Hydrogeologic Investigations by the U.S. Geological Survey at the Former Fort Benjamin Harrison, Marion County, Indiana
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Prepared for the Department of Defense Environmental Conservation Program National Meeting, April 26-30, 1999, Tacoma, Washington Hydrogeologic Investigations by the U.S. Geological Survey at the Former Fort Benjamin Harrison, Marion County, Indiana 86 15' 86 00' 465 Background 39 55' 69 EXPLANATION 65 FORMER FORT BENJAMIN As part of the U.S. Department of HARRISON River 71 st Street Defense Base Realignment and Closure CITY OF LAWRENCE CLOSED EAST LANDFILL process, the former Fort Benjamin Harri- 431 son in Marion County, Indiana (called CLOSED WEST LANDFILL White 56th Street Creek 0 1 2 3 5 MILES 4 36 “Fort Harrison” in this fact sheet), was Fall Post Road Post placed on the Base Closure List in 1991. 0 1 2 3 4 5 KILOMETERS 38th Street 74 Property disposal and reuse activities 31 began when Fort Harrison was decom- 70 missioned in 1995; work continues through 1999. Run 40 Pogues Fort Harrison was located on approxi- Indianapolis Run mately 2,500 acres about 10 miles Pleasant northeast of downtown Indianapolis, Ind., 40 in the City of Lawrence (fig. 1). Since 74 1903, the installation served as a major River INDIANA training facility that at times included 70 465 schools, a hospital, and Army Finance 65 and Soldier Support Centers. White Marion 39 40' County Base from U.S. Geological Survey digital data 1:1,000,000, 1983 In 1996, the Army leased 1,700 acres Albers Equal-Area projection of woodland and recreational facilities Standard parallels 29 30' and 45 30' to the Indiana Department of Natural Resources as Fort Harrison State Park. Figure 1. Location of the former Fort Benjamin Harrison, Marion County, Indiana. Another 550 acres became privately owned for industrial, commercial, and residential purposes. Water-Quality at Two Closed Landfills The USGS provided monitoring of water quality and ground-water flow from 1995 Hydrogeologic Investigations The 29-acre east landfill (fig. 1) was through 1997. Water from natural springs used by the Army for less than 10 years along a streambank below the landfill during the 1950’s and 1960’s and was During base closure, the Army initi- were sampled as part of the monitoring. closed in 1971. Property that included ated an evaluation of about 36 individual The analytical data indicated water qual- the closed east landfill was deeded to the sites at Fort Harrison for compliance ity at the springs was similar to that in City of Lawrence in 1974 and is currently with Federal and State environmental monitoring wells downgradient from the part of a park with baseball fields. requirements. The U.S. Geological Sur- closed west landfill and that the springs vey (USGS) provided technical assistance In response to uncertainty among area were hydraulically connected with the to the Army through hydrogeologic residents about water quality near the aquifer below the landfill. These findings investigations that examined: landfill, the Army requested the USGS led to an additional study by the USGS investigation in 1997 during the closure of the interaction of surface water and • ground-water quality and ground- of Fort Harrison. For the study, groups of ground water near the west landfill. water flow at two closed landfills; new monitoring wells were screened at • surface-water/ground-water inter- several depths around the landfill bound- Surface-Water/Ground-Water Interaction action near one closed landfill; ary. Two sets of water-quality data from these wells indicated the landfill was not During 1996, the USGS collected the • hydrogeologic mapping of the thick- having an adverse effect on streams or following hydrologic data near the closed ness and horizontal extent of glacial aquifers in the area. west landfill: precipitation, evaporation, aquifers throughout Fort Harrison; The Army operated the west landfill ground-water levels, streamflow, flow at and (fig. 1) for about 50 years until 1991; springs, soil permeability and infiltration, • ground-water age in these aquifers. closure activities were completed in 1994. and hydraulic conductivity. U.S. Geological Survey USGS Fact Sheet FS-105–99 U.S. Department of the Interior April 1999 Quick responses of ground-water WEST EAST “Young” ground water levels to precipitation indicated infiltration less than 10 years in age Land surface through fractures and macropores because permeability and infiltration were slow SHALLOW AQUIFER SHALLOW TILL UNIT through the soil cover and clay cap on the landfill. Flow from the natural springs and Sand and “Old” ground water gravel more than 46 years MIDDLE TILL UNIT streamflow were affected by precipitation in age and evaporation. Flow from the springs contributed very little to streamflow. MIDDLE AQUIFER Hydrogeologic Mapping DEEP TILL UNIT Previous site-specific studies initiated Silty, sandy clay by the Army provided data from numerous monitoring wells completed in the upper 30 feet of glacial sediments at Fort Harri- son. Deeper hydrogeology had not been ? FALL CREEK AQUIFER Sand and gravel mapped because too few wells had been installed to greater depths. The USGS CARBONATE investigation in 1998 broadly defined the BEDROCK AQUIFER thickness and horizontal extent of aquifers within the glacial sediments at Fort Harri- son and described horizontal and vertical Figure 2. Generalized cross section showing conceptual model of the hydrogeology at the former ground-water flow. Fort Benjamin Harrison, Marion County, Indiana. For the hydrogeologic mapping, nearly northwest toward Fall Creek; this is the continuous cores of sediment were it is unchanged by physical and biological only area with sufficient data to map described at new, deep boreholes. New processes underground. the horizontal-flow direction. Local flow monitoring wells were constructed, and Prior to 1952, tritium originating from directions in the shallow and middle till geophysical logs were made in the deep natural cosmic rays was at a steady state units near the two closed landfills were wells. The new data were combined with in precipitation. When above-ground testing toward surface streams. information from previous investigations of nuclear-fusion bombs began in 1952, at Fort Harrison. These water-level data also indicated manmade tritium was introduced into the atmosphere and concentrations in pre- In a conceptual model of the hydro- the vertical flow of ground water was cipitation peaked during 1963-64. Tritium geology (fig. 2), the glacial sediments are downward from the shallow aquifer to concentrations in ground water can be used vertically divided into shallow, middle, and the middle aquifer and the Fall Creek to detect if and when water was recharged deep till units. Layers consisting predomi- aquifer. after the nuclear-bomb testing enriched nantly of sand or sand and gravel are the precipitation with tritium. aquifers within the glacial till that is mostly Ground-Water Age silty, sandy clay. Corresponding to the With qualitative interpretations of tritium shallow, middle, and deep till units were The date of recharge of the water in concentrations, the following judgments the shallow, middle, and deep (called an aquifer is the year when the precipita- were made about ground-water age (fig. 2). “Fall Creek”) aquifers. tion that replenished the aquifer became In the shallow aquifer in the eastern and isolated from the atmosphere; ground- central part of Fort Harrison, ground water The shallow aquifer consists of verti- is mostly “modern” and the water is less than cally and horizontally discontinuous water age is determined by the date of recharge subtracted from the date when 10 years old; in some places, the modern layers. The middle aquifer, mapped as water is mixed with water that is as much continuous in the eastern part of Fort the environmental tracer for age was analyzed in a ground-water sample. as 46 years old. In the middle aquifer and Harrison, was found to be thickest near the Fall Creek aquifer, ground water is more the central part and thinnest toward the Estimates of ground-water age can be used to assess the relative vulnerability of than 46 years old. On the basis of relative east. Geologic logs indicated that the mid- ground-water age, the shallow aquifer can dle aquifer was discontinuous between the an aquifer to contamination from sources at or very near the land surface. be considered to be highly vulnerable to central and western parts of Fort Harrison, contamination from activities at the former although a thick section of the aquifer also Tritium was used as the environmen- Fort Harrison; the middle aquifer and the was mapped near the western boundary. tal tracer to estimate ground-water age. Fall Creek aquifer have a low vulnerability. The Fall Creek aquifer was found to be Tritium is the radioactive isotope of —by Martin R. Risch as thick as 15 feet; however, only two hydrogen with an atomic mass of three. wells penetrated this aquifer. No data Tritium in water can originate from For more information, please contact: were obtained for the Fall Creek aquifer natural radiation sources like cosmic District Chief in the west, south, or central parts of rays and from manmade sources like U.S. Geological Survey Fort Harrison. 5957 Lakeside Boulevard nuclear-fusion bombs. Water molecules Indianapolis, IN 46278 Data from the two synoptic water-level containing the tritium atom, substituted (317) 290-3333 measurements indicated the predominant for the hydrogen atom, will follow the Indiana District Home Page: direction of horizontal ground-water flow same path as water molecules with no http://in.water.usgs.gov in the shallow and middle till units beneath tritium atoms. Therefore, tritium makes USGS Home Page: the southeastern part of Fort Harrison was a good age tracer for recharge because http://www.usgs.gov.