Figure 1. Generalized hydrogeologic framework of the 

glacial-aquifer system, Cortland County, New York.

Cosmos Hill

Carr Hill

Till

Bedrock

(fine sand, silt, and clay)

Bedrock

Unconfined sand and gravel aquifer

Confining unit

Confined sand and gravel aquifer

Bedrock

Hill

Hydrogeology and Simulation of GroundWater Flow in a Glacial-Aquifer System 

at Cortland County, New York

In Cooperation with Cortland County Soil and Water Conservation District

U.S. Department of the Interior Fact Sheet FS 054-03

U.S. Geological Survey April 2004

The City of Cortland and surrounding communities obtain water from a highly productive glacial-aquifer system 

that underlies the western part of Cortland County (figs. 1 and 2). The study area encompasses about 12 square miles 

and includes the Otter Creek-Dry Creek valley and parts of the West Branch, East Branch, and Tioughnioga River 

valley and surrounds the bedrock hill (figs. 1 and 2) in Cortland upon which the State College campus stands. 

This aquifer system has been designated as a “Primary Aquifer” by the New York State Department of 

Environmental Conservation and as a “Sole Source Aquifer” by the U.S. Environmental Protection Agency (EPA). 

The upper (unconfined) aquifer is highly permeable and close to 

land surface, which makes it highly susceptible to contamination. 

Potential sources of contamination include leaking petroleumproduct storage tanks, leachate from landfills and septic 

systems, road-deicing salts, agricultural pesticides 

and fertilizers, and chemical spills (such as solvents 

and degreasers) at commercial and industrial 

facilities. Protection of this aquifer system 

from contamination is critical to ensure a safe 

drinking-water supply for the area.

In 1989, the U.S. Geological Survey 

(USGS), in cooperation with Cortland 

County Departments of Health and 

Planning, began a 3 1/2-year study 

to define the hydrogeology of the 

glacial aquifer. The results of the 

study were published in Miller 

and others (1998). This Fact Sheet 

summarizes the results of that 

study and depicts the stratigraphy 

and model-generated areas that 

contribute ground water to wells. 
2

Figure 2. Location and principal features of study area, Cortland County, New York.

1

Boldface terms are explained in glossary

10'

HOMER

Bedrock Hill

CITY OF

CORTLAND

0

0

1

1 2

2 MILES

McGraw

Blodgett

Mills

9.5 miles

to Marathon

7'30" NEW

YORK

Cortland

County

Cortland

Fish

Hatchery

EXPLANATION

TOWN OF CORTLANDVILLE

TOWN OF VIRGIL

DIRECTION OF STREAMFLOW 3 KILOMETERS

Terrace Road

well field

City of Cortland

well field

Lime Hollow Road

production well

Fall Creek

Valley

TCE 

spill

site

Superfund

site

Area shown

in this figure Sewage-treatment

plant

A

A/

A A/

76o15' 12'30"

42o

37' 30"

35'

Base from U.S. Geological Survey 1:62,500 series:

Cortland (1903) and Groton (1903)

STUDY AREA

AQUIFER BOUNDARY

MUNICIPALITY BOUNDARY

GROUND-WATER DIVIDE

between Oswego River basin

and Susquehanna River basin

PRODUCTION WELL FIELD

LINE OF HYDROGEOLOGIC

SECTION

(section shown in fig. 3)

A supply well in Cortland aquifer

HYDROGEOLOGY OF THE GLACIAL-AQUIFER SYSTEM

The glacial-aquifer1 system in the Cortland area is 

bounded laterally by till-covered bedrock hills and beneath 

by the bedrock valley floor (figs. 1 and 3). It consists of 

an unconfined sand and gravel aquifer 40 to 80 feet thick 

that overlies a lacustrine confining layer 1 to 155 feet 

thick that, in turn, overlies a confined sand and gravel 

aquifer that ranges from 1 to 170 feet thick (figs. 1 and 3). 

The confining unit impedes vertical movement of ground 

water between the upper and lower aquifers in the middle 

of the valley, but the two aquifers are connected in many 

places along the valley walls where the confining layer is 

absent (fig. 3).
3

Figure 4. Positions of Valley Heads ice and 

of outwash deposits in the Tioughnioga River 

basin, Cortland County, New York.

VERTICAL EXAGGERATION X 20

DATUM IS NGVD OF 1929

0 1,000 2,000 FEET

0 500 METERS

Qosg

Qkm

WELL AND WELL NUMBER-- well number assigned by USGS

EXPLANATION KAME MORAINE - poorly sorted silt, sand, and gravel deposited during

Valley Heads episode

OUTWASH - stratified sand and gravel

LACUSTRINE DEPOSITS - stratified very fine

sand, silt, and clay

TILL - poorly sorted clay, silt, sand, and

stones

SHALE AND SILTSTONE

QUATERNARY AGE DEVONIAN AGE Qk

Qt

Dss

Qlsc

KAME DEPOSITS - hummocks composed of

stratified, poorly sorted silt, sand, and gravel

Qosg Qosg

Qkm

Qkm

A A/

West East

FEET

BEND INSECTION

Pond

Otter

Creek 1,250

1,200

1,150

1,100

1,050

1,000

950

900

850

326 20 329

110 320

378

381 400 402

Qk

Qt Qlsc

Qt

Water table

May 28-29, 1991

Dss

Qk Qlsc

Qk

Dss

Qk

Dss

Qt

Figure 3. Hydrogeologic section A-A′ (Line of section shown in fig. 2).

76o15' 76o05'

42o45'

1500

1500

1500

1500

1000

1500

1500

1500

1500

1500

1000

0

0

5 MILES

5 KILOMETERS

Base from U.S. Geological Survey,

1954, 1:250,000

1500

1500

1500

Marathon

Messengerville

Outwash drains 

south through

Tioughnioga 

River valley

42o30'

76o10'

Tully

OUTWASH DEPOSITS.- 

Dashes indicate direction

of meltwater flow

POSITIONS OF VALLEY 

HEADS ICE, hachures on 

ice side

Limit of

study area

City of 

Cortland

ONONDAGA CO

CORTLAND CO

CAYUGA CO TOMPKINS CO

1500 TOPOGRAPHIC 

CONTOUR.- Datum is 

NGVD of 1929

EXPLANATION

Area shown

in figure 1

GLACIAL HISTORY

Glaciers covered central New York several times 

during the Ice Age, or Pleistocene Epoch, which began 

around 1.6 million years ago and ended when the ice 

left the New York area about 10,000 years ago. A major 

readvance (Valley Heads readvance) and standstill of 

the ice in central New York between 14,000 and 14,900 

years ago resulted in the deposition of large amounts of 

sediment at the ice front. This material formed several 

types of deposits, one of which was a series of hummocky 

ridges that blocked several north-south-trending valleys. 

These ridges form a complex that extends across central 

New York and is known as the Valley Heads Moraine. 

Segments of the Valley Heads Moraine are found in the 

western part of the study area and in valleys to the north 

(fig. 4). The upper part of these segments consists of 

unsorted sediments, mainly coarse sand and gravel; the 

lower part consists of mostly fine-grained material such as 

till and lacustrine sand, silt, and clay (fig. 3).

The Valley Heads Moraine formed plugs in the major 

valleys; these plugs blocked the natural drainage and 

resulted in the formation of lakes. One such lake formed 

in the valleys of the Tioughnioga River basin. Upland 

streams and meltwaters from the glacier transported large 

amounts of sediment into the lake; the coarse-grained 

sediments (sand and gravel) settled near the water’s 

edge, whereas the fine-grained sediments (very fine sand, 

silt, and clay particles) were carried farther out into the 

lake, where they settled to form lacustrine (lake-bottom) 

deposits. These lacustrine deposits typically range from 

90 to 155 feet thick in the central parts of the valleys and 

pinch out along the valley edges (fig. 3). The lacustrine 

unit forms the bottom of the surficial (unconfined aquifer) 

and the top boundary of the confined basal aquifer in the 

study area (figs. 1 and 3).

The outlet of the lake (at Messengerville, fig. 4) was 

gradually lowered by erosion, and this lowering eventually 

allowed the lake to drain. Subsequent meltwater from the 

retreating ice developed a braided-stream system within 

the valleys, and large amounts of outwash sand and gravel 

(fig. 4) were deposited on top of the former lakebed 

(fig. 3). This outwash forms a wedge-shaped deposit that is 

more than 100 ft thick in the western part of the study area 

and thins eastward to the Tioughnioga River, where it is 35 

to 45 feet thick. The outwash and morainal sediments form 

the highly permeable unconfined surficial aquifer in the 

Cortland area.
4

Figure 5. Sources of recharge to the glacial-aquifer system at Cortland County, NewYork.

Large valley

Uplands

EXPLANATION

Terrace

River

Small upland

tributary

Large upland

tributary

B A

SAND AND GRAVEL

LACUSTRINE FINE SAND, SILT, AND CLAY

TILL 

BEDROCK

Reach of tributary stream that gains water from ground-water discharge

Reach of tributary stream that loses water to aquifer

SOURCES OF RECHARGE TO SAND AND GRAVEL AQUIFERS IN LARGE VALLEYS

Infiltration of precipitation that falls directly over the valley

Unchanneled runoff and (or) ground-water flow from hillsides

Regional ground-water flow through bedrock and till

Infiltration from tributary stream (see letters A and B)

A Recharge that moves laterally to river

B Recharge that moves downward to confined aquifer

Alluvial

fan

AQUIFER RECHARGE AND DISCHARGE

The unconfined aquifer receives recharge from 

three sources under natural (nonpumping) conditions— 

(1) infiltration of precipitation that falls directly on 

the aquifer, (2) upland sources, such as runoff from 

unchanneled hillsides and seepage from bedrock slopes 

that border the aquifer, and (3) seepage from tributaries 

that flow onto the aquifer (fig. 5). The aquifer receives 

additional recharge from (1) infiltration beneath recharge 

basins at an industrial site in the western part of the aquifer 

(fig. 6), and (2) induced infiltration from streams and 

ponds near the major pumping wells. The confined aquifer 

is recharged along the edges of the valley (fig. 5).

Water in the unconfined aquifer discharges (1) into 

the West Branch and main stem of the Tioughnioga River 

and, during seasonally high water-level conditions, to 

the lower reaches of Otter Creek, (2) to pumping wells, 

and (3) to springs that are the headwaters of Fall Creek 

valley in the western part of the study area (fig. 2). The 

study area contains four major pumping centers— the 

City of Cortland well field, the well field for the Town 

of Cortlandville on Terrace Road, a well for the Town 

of Cortlandville on Lime Hollow Road, and a purge well 

at the former typewriter plant in the western part of the 

study area (fig. 6). Most of the water pumped from the 

production wells is eventually routed to the sewagetreatment plant as wastewater (fig. 2), where it is treated 

and discharged into the Tioughnioga River.

SIMULATION OF GROUND- WATER FLOW

A numerical ground-water flow model was constructed 

through the computer program MODFLOW to calculate 

hydraulic heads (water-table elevations) in the aquifer 

system and to derive water budgets. The directions of 

ground-water flow can be inferred from the hydraulic 

heads calculated by the model. Ground water moves 

from areas of high head to areas of low head, and the 

direction of flow is controlled by local factors such as 

aquifer geometry, distribution of recharge, and location of 

discharge areas (streams, ponds, and pumping wells), all 

of which are represented in the model. Model simulations 

indicate that water in the unconfined aquifer moves 

laterally from the edges of the valley toward the center, 

then flows northeastward along the axis of the Otter CreekDry Creek valley, where it discharges to pumping wells, 

the West Branch Tioughnioga River, and the main stem of 

the Tioughnioga River.
5

Aquifer - A geologic formation, group of formations, or 

part of a formation that contains sufficient saturated 

permeable material to yield significant quantities of 

water to springs and wells. 

Confined aquifer (artesian aquifer) - An aquifer that is 

completely filled with water under pressure and that 

is overlain by material that restricts the movement 

of water. 

Confining layer (confining unit) - A body of impermeable 

or distinctly less permeable (see permeability) material 

stratigraphically adjacent to one or more aquifers 

that restricts the movement of water into and out of 

the aquifers. 

Contributing area - The area in a drainage basin that 

contributes water to streamflow or recharge to 

an aquifer. 

Discharge - The volume of fluid passing a point per unit of 

time, commonly expressed in cubic feet per second, 

million gallons per day, gallons per minute, or seconds 

per minute per day. 

Discharge area (ground water) - Area where subsurface 

water is discharged to the land surface, to surface water, 

or to the atmosphere. 

Drawdown - The difference between the water level in a 

well before pumping and the water level in the well 

during pumping. Also, for flowing wells, the reduction 

of the pressure head as a result of the discharge 

of water. 

Flowpath - An underground route for ground-water 

movement, extending from a recharge (intake) zone to 

a discharge (output) zone such as a pumping well or 

shallow stream. 

Glacial - Of or relating to the presence and activities of ice 

or glaciers. 

Lacustrine - Pertaining to, produced by, or formed in a lake. 

Moraine - A mound, ridge, or other distinct accumulation 

of glacial drift, deposited chiefly by direct action of 

glacier ice. 

Permeability - The capacity for transmitting a fluid; a 

measure of the relative ease with which a porous 

medium such as unconsolidated sediment can transmit 

a liquid. 

Recharge (ground water) - The process involved in 

the absorption and addition of water to the zone of 

saturation. 

Recharge area (ground water) - An area within which 

water infiltrates the ground and reaches the zone of 

saturation. 

Runoff - That part of precipitation or snowmelt that appears 

in streams or surface-water bodies. 

Till - Predominantly unsorted and unstratified drift, 

deposited directly by and underneath a glacier without 

subsequent reworking by meltwater, and consisting of 

a heterogeneous mixture of clay, silt, sand, gravel, and 

boulders. 

Unconfined aquifer - An aquifer whose upper surface is a 

water table free to fluctuate under atmospheric pressure. 

Upgradient - Of or pertaining to the place(s) from which 

ground water originated or traveled through before 

reaching a given point in an aquifer. 

RECHARGE AND DISCHARGE GLOSSARY

Water from the uplands is the largest source of aquifer 

recharge under average-recharge conditions and provides 

55 percent of total recharge; this includes seepage from 

upland streams that flow onto the aquifer (32 percent of total 

recharge) plus unchanneled runoff and ground-water inflow 

from uplands (23 percent, table 1). The second-largest source 

is precipitation that falls directly onto the aquifer (38 percent 

of total recharge). The greatest discharge from the aquifer 

occurs as leakage to streams (69 percent of total discharge, 

table 1); the second largest is to pumping wells (28 percent 

of total discharge).

AREAS CONTRIBUTING RECHARGE TO LARGE PUMPING WELLS

Contributing areas to major pumping wells were 

calculated through the computer program MODPATH, 

which computes hypothetical paths of imaginary “particles” 

of water moving through a simulated ground-waterflow system and their traveltimes (fig. 6). Pumping 

large quantities of water from an aquifer system causes 

a drawdown of water levels within the aquifer, and the 

drawdown decreases with increasing distance from the 

pumping well. The lowering of the water level by pumping 

causes ground water to flow to the well. The flowpaths, and 

the size and extent of the well’s contributing area depend 

on the hydraulic characteristics of the flow system, such as 

aquifer geometry, recharge rate, discharge rate, permeability

of aquifer material, and type of well construction, including 

location, pumping rate, and position and length of the screen. 

Contributing-area analyses were done for low-, average-, 

and high-recharge conditions. The analysis for low-recharge 

conditions (fig. 6) resulted in the largest contributing areas. 

The model-generated contributing areas are U-shaped, with 

the open end facing upgradient from the well, and extend 

over most of the unconfined-aquifer area upgradient from 

the wells (fig. 6). The City of Cortland municipal well had 

the largest contributing area of all wells simulated. Recharge 

from tributaries such as Otter Creek and the unnamed 

tributary north of Otter Creek were indicated to be sources 

of water to the city well; thus, evaluations of the quality of 

water pumped by the city well need to consider the water 

quality of these two streams. 

The largest contributing areas resulted from the lowrecharge condition; therefore, the low-recharge condition 

defines the “worst case” (largest area) that water managers 

will need to consider when evaluating potential sources of 

contaminants that may threaten the water supply. 
6

Figure 6. Model-calculated contributing recharge areas for major production wells during lowrecharge conditions, in the unconfined aquifer, Cortland County, New York.

Recharge 

lagoons

EXPLANATION

MODEL-CALCULATED CONTRIBUTING RECHARGE AREAS

Area contributing recharge to City of Cortland well no. 3

Area contributing recharge to industrial recovery well

Area contributing recharge to Town of Cortlandville

production well, Lime Hollow Road

Area contributing recharge to Town of Cortlandville

production well, Terrace Road

Boundary of ground-water-flow model

Production wellsIndustry purge well (former typewriter plant)

1 = City of Cortland

2 = Town of Cortlandville (Terrace Road site)

3 = Town of Cortlandville (Lime HolLow Road site)

1

3

2

0 0.5

0 0.5

1 MILE

1 KILOMETER

42o

37'

30"

42o

32'

30"

42o

35'

76o15' 76o10'

Otter Creek

Stupke

Pond

REFERENCE CITED

Miller, T.S., Sherwood, D.A., Jeffers, P.M., and Mueller, 

Nancy, 1998, Hydrogeology, water quality, and simulation 

of ground-water flow in a glacial-aquifer system, Cortland 

County, New York: U.S. Geological Survey WaterResources Investigations Report 96-4255, 84 p.

Budget component

Amount 

(ft3/s)

Percent 

of total

A. Recharge to the aquifer system

Precipitation on the aquifer 14.4 38

Upland sources

Seepage losses from tributary 

streams

12.2 32

Unchanneled runoff and groundwater inflow from uplands8.8 23

Ground-water inflow from valleys to

model area

.9 3

Infiltration at recharge basins 1.7 4

TOTAL 38.0 100

B. Discharge from aquifer system

Pumping wells 10.7 28

Discharge from aquifer to streams 26.1 69

Ground-water outflow from model area 1.2 3

TOTAL 38.0 100

Table 1. Steady-state water budget for glacial 

aquifer at Cortland, N.Y., for average-recharge 

conditions, May 28 through June 4, 1991. 

[ft 3 /s, cubic feet per second]

by Todd S. Miller

FOR MORE INFORMATION: 

Subdistrict Chief

U.S. Geological Survey

30 Brown Rd

Ithaca, N.Y. 14850 

This fact sheet and related information can be found on 

the world wide web at http://ny.usgs.gov