U.S. Department of the Interior

U.S. Geological Survey

USGS Fact Sheet 009-99

November 1999

Delaware

Water-Quality Assessment of the

Delmarva Peninsula

The effect of human activity on water

quality is an important and visible

national environmental issue. In

response to this concern, the U.S.

Geological Survey (USGS) is conducting the National Water-Quality

Assessment (NAWQA) Program, a

comprehensive assessment of water

quality in 59 large regions across the

Nation. The Delmarva Peninsula,

which contains most of Delaware, is

one of the study areas included in the

NAWQA Program. The USGS is

working with Federal, State, and

local agencies that conduct waterresources research, regulate water

quality, and manage water resources.

The Delmarva Peninsula study has

provided useful information on the

relation of water quality to residential

and agricultural land-use practices. In

1991, study results indicated that

concentrations of fertilizer-derived

nitrate in shallow ground water vary

across the region with differences in

geology, soil chemistry, and land use.

High concentrations of nitrate in

shallow ground water are more

common in upland areas, where soils

are well-drained and sandy, and land

use is primarily agricultural. Nitrate

currently in the Delmarva groundwater system will continue to discharge into streams through springs

and seeps for many years. Pesticides

were detected in the 1991 samples at

very low concentrations (less than 1

microgram per liter) in shallow

ground water from many wells near

agricultural fields. Pesticide concentrations were below detection limits

in samples collected in 1991 from the

lower part of the surficial aquifer in

the Delmarva Peninsula and in the

underlying confined aquifers (fig. 1).

A new NAWQA study, scheduled to

start in 1999, will build upon the

earlier results, and attempt to define

the relations between land-surface

properties and water quality. Factors

such as forest cover, types of agriculture, land-surface slopes, natural and

artificial drainage patterns, and

underlying geologic properties can

Figure 1. Generalized north-south geologic cross section of the Delmarva Peninsula, showing major aquifers.

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AND SALINE WATER 

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science for a changing world

have a significant effect on groundwater quality.

Environmental Studies at Dover

Air Force Base

Since World War II, Dover Air Force

Base in Delaware has been a center

for military air-cargo operations on

the East Coast of the United States.

The base has ground-water contamination resulting from past fuel

spillage, disposal of degreasing

solvents, and the burial of hazardous

materials in landfills.

The USGS is providing multidisciplinary technical assistance to

the U.S. Air Force to monitor soil and

ground-water contamination on the

base, and to assess ground-water-flow

rates and directions. The Air Force

remediation procedures approach the

problem in one of two ways: either by

retrieving the material from the

ground by pumping wells or excavating soil, or by allowing the contaminants to attenuate naturally as they

are transported by ground water

toward the boundaries of the base.

Attenuation processes include the

dilution and dispersion of contaminants in ground water to low levels,

adhesion of pollutants onto mineral

grains in the soil and rocks, and

microbial breakdown of hazardous

compounds into harmless chemicals.

At Dover Air Force Base, the USGS

is installing monitoring wells, sampling and analyzing ground water and

soil, determining the natural capacity

of geologic materials to attenuate

contaminants, and developing

computer models of ground-water

flow and pollutant transport on the

base. The results of these studies

have shown that natural attenuation

is a viable remediation process for

decreasing contaminant concentrations to levels considered acceptable

by the U.S. Environmental Protection

Agency (EPA) before the contaminants are transported beyond the

base boundaries.

Streamflow, Ground-Water, and

Water-Quality Information

Information about the amount and

quality of ground water and surface

water is vital to the citizens of

Delaware. Most of the water supply

in the urbanized northern part of the

State comes from surface reservoirs,

whereas drinking water in central and

southern Delaware is supplied

primarily by wells. Floods and

droughts affect agriculture and the

economy, and threaten public safety.

State, county, and local planning

officials use hydrologic data from the

USGS for water management and for

the design of roads and bridges.

The USGS operates a network of 15

long-term streamflow-gaging stations, 6 tidal gages, and numerous

water-level recorders in wells to

collect data needed for assessing and

evaluating hydrologic conditions.

Most of these gages are operated in

cooperation with the Delaware

Geological Survey (DGS), Delaware

Department of Transportation

(DelDOT), Delaware Department of

Natural Resources and Environmental

Control (DNREC), EPA, and the U.S.

Army Corps of Engineers. Streamflow data from many of these gages

are available in real time on the

World Wide Web.

Ground water in Delaware is produced from porous and permeable

geologic formations known as

aquifers that are separated by lowporosity, relatively impermeable

confining layers. Alternating layers of

confining units and aquifers dip

gently to the southeast below an

unconfined surface aquifer composed

primarily of sands and gravels (fig.

1). The quality of water in a well can

be affected by a number of factors,

including ground-water-flow paths

into the well and minerals within the

aquifer. The USGS is participating in

the Delaware Source-Water Assessment and Protection Program with

State, Federal, and local agencies, and

other interested parties to develop a

plan to delineate source areas in

Delaware and identify potential

sources of contamination.

The USGS is cooperating with DGS

and DNREC to address nutrient

loading through direct measurements

of surface water into Rehoboth,

Indian River, and Little Assawoman

Bays. USGS work with DelDOT

provides the State agency with

information on flood magnitude and

frequency, which is used in designing

and maintaining highway bridges.

Water-level measurements in natural

and created wetlands also are obtained for DelDOT to determine the

effect of road construction on marshy

areas and swamps.

Regional Assessment of Land-Use

Changes

The rapid increase of urbanization in

the United States has affected the

environment, leading to problems for

both the local urban population and

the global environment. Cities

Figure 2. USGS personnel install a

water-level gage in a dredge pond

near Dover Air Force Base.
Delaware

consume large quantities of energy

and produce concentrated pollution.

Decreased vegetation leads to climatic and atmospheric changes,

which together with higher noise and

physical stress levels affect human

health and animal habitat. Impermeable ground cover allows less infiltration of water and puts people and

property at risk from flooding.

To study the nature and effects of

urban growth, the USGS implemented the Urban Dynamics Program, in which the unique problems

of cities and their surrounding areas

are investigated. One of these study

sites is the Philadelphia-WilmingtonTrenton metropolitan area. This study

builds on earlier research that mapped

urban land-use change for the San

Francisco Bay area and the Baltimore-Washington region. USGS

researchers converted topographic

maps of the area dating from 1940 to

1990 to digital form to create a data

base of land-use change. The resulting data layers include those for

urban or built-up land, transportation,

hydrography, slope, and woodland

areas. The data base is used with

digital visualization techniques to

display urban growth over time and to

show the growth of the metropolitan

area. This provides a picture of the

urban dynamics in the PhiladelphiaWilmington-Trenton corridor.

The data are being applied to an

urban growth model that is calibrated

by comparing the modeled projections of urban expansion at chosen

years to the data base described

above. This model, developed by the

USGS and the University of California at Santa Barbara, will be applied

to other cities to predict potential

urban growth patterns. This study is

intended to assist those involved in

understanding the effects of historical

and future urban growth on regions

surrounding major metropolitan

areas.

An understanding of where and when

urban growth is likely to occur helps

planners anticipate and plan for the

mitigation of environmental impacts.

The Urban Dynamics Program is

intended to contribute information to

help solve problems involving urban

sprawl, ground water, patterns of

shifting land surface, and hydrologic

and climatic temperature models.

Horseshoe Crab Population

Monitoring in Delaware Bay

The horseshoe crab supports a fishery

of growing value in the Mid-Atlantic

region. In the Delaware Bay area,

horseshoe crab eggs constitute a

critical resource for migrating shorebirds, which stop every spring to

replenish energy reserves before

continuing on to breeding grounds in

northern Canada.

Horseshoe crabs also have commercial value stemming from their use as

bait and their use in medical research.

Increased harvesting of horseshoe

crabs during the past decade has

prompted concern for the sustainability of this valuable ecological and

commercial resource. In 1996, USGS

scientists began a study to determine

how and when horseshoe crabs used

beaches for spawning. The goal was

to develop a consistent sampling

procedure that would provide a

measurement for use in population

monitoring. The researchers found

considerable variation in spawning

activities associated with water depth,

tidal cycle, and moon phase. Preliminary analysis suggests that surveys

Figure 4. Horseshoe crab on the

beach.

Figures 3A and 3B. Areal changes around Philadelphia, Pa. from 1940 to 1990.

1940 1990

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PHILADELPHIA POPULATION HISTORY

Population (Millions)

Regional Assessment of Land Use Change

Mixed Urban

Other Urban

Forest

Water

1940

1990

Area Covered

Mixed Urban land is a mixture of residential, commercial, and industrial land. Other Urban land consists of golf 

courses, zoos, urban parks, cemeteries, waste dumps, water-control structures and spillways, and undeveloped 

land in an urban setting.
Printed on recycled paper

USGS office locations USGS State Representative

1289 McD Drive

Dover, DE 19901-4907

(302) 734-2506

FAX (302) 734-2964

USGS Home Page

http://www.usgs.gov

Reports and products

1-888-ASK-USGS

should be concentrated in the shallowest waters, and be carried out on

the higher of the two daily high tides,

immediately following a new or full

moon when tides are at their highest.

Effects of Snow Geese on Food

Resources for Migratory

Shorebirds

Populations of North American snow

geese are increasing, leading to high

winter concentrations of the birds at

several National Wildlife Refuges

along the Atlantic Flyway. Wintering

snow geese feed extensively on the

emergent shoots of marsh plants.

This feeding habit can dramatically

alter the plant communities of tidal

marshes and freshwater impoundments, and even convert large

vegetated areas to mud flats. Thus,

the geese may help to create the

kinds of habitats favored by migratory shorebirds. It is still uncertain,

though, how removal of vegetation

and disturbance of the soil surface by

snow geese affect the numbers and

availability of subsurface invertebrates upon which shorebirds feed.

At Prime Hook National Wildlife

Refuge in Delaware, USGS scientists

have been studying how the foraging

of geese affects habitat quality for

shorebirds. Preliminary results

suggest that invertebrate populations

may decrease in areas where geese

have foraged extensively. Invertebrate densities may remain low for

long periods of time due to reduced

rates of emergence and reproduction

of plants. These results are important

for wildlife managers trying to

maintain habitat for both geese and

shorebird populations.

Structural Geology in Delaware

USGS geologists are developing a

cooperative program with DGS

geologists to provide detailed information on the age, structure, and

distribution of deformed and metamorphosed sedimentary and igneous

crystalline rock types that make up

the Delaware Piedmont. Information

obtained from detailed structural

analyses, dating the time sequence of

events in the Earth’s history, and

determining the intensity of crustal

deformation will be integrated into

the 1:24,000-scale quadrangles being

mapped by DGS geologists. Integration of map and analytical data is

intended to provide a complete

picture of the complex crust that

underlies the State. This information

is important for understanding

ground-water movement, water

chemistry, source-water protection,

and potential geologic hazards.

Cooperative Programs

The DGS is the official point of

contact for cooperative programs

between the USGS and the State of

Delaware. The USGS is an active

participant on the Delaware State

Mapping Advisory Committee to help

DGS assess the cartographic and data

The USGS has 19

employees in Delaware

Dover

needs of the State. In cooperation

with the USGS, Delaware recently

became one of the first States to offer

full mapping coverage using digital

line graphs, which allow overlays of

different features such as land use,

roads, vegetation, and manmade

structures on a topographic base.

USGS activities in Delaware conducted in cooperation with other

agencies include water-resource data

collection and water-quality assessments. Past studies have included

water availability, ground-water-flow

modeling, investigation of potential

saltwater intrusion into aquifers,

relation of wetlands to surface- and

ground-water quality, and documentation of floods.

For information on geologic and

hydrologic reports published by the

State of Delaware, and to obtain

USGS map products (including

topographic maps, images, and digital

data) contact the Delaware Geological Survey, DGS Building, University

of Delaware, Newark, DE 19716,

(302) 831-2833, e-mail at

dgs@mvs.udel.edu, or visit their web

site at http://www.udel.edu/dgs/

dgs.html. Additional information

about USGS programs and activities

in Delaware can be found on the web

at: http://md.usgs.gov.