifer is separated from the upper surficial aquifer by a leaky, 

black organic-clay sequence of varying thickness. This clay is part of the old salt marsh 

on which the artificial fill was deposited. The lower surficial aquifer is composed of the 

barrier-sand facies and possibly the fossiliferous shelf-sand facies of the Wando 

Formation. This aquifer is partially to fully confined by the overlying clay.

60
The Santee Limestone/Black Mingo aquifer is effectively confined by the dense, 

low permeability sediments of the Cooper Group and Cross Formation, which are 

approximately 280-ft thick beneath the NPS site. The Santee Limestone aquifer is made 

up of alternating hard and soft, light-gray sandy, fossiliferous limestone. The Black 

Mingo sediments consist of dark- to light-gray sandy, micaeous, calcareous clays and 

loose, dark-green glauconitic sand. These two units are usually hydraulically connected 

and form one aquifer.

The Black Creek aquifer is a confined sandy aquifer, which is effectively confined 

by the overlying Peedee Formation and parts of the Black Mingo Formation. The 

Middendorf aquifer is composed of late Cretaceous-age sands of the Middendorf 

Formation, and locally, sands of the overlying Shepard Grove Formation and the 

underlying Cape Fear Formation. This aquifer is confined by the low-permeability 

sediments of the Cane Acre and Caddin Formations. The Cape Fear aquifer is the lowermost late Cretaceous-age Coastal Plain aquifer. It is composed of thick, red clays with 

immature, poorly sorted quartz and feldspar. In the Charleston area, thick sand units 

are present in the lower part of the formation. The clays of the upper part of the 

formation effectively confine the lower sands from the overlying aquifers.

Regional ground-water flow on the Charleston peninsula is from the topographic 

divide along the center axis toward the Cooper River. Local gradients caused by 

topographic highs (electrical substation fill) or by the underground drainage structures 

(brick archways) cause variations in the overall flow direction.

A recharge value determined for this area through the use of the USGS code 

MODFLOW was 0.2 in/yr. This value is believed to be a low estimate because the 

MODFLOW simulations were not detailed enough to simulate variable recharge and 

evapotranspiration zones or cells that accurately represent the storm-water archways 

beneath the city.

Several slug tests were completed in the upper and lower surficial aquifer to 

determine the lateral hydraulic conductivity of these systems. Calculated lateral 

hydraulic conductivity values for the upper surficial aquifer varied between 0.1 and 

10 ft/d. Aquifer-test results evaluated for a well screened in the partially confined to 

confined lower surficial aquifer produced a lateral hydraulic conductivity value equal to 

16 ft/d.

An inventory of all wells within 1- and 3-mi radii of the site was completed. Wells 

located within a 1-mi radius are either recreational wells, monitoring wells, or city of 

Charleston water-supply wells. The wells within a 3-mi radius, and not previously 

mentioned, are either unused, used as water-supply wells for the cities of Charleston or 

Mount Pleasant, or used for recreation, irrigation, domestic use, or monitoring purposes.

Microbial biodegradation rates determined for toluene in aquifer sediments on the 

NPS property were 0.84 and 0.0020 d'1 for aerobic and anaerobic environments, 

respectively. A laboratory adsorption coefficient of 3.32 X 10'8 ft3 /rng was determined 

for toluene in contact with upper surficial aquifer sediments. Microbial biodegradation 

rates determined for naphthalene in aquifer sediments on the NPS property were 0.88 

and 4.6 X 10~5 for aerobic and anaerobic environments, respectively. Naphthalene 

adsorption coefficients determined for these sediments were equal to or greater than 

4.84 X 10-6 ft3 /mg.

61
By incorporating appropriate hydrologic, geochemical, and microbiological 

parameters into the solute transport model SUTRA, toluene and naphthalene plumes 

were simulated that approximated the January 1994 plumes. The modeling approach 

used was an exploratory type. Various input parameters, such as hydraulic 

conductivity, microbial degradation, and adsorption were varied within reasonable 

ranges to determine under what conditions, if any, toluene or naphthalene would reach 

the Cooper River. The model grid used was a 1,320 ft by 1,320 ft area discretized into 30 

ft by 30 ft nodes. The grid was aligned with the x-axis parallel to the Cooper River and 

extended across the NFS property and the former manufactured gas plant site. Water 

levels were calibrated to a set of synoptic measurements collected in the model area on 

January 8,1994.

For the toluene simulation, the best estimates of lateral hydraulic conductivity were 

4 ft/d on the western part of the modeled area and 0.4 ft/d on the eastern part. The best 

estimates of microbial degradation and adsorption were 9.0 X 10'5 d' 1 and 2.2 X 10'8 

ft3 /nig, respectively.

For the naphthalene simulation, the best estimates of lateral hydraulic conductivity 

were the same as the toluene simulation. The best estimates of microbial degradation 

and adsorption were 6.9 X 10~5 d' 1 and 4.84 X 10' 11 ftYrng, respectively.

Using the laboratory and field results as initial conditions for predictive 

simulations and testing the variability of the model input parameters produced a 

majority of toluene transport simulations that did not reach the Cooper River within 150 

years. Predictive simulations using the calibrated naphthalene model suggest that 

conditions at the site are favorable for transport of naphthalene to the Cooper River at 

concentrations ranging from 0.0 to greater than 5.0 mg/L.

62
REFERENCES

Abbott, W.H., and Huddlestun, RE, 1980, The Miocene of South Carolina, in DuBar, J.R., 

DuBar, S.S., Ward, L.W., and Blackwelder, B.W., Cenozoic biostratigraphy of the 

Carolina outer Coastal Plain: Geological Society of America Field Trip Guidebook 

9, p. 208-210.

Aucott, W.R., 1988, The predevelopment ground-water flow system and hydrologic 

characteristics of the Coastal Plain aquifers of South Carolina: U.S. Geological 

Survey Water-Resources Investigation Report 86-4347,66 p.

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65
APPENDIX I

Description of boring logs for wells drilled on the National Park Service property, 

Charleston, S.C, November 1993

66
Appendix I. Description of boring logs for wells drilled on the National Park Service property, 

Charleston, S.C., November 1993

[USGS, U.S. Geological Survey; bis, below land surface]

Well USGS-1

Depth

bis

(feet)

0-14

14-38

38-43.5

43.5-46

Soil description

Sand, gray to black; fine- to medium-grained with some wood, concrete, and gravel. 

Clay, gray to black; very soft with some fine-grained sand and silt. 

Sand, gray to black; very fine- to medium-grained with trace silt and clay. 

Clay, gray to black; very soft with some very fine- to fine-grained sand.

Well USGS-2

0-8

8-31

31-41

41-45

Sand,

Clay,

Sand,

black; fine- to medium-grained with little clay and gravel.

gray to black; soft with little silt and trace sand.

gray to black; fine- to medium-grained with some silt and trace clay.

Clay, gray to black; very soft with trace sand.

Well USGS-2S

0-8

8-13

Sand,

Clay,

black; fine- to medium-grained with some silt and wood debris.

gray to black; very soft with some silt and trace sand.

Well USGS-3

0-8

8-33

33-50

50-51

Sand,

Clay,

Sand,

Clay,

brown to black; fine- to medium-grained with some gravel, silt, and wood debris.

gray to black; very soft with some silt and very fine- to fine-grained sand.

gray to black; very fine- to fine-grained with some silt and trace clay.

green to gray; very soft with little very fine- to fine-grained sand.

67
APPENDIX II

Well identification, test dates, hydraulic conductivity values, and method of water 

displacement for aquifer tests conducted in the surficial aquifers beneath the National 

Park Service property, Charleston, S.C., 1993

68
Appendix II. Well identification, test dates, lateral hydraulic conductivity, and method of water 

displacement for aquifer tests conducted in the surficial aquifers beneath the National 

Park Service property, Charleston, S.C., 1993

[PVC, polyvinyl chloride]

Well identification

] MW-2

J MW-3

J MW-4

J MW-5

J MW-7

'MW-8

J MW-9

'MW-10

J MW-11

2USGS-2

Test dates

09/13/93

09/10/93

09/13/93

09/13/93

09/13/93

09/13/93

09/13/93

09/13/93

09/13/93

12/06/93

Lateral hydraulic 

conductivity 

(feet per day)

10

.5

.3

.4

.7

1

.1

.1

.3

16

Method of water 

displacement

air compressor

air compressor

air compressor

air compressor

air compressor

air compressor

air compressor

air compressor

air compressor

PVC slug 

displacement

'Well screened in the upper surficial aquifer. 

Well screened in the lower surficial aquifer.

69