By 

Pixie A. Hamilton and Robert J. Shedlock 

Graphic design and layout by Joan M. Rubin 

U.S. GEOLOGICAL SURVEY CIRCULAR 1080 
U.S. DEPARTMENT OF THE INTERIOR 

MANUEL LUJAN, Jr., Secretary 

U.S. GEOLOGICAL SURVEY 

Dallas L. Peck, Director 

Any use of trade, product, or firm names in this publication is for descriptive purposes 

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

UNITED STATES GOVERNMENT PRINTING OFFICE: 1992 

Free on application to the 

Books and Open-File Reports Section 

U.S. Geological Survey 

Federal Center, Box 25425 

Denver, CO 80225 

Library of Congress Cataloging in Publication No. 92-10922 
~\) 0 

us 

GS 

Established in 1879, the U.S. Geological Survey (USGS) 

has provided scientific information on the Nation's 

water, energy, and mineral resources, and research on 

processes related to those resources for the benefit of all 

Americans. A major part of the mission of the USGS is 

to assess the quantity and quality of the Nation's water resources and to 

provide information and data to assist resource managers and policymakers at Federal, State, and local levels in making sound management 

decisions. To a significant extent, these responsibilities are being carried 

out by the USGS National Water-Quality Assessment (NA WQA) 

Program, whose goals include providing a sound understanding of the 

natural and human factors that affect water quality. 

The NA WQA Program consists of investigations in 60 study areas 

throughout the Nation that represent a variety of geologic, hydrologic, 

climatic, and cultural conditions. These study areas are the building 

blocks for understanding regional differences in the chemical and 

biological quality of the Nation's ground water and streams. Information 

from the NA WQA Program will address specific water-quality concerns 

through comparative studies. An important goal of the program is to 

ensure that key findings are available to the public so that they can be 

aware of the quality of the Nation's water resources. 

This report is the first in a series of non-technical publications on 

the NA WQA Program. The purpose of these publications is to describe 

key findings from the individual investigations and to relate those findings 

to water-quality issues that are of regional and national concern. By disseminating this information, the USGS seeks to increase awareness of 

water-quality concerns when considering the Nation's environmental issues. 

Director 
A c 0 N c E R N s 

IN THE NATION AND 

W. must recognize that 

productive agriculture and 

a sound environment can 

be compatible, especially 

in terms of water quality. 

The administration has initiated a concentrated 5-year effort 

to work with the Nation's farmers to protect our ground 

water from contamination by fertilizers and pesticides ... We 

must keep your good land in business without unreasonable 

burdens, but we must also keep it good land. 

President George Bush in his remarks 

to members of the American Farm 

Bureau Federation, January 8, 1990 

Asystematic assessment of 

the status, changes, and 

causes of water-quality conditions across the country is a 

key element of President 

Bush's water-quality initiative. I am confident that, by 

working together, we can begin to develop practical solutions to some of the Nation's 

critical water-quality problems. NAWQA will provide 

the first systematic assessment of water-quality conditions across the United States. 

Its goals are to provide 

nationally consistent waterquality information, to define 

long-term water-quality 

trends, and to describe the 

factors that affect water 

quality. 

Manuel Lujan, Jr., Secretary 

US. Department of the Interior 

H ) 

IN 

NAWQA STUDY AREAS 

EXPLANATION 

D STUDIES STARTED 

IN 1991 

STUDIES TO BEGIN 

AFTER 1991 

-- BOUNDARY OF 

STUDY AREA 
E 

'HE 

D B y M A 1 N y • • 

DELMARVA PENINSULA 

The 60 study-area design 

of the NAWQA Program is 

based on the observation that 

the Nation's water resources 

are an aggregation of many 

surface- and ground-water 

systems, each of which has 

its own set of hydrologic and 

chemical characteristics and 

each of which responds to 

natural and human-induced 

stress in its own way. Investigations in these individual 

areas are the foundation for 

understanding regional differences in the quality of the 

Nation's streams and ground 

water, as well as for addressing issues that are of both 

regional and national concern. One primary national 

issue is the degradation of 

water quality from nonpoint 

sources of pollution, including the prevalent use of fertilizers and pesticides on agricultural land. This concern is 

shared by the residents, waterresource managers, and 

policymakers associated with 

one of the first NAWQA study 

areas, the agricultural community of the Delmarva 

Peninsula. 

The Delmarva Peninsula, 

which includes most of 

GENTLY R OLLING FARM L A N D IN T HE DELM ARVA 

PENINSULA. T H E RELATIV E LY F L AT T OPOGRAP H Y AN D 

PORO U S SOI L S I N TH E PEN I NSULA PROVIDE FAVO R · 

ABL E CO N D I T I O N S F OR C HEM ICA L S AP PL I E D O N T HE 

LAND TO MOVE DOWNWARD T O T HE G R OU N D WA T ER. 

Delaware and the entire 

Eastern Shore of Maryland 

and Virginia, remains primarily a rural area where the lives 

of many residents depend one 

way or another on farming. 

As in many agricultural areas, 

crop yields are linked to the 

amounts and kinds of fertilizers and pesticides that are 

applied to the soil. The potential movement of these chemicals into ground water is 

a concern among waterresource managers and residents of the Delmarva Peninsula because ground water is 

the sole source for both drinking and irrigation purposes 

and because it is a major 

source of surface water. The 

relatively flat topography and 

porous soils provide fuvorable 

conditions for chemicals applied on the land to move 

downward to the water table. 

Are fertilizers and pesticides affecting 

the ground water? 

What are the risks to human health 

and the environment? 

How do soils, land use, and hydrology 

affect the movement of fertilizers and 

pesticides to ground water? 


4 GROUND WATER 

round water ongtnates as rainfall that percolates through the soiL Annual 

rainfall on the Delmarva 

Peninsula is about 44 inches. 

Most of this is used by plants 

or flows over the land to surface water, such as streams, 

ponds, and bays. The remaining water moves through the 

soil to ground water. Contrary 

to popular belief, ground 

water does not form underground "rivers." Instead, it 

fills and flows very slowly 

through tiny spaces between 

sediment grains. 

Underground sediments 

are not uniform. In the Delmarva Peninsula they are arranged in a layered sequence 

of sandy water-bearing formations, known as aquifers, 

separated from one another 

by layers of clay, known as 

confining units. The uppermost sandy layer, extending 

to a depth of 40 to 100 feet, 

is known as the water-table 

aquifer. The deeper sandy 

layers, extending to about 

8,000 feet, are known as 

confined aquifers because 

they are confined by clay 

at both their top and bottom margins. Although the 

clay layers impede the 

flow of ground water between the aquifers, 

some downward 

movement does 

occur. 

Water flows 

more freely in 

sand than it 

does in clay, 

and the 

sand aquifers readS URFA C E WA TE R , SUC H AS S TREAM S, 

AN D GROU ND WA TER AR E INTER CO N · 

NEC T E D . GRO UND WA TE R C AN SI GNI F· 

ICA NTL Y AFFEC T THE Q UALITY A N D Q UAN· 

TIT Y OF S URF AC E WA TE R , P ARTI C UL A R· 

LY O N TH E P E NIN S UL A W HERE IT 

IS TH E M AJOR SOU R C E O F S T R EAM F L OW. 

mit useful amounts of water 

to wells. The confined aquifers are the primary source of 

public-drinking water, except 

in the southern counties of 

Maryland and in Sussex 

County, Delaware, where the 

water-table aquifer is the 

primary source. The watertable aquifer also supplies 

large quantities of water for 

irrigation, and is tapped by 

domestic wells in rural areas. 

About half of the 170 million 

gallons per day pumped from 

wells on the peninsula is from 

the water-table aquifer. The 

water-table aquifer is the focus of the Delmarva NAWQA 

study because of its extensive 

use and because it supplies 

water to the underlying confined aquifers. 

Rainfall percolates 

FEET 

~;;~~~~~~~==~~~~~~~~::~~::~===filytrans- sEA LEVEL ~ 

400 

through the soil and recharges 

the water-table aquifer. 

Ground water moves by 

gravity from these recharge 

areas through the aquifer to 

low-elevation discharge areas, 

such as streams, agricultural 

ditches and ponds, bays, and 

the Atlantic Ocean. It is 

common to think of surface 

water and ground water as 

separate resources; however, 

they are highly interconnected. Ground water can significantly affect the quality and 

quantity of surface water. 

This is particularly important 

on the Delmarva Peninsula 

where ground water is the 

major source of streamflow. 

800 

1,200 

1,600 

2.000 10 20 MILES 

10 20 KILOMETERS 

2

'

400 Vertical scale greatly exaggerated 
r HE UNSEEN RESOURCE 

HYDROLOGISTS COLLECTING WATER 

SAMPLES FROM WELLS F O R ANALYSES 

OF N I TRATE. PES T ICIDES. AND OTHER 

CONSTITUENTS. 

Flow lines __ 

Ground-water movement is 

very slow. Typically, water in 

the water-table aquifer moves 

one-quarter to 2 feet per day. 

Total distance that this water 

travels under ground varies 

from hundreds of feet to several miles. Depth of flow 

varies from near the surface 

to about 100 feet. The depth 

of flow usually increases with 

increasing distance between 

recharge and discharge areas. 

As a result of the slow movement, water can remain in the 

water-table aquifer for several 

decades. Because of the even 

slower movement of water in 

the intervening clay layers, as 

well as deep (thousands of 

feet) and long (hundreds of 

miles) travel paths, water 

could remain in the confined 

aquifers for centuries or 

longer. 

The USGS began the 

NA WQA study of ground 

water in the Delmarva 

Peninsula in 1986. Hydrologists collected water samples 

from more than 200 wells in 

the water-table aquifer and 

more than 35 wells in the underlying confined aquifers. 

The samples were analyzed 

for nitrate, pesticides, and 

other dissolved constituents 

that can affect water quality. 

Locations of the wells were 

selected without bias toward 

any known or suspected 

problem areas. Areas around 

the wells differ in land use 

and soils, as well as in geologic characteristics and landscape. This site diversity 

ensures that the NA WQA 

analysis include a peninsulawide characterization of 

ground-water quality and 

problems, and a detailed assessment of cause-and-effect 

relations between water 

quality and ground-water 

flow, land use, soils, and 

geology. 

"Natural" ground-water 

quality (not affected by human activities) is controlled 

primarily by the chemical 

properties of rainwater in 

combination with minerals 

and biological activity in the 

soil and aquifers. Like rainwater, natural water in the 

water-table aquifer is moderately acidic with a pH of 

about 5.5 (a pH of 7.0 is 

neutral). It contains a lower 

concentration of dissolved 

constituents (generally less 

than 100 milligrams per liter)' 

compared to ground water in 

other parts of the country 

because aquifer materials on 

the Delmarva Peninsula consist mostly of quartz sand, 

which does not readily 

dissolve. Because of the relatively dilute concentrations 

of dissolved constituents, 

additional inputs, such as 

fertilizers applied to the land, 

could significantly change 

the chemical properties of 

the water. The quality of 

natural water in the watertable aquifer is generally 

good and suitable for most 

purposes. In some areas, the 

water has concentrations of 

iron and manganese in excess of 300 and 50 micrograms per liter, respectively, 

which can cause brownish 

discolorations to plumbing 

fixtures and laundry and a 

bitter taste. Chloride concentrations in excess of250 milligrams per liter, which can 

make the water taste salty, 

can result from intrusion of 

saltwater into aquifers along 

coasts and tidal streams. 

As water moves from the 

water-table aquifer to the 

confined aquifers, it dissolves various minerals and 

its chemistry changes. Confined ground water is less 

acidic and has a greater 

amount of dissolved constituents then does water in the 

water-table aquifer. Natural 

water in the confined aquifers also has concentrations of 

iron that reach a maximum 

of 27,000 micrograms per 

liter. 

'The terms milligrams and micrograms per liter are used in this report. A milligram is equal to one-thousandth of a gram, and is approximately equal to the weight 

of 6 crystals of common table salt. A microgram is a smaller quantity , and is 

equal to one-millionth of a gram. 

5 
6 IS NITRATE IN THE 

A water seeps through 

the soil to the water table, it 

can be affected by substances 

applied to the land, such as 

lime and inorganic and 

organic fertilizers. More than 

40 millions tons of inorganic 

fertilizers are used annually in 

the Nation. Not all of it is 

used by plants, and the excess 

might enter ground water. On 

the Delmarva Peninsula, 

chicken manure is an important additional source of 

nutrients. In Delaware alone, 

about 140 million chickens 

are raised annually. Even 

though the birds generally are 

raised indoors, the litter 

(about 5 tons per 1,000 chickens per year) is stored in piles 

outdoors or spread on fields. 

Applications of lime, inorganic fertilizers, and manure 

have changed the natural 

chemical properties of water 

in the water-table aquifer in 

the Delmarva Peninsula. 

Nitrate, derived from nitrogen 

in the inorganic fertilizers and 

manure, is a major constituent in the water-table aquifer 

in agricultural areas, partly 

because nitrate readily dissolves and moves freely to the 

water table with rainwater or 

irrigation water that is applied 

to the land. Concentrations of 

potassium and chloride from 

inorganic potash fertilizers, 

and calcium and magnesium 

from liming, also are significantly elevated. These constituents together impart a distinctive agricultural-chemical 

trademark to the ground 

water, different from the 

natural water. Except for 

nitrate, these constituents do 

not pose a health risk; however, their presence does provide an efficient means for 

distinguishing ground water 

affected by agricultural 

practices and can be used to 

identify areas that might be 

vulnerable to contamination 

from other agricultural chemicals, such as pesticides. 

MA JO R CO N S TIT UE NT S I N WA TE R I N THE 

WA TER - TABLE AQ UIF E R I N AG RI CU LT URA L 

A REA S A RE N I TR A TE FRO M I N O R GA NI C FERTIL I ZER S A ND MAN UR E , C A LC IUM AND M AG -

NE S I U M FR O M LIMIN G, AN D P O T ASS I UM AND 

C HL O RIDE FR O M PO T AS H . 

N I TROG EN F E R T I LI ZER G EN -

ERALLY IS APPLI E D T O 

F IEL DS I N THE FOR M O F AMMONIA , LI QUID N IT ROGEN . 

A N D POUL TR Y MA NURE , AL L 

O F WHIC H READ I LY CO N -

V E R T T O NI T R A TE . 

The peninsula-wide survey showed that water from 

more than 70 percent of all wells in the water-table 

aquifer has detectable concentrations of nitrate and 

that about 15 percent contain concentrations that 

exceed 10 milligrams per liter, the maximum contaminant level for drinking water established by the 

U.S. Environmental Protection Agency. 
GROUND WATER 

S 0 M E NITRATE F A C T S 

NATURAL SOURCES: Insignificant on the Delmarva 

Peninsula (generally less than 1 milligram per liter); 

some nitrogen in soil and atmospheric deposition 

HUMAN-RELATED SOURCES: Inorganic fertilizers, 

manure, and septic effluent 

HOW MUCH IS TOO MUCH? 10 milligrams per liter (maximum contaminant level for drinking water, established by the U.S. Environmental Protection 

Agency, 1986) 

POSSIBLE HEALTH IMPACTS: Methemoglobinemia or 

"blue-baby syndrome" in infants; stomach disorders in some animals 

TERMINOLOGY: Nitrate concentrations in this report are expressed as nitrogen content. 

Nitrate concentrations in 

some water samples are as 

high as 48 milligrams per 

liter. How vulnerable ground 

water is to nitrate contamination depends on a combination of factors such as geology, soils, land use, and hydrology. For example, nitrate 

concentrations are not commonly elevated in the central 

part or the western fringes of 

the peninsula. This is in part 

because the water-table aquifer in these areas contains a 

substantial amount of clay and 

silt instead of sand. The abundant clay and silt impedes 

downward movement of 

water. Clay and silt also 

enhance nitrogen uptake by 

plants; thus, less nitrogen is 

available to move through the 

soil to the ground water. In 

general, agricultural plots are 

small and there is a higher 

percentage of woodlands in 

these parts of the peninsula 

than elsewhere. 

In contrast, nitrate concentrations are elevated in the 

water-table aquifer in the 

northern part and southern tip 

of the peninsula, particularly 

in the areas that flank the central upland. This is mostly 

because the sandy soils and 

aquifer sediments are more 

permeable, allowing nitrate to 

move readily to the water 

table. Agricultural plots are 

large and well drained in 

these areas, with woodlands 

primarily confined to borders 

along streams. 

Nitrate is not commonly 

detected in the underlying 

confined aquifers. None of 

the water samples had nitrate 

concentrations that exceeded 

the maximum contaminant 

level for drinking water. This 

is mostly attributable to the 

slow movement of water in 

the clay confining layers that 

separate the confined aquifers 

from the overlying water-table 

aquifer. 

? 

• 

EXPLANATION 

7 

25 MILES 

h, _j_j ,--, -,J,'c...,-, .,., l___j____jl 

0 25 KILOMETERS 

NITRATE CONCENTRATIONS VARY REGIONALLY, 

DEPENDING ON FACTORS SUCH AS GEOLOGY, 

SOILS, LAND USE, AND HYDROLOGY 

AREA WITH LITTLE NITRATE 

AREA WITH DETECTABLE CONCENTRATIONS OF 

NITRATE, GENERALLY LESS THAN 10 MILLIGRAMS 

PER LITER 

c=:J AREA WITH DETECTABLE CONCENTRATIONS OF 

NITRATE, COMMONLY NEAR OR EXCEEDING 10 

MILLIGRAMS PER LITER 
8 NITRATE • 

• 

Woodland and 

residential Farm field 

Wooded area 

along stream 

Elevated nitrate concentrations are not 

limited to nearsurface ground water, 

but occur in the 

deepest part of the 

water-table aquifer, 

80 to 100 feet below 

the land surface. 

Q) 

2 

0 

0 

s 

0 

<t 

l ----

EXPLANATION 

CONCENTRATION 

OF NITRATE 

Significant nitrate 

levels 

Minimal or no 

nitrate 

--Direction of groundwater flow 

...--------------1 to 3 miles-------------

NITRATE CONCENTRATIONS ARE VARIABLE O VER SMALL DISTANCES , BOTH HORIZONTALLY AND 

VERTICALLY, DEPENDING ON LAND USE AND THE MOVEMENT OF WATER . NITRATE CO N CEN TRATIONS ARE HIGHEST IN NEAR -S URFACE GROUND WATER BENEATH FARMLAND AND LOWEST 

BENEATH WOODLANDS AND MARSHES. NITRATE CONCENTRATIONS ARE ELEVATED IN DEEP 

GROUND WATER WHERE DISTANT RECHARGE AREAS ARE AGRICULTURAL OR RESIDENTIAL. 

US hydrologists LJJS studied the local GfS d~stribut~on of 

mtrate m the 

water-table aquifer in a network of wells in several small 

watersheds (1 to 3 square 

miles). Concentrations of 

nitrate vary over small distances, both horizontally and 

vertically, depending on 

ground-water flow and land 

use. The typical land-use 

pattern includes woodlands 

and residential areas in the 

upland regions of the watersheds, woodlands and 

marshes along streams and 

coasts, and agricultural areas 

in between. In ground water 

near the land surface (less 

than 20 feet deep), nitrate 

concentrations generally reflect overlying land use within 100 to 200 feet of the well. 

Nitrate concentrations are 

highest beneath farmland and 

lowest beneath woodlands 

and marshes. Nitrate concentrations also are elevated in 

near-surface ground water 

beneath residential areas, 

which is attributable to septic effluent and lawn fertilizers. These nitrate concentrations, however, are not as 

elevated as they are in water 

beneath farmland. 

Elevated nitrate concentrations are not limited to 

near-surface ground water 

but occur in the deepest parts 

of the water-table aquifer, 80 

to 100 feet below the land 

surface. The deep ground 

water flows along longer 

paths in the water-table aquifer than does the nearsurface ground water and 

can remain in the aquifer for 

several decades. As a result, 

water from a deep well 

reflects land use at a distant 

recharge area rather than 

land use directly around the 

well. 

ROTATION OF WHEAT WITH SOY BEANS IS A CROPMANAGEMENT STRATEGY THAT CAN REDUCE THE 

AMOUNT OF NITRATE LEAVING THE ROOT ZONE, THUS RE· 

DUCING THE AMOUNT AVAILABLE TO GROUND WATER. 

A 
LOSER LOOK 

In some areas of the 

Delmarva Peninsula, deep 

ground water with elevated 

nitrate concentrations is 

overlain by near-surface 

ground water with low nitrate concentrations. This 

seemingly unexpected pattern of nitrate concentrations 

is most commonly found in 

marshes and wooded areas 

next to streams. In these 

areas, the near-surface 

ground water is recharged 

through soils covered with 

natural vegetation and the 

deeper ground water is 

recharged in distant agricultural or residential areas. 

Many Federal, State, and 

local agencies are recommending changes in cropmanagement strategies to 

reduce inputs of nitrate in 

farm fields in ground-waterrecharge areas. These strategies are designed to reduce 

the amount of nitrate leaving 

the root zone, and therefore 

the amount of nitrate 

available to move to the 

water table. Typical strategies include the rotation of 

crops that require high fertilization rates (such as 

wheat) with those 

that require little 

fertilization (such 

as soybeans). 

As more research is conducted on 

nitrogen needs and uptake by 

individual crops, farmers 

have learned to optimize the 

amount and timing of fertilizer applications, which also 

minimizes the amount of 

nitrate available to ground 

water. These strategies are 

critical; however, in order to 

properly evaluate their effectiveness, one must understand how ground-water 

flow and land use affect 

water quality over both time 

9 

and space. Shallow groundwater quality below farmland will improve first, in 

several years or less. Decades may pass, however, 

before water improves in the 

deep parts of the aquifer. 

The time lag between the 

adoption of crop-management 

strategies and water-quality 

improvement also affects 

surface-water quality. Deep 

ground water containing elevated nitrate concentrations 

can discharge directly to 

streams and bays. These deep ~ waters commonly bypass the 

rich organic matter and low 

dissolved oxygen conditions 

in the marshes and wooaed 

areas that tend to reduce if: 

even eliminate nitrate I. 

water. Therefore, impr?rements in surface-water qwillty \ 

might also lag changes in ~ 

agricultural practices by years 

or decades. \ 
10 ARE 

. • , . '• ,1 ,1 ·,: 

' \ 

A large quantity (about 

570 million pounds) of herbicides, insecticides, and fungicides is used annually 

throughout the Nation to 

enhance agricultural production by controlling weeds, 

insects, and fungi. In the 

Delmarva Peninsula, nearly 3 

million pounds of these 

chemicals are used annually 

for agricultural purposes. 

Most by far are herbicides, 

with metolachlor (such as 

Dual), alachlor (such as 

Lasso), and atrazine (such as 

AAtrex) accounting for about 

70 percent. These herbicides 

are used primarily on corn 

and soybeans, the two most 

widespread crops in the 

Delmarva Peninsula. 

Water samples from more 

than 100 wells in the watertable aquifer were analyzed 

PESTICIDE S IN 

NEARLY 3 MILLION POUNDS OF AGRICULTURAL HERBICIDES, INSECTICIDES, 

AND FUNGICIDES ARE USED ANNUALLY IN THE DELMARVA PENINSULA TO 

ENHANCE PRO DUCT 10 N BY CONTROLLING WEEDS. INSECTS, AND FUNGI. 

for about 40 different pesticides. These include metolachor, alachlor, and atrazine, 

and most of the other commonly used agricultural 

pesticides in the peninsula. 

One of the fmdings of the 

peninsula-wide sampling is 

that two of the most commonly used herbicides, alachor 

and atrazine, were also the 

most likely to be detected in 

ground water. Atrazine and 

(or) alachlor were detected in 

more than 20 water samples. 

The only insecticide detected 

was carbofuran, in only two 

water samples. The frequency 

at which pesticides were detected is roughly related to the 

amount of the pesticide 

applied and the total number 

of acres treated with it. Some 

variability is probably attributable to the varying solubility and mobility of individual 

pesticides in soil. 

Concentrations of pesticides were generally low: 94 

percent of the water samples 

with detectable concentrations 

of pesticides were less than 

the U.S. Environmental Protection Agency maximum 

contaminant and health advisory levels for drinking 

water. 

2 Concentrations above 

these levels are thought to 

contribute to long-term health 

problems. Atrazine exceeded 

the maximum contaminant 

level in one sample. Alachlor 

exceeded the level in two 

samples. Pesticides were not 

found in ground water used 

for public or private water 

supply except for trace concentrations in water samples 

collected from a few domestic 

wells. 

'Maximum contaminant levels and health advisory levels are established by the U.S. 

Environmental Protection Agency. Maximum contaminant levels are enforceable, and 

represent the maximum permissable level of a contaminant in water that is delivered 

to any user of a public-water system. Health advisory levels are not enforceable, 

and represent the maximum concentration of a contaminant in water that may be 

safely consumed over a specific length of time. 
f HE GROUND WATER ? 11 

• 

PLANE DUSTING C R 0 P S WITH PESTICIDES, P R I 0 R T 0 

The distribution of 

detected pesticides depends 

on land use, crop type, and 

ground-water flow. In most 

water samples in which herbicides were detected, the well 

was near farmland (generally 

within 100 feet) used to grow 

com and soybeans, the two 

crops associated with the 

highest herbicide use and 

most extensive acreage. These 

water samples commonly 

contained calcium, magnesium, and nitrate as major 

constituents, indicating that 

the water also had been 

affected by agricultural lime 

and fertilizers. Water samples 

in which pesticides were 

detected were generally collected from no more than 20 

feet below the water table, 

and generally reflected pesticide use in the immediate 

vicinity (within 100 to 200 

feet of the well). Only a few 

pesticides were detected in 

samples from wells greater 

than 50 feet below the water 

table. The apparent absence 

of the pesticides in deep 

ground water may relate to 

chemical changes or breakdown of the pesticides to 

other products. Desethylatrazine, a breakdown product of 

atrazine, was detected in 

water samples from a few 

wells at depths as great as 

70 feet below the water table. 

Atrazine was not detected in 

several water samples in 

which the breakdown product 

desethylatrazine was detected. 

These breakdown products 

probably were derived from 

applications of atrazine in distant farmland in the past, 

perhaps during its early use 

in the late-1950's and 1960's 

in the peninsula. 

EMERGENCE OF CROPS. 

HOW DOES A TRAZINE IN THE DELMARVA PENINSULA 

AND IOWA COMPARE? 

[Atrazine, commonly used on corn, was the most frequently detected pesticide in rural ground 

water in both the cornbelt State of Iowa and in the Delmarva Peninsula. Atrazine was detected 

at a similar frequency in wells tapping the aquifer less than 50 feet below land surface, and 

most of the concentrations were below the national maximum contaminant level for drinking 

water established by the U.S. Environmental Protection Agency.] 

Number of wells tapping the aquifer 

less than 50 feet below the 

surface: 

Percentage of wells with atrazine 

detections greater than 0.13 

micrograms per liter2 : 

Percentage of wells with atrazine 

concentrations greater than the 

national maximum contaminant 

level for drinking water, 3.0 

micrograms per liter: 

Maximum atrazine concentration, in 

micrograms per liter: 

Delmarva Peninsula 

89 

4.5 

1.1 

11.0 

Iowa' 

192 

5.2 

1.6 

6.6 

'The Iowa State-Wide Rural Well-Water Survey, Iowa Department of Natural Resources, 

November 1990 

'A higher detection level was used in the Iowa study 10.13 micrograms per liter) than in the 

Delmarva Peninsula NAWOA study 10.05 micrograms per liter) because of differences in 

laboratory techniques; therefore, only detections in ground water in the Delmarva Peninsula 

above 0.13 micrograms per liter are cited in this table. Differences in sampling times, climate, 

soil type, hydrology, anq land use may affect the comparison between the two studies. 
12 

Agricultural applications 

of lime, inorganic fertilizers, 

and manure have changed the 

natural composition of water 

in the water-table aquifer in 

large areas of the peninsula, 

and nitrate has become one of 

the major constituents in the 

water. Nitrate concentrations 

exceed the maximum contaminant level for drinking water 

of 10 milligrams per liter in 

about 15 percent of the wells 

that tap the water-table aquif~ 

er, and pose a health risk for 

residents who drink this 

water. Nitrate does not pose 

a health risk for residents who 

drink water from the deeper 

and relatively uncontaminated 

confmed aquifers. However, 

there is a long-term concern 

that contaminated water might 

move from the water-table 

aquifer down to the underlying confmed aquifers, which 

are the chief source of publicwater supply in the peninsula. 

Nitrate contamination in the 

deep aquifers is a major problem for water-resource managers on Long Island, New 

York-an area that is similar to 

the Delmarva Peninsula in 

hydrology and topography. 

A more immediate concern is the effect of elevated 

nitrate concentrations in 

ground water on the Chesapeake Bay and its ecosystem. 

Recent studies have shown 

that the contribution of 

ground water to this immense 

estuary might be similar in 

quantity to that of a major 

tributary, such as the James 

IMPLICATIONS OF 

OF WATER QUALITY 

FIN I 

ON 

River in Virginia. Increased 

concentrations of nitrate can 

contribute to excessive growth 

of algae whose subsequent 

decay results in a decline in 

dissolved-oxygen in the water. 

Low dissolved oxygen concentrations can harm fish and 

shellfish that are ecologically 

and economically important 

to the Bay. 

Many local, State, and 

Federal programs have been 

implemented to monitor and 

protect surface water (including the entire Chesapeake 

Bay) and ground water from 

NITRATE : IS THERE A CONCERN? 

What do these results mean to 

residents who drink the water? 

What are the other concerns ? 

Potential concern to residents who drink 

water from wells in the water-table 

aquifer. 

Long-term concern that contaminated 

ground water might move from the 

water-table aquifer to the underlying confined aquifers. 

Little to no concern to residents who 

drink water from wells in the underlying confined aquifers. 

Potential effects of elevated nitrate concentrations in ground water on the 

Chesapeake Bay and its ecosystem. 

potential nitrate contamination. These programs include 

the protection of marshes and 

wetlands, crop-management 

strategies, and wellhead protection strategies. Patterns of 

ground-water flow and land 

use are important considerations in the implementation, 

management, and evaluation 

of these programs (see inset). 

Rates and paths of groundwater flow, as well as character of the land in which the 

ground water originates, can 

substantially affect improvement efforts. 

Patterns of ground-water 

flow and land use also are 

important factors in the distribution of pesticide contamination in the peninsula. For example, in most cases in which 

pesticides were detected, the 

sampled water was within 20 

feet of the water table. These 

samples generally reflect 

overlying farmland, used to 

grow com and soybeans, that 

is within 100 to 200 feet of the 

well. Breakdown products of 

selected pesticides were detected in some water samples 

at depths as great as 70 feet 

Ground-water contribution to the Chesapeake 

Bay is seemingly invisible but may be the equivalent to that of a major tributary, such as the James 

River in Virginia. Ground water, like surface 

water, can carry excessive nutrients from farmers' 

fields, urban areas, and residential developments 

which routinely deprive the Bay of the oxygen 

needed to support more than 2,700 species of 

plants and animals. It is now time to consider the 

role of ground water in the decline of this fragile 

and immense national treasure. 

Charles Spooner, U. S. Environmental Protection Agency, 

Deputy Director of the Chesapeake Bay Program 

THE C HE S APEA KE BA Y AT SUNSE~ 
\IGS ON MANAGEMENT 13 

E D E .L M A R V A P E N I N S U L A 

LITTLE IS KNO W N ABOUT THE EFFECTS OF LONG-TERM 

E X POSURE OF AQUATIC PLANTS AND AN IM ALS TO GROUND 

WATER THAT CONTAINS LOW CONCENTRATIONS OF 

PESTICIDES. 

PESTICIDES: IS THERE A CONCERN? 

Mat do these results mean to residents who drink the water? 

Mat are the other concerns? 

Minimal health risk from agricultural 

pesticides for residents who drink 

ground water in the Delmarva 

Peninsula. Pesticides were detected 

at very low levels; 94 percent 

of those detected were less than 

U.S. Environmental Protection 

Agency maximum contaminant and 

health advisory levels for drinking 

water. 

Unknown health risk's of pesticide 

breakdown products and of pesticides in combination with each 

other. 

Undefined presence of homeowner and 

agricultural pesticides for which 

water samples were not tested. 

Unknown environmental effects of low 

concentrations of pesticides in 

ground water on the Chesapeake 

Bay and other surface water. 

Inadequate information on historic and 

current use of pesticides. 

below the water table. An 

understanding of the groundwater-flow and land-use patterns can help water-resource 

managers to identify areas 

most likely to be affected and, 

thus, be useful for optimizing 

resources required for monitoring pesticides (see inset). 

Most of the pesticides 

were detected at very low 

concentrations, and concentrations of 94 percent of those 

detected were less than U.S. 

Environmental Protection 

Agency maximum contaminant and health advisory 

levels for drinking water. On 

the basis of these levels for 

the compounds tested and 

analyzed, the findings suggest 

that there is no immediate 

peninsula-wide health risk to 

the residents of the Delmarva 

Peninsula who drink ground 

water. There are some further 

considerations, however. The 

first relates to the breakdown 

products of the pesticides, 

which were only monitored in 

a limited number of wells 

because of the relatively new 

laboratory techniques used 

to measure them. Little is 

known about the chemical 

properties and possible health 

effects of these breakdown 

products. Additional sampling 

is needed to assess their distribution across the region, 

particularly in deep ground 

water. A second consideration 

involves the effects of pesticides in combination with 

each other. Concentrations of 

individual pesticides were 

generally less than U.S. 

Environmental Protection 

Agency maximum contaminant and health advisory levels for drinking water; however, possible health effects of 

combinations of these pesticides are unknown. A third 

consideration relates to the 

scope of the pesticides that 

were analyzed. Water samples 

were tested for about 40 pesticides for which laboratory 

techniques were available. 

Some commonly used agricultural pesticides, such as 

linuron, were not tested; the 

concentrations of these pesticides in ground water and the 

potential effects on the potability of ground water are 

unknown. In addition, most 

of the pesticides tested were 

designed to control weeds, 

insects, and fungi on agricultural land. Many of the 

pesticides commonly used by 

homeowners were not tested. 

The fourth consideration is 

the lack of information on the 

environmental effects of these 

chemicals when they ultimately discharge into surface 

water. Little is known about 

the long-term exposure of 

aquatic plants and animals to 

low concentrations of pesticides. A final consideration is 

the inadequacy of information 

on historic agricultural and 

residential use of pesticides, 

including the kinds used and 

the rates of application. Because of the typically slow 

movement of ground water, 

pesticides applied in the past 

can affect deep ground water 

for many decades. 
IMPLICATIONS OF FINDINGS ON 

MANAGEMENT OF WATER QUALITY 

ON THE DELMARVA PENINSULA 

IMPLICATIONS OF FINDINGS ON THE MANAGEMENT 

OF PROGRAMS THAT MONITOR AND PROTECT 

GROUND-WATER QUALITY 

CROP-MANAGEMENT PRACTICES: 

Changes in crop management are designed to reduce inputs of nitrate 

in farm fields. Reduction in nitrate will be slow, however, 

because of the slow rates at which ground water flows. The 

quality of water will improve first in near-surface parts of the 

water-table aquifer beneath farmland; decades might pass before 

quality improves in deep parts of the aquifer. 

WELLHEAD PROTECTION STRATEGIES: 

The appropriate recharge area needed to be protected depends on 

land use, the depth of the well, and ground-water flow. The 

quality of water in near-surface parts of water-table aquifer 

reflects land use in a recharge area usually within 100 to 200 

feet ofthe well; the quality of water in deep parts of the aquifer 

reflects land use at a distant recharge area. 

PROTECTION OF WETLANDS, MARSHES, AND WOODED 

AREAS ALONG STREAMS: 

Wetlands, marshes, and wooded areas along streams are protected 

to help maintain the quality of nearby surface waters and 

associated ecosystems. Deep ground water, however, frequently 

bypasses these areas and discharges directly to adjacent streams 

and bays. This deep ground water can, therefore, potentially 

degrade the quality of the surface water associated with the 

wetlands, marshes, and wooded areas. 

IMPLICATIONS OF FINDINGS ON PESTICIDE 

SAMPLING STRATEGIES: 

How to identify areas most likely to be affected in order to 

optimize limited resources for monitoring pesticides ... 

Commonly used pesticides are present in ground water near farmland 

used to grow com and soybeans-two crops that account for the 

highest pesticide use and most extensive acreage. Areas where 

ground water is most likely to contain pesticides could, therefore, 

be identified from available information on land and pesticide use 

and crop type. 

Nitrate, calcium, and magnesium are major constituents in water 

affected by agriculture. Relatively inexpensive analyses for these 

constituents could be used to help identify areas that might be 

vulnerable to other agricultural chemicals, such as pesticides. 

Pesticides are most common in water within 20 feet of the water table. 

Breakdown products of pesticides are in water in both shallow and 

deep parts of the water-table aquifer. An understanding of groundwater-flow patterns is useful for identification of the distribution 

of pesticides and their breakdown products in ground water. 

E xtensive agricultural 

land use on the Delmarva 

Peninsula has introduced 

nitrate and pesticides to 

ground water. This study has 

helped identify where the 

contamination is most likely 

to occur. The pattern of contamination depends on a 

number of factors, including 

crop type, geology, soils, 

land use, and ground-water 

flow. An understanding of 

these factors is critical to 

those individuals who make 

decisions about cropmanagement practices, landuse planning, and water 

management. Facilitating 

data exchange amol}g waterresource managers in agencies at the Federal, State, and 

local levels, as well as 

university researchers and 

extension personnel, is a 

major mission of the 

NA WQA Program, and will 

remain so for its duration. 

Communication and coordination among the USGS and other 

interested scientists and water-management personnel are important components of the NA WQA Program. To make best use of 

the resources available, we are committed to foster information 

exchange and cooperation among all relevant agencies through the 

duration of this long-term program. Every level of government and 

the private sector has a role to play. 

Philip Cohen, U.S. Geological Survey, 

Chief Hydrologist, Water Resources Division 
A COORDINATED EFFORT 

Coordination among agencies and organizations at all levels is essential to understanding effects of agricultural chemicals in ground water on the Delmarva Peninsula. This publication was coordinated with the following organizations: 

FEDERAL AGENCIES: 

U.S. Department of Agriculture 

Agricultural Research Service 

Economic Research Service 

Soil Conservation Service 

U.S. Army Corps of Engineers 

DELAWARE STATE AGENCIES: 

Delaware Geological Survey 

Delaware Water Resources Center 

Department of Natural Resources 

and Enviromental Control 

VIRGINIA STATE AND LOCAL AGENCIES: 

Accomack-Northampton Planning 

District Commission 

Department of Agricultural and 

Consumer Services 

Department of Mines, Minerals, and Energy 

Vrrginia Eastern Shore Soil and 

Water Conservation District 

Vrrginia Water Control Board 

Vrrginia Water Resources Research Center 

U.S. Department of the Interior 

Fish and Wildlife Service 

U.S. Environmental Protection Agency 

MARYLAND STATE AGENCIES: 

Maryland Department of Agriculture 

Maryland Department of the Environment 

Maryland Geological Survey 

Maryland Institute for Agriculture 

and Natural Resources 

UNNERSITY AND NONPROFIT 

ORGANIZATIONS: 

The Nature Conservancy 

University of Maryland, Department 

of Agricultural Engineering 

Virginia Polytechnic Institute 

and State University 

Much appreciation is extended to U.S. Geological Survey employees for their expertise in the production of illustrations 

by Leslie J. Robinson and James Q Whitmer; type composition by Shirlie A. McManus; and photography by David E Usher. 

Appreciation is also extended to those individuals and agencies that contributed photographs: 

Delaware Department of Natural Resources 

and Environmental Control 

Dwight Dyke, Richmond, Virginia 

Maryland Institute for Agriculture 

and Natural Resources 

Maryland Department of Agriculture 

Soil Conservation Service, U.S. Department 

of Agriculture 

Virginia Eastern Shore Soil and Water 

Conservation District 

15 
FOR ADDITIONAL INFORMATION· 

Many Federal, State, and local agencies and non-profit organizations involved with general ground-water research and regulatory 

functions have published numerous reports on ground water in the Delmarva Peninsula. The reports provide results of studies on 

movement of ground water, chemical quality of the water, and general ground-water resources. General information on water resources 

can be obtained by writing to: 

FEDERAL ORGANIZATIONS: 

U.S. Department of Agriculture, 

Soil Conservation Service 

U.S. Environmental Protection Agency 

Region 3, Ground Water Protection 

U.S. Geological Survey, Water 

Resources Division 

DELAWARE ORGANIZATIONS: 

Delaware Department of Natural 

Resources and Environmental 

Control 

Delaware Geological Survey 

Delaware Water Resoirrces Center 

MARYLAND ORGANIZATIONS: 

Maryland Department of Agriculture 

Maryland Department of the 

Environment, Water-Quality Program 

Maryland Geological Survey 

Maryland State Soil Conservation 

Committee 

University of Maryland, Department of 

Agricultural Engineering 

VIRGINIA ORGANIZATIONS: 

Accomack-Northampton Planning 

District Commission 

Department of Mines, Minerals, 

and Energy 

Virginia Department of Agricultural 

and Consumer Services, Pesticides 

Virginia Eastern Shore Soil and 

Water Conservation District 

Vlrginia Water Control Board, 

Ground Water Program 

Vlrginia Water Resources 

Research Center 

339 Revell Highway 

Annapolis, Md. 21401 

841 Chestnut Bldg. 

Philadelphia, Pa, 19107 

208 Carroll Building 

Towson, Maryland 21204 

P.O. Box 1401 

89 Kings Highway 

Dover, Delaware 19903 

University of Delaware 

Newark, Delaware 19716 

101 Hullihen Hall, U. of Del. 

Newark, Delaware 19903 

50 Harry S Truman Parkway 

Annapolis, Maryland 21401 

2500 Broening Highway 

Baltimore, Maryland 21224 

2300 St. Paul Street 

Baltimore, Maryland 21218 

50 Harry S Truman Parkway 

Annapolis, Maryland 21401 

1126 Shriver Laboratory 

College Park, Maryland 20742 

P.O. Box 417 

Accomac, VIrginia 23301 

Box 3667 

Charlottesville, Virginia 22903 

P.O. Box 1163 

Richmond, Vlrginia 23209 

P.O. Box 127 

Accomack, Va. 23301 

P.O. Box 11143 

Richmond, VIrginia 23230-1143 

617 N. Main Street 

Blacksburg, VIrginia 24060 

301-757-2872 

215-597-8826 

301-828-1535 

302-739-4556 

302-831-2834 

302-831-2191 

301-841-5770 

301-631-3572 

301-554-5503 

301-841-5871 

301-454-3901 

804-787-2936 

804-293-5121 

804-371-0152 

804-787-1251 

804-527-5203 

703-231-5624 

Additional information on the National Water-Quality Assessment Program can be obtained by writing to: 

Deputy Assistant Chief Hydrologist NAWQA Program 

U.S. Geological Survey 

National Center, 12201 Sunrise Valley Drive, MS 413 

Reston, Virginia 22092 

Suggested Readings: 

Bachman, L.J., 1984, Nitrate in the Columbia aquifer, central Delmarva Peninsula, Maryland: U.S. Geological Survey Water-Resources Investigations Report 

84-4322, 51 p. 

Cushing, E. M., Kantrowitz, I. H., and Thylor, K. R., 1973, Water Resources of the Delmarva Peninsula: U.S. Geological Survey Professional Paper 822, 58 p. 

Denver, J.M., 1989, Effects of agricultural practices and septic-system effluent on the quality of water in the unconfined aquifer in parts of eastern Sussex 

County, Delaware: Delaware Geological Survey Report of Investigations No. 45, 66 p. 

Hamilton, P.A., Shedlock, R.J., and Phillips, P.J., 1989, Ground-water-quality assessment of the Delmarva Peninsula, Delaware, Maryland, and Vrrginia: Analysis 

of available water-quality data through 1987: U.S. Geological Survey Water-Supply Paper 2355-B, 65 p. 

Robertson, F. N., N77, The quality and potential problems of the ground water in coastal Sussex County, Delaware: University of Delaware Water Resources 

Center, Newark, Delaware, 58 p.