GEOLOGICAL SURVEY CIRCULAR 674

Geologic and Hydrologic Maps for 

Land-Use Planning in the Connecticut Valley 

With Examples From the Folio of the 

Hartford North Quadrangle, Connecticut

Geologic and Hydrologic Maps for 

Land-Use Planning in the Connecticut Valley 

With Examples From the Folio of the 

Hartford North Quadrangle, Connecticut

By Fred Pessl, Jr., William H. Longer, and 

Robert B. Ryder

GEOLOGICAL SURVEY CIRCULAR 674

Washington 1972
United States Department of the Interior

ROGERS C. B. MORION, Secretary

Geological Survey

V. E. McKelvey, Director

Free on application to the U.S. Geological Survey, Washington, D.C. 20242
CONTENTS

Abstract ___________________________

'ntroduction _______________________

Objective _______________________

Earth-resource information ____________

Basic data ____________________

Resource-characteristic maps ____ ______

Resource evaluation _______________

Descriptions of resource-characteristic maps of 

the Hartford North quadrangle, Connecticut _____________________

Unconsolidated materials ___________

Bedrock geology ____________________

Depth to bedrock and contour map of the 

bedrock surface -__ _______ _____

Thickness of principal clay unit and thickness of material overlying principal clay 

unit _____________________________

Resources of coarse aggregate __________

Page 

1 

1

3

3

3

4

5

Page

Descriptions of resource-characteristic maps of 

the Hartford North quadrangle, Connecticut Continued

Natural land slopes and landforms __ 9 

Drainage areas _______ _ 9

Availability of ground water __ 9 

Depth to water table __ 9

Flood-prone areas _______ _ _ 10

Low flow of streams _________ _ 10

Maximum concentration of dissolved solids

in surface water _____ 10

Location of wells and test holes __ _ 11 

Sites of solid-waste storage and liquidwaste discharge __ 11

Sanitary and water-related facilities,

services, and use, July 1970 ____ _ _ 11

References cited ___ _ 11

ILLUSTRATIONS

FIGURE 1. Index map showing area of Connecticut Valley Urban Area Project and topographic quadrangle coverage _ _______ __ __ __ ___ - __ -

2. Flow chart showing procedure of resource evaluation for a sanitary landfill _____

Page

2

5

Geologic and Hydrologic Maps for 

Land-Use Planning in the Connecticut Valley

With Examples From the Folio of the 

Hartford North Quadrangle, Connecticut

By Fred Pessl, Jr., William H. Longer, and Robert B. Ryder

ABSTRACT

Decisions that affect land and water use require an 

understanding of the complex geologic and hydrologic 

systems that exist within the earth's crust. There is, 

therefore, a need for earth-resource information in a 

form that is easily understandable and readily available to planners and other decision makers responsible for land use and resource management. The U.S. 

Geological Survey's Connecticut Valley Urban Area 

Project is developing a flexible resource data base that 

is designed to supply such information. This data 

base is in the form of maps that present a single 

characteristic or a combination of related characteristics of the land surface, earth materials, or water 

resources at a common scale and in a simplified 

format.

The maps are prepared by interpretation of existing 

geologic and hydrologic maps and data available from 

ongoing cooperative programs between the U.S. Geological Survey and the State and from State programs. 

Map subjects include unconsolidated materials, depth 

to bedrock, depth to water table, thickness and distribution of extensive clay deposits, resources of aggregate, slopes, availability of ground water, flood-prone 

areas, and quality and quantity of surface water.

A single planning decision commonly involves information on several aspects of earth resources. Superposition of copies of two or more maps printed on 

transparent plastic may be necessary to provide the 

information needed for a specific planning problem. 

Combinations of these maps can be adapted to changing technological, economic, statutory, and social 

conditions.

INTRODUCTION

Decisions affecting land use and resource 

management are being made every day. These 

decisions frequently require an understanding

of the distribution and the physical and chemical properties of our earth resources, but the 

decisions are often made by people who are not 

trained in the earth sciences. There is, therefore, a need for earth-resource information presented in a manner that is understandable and 

useful to the general public. Several groups 

within the earth-science professions are attempting to provide for this public need. One 

such effort is the Connecticut Valley Urban 

Area Project (CVUAP) of the U.S. Geological 

Survey. The project area is shown in figure 1.

The Connecticut Valley was chosen as an 

urban area project largely because the existing programs for geologic and hydrologic mapping within a four-state area are an excellent 

source of basic natural-resource information. 

In Connecticut the (1) State-U.S. Geological 

Survey cooperative programs, (2) geologic 

mapping program of the State Geological and 

Natural History Survey, and (3) information 

from other State agencies such as the Department of Transportation and the Office of State 

Planning provide the essential basic data. 

Similar programs exist in Massachusetts. In 

Vermont and New Hampshire, U.S. Geological 

Survey State Geological Survey cooperative 

hydrologic programs have provided the basic 

data. Furthermore, in Connecticut the GeologySoils Task Force, a volunteer group of geologists, hydrologists, soil scientists, engineers, 

and planners representing State and Federal 

agencies and universities, was already studying
73-00' 

43*00'

VERMONT 

MASSACHUSSETT

MASSACHUSETTS

CONNECTICUT

42°00'

41-0730"

73°00'

VERMONT NEW HAMPSHIRE72* 07'30"

s

/ «

Gr'

\ *

\

NEW HAMPSHIRE 

MASSACHUSETTS

MASSACHUSETTS 

CONNECTICUT 42°00'

1,0 2p MILES

FIGURE 1. Index map showing area of Connecticut Valley Urban Area Project 

and topographic quadrangle coverage. The project area covers about 5,000 

square miles in parts of Connecticut, Massachusetts, New Hampshire, and Vermont. Hartford North quadrangle patterned.
the feasibility of integrating earth-science data 

for land-use planning in the Ellington quadrangle within the Connecticut Valley. CVUAP 

has been able to draw on the experience of this 

task force and some of the concepts and methods presented herein are derived from its 

work.

OBJECTIVE

The objective of the Connecticut Valley Urban Area Project is to provide geologic and 

hydrologic information to aid in planning and 

resource management. Some limitations are 

implicit in this objective.

We have chosen to present our resource information at two map scales, 1:24,000 (1 

inch = 2,000 feet) and 1:125,000 (1 inch = 

approx 2 miles). The 1:24,000 scale provides 

information for local (town) planning. The 

1:125,000 scale aids in regional and state planning. The difficulty in establishing precise 

ground locations for the data presented at 

these scales emphasizes the necessity of onsite 

studies in the planning and development process. For example, a circle that is 40 acres in 

area is about the size of a dime at 1:24,000 

scale. Therefore, our information is for planning purposes and must not be considered a 

substitute for detailed onsite investigations. 

Although the planning process can determine 

potentially favorable areas for a particular use, 

potential sites must be studied in detail.

Geologic and hydrologic data provide only 

part of the resource information necessary for 

effective planning. Information from the soil 

scientist, engineer, biologist, ecologist, meteorologist and other natural scientists and information on human resources must ultimately be 

integrated to form a satisfactory information 

base.

With these limitations in mind, we are producing a series of maps, each map showing a 

single earth-resource characteristic or combination of related characteristics. These maps are 

designed to be used by people directly involved 

in making land-use decisions. Insofar as possible, technical data are presented in nontechnical terms and the complex symbolism of standard geologic maps is simplified. The intent is 

to provide a flexible resource-data base that can 

be used for the widest possible range of decisions by people with diverse backgrounds, all

concerned with wise land use. The data base 

is made as flexible as possible so that it can 

respond to the great variety of today's planning problems and still remain relevant for 

future needs. We are not, therefore, making 

suitability maps that show areas suitable or 

unsuitable for a given land use suitable in the 

opinion of the map compilers. Such maps may 

appear attractive to those looking for a quick 

and simple dictate, but suitability is a complex 

judgment involving many factors, some of 

which are well outside the technical competence of the geologist or hydrologist. Suitability maps also tend to become outdated as 

soon as the assumptions defining suitability 

change. Such factors as technological capability, economics, statutory regulations, and 

social attitudes are all part of a suitability 

judgment. Today, many of these factors vary 

from place to place, and all of them can be expected to change with time; what is unsuitable 

today may well be suitable tomorrow, and vice 

versa. On the other hand, maps that directly 

show the physical and chemical characteristics 

of our earth resources do not reflect such limited judgments. They can be used in a variety 

of ways according to local or regional priorities and can easily be adapted to changing planning requirements.

EARTH-RESOURCE INFORMATION

Earth-resource map information may be divided into two groups basic data and resourcecharacteristic maps. For the purposes of illustration, basic data and resource-characteristic 

maps for a single 7 V-j-minute quadrangle in the 

project area, the Hartford North quadrangle, 

Connecticut, are discussed below. 

BASIC DATA

The basic data for the Hartford North quadrangle consist of a standard topographic quadrangle map at 1:24,000 scale, a U.S. Geological 

Survey geologic quadrangle map (Cushman, 

1963) at the same scale, a 1:62,500-scale map 

from a U.S. Geological Survey water-supply 

paper (Cushman, 1964), and subsurface information from water wells and test holes. The 

topographic map is the base for our resourcecharacteristic maps and provides important information on landforms, the drainage network, 

and the road system and buildings. The geologic map provides basic geologic information
such as the location of bedrock outcrops (solid 

rock exposed at the surface of the ground) and 

the general nature of the surface materials. 

Some of the technical terminology used on the 

geologic map creates problems for a nongeologist. For example, one unit on the geologic 

map of the Hartford North quadrangle (Gushman, 1963) is defined as "ice-contact stratified 

drift." This unit is mostly mixtures of sand 

and gravel in varying proportions, and for our 

purposes can be divided into map units of sand, 

sand and gravel, or gravel. Similarly, another 

unit, "lake-bottom deposits," can be defined as 

fine deposits which are predominantly fine sand, 

silt, and clay. The map from the U.S. Geological Survey water-supply paper (Cushman, 

1964) contains information on the water-bearing properties of the loose unconsolidated materials that overlie the bedrock and provides 

more specific information from selected test 

holes and water wells. This map, however, is 

a different scale (1:62,500) than the topograpic and geologic maps, so the information 

on this map must be adjusted in order to be 

useful at the scale of 1:24,000.

RESOURCE-CHARACTERISTIC MAPS

Resource-characteristic maps are made from 

the basic data. They show selected elements of 

the earth resources. Some elements play a relatively static role and others play a dynamic role 

in the geohydrologic system. Static elements 

such as bedrock geology, the nature and thickness of unconsolidated materials overlying bedrock, landforms, and slopes vary from place 

to place but remain virtually unchanged from 

season to season and from year to year unless 

altered by large-scale manmade excavation or 

filling, or by natural catastrophic events such 

as landslides, earthquakes, storms, and floods. 

At present, natural catastrophic events other 

than floods and storms are not of major importance in the Connecticut Valley. Where 

conditions have been extensively altered by man 

prior to the date of mapping, special map symbols identify and locate these changes.

Dynamic elements such as depth to water 

table and streamflow not only vary from place 

to place, but also vary significantly from year 

to year, season to season, and even day to day. 

Accordingly, the mapped distribution of such 

dynamic elements may either be shown for a

particular time and place, or may be expressed 

in some graphic or statistical summary that 

generalizes the expected effect of natural 

changes. Any manmade changes occurring 

after preparation of these maps may alter conditions significantly.

Resource-characteristic maps are the principal products of the Connecticut Valley Urban 

Area Project and deal with a variety of subjects. The following is a list of such maps published for the Hartford North quadrangle, 

Connecticut:

U.S. Gfol. Survey Misc. 

Geol. Inv. Map Subject

1-784 A (Pessl and Hildreth,

1972) ________ Unconsolidated materials.

B (Pessl and Langer,

1972) _________Bedrock geology.

C (Ryder, 1972b) ____Contour map of the

bedrock surface.

D (Handman and Hildreth, 1972) ____Depth to bedrock.

E (Langer, 1972c) ___ Thickness of principal

clay unit.

F (Langer, 1972b) ___Thickness of material

overlying principal 

clay unit.

G (Langer, 1972a) ___Resources of coarse

aggregate.

H (Barker, 1972) ____Landforms.

I (Barker and Stone,

1972) _________Natural land slopes.

J (Thomas, 1972a) ___Drainage areas.

K (Ryder, 1972a) ____ Availability of ground

water.

L (Handman, 1972) __Depth to water table.

M (Thomas, 1972b) __Flood-prone areas.

N (Olin, 1972) ______ Low flow of streams.

0 (Weiss, 1972a) _____ Maximum concentration of dissolved 

solids in surface 

water.

P (Hildreth and Keune,

1972) ________Location of wells and 

test holes.

Q (Weiss, 1972b) ____Sites of solid-waste

storage and liquidwaste discharge.

R (Office of State Planning, State of

Connecticut, 1972) __Sanitary and waterrelated facilities, 

services, and use, 

July 1970.

These maps are described in more detail below. All of these maps will not be prepared for 

each quadrangle in the project area. They are, 

however, examples of the kinds of maps that 

can be made for quadrangles throughout the 

project area, although the elements shown may 

vary from place to place because the geology 

may differ and the availability of information 

is not uniform. The maps are also available on 

transparent scale-stable material to facilitate
Depth to bedrock 

(0-10 ft)

Depth to water

table 

(0-10 ft)

Avallability

\

/

Current land use

Compos Ite # 1

Flood-prone 

areas

Composite # 2 N . Sewer service areas

Resources 

of aggregate

ExI sting 

waste-disposal sites

Slopes 

(greater than 15%)

FIGURE 2. Flow chart showing procedure of resource evaluation for a sanitary landfill using criteria suggested

in this paper as an example.

their use in various combinations depending on 

the nature of the planning problem at hand. 

RESOURCE EVALUATION

One way in which our information can be 

used by planners and other decision makers in 

evaluating earth resources for a particular 

land use is described below. The first step in 

this method of resource evaluation is to establish guidelines which define basic criteria such 

as the type of facility desired, the area of land 

required, limits of funding, and pertinent statutory regulations. Other guidelines which establish priorities on uses of resources, such as protecting potential water-supply areas or encouraging preservation of open space can also be 

formulated. Once these guidelines have been

established, the distribution of significant earth 

resources, in terms of the land use in question, 

can be determined by stacking the appropriate 

resource-characteristic map transparencies on 

one another. From the resulting composite 

map, areas where existing earth resources are 

incompatible with the intended land use can 

be identified. The remaining areas on the 

composite map indicate potentially favorable 

areas. Maps that identify protected resources 

or preempted land uses can be added to the 

composite. Where such resources or land uses 

coincide on the map with potentially favorable 

areas for the land use in question, decisions on 

priority of use or sequence of uses can be made. 

Figure 2 illustrates the use of several maps
that show the distribution of some of the 

factors that may affect the use of land for a 

sanitary landfill. In this example the following 

guidelines have been chosen:

1. A trench-fill operation is desired.

2. At least 25 acres is necessary.

3. Minimum depth of trench is 10 feet.

4. Cost must be minimized; that is, no funds 

can be used for special engineering-design 

modifications.

5. Conformity to all State and local statutes 

regulating location and operation of a 

sanitary landfill.

6. Protection of potential sources of ground 

water will have highest priority in cases 

of competing resources.

These guidelines have been established arbitrarily for the purposes of the example presented here. Other guidelines and other priorities could have been selected, and others probably would be selected in actual practice.

Regulations in many states define three of 

the resource limitations shown in the example:

1. Minimum distance between bedrock surface 

and the base of landfill (depth to bedrock) .

2. Minimum distance between high water table 

and the base of landfill (depth to water 

table).

3. Minimum distance from high-water mark

(flood-prone areas).

A fourth factor, slopes greater than 15 percent, 

is considered a limitation here because of potential increased costs for special erosioncontrol and access-road design in areas where 

slopes are greater than 15 percent. From composite 1 (fig. 2), potentially favorable areas for 

a landfill will appear as clear windows surrounded by areas in which incompatible factors 

occur.

The map showing availability of ground 

water identifies a protected resource under the 

established guidelines. The map showing resources of coarse aggregate identifies a resource 

which might be exploited prior to development 

of a landfill site. If an area is capable of supporting two potentially incompatible land uses 

(composite 2, fig. 2), such as an area where an 

aquifer occurs beneath a possible landfill site, a 

planning decision establishing some priority of 

use should be made. This may require additional detailed information such as the quality

and quantity of the available ground water. 

The resource-characteristic maps only identify 

the existing situation.

Other considerations in the planning process 

such as current land use, sewer-service areas, 

and existing waste-disposal sites can also be 

presented as maps and added to the analysis. 

Current land-use maps identify preempted land, 

such as industrial, commercial, and highdensity residential areas. Sewer-service areas 

near potentially favorable landfill sites might 

influence design criteria for the control and 

treatment of leachate from the landfill. Knowledge of existing waste-disposal facilities combined with data on low streamflow might influence the selection of future sites in order to 

minimize pollution of surface water.

The product of the analysis in this example 

is several potentially favorable areas for the 

location of a sanitary landfill. Many other possible areas have been eliminated from consideration because of incompatible or competing 

resources and land uses of higher priority. Detailed site investigations in the potentially 

favorable areas can now be efficiently planned 

with a minimum of wasted time and unnecessary cost. If site studies show that none of the 

areas are actually acceptable for development of 

a landfill, the planning process must begin again 

with a new look at the initial guidelines to determine what modifications are possible. The 

analysis can then be repeated within the framework of the revised guidelines.

The resource evaluation shown here is only 

an example of a suggested methodology, as not 

all considerations for successful location and 

operation of a sanitary landfill have been included. This method can also be applied to almost any other land-use planning problem. 

Many different resource factors should be considered for proper land-use planning; a flexible 

resource-data base can provide information 

that is essential to the planning process.

DESCRIPTIONS OF RESOURCECHARACTERISTIC MAPS OF THE 

HARTFORD NORTH QUADRANGLE, 

CONNECTICUT

UNCONSOLIDATED MATERIALS

(Map 1-784 A)

Unconsolidated materials are nonrenewable 

resources, composed predominantly of sand,
gravel, silt, and clay. These materials cover 

large areas in most regions and consequently 

are the earth materials most commonly involved 

in our everyday affairs. They must be used as 

necessary, but they should not be wasted and 

should, therefore, be an important consideration in many land-use decisions.

The nature of the unconsolidated materials 

and the slopes on which they lie determine the 

characteristics of agriculture soils. The characteristics of unconsolidated material can also 

determine (1) its suitability for construction 

materials, (2) engineering properties, and (3) 

capability for effective waste disposal. The 

three-dimensional distribution of unconsolidated materials below the water table is a 

critical factor in the occurrence and availability 

of ground water. The shape of the land in areas 

underlain by unconsolidated materials reflects 

the physical properties and origin of these materials and provides an important aesthetic element in natural settings.

Most unconsolidated materials are mixtures 

of different sizes of rock fragments. These 

fragments can be separated into three classes 

on the basis of size: coarse, sand-sized, and 

fine. The map units "gravel," "sand and gravel," "sand," and "fine deposits" as used on the 

unconsolidated materials map of the Hartford 

North quadrangle (Pessl and Hildreth, 1972) 

are defined by the percentage of each size class 

present in the deposit. For example, "gravel" 

is defined according to this system as a mixture 

of coarse and sand-sized particles containing 

50 percent or more coarse particles. Other map 

units, most notably till and swamp deposits, 

contain a wide range of particle sizes in such 

variable proportions that they are defined on 

the basis of origin as well as composition. Till, 

for example, is a material deposited primarily 

by glacier ice. It is composed of a heterogeneous mixture of boulders and stones with sand, 

silt, and clay in varying proportions. Some till 

is loose, sandy, and very stony. Other till is less 

sandy, less stony, and very compact. The two 

varieties of till are not differentiated on most 

maps, but they differ so significantly in physical properties that onsite investigations of till 

deposits are necessary for specific uses.

Areas where the land surface has been extensively altered by urbanization and development are shown by a gray pattern superimposed 

on the color for the natural unconsolidated 

material. Specific deposits of fill materials 

(map units af and aft) resulting from road 

building, landfills, and other major construction 

are also shown.

BEDROCK GEOLOGY 

(Map 1-784 B)

These maps show bedrock types (rocks having similar mineral composition) at and below 

the land surface. Structural characteristics of 

these rock units such as faults joints, strike and 

dip of inclined units, and boundaries between 

rock units are also shown. Each bedrock map 

differs in the ease with which the information 

presented can be used for planning purposes. 

These differences in part reflect the degree to 

which engineering properties of the bedrock 

units are included on the maps and in the 

reports.

For the Hartford North quadrangle, information from the published geologic map (Gushman, 1963) has been combined with data from 

wells and test holes and tunnels to show the 

various types of rock that occur in the area. 

Thickness, strike and dip, color, and general 

rock type are shown at localities where bedrock 

is exposed at the land surface. Color and general rock type are also given for the first rock 

layer beneath the unconsolidated materials at 

localities where drilling data are available.

DEPTH TO BEDROCK AND CONTOUR MAP 

OF THE BEDROCK SURFACE

(Maps 1-784 D and C, respectively)

Depth to bedrock is expressed in feet below 

the land surface and is a measure of the thickness of the unconsolidated material that overlies the bedrock. It is a limiting factor of 

special importance in planning for and designing storage facilities, foundations, industrial 

and municipal waste disposal systems, residential septic systems, municipal water services, 

tunnels, highway alinements, and utility corridors. Specific mention of depth to bedrock is 

made in many state regulations pertaining to 

sanitary landfills and septic systems.

Map 1-784 D (depth to bedrock) was prepared from records of water wells, test holes, 

structure borings and trench lines, together 

with projections from the topographic surface
and interpretations of geologic history. The 

map shows areas where the thickness of unconsolidated material overlying the bedrock is 

within stated ranges. These ranges in thickness reflect the degree of accuracy of the available data.

The contour map of the bedrock surface 

(map 1-784 C) shows, by contours in feet 

above or below sea level, the shape of the bedrock surface.

THICKNESS OF PRINCIPAL CLAY UNIT AND

THICKNESS OF MATERIAL OVERLYING

PRINCIPAL CLAY UNIT

(Maps 1-784 E and F, respectively)

The principal clay unit may consist of a 

thick, massive bed of relatively pure clay, or it 

may occur with discrete layers of silt and very 

fine sand. The upper layers of the clay unit 

commonly grade upward into layers of silt and 

very fine sand. The properties of clay are distinctive where it occurs in extensive or thick 

deposits, the possible effects on land use should 

be considered. When wet, clay may become exceedingly mobile under even slight stresses and 

thus creates problems of landsliding, foundation 

failure, uneven settling, and other engineering 

problems. In addition, clay has a relatively low 

permeability water or liquid wastes move 

through it very slowly. Production of ground 

water is generally low from saturated deposits 

of clay and other fine-grained materials. Precipitation does not soak readily into the ground 

in areas of near-surface clay, often resulting in 

temporary ponds and wet ground in flat areas. 

Rapid runoff is common in sloping areas underlain by clay and may cause serious problems of 

flash flooding. On the other hand, the low permeability of clay and its potential for renovating some kinds of liquid waste may make it 

suitable host material for some waste-disposal 

sites. Clays are also a source material for 

bricks, expanded aggregate, and other construction materials. Clay, therefore, may be a 

limitation or extra-cost factor in the development of land for some uses, a favorable factor for other uses, or a potentially exploitable 

mineral deposit.

The thickness of unconsolidated material 

overlying clay deposits is an important consideration. Substantial thicknesses of material 

overlying clay may allow the founding of a

structure in these overlying materials. Where 

the overlying material is thick and easily 

worked, it may provide cover material for a 

landfill operation in which the host material is 

the clay deposit. Areas with thin deposits overlying clay are potentially favorable for extracting clay at minimum cost for stripping.

Clay maps are prepared with information 

from geologic and topographic maps, and with 

information from wells, test holes, structure 

borings, and other sources of subsurface data. 

Most extensive clay deposits in the project area 

occur as lakeJbottom sediments laid down in the 

relatively quiet waters of former or present 

lakes. An understanding of the geologic history 

and of the geologic and hydrologic processes are 

important elements in the preparation of such 

maps. The contour intervals shown on the maps 

are chosen according to the accuracy and distribution of the available data.

RESOURCES OF COARSE AGGREGATE

(Map 1-784 G)

This map shows the distribution of resources 

of coarse aggregate compiled from the unconsolidated materials map and from other sources 

such as highway department aggregate surveys 

and limited field observations. No information 

is given about value, quality, or quantity of the 

aggregate. Such information should be obtained from onsite investigations. The texture 

of coarse aggregate shown on this map is variable and some areas may contain as much as 

75 percent sand.

Availability of coarse aggregate is a critical 

cost factor in many construction projects. Location of deposits close to market areas is important. Construction aggregate is obtained 

from naturally occurring sources such as sand 

and gravel deposits and from quarrying and 

crushing certain kinds of bedrock such as basalt 

(traprock).

As urban and suburban development increases, the need for construction aggregate 

also increases. However, the future use of sand 

and gravel deposits and traprock for construction aggregate is likely to be increasingly restricted through zoning regulations and regulations pertaining to the operations of processing 

plants. Residential housing and commercial 

and industrial developments built on sand and 

gravel deposits further restrict exploitation of

8
this resource. Planning decisions which are 

based on knowledge of the distribution of this 

important resource and on concepts of multiple 

use may permit extraction of this resource prior 

to other types of land use.

NATURAL LAND SLOPES AND LANDFORMS

(Maps 1-784 I and H, respectively)

Slope maps characterize areas of the land surface in terms of their prevalent slopes. The 

slope units are chosen to emphasize ranges relevant to land use. Use of the land and the cost 

of developing land are strongly influenced by 

slopes. Restrictions on alinements and cost of 

construction are generally less in areas of gentle slopes. Special construction practices and 

foundation designs are commonly necessary for 

development of residential and commercial 

buildings in areas of steep slopes and rugged 

topography. Some steep slopes and some areas 

where slope values change abruptly over short 

distances, especially where vegetation is sparse, 

are subject to intense erosion. Accumulations 

of rock fragments (sliderock or talus) are common in rocky areas with very steep slopes. Septic systems require special design modifications 

in areas of steep slopes.

A landform map showing shape elements of 

the landscape, complements the slope map and 

provides a different picture of the terrain. Individual landforms are seldom well displayed on 

slope maps. A hill, for example, may be composed of several slope units and may be obscured as a unified element of the landscape. 

The landform map shows areas that differ with 

respect to relief, altitude, shape, and slope.

DRAINAGE AREAS

(Map 1-784 J)

This map shows drainage areas that contribute streamflow to selected sites on streams. 

Drainage areas shown have not been adjusted 

for the changes man has made in the natural 

regimens such as diversion dams, canals, and 

tunnels.

The drainage areas, in square miles, shown 

on the map are the total of as many as several 

hundred component areas upstream from the 

selected site. The area, in square miles, of individual component drainage areas can be determined by subtracting the area of the site next 

upstream from the area at the site of interest.

The selected sites shown on the map include 

stream-gaging sites, outlets of surface-water 

impoundments, surface-water sampling sites, 

mouths of tributary streams, and supplemental 

sites. Supplemental sites include highway and 

railroad bridges, outfalls from sewage-treatment plants, and main stems of streams immediately upstream from mouths of tributary 

streams.

The size and location of drainage areas can 

be used in a regional streamflow analysis for 

the design of water-supply and waste-disposal 

facilities and to determine the flow direction of 

wastes discharged at a point on the land 

surface.

AVAILABILITY OF GROUND WATER

(Map 1-784 K)

The availability of ground water is expressed 

in terms of yields that can be expected from 

properly developed individual wells that tap unconsolidated and consolidated earth materials.

The map is a generalization of several hydrogeologic factors. Consequently it provides only 

a planning guideline that shows the relative 

availability of ground water from place to 

place. It does not describe the absolute quantities of ground water available. The map should 

not be used in lieu of detailed test drilling and 

hydrologic investigations at specific sites, because well yields can be affected by local variations in the materials of the aquifer, as well as 

mutual interference effects between closely 

spaced wells and effects of boundary conditions 

such as the location of streams and abrupt 

changes in water transmitting characteristics.

DEPTH TO WATER TABLE

(Map 1-784 L)

The water table is an uneven surface below 

which earth materials are completely saturated 

with water. The water table intersects the land 

surface in almost all natural surface water 

bodies, and when a hole excavated in earth materials is extended below the water table, water 

will rise in the hole to the level of the water 

table. Deepening the excavation generally will 

not significantly affect the vrater level in the 

excavation because deeper earth materials will 

always be saturated with water.

Depth to water table varies both areally and 

temporally. The water table is generally deep-
est below the land surface under hilltops and 

shallowest under broad valleys. It is exposed at 

land surface in swamps, ponds, lakes, and 

streams. At any site, the depth to water table 

fluctuates seasonally. It generally is closest to 

the land surface during late fall and early 

spring, and deepest below land surface during 

late summer and early fall. Seasonal fluctuations may range from tens of feet under some 

hilltops and upper hillsides to less than a foot 

under broad valleys. Accordingly, in areas 

where depth to water table is shown on the 

map to be 10 feet or less at least part of the 

year, depths may be within this range for the 

entire year or for only short periods during a 

year.

The depth to water table map is based on 

average precipitation. During two or more 

consecutive years of significantly below-average 

precipitation, the water table within areas mapped as 10 feet or less may be deeper than 10 

feet all year. In contrast, during two or more 

consecutive years of significantly above-average 

precipitation, the water table within areas mapped as deeper than 10 feet may be within 10 

feet of the land surface during some part of the 

year.

Manmade conditions can also affect the 

depth to water table. Extensive ground-water 

development, drainage of swamps and other 

long-term ground-water dewatering operations 

and long-term lowering of water levels in large 

impoundments can significantly lower the water 

table locally. In contrast, extensive irrigation, 

water-spreading operations, and long-term raising of water levels in existing or new impoundments can raise the water table.

FLOOD-PRONE AREAS

(Map 1-784 M)

Floods of different recurrence intervals can 

be shown on maps. Maps based on the 100-year 

recurrence interval show areas that have a 1 

in 100 chance, on the average, of being inundated in any year. Such maps are based on natural conditions adjusted for flood-retention and 

flood-prevention structures, channel improvements, and degree of urbanization existing as 

of the date of the map. Changes made by man 

after this date can affect the extent and the 

chances of inundation of the mapped floodprone area. Changes such as additional paved

areas, installation of storm sewers, and construction in the flood-prone area tend to increase the extent and chances of inundation. 

Changes such as additional flood-retention 

structures tend to decrease the extent and 

chance of flooding downstream of the structures, but tend to increase the extent and 

chance of flooding upstream. In contrast, channel improvements tend to decrease the extent 

and chance of flooding upstream of the channeled area, but tend to increase the extent and 

chance of flooding downstream.

LOW FLOW OF STREAMS

(Map 1-784 N)

This map shows the lowest average daily 

flow for a 7-consecutive-day period that has an 

average recurrence interval of once in 10 years. 

Generally such a 7-consecutive-day period occurs during late summer or early falJ- In terms 

of flow duration, daily flow equal to or greater 

than the mapped values has a 99 percent chance 

of occurring on any day in a year. The map is 

based on natural and manmade conditions as of 

the date of the map. Changes in conditions after 

this date can either increase or decrease the 

low-flow value at a given site. Changes such as 

new or additional releases from upstream impoundments and new or additional discharges 

from sewage-treatment plants and septic tanks 

tend to increase low flow. In contrast, changes 

such as new or additional upstream withdrawals from the stream or a nearby well field and 

new or additional areas served by storm sewers 

or paved tend to decrease low flow

MAXIMUM CONCENTRATION OF DISSOLVED 

SOLIDS IN SURFACE WATER

(Map 1-784 O)

The dissolved-solids concentration is the concentration, in mg/1 (milligrams per liter), of 

all mineral (inorganic) constituents dissolved 

in the water. The concentration is measured in 

a clear water sample either directly by chemical analysis or indirectly by electrical conductivity. The dissolved-solids concentration does 

not include the concentration of any dissolved 

organic material or suspended material such as 

silt and clay or any organic or inorganic material adsorbed on suspended material.

Information on the areal variability of dissolved-solids concentrations is helpful in planning the location of surface-water withdrawals,

10
particularly when low concentrations are required. For example the U.S. Public Health 

Service (1962) recommends, among other 

quality parameters, that the dissolved-solids 

concentration of water used for public supply 

not exceed 500 mg/1.

LOCATION OF WELLS AND TEST HOLES

(Map 1-784 P)

This map shows locations at which subsurface 

information is available. The data points are 

identified according to the filing system of the 

U.S. Geological Survey in Hartford and information from them can be retrieved by individuals with special interest. The subsurface data 

were used in compiling maps showing separate 

elements of the geologic and hydrologic conditions beneath the land surface. The map also 

shows the density of subsurface data and thus 

provides a partial measure of the reliability for 

resource maps based on the subsurface 

information.

SITES OF SOLID-WASTE STORAGE AND 

LIQUID-WASTE DISCHARGE

(Map 1-784 Q)

This map shows industrial and municipal 

facilities in existence or under construction in 

1968. The map locates solid-waste-storage and 

liquid-waste-discharge sites and identifies 

liquid-waste sites as municipal or industrial. 

The average daily discharge for liquid-waste 

sites is expressed in gallons. Liquid-waste is 

classified as (1) discharge to surface water, 

(2) discharge into the ground, and (3) discharge to surface water and into the ground.

The location of existing waste-disposal facilities may be an important consideration in 

decisions affecting future waste-disposal sites. 

Comparison of this map with maps showing 

drainage areas, surface-water quality, and low 

streamflow can help in determining potential 

pollution-loading effects from existing and proposed waste-disposal facilities.

SANITARY AND WATER-RELATED FACILITIES, 

SERVICES, AND USE, JULY 1970

(Map 1-784 R)

This map was prepared by the Connecticut 

Office of State Planning and identifies areas 

served by sewer systems and water utilities in 

July 1970. It also locates solid-waste disposal

sites, sewage treatment plants, incinerators, 

and identifies water-based recreational activities. Such information may help in determining 

the feasibility of integrating existing service 

facilities with proposed waste-disposal facilities, residential subdivisions, and industrialcommercial developments.

REFERENCES CITED

Barker, R. M., 1972, Landforms, Hartford North quadrangle, Connecticut: U.S. Geol. Survey Misc. Geol. 

Inv. Map 1-784 H.

Barker, R. M., and Stone, C. S., 1972, Natural land 

slopes, Hartford North quadrangle, Connecticut: 

U.S. Geol. Survey Misc. Geol. Inv. Map 1-784 I.

Cushman, R. V., 1963, Geology of the Hartford North 

quadrangle, Connecticut: U.S. Geol. Survey Geol. 

Quad. Map GQ-223.

 1964, Ground-water resources of north-Central

Connecticut: U.S. Geol. Survey Water-Supply

Paper 1752, 96 p. 

Handman, E. H., 1972, Depth to water table, Hartford

North quadrangle, Connecticut: U.S. Geol. Survey

Misc. Geol. Inv. Map 1-784 L. 

Handman, E. H., and Hildreth, C. T., 1972,. Depth to

bedrock, Hartford North quadrangle, Connecticut:

U.S. Geol. Survey Misc. Geol. Inv. Map 1-784 D. 

Hildreth, C. T., and Keune, C. H., 1972, Location of

wells and test holes, Hartford North quadrangle,

Connecticut: U.S. Geol. Survey Misc. Geol. Inv.

Map 1-784 P. 

Langer, W. H., 1972a, Resources of coarse aggregate,

Hartford North quadrangle, Connecticut: U.S.

Geol. Survey Misc. Geol. Inv. Map 1-784 G.

 1972b, Thickness of material overlying principal clay unit, Hartford North quadrangle, Connecticut: U.S. Geol. Survey Misc. Geol. Inv. Map 

1-784 F. 

-1972c, Thickness of principal clay unit, Hartford North quadrangle, Connecticut: U.S. Geol. 

Survey Misc. Geol. Inv. Map 1-784 E.

Office of State Planning, State of Connecticut, 1972, 

Sanitary and water-related facilities, services, 

and use, July 1970, Hartford North quadrangle, 

Connecticut: U.S. Geol. Survey Misc. Geol. Inv. 

Map 1-784 R.

Olin, D. A., 1972, Low flow of streams, Hartford 

North quadrangle, Connecticut: U.S. Geol. Survey 

Misc. Geol. Inv. Map 1-784 N.

Pessl, Fred, Jr., and Hildreth, C. T., 1972, Unconsolidated materials, Hartford North quadrangle, Connecticut: U.S. Geol. Survey Misc. Geol. Inv. Map 

1-784 A.

Pessl, Fred, Jr., and Langer, W. H., 1972, Bedrock 

geology, Hartford North quadrangle, Connecticut: 

U.S. Geol. Survey Misc. Geol. Inv. Map 1-784 B.

Ryder, R. B., 1972a, Availability of ground water, 

Hartford North quadrangle, Connecticut: U.S. 

Geol. Survey Misc. Geol. Inv. Map 1-784 Kl

11
 1972b, Contour map of the bedrock surface,

Hartford North quadrangle, Connecticut: U.S.

Geol. Survey Misc. Geol. Inv. Map 1-784 C. 

Thomas, M. P., 1972a, Drainage areas, Hartford North

quadrangle, Connecticut: U.S. Geol. Survey Misc.

Geol. Inv. Map 1-784 J.

 1972b, Flood-prone areas, Hartford North quadrangle, Connecticut: U.S. Geol. Survey Misc. Geol. 

Inv. Map 1-784 M.

U.S. Public Health Service, 1962, Public Health Service drinking water standards, 1962: U.S. Public 

Health Service Pub. 956, 61 p.

Weiss, L. A., 1972a, Maximum concentration of dissolved solids in surface water, Hartford North 

quadrangle, Connecticut: U.S. Geol. Survey Misc. 

Geol. Inv. Map 1-784 O.

 I972b, Sites of solid-waste storage and liquidwaste discharge, Hartford North quadrangle, Connecticut: U.S. Geol. Survey Misc. Geol. Inv. Map 

1-784 Q.

12

!NT: 2459-72