U.S. Department of the Interior

U.S. Geological Survey

Hydrogeologic Investigations by the U.S. Geological Survey at

the Former Fort Benjamin Harrison, Marion County, Indiana

Background

As part of the U.S. Department of

Defense Base Realignment and Closure

process, the former Fort Benjamin Harrison in Marion County, Indiana (called

“Fort Harrison” in this fact sheet), was

placed on the Base Closure List in 1991.

Property disposal and reuse activities

began when Fort Harrison was decommissioned in 1995; work continues

through 1999.

Fort Harrison was located on approximately 2,500 acres about 10 miles

northeast of downtown Indianapolis, Ind.,

in the City of Lawrence (fig. 1). Since

1903, the installation served as a major

training facility that at times included

schools, a hospital, and Army Finance

and Soldier Support Centers.

In 1996, the Army leased 1,700 acres

of woodland and recreational facilities

to the Indiana Department of Natural

Resources as Fort Harrison State Park.

Another 550 acres became privately

owned for industrial, commercial, and

residential purposes.

Hydrogeologic Investigations

During base closure, the Army initiated an evaluation of about 36 individual

sites at Fort Harrison for compliance

with Federal and State environmental

requirements. The U.S. Geological Survey (USGS) provided technical assistance

to the Army through hydrogeologic

investigations that examined:

• ground-water quality and groundwater flow at two closed landfills;

• surface-water/ground-water interaction near one closed landfill;

• hydrogeologic mapping of the thickness and horizontal extent of glacial

aquifers throughout Fort Harrison;

and

• ground-water age in these aquifers.

Water-Quality at Two Closed Landfills

The 29-acre east landfill (fig. 1) was

used by the Army for less than 10 years

during the 1950’s and 1960’s and was

closed in 1971. Property that included

the closed east landfill was deeded to the

City of Lawrence in 1974 and is currently

part of a park with baseball fields.

In response to uncertainty among area

residents about water quality near the

landfill, the Army requested the USGS

investigation in 1997 during the closure

of Fort Harrison. For the study, groups of

new monitoring wells were screened at

several depths around the landfill boundary. Two sets of water-quality data from

these wells indicated the landfill was not

having an adverse effect on streams or

aquifers in the area.

The Army operated the west landfill

(fig. 1) for about 50 years until 1991;

closure activities were completed in 1994.

The USGS provided monitoring of water

quality and ground-water flow from 1995

through 1997. Water from natural springs

along a streambank below the landfill

were sampled as part of the monitoring.

The analytical data indicated water quality at the springs was similar to that in

monitoring wells downgradient from the

closed west landfill and that the springs

were hydraulically connected with the

aquifer below the landfill. These findings

led to an additional study by the USGS

of the interaction of surface water and

ground water near the west landfill.

Surface-Water/Ground-Water Interaction

During 1996, the USGS collected the

following hydrologic data near the closed

west landfill: precipitation, evaporation,

ground-water levels, streamflow, flow at

springs, soil permeability and infiltration,

and hydraulic conductivity.

USGS Fact Sheet FS-105–99

April 1999

Prepared for the Department of Defense Environmental Conservation Program National Meeting, April 26-30, 1999, Tacoma, Washington

Figure 1. Location of the former Fort Benjamin Harrison, Marion County, Indiana.

39 40'

39 55'

86 15' 86 00'

Indianapolis

465

465

65

74

70

69

74

65

31

431

40

36

40

38th Street

White

River

Pleasant Run

Pogues Run

Fall

White

River

Creek

Post Road

56th Street

71 st Street 

70

INDIANA

Marion 

County

FORMER FORT BENJAMIN 

HARRISON

EXPLANATION

CLOSED EAST LANDFILL

CLOSED WEST LANDFILL

CITY OF LAWRENCE

0 1 2 3 4 5 KILOMETERS

0123 4 5 MILES

Base from U.S. Geological Survey digital data 1:1,000,000, 1983

Albers Equal-Area projection

Standard parallels 29 30' and 45 30'
Quick responses of ground-water

levels to precipitation indicated infiltration

through fractures and macropores because

permeability and infiltration were slow

through the soil cover and clay cap on the

landfill. Flow from the natural springs and

streamflow were affected by precipitation

and evaporation. Flow from the springs

contributed very little to streamflow.

Hydrogeologic Mapping

Previous site-specific studies initiated

by the Army provided data from numerous

monitoring wells completed in the upper

30 feet of glacial sediments at Fort Harrison. Deeper hydrogeology had not been

mapped because too few wells had been

installed to greater depths. The USGS

investigation in 1998 broadly defined the

thickness and horizontal extent of aquifers

within the glacial sediments at Fort Harrison and described horizontal and vertical

ground-water flow.

For the hydrogeologic mapping, nearly

continuous cores of sediment were

described at new, deep boreholes. New

monitoring wells were constructed, and

geophysical logs were made in the deep

wells. The new data were combined with

information from previous investigations

at Fort Harrison.

In a conceptual model of the hydrogeology (fig. 2), the glacial sediments are

vertically divided into shallow, middle, and

deep till units. Layers consisting predominantly of sand or sand and gravel are the

aquifers within the glacial till that is mostly

silty, sandy clay. Corresponding to the

shallow, middle, and deep till units were

the shallow, middle, and deep (called

“Fall Creek”) aquifers.

The shallow aquifer consists of vertically and horizontally discontinuous

layers. The middle aquifer, mapped as

continuous in the eastern part of Fort

Harrison, was found to be thickest near

the central part and thinnest toward the

east. Geologic logs indicated that the middle aquifer was discontinuous between the

central and western parts of Fort Harrison,

although a thick section of the aquifer also

was mapped near the western boundary.

The Fall Creek aquifer was found to be

as thick as 15 feet; however, only two

wells penetrated this aquifer. No data

were obtained for the Fall Creek aquifer

in the west, south, or central parts of

Fort Harrison.

Data from the two synoptic water-level

measurements indicated the predominant

direction of horizontal ground-water flow

in the shallow and middle till units beneath

the southeastern part of Fort Harrison was

northwest toward Fall Creek; this is the

only area with sufficient data to map

the horizontal-flow direction. Local flow

directions in the shallow and middle till

units near the two closed landfills were

toward surface streams.

These water-level data also indicated

the vertical flow of ground water was

downward from the shallow aquifer to

the middle aquifer and the Fall Creek

aquifer.

Ground-Water Age

The date of recharge of the water in

an aquifer is the year when the precipitation that replenished the aquifer became

isolated from the atmosphere; groundwater age is determined by the date of

recharge subtracted from the date when

the environmental tracer for age was

analyzed in a ground-water sample.

Estimates of ground-water age can be

used to assess the relative vulnerability of

an aquifer to contamination from sources

at or very near the land surface.

Tritium was used as the environmental tracer to estimate ground-water age.

Tritium is the radioactive isotope of

hydrogen with an atomic mass of three.

Tritium in water can originate from

natural radiation sources like cosmic

rays and from manmade sources like

nuclear-fusion bombs. Water molecules

containing the tritium atom, substituted

for the hydrogen atom, will follow the

same path as water molecules with no

tritium atoms. Therefore, tritium makes

a good age tracer for recharge because

it is unchanged by physical and biological

processes underground.

Prior to 1952, tritium originating from

natural cosmic rays was at a steady state

in precipitation. When above-ground testing

of nuclear-fusion bombs began in 1952,

manmade tritium was introduced into

the atmosphere and concentrations in precipitation peaked during 1963-64. Tritium

concentrations in ground water can be used

to detect if and when water was recharged

after the nuclear-bomb testing enriched

precipitation with tritium.

With qualitative interpretations of tritium

concentrations, the following judgments

were made about ground-water age (fig. 2).

In the shallow aquifer in the eastern and

central part of Fort Harrison, ground water

is mostly “modern” and the water is less than

10 years old; in some places, the modern

water is mixed with water that is as much

as 46 years old. In the middle aquifer and

the Fall Creek aquifer, ground water is more

than 46 years old. On the basis of relative

ground-water age, the shallow aquifer can

be considered to be highly vulnerable to

contamination from activities at the former

Fort Harrison; the middle aquifer and the

Fall Creek aquifer have a low vulnerability.

—by Martin R. Risch

For more information, please contact:

District Chief

U.S. Geological Survey

5957 Lakeside Boulevard

Indianapolis, IN 46278

(317) 290-3333

Indiana District Home Page:

http://in.water.usgs.gov

USGS Home Page:

http://www.usgs.gov

FALL CREEK AQUIFER

MIDDLE AQUIFER

SHALLOW AQUIFER SHALLOW TILL UNIT

MIDDLE TILL UNIT

DEEP TILL UNIT

BEDROCK AQUIFER

CARBONATE

Sand and gravel

Silty, sandy clay

Sand and

gravel

Figure 2. Generalized cross section showing conceptual model of the hydrogeology at the former

Fort Benjamin Harrison, Marion County, Indiana.

“Old” ground water

more than 46 years in age

“Young” ground water

 less than 10 years in age Land surface

WEST EAST

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