Aquifer Geochemistry and 

Effects of Pumping on 

Ground-Water Quality at 

the Green Belt Parkway 

Well Field, Holbrook, 

Long Island, New York

In cooperation with Suffolk County Water Authority

U.S. Department of the Interior

U.S. Geological Survey

Water-Resources Investigations Report 01-4025
This page has been left blank intentionally.
Aquifer Geochemistry and Effects of 

Pumping on Ground-water Quality at the 

Green Belt Parkway Well Field, Holbrook, 

Long Island, New York

By Craig J. Brown, Steven Colabufo, and John D. Coates

____________________________________________________________

U.S. GEOLOGICAL SURVEY

Water-Resources Investigations Report 01-4025

Prepared in cooperation with the

SUFFOLK COUNTY WATER AUTHORITY

Coram, New York

2002
U.S. DEPARTMENT OF THE INTERIOR

GAIL NORTON, Secretary

U.S. GEOLOGICAL SURVEY

For additional information write to: Copies of this report can be purc

from:

U.S. Geological Survey

Branch of Information Services

Box 25286 

Denver, CO 80225-0286

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. Geological Survey.

Charles G. Groat, Director

ii Contents

District Chief

U.S. Geological Survey

2045 Route 112, Bldg. 4

Coram, NY 11727
Contents III

CONTENTS

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

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

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

Study Methods....................................................................................................................................................................... 5

Drilling and Sediment Sampling ................................................................................................................................. 5

Ground-Water Sampling.............................................................................................................................................. 5

Laboratory Analyses .................................................................................................................................................... 5

Ground Water..................................................................................................................................................... 5

Pore Water.......................................................................................................................................................... 6

Sediment Bacteria.............................................................................................................................................. 6

Iron Coatings, Carbon, and Sulfur within Sediments........................................................................................ 6

Aquifer Geochemistry ........................................................................................................................................................... 6

Lithology ..................................................................................................................................................................... 6

Geochemistry and Microbiology ................................................................................................................................. 10

Ground-Water Quality ................................................................................................................................................. 12

Effects of Pumping on Ground-Water Quality ...................................................................................................................... 14

Conclusions ........................................................................................................................................................................... 20

References Cited.................................................................................................................................................................... 20

FIGURES

1. Map showing location of study area at Green Belt Parkway wellfield at Holbrook, Suffolk County, N.Y. .................... 2

2. Vertical section along section A-A ́ through central Suffolk County, showing hydrogeologic units ............................... 3

3. Map of Green Belt Parkway well field............................................................................................................................. 4

4. Vertical profiles of borehole GB-1A, showing: (A) gamma-radiation and predominant TEAPs, (B) single-point 

resistance log with position of clay lenses (F1, F2, F3) and well screen intervals, (C) concentration of sulfate and iron 

in pore water, (D) organic carbon and total sulfur content in sediment, and (E) concentration of Fe(III) coatings and 

rate of 14C oxidation in sediments .................................................................................................................................. 7

5. Vertical section through study area showing hydrogeologic units, upper glacial-Magothy aquifer contact, silt and clay 

lenses, and wells.............................................................................................................................................................. 8

6. Graph showing total sulfur concentration as a function of the concentration of 0.5M HCl-extractable Fe(III) coatings 

in Magothy aquifer core samples from borehole GB-1A................................................................................................ 11

7. Graph showing the square of the 14C-oxidation rate in acetate-amended sediment as a function of the square of the organic 

carbon concentration in sediment cores from borehole GB-1A...................................................................................... 11

8. Stiff diagrams representing ion concentrations in water samples from wells during static, nonpumping conditions of 

April 19-20, 1999 ............................................................................................................................................................ 15

9. Vertical section and hydrograph showing ground-water levels in the Magothy aquifer along section B-B ́ during static, 

prepumping conditions and the pumping period: A. Drawdowns along section B-B ́. B. Water levels in pumping well 

and two observation-well clusters. .................................................................................................................................. 16

10. Graphs showing concentrations of selected constituents in ground-water samples from pumping well GB-1A and 

observation well OW-1C during static, prepumping conditions and pumping period: A. Phosphate and dissolved 

oxygen. B. Dissolved iron and bicarbonate. C. Total organic carbon (TOC) and dissolved organic carbon (DOC)...... 17

11. Well-construction diagram for GB-1A showing gravel-filled annulus that could provide a downward flow path from

the upper glacial through clay unit F3 to the well screen................................................................................................ 17

12. Graphs showing isotopic composition of ground water from the Green Belt Parkway well field: A. δ13C of dissolved 

inorganic carbon. B. δ34S of sulfate. .............................................................................................................................. 19
IV Contents

TABLES

1. Color, lithology, hydrologic unit, dominant TEAP (terminal electron-accepting process), and sedimentary organic 

carbon, total sulfur, and Fe(III) content of core samples from borehole GB-1A (S113812T) ....................................... 10

2. Data on construction of wells at the Green Belt Parkway well field ................................................................................ 11

3. pH and concentrations of selected constituents in pore-water samples from borehole GB-1A ....................................... 13

4. Concentrations of major elements, chemical species, δ13C, and δ34S, in water samples from wells.............................. 14
Contents V

CONVERSION FACTORS, ABBREVIATIONS AND VERTICAL DATUM

Multiply By To Obtain

Length

inch 2.54 centimeter (cm) 

foot 0.3048 meter (m)

mile 0.6214 kilometer (km)

acre 43,560 square feet (ft2)

Hydraulic conductivity

feet per day (ft/d) 0.3048 meters per day (m/d)

0.0003527 centimeters per second (cm/s) 

Transmissivity

feet squared per day (ft2/d) 0.0929 meters squared per day (m2/d)

1.075 x 10-10 centimeters squared per second (cm2/s)

Pumpage

gal/min gallons per minute

Mgal/d millions of gallons per day

Temperature

degrees Fahrenheit (o

F) 0.0929 degrees Celsius (oC)

Chemical Concentration

mg/L milligram per liter

M moles per liter

mmol/L millimoles per liter

μmol/L micromoles per liter

μmol/g micromoles per gram

μCi microcuries

‰ per mil

Other abbreviations used

< less than

> greater than

δ delta

min minutes

h hours

psi pounds per square inch

Vertical datum: In this report, “sea level” refers to the National Geodetic Vertical Datum of 1929 (NGVD 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.
This page has been left blank intentionally.
Introduction 1

Aquifer Geochemistry and Effects of Pumping on 

Ground-water Quality at the Green Belt Parkway 

Well Field, Holbrook, Long Island, New York 

Craig J. Brown1, Steven Colabufo2, and John D. Coates3

ABSTRACT

Geochemistry, microbiology, and water 

quality of the Magothy aquifer at a new supply 

well in Holbrook were studied to help identify 

factors that contribute to iron-related biofouling 

of public-supply wells. The organic carbon 

content of borehole sediments from the screen 

zone, and the dominant terminal electronaccepting processes (TEAPs), varied by depth. 

TEAP assays of core sediments indicated that iron 

reduction, sulfate reduction, and undetermined 

(possibly oxic) reactions and microbial activity 

are correlated with organic carbon (lignite) 

content. The quality of water from this well, 

therefore, reflects the wide range of aquifer 

microenvironments at this site.

High concentrations of dissolved iron (3.6 to 

6.4 micromoles per liter) in water samples from 

this well indicate that some water is derived from 

Fe(III)-reducing sediments within the aquifer, but 

traces of dissolved oxygen indicate inflow of 

shallow, oxygenated water from shallow units that 

overlie the local confining units. Water-quality 

monitoring before and during a 2-day pumping test 

indicates that continuous pumping from the 

Magothy aquifer at this site can induce downward 

flow of shallow, oxygenated water despite the 

locally confined conditions. Average 

concentrations of dissolved oxygen are high (5.2 

milligrams per liter, or mg/L) in the overlying 

upper glacial aquifer and at the top of the Magothy 

aquifer (4.3 mg/L), and low (<0.1 mg/L) in the 

deeper, anaerobic part of the Magothy; average 

concentrations of phosphate are high (0.4 mg/L) in 

the upper glacial aquifer and lower (0.008 mg/L) at 

the top of the Magothy aquifer and in the deeper 

part of the Magothy (0.013 mg/L). Concentrations 

of both constituents increased during the 2 days of 

pumping. The δ34S of sulfate in shallow ground 

water from observation wells (3.8 to 6.4 per mil, 

or ‰) was much heavier than that in the supplywell water (-0.1 ‰) and was used to help identify 

sources of water entering the supply well. The δ34S 

of sulfate in a deep observation well adjacent to the 

supply well increased from 2.4 ‰ before pumping 

to 3.3 ‰ after pumping; this confirms that the 

pumping induced downward migration of water. 

The lighter δ34S value in the pumped water than in 

the adjacent observation well probably indicates 

FeS2 oxidation (which releases light δ34S in 

adjacent sediments) by the downward flow of 

oxygenated water.

INTRODUCTION

High concentrations of dissolved iron in ground 

water can lead to screen encrustation and iron-related 

biofouling of wells and requires costly wellreconditioning and replacement programs for water 

suppliers. This condition arises from the redox 

gradient created in the aquifer material surrounding 

1

 U.S. Geological Survey, 101 Pitkin St., East Hartford, CT 

06108

2

 Suffolk County Water Authority, Engineering Department, 

P.O. Box 37, Oakdale, NY 11769

3

 Department of Microbiology, Southern Illinois University, 

Carbondale, IL 62901
2 Aquifer Geochemistry & Effects of Pumping on Ground-Water Quality at the Green Belt Parkway Well Field, Holbrook, New York 

the well screen when a well is drilled and operated. 

The gradient typically forms between shallow, oxic 

ground water, and deeper, iron-rich ground water that 

is anoxic. 

Declines in the specific capacity of Suffolk 

County Water Authority (SCWA) supply wells on 

Long Island were correlated with elevated 

concentrations of iron in ground water (Walter, 

1997a) and are attributed to iron encrustation and 

biofouling of the well screens and surrounding aquifer 

sediments. The oxidation of ferrous iron and 

subsequent encrustation of iron on the well screen is 

catalyzed by highly resilient and nearly ubiquitous 

bacteria, which form a biofilm that also clogs the 

screen (Walter, 1997b). Methods to eliminate the 

bacteria problem are limited; therefore, emphasis is 

placed on preventive treatment. Factors related to 

supply-well pumping (such as pumping rates and 

frequency) also can affect the biofouling 

process—cyclic pumping or long periods of 

idleness can promote biofilm growth and 

associated encrustation (Smith, 1992); a 

biofouling study in Suffolk County by Walter 

(1997b) showed that most of the well-encrusting 

material is deposited when the wells are shut 

down. Recent work (Brown and others, 1999; 

2000) has shown that the concentrations of iron 

and other redox-active constituents in ground 

water are affected by (1) the organic carbon 

content of the aquifer material, which varies 

spatially, (2) microbially mediated redox 

processes within the aquifer, and (3) the 

distance of the screen from the source of 

recharge. Thus, the location of the well and the 

depth of the screened interval can affect the 

degree of biofouling.

Routine monitoring of water quality and 

supply-well performance is necessary to (1) 

detect deleterious water-quality changes and 

assess the potential for biofouling and 

encrustation, and (2) assess the need for 

maintenance and treatment to prolong optimal 

performance (Cullimore, 1986). For example, 

pumping from an anoxic aquifer can induce the 

downward movement of shallow ground water 

that may contain dissolved oxygen, phosphate, 

and other constituents that can promote well 

encrustation and bacterial growth. Dissolved 

oxygen promotes iron encrustation through the 

oxidation of ferrous iron, and phosphate can be a 

limiting nutrient for iron-bacteria biofilms (Cullimore, 

1986; Walter, 1997b). Thus, study of the effects of 

pumping practices and well placement on the chemical 

reactions and water-quality characteristics that are 

related to biofouling is necessary for understanding of 

the biofouling process.

In 1998, the U.S. Geological Survey (USGS), in 

cooperation with the SCWA, began a study of ironrelated biofouling at the Green Belt Parkway well field 

in Holbrook, N.Y (fig. 1) to examine the effects of 

well-screen placement and pumping on factors and 

chemical constituents that affect iron-related 

biofouling. The study focused on a new supply well 

screened in the Magothy aquifer, and on several 

nearby observation wells screened in the upper glacial 

and Magothy aquifers. The spatial extent of aquifer 

redox zones and their associated microbial 

communities in core sediments from the borehole at 

the proposed screen zone were examined to document 

5

0 1 2 3 4 5

0 1 2 3 4 Miles

Kilometers

 Inferred 

 direction of

ground-water 

 flow

Base digitized from New York State 

Department of Transportation, 1981, 1:24,000

A'

A

ground-water divide

Approximate location of regi onal

73°07'30"

40°52'30"

40°45'30"

72°52'30"

NEW YORK

map

area

Long Island

GREAT

SOUTH

BAY

ATLANTIC OCEAN

LONG

ISLAND SOUND

SUFFOLK

COUNTY

Green Belt Parkway site

 (Detail is shown in fig.3)

Figure 1. Location of study area at the Green Belt Parkway 

wellfield at Holbrook, Suffolk County, N.Y. (Section A-A ́ is 

depicted in fig. 2)
3

A'

Raritan Clay

A

FEET FEET

SEA

LEVEL

-200

200

-400

-600

-800

-1200

-1000

Lloyd aquifer

Magothy aquifer

Atlantic Ocean Long Island Upper Glacial

aquifer

Green Belt Parkway site

(projected)

Vertical Exaggeration X45

Sound

Bedrock

Monmouth

 green sand

Great South Bay

GB-1A

North South

Gardiners clay

0

0

2

2 4

4 6

5

KILOMETERS

1 3 MILES

their effects on the quality of water that enters the 

well. The new supply well and the three adjacent 

observation wells were monitored before and during a 

2-day pumping test to detect changes in concentrations 

of selected constituents (including dissolved oxygen, 

iron, organic and inorganic carbon, and phosphorus) 

that are related to iron biofouling.

This report presents and interprets data on 

sediment microbiology and geochemistry of the 

Magothy aquifer at the new well site, and discusses the 

effects of pumping this well on water quality to 

determine the potential for iron-related biofouling.

Gratitude is extended to Richard Bova and Paul 

Kuzman of SCWA for assistance with drilling and 

coring, and coordination of water sampling.

HYDROGEOLOGIC SETTING

Long Island is underlain by a sequence of upper 

Cretaceous and Pleistocene sediments that were 

deposited on a southeastward dipping bedrock surface 

(figs. 1 and 2). The deposits reach a maximum 

thickness of more than 2,000 ft in southeastern Long 

Island. The principal aquifer on Long Island is the 

Magothy aquifer, which consists of the Matawan 

Group and Magothy Formation, undifferentiated, of 

Cretaceous age. Along the southern shore, the 

Magothy aquifer is unconformably overlain by the 

Monmouth Group (Monmouth greensand) of 

Cretaceous age; elsewhere in the southern part of the 

island, it is unconformably overlain by the Gardiners 

Clay (an upper Pleistocene interglacial unit) and by 

glacial deposits of Pleistocene age (upper glacial 

aquifer). Cretaceous deposits north of the Gardiners 

Clay are unconformably overlain by the upper glacial 

aquifer (Smolensky and others, 1989). The lateral 

extents of the Monmouth greensand and the Gardiners 

Clay appear to be south of the 6-acre study area.

The Magothy aquifer consists of alternating 

beds and lenses of clay, silt, sand, and some gravel, as 

well as some mixtures of these materials (Perlmutter 

and Geraghty, 1963); these sediments were deposited 

in a transitional fluviodeltaic environment (Lonnie, 

1982). The sand consists mostly of quartz but contains 

some lignite, muscovite, and iron concretions and 

contains about 2 to 3 percent heavy minerals by 

Figure 2. Vertical section A-A ́ through central Suffolk County, N.Y., showing hydrogeologic units and location of 

study area. (Modified from Smolensky and others, 1989, sheet 1.)

Hydrogeologic Setting
4 Aquifer Geochemistry & Effects of Pumping on Ground-Water Quality at the Green Belt Parkway Well Field, Holbrook, New York 

10 25 METERS

FEET

0

0 25 50 100

ROAD

NICOLLS

B'

B

OW-1

OW-2

GB-1

GB-2

GB-3

GB-4

GB-1A

OW-3

GB-1A

OW-1

GB-1 Supply Well

New Supply Well

EXPLANATION

Observation Well Cluster

Vertical Section - shown in figs. 5 and 9

 (wells are projected)

B B'

Direction of

regional groundwater flow

GREEN BELT

PARKWAY

Pump

Station

weight; it generally has no carbonate minerals and few 

other reactive minerals, although organic carbon in the 

form of lignite is a reactive electron donor in redox 

reactions (Pearson and Friedman, 1970). Lignite is 

typically present in silt and clay but may also be 

dispersed through the sand (Smolensky and others, 

1989). Much of the iron in the Magothy aquifer on 

Long Island is in the form of Fe(III) oxyhydroxides, 

iron-sulfide minerals (FeS2), iron-rich clay minerals, 

and other less soluble minerals, including hematite, 

leucoxene, ilmenite, and magnetite (Brown, Rakovan, 

and Schoonen, 2000).

The upper glacial aquifer, which contains the 

water table, is characterized mainly by coarse sand but 

also contains gravel, silt, and clay. The glacial deposits 

can contain the same minerals as the Cretaceous 

sediments but have a greater variety and abundance of 

heavy minerals such as amphibole, pyroxene, fresh 

muscovite, biotite, and chlorite, as well as rock 

fragments and unweathered feldspar (Suter and others, 

1949). In general, upper glacial aquifer sands are 

coarser grained and contain a smaller silt and clay 

fraction than Magothy sands. 

The Long Island ground-water system is 

recharged solely by precipitation. Most of the recharge 

that enters the water table moves laterally through the 

upper glacial aquifer and discharges to streams or to 

coastal waters. Precipitation near the mid-island 

ground-water divide (fig. 1) flows downward through 

the upper glacial aquifer, recharges the Magothy and 

Lloyd aquifers, then flows to either the north or the 

south shore. 

Water in the upper glacial aquifer generally is 

oxic and contains low concentrations of dissolved iron 

and other cations, except in areas of discharge near the 

south shore, where it has become anoxic through 

microbially mediated redox reactions along its 

flowpaths. Water in the Magothy aquifer generally 

contains higher concentrations of dissolved iron than 

water in the upper glacial aquifer and, therefore, can 

cause more pronounced iron-related biofouling of 

wells. Dissolved-oxygen concentrations in the 

Magothy aquifer in Suffolk County can be high (up to 

0.34 mmol/L) near the ground-water divide but 

decrease with distance southward along the deep flow 

path; dissolved iron concentrations, in contrast, are 

low near the divide and increase with distance 

southward (Brown and others, 1999).

The Magothy aquifer at the Green Belt Parkway 

well field (fig. 3) is locally confined by fine-grained 

Figure 3. Principal features of Green Belt Parkway well field 

(site GB), Holbrook, N.Y. (Location is shown in fig. 1. Section 

B-B ́ is depicted in fig. 5.)
5

units (varying mixtures of fine sand, silt, and clay) at 

the contact between the Pleistocene and Cretaceous 

deposits. An aquifer-test study conducted at the site 

(ERM-Northeast, 1991) reported that the pumping of 

supply wells screened in the Magothy aquifer had little 

effect on water levels in the upper glacial aquifer. 

Magothy transmissivity ranges from 6,000 to 14,000 

ft2

/d (64 to 140 cm2/s), storativity from 10-4 to 10-3, and 

vertical hydraulic conductivity from 0.93 to 1.4 ft/d 

(3.3 to 5.1 x 10-4 cm/s) (ERM-Northeast, 1991).

STUDY METHODS

The borehole was drilled to a depth of 310 ft, 

and core sediments were obtained for geochemical and 

microbial analysis. The borehole was subsequently 

converted to a public-supply well (GB-1A, fig. 3). 

Water samples were collected from GB-1A and three 

adjacent observation wells (OW-1, 2, and 3), and water 

levels in these wells were monitored. 

Drilling and Sediment Sampling 

Split-spoon cores were obtained from Magothy 

sediments at borehole GB-1A with a reverse-rotary 

drill rig. Natural gamma-radiation and electricalresistance logs were collected from the borehole 

before the installation of casing material. Eleven cores 

from the borehole were selected for analysis and were 

designated C1 through C11. Sediment subsamples 

were collected from the center of a split-spoon core 

sample lined with a plastic sleeve, with a modified 

syringe under a stream of N2, as described by Chapelle 

and others (1987). 

The sediment samples for microbial analyses 

were placed in 20-mL serum vials and sealed with 

butyl stoppers and crimp caps. The headspace and 

interstitial space were purged by injecting N2 and 

venting purged gas through an exit needle. Part of each 

core sample was placed in septa vials and used for the 

extraction and analysis of pore water and iron 

coatings. Sediment (0.1 to 0.2 g) was later transferred 

from septa vials to 20-mL plastic scintillation vials 

within an anaerobic glovebox for iron-coating 

extractions. About 3 g of sediment subsample was also 

collected for organic carbon and total sulfur analyses. 

Pore-water samples were later inspected for drillingfluid contamination through a comparison of anion 

concentrations—chloride and sulfate concentrations in 

core samples were much higher than in the drilling 

fluid, and the ion ratios differed considerably. Some 

cores with a high sand content were contaminated with 

drilling fluid (that is, anion ratios were similar to those 

in drilling fluid); their chemical data (table 1) are 

flagged.

Ground-Water Sampling

Water-chemistry data were collected during 

sampling by standard procedures (Wilde and Radtke, 

1998). Colorimetric procedures (Hach Company, 

1993) were used onsite to measure concentrations of 

total dissolved sulfide (H2S and HS-), Fe(II) and 

Fe(III), and dissolved oxygen (< 0.025 mmol/L); a 

dissolved oxygen meter and the revised Winkler 

method were used to measure dissolved-oxygen 

concentrations exceeding 0.025 mmol/L. Dissolved 

SO4

2

- in ground water was collected on an anionexchange resin column for sulfur-isotope analysis and 

was analyzed for BaSO4 precipitates by procedures 

described in Carmody and others (1998). Water 

samples for δ13C analysis of dissolved inorganic 

carbon (DIC) were collected in 1-L glass bottles, 

which were filled from the bottom up and sealed with 

a Teflon/silicon septa cap after 3 to 5 L had overflowed 

to eliminate oxygen.

Laboratory Analyses

Ground water, pore water, sediment bacteria, 

and sediment coatings were analyzed by the 

techniques described in the following paragraphs.

Ground Water

All ground-water samples were measured for 

alkalinity by incremental titration within a few hours 

after sample collection, and for major elements by 

Inductively Coupled Plasma-Atomic Emission 

Spectrometry and Ion Chromatography at the USGS 

National Water Quality Laboratory in Arvada, Colo. 

Sulfur-isotope analyses of water and iron disulfide 

samples were conducted at the USGS Geochemistry 

Laboratory in Reston, Va.; results are reported (in ‰) 

relative to the Vienna Canyon Diablo Troilite (VCDT) 

standard. Carbon-isotope analyses of water samples 

and lignite samples were conducted at the University 

of Waterloo, Ontario, Canada, and are reported (in ‰) 

relative to the Vienna Peedee Belemnite (VPDB) 

Hydrogeologic Setting
6 Aquifer Geochemistry & Effects of Pumping on Ground-Water Quality at the Green Belt Parkway Well Field, Holbrook, New York 

standard. The uncertainty associated with δ34S and 

δ13C values for water is ± 0.2 ‰; the uncertainty 

associated with δ34S of iron disulfide is ± 0.4 ‰.

Pore Water

The inner, sampled part of core samples 

generally yielded insufficient pore water for analysis; 

therefore, 5 g of subsampled core material was mixed 

with 2 to 40 mL of deionized water for 1 to 3 min, 

followed by filter pressing with N2 (Lusczynski, 1961) 

as described in Brown and others (1999). The diluted 

pore water was measured for pH, then placed in plastic 

scintillation vials and refrigerated until further 

analysis. Pore water analyzed for dissolved iron was 

acidified immediately after extraction. Some ferrous 

iron in pore water may have been oxidized during 

pore-water extraction, however, because anaerobic 

conditions are difficult to maintain during extraction; 

further discussion is given in Brown, Schoonen, and 

Candela (2000). Moisture content of the sediments 

was measured by oven drying (to 110° C) a separate 

subsample of the same material; the resulting values 

were used to calculate the extent of pore-water 

dilution by deionized water. Concentrations of porewater constituents were then multiplied by the dilution 

factor for correction.

Sediment Bacteria

Subsamples of sediment cores from several 

depths were examined to identify the predominant 

anaerobic microbial populations through terminalelectron-accepting process (TEAP)-identification 

assays. Sulfate-reducing bacteria (SRB), Fe(III)-

reducing bacteria (IRB), and methanogenic bacteria in 

sediment samples were qualitatively identified through 

[

14C]-labeled acetate procedures as described by 

Lovley (1995) and Coates and others (1996a). In brief, 

soil samples (2 g) were transferred in duplicate into 

10-mL serum vials under a headspace of 95 percent N2

and 5 percent CO2 by volume. The vials were sealed 

with thick butyl rubber stoppers, and the samples were 

amended with 1 μCi of [2-14C]-acetate. The 

production of 14CO2 and 14CH4 in each vial in the 

presence and absence of 10-mmol/L molybdate, which 

specifically inhibits the sulfate-reducing organisms, 

was monitored by gas chromatography with gasproportional counting of 1.0-mL-headspace samples. 

The profile of biogas production was used to identify 

the predominant microbial TEAP (Coates and others, 

1996b). Assays were described as “undetermined” if 

the 14C-amended sediment samples did not generate a 

measurable amount of 14CO2 and 14CH4 within an 8-h 

period.

Iron Coatings, Carbon, and Sulfur Within 

Sediments

Iron coatings on sediments were measured by 

0.5-M HCl and 6-M hydroxylamine extraction 

(Lovley and Phillips 1987), which indicates (1) the 

amount of poorly crystalline Fe(III), and (2) the iron 

fraction that is readily available to microbes in the 

sample (Heron and others, 1994). The detection limit 

of this method is about 0.1 μmol Fe(III) per gram of 

sediment. Percentages of carbon forms and total sulfur 

in sediments were measured by combustion 

(Arbogast, 1996).

AQUIFER GEOCHEMISTRY

The following sections describe (1) the 

lithology at supply well GB-1A and observation wells 

OW1, OW-2, and OW-3, (2) the concentrations of iron 

coatings, organic carbon, total sulfur, and constituents 

of pore water in borehole sediments, and results of the 

TEAP assays, and (3) water quality and water levels 

near GB-1A before and during the 2-day pumping test. 

Gamma-radiation and electrical-resistance logs, and 

lithologic descriptions are shown in figure 4, with 

depth profiles of organic carbon, total sulfur, and ironcoatings concentrations in sediments, and of dissolved 

iron, sulfate, and dissolved organic carbon (DOC) 

concentrations in pore water. Where more than one 

subsample of the same core interval was analyzed for a 

particular constituent, average values were plotted 

with the measured values (figs. 4C, D, and E), so that 

connecting lines could be added.

Lithology

The contact between upper glacial aquifer 

sediments and Magothy aquifer sediments at the study 

site is characterized by interfingered layers of medium 

to coarse sand with lenses of fine sand, silt, and clay 

are present near the upper glacial-Magothy aquifer 

contact (figs. 4 and 5). The fine-grained units were 

informally named F1, F2, and F3 in a previous aquifertest report (ERM-Northeast, 1991) and are so 

designated here (fig. 5). The contact between the upper 
7

upper glacial aquifer

Magothy aquifer

OW-1A

OW-1B

OW-1C

GB-1A

F1

F3

F2

Pore water,

contaminated 

by drilling fluid

Sulfate (measured)

Iron (measured)

Iron (average)

Sulfate (average) Total sulfur

 (average)

Total sulfur

 (measured)

Organic carbon

 (measured) 

Average organic

 carbon

Fe(III) coatings

 (measured)

% C-14 oxid./hr

 (average)

% C-14 oxid./hr

 (measured)

Fe(III) coatings

 (average)

EXPLANATION

Core sample

FeS2-encrusted 

 sand

FeS2

Lignite

Predominant TEAPs

SR Sulfate reduction F2 Clay lens

IR Iron reduction

UND Undetermined

GB-1A Supply-well screen

 interval

C1

OW-1C Observation-well

 screen interval

sand

sand

clay

sand

clayey sand

silty sand

silty sand

silty/clayey sand

silty sand

clay

clay

sand, some silt

sand

sand with silt/clay

clay

sand

clay

C1

C2

C3

C4

C5

C6

C7

C8

C9

C10

C11

IR

IR

IR

SR/IR/UND

SR

IR/SR/UND

UND

UND

IR

UND

01 2 3 4 56 7 300

PORE-WATER

CONCENTRATION,

IN MILLIMOLES 

PER LITER

ORGANIC-CARBON

CONTENT, IN

PERCENT BY WEIGHT

PERCENTAGE OF

14C OXIDATION

PER HOUR

0 0.5 1.0 1.5 2.0 2.5 3.0 0 0.2 0.4 0.6 0.8 1.0

180

200

220

240

260

280

A. B. C. D. E.

TOTAL SULFUR 

CONCENTRATION,

IN MICROMOLES PER 

GRAM OF SEDIMENT

FE(III) COATINGS 

CONCENTRATION,

 IN MICROMOLES PER 

GRAM OF SEDIMENT

0 0.01 0.02 0.03 0.04 0.05 0 5 10 15 20 25 30

0 20 40 60 80 1400 1600 1500

GAMMA RADIATION, IN

COUNTS PER SECOND

SINGLE-POINT RESISTANCE,

IN MILLIVOLTS

DEPTH BELOW LAND SURFACE, IN FEET

120

160

180

200

220

240

260

280

300

140

Figure 4. Vertical profiles of borehole GB-1A at Holbrook, N.Y.: A. 

Gamma-radiation log and predominant TEAPs. B. Single-point 

resistance log showing position of clay lenses (F1, F2, and F3) and 

well screen intervals for GB-1A and OW-1A, OW-1B, and OW-1C. C. 

Concentration of sulfate and iron in pore water. D. Organic carbon 

and total sulfur content of sediment. E. Concentration of Fe(III) 

coatings and rate of 14C oxidation in sediments. (Locations of 

borehole and wells are shown in fig. 3.) 

Aquifer Geochemistry
8 Aquifer Geochemistry & Effects of Pumping on Ground-Water Quality at the Green Belt Parkway Well Field, Holbrook, New York 

EXPLANATION

Silt or clay lens

C Well and screen interval –

 letter denotes relative depth

OW-1

Aquifer contact

Water table

F2 Well identifier –

 prefix GB denotes green belt supply well

 OW denotes observation well

20 Meters

75 Feet

0 10

0 25 50

GB-2 OW-2 GB-1 OW-1 GB-3 OW-3

GB-1A

(S113812)

Upper glacial 

aquifer

Magothy

aquifer

F1

F3

F2

silt and fine sand

silt and clay

silt and clay

Water table

C

B

A

C

B

A A

B

C

SEA

LEVEL

-100

100

-200

B'

NORTH

Altitude

(feet)

B

SOUTH

200

0

Depth

100

SEA

LEVEL

(feet)

50

150

250

LAND

SURFACE

glacial aquifer and the Magothy aquifer at well GB-1A 

is 186 ft below land surface (108 ft below sea level), as 

indicated by the lithology of the GB-1A borehole 

(table 1; figs. 4, 5). Unit F1 is a lens of silt and fine 

sand that lies near the bottom of the Pleistocene 

deposits between depths of 140 to 148 ft below land 

surface. Unit F2 is a fine-grained unit of silt and clay 

near the bottom of the Pleistocene deposits (upper 

glacial aquifer) between 171 and 180 ft below land 

surface. Unit F3 is a fine-grained unit of silt and clay 

at the top of the Magothy aquifer between depths of 

197 and 220 ft below land surface.

The lithology of borehole GB-1A is 

summarized in table 1. Public-supply well GB-1A is 

screened from 232 to 282 ft below land surface (table 

2), directly below F3 (fig. 5). Well GB-1 has two 

separate screen zones_the upper part is screened in 

Magothy aquifer sand between units F2 and F3, from 

187 to 210 ft below land surface, and the lower part is 

screened below, and partly in, unit F3, from 225 to 255 

ft below land surface. Three observation-well clusters 

(OW-1, OW-2, and OW-3, figs. 3, 5) each consist of 

three 2-in-diameter polyvinyl chloride (PVC) wells. At 

each cluster, the shallow well (A) is screened above 

F1, the intermediate well (B) is screened between F1 

and F2, and the deep well (C) is screened below F3 

(fig. 5). Observation-well cluster OW-1 is 82 ft 

southeast of GB-1A and is the only well that was 

sampled for water quality. Well OW-1A is screened 

partly in upper glacial sand and partly in the silt and 

fine sand of F1, from 130 to 140 ft below land surface; 

OW-1B is screened in the Magothy between units F2 

and F3, from 190 to 200 ft below land surface; and 

OW-1C is screened in the Magothy below F3; from 

245 to 255 ft below land surface (table 2). Observation 

well clusters OW-2 and OW-3 were used only for 

water-level measurements; OW-3 is 150 ft north of 

GB-1A, and OW-2 is 205 ft south of GB-1A.

Figure 5. Vertical section through study area at Holbrook, N.Y., showing hydrogeologic units, contact between upper glacialMagothy aquifers, silt and clay lenses F1, F2, and F3, and wells. (Well locations and trace of section are shown in fig. 3.)
9

Table 1. Color, lithology, hydrologic unit, dominant TEAP (terminal electron-accepting process), and sedimentary organic carbon, total sul

samples from borehole GB-1A (S113812T) at Green Belt Parkway well field in Holbrook, Suffolk County, N.Y. 

[Depths and altitudes are in feet below land surface, numbers in parentheses are meters. μmol/g, micromoles per gram of sediment. UG, upper glacia

F2 is a fine-grained unit near the bottom of the Upper glacial aquifer between depths of 171 and 180 ft; F3 is a fine-grained unit at the top of the Mag197 and 220 ft. NM, not measured; IRB, Fe(III)-reducing bacteria, SRB, sulfate-reducing bacteria, UND, no activity observed after 10 hours. Dashes Borehole locations are shown in fig. 3]

*Core sample had some contamination with drilling fluid

Sample 

Sampling 

depth 

(feet) 

Sampling altitude

 (datum is sea level)

 Color

(Geological Society of America

 rock-color chart) Lithology

Hydrogeologic

unit TEAP 

Sedim

organi

(perc

we

C1 180 -102 ft (-30.6 m) Dark yellowish brown (10YR 4/2) Very hard sand; some silt; trace clay, 

lignite, muscovite

UG (F2) NM -- 

C2-A* 185.0 -107 ft (-31.6 m) Brownish gray (5YR4/1) to medium

 dark gray (N4)

Fine to medium sand, some silt and clay

UG IRB 2.5

C2-B 186.5 -108 ft (-32.8 m) Brownish gray (5YR4/1) to olive gray

 (5Y4/1)

Same, some silt and clay pockets UG IRB -- 

C2-C 185.7 -108 ft (-33.1 m) Olive gray (5Y4/1) and gray black (N2) Fine-medium silty sand, some clay;

lignite laminae; ferric oxide grains

UG IRB 2.3 

C3-A* 195 -117 ft (- 35.7 m) Dark yellowish brown (10YR4/2) to 

medium gray (N5)

Medium to coarse, silty sand to sand with silt, some lignite laminae.

Mag IRB 

C3-B 196 -118 ft (-36 m) Grayish black (n2) to black (N1) Fine silty sand Mag IRB 1.3C4-A 205 -127 ft (-38.7 m) Medium gray (N5) Silty fine-to-medium sand, trace clay Mag (F3) IRB 1.0C4-B 205.6 -128 ft (-38.9 m) Dark gray (N3) to medium gray Silty fine sand with clay Mag (F3) SRB 2.6C4-C 206.2 -128 ft (-39.1 m) Medium gray (N5) Silty fine-to-medium sand, trace clay Mag (F3) UND 0.5C5-A* 215 -137 ft (-41.8 m) Dark gray (N3) to grayish black (N2) Clayey sand, some silt Mag -- C5-B 216 -138 ft (-42.1 m) Medium gray (N5) Fine-medium silty sand, trace clay Mag SRB 0.0C6 225 -147 ft (-44.8 m) Medium-light gray (N6) to medium gray 

(N5) to dark gray (N3)

Silty fine-to-medium sand to clayey sand, some lignite laminae

Mag UND 1.4 

C7* 235 -157 ft (-47.9 m) Medium gray (N5) Silty sand, trace clay, some pockets

of silt or sand

Mag UND 

C8 245 -167 ft (-50.9 m) Medium dark gray (N4) to dark gray (N3) Medium-coarse sand, some silt Mag IRB 2.2 C9 255 -177 ft (-54 m) Grayish black (N2) Silty very coarse to coarse sand, trace 

to some clay (layers), some silt

Mag IRB .8

C10-A 265 -187 ft (-57 m) Medium gray(N5) to medium dark gray 

(N5)

Medium-coarse to coarse sand with silt, with clay, some silt

Mag IRB/

SRB

.3

C10-B 266 -188 ft (-57.3 m) Medium-coarse sand with silt, some clay Mag UND C11-A 285 -207 ft (-63.1 m) Grayish black (N2) to 

medium dark gray (N5)

Silty clay to clay (lignitic) with laminae of very fine to fine sand and silt

Mag UND 

C11-B 286.5 -208 ft (-63.6 m) Dark gray (N3) to grayish black (N2) Very fine-to fine sand, some clay, 

some silt; laminae of lignitic silt

Mag UND 1.6

Aquifer Geochemistry
10 Aquifer Geochemistry & Effects of Pumping on Ground-Water Quality at the Green Belt Parkway Well Field, Holbrook, New York 

Table 2. Well-construction data for wells at Green Belt Parkway well field in Holbrook, Suffolk County, N.Y.

[Borehole locations are shown in fig. 3.]

Well 

identifier Well number

Land-surface 

elevation, in 

feet above sea 

level

Well-construction and borehole details

Well depth,

in feet below 

land surface

Depth of screen 

interval, in feet 

below land surface

Elevation of screen 

interval, in feet 

below (-) sea level

Elevation of screen 

interval, in meters 

below (-) sea level

OW-1A S114872 78.3 140 130-140 -51.7 to -61.7 -15.8 to -18.8

OW-1B S114874 78.3 200 190-200 -111.7 to -121.7 -34.1 to -37.1

OW-1C S97070 78.3 255 245-255 -166.7 to -176.7 -50.8 to -53.9

OW-2A S114870 78.3 130 120-130 -41.7 to -51.7 -12.7 to -15.8

OW-2B S114875 78.3 205 195-205 -116.7 to -126.7 -35.6 to -38.6

OW-2C S114876 78.3 250 240-250 -161.7 to -171.7 -49.3 to -52.4

OW-3A S114873 78.8 137 127-137 -48.2 to -58.2 -14.7 to -17.7

OW-3B S114869 78.8 197 187-197 -108.2 to -118.2 -33.0 to -36.0

OW-3C S114871 78.8 250 240-250 -161.2 to -171.2 -49.1 to -52.2

GB-1A S113812 77.9 282 232-282 -154 to -204 -47.0 to -62.2

GB-1 S54730 77.7 258 187-210 -109.3 to -132.3 -33.3 to -40.3

225-255 -147.3 to -177.3 -44.9 to -54.0

GB-2 S59744 76.5 301 237.5-299 -161 to -222.5 -49.1 to -67.8

GB-3 S66183 78.1 543 425.5-454 -347.4 to -375.9 -105.9 to -114.6

463-473 -384.9 to -394.9 -117.3 to -120.4

507-532 -428.9 to -453.9 -130.8 to -138.4

GB-4 S66184 75.0 384 293-318.5 -218 to -243.4 -66.4 to -74.2

345.5-381 -270.4 to -305.6 -82.4 to -93.2

Geochemistry and Microbiology

Geochemistry and microbiology of core 

samples from the borehole sediments were 

characterized through analyses of iron coatings, 

sedimentary organic matter (SOM), and total sulfur 

content, and through TEAP assays. Concentrations of 

0.5-M HCl-extractable iron coatings in core sediments 

from the upper glacial aquifer were higher (as much as 

29 μmol/g of sediment; table 1; fig. 4) than in 

Magothy sediments at depths greater than 195 ft

 (0.36 to 4.4 μmol/g) and than in deeper Magothy 

aquifer sediments elsewhere in Suffolk County 

(<0.1 to 4.3 μmol/g, Brown and others, 1999). The 

comparatively low Fe(III) concentrations in Magothy 

sediment coatings reflect the Fe(III)-reducing and 

sulfate-reducing TEAPs, both of which can lead to the 

reduction of Fe(III) (Lovley, 1987; Coleman and 

others, 1993). 

Organic carbon (or) content of core-sample 

sediments ranged from 0.06 percent to 2.6 percent by 

weight (table 1), and total sulfur content ranged from 

0.0019 to 0.047 μmol/g of sediment. The SOM 

content of Magothy aquifer sediments in Suffolk 

County generally is positively correlated with the silt 

and clay content and the total sulfur content (Brown, 

Rakovan, and Schoonen, 2000). The SOM in core 

samples from the upper glacial deposits was higher 

than in other parts of Long Island (Brown and others, 

1999; Brown, Rakovan, and Schoonen, 2000) and may 

result from reworking of Magothy aquifer sediments 

during Pleistocene deposition of overlying glacial 

deposits. Sulfur content in Magothy sediments on 

Long Island generally is associated with iron-sulfide 

minerals (Brown, Rakovan, and Schoonen, 2000). The 

total sulfur content at the Green Belt Parkway site was 

positively correlated with the concentration of 0.5 M 

HCl-extractable iron coatings in Cretaceous 

(Magothy) deposits at GB-1A (fig. 6). The absence of 

a similar correlation in deep Magothy sediments in 

Suffolk County (Brown, Rakovan, and Schoonen, 

2000) suggests that Fe(III) oxyhydroxide coatings in 

the shallow, slightly oxygenated part of the aquifer 

originate from the oxidative weathering of iron sulfide 

(FeS2) and the subsequent oxidation of dissolved 

Fe(II). Evidence of iron-sulfide-mineral oxidation was 

found also in the shallow part of the Magothy aquifer 

of eastern Suffolk County (Brown and others, 1999; 
11

y = 0.0026x + 0.0014

R2 = 0.9442

Outlier omitted from trendline and equation

CONCENTRATION OF Fe(III) COATINGS, 

IN MICROGRAMS PER GRAM OF SEDIMENT

CONCENTRATION OF TOTAL SULFUR,

IN MICROMOLES PER GRAM OF SEDIMENT

0

0.008

0.016

0.024

0.032

012345

Brown, Schoonen, and Candela, 2000). 

Concentrations of pore-water sulfate 

were higher in shallow cores than in 

deep cores and, thus, could indicate 

localized pyrite oxidation. The uneven 

distribution of Fe(III) concentrations, 

carbon, total sulfur, and TEAPs in 

Magothy aquifer sediments is consistent 

with that in intermediate and deep parts 

of the Magothy farther to the west in 

Suffolk County (Brown and others, 

1999). These geochemical data, together 

with the varied distribution of TEAPs in 

GB-1A sediments (table 1 and fig. 4A), 

indicate that localized 

microenvironments are prevalent in the 

shallow parts of the Magothy aquifer.

The TEAP assays indicated a 

range from iron reduction to sulfate 

reduction; the TEAPs in some samples 

were undetermined (table 1). 

Methanogenesis was not observed in any 

of the samples, probably because sulfate 

is ubiquitous in the pore water, and 

methanogenic bacteria cannot proliferate 

if preferred electron acceptors (Fe(III) or 

sulfate) are present. The undetermined 

TEAP results in samples can result from 

several factors, including locally oxic 

conditions (possibly sample C4-C), clay, 

which can inhibit the transport of 

nutrients and microbial waste 

(possibly samples C5-A, C11-A, -B), 

low concentrations of electron 

acceptors, or the absence or 

recalcitrance of an organic carbon 

electron donor (possibly samples 

C-5A); all of these factors can be 

inhibitory to anaerobic bacteria. 

Microbial activity, as measured in 

the acetate-amended core sediments 

by the rate of 14C acetate oxidation 

(% 14C oxidation/h), generally was 

highest in sediments with a high 

percentage of organic carbon; figure 

7 shows the square of the rate of 14C

acetate oxidation in core sediment 

as a function of the square of the 

percentage of organic carbon. The 

0.5M HCl-extractable Fe(III) is the 

Figure 6. Concentration of total sulfur as a function of the concentration of 

0.5M HCl-extractable Fe(III) coatings in Magothy aquifer core samples from 

borehole GB-1A, Holbrook, N.Y. (Borehole location is shown in fig. 3.)

0

0.02

0.04

0.06

0.08

02468

SQUARE OF 14C-OXIDATION RATE,

IN PERCENT PER HOUR

SQUARE OF PERCENT ORGANIC CARBON 

IN CORE SEDIMENT, BY WEIGHT

Core sample

contaminated 

by drilling fluid

y = 0.0081x - 0.0029

R2= 0.6233

Figure 7. Square of the 14C-oxidation rate in acetate-amended sediment as a 

function of the square of the organic carbon concentration in sediment cores from 

borehole GB-1A, Holbrook, N.Y. (Borehole location is shown in figs. 3 and 5).

Aquifer Geochemistry
12 Aquifer Geochemistry & Effects of Pumping on Ground-Water Quality at the Green Belt Parkway Well Field, Holbrook, New York 

most microbially reactive iron fraction (Lovley and 

Phillips, 1987) and, therefore, should be favorable for 

Fe(III)-reducing bacteria. No correlation was observed 

between this Fe(III) fraction and iron-reducing TEAPs 

in sediments; this indicates that iron-reducing bacteria 

are limited by the pool of electron donor (organic 

carbon) available, as observed in a previous study of 

borehole sediments from the middle part of the 

Magothy aquifer about 10 mi southeast of the GB-1A 

study area (Brown and others, 1999). The greatest 

anaerobic microbial activity (0.9 percent acetate 

oxidized/h) was in a sample from a 216-ft depth (core 

C5-B in table 1). This sample had a low SOM content 

(0.06 percent); however, the predominance of a 

sulfate-reducing TEAP, together with the high total 

sulfur concentration in these sediments, indicates that 

iron-sulfide minerals have formed at this horizon. 

Although the SOM content was low in sample C5-B, 

dissolved organic acids could leach from lignite in an 

overlying clayey sand (fig. 4A) and provide an 

organic-carbon source for the iron-reducing bacteria.

Sulfate concentrations in pore water from GB1A (table 3) were from 2 to 50 times greater than in 

water from nearby wells (OW-1B and OW-1C) 

screened in the Magothy aquifer (table 4). High 

concentrations of sulfate in pore water have been 

observed in Magothy borehole sediments from other 

parts of Suffolk County and probably result from a 

seawater transgression in the past (Brown, 1998). 

These locally high sulfate concentrations can result in 

localized microbial and geochemical reactions that are 

not apparent in large-scale aquifer studies that depend 

solely on well-water analyses. Similar results were 

observed in this study and probably reflect the thin 

(<0.5-ft) interval from which pore-water samples were 

obtained, unlike the much wider (10- to 50-ft) 

screened intervals from which ground-water samples 

were obtained. Furthermore, the disturbance of the 

sediment samples, and the ion desorption that 

probably occurs during sediment dilution with 

deionized water, result in the release of pore water that 

is not represented in well-water samples because it is 

not removed by pumping (Brown, 1998). 

Dissolved iron concentrations in pore water 

ranged from below the detection limit 

(<1.8 μmol/L) in several cores to 6.5 μmol/L in 

sample C4-C. The low pH (4.93) and the absence of 

anaerobic microbial activity in sample C4-C may 

result from the local presence of dissolved oxygen in 

pore water and subsequent oxidation of pyrite, which 

would release dissolved iron and acidity.

Ground-Water Quality

Water quality in the upper glacial aquifer in the 

study-site vicinity differs from that in the Magothy 

aquifer. Water from both aquifers generally can be 

characterized as a low ionic strength, sodium-chloride 

type, but the upper glacial aquifer is more prone to 

point- and nonpoint-source contamination. The 

Magothy aquifer at this location is confined by silt and 

clay layers at the top of the Cretaceous surface and at 

the bottom of the Pleistocene deposits (upper glacial 

aquifer). Water in the Magothy aquifer generally is 

older, contains more reduced species, such as 

dissolved (ferrous) iron, manganese, and sulfide, and 

contains less dissolved oxygen, than water in the upper 

glacial aquifer. 

Local water quality in the upper glacial aquifer 

and the upper part of the Magothy aquifer at the study 

site is reflected in the chemistry of samples from the 

pumping well (GB-1A) and the adjacent observationwell cluster (OW-1A, OW-1B, and OW-1C; fig. 8; 

table 4). Concentrations of ions in the upper glacial 

aquifer (OW-1A) reflect effects of human activities 

and generally are higher than those in the Magothy 

aquifer (OW-1B, OW-1C, and GB-1A; fig. 8), 

although the concentrations of nitrogen species at 

Magothy wells GB-1A and OW-1C also reflect human 

activity (table 4). The presence of nitrate in GB-1A 

and OW-1C probably results from the downward flow 

of shallow water induced by pumping of supply wells 

in the Magothy aquifer. The presence of nitrate in GB1A (6.3 μmol/L) during a static period of nonpumping 

(April 20, 1999) indicates that ground water that 

contributes to this well is from a less reducing 

environment than that in OW-1C, where nitrate 

concentrations were below the detection limit (<3.6 

μmol/L). The part of the aquifer from which OW-1C 

obtains water is small compared to the part tapped by 

GB-1A, which has a much longer screen, is pumped at 

large rates, and, therefore, obtains much larger 

volumes of water. The low concentrations of nitrate in 

OW-1C, therefore, probably reflect local conditions.
13

Table 3. pH and concentrations of selected constituents in pore-water samples from borehole GB-1A in Holbrook, 

Suffolk County, N.Y.

[Concentrations in micromoles per liter. Diss, dissolved. NM, not measured. <dl, below detection limit. Borehole location 

is shown in fig. 3.]

Sample 

identifier

Sample depth,

in feet below (-) land 

surface

Sample altitude, 

in feet below (-) 

sea level

pH Iron, dissolved SO4

2- ClC1-A 180 -102 NM NM NM NM

C2-A 185 -107 5.7 0.46 2.5 410

C2-B 185.7 -107.7 5.9 NM NM NM

C2-C 186.5 -108.5 5.6 1.3 230 190

C3-A 195 -117 5.6 .67 2,800 240

C3-B 196 -118 5.2 <dl 1,000 200

C4-A 205 -127 5.3 <dl 1,300 200

C4-B 205.6 -127.6 5.3 NM NM NM

C4-C 206.2 -128.2 4.9 6.5 100 190

C5-A 215 -137 6.1 <dl 660 310

C5-B 216 -138 5.7 2.1 510 220

C6 225 -147 5.6 <dl 590 120

C7 235 -157 5.8 <dl 820 180

C8 245 -167 5.1 <dl 770 240

C9 255 -177 5.4 <dl 1,500 200

C10-A 265 -187 6.2 .71 760 310

C10-B 266 -188 5.4 <dl 570 98

C11-A 285 -207 NM <dl 810 84

C11-B 286.5 -208.5 6.8 <dl 210 110

Aquifer Geochemistry
14 Aquifer Geochemistry & Effects of Pumping on Ground-Water Quality at the Green Belt Parkway Well Field, Holbrook, New York Table 4. Concentrations of major elements and chemical species, and δ13C, and δ34S of sulfate in water samples from wells at Green Belt Par

Holbrook, Suffolk County, N.Y., 1999. [Dissolved concentrations in milligrams per liter (and micromoles per liter). Diss, dissolved. TOC, total organic carbon; DOC, dissolved organic carbon. δ1

Screen interval in feet (and meters) above or below (-) sea level. Dashes indicate data not available. Locations shown in fig. 1.]

Well site 

 screen interval

Date

time

Water 

temp. 

( ̊C)

NH4

+

as N

NO3

-

as N

P Fe 

pH O2 Ca2+ Mg2+ Na+ K+ HCO3

- H2S SO42- Cl- Silica Total Diss PO42- Total Dis

 GB-1A

(S113812) 

-154 to -204

(-47.0 to -62.2)

4/8/991

12:40

1 Sample collected after well development; nearby supply wells were pumped intermittently at this time

10.7 5.8 0.21

(6.6)

3.8

(95)

1.5

(62)

4.3

(190)

0.56

(14)

8.2

(140)

-- 10

(100)

5.9

(170)

15

(250)

<.02

(<1.1)

<.05

(<3.6)

<.05

(<1.6)

<.05

(<1.6)

0.007

(0.23)

0.30

(5.3)

0.2

(4.8

4/20/992

16:00

2 Sample collected during static conditions

10.5 6.0 <.1

(<3.1)

4.0

(100)

1.8

(74)

4.7

(200)

.5

(13)

10

(166)

<.004

(<.1)

10

(100)

6.8

(190)

15

(250)

.024

(1.3)

.088

(6.3)

<.05

(<1.6)

<.05

(<1.6)

.006

(.19)

.19

(3.4)

.20

(3.6

4/22/993

16:30

3 Sample collected during pumping conditions

10.6 6.0 .18

(5.6)

3.5

(87)

1.6

(66)

4.4

(190)

.43

(11)

11

(180)

.004

(.12)

10

(100)

6.0

(170)

15

(250)

.034

(1.9)

.051

(3.6)

<.05

(<1.6)

<.05

(<1.6)

.013

(.42)

.35

(6.3)

.36

(6.4

OW-1A

(S114872) 

-51.7 to -61.7 

(-15.8 to -18.8) 

 4/20/99 

10:00

12.1 6.2 4.8

(150)

5.5

(140)

5.8

(240)

20

(870)

1.2

(31)

29

(470)

-- 8.8

(92)

32

(900)

10

(170)

.042

(2.3)

2.3

(16)

.44

(14)

.48

(15)

.49

(16)

.26

(4.6)

.28

(5.0

4/22/99 

14:00

11.4 6.1 5.5

(170)

5.5

(140)

5.7

(230)

20

(870)

1.8

(46)

19

(310)

-- 9.3

(97)

34

(960)

10

(170)

.055

(3.0)

2.3

(160)

.30

(9.7)

.30

(9.7)

.32

(10)

.23

(4.1)

.22

(3.9

 OW-1B 

(S114874)

 -111.7 to -

121.7

 (-34.1 to -37.1)

4/19/99 

15:00

11.5 6.1 3.1

(97) 

6.6

(160) 

3.0

(120) 

5.7

(250) 

.54

(14) 

28

(460)

-- 6.4

(67)

8.8

(250)

17

(280)

.059

(4.2)

.79

(56)

<.05

(<1.6)

<.05

(<1.6)

.015

(.48)

<.012

(<.22)

<.01

(<.1

4/22/99 

13:00

11.4 6.1 5.5

(170)

8.3

(207)

3.6

(150)

6.3

(270)

.95

(24)

32

(520)

-- 5.0

(52)

11

(310)

17

(290)

.033

(2.4)

1.2

(86)

<.05

(<1.6)

<.05

(<1.6)

.001

(.03)

<.012

(<.22)

<.01

(<.1

OW-1C

(S97070)

-166.7 to -176.7

(-50.3 to -53.9)

4/19/99 

11:45

11.0 5.9 <.1

(<3.1)

3.0

(75)

1.3

(53)

4.3 

(190)

.39

(10)

8.0

(130)

.010 

(.29)

11

(110)

5.0

(140)

15

(250)

.059

(1.7)

.79

(56)

<.05

(<1.6)

<.05

(<1.6)

.008

(.26)

.16

(29)

.17

(30

4/19/994

11:46

4 Replicate analysis

-- -- -- 3.0

(75)

1.3

(53)

4.3

(190)

.40

(10)

8.2

(130)

.010

(.29)

11

(110)

5.0

(140)

16 

(260)

.059

(1.8)

.79

(56)

<.05 

(<1.6)

<.05 

(<1.6)

.008

(.26)

.16

(28)

.17

(31

4/22/99 

10:00

11.0 5.9 <.1

(<3.1)

3.2

(80)

1.3

(54)

4.4

(190)

.42

(11)

7.2

(120)

.012

(.35)

12.1

(120)

5.3

(150)

15

(250)

.031

(1.7)

<.05

(<3.6)

<.05 

(<1.6)

<.05 

(<1.6)

.022

(.71)

.16

(28)

.16

(29
15

EFFECTS OF PUMPING ON GROUNDWATER QUALITY

Pumping of supply well GB-1A lowered water 

levels in nearby observation wells and altered the 

water quality. All supply-well pumping at the site was 

stopped on April 17, 1999 for 2 days to achieve static 

water-level conditions. Well GB-1A was then turned 

on and pumped for 2 days at a rate of about 700 gal/

min. Water samples were collected from GB-1A and 

from OW-1 wells A, B, and C during the nonpumping 

period (GB-1A was sampled about 20 min. after its 

pump was turned on), and at the end of the 2-day 

pumping period. Water levels in all nine observation 

wells were monitored before, during, and after the test 

(fig. 9). The water level in GB-1A generally was stable 

at 37.2 ft above sea level before the test, then declined 

to 3.4 ft above sea level once pumping began (fig. 9). 

Water levels in nearby Magothy aquifer observation 

wells OW-1B and -1C and OW-3B and -3C also were 

steady before the test, then declined almost 

immediately in response to pumping in GB-1A. Water 

levels in wells screened in the upper glacial aquifer 

(OW1-A, -2A, and -3A) showed little, if 

any, decline in response to the 

pumping—the water levels in OW-1A and -

2B did not decline at all, and the water level 

in OW-3A declined from 38.46 ft above sea 

level before pumping to 38.33 ft above sea 

level during the pumping. This indicates 

that extended pumping in the Magothy 

aquifer during the nonsummer months has 

little or no effect on water levels in the 

upper glacial aquifer. The summer demand 

often requires pumping of more than one 

supply well, however. For example, total 

combined pumpage from wells GB-1 

through GB-4 for July 1999 ranged from 

1.4 to 6 Mgal/d, whereas the combined 

pumpage for the preceding January ranged 

from 0.02 to 0.17 Mgal/d. Water levels 

measured in Magothy wells OW-1C and 

OW-3C on July 20, 1999, at a time when 

GB-1, - 2, and -3 were pumping 

simultaneously, were 26.96 and 31.71 ft 

above sea level, respectively—nearly 3 ft 

lower than water levels measured during 

the pumping of GB1A alone on April 22, 

1999. Water levels measured in upper 

glacial wells OW-1A and OW-3A on July 

in 1999 were 35.20 and 35.75 ft above sea 

level, respectively, and also were nearly 3 feet lower 

than water levels measured on April 22. Water-table 

fluctuations generally are caused by variations in the 

amount of water entering or discharging from the 

aquifer, such as from precipitation or pumping 

(Busciolano and others, 1998). Precipitation had been 

low in the 4 months preceding the test and probably 

provided little ground-water recharge and, thus, led to 

water-level declines. Intensive pumping of the 

Magothy aquifer during the summer probably lowered 

water levels in the upper glacial aquifer as well.

Chemical analyses of ground-water samples 

collected from well GB-1A during pumping indicate 

that the water originated from a wide range of depths. 

Dissolved oxygen concentrations increased from <3.1 

μmol/L on April 20 to 5.6 μmol/L on April 22, and 

phosphate concentrations increased from 0.19 to 0.42 

μmol/L as P (fig. 10A); these increases probably 

resulted from the induced inflow of water from 

shallow depths, such as near the well screens of OW1A and 1B (fig. 9A). Phosphate concentrations in OW1C increased also (fig. 10A). Dissolved iron 

Figure 8. Stiff diagrams representing ion concentrations in water samples 

from public-supply well GB-1A and observation wells OW-1A, OW-1B, 

and OW-1C, at Green Belt Parkway well field, Holbrook, N.Y., during 

static, nonpumping conditions of April 19-20, 1999 (Well locations are 

shown in fig. 3.)

1 .5 .5 1

Na HCO3

Ca SO4

Mg Cl

OW-1A

4/20/99

1 .5 .5 1

Na HCO3

Ca SO4

Mg Cl

OW-1B

4/19/99

1 .5 .5 1

Na HCO3

Ca SO4

Mg Cl

OW-1C

4/19/99

1 .5 .5 1

Na HCO3

Ca SO4

Mg Cl

GB-1A

4/20/99

CONCENTRATION, IN 

MILLIEQUIVALENTS PER LITER

Effects of Pumping on Ground-Water quality
16 Aquifer Geochemistry & Effects of Pumping on Ground-Water Quality at the Green Belt Parkway Well Field, Holbrook, New York 

STATIC CONDITIONS PERIOD OF PUMPING

WATER LEVEL, IN FEET ABOVE SEA LEVEL

B. DRAWDOWNS AT WELLS APRIL 1999

A. DRAWDOWN ALONG SECTION B-B'

B

SOUTH

Depth

(feet)

B'

NORTH

Altitude

(feet)

GB-2 OW-2 GB-1 OW-1 GB-3 OW-3

GB-1A

(S113812T)

A

B

C

A

B

C

A

B

C

STATIC

silt and fine sand F1

silt and clay F2

silt and clay F3

Upper glacial

aquifer

Magothy aquifer

PUMPING

0

10

20

30

40

16 18 20 22 24

Sea Level

-100

100

-200

200

0

100

Sea Level

GB-1A (Pumping well) 

OW-3A (Upper glacial)

OW-3B (Magothy)

OW-3C (Magothy, measured using a transducer)

OW-1A (Upper glacial)

OW-1B (Magothy)

OW-1C (Magothy)

EXPLANATION

Static Water Level

EXPLANATION

Silt Or Clay Lens

C

Well And Screen

 Interval

OW-1

Aquifer Contact

Sea Level

Pumping Water Level

F2

75

0 10 20

0

METERS

25 50 FEET

Figure 9. Water levels in the Magothy aquifer (for wells screened below clay lens F3) along Section B-B ́ at the Green Belt 

Parkway well field, Holbrook, N.Y., during static, prepumping conditions and the pumping period, April 19-22, 1999: A. 

Drawdowns along B-B ́. B. Water levels in pumping well (GB-1A) and two observation-well clusters (OW-1 and OW-3). (Trace 

of Section B-B ́ is shown in fig. 3.)
17

APRIL 1999

A. PHOSPHATE (PO4)

 DISSOLVED OXYGEN (O2)

B. DISSOLVED IRON (Fe) 

 AND BICARBONATE (HCO3)

C. TOTAL ORGANIC CARBON (TOC) 

 AND DISSOLVED ORGANIC CARBON 

 (DOC)

CONCENTRATION, IN MICROMOLES PER LITER

0

1

2

3

4

5

6

0

100

200

0

5

10

15

20

25

30

19 20 21 22

ALL PUMPS OFF

(STATIC)

GB-1A PUMP ON

(PUMPING)

PUMP

OFF

GB-1A, O2

GB-1A, PO4

OW-1C, O2

OW-1C, PO4

GB-1A, Fe, dissolved

GB-1A, HCO3

OW-1C, Fe, dissolved

OW-1C, HCO3

OW-1C, TOC

OW-1C, DOC

GB-1A, TOC

GB-1A, DOC

Figure 10. Concentrations of selected constituents in 

water samples from pumping well GB-1A and 

observation well OW-1C, Holbrook, N.Y., during static, 

prepumping conditions and the pumping period, April 19-

22, 1999: A. Phosphate and dissolved oxygen. B. 

Dissolved iron and bicarbonate. C. Total organic carbon 

(TOC) and dissolved organic carbon (DOC). (Well 

locations are shown in fig. 3.) DEPTH BELOW LAND SURFACE, IN FEET

100

120

160

180

200

220

240

260

280

300

140

upper glacial aquifer

Magothy aquifer

cement

#2 well gravel

14"- diameter inner casing

20" x 14" packer

36"- diameter borehole

20"- diameter outer casing

14"- diameter screen,

 stainless steel, 0.050 slot

3' sump

EXPLANATION

Clay/Silt Lens

GB-1A Screen 

Interval

Sand

Sand With Silt

Downward Flow 

Of Water

#2 Gravel

Cement

F2

F1

F3

F2

Figure 11. Construction diagram for well GB1A at Green Belt Parkway wellfield, Holbrook, 

N.Y., showing gravel-filled annulus that could 

provide a downward flow path from the upper 

glacial aquifer through clay unit F3 to the well 

screen. (Well location is shown in fig. 3.)

Effects of Pumping on Ground-Water quality
18 Aquifer Geochemistry & Effects of Pumping on Ground-Water Quality at the Green Belt Parkway Well Field, Holbrook, New York 

concentrations in samples from GB-1A (fig. 10B) 

increased during the pumping and may reflect inflow 

from anoxic, high-iron horizons such as near the 

screen zone of OW-1C; this trend is consistent with the 

increase in other reduced species such as ammonium 

and sulfide during pumping. Bicarbonate 

concentrations in GB-1A also increased during 

pumping, possibly from an increase in the percentage 

of water pumped from shallow depths, such as near the 

screen zones of OW-1A and OW-1B (fig. 9A), where 

bicarbonate concentrations are much higher than in the 

Magothy and (or) in pristine settings (table 4).

Water from the upper glacial aquifer could flow 

downward to the Magothy aquifer through gaps in the 

confining units or through coarse parts of the confining 

unit. The downward flow of shallow ground water 

could be enhanced by the sand pack around the outside 

of the screen and casing and the gravel-filled annulus, 

which continues from around the screen upward to a 

depth of 215 ft (fig. 11); together, these could provide 

a direct pathway for water from the upper glacial 

aquifer to flow downward through clay unit F3.

The δ13C of DIC and the δ34S of sulfate 

generally were measured in the observation wells 

before the pumping test and in the supply well 

(GB-1A) at the end of the pumping test. The stableisotope values were not measured in GB-1A before 

pumping, but the available δ34S data were sufficient to 

identify changes in the contribution of water to GB-1A 

from the depths represented by the observation-well 

screens. The δ13C values of DIC in ground water at the 

site ranged from -22.4 ‰ to -19.8 ‰ (table 4) and 

were heavier than the δ13C of a lignite sample 

(-22.9 ‰) from 280 ft below land surface (shallow 

Magothy). The δ13C of lignite from the intermediate 

and deep parts of the Magothy aquifer elsewhere in 

Suffolk County range from -24.3 ‰ to –22.5 ‰ 

(Brown, Schoonen, and Candela, 2000). The relatively 

light δ13C of -22.4 ‰ in DIC from OW-1A may be 

caused by aerobic heterotrophs, which can deplete 13C 

through oxidation of organic carbon (Blair and others, 

1985). The δ13C of DIC became enriched with 

increasing depth in samples from OW-1B (-22.3‰), 

OW-1C (-21.1‰), and GB-1A (-19.8‰) (fig. 12A). 

Similar trends in 13C enrichment were observed in the 

Magothy aquifer in western Suffolk County (Brown, 

Schoonen, and Candela, 2000) and in deep coastalplain aquifers in South Carolina and probably result 

from some form of fractionation associated with 

lignite oxidation (McMahon and others, 1992). TOC 

and DOC, which probably had built up from the 

oxidation of SOM and detritus released from 

microbial activity, decreased in all wells during 

pumping as the organic carbon was evacuated from the 

vicinity of the redox gradients around well screens.

The δ34S of sulfate in ground water at the well 

field ranged from –0.1 ‰ to 6.4 ‰ (table 4). Sulfate in 

shallow ground water collected from OW-1A during 

nonpumping conditions had a δ34S of 6.4 ‰, which is 

the heaviest of the samples collected and reflects the 

high δ34S values in atmospheric deposition (0 ‰ to 

20 ‰; Coplen, 1993) and in shallow ground water in 

areas of recharge on Long Island (13 ‰; Brown, 

Schoonen, and Candela, 2000). The δ34S values in 

ground water from deeper wells (OW-1B and OW-1C) 

during prepumping conditions indicated a decrease 

with depth—3.8 ‰ and 2.4 ‰, respectively (fig. 12B). 

The δ34S of sulfate in OW-1C increased to 3.3 ‰ after 

pumping and indicates that sulfate of heavier δ34S was 

drawn down from shallower depths by the pumping of 

GB-1A. Water from well GB-1A, which was sampled 

only once after the 2-day pumping period, had the 

lightest δ34S (–0.1 ‰) and indicates FeS2 oxidation. 

The δ34S of sulfate along a southward flow path 

farther west in Suffolk County becomes “lighter” with 

depth through the oxidation of FeS2, but gradually 

becomes “heavier” with distance from the recharge 

area and at depths greater than 350 ft along deep 

Magothy flow paths as a result of (1) mixing with 

“heavier” sulfate that originates from seawater anion 

complexes sorbed in poorly permeable sediments, and 

(2) sulfate reduction and the subsequent formation of 

FeS2 (Brown, 1998). The depths of wells sampled at 

the Green Belt Parkway site are less than 300 ft below 

land surface, and the lightest δ34S value-in water from 

GB-1A-is equivalent to that at a depth of about 500 ft 

below the zone of deep recharge in wells in 

southwestern Suffolk County (Brown, Schoonen, and 

Candela, 2000). The δ34S of iron-sulfide cemented 

sand, which was collected from a depth of 280 ft 

below land surface at GB-1A, was –41.3 ‰. The δ34S 

of iron-sulfide minerals at other depths (intermediate 

and deep) in the Magothy aquifer elsewhere in Suffolk 

County ranged widely-from -44.1 ‰ to 10.6 ‰. The 

δ34S ranges of iron sulfide minerals typically are 

“heavy” in isolated aquifer environments, where 

sulfate reduction and the formation of iron-sulfide 

minerals leave the remaining sulfate enriched in 34S, 

which subsequently forms heavy iron-sulfide minerals 
19

(Canfield and others, 1992; Brown, Schoonen, and 

Candela, 2000).

Supply-well pumping in the Magothy aquifer 

probably causes downward flow of oxygenated water 

from the upper glacial aquifer and contributes to 

biofouling at the site by promoting the oxidation of 

ferrous iron and the growth of iron-oxidizing and 

heterotrophic bacteria. This is supported by the 

increased concentrations of oxygen and phosphate in 

the sample from GB-1A after the 2-day pumping 

period, despite the locally confined nature of the 

Magothy aquifer at this site.

50

100

150

200

250

300

-23 -22 -21 -20 -19

DEPTH BELOW LAND SURFACE, IN FEET DEPTH BELOW LAND SURFACE, IN FEET

50

100

150

200

250

300

-1 0 1 2 3 4567

GB-1A OW-1C

OW-1A

OW-1B

δ13C OF DISSOLVED INORGANIC CARBON, IN PER MIL

B. δ34S

A. δ13C

δ34S OF SULFATE, IN PER MIL

GB-1A

OW-1C

OW-1A

OW-1B

Figure 12. Isotopic composition of water from the Green Belt Parkway well field, Holbrook, N.Y.: 

A. δ13C of dissolved inorganic carbon. B. δ34S of sulfate. (Well locations are shown in fig. 3.)

Effects of Pumping on Ground-Water quality
20 Aquifer Geochemistry & Effects of Pumping on Ground-Water Quality at the Green Belt Parkway Well Field, Holbrook, New York 

CONCLUSIONS

Aquifer lithology, geochemistry, microbiology, 

and water quality at a new supply well screened in the 

Magothy aquifer at the Green Belt Parkway well field 

in Holbrook were studied to help identify factors that 

can contribute to iron-related biofouling and wellscreen encrustation. Concentrations of sedimentary 

organic matter, and the terminal electron-accepting 

processes (TEAPs), in core-sample sediments from the 

screen zone varied from well to well. The principal 

TEAPs were iron reduction, sulfate reduction, and 

undetermined (possibly oxic); microbial activity was 

positively correlated with organic carbon content. 

Water quality was monitored at the supply well and in 

nearby observation wells screened in the upper glacial 

and Magothy aquifers.

Ground-water quality in the supply well (GB1A) and in an adjacent observation-well cluster 

indicates that pumping of the supply well can cause 

downward flow of shallow, oxygenated water from 

overlying aquifers; this, in turn, probably contributes 

to iron-related biofouling and well-screen encrustation 

at the site. Concentrations of dissolved oxygen and 

phosphate were higher after 2 days of pumping of GB1A than before the pumping, probably as a result of 

the downward flow of shallow water, which contains 

high concentrations of dissolved oxygen and 

phosphate. The δ34S of sulfate in the nearby deep 

observation well (OW-1C) increased from 2.4 ‰ 

before pumping to 3.3 ‰ after pumping; this confirms 

that water with heavier δ34S was drawn down from 

shallower depths by the pumping of GB-1A. The 

gravel-filled annulus, which extends from around the 

screen upwards to a depth of 215 ft, provides a 

potential flowpath downward through clay unit F3. 

The increase in the iron concentration of water from 

GB-1A during pumping may reflect an increased 

contribution from the deep, anoxic, iron-rich horizons, 

such as those near the screen zone of well OW-1C. 

Extended pumping from the Magothy aquifer in April 

1999, when water demand was low, had little effect on 

water levels in the upper glacial aquifer, but the 

increased water-supply pumping of more than one 

supply well at a time during the summer could lower 

water levels in the upper glacial aquifer. The induced 

downward flow of shallow ground water by intensive 

pumping probably aggravates iron-related biofouling 

and well-screen encrustation.

REFERENCES CITED

Arbogast, B.F., 1996, Analytical methods for Mineral 

Resource Surveys Program: U.S. Geological Survey 

Open-File Report OFR 96-525.

Brown, C.J., 1998, Effects of geochemical and microbial 

reactions on iron and other redox-related constituents 

in the Magothy aquifer, Long Island, New York: State 

University of New York at Stony Brook Department of 

Geosciences, Ph.D. dissertation, 163 p.

Brown, C.J., Coates, J.D., and Schoonen, M.A.A., 1999, 

Localized sulfate-reducing zones in a coastal plain 

aquifer: Ground Water, v. 37, p. 505-516.

Brown, C.J., Rakovan, John, and Schoonen, M.A.A., 2000, 

Heavy minerals and sedimentary organic matter in 

Pleistocene and Cretaceous sediments on Long Island, 

New York, with emphasis on pyrite and marcasite in 

the Magothy aquifer: U.S. Geological Survey WaterResources Investigations Report 99-4216, 22 p.

Brown, C.J., Schoonen, M.A.A., and Candela, J.L., 2000, 

Geochemical modeling of iron, sulfur, oxygen, and 

carbon in a coastal plain aquifer: Journal of Hydrology, 

v. 237, p. 147-168.

Busciolano, R.J., Monti, Jack, Jr., and Chu, Anthony, 1998, 

Water-table and potentiometric-surface altitudes of the 

upper glacial, Magothy, and Lloyd aquifers on Long 

Island, New York, in March-April 1997, with a 

summary of hydrogeologic conditions: U.S. 

Geological Survey Water- Resources Investigations 

Report 98-4019, 17 p.

Canfield, D.E., Raiswell, Robert, and Bottrell, Simon, 1992, 

The reactivity of sedimentary iron minerals toward 

sulfide: American Journal of Science, v. 292, p. 659-

683.

Carmody, R.W., Plummer, L.N., Busenberg, Eurybiades, 

and Coplen, T.B., 1998, Methods for collection of 

dissolved sulfate and sulfide and analysis of their sulfur 

isotope composition: U.S. Geological Survey OpenFile Report 97-234, 91 p.

Chapelle, F.H., Zelibor, Jr., J.L., Grimes, D.J., and Knobel, 

L.L., 1987, Bacteria in deep coastal plain sediments of 

Maryland_a possible source of CO2 to ground water: 

Water Resources Research, v. 23, no. 8, p. 1625-1632.

Coates, J.D., Anderson, R.T., and Lovley, D.R., 1996a, 

Oxidation of polycyclic aromatic hydrocarbons under 

sulfate-reducing conditions: Applied and 

Environmental Microbiology. v. 62, no. 3, p. 1099-

1101.

Coates, J.D., R.T. Anderson, Woodward, J.C., Phillips, 

E.J.P., and Lovley, D.R., 1996b, Anaerobic 

hydrocarbon degradation in petroleum-contaminated 

harbor sediments under sulfate-reducing and 

artificially imposed iron-reducing conditions: 

Environmental Science and Technology, v. 30, no. 9, p. 

2784-2789.
21

Coleman, M.L., Hedrick, D.B., Lovley, D.R., and others, 

1993. Reduction of Fe(III) in sediments by sulphatereducing bacteria: Letters to Nature, v. 361, 

p. 436-438.

Coplen, T.B., 1993, Chap. 10—Uses of environmental 

isotopes, in Alley, W.M., ed., Regional ground-water 

quality: New York, Van Nostrand Reinhold, p. 227-

254.

Cullimore, D.R., 1986, Physico-chemical factors in 

influencing the biofouling of groundwater, in

Cullimore, D.R., ed., International symposium on 

biofouled aquifers, prevention and restoration, 

November, 1986, Proceedings: American Water 

Resources Association, p. 23- 26.

ERM-Northeast, 1991, Suffolk County Water Authority 

Greenbelt Parkway well field pump test report: 

Woodbury, N.Y., ERM-Northeast, 48 p.

Hach Company, 1993, DR/2000 Spectrophotometer 

procedures manual: Loveland, Colo., Hach Co., 450 p.

Heron, Gorm, Christensen, T.H., and Tjell, J.C., 1994, 

Oxidation capacity of aquifer sediments: 

Environmental Science and Technology, v. 28, p. 153-

158.

Lonnie, T.P., 1982, Mineralogic and chemical comparison 

of marine, nonmarine and transitional clay beds on 

south shore of Long Island, New York: Journal of 

Sedimentary Petrology, v. 52, no. 2, p. 529-536.

Lovley, D.R., 1987, Organic matter mineralization with the 

reduction of ferric iron—a review: Geomicrobiology 

Journal, v. 5, no. 3/4, p. 375-399.

Lovley, D.R., 1995, Benzene oxidation coupled to sulfate 

reduction: Applied and Environmental Microbiology, 

v. 61, no. 3, p. 953-958.

Lovley, D.R., and Phillips, E.J.P., 1987, Rapid assay for 

microbially reducible ferric iron in aquatic sediments: 

Applied Environmental Microbiology, v. 53. no. 7, p. 

1536-1540.

Lusczynski, N.J., 1961, Filter-press method of extracting 

water samples for chloride analysis: U.S. Geological 

Survey Water-Supply Paper 1544-A, 8 p.

McMahon, P.B., Chapelle, F.H., Falls, W.F., and Bradley, 

P.M., 1992, Role of microbial processes in linking 

sandstone diagenesis with organic-rich clays: Journal 

of Sedimentary Petrology, v. 62, p. 1-10.

Pearson, F.J., Jr., and Friedman, Irving, 1970, Sources of 

dissolved carbonate in an aquifer free of carbonate 

minerals: Water Resources Research. v. 6, no. 6, p. 

1775-1781.

Perlmutter, N.M., and Geraghty, J.J., 1963, Geology and 

ground-water conditions in southern Nassau and 

southeastern Queens Counties, Long Island, N.Y.: U.S. 

Geological Survey Water-Supply Paper 1613-A, 205 p.

Smith, S.A., 1992, Methods for monitoring iron and 

manganese biofouling in water wells: AWWA 

Research Foundation, Denver, Colo., 96 p.

Smolensky, D.A., Buxton, H.T., and Shernoff, P.K., 1989, 

Hydrologic framework of Long Island, New York: U.S. 

Geological Survey Hydrologic Investigations Atlas 

HA-709, 3 sheets, scale 1:250,000.

Suter, Russell, de Laguna, Wallace, and Perlmutter, N.M., 

1949, Mapping of geologic formations and aquifers of 

Long Island, New York: New York State Water Power 

and Control Commission Bulletin GW-18, 212 p.

Walter, D.A., 1997a, Effects and distribution of iron-related 

well-screen encrustation and aquifer biofouling in 

Suffolk County, Long Island, New York: U.S. 

Geological Survey Water- Resources Investigations 

Report 96-4217, 29 p.

—, 1997b, Geochemistry and microbiology of iron-related 

well-screen encrustation and aquifer biofouling in 

Suffolk County, Long Island, New York: U.S. 

Geological Survey Water-Resources Investigations 

Report 97-4032, 37 p.

Wilde, F.D., and Radke, D.B., 1998, National field manual 

for the collection of water-quality data: U.S. 

Geological Survey Techniques of Water-Resources 

Investigations, book 9, chap. A6 [variously paged].

References Cited