CONTENTS 

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

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

Background....................................................................................................................................................................2

Previous investigations ..................................................................................................................................................2

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

Acknowledgments.........................................................................................................................................................5

Methods of study....................................................................................................................................................................6

Well installation .............................................................................................................................................................6

Year 2000 ..............................................................................................................................................................7

Year 2001 ..............................................................................................................................................................7

Water sample collection and analysis ............................................................................................................................8

Soil and sediment sampling.........................................................................................................................................11

Ground-penetrating radar ............................................................................................................................................13

Ground-water contamination................................................................................................................................................13

Hydrogeologic framework...........................................................................................................................................14

Ground-water traveltime..............................................................................................................................................20

Summary and conclusions....................................................................................................................................................21

References cited ...................................................................................................................................................................22

Appendix: Prime Hook core lithologic descriptions ...........................................................................................................23

FIGURES

 1a–b. Maps showing:

1a. Location of Prime Hook National Wildlife Refuge and the Broadkiln Sportsman’s Club

 study area, Sussex County, Delaware ...................................................................................................2

1b. Detailed view of Prime Hook National Wildlife Refuge and the Broadkiln Sportsman’s Club

study area ...............................................................................................................................................3

 2. Photograph showing view of one of the five trap shooting ranges at the Broadkiln Sportsman’s Club................4

 3. Oblique aerial photograph showing Broadkiln Sportsman’s Club and Prime Hook National

 Wildlife Refuge, looking southwest..................................................................................................................5

 4. Photograph of “drop zone” of high-density pellets covered with geotextile fabric to protect waterfowl

and other birds ....................................................................................................................................................6

 5. Close-up photograph of lead shot in the drop zone at the Broadkiln Sportsman’s Club, with white oxide

or carbonate coatings on surface pellets.............................................................................................................7

 6. Photograph showing the seating of a plastic well casing into a pre-dug hole at Prime Hook National

 Wildlife Refuge .................................................................................................................................................8

 7. Photograph of shallow/deep well pair at upgradient location, Prime Hook National Wildlife Refuge ................9

 8. Aerial photograph of Broadkiln Sportsman’s Club and Prime Hook National Wildlife Refuge,

showing locations of all 19 wells installed at the site as of May 2001 ............................................................10

 9. Photographs of vibracore rig used at Prime Hook National Wildlife Refuge.....................................................12

10. Generalized geologic cross section of the study area, from well DZ-1 to well DZ-2.........................................13

11. Aerial photograph showing the ground-water table and flow directions in the study area.................................15

12. Map showing interpolated lead concentrations in ground water at Prime Hook National Wildlife Refuge.......19

13. Conceptual model of ground-water flow and contaminant transport in the study area ......................................20

iii 
_____________________________________________________________________________________________________________________________________ 

_____________________________________________________________________________________________________________________________________ 

TABLES 

1. Sampling locations and well-construction data for Prime Hook National Wildlife Refuge, 

Sussex County, Delaware ...............................................................................................................................11 

2. Concentrations of dissolved metals in ground water and surface water at Prime Hook 

National Wildlife Refuge................................................................................................................................16 

3. Major ions and field parameters in water samples from Prime Hook National Wildlife Refuge ........................17

Conversion Factors and Vertical Datum 

Multiply

_________________________________________________________

 By

________________________

 To obtain 

____________________________________________________ 

inch (in.) 2.54 centimeter 

foot (ft) 0.3048 meter 

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

mile (mi) 1.609 kilometer 

square mile (mi

2

) 2.590 square kilometer 

acre 4,047 square meter 

acre 43,559 square kilometer 

square foot (ft

2

) 0.0929 square meter 

gallon (gal) 3.785 liter 

Temperature in degrees Fahrenheit ( °F) may be converted to degrees Celsius ( °C) by the following equation: 

°

C = ( °F – 32) / 1.8 

Vertical Datum: In this report, “sea level” refers to the National Geodetic Vertical Datum of 1988—a geodetic datum 

derived from a 1988 update of the reference geoid and first-order level nets of the United States and Canada. 

In USGS standard usage, “Altitude” refers to height above mean sea level; “Elevation” refers to height above a defined 

reference datum. The reference datum used throughout this report is mean sea level, so in this instance the two terms are 

interchangeable. 

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

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

(μg/L). 

iv 
Acronyms and Abbreviations 

DG Prefix for sampling wells emplaced downgradient from the main lead shot deposits 

DI Deionized water 

DZ Prefix for sampling wells emplaced within the main “drop zone” of lead shot deposits 

GPR Ground-penetrating radar 

mg/L milligrams (10-3 gram) per liter 

μg/L micrograms (10-6 gram) per liter 

mL milliliter 

μm micrometer 

NWQL National Water-Quality Laboratory (USGS) 

NWR National Wildlife Refuge 

Pb Chemical symbol for lead 

PVC Polyvinyl chloride (plastic) pipe used for well casing 

UG Prefix for sampling wells emplaced upgradient of the lead shot deposits; sampled as a control. 

USEPA U.S. Environmental Protection Agency 

USFWS U.S. Fish and Wildlife Service (Department of the Interior) 

USGS U.S. Geological Survey (Department of the Interior) 

A note on nomenclature: 

Primehook and Prime Hook: On the USGS 7.5-minute topographic quadrangle map for Milton, Delaware, the tributary 

stream to the Broadkill River draining the study area is referred to as “Primehook Creek,” whereas the wildlife refuge is named 

“Prime Hook National Wildlife Refuge.” The name “Primehook” as a single word is an Anglicized version of an earlier, 

similar-sounding Dutch name meaning “Plum Point,” a local landscape feature (G. O’Shea, U.S. Fish and Wildlife Service, oral 

commun., 2002). Similar English adaptations of Dutch names are common in Delaware. The name was split into two words 

when the National Wildlife Refuge was established in 1964. This naming convention (one word for the creek and two words 

for the refuge) is used throughout the report. 

v 
Ground-Water Contamination from Lead Shot at Prime Hook 

National Wildlife Refuge, Sussex County, Delaware 

By Daniel J. Soeder and Cherie V. Miller 

Abstract 

Prime Hook National Wildlife Refuge is 

located in southeastern Delaware in coastal lowlands along the margin of Delaware Bay. For 

37 years, the Broadkiln Sportsman’s Club adjacent 

to the refuge operated a trap-shooting range, with 

the clay-target launchers oriented so that the 

expended lead shot from the range dropped into 

forested wetland areas on the refuge property. 

Investigators have estimated that up to 58,000 

shotgun pellets per square foot are present in locations on the refuge where the lead shot fell to the 

ground. 

As part of the environmental risk assessment 

for the site, the U.S. Geological Survey (USGS) 

investigated the potential for lead contamination in 

ground water. Results from two sampling rounds 

in 19 shallow wells indicate that elevated levels of 

dissolved lead are present in ground water at the 

site. The lead and associated metals, such as antimony and arsenic (common shotgun pellet alloys), 

are being transported along shallow ground-water 

flowpaths toward an open-water slough in the forested wetland adjacent to the downrange target 

area. Water samples from wells located along the 

bank of the slough contained dissolved lead concentrations higher than 400 micrograms per liter, 

and as high as 1 milligram per liter. In contrast, a 

natural background concentration of lead from 

ground water in a well upgradient from the site is 

about 1 microgram per liter. Two water samples 

collected several months apart from the slough 

directly downgradient of the shooting range contained 24 and 212 micrograms per liter of lead, 

respectively. 

The data indicate that lead from a concentrated 

deposit of shotgun pellets on the refuge has been 

mobilized through a combination of acidic water 

conditions and a very sandy, shallow, unconfined 

aquifer, and is moving along ground-water flowpaths toward the surface-water drainage. Data 

from this study will be used to help delineate the 

lead plume, and determine the fate and transport of 

lead from the source area. 

Introduction 

Prime Hook National Wildlife Refuge (NWR) is located 

along Primehook Creek and the western shore of Delaware 

Bay in Sussex County, Delaware, approximately 3 mi (miles) 

northeast of the town of Milton (figs. 1a–1b). The 9,700­

acre refuge was established in 1963 and consists of approximately 7,400 acres of freshwater and tidal marsh, 1,000 

acres of timber and brush, and 1,300 acres of grassland and 

croplands (U.S. Fish and Wildlife Service, 2000). 

Large numbers of birds, including Canada geese, snow 

geese, black ducks, mallards, pintails, teal ducks, and wood 

ducks either live on the refuge year round, or pass through 

the area during spring and fall migrations (U.S. Fish and 

Wildlife Service, 2000). Because significant numbers of 

waterfowl use the refuge, the U.S. Fish and Wildlife Service 

(USFWS) was concerned about the potential environmental 

impact of large amounts of lead shotgun pellets deposited on 

the property by a shooting range adjacent to the refuge. The 

wildlife biologists and refuge managers were worried that 

the birds would ingest the lead pellets, which are approximately 1–2 mm (millimeters) in diameter, as “grit,” a single 

one of which could potentially kill an animal from lead poisoning (Crowley and Richardson, 2001). The USFWS was 

also concerned that the soil and ground water might be contaminated with lead, possibly creating paths by which it 

could enter the local food chain. 

The USGS learned of the concerns of the USFWS in 

March 2000. The two agencies cooperated on an initial 

round of sampling in May 2000 of six shallow wells to determine if lead was present in the ground water at the site. 

When analysis of these samples showed the presence of lead, 

a second sampling round was carried out in April 2001 on 

13 wells and the nearby stream. The USGS study was 

designed as a “field screening” to give USFWS some indication of the scope of the lead problem, and to assess where 

and how fast the contamination might be moving. Lead 

transport through shallow ground water is an unusual occurAbstract 1 
rence, as metallic lead is generally considered immobile, and 

the chemistry of this process was also investigated. 

Background 

The Broadkiln Sportsman’s Club (referred to in this 

report as “the club”) was founded in 1962 in an area known 

as Pikes Neck, in Sussex County, Delaware. Property 

boundaries of Prime Hook NWR adjacent to the club were 

established by the USFWS in 1964. The club used five 

shooting ranges, each built behind a small (approximately 

10 by 10 ft, or feet) concrete block bunker known as the trap 

house, which launched the clay targets into the air. Individual ranges had an arrangement of five angled concrete walkways behind the trap house, with shooting stations and 

distances marked on the walkways (fig. 2). The club members fired shotgun rounds from shooting stations on the 

walkways across a grassy field and toward a wooded area, 

intending to hit the airborne clay targets above the field. 

Numerous lead shotgun pellets from misses and overshot 

followed ballistic trajectories downrange, eventually losing 

velocity and/or hitting trees inside the refuge boundary and 

falling to the ground. 

The club is located in an upland area that acts as a drainage divide for two wooded wetlands containing unnamed 

tributaries of Primehook Creek. The highest land elevation 

on the axis of the upland is about 10 ft above sea level; most 

of the land in the wooded wetland areas is 5 ft or less in elevation. Primehook Creek is fresh through this area, with 

levels controlled by a dam downstream. The Broadkill 

River is tidal through the refuge, but Primehook Creek 

behind the flow-control structure is not (G. O’Shea, USFWS, 

oral commun., 2000). 

The part of Prime Hook NWR bordering the club downrange from the trap-shooting area consists of a forested 

wetland along a small, unnamed tributary or slough to 

Primehook Creek shown in figure 3 as the wooded area to 

the left of the club facility. The slough consists of a series of 

small, shallow ponds or pools, a few to possibly a dozen feet 

wide, and only a few feet deep, separated by saturated hummocks of mud, fallen trees, and organic matter. The water is 

nearly stagnant with very slow drainage to Primehook 

Creek. The size and shape of the slough varies greatly with 

the seasonal rise and fall of the water table, and it dries up 

completely on occasion. The slough is heavily forested, and 

is not used much by migratory fowl, which prefer open 

water. There are numerous small mammals, birds, amphibians, and insects that are common in and around the slough, 

however, and use it as a water supply. Reference to the 

“unnamed tributary” or “slough” in this report denotes only 

the Primehook Creek tributary east of the club, in the area 

downrange from the trap houses. No work in the western 

tributary, indicated on figure 3 by the wooded area to the 

right of the club facility, was performed by the USGS as part 

of this study. 

Previous Investigations 

The trap-shooting range was operated from 1962–1998, 

until a proposed land trade with the USFWS was initiated by 

2 Ground-Water Contamination from Lead Shot at Prime Hook National Wildlife Refuge, Sussex County, DE 
the club. As part of the proposed trade, the USFWS began a 

review of potential contamination of the site. In August and

October 1998, USFWS personnel collected soil samples to

determine the extent of lead shot deposition and lead soil 

concentrations on the land parcel. Results indicated that the 

surface soils within the shooting trajectory contained elevated concentrations of lead and high numbers of lead shotgun pellets. The USFWS ordered the club to discontinue 

shooting onto the refuge property, and in 2000 funded the 

first year of a proposed 3-year Refuge Cleanup project to

delineate the magnitude and extent of soil contamination. 

A preliminary assessment by a USFWS contractor concluded that lead shotgun pellets from the trap shooting range

had accumulated on the refuge property in an area of about 

22 acres downrange from the club (Crowley and Richardson,

2001). The highest density of pellets on the refuge was concentrated in a zone of approximately 26,200 ft2 (square feet) 

immediately adjacent to the club property and directly downrange from the trap houses. Investigators counted as many

as 57,868 lead pellets per square foot in the center of this 

high-density area, which is referred to as the “drop zone” in

this report. 

Introduction 3 
A synthetic geotextile cover was placed over the highest 

concentrations of lead pellets in July 2000, with the intention 

of preventing waterfowl and other birds from ingesting the 

shot as grit (fig. 4). This material is identified by Crowley 

and Richardson (2001) as Geotex Model 315 ST, designed to 

resist degradation under ultraviolet light, and rated permeable to 5 gallons per square foot per minute. The textile 

material was anchored in place using 18-in. (inch) steel 

spikes, but after deployment, it was determined that placing 

numerous 6-in. concrete blocks on top of the cover would 

help it resist wind damage. 

In addition to this study, the USFWS and their contractors carried out a contaminant investigation in Primehook 

Creek, as well as aquatic toxicity measurements, bioaccumulation testing, and an ecological risk assessment. The risk 

assessment identified the source remediation area as approximately 5 acres of both wetlands and uplands. The cleanup 

plan involved removal of the soil and lead pellets, grading, 

and reseeding (B. Crawford, USFWS, written commun., 

2002). 

Purpose and Scope 

The purpose of this report is to provide water-quality 

data and interpretation to the USFWS for use in environmental risk assessment. The work was performed to analyze the 

spatial occurrence of lead in ground water at Prime Hook 

NWR, develop an understanding of the subsurface stratigraphy of the shallow aquifer system in the vicinity of the 

shooting range, and describe the plume of lead contamination in the study area. 

4 Ground-Water Contamination from Lead Shot at Prime Hook National Wildlife Refuge, Sussex County, DE 
An initial, preliminary field screening was performed to 

determine if lead from the shotgun pellets was present in the 

ground water, and subsequently, a more detailed field screening was done to try to assess the nature and extent of the 

contamination. The ground-water flow system also was 

analyzed to infer the fate and transport of lead in the ground 

water, and to determine the direction of movement and the 

potential for discharge of dissolved lead into nearby bodies 

of surface water. 

Acknowledgments 

The authors would like to thank Daniel Murphy 

and Sherry Krest of the U.S. Fish and Wildlife Service, 

Chesapeake Bay Field Office, and Barron Crawford, 

Annabella Larsen, and George O’Shea of Prime Hook 

National Wildlife Refuge for providing background information, access to the site, and assistance with some of the field 

work. USGS volunteer John Battista assisted with field 

work and took several of the photographs used in this report. 

David Krantz and Joseph Beman performed coring and 

installed the second set of wells, using a vibracore rig loaned 

by the University of Delaware (UD). Beman surveyed the 

well locations and measured ground-water levels. Mark 

Nardi assembled the survey data into a GIS data base, and 

produced site maps. Shannon Collier of UD and David 

Krantz ran the ground-penetrating-radar survey, also using 

equipment generously loaned by UD. Michael Smigaj performed the core lithologic analysis, and Britta Hoehndorf 

transcribed his field notes onto a stratigraphic spreadsheet. 

Hoehndorf also produced the water-table map and lead concentration gradient map. The authors are grateful to all of 

these individuals for their help and dedication. 

Introduction 5 
Methods of Study 

The objective of this study was to determine the presence 

and concentrations of lead, antimony, arsenic, and associated 

shotgun-pellet metal alloys, along with major ions and field 

parameters, in shallow ground water at Prime Hook NWR in 

an area downgradient from the club. To obtain the necessary 

data, a total of 19 shallow wells were installed on the site. 

Sediment cores and ground-penetrating-radar data were collected to help define the geology and geohydrology of the 

area. Water levels were measured to determine hydraulic 

gradients and flow directions, and water samples were collected for chemical analysis of lead and other compounds. 

In April 2000, the USGS performed an initial field reconnaissance of the site to assess possible lead contamination in 

the ground water. Observations of lead pellets on the surface of the drop zone showed that many were coated with a 

white oxide or carbonate layer (fig. 5), while those a few 

centimeters down into the upper soil horizon were shiny and 

metallic. The absence of the coating was interpreted as evidence of corrosion, and indicated that significant amounts of 

lead could be dissolving from the shot. The dissolved lead 

might then be transported into the shallow ground water. 

USFWS asked the USGS to carry out ground-water sampling and metals analysis as part of the site characterization 

work. Water samples were collected and analyzed by the 

USGS in May 2000 and again in April 2001. 

Well Installation 

Seven drive-point well casings, each consisting of a 

Schedule 40 plastic (PVC) pipe, 1.5 in. in diameter and 3 ft 

in length, screened the entire length and fitted with a solid 

PVC point, were installed at Prime Hook NWR in April 

2000 for initial shallow ground-water sampling. The casings 

were put in place using hand tools, by first clearing the 

ground surface of leaves, rubble, and lead shot with a shovel, 

and then manually digging a hole approximately a foot deep 

and a foot in diameter. After carefully checking the bottom 

of the hole to ensure that it was free of any remnant lead 

shot, a 2-in.-diameter, hand-operated soil auger was used to 

dig a round hole approximately 2 to 4 ft deep. Each casing 

was inserted into the hole, and a threaded steel cap on the 

upper end was hit several times with a sledgehammer to seat 

the point (fig. 6). Clean building supply sand was then 

placed into the annulus of the hole around the outside of the 

casing. Because the casings are screened over their entire 

3-ft length, no attempt was made to pack off zones within the 

shallow soil profile penetrated by the emplacement hole. 

Finally, clean soil from the hand auger excavation was used 

to fill in the top of the hole and make it level with the ground 

surface. Great care was taken at every step of the installation process to ensure that no lead pellets were introduced 

into the hole or into the casing that might affect the results of 

the water sampling and metals analysis. 

In April and May 2001, 12 additional wells were 

installed on Prime Hook NWR near the club. Using a vibracore rig, seven wells were installed in cored holes; the 

remaining five were installed in hand-augered holes using 

the method described previously. The operational details of 

the vibracore rig are discussed in a later section. After the 

cores were recovered, plastic pipe was inserted into the drill 

holes as casing to create a well for sampling. In most cases, 

the plastic casing was not set as deep as the total cored depth 

of the hole, because the deeper portions of the holes typically 

collapsed immediately after the core was removed. Casing 

was set as deeply as possible, and clean sand was packed 

into the annulus as it was in the hand-augered wells. Some 

of these later wells have screened intervals only 1 ft long, 

instead of the standard 3-ft screen. The shorter screens were 

used in selected locations to try to reduce the vertical component of the ground-water sample. 

Two of the vibracored holes were relatively deep in locations near the unnamed tributary to Primehook Creek. Both 

of these penetrated a dense clay layer above a coarse, clean 

sand. Bentonite clay was used to seal the annulus of these 

6 Ground-Water Contamination from Lead Shot at Prime Hook National Wildlife Refuge, Sussex County, DE 
holes where they penetrated the clay. This material swells 

in water, and forms an effective low permeability barrier. 

Year 2000: The first well was placed upgradient and to 

the south of the main drop zone, in an area of the refuge that 

was free of visible lead pellets on the ground surface. This 

location was chosen as a control point to sample background 

levels of lead in the ground water. A second well was 

emplaced within the drop zone itself. This location was 

selected to sample the ground water directly beneath the 

highest concentrations of lead pellets to check for contamination. Five additional wells were then placed in various 

locations downgradient of the drop zone near the banks of 

the slough. These were intended to capture samples of any 

lead moving toward this surface-water body through the 

shallow ground water. 

Year 2001: The original well in the drop zone (DZ) broke 

off in January 2001 when a windstorm blew the geotextile 

cover off the area. The plastic pipe remaining in the ground 

was unsalvageable, so a new shallow well (DZ-0) was 

emplaced in the drop zone about 5 ft northeast of DZ. 

Several additional wells were installed next to existing Year 

2000 sites using the vibracore rig in order to create shallow/ 

deep well pairs (fig. 7). This was done at the upgradient 

site (UG, UG-1), the drop zone (DZ-0, DZ-1), and two of the 

downgradient sites (DG-5, DZ-2) and (DG-2, DG-7). The 

purpose of this type of emplacement was to collect data on 

the stratigraphy and lateral continuity of units across the site, 

as well as to investigate the depth of vertical penetration of 

lead in the shallow ground water. Well DZ-2 was set 10.2 ft 

deep near the slough, next to well DG-5, installed in 2000. 

DG-5 had shown a significant concentration of lead in the 

2000 sampling, and emplacement of DZ-2 next to it was 

intended to capture a deeper part of the discharge flowpath. 

Coring of DZ-2 encountered a dense sandy clay from a depth 

of about 6 to 8 ft, with a coarse sand beneath. The 3-ft 

screen was set below the clay layer into this coarse sand, and 

Methods of Study 7 
the sandy clay was sealed off with swelling bentonite. 

Hence, the ground water in the DZ-2 well is entirely from 

the deeper sand, and it is under a slightly higher pressure 

head than the near-surface ground water. The water level in 

the DZ-2 well was approximately 1.5 in. above ground surface at the time of installation. 

In addition to the vibracored holes, wells were installed 

with the hand auger along the western bank of the slough 

at intervals of about 30 to 50 ft to the south of the DG-5 location. This was done in an attempt to constrain the southern 

boundary of the lead plume moving from the drop zone 

toward the tributary. The hand-augered well pair DG-8 and 

DG-8S, set approximately 5 ft and 2 ft deep respectively, 

were intended to capture deeper and shallower ground-water 

flowpaths in a visible discharge area or spring. DG-8 has a 

1-ft screen instead of a 3-ft screen in an attempt to better 

isolate the slightly deeper flowpaths. Locations of all 19 

wells, the trap shooting range, drop zone, and tributary are 

shown in the annotated aerial photo in figure 8. Construction details of the wells installed at Prime Hook NWR are 

summarized in table 1. 

Water levels in all wells were collected during a synoptic 

measurement on September 24, 2001, using a Solinst waterlevel tape. Absolute water levels tend to be higher in the 

spring, when the wells were installed and sampled, but 

because the levels of all the wells were measured within a 

few hours of one another, the data provide a relatively 

precise “snapshot” of ground-water conditions at the time 

the measurement was made. To better understand groundwater behavior on a long-term basis, synoptic measurements 

should be repeated in different seasons under different 

hydrologic conditions over a period of several years. However, even a single synoptic can provide a great deal of information on the fate and transport of contaminants in ground 

water. Water levels from this measurement are included in 

table 1. 

Water Sample Collection and Analysis 

Water samples were collected by the USGS from 6 wells 

at Prime Hook National Wildlife Refuge in June 2000, and 

from 12 wells and the surface stream in May 2001. Additional samples were collected from the surface-water site and 

well DG-5 in August 2001. Sample handling was minimized to avoid contamination, and ultra-clean techniques 

were used. Prior to sampling, all of the sampling equipment, filters, and bottles were washed with a Liquinox detergent solution, flushed with tap water, and sequentially rinsed 

with a 10 percent solution of nitric acid (HNO3), ultra-pure 

deionized water (DI), and three rinses of ground water just 

prior to sample collection. Water was collected with a peristaltic pump using Tygon tubing. Wells were purged until 

field parameters—pH, temperature, dissolved oxygen (DO), 

and specific conductance—had stabilized. Samples for the 

analysis of dissolved trace metals and major ions were filtered with an in-line 0.45-μm (micrometer) polycarbonate 

capsule filter. Samples for dissolved metals were immediately fixed with 2 mL (milliliters) of Ultrex concentrated 

HNO3 per 250 mL and bagged in acid-washed zipper-lock 

plastic bags. Samples for the analysis of cations, silica, iron, 

and manganese were filtered into a separate 250-mL polyethylene bottle and fixed with 2 mL of concentrated nitric 

acid. Samples for anions were not fixed with acid. Whole 

water was collected with the peristaltic pump into a 125-mL 

baked amber glass bottle for the analysis of total organic 

carbon. Samples were shipped on ice overnight to the 

USGS National Water-Quality Laboratory (NWQL) in 

Denver, Colorado. All sample collection and quality-assurance techniques for fieldwork are documented in the USGS 

National Field Manual (U.S. Geological Survey, 1999). 

Field parameters were determined with a variety of 

standard probes and field meters. Orion meters were used 

for pH and specific conductance. A YSI dissolved-oxygen 

meter was used for DO. Alkalinity was determined by fixedincrement titration (U.S. Geological Survey, 1999). Water 

samples were collected from all wells except DG-6 and 

DG-7. These two holes were installed to provide a geological transect across the northern part of the site, and are 

located well away from the lead contamination zone. Well 

DG-2, located a few feetfrom DG-7, was sampled during the 

8 Ground-Water Contamination from Lead Shot at Prime Hook National Wildlife Refuge, Sussex County, DE 
Year 2000 sampling round, and contained lead at concentrations below 1 μg/L, which is essentially background level. 

Due to financial and time constraints, wells DG-6 and DG-7 

were not sampled. 

Concentrations of dissolved trace metals were analyzed 

by direct-injection Inductively Coupled Plasma-Mass 

Spectroscopy (ICP-MS) with corrections for ion interferences. Documentation and quality assurance for the ICPMS method for low-level trace-element analysis is described 

in Garbarino and Taylor (1994) and Garbarino (1999). Concentrations of metals in field blanks collected for this study 

were typically not detected except for one blank sample collected on May 23, 2001 that may have had contamination 

either in the blank water or in the fixing acid. This sample 

was recollected in August 2001 and was clean the second 

time. High concentrations of trace metals that were detected 

in the contaminated blank were within the range of background levels in the August sample, and therefore did not 

affect the interpretation. Analytical precision for dissolved 

metals was better than ± 5 percent for samples collected 

at well DG-2 on June 13, 2000. Precision was not as 

good for a set of replicates collected from well DG-5 on 

May 16, 2001, possibly due to large spatial gradients in the 

concentrations of some metals, particularly lead, in the 

ground water near the drop zone. The well-purging process 

may have caused or exacerbated the problem by drawing 

water from around the well annulus where there was likely a 

large gradient in the concentration of lead. Analysis of a 

third sample from this well, collected on August 23, 2001, 

also indicated substantial variability in the concentrations of 

lead and other metals at this site. Samples for the concentrations of total organic carbon and major ions were analyzed 

according to USGS protocols (Wershaw and others, 1987; 

Fishman, 1993). 

Methods of Study 9 
10 Ground-Water Contamination from Lead Shot at Prime Hook National Wildlife Refuge, Sussex County, DE 
Table 1. Sampling locations and well-construction data for Prime Hook National Wildlife Refuge, 

Sussex County, Delaware 

[ft, feet; UG, upgradient; DZ, drop zone; DG, downgradient; SW, surface water; N/A, not applicable] 

Station 

name 

Station 

number 

Ground 1 

altitude 

Water 1, 2 

altitude

 Total 3

 depth

 (ft) 

Screen 4 

length 

(ft) 

Date 

installed 

Sample 

date 

Date of 

replicate 

UG 

UG-1 

UG-2 

DZ 

DZ-0 

384923075170901 

384923075170900 

384923075170601 

384925075170601 

384926075170601 

4.80 

4.70 

2.40 

3.90 

3.90 

2.63 

2.63 

2.36 

no data 5 

2.41 

4.22 

8.69 

8.89 

3.25 

3.12 

3

3 

3 

3 

3

 20-Apr-00 

16-Apr-01 

16-Apr-01 

20-Apr-00 

 24-Apr-01 

13-Jun-00 

16-May-01 

16-May-01 

13-Jun-00 

18-May-01 

16-May-01 

DZ-1 

DZ-2 

DZ-3 

DG-1 

DG-2 

384926075170602 

384926075170504 

384926075170603 

384926075170401 

384931075170401 

3.90 

2.20 

2.60 

2.80 

2.30 

2.36 

2.33* 

2.30 

1.96 

1.01 

4.66 

10.17 

7.58 

3.51 

2.23 

3

3

1

3 

3 

 18-Apr-01 

 18-Apr-01 

 19-Apr-01 

20-Apr-00 

20-Apr-00 

18-May-01 

16-May-01 

18-May-01 

13-Jun-00 

13-Jun-00 

DG-3 

DG-4 

DG-5 

DG-6 

DG-7 

384932075170201 

384927075170501 

384926075170501 

384931075170801 

384932075170501 

3.15 

2.50 

2.30 

7.20 

2.40 

2.71 

2.01 

2.02 

2.23 

1.99 

4.01 

4.72 

1.85 

11.45 

8.33 

3 

1 

3 

3

3 

20-Apr-00 

20-Apr-00 

20-Apr-00 

 19-Apr-01 

19-Apr-01 

13-Jun-00 

23-May-01 

13-Jun-00 

no sample 

no sample 

16-May-01 

DG-8 

DG-8S 

DG-9 

DG-10 

SW-1 

384926075170502 

384926075170503 

384925075170501 

384924075170501 

01484310 

2.10 

2.10 

2.00 

2.30 

1.80 

2.22* 

2.04 

2.18* 

2.22 

1.80 

4.97 

1.94 

3.08 

3.22 

N/A 

1

3

1

1

N/A 

 1-May-01 

 1-May-01 

 1-May-01 

 1-May-01 

N/A 

23-May-01 

23-May-01 

23-May-01 

16-May-01 

16-May-01 23-Aug-01 

1 All altitudes are in feet above sea level.


2 Synoptic water levels measured on 24-Sep-01.


3 Total depth is depth to bottom of casing below ground surface.


4 Screens are set at base of casing; DG-5, DG-2, and DG-8S are exposed above ground in shallow holes.


5 Casing broke off and well was abandoned before water level could be measured.


* Water under artesian pressure, slightly elevated above ground surface. 

Soil and Sediment Sampling 

Soil and sediment core samples were obtained from 7 of 

the 12 well holes installed at Prime Hook NWR in April and 

May 2001. The core was collected using a “vibracore” rig 

on loan from the University of Delaware. This soft-sediment 

coring rig used 4-in.-diameter thin-walled aluminum irrigation tubing as drill pipe. The tubing, which can be up to 

15 ft long, was mounted vertically under a tripod-like drilling support. A vibrator designed for de-aerating concrete 

was attached to the upper end of the tubing using u-bolts. 

The intense vibration caused the tubing to cut into the 

ground, and a core of soft sediment was captured inside the 

pipe. When the pipe penetrated to sufficient depth, the 

vibrator was removed, and an automotive engine winch was 

then used to pull the pipe and core up out of the ground. 

Small metal flanges riveted to the inside of the bottom end of 

the pipe helped keep the core inside. Details of the coring 

apparatus are shown in figure 9. Cores were measured, 

capped, and labeled before being transported to the USGS 

office in Dover, Delaware. 

Cores were analyzed in the lab by cutting the thin aluminum pipe with a circular saw blade designed for use on 

aluminum house siding. The pipe was cut lengthwise, and 

the soft sediment core inside was then sliced with a knife. 

The pipe was split open, exposing the flat, cut center of the 

core. Core lithologic descriptions were based on standard 

USGS protocols (Powars, 1997), and are included in the 

Appendix of this report. 

Methods of Study 11 
12 Ground-Water Contamination from Lead Shot at Prime Hook National Wildlife Refuge, Sussex County, DE 
Ground-Penetrating Radar 

Ground-penetrating radar (GPR) surveys were run on 

several transect lines across the site. The GPR equipment 

was generously loaned by the University of Delaware. It 

consists of a transmitter and receiver, each about 3 ft in 

length, which are placed on the ground and moved at fixed 

intervals along a measuring tape. A central laptop computer 

unit controls the radar impulses and collects the data. 

Radar transects were run in both north-south and eastwest directions across the site. The first transect was run 

from north to south from the edge of the woods into a grassy 

field along a line approximately 50 ft east of the trap houses. 

This line was 630 ft long, using 50 MHz antennas on 15-ft 

spacing and 1.5-ft steps. A second line was run from west to 

east along the southern boundary of the grassy field from the 

old entrance road to the edge of the woods. This transect 

was 590 ft long, again using the 50 MHz antennas on 15-ft 

spacing and 1.5-ft steps. A third GPR transect was run 

eastward from the edge of the woods to the unnamed tributary, following a path that connected the UG-1 and UG-2 

well sites. Because of the dense woods, the smaller 100 

MHz antennas were used on a 1.5-ft spacing with 1-ft steps. 

Several other short transects were run in the drop zone on top 

of the geotextile cover, and near the trap houses. 

Ground-Water Contamination 

Interpretation of the lithostratigraphy indicates that the 

geology of this area is complex. A generalized cross section 

of the geologic units encountered in wells DZ-1, DZ-2 and 

DZ-3 is shown in figure 10. It is obvious from the cross section that the thicknesses and properties of the sediment 

change significantly over the relatively short distances 

between individual wells. 

Ground-Water Contamination 13 
Hydrogeologic Framework 

The very uppermost sediments in the sequence at the site 

are Holocene-age swamp deposits, consisting of organicrich, clayey sand with thin interbeds of medium to coarse 

quartz sand (Ramsey, 2001). These are interpreted as 

swamp and stream deposits near the tributary, formed when 

the slough was a more active stream channel, probably 

during the most recent lowstand of Delaware Bay. These 

sediments are described in the cores as predominantly sandy 

clay, overlying and underlying a wedge of fine sand in well 

DZ-1 under the drop zone. This fine sand wedge thins 

toward the east in well DZ-3, and pinches out before reaching well DZ-2. 

Beneath the sandy clay of the swamp deposits is a 

coarse, pebbly sand, interpreted as the upper part of the late 

Pleistocene Scotts Corners Formation. On the geologic map 

of the area, this unit is shown at the surface in the upland part 

of the neck area near the club location (Ramsey, 2001). It is 

overlain by the swamp deposits to the east toward the 

slough. The Scotts Corners Formation consists of coarse to 

fine sand, with discontinuous beds of clayey silt, very coarse 

quartz sand, and pebble gravel. It is interpreted as a transgressive unit consisting of bay, beach, and estuarine deposits 

formed during a previous highstand of Delaware Bay 

(Ramsey, 2001). The cores collected for this study penetrated a coarse sand unit, which is interpreted to be a beachface deposit. It is continuous across the study area and dips 

slightly from west to east, in the direction of Delaware Bay. 

This coarse sand, partially confined under the Holocene 

sandy clay, is the apparent “artesian” unit encountered at 

depth in well DZ-2. 

The GPR data were used to attempt to determine the 

lateral continuity of stratigraphic units identified in the 

cores. The radar data were difficult to interpret due to interference from roots, building foundations, and other structures, but do support the notion of lateral continuity in the 

coarse sand unit, as well as the wedge shape of some of the 

finer sandy clay layers, as shown in figure 10. 

Results of water-level measurements in the wells in the 

study area show that the altitude of the water table decreases 

gradually from the upland areas toward the stream (fig. 11). 

Ground water also moves in this direction, from upland areas 

on the club property toward the wetland, eventually discharging into the slough, which is a tributary of Primehook 

Creek. Any lead mobilized in the ground water flowing 

under the drop zone could be expected to move toward the 

slough. It is important to note that dissolved lead at concentrations significantly above background levels was detected 

in the surface water of the slough near the seep discharge 

area during two different sampling rounds (May 16, 2001 

and August 23, 2001). 

Hydraulic gradients in the study area are generally low, 

averaging about 0.1 ft drop per 75 ft from the edge of the 

shooting range to the slough. The gradient is approximately 

0.0013. A locality with a somewhat higher gradient is 

present along the line from the drop zone to the stream 

defined by wells DZ-1 to DG-5, ending at a well-defined 

ground-water discharge zone on the bank of the slough near 

well DG-5. The highest concentrations of lead in ground 

water at the site were found at well DG-5. 

USGS topographic maps indicate that the drainage divide 

on the small neck of land where the club is located lies 

upgradient of the drop zone. Ground water under the lead 

pellets in the drop zone flows east, toward the slough. Lead 

mobilized in this ground water will remain within the refuge 

boundaries and discharge into the slough. It is highly 

unlikely that any lead from this site will leave the boundaries 

of Prime Hook NWR by way of the ground water. 

The results of the laboratory analyses of ground-water 

samples from Prime Hook NWR are shown in tables 2 and 3. 

Table 2 lists metals in water samples that were collected in 

June 2000, May 2001, and some repeat sampling in August 

2001. Replicate samples and field blanks were included for 

quality assurance. Major ions and field parameters from the 

ground water at Prime Hook NWR are shown in table 3. 

Low levels of lead occur naturally in ground water from 

Coastal Plain sediments. Contamination is defined by the 

degree of exceedance of these natural background levels. 

Lead concentrations in the wells upgradient of the drop zone 

were assumed to be at natural background levels. The 

values agreed with background lead levels from a study done 

in New Jersey streams (Stansley and others, 1992), indicating that a concentration of 1-2 μg/L was reasonable for naturally occurring lead in ground water at Prime Hook. The 

laboratory analyses show that lead concentrations significantly above background levels were found in a number of 

the wells sampled at Prime Hook NWR. Concentrations of 

lead approximately one order of magnitude or more above 

background levels were found at wells DZ-0, DG-8, DG-10, 

and the May 2001 sample from the surface-water seep. 

Lead concentrations approximately two orders of magnitude 

or more above background levels were found at wells DZ, 

DZ-2, DZ-3, DG-4, DG-8S, DG-9, and the August 2001 

surface-water sample. Lead concentrations three orders of 

magnitude or more above background levels were found in 

DG-5 (table 2). Water samples from the shallow/deep well 

pair located in the drop zone (DZ-0 and DZ-1) had nearly 

twice as much lead in the deeper sample compared to the 

shallow one. In contrast, two of the shallow/deep well pairs 

located along the banks of the slough in discharge areas had 

higher concentrations of lead in water from the shallower 

well. These differences in lead concentration with depth 

may be related to the downward or upward movement of the 

ground water, or could represent flow lines from different 

recharge areas. 

14 Ground-Water Contamination from Lead Shot at Prime Hook National Wildlife Refuge, Sussex County, DE 
Ground-Water Contamination 15 
Ground-Water Contamination from Lead Shot at Prime Hook National Wildlife Refuge, Sussex County, DE Ta

ble 2. Concentrations of dissolve

d metals i

n ground w

ater and surface water at Prime Hook National Wildlife R

efug

e

[Values from replicate (rep) samples and field blanks are included for quality assurance (in italics). All units are in micrograms per liter. Al, aluminum; Sb, antimony;

As, arsenic; Ba, barium; Be, beryllium; Cd, cadmium; Cr, chro

mium; Co, cobalt; Cu, copper; Fe, iron; Pb, lead; Mn, manganese; 

Mo, 

molybdenum; Ni, nickel; Ag, silver; Zn, zinc.

Wells D

G-6 and D

G-7 were not sampled for water quality and are not included in this table; <, less than; E, estimated value; --, no data]

Station name Date Al Sb As Ba Be Cd Cr Co Cu Fe Pb Mn Mo Ni Ag Zn UG 6/13/2000 <16 <1 <0.9 63.1 <1 <1 <0.8 2.11 <1 -- 1.12 89.6 <1 1.36 <1 <4 UG 5/16/2001 1 0.07 -- 73.8 <0.06 0.06 <0.8 0.6 <0.2 <10 0.8 41.5 <.2 0.34 <1 <1 UG-1 5/16/2001 -- <0.05 <0.2 -- -- -- -- -- -- 410 1.91 132 -- 2.61 -- --UG-2 5/16/2001 -- 0.14 

E 0.2 -- -- -- -- -- -- 20 6.25 76.5 -- 3.02 -- --

DZ 6/13/2000 <19 9.61 1.3 67.7 <1 <1 <0.8 1.52 <1 -- 392 78.9 <1 <1 <1 <4 DZ-0 5/18/2001 3 0.43 -- 23.5 E 0.04 1.01 <0.8 1.81 

E 0.2 2,180 7.56 -- <.2 0.52 <1 3 

DZ-1 5/18/2001 -- 0.4 1.5 -- -- -- -- -- -- 3,160 14.4 120 -- 1.07 -- --DZ-2 5/16/2001 12 17 -- 118 0.07 0.22 <0.8 1.05 <0.2 800 529 67.9 <.2 1.6 <1 5 DZ-3 5/18/2001 -- 13.9 11 -- -- -- -- -- -- 550 491 67.9 -- 1.35 -- --DG-1 6/13/2000 154 1.96 5.2 15.7 <1 <1 0.9 2.1 <1 -- 1.42 43.4 <1 1.26 <1 5 DG-2 6/13/2000 <41 <1 <2 17.1 <1 <1 <0.8 1.54 <1 -- <1 19.1 <1 <1 <1 <5 DG-2 rep 6/13/2000 <44 <1 <2 16.7 <1 <1 <0.8 1.49 <1 -- <1 18.1 <1 <1 <1 <5 DG-3 6/13/2000 628 <1 2.6 37.3 <1 <1 2.2 2.02 <1 -- 1.55 20.3 <1 2.53 <1 9 DG-4 5/23/2001 -- 1.58 0.2 -- -- -- -- -- -- 50 131 12.2 -- 0.82 -- -­DG-5 6/13/2000 -- -- -- -- -- -- -- -- -- -- 965 -- -- -- -- -­DG-5 5/16/2001 60 51.8 -- 35.4 E 0.04 0.8 <0.8 0.93 0.3 540 1,010 19 <.2 1.46 <1 8 DG-5 rep 5/16/2001 53 59.9 -- 39 

E 0.03 0.5 <0.8 0.91 <0.2 590 777 19 <.2 0.86 <1 6 

DG-5 8/23/2001 -- 65 -- -- -- -- -- -- -- -- 1,420 -- -- -- -- --DG-8 5/23/2001 -- 5.54 1.2 -- -- -- -- -- -- 220 11.3 43.9 -- 2.43 -- -­DG-8S 5/23/2001 -- 22.9 22 -- -- -- -- -- -- 270 357 35 -- 1.6 -- --DG-9 5/25/2001 -- 2.78 0.2 -- -- -- -- -- -- <10 112 39.6 -- 2.33 -- --DG-10 5/16/2001 -- 0.7 E 0.2 -- -- -- -- -- --

E 8.7 7.77 36.5 -- 1.65 -- -­

SurfaceWater Seep 5/16/2001 25 10.9 -- 150 0.08 0.12 <0.8 3.08 <0.2 170 23.7 53.5 <.2 0.98 <1 5 Surface-Water Seep 8/23/2001 -- 22.8 -- -- -- -- -- -- -- -- 212 -- -- -- -- --Field Blank 6/13/2000 <5 <1 <2 <1.0 <1 <1 <0.8 <1.00 <1 -- <1 <1.0 <1 <1 <1 <1 Field Blank 5/16/2001 <1 <0.05 -- <1.0 <0.06 <0.04 <0.8 <.01 <0.2 <10 <0.08 <.1 <.2 <0.06 <1 <1 Field Blank 5/23/2001 -- 0.09 <0.2 -- -- -- -- -- -- -- 1.44 -- -- 0.06 -- --Equipment Blank 8/23/2001 -- 0.14 -- -- -- -- -- -- -- -- 0.09 -- -- -- -- --

Field Blank 8/23/2001 -- <0.05 -- -- -- --- -- -- -- -- <0.08 -- -- -- -- --

16 
Table 3. Major ions and field parameters in water samples from Prime Hook National Wildlife Refuge

[Concentrations are in milligrams per liter (mg/L). μS/cm, microsiemens per centimeter; <, less than; E, estimated value; --, no data] 

Ground-Water Contamination 

Totalorganic

Temperature, Specific Dissolved carbon Calcium Magnesium Sodium Potassium Bicarbonate Chloride Sulfate Fluoride Silica

Station degrees conductance oxygen (mg/L (mg/L (mg/L (mg/L (mg/L (mg/L (mg/L (mg/L (mg/L (mg/Lname Date Celsius (μS/cm) (mg/L) pH as C) as Ca) as Mg) as Na) as K) as HCO3 ) as Cl) as SO4 ) as F) as SiO2) 

UG 6/13/2000 15.2 157 3.0 5.6 1.3 -- -- -- -- -- -- -- -- -­UG 5/16/2001 13.0 173 2.0 5.9 2.2 14.10 6.76 2.2 6.83 16 15.4 15.6 <.2 3.3 UG-1 5/16/2001 12.0 146 4.6 5.0 -- 7.16 7.79 2.6 3.39 -- 10.2 18.4 <.2 8.9 UG-2 5/16/2001 13.4 191 3.3 4.8 4.5 4.94 9.67 6.8 5.36 -- 17.3 23.1 <.2 11.8 DZ 6/13/2000 20.6 32 2.5 5.1 3.3 -- -- -- -- -- -- -- -- -­DZ-0 5/18/2001 17.2 37 1.3 5.2 1.6 1.89 0.50 2.6 0.55 6 2.8 3.6 <.2 5.4 DZ-1 5/18/2001 16.4 66 1.7 5.3 -- 3.26 1.11 2.7 2.27 18 3.4 6.1 <.2 4.4 DZ-2 5/16/2001 12.8 88 3.1 5.3 5.5 2.95 4.59 2.3 2.68 -- 4.4 21.9 <.2 10.7 DZ-3 5/18/2001 -- 81 2.2 5.3 -- 2.77 3.76 1.8 2.00 3 3.0 21.9 <.2 7.9 DG-1 6/13/2000 16.0 111 <0.1 5.8 34.0 -- -- -- -- -- -- -- -- -­DG-2 6/13/2000 16.3 95 1.9 5.2 27.0 -- -- -- -- -- -- -- -- -­DG-3 6/13/2000 15.3 84 5.7 5.0 33.0 -- -- -- -- -- -- -- -- -­DG-4 5/23/2001 14.4 106 3.0 6.0 -- 3.54 1.27 3.3 2.03 10 5.3 8.9 <.2 5.8 DG-5 6/13/2000 -- -- -- -- -- -- -- -- -- -- -- -- -- -­DG-5 5/16/2001 14.8 67 1.4 5.5 12.0 3.70 1.37 4.1 2.87 23 6.6 0.6 <.2 8.2 Replicate 5/16/2001 -- -- -- -- 11.0 3.67 1.34 4.2 3.18 -- 6.4 0.8 <.2 8.0 DG-5 8/23/2001 23.1 82 2.0 5.5 -- -- -- -- -- 27 -- -- -- -­DG-8 5/23/2001 15.0 144 3.0 6.1 -- 15.90 3.94 3.3 2.22 32 6.4 21.8 <.2 7.9 DG-8S 5/23/2001 16.1 94 1.9 5.6 -- 6.19 3.98 2.7 2.16 15 5.5 16.9 <.2 9.1 DG-9 5/25/2001 15.2 152 6.0 6.4 -- 7.44 6.78 6.4 3.98 4 16.2 0.8 <.2 10.4 DG-10 5/16/2001 13.5 149 1.1 6.4 -- 6.30 5.22 8.5 3.46 8 12.8 3.3 <.2 9.5 Seep 5/16/2001 14.9 128 <1.0 6.0 4.4 4.60 5.72 6.8 3.15 30 15.9 3.1 <.2 11.5 Seep 8/23/2001 25.5 68 0.5 5.7 -- -- -- -- -- 16 -- -- -- -­Blank 5/16/2001 -- -- -- -- E .47 <0.01 <0.01 <0.1 <0.09 -- <0.1 <0.1 <.2 <0.5 

17 
Changes in lead concentration over time at two sites 

indicate a large degree of variability in ground-water levels 

and chemistry. The lead content in water collected from the 

surface-water seep increased by nearly an order of magnitude between the sample collected in May 2001, and the follow-up sample collected in August 2001. Wetter conditions 

and higher water volumes in May may have diluted the lead 

concentration, whereas during the low-flow period in 

August, it was much more concentrated. Antimony in these 

samples showed an increase as well, doubling in concentration in August compared to May. 

Another temporal change might be present between 

well DZ, emplaced in the drop zone in 2000, and well pair 

DZ-0/DZ-1, emplaced in 2001. The drop zone was covered 

with a geotextile fabric a few weeks after shallow well DZ 

was emplaced and sampled to prevent migratory waterfowl 

from landing in the area and ingesting the lead shotgun 

pellets as grit. Concentrations of lead in samples from well 

DZ collected in 2000 were nearly 50 times higher than those 

collected at nearby well DZ-0 in 2001 from the same depth. 

Although the geotextile barrier was permeable to rainwater, 

it is possible that the material still reduced infiltration and 

may have limited additional lead from making its way from 

the pellets into the ground water. This could explain the 

reduced lead concentrations in the more recently collected 

water samples, although natural variability in the groundwater system also could be a factor. 

The mobility of lead depends upon the metal’s corrosion 

or passivation behavior in each geochemical environment. 

The oxidation of metallic lead is rapid under normal environmental conditions, but the oxidized lead reacts readily with 

other species to form insoluble precipitates that coat and 

passivate the surface of the metal. Available literature on 

environmental lead commonly cites examples such as lead 

bullets found on Revolutionary War or Civil War battlefields 

that have been well-preserved under an oxide or carbonate 

coating for sometimes hundreds of years (Rimstidt and 

Craig, 2000). The mobility of lead, however, is controlled 

by processes that may override the passivation. Low pH, in 

particular, is suspected of being a major agent in the 

increased solubility of the lead carbonate hydrocerrusite. 

Relatively low pH was found in the shallow ground 

water at Prime Hook NWR. Values in the range of about 4.8 

to 6.4 were common during the field sampling. The acidic 

conditions are responsible for dissolving the lead carbonate 

off the pellets. Because of the apparent lack of buffering 

capacity and adsorption sites in the silica-rich sediments, the 

dissolved lead was mobilized and moved into the ground 

water. Many of the stratigraphic horizons are sandy, with 

little or no clay or iron oxide coatings that could trap and 

hold the lead. Once lead was in the ground water, however, 

it is possible that its solubility was enhanced by the formation of dissolved organic-carbon complexes. Total organic 

carbon in the water samples ranged from approximately 1 to 

34 mg/L. 

Concentrations of dissolved iron were relatively high in 

many of the Prime Hook ground-water samples, up to 2 or 

3 mg/L. High iron concentrations are not unusual in ground 

waters from the Delaware Coastal Plain, and these values 

appear to represent natural background levels. At a number 

of locations in the sediment cores, iron hydroxides were 

found in abundance, commonly at contacts between sand 

and clay layers. This could potentially be the result of iron 

oxide precipitation at oxidation-reduction boundaries, but 

it is more likely that these iron-stained layers represent 

episodes of subaerial exposure or ancient soil horizons 

(Ramsey, 2001). An active geochemical boundary may 

result in the precipitation of lead at the same locations as the 

iron, or the lead may simply be captured by pre-existing iron 

oxide deposits in the sediments. The detailed chemical analysis of the sediments required to investigate this hypothesis 

was beyond the scope of this study. Once the drop zone is 

remediated and the source area removed, the lead in the 

ground-water system may eventually be naturally attenuated 

as the system flushes out. However, some of the lead also 

may be immobilized as it becomes bound to iron oxides at 

the margins of the sand units, making the natural attenuation 

process very lengthy. 

A map view of interpolated lead concentrations in the 

ground water is shown in figure 12, based on data from table 

2. The highest concentration of lead is in the vicinity of 

well DG-5, which is in a discharge area near the slough. The 

ground water appears to be actively transporting lead to this 

point. A lower concentration of lead surrounds this core 

region, with the axis of the concentration oriented from the 

drop zone toward well DG-5. On the basis of existing data, 

this is the most well-defined plume of lead contamination in 

the ground water at Prime Hook NWR. 

Lower concentrations of lead in the ground water are 

spread out, and appear to be oriented in a direction more 

parallel than perpendicular to the banks of the slough. One 

reason for this may be a wider areal distribution of source 

pellets in fewer numbers on the ground in locations that are 

still downrange, but outside of the main drop zone. Lead 

may be moving into the ground water just as readily, but in 

lower initial concentrations because of a more sparse pellet 

count. Also, the ground-water table map in figure 11 shows 

that the hydraulic gradient is lower in the area to the south of 

the drop zone. This lower gradient, combined with the seasonal rise and fall of the water table, may average out the 

concentration of lead over a broad area, instead of transporting it in a directional manner as it does at well DG-5. A conceptual model of ground-water flow and transport of the lead 

from the drop zone to the stream is shown in cross section in 

figure 13. Ground water discharging into the slough is carrying lead into the surface water. 

No data were collected from the far side of the slough 

because the area is virtually inaccessible. Although it is 

possible that lead traveling along deeper, confined flowpaths 

could be present in ground water east of the slough, this was 

beyond the range of the investigation. The issue of ecological concern for the USFWS was whether or not lead was getting into the surface water of the intermittent stream, and 

hence potentially into the biota. Because the shallow 

18 Ground-Water Contamination from Lead Shot at Prime Hook National Wildlife Refuge, Sussex County, DE 
Ground-Water Contamination 19 
ground water in this area is not used for water supply, if lead

is indeed present in ground water east of the slough, it is

likely to remain there. 

Ground-Water Traveltime 

The well-defined plume of dissolved lead now being 

discharged into the slough formed within the last 37 years, 

after shooting began in the early 1960s. This indicates that if

the source area is cleaned up, the lead may eventually flush

out of the ground water. Some lead may have been deposited on clays or in iron-rich zones along the flowpaths, however, and could take a relatively long time to clear out of the 

system. 

A rough estimate of ground-water traveltime (GWTT) at 

the Prime Hook NWR site can be derived from the head 

contours and some estimates of sediment properties. The 

following assumptions were used for this calculation: 

1. The range of hydraulic conductivity in fine sand can

be quite variable. Numbers taken from Freeze and 

Cherry (1979) estimate it to be between 1 and 

50 ft/day (feet per day). There is a fairly large error

range associated with this estimate, but it is reasonable as an order of magnitude. 

2. Porosity of the aquifer is assumed to be 25 percent

(0.25) for compacted, uncemented sand (Heath, 

1983). 

3. Hydraulic gradient is approximately a 0.1-ft drop 

per 75 ft from the edge of the shooting range to the 

slough. The gradient is approximately 0.0013. 

4. These estimates apply only to the unconfined surficial 

aquifer. There are insufficient data from the partially confined aquifer in the coarse beach-face sand

at depth to estimate GWTT. 

20 Ground-Water Contamination from Lead Shot at Prime Hook National Wildlife Refuge, Sussex County, DE 
Calculations: 

Estimated ground-water velocity (Heath, 1983) 

v = (K/n) x dh/dl, 

where 

v = velocity, 

K = hydraulic conductivity, 

n = porosity, and 

dh/dl = hydraulic gradient. 

For 

K = 1 to 50 ft/day, 

n = 0.25, and 

dh/dl = 0.0013, 

v = 0.0052 to 0.26 ft/day. 

The estimated time of ground-water travel, assuming the 

distance from the drop zone to the discharge area is about 

200 ft, would range from approximately 800 to 38,000 days 

(26 months to 104 years). The 37-year maximum limit on 

the transport time of the present contamination fits into this 

range. 

Ground water traveling from farther upgradient off the 

shooting range itself would likely be moving along a longer, 

deeper flow path through the semiconfined, coarse sand 

beach face, as indicated by the higher hydraulic heads measured in this unit. It is possible that there may be some 

downward leakage or percolation into this sand from the 

overlying system, contributing to the relatively high concentrations of lead in the deeper samples. Most of the ground 

water in this beach face sand would have entered it from 

upgradient, on the club property, however, not by infiltrating 

through the drop zone. 

Actual traveltimes for contaminants transported by the 

ground water may be significantly longer than those for the 

water alone, due to retardation factors such as adsorption in 

the sediments. An assessment of the potential for natural 

attenuation would require an in-depth analysis of the sediment geochemistry, and a better understanding of the site 

geology and hydrology. Due to the low hydraulic gradient 

and the opportunity for lead to interact and bond with sediments, it may actually take a considerable amount of time for 

the system to naturally attenuate. After the source area is 

remediated, periodic, long-term monitoring of metals in the 

ground water downgradient of the source and in the discharge areas would provide data on the performance of natural attenuation in the ground-water system. 

Summary and Conclusions 

The Broadkiln Sportsman’s Club in Sussex County, 

Delaware, northeast of the town of Milton, operated a trap 

shooting range adjacent to Prime Hook National Wildlife 

Refuge for a period of 37 years. Lead shotgun pellets from 

misses and overshot accumulated on the refuge within a forested wetland downrange, in numbers as high as 57,868 pellets per square foot. Because of acid rain and low pH 

conditions in the wetland, the lead dissolved and infiltrated 

into the ground water. The metal is being transported downgradient along shallow flowpaths, and discharging into an 

unnamed tributary of Primehook Creek. Lead concentrations in the ground water near a discharge zone into the 

unnamed tributary range from 10 to 1,000 times above natural background levels. 

An initial round of sampling by the U.S. Geological 

Survey in cooperation with the U.S. Fish and Wildlife 

Service was done in May 2000 on six shallow wells to determine if lead was present in ground water at the site. When 

analysis of these samples showed the presence of lead, a 

second sampling round was carried out in April 2001 on 

13 wells and the nearby stream. The U.S. Geological 

Survey study was designed as a “field screening” to give the 

U.S. Fish and Wildlife Service some indication of the scope 

of the lead problem, and to assess where and how fast the 

contamination might be moving. 

Most of the ground-water movement at the site is lateral, 

from the upland areas near the club toward the slough. The 

near-surface geology consists of gently eastward-dipping 

beach face and foreshore sand units from a previous highstand of Delaware Bay, overlain by swamp deposits consisting of clayey sand. Discontinuous clay layers and lenses 

occur throughout, several with pronounced iron-oxide stains 

indicating potential oxidation-reduction boundaries. 

The highest concentrations of lead are present in a fairly 

narrow plume in an area of higher than average hydraulic 

gradients. Lower concentrations of lead are present in 

ground water throughout a broader area of the site. The lead 

is mobilized by low pH precipitation and ground water, and 

transported into a silica-rich sand with little capacity for 

buffering. The lead may eventually be trapped in iron-oxide 

rich layers in sands and clays. 

Planned cleanup of the site by the U.S. Fish and Wildlife 

Service includes physical excavation and removal of the 

pellet-contaminated soil, offsite disposal, grading, and 

revegetation of the area. Once the source area is remediated, 

the lead may eventually be flushed out of the ground water, 

but additional ground-water monitoring data would be 

needed to assess the potential for natural attenuation in this 

system. 

Summary and Conclusions 21 
References Cited 

Crowley, D.M., and Richardson, Norm, 2001, 

Preliminary assessment-site investigation, shotgun 

range, Prime Hook National Wildlife Refuge, 

Milton, Delaware: Report prepared under contract no. 

1448–98695–98–C007 for U.S. Fish and Wildlife 

Service, Annapolis, MD by Harding ESE, Engineering 

and Environmental Services, Pittsburgh, PA, 25 p. plus 

appendices. 

Fishman, M.J., ed. 1993, Methods of analysis by the 

U.S. Geological Survey National Water-Quality 

Laboratory—Determination of inorganic and organic 

constituents in water and fluvial sediments: U.S. 

Geological Survey Open-File Report 93–125, 217 p. 

Freeze, R.A., and Cherry, J.A., 1979, Groundwater: 

Englewood Cliffs, NJ, Prentice-Hall, Inc., 604 p. 

Garbarino, J.R., 1999, Methods of analysis by the 

U.S. Geological Survey National Water-Quality 

Laboratory—Determination of dissolved arsenic, boron, 

lithium, selenium, strontium, thallium, and vanadium 

using inductively coupled plasma-mass spectrometry: 

U.S. Geological Survey Open-File Report 99–093, 31 p. 

Garbarino, J.R., and Taylor, H.E., 1994, Inductively 

coupled plasma-mass spectrometric method for the 

determination of dissolved trace elements in natural 

water: U.S. Geological Survey Open-File Report 

94–358, 49 p. 

Heath, R.C., 1983, Basic ground-water hydrology: 

U.S. Geological Survey Water-Supply Paper 2220, 84 p. 

Powars, D.S., 1997, Stratigraphy and geophysical logs from 

a corehole drilled to bedrock at Robins Point, J-Field, 

Edgewood Area, Aberdeen Proving Ground, Maryland: 

U.S. Geological Survey Open-File Report 97–357, 68 p. 

Ramsey, K.W., 2001, Geologic map of Ellendale and 

Milton Quadrangles, Delaware: Newark, DE, Delaware 

Geological Survey, Geologic Map Series, No. 11, 

1 sheet, scale 1:24,000. 

Rimstidt, J.D., and Craig, J.R., 2000, Corrosion of lead 

shot and bullets on shooting ranges [abs], in Proceedings 

of the Geological Society of America Annual Meeting, 

Reno, NV, November 9–18, 2000. 

Stansley, W., Widjeskog, L., and Roscoe, D.E., 1992, Lead 

contamination and mobility in surface water at trap and 

skeet ranges: Bulletin of Environmental Toxicology, 

v. 49, p. 640–647. 

U.S. Fish and Wildlife Service, 2000, Prime Hook National 

Wildlife Refuge: Milton, DE, Park Brochure, 9 p. 

U.S. Geological Survey, 1999, National field manual for the 

collection of water-quality data: U.S. Geological Survey 

Techniques of Water-Resources Investigations [Chapters 

were published from 1997–1999; updates and revisions 

are ongoing, and can be viewed at http://water.usgs.gov/ 

owq/FieldManual/mastererrata.html] 

Wershaw, R.L., Fishman, M.J., Grabbe, R.R., and Lowe, 

L.E., 1987, Methods for the determination of organic 

substances in water and fluvial sediments: Techniques 

of Water-Resources Investigations of the U.S. Geological 

Survey, book 5, chap. A3, 80 p. 

22 Ground-Water Contamination from Lead Shot at Prime Hook National Wildlife Refuge, Sussex County, DE 
Appendix. Prime Hook core lithologic descriptions 

(Lithology by Michael Smigaj, U.S. Geological Survey; transcription by Britta Hoehndorf, U.S. Geological Survey.) 

[UPPER CASE terms represent the major sediment type present. Depths are given as cm (centimeters) below land surface. Depths to 

the top of the water in the well, mean sea level, bottom of casing, and base of core are noted. Cores are deeper than the bottom of the 

well casing, because the lower parts of the holes typically collapsed between the removal of the core and the insertion of the plastic 

casing.] 

Well DG-6: Depth below land surface 

0 cm Sandy clay, organic-rich, tan brown 

8 cm clayey SAND, fine to medium, tan to brown (plant root extending to 34 cm depth) 

48 cm clayey SAND, fine to medium, tan to brown, fine scattered gravel decreasing downward 

82 cm clayey SAND, fine to medium, tan-light gray to tan-gray 

140 cm clayey Sand, fine to medium, light tan with fine gravel 

145 cm clayey Sand, fine, light tan-gray 

151 cm - water level in well ­

157 cm CLAYEY SILT, light tan to light gray 

163 cm sandy CLAY, light tan 

172 cm 2nd core (debris, collapse) 

183.5 SAND, medium to coarse, opaque to white; gravel, fine to coarse, opaque, white to gray 

219.5 - mean sea level ­

220.5 sandy CLAY, tan to gray; with coarse sand and gravel, clayey gray stringer 

294.5 CLAY, light gray to gray; with fine sand, yellow-orange at base 

305.5 sandy CLAY, yellow-orange 

349 cm - bottom of well casing ­

367.5 SAND, fine to medium, opaque, yellow-orange stained, with some clay 

371.5 sandy CLAY, gray; with cherty gravel, fine to medium 

379.5 yellow-orange clayey SAND, fine to medium, opaque; with fine gravel at base 

390 cm light gray and yellow-orange clayey SAND, fine to medium, opaque 

397 cm sandy CLAY, light gray 

435.5 sandy CLAY, light gray; sand coarsens downward near base 

475.5 clayey SILT, light gray 

477.5 sandy CLAY, light gray 

508.5 CLAY, light yellow-orange to yellow-orange, with stringers of coarse sand 

524.5 sandy CLAY, light gray 

539.5 fine to coarse sandy CLAY, light gray; sand coarsens downward 

543.5 Peat, base of core 

Well DG-7: Depth below land surface 

0 cm sandy light tan to light gray CLAY, fine white to black gravel at base 

12.5 - water level in well ­

38 cm light gray, clayey fine SAND

53 cm light tan-gray, clayey fine SAND, scattered fine gravel near top

71 cm light tan-gray clayey, fine to medium SAND, coarsening downward

73 cm - mean sea level ­

96 cm light tan to tan-gray sandy CLAY 

136 cm dark tan clayey, fine to medium SAND, some fine gravel 

156 cm yellow-tan clayey, fine to medium SAND 

162 cm gray and yellow-orange clayey, fine to medium SAND, some fine gravel 

Appendix 23 
[Lithology by Michael Smigaj, U.S. Geological Survey; transcription by Britta Hoehndorf, U.S. Geological Survey

UPPER CASE terms represent the major sediment type present. Depths are given as cm (centimeters) below land surface. Depths to 

the top of the water in the well, mean sea level, bottom of casing, and base of core are noted. Cores are deeper than the bottom of the

well casing, because the lower parts of the holes typically collapsed between the removal of the core and the insertion of the plastic

casing.]

Appendix. Prime Hook core lithologic descriptions—Continued 

Well DG-7: Depth below land surface—Continued 

191 cm yellow-tan to tan-brown, fine to coarse SAND 

198 cm dark tan-gray clayey, fine to medium SAND, with fine gravel 

254 cm - bottom of well casing ­

298 cm gray clayey, fine to medium SAND, some coarse, fine gravel throughout with gravel base 

355.5 tan-gray clayey, fine to medium SAND, with fine gravel, more clay at bottom, with mottled white-gray to tan-brown 

streaks 

380 cm light tan-brown clayey; fine to coarse SAND, darker tan-brown clay at base 

393 cm light tan-gray clayey, fine to coarse SAND, some fine gravel 

413 cm light tan-gray clayey, fine SAND; some light tan and orange-brown streaks 

465.5 fine sandy, gray, light tan, orange-brown mottled CLAY, fine gravel at base 

485 cm fine, some coarse, sandy light tan-gray CLAY, some fine gravel 

593 cm light gray to orange-tan clayey fine SAND, fine gravel at base 

598 cm light tan, orange-tan CLAY, with fine sand 

602 cm light gray clayey, fine SAND, with fine gravel 

612 cm sandy, light tan to tan CLAY 

635 cm gray to light tan clayey fine to coarse SAND, some fine gravel 

641 cm light gray, light tan, tan-orange stratified clayey, fine to coarse SAND 

731 cm light tan-gray, fine to medium SAND 

739.5 base of core 

Well DZ-1: Depth below land surface 

0 cm fine to medium sandy, tan-gray CLAY 

4 cm fine to medium sandy, tan-gray SILTY-CLAY

30 cm gray to brownish-tan, clayey fine to medium SAND

47 cm - water level in well ­

62.5 tan-gray clayey, fine to coarse SAND, with fine gravel 

118 cm - mean sea level ­

122.5 tan-brown clayey, fine SAND 

127.5 clayey, white to gray, fine to medium SAND, fining upward 

140 cm light tan, fine sandy CLAY, stratified bands of tan-gray and yellow-orange clay 

142 cm - bottom of well casing ­

186 cm tan-brown, clayey fine to coarse SAND, with fine gravel 

191 cm clayey, white-gray, fine to medium SAND, fining upwards 

195.5 clayey, white fine SAND, stratified, with fine gravel 

228.5 dark tan-brown, fine sandy CLAY 

233 cm light tan-gray, fine sandy CLAY 

237 cm tan-gray, fine sandy CLAY 

241 cm light-tan, fine sandy CLAY 

244.5 dark tan, fine sandy CLAY, some coarse sand 

252 cm light gray, fine sandy CLAY (compact) 

264.5 light gray, fine sandy CLAY (loose) 

24 Ground-Water Contamination from Lead Shot at Prime Hook National Wildlife Refuge, Sussex County, DE 
[Lithology by Michael Smigaj, U.S. Geological Survey; transcription by Britta Hoehndorf, U.S. Geological Survey

UPPER CASE terms represent the major sediment type present. Depths are given as cm (centimeters) below land surface. Depths to 

the top of the water in the well, mean sea level, bottom of casing, and base of core are noted. Cores are deeper than the bottom of the

well casing, because the lower parts of the holes typically collapsed between the removal of the core and the insertion of the plastic

casing.]

Appendix. Prime Hook core lithologic descriptions—Continued 

Well DZ-1: Depth below land surface—Continued 

271.5 orange-tan, fine sandy CLAY 

278.5 light tan, fine sandy CLAY 

294 cm light tan, clayey fine to coarse SAND, with fine gravel 

306 cm light tan, clayey, fine SAND 

319.5 base of core 

Well DZ-2: Depth below land surface 

+3.96 - water level in well - (elevated nearly 4 cm above ground surface)

0 cm fine sandy, dark gray silty CLAY, (plant root extending down)

11.5 fine sandy, gray CLAY, clasts of yellow-orange clay and fine to medium gravel

67 cm - mean sea level ­

91.5 fine sandy, light gray to tan-gray CLAY 

139 cm fine sandy, gray and orange-tan CLAY 

144.5 fine sandy gray CLAY 

148.5 fine sandy, light to dark gray CLAY, clasts of light gray silt, occasional fine gravels 

196.5 tan-gray, clayey fine SAND, occasional fine gravel 

310 cm - bottom of well casing ­

395 cm light to dark tan, clayey, fine to coarse SAND, some fine to coarse gravel 

441 cm base of core 

Well DZ-3: Depth below land surface 

0 cm fine sandy, gray to tan-gray CLAY, occasional fine gravel 

9.144 - water level in well ­

36 cm tan-gray, clayey, fine to coarse SAND, with some fine to coarse gravel

79.248 - mean sea level ­

102 cm fine to medium sandy, tan-gray CLAY, with reddish-brown clay at base 

112.5 tan-gray SILT 

122 cm fine sandy gray CLAY, some reddish-brown clay 

145.5 tan-gray, clayey fine SAND, with fine to coarse gravel 

198.5 gray to light gray SILT, reddish-brown at upper contact 

219.5 fine sandy, light gray to gray SILT; sand increasing downward 

231.01 - bottom of well casing ­

251.5 tan-gray, clayey fine to coarse SAND, sand coarsens downward with a decrease in clay 

357.5 fine sandy, tan-gray CLAY 

377.5 fine sandy, dark tan-gray CLAY 

384 cm fine sandy, tan-gray CLAY 

387.5 fine sandy, dark tan-gray CLAY 

392.5 fine to coarse sandy, tan-gray CLAY 

427.5 fine sandy, yellow-orange CLAY, with fine to coarse gravel at upper contact, decreasing downward 

438.5 fine to medium sandy, tan-gray CLAY, fine gravel, dark gray clay clast near base 

509.5 base of core 

Appendix 25 
[Lithology by Michael Smigaj, U.S. Geological Survey; transcription by Britta Hoehndorf, U.S. Geological Survey

UPPER CASE terms represent the major sediment type present. Depths are given as cm (centimeters) below land surface. Depths to 

the top of the water in the well, mean sea level, bottom of casing, and base of core are noted. Cores are deeper than the bottom of the

well casing, because the lower parts of the holes typically collapsed between the removal of the core and the insertion of the plastic

casing.]

Appendix. Prime Hook core lithologic descriptions—Continued 

Well UG-1: Depth below land surface 

0 cm orange-brown, silty-clayey coarse SAND and fine gravel

47 cm orange-brown, clayey fine to medium SAND, fine to medium gravel

63.1 cm - water level in well ­

77.5 sandy, orange-brown SILT and CLAY, gray clay clasts throughout

94 cm sandy, gray, orange SILT

121 cm sandy, orange-brown CLAY, with gray silt stringers 

131.5 yellow-orange, clayey fine Sand, with fine gravel 

143.3 - mean sea level ­

202 cm sandy, yellow-orange silty CLAY 

250.5 orange-brown clay, mottled with gray SILT 

265 cm - bottom of well casing ­

309.5 sandy, orange-brown CLAY, with fine chert 

313.5 orange-brown CLAY, mottled with gray silt 

351.5 orange-brown CLAY, darkening to base 

362.5 base of core 

Well UG-2: Depth below land surface 

0 cm sandy, dark gray SILT, with organic plant root 

1.3 cm - water level in well ­

9 cm fine sandy gray SILT, with orange-brown clay 

61 cm reddish-brown, fine to medium SAND, coarsening downward with fine gravel at base 

73 cm - mean sea level ­

83.5 light tan-gray, clayey fine to medium SAND, some coarse sand 

176.5 tan, yellow-orange, clayey fine to medium SAND 

267 cm sandy, tan to yellow-orange CLAY, with coarse sand 

271 cm - bottom of well casing ­

305.5 sandy, light tan to yellow-orange CLAY, with fine gravel and clay clasts 

320.5 sandy, tan to yellow-orange CLAY, stratified, with fine gravel 

339.5 orange-brown SILT 

344.5 yellow-orange CLAY 

348.5 light tan-gray CLAY, with coarse gravel 

360 cm tan-yellow, fine to medium SAND, traces of coarse sand and fine gravel at base 

427 cm light tan, medium SAND, with fine gravel and coarse chert at base 

487 cm light tan, medium to coarse SAND 

504.5 white to gray, medium SAND 

507 cm tan to yellow, medium stratified SAND, fining upward 

526.5 iron stained, fine SAND (0.5 cm layer) 

527 cm clayey, medium to coarse stratified, yellow to tan SAND 

534.5 base of core 

26 Ground-Water Contamination from Lead Shot at Prime Hook National Wildlife Refuge, Sussex County, DE