For more than 100 years, the U.S. Geological Survey (USGS) has provided the 

information needed to manage the 

Nation’s earth resources, to mitigate geologic hazards, and to understand the environment. In Connecticut, the USGS 

works cooperatively with local, State, and 

other Federal agencies, as well as with 

universities, to study earth science.

Geologic Mapping

Geologic maps, which describe and 

delineate bedrock units, surficial deposits, 

and geologic structures, are fundamental 

tools necessary for analyzing earthrelated resources. Substantial cost savings 

can be realized by using geologic map 

information to site highways, structures, 

or landfills. Geologists from USGS have 

worked cooperatively with the Connecticut Geological and Natural History Survey (CGNHS) for many years to map 

Connecticut’s geologic units and natural 

resources. The STATEMAP component of 

the National Cooperative Geologic Mapping Program funded detailed mapping in 

the Rockville quadrangle during fiscal 

year 1996.

A key result of the USGS/State cooperation is a series of bedrock and surficial 

geologic maps for the State. Bedrock geologic maps describe the character and distribution of the bedrock that underlies all 

areas of the State. Surficial geologic maps 

describe the character, distribution, and 

thickness of the unconsolidated glacial 

and alluvial deposits that overlie the bedrock surface in most places. Maps at the 

1:24,000 scale are available for most 

quadrangles in the State; statewide maps 

at the 1:125,000 scale include the “Bedrock Geological Map” and the “Surficial 

Materials Map of Connecticut.”

Digital coverage of surficial materials 

units shown on the State map is available 

by quadrangle. An area near Hartford is 

shown in figure 1. The materials map has 

many uses, including water-resources 

evaluation and protection, engineering 

and construction projects, and slope-stability studies. 

USGS geologists, in cooperation with 

the CGNHS, are working on the “Quaternary Geologic Map of Connecticut and 

Long Island Sound Basin,” which is a 

geologic map that describes glacial 

deposits in terms of their depositional 

environment and geologic history.

Index of Subjects

Geologic Mapping 

Water-Data Collection

Topographic Mapping

Earth Science Information Centers

Contamination of Sediments in 

Long Island Sound

Channel Scour Potential at Bridges

Mineral-Resource Information

Urban Ground-Water Quality

Ground-Water Contamination in 

Fractured Rocks

Ecosystem Studies

Outreach

Water-Quality Trends

Figure 1. Surficial materials of the Hartford North quadrangle, Connecticut. Materials maps, 

such as this, are very useful for engineering and construction projects.

Sand and gravel

Sand

Fines

Sand overlying

fines

Alluvium

overlying fines

Till

EXPLANATION 72°44' 72°39'

41°46'

41°51'

Connecticut River

HARTFORD

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Earth Science in the Public Service
Water-Data Collection

Complete and accurate hydrologic data 

are needed by water-resource managers, 

engineers, planners, public safety officials, 

consultants, and researchers. To meet their 

needs, the USGS maintains a national network of data-collection stations. In Connecticut, there are currently about 75 

surface-water stations, 70 ground-water 

stations, and 33 surface-water-quality stations. Records of historical data, in some 

cases dating to 1905, also are maintained 

for additional locations.

About one-third of the surface-water 

stations in Connecticut use satellites or 

modems to transmit real-time data measurements of instantaneous discharge 

(the volume of water flowing in the river). 

These data are important for several reasons. Real-time measurements of high 

water are used by the National Weather 

Service and the Connecticut Department 

of Environmental Protection (DEP) to 

issue warnings during periods of flooding. 

Real-time measurements of low water are 

used to alert power and water companies 

when water supplies may become 

depleted. For example, during July 1995, 

when water levels throughout the State 

fell to very low levels, officials from 

water companies used the Survey’s realtime data to determine when certain 

pumps in well fields near rivers should be 

turned off. 

The USGS water-quality network in 

Connecticut, which is operated in cooperation with the DEP, provides data that are 

used to determine the quality of streams 

and lakes and trends in water quality, to 

demonstrate effects of management practices on water quality, and to highlight 

unforeseen changes in water quality. 

Water-quality data also are used by the 

State to monitor compliance with established water-quality standards. Stations 

are selected to provide data from different 

parts of the State or to represent different 

land uses. The station on the Connecticut 

River at Thompsonville monitors the largest drainage area (almost 10,000 square 

miles) and provides data on the quality of 

the river as it enters the State. Stations on 

the Salmon and the Shepaug Rivers provide data on more natural areas of the 

State, whereas stations on the Quinnipiac, 

the Naugatuck, and the Hockanum Rivers 

monitor urban areas. 

Topographic Mapping 

The National Mapping Program (NMP) 

of the USGS fosters partnerships with 

State and other Federal agencies to 

improve the effectiveness of data-collection activities, to maximize resource sharing, and to enhance availability of timely 

and accurate data to the public. The Program strives to ensure the availability of 

map data in graphic and digital form to the 

public. Among the most popular and versatile products of the USGS are 1:24,000-

scale topographic maps (1 inch on the map 

represents 2,000 feet on the ground). Connecticut is covered by 125 of these maps, 

which depict natural and cultural features 

of the landscape, such as lakes and 

streams, highways and railroads, boundaries, and geographic names. Contour lines 

are used to show the elevation and shape of 

the terrain. Digital cartographic data, 

which include boundaries, transportation, 

hydrography, and digital elevation models, 

are available statewide at the 1:24,000 

scale. 

Earth Science Information 

Centers

Earth Science Information Centers 

(ESIC’s) provide information about USGS 

programs, products, and technological 

developments to the public. The ESIC in 

Hartford was established under a cooperative agreement with the DEP. The University of Connecticut Map Library in Storrs 

also is a State ESIC. These offices provide 

information on earth science topics, such 

as cartography, geography, digital data, 

remote sensing, geology, geophysics, 

geochemistry, hydrology, geohydrology, 

aerial photography, and land use.

Contamination of Sediments in 

Long Island Sound

The USGS, in cooperation with the 

CGNHS and the DEP, is studying the contamination of sediments in Long Island 

Sound, which is a major urbanized estuary 

that lies near the most densely populated 

region of the United States. Sewage, 

wastes, and chemicals enter the Sound 

from direct discharges, river runoff, and 

the atmosphere; this has caused widespread contamination of bottom sediments 

and loss of habitat for bottom-dwelling 

(benthic) organisms and affects millions of 

people who use the Sound for recreational 

and commercial activities.

This study is part of a multidisciplinary, 

basinwide program to document the seafloor processes that control distribution of 

benthic habitats and sediment-related contaminants (fig. 2). This program uses 

unique USGS capabilities in sea-floor 

imaging, contaminant-transport modeling, 

and geochemical sampling. This study and 

other geological, geophysical, and mapping investigations of the continental margins of the United States and around the 

world are being conducted by the USGS at 

Woods Hole, Massachusetts. These studies 

address critical issues in environmental 

quality and preservation, geologic hazards 

and public safety, natural resources, global 

environmental change, and information. 

The long-range goals of the research and 

mapping efforts are to provide a comprehensive understanding of the geology, hisFigure 2. Portion of a high-resolution sidescan 

sonar mosaic obtained off the Connecticut coast 

in Long Island Sound. Dark tones on the image 

represent areas of weak acoustic backscatter 

produced by finer grained sediments; light tones 

represent areas of strong acoustic backscatter 

produced by courser grained sediments. 

Selected features that reflect natural processes 

and human influences are labeled on the image. 

[200 meters equal about 655 feet.]
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WATERBURY

NEW

LONDON

NEW HAVEN

BRIDGEPORT

Salmon R

Connecticut R

Thames R

Housato nic R

Shepaug R

Naugatuck R

Quinnipiac R

Farmington R

Hockanum R

Shetucket R

Quinebaug R

tory, and processes of the continental margins and to develop a predictive capability 

to determine the consequences of using the 

continental margins.

Channel Scour Potential at 

Bridges

Changes in stream channels and scouring of riverbeds near bridges is a widespread problem throughout the United 

States. To protect public safety, the USGS, 

in cooperation with the Connecticut 

Department of Transportation, assessed 

and evaluated channel stability and potential for scour at about 1,600 bridges in 

Connecticut that span waterways. The 

bridges range in size from simple span 

structures to multilane highways that carry 

thousands of vehicles every day, such as 

the Interstate 91 bridge over the Connecticut River in Windsor Locks. On the basis 

of this assessment, bridges with observed 

scour or high scour potential have been 

identified for detailed study.

Mineral-Resource Information

The USGS maintains two minerals data 

bases, the Mineral Resources Data System 

(MRDS) and the Mineral Availability System (MAS), that contain information on 

hundreds of thousands of deposits and 

mineral processing locations worldwide. 

The MRDS and MAS contain information 

on about 550 sites in Connecticut, including metallic and nonmetallic deposits. 

Information from MRDS and MAS assists 

Federal and State land-management agencies, regional planners, industry, and local 

governments in planning environmentally 

sound and economically viable mineralsrelated development. The data bases are 

the principal tools that the USGS uses for 

mineral-resource and mineral-related environmental research. CD-ROM’s of the data 

bases and other information from USGS 

minerals research are available to government agencies and the general public.

The USGS is compiling digital geological, geophysical, geochemical, and mineral-deposit data on Connecticut to 

delineate tracts that may contain different 

kinds of copper, lead, and zinc deposits. 

New geologic data indicate that there is the 

potential for kinds of mineral deposits that 

had not previously been found in the State.

Urban Ground-Water Quality 

Protecting the quality of the Nation’s 

streams, lakes, and ground water continues 

to be a high priority for many government 

agencies and the public. The National 

Water-Quality Assessment (NAWQA) Program was designed to describe the status 

and trends in the quality of the Nation’s 

ground- and surface-water resources and to 

provide an understanding of the natural 

and human factors that affect the quality of 

these resources. A NAWQA study is 

underway in the Connecticut, the Housatonic, and the Thames River Basins, which 

is a 16,000-square-mile area in the Northeastern United States that includes most of 

Connecticut. 

As part of the NAWQA Program, a 

detailed study of ground-water quality in 

urban areas is being done along a flowpath 

in the Hockanum River aquifer in 

Manchester (fig. 3). Water-quality samples 

are collected along the direction of 

ground-water flow—from upgradient 

recharge areas to downgradient discharge 

areas. Flowpath studies are designed to 

understand the spatial and seasonal variations in ground-water quality, to increase 

understanding of the natural processes and 

man-made factors that control groundwater quality along flowpaths, and to compare shallow ground- and stream-water 

quality under base-flow conditions. 

In Manchester, 14 observation wells 

were installed to determine concentrations 

of nutrients, pesticides, and volatileorganic compounds (VOC’s) in ground 

water. Preliminary findings show that concentrations of nitrate nitrogen (a nutrient), 

were elevated in water samples from 13 of 

the wells. Although no concentrations 

exceeded the U.S. Environmental Protection Agency (USEPA) maximum contaminant level (MCL) of 10 milligrams per liter 

(mg/L), concentrations ranged from 1.9 to 

5 mg/L. Potential sources of this nutrient 

include lawn fertilizers, animal wastes, 

leaking sanitary sewer lines, and rainfall. 

Also, at least one VOC was detected in 

water samples from 12 of the 14 wells. 

Trichloroethylene (a VOC) was detected at 

a level higher than the MCL (5 micrograms per liter) in four samples from one 

well.

Ground-Water Contamination 

in Fractured Rocks

Central Connecticut is underlain by a 

thick sequence of sedimentary rocks. 

Aquifers within these rocks provide water 

to single-family domestic, public supply, 

and industrial supply wells. The rocks do 

not yield much water; however, fractures 

in them store and transmit ground water—

from precipitation at the land surface 

through the subsurface to wells. At several 

sites in Connecticut, fractured-rock aquifers have been contaminated with hazardous substances.

To clean up contaminated aquifers, 

information on the factors that control the 

rate and direction of ground-water flow, 

such as the location of ground-water 

recharge and discharge areas, is needed. 

Hydrologists and geologists at the USGS, 

in cooperation with the USEPA and the 

Agency for Toxic Substances and Disease 

Registry (ATSDR), have used boreholeand surface-geophysical methods, surface- and ground-water surveillance, 

hydraulic testing, and computer modeling 

to identify fracture patterns and characteristics at several sites in Connecticut. The 

ATSDR is using the results of these hydrogeologic studies to assess potential exposure by citizens to hazardous materials.

Ecosystem Studies

The Biological Resources Division 

(formerly the National Biological Service) 

is participating in the Connecticut River 

Ecosystem Initiative, which highlights an 

ecosystem approach to resource management. Initiative activities include incorporating biological data into a geographic 

information system, inventorying the existing barriers to Atlantic salmon migrations, 

mapping the distribution of fish Figure 3. Major rivers and towns in 

Connecticut.
For More

Information

populations, and cataloguing information 

sources and data bases. In addition, the 

New England Gap Analysis program identifies significant ecological areas by overlaying maps of land cover and species 

occurrence onto maps of protected areas. 

The program, in cooperation with the DEP 

and the Connecticut Geological and Natural History Survey, is developing a highresolution map of the vegetation in central 

and western Connecticut in order to evaluate the efficiency of mapping methods for 

eastern deciduous forests in New England.

Outreach

The USGS has a long history of providing speakers and fieldtrip leaders for 

schools, colleges, scout troops, and other 

community groups. This outreach effort 

was expanded in 1995 when the USGS 

signed a Partners-in-Education agreement 

with Parish Hill High School Regional 

District #11 in the towns of Chaplin, 

Hampton, and Scotland. The goal of the 

Partnership is to improve the quality of 

education in earth and physical sciences 

and related subjects by assisting the school 

system in providing long-term, active 

learning projects related to the environment. USGS personnel participated in the 

school’s Environmental Technology Day 

and the Freshman Environmental Studies 

fieldtrip (fig. 4), conducted a local geology 

field trip, installed monitoring wells at the 

high school and elementary schools so students can study local hydrology, and supplying USGS teaching packages to 

teachers at several grade levels. 

Water-Quality Trends

Surface-water-quality data from 39 

monitoring stations in Connecticut were 

analyzed for trends for water years 1969 to 

1988. Specific conductance and concentrations of calcium, magnesium, chloride, 

dissolved solids, and total solids generally 

increased from 1975 through 1988 and 

indicate a general increase statewide in 

dissolved constituents in streamflow. 

Increasing trends in chloride concentrations were more numerous than any other 

dissolved constituents measured at the 

monitoring sites (fig. 5). The effects of 

increased urbanization, which include 

municipal and industrial wastewater, septic system leachate, and runoff from 

streets and highways, are possible causes 

for increases in chloride concentration.

Increasing concentrations of dissolved 

and suspended constituents, which indicate deterioration in water quality, have 

been detected in small, sparsely developed 

drainage basins that previously were considered to represent water quality that is 

relatively unaffected by human activities. 

Although typically small in magnitude, 

these changes may indicate increasing 

contamination from various nonpoint 

sources in the less developed areas of the 

State. 

Continued water-quality sampling 

since 1988 will permit further analysis of 

water-quality trends throughout the State.

USGS State representative

450 Main St., Rm. 525

Hartford, CT 06103

(860) 240-3060

Fax: (860) 240-3298

Email: dc_ct@usgs.gov

Additional earth science

information can be found by

accessing the USGS Home Page

on the World Wide Web at

http://www.usgs.gov/

For more information on

all USGS reports and products

(including maps, images,

and computerized data), call

1-800-USA-MAPS

The USGS provides maps,

reports, and information to help

others meet their needs to manage,

 develop, and protect America’s water,

energy, mineral, biological and land

resources. We help find the natural

resources needed to build tomorrow,

and supply the scientific understanding needed to help minimize or mitigate the effects of natural hazards

and environmental damage caused

by natural and human activities. The

results of our efforts touch the daily

 life of almost every American.

U.S. Geological Survey

Fact Sheet FS-007-96

Figure 5. Surface-water stations with 

increasing trends in chloride concentration, 

1981-88. Blue dots are stations with no 

significant trend.

Figure 4. A USGS employee describes 

sediment characteristics in a split-spoon 

sample to teachers and students from Parish 

Hill Regional High School. (USGS photograph)