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Ground-water and sediment contamination by petroleum hydrocarbons resulting from leaks and overfills was detected during tank removal activities at three former underground storage tank locations at Fort Jackson, near Columbia, South Carolina. Investigations were initiated to assess the effect of contamination to the surficial aquifer at Sites 1062, 2438, and 2444. These investigations involved the installation of permanent monitoring wells and the collection and analysis of sediment and ground-water samples at the three sites. Water-level data were collected at all sites to determine hydraulic gradients and the direction of ground-water flow. In addition, aquifer tests were made at Site 1062 to determine the hydraulic conductivity of the surficial aquifer at that site. Sediment borings were made at the three sites to collect subsurfacesediment samples for lithologic description and laboratory analyses, and for the installation of ground-water monitoring wells. Laboratory analyses of sediment samples collected from boreholes at Site 1062 indicated elevated concentrations of petroleum hydrocarbons at three locations. Total Petroleum Hydrocarbons Diesel Range Organics were detected at one borehole at a concentration of 388,000 micrograms per kilogram. Total benzene, toluene, ethylbenzene, and xylene concentrations in sediment from the site ranged from less than 350 to over 100,000 micrograms per kilogram. Total lead was detected at concentrations ranging from 2,900 to 5,900 micrograms per kilogram. Petroleum hydrocarbons were detected at Site 2438 in one borehole at a trace concentration of 112 micrograms per kilogram of paraand metaxylenes. No concentrations exceeding the detection limits were reported for petroleum hydrocarbons in sediment samples collected from Site 2444; however, total lead was detected in sediment samples from two boreholes, each at concentrations of 600 micrograms per kilogram. Ground-water samples were collected from each site for laboratory analysis and field-property determinations. Petroleum hydrocarbons and lead were detected at concentrations exceeding regulatory limits for drinking water in ground water from Site 1062 only. Petroleum hydrocarbons were detected in ground water from three wells at Site 1062, with the highest concentrations occurring in the area of the former underground storage tanks. Benzene was detected at concentrations as much as 28 micrograms per liter; toluene as much as 558 micrograms per liter; paraand meta-xylenes as much as 993 micrograms per liter; and naphthalene as much as 236 micrograms per liter. Ethylbenzene and ortho-xylene were detected in one well at concentrations of 70 and 6 micrograms per liter, respectively. Dissolved lead was detected in ground water from four wells at concentrations from 5 to 152 micrograms per liter. Analysis of ground-water samples collected from Sites 2438 and 2444 showed little evidence of petroleum-hydrocarbon contamination. Petroleum hydrocarbons were not detected in any of the ground-water samples collected from Site 2438. With the exception of a low concentration of naphthalene (11 micrograms per liter) detected in ground water from one well, petroleum hydrocarbons and lead were not detected in ground water collected from Site 2444. INTRODUCTION During the past 6 years, the U.S. Department of the Army has located and removed numerous underground storage tanks (UST's) from various locations at Fort Jackson, near Columbia, S.C. Ground-water and sediment contamination by petroleum hydrocarbons resulting from leaks and overfills was detected during tank removal activities at three of the former UST sites. To assess the effect of contamination on the surficial aquifer at these three sites, investigations were initiated by the U.S. Geological Survey (USGS) in cooperation with the U.S. Army Corps of Engineers, Charleston District. The results of these investigations are presented in two reports, Phase One (Robertson and others, 1994) and Phase Two, this report. Purpose and Scope The purpose of this report is to present the results of investigations designed to provide data on the concentrations of petroleum-related contaminants in the surficial sediment and ground water, and to address the horizontal and, to a lesser degree, vertical extent of contamination in the surficial aquifer at study Sites 1062, and 2438 and 2444 at Fort Jackson, S.C. (fig. 1). These tasks were completed during January, February, March, October, and November 1995. The report describing Phase One of these investigations (Robertson and others, 1994) provided an initial qualitative delineation of petroleumhydrocarbon contamination. The results from the Phase One investigations were used to direct the Phase Two investigations, which were more quantitative in nature. This report presents data collected during the Phase Two investigations, which involved the installation of permanent monitoring wells and the collection and analysis of sediment and ground-water samples at three former UST locations (Sites 1062, 2438, and 2444). Ground-water and sediment samples were collected for laboratory analysis of various petroleum constituents. Water-level data were collected at all sites to determine hydraulic gradients and the direction of ground-water flow. In addition, aquifer tests were made at Site 1062 to determine the hydraulic conductivity of the surficial aquifer at that site. O O O P J r t H « O P 3 e n o l h H f t 0 > o r o C O r t r o o o 0 . C O H r o o r t U O e n O C O O Description of Study Area Study area Sites 1062, 2438, and 2444 are located in the upper Coastal Plain (fig. 1) and are underlain by unconsolidated, kaolinitic sands, clay, and gravel of Late Cretaceous age which unconformably overlies crystalline rock of pre-Cretaceous age. Previous studies (Ebasco Services Inc., 1992; Robertson and others, 1994) have indicated that the sediments comprising the surficial aquifer beneath Site 1062 are generally sands with appreciable quantities of silt and clay. These sediments have a low permeability and yield relatively small amounts of water. Continuous cores collected at Site 2438 (Robertson and others, 1994) indicated the presence of a dense kaolin layer at a depth of about 6 ft bis. The clay layer was approximately 7-ft thick and appeared to be laterally extensive beneath the study area. The primary surface-water feature in the vicinity of Site 1062 is Wildcat Creek, which is approximately 450 ft south (downgradient) of the site (fig. 1). From a point south of Site 1062, Wildcat Creek flows westwardly for approximately 0.75 mi to Lake Katherine. A north-south oriented reach of Wildcat Creek, located upstream from Site 1062, is also the primary surfacewater feature in the vicinity of Sites 2438 and 2444, and is located approximately 2,000 ft and 1,700 ft southeast (downgradient) of these sites, respectively. History of Sites Hydrogeologic investigations made at several of the former UST sites, including Site 1062, indicated that petroleum-hydrocarbon contamination was present in ground water (Ebasco Services Inc., 1992); however, the extent of contamination was not determined. Additionally, preliminary testing of ground water and sediments collected during UST removal activities at Sites 2438 and 2444 suggested the possibility of hydrocarbon contamination. Reconnaissance investigations of Sites 1062, 2438, and 2444 (Robertson and others, 1994) were made during March 1994. These investigations involved the collection of ground-water or sediment samples, or both, by using a hydraulically driven coring device or temporary well point. Samples were analyzed on-site for benzene, toluene, ethylbenzene, and total xylenes (collectively termed BTEX), Total Petroleum Hydrocarbons-Gasoline Range Organics (TPH-GRO), and Total Petroleum Hydrocarbons-Diesel Range Organics (TPH-DRO) using gas chromatography. Additional samples were collected for laboratory analysis of BTEX compounds as a confirmation of on-site analytical results. Site 1062 Site 1062 was used as the main Base gas station during the 1980's. When the site was abandoned, Building 1062 was demolished, but the concrete pad was left intact. In December 1990, the three abandoned 10,000-gal storage tanks at this site were removed. One of the three tanks contained less than 6 in. of gasoline product, and the other two tanks each contained less than 6 in. of #2 fuel oil or diesel fuel. Plastic sheeting was placed in the bottom of the excavation, and the hole was reportedly backfilled with the excavated sediment (Ebasco Services Inc., 1992). Samples collected after the tank removal contained BTEX compounds in concentrations ranging from 360 to 3,500 /^g/L in ground water and from 1 to 570 /^g/kg in sediment (Ebasco Services Inc., 1992). To evaluate the spatial distribution of contamination, sediment borings were made at four locations, and monitoring wells MW-01, MW-02, MW-03, and MW-04 were installed. Analyses of ground-water and sediment samples indicated that BTEX contamination was present; however, the extent of contamination was not determined (Ebasco Services Inc., 1992). Ground-water levels during the time of sample collection (1992) were above the screened interval in three of the monitoring wells. If the ground-water level is above the screened interval of a well during sampling, the existence of floating product on the water table could be undeterminable. Data collected by Robertson and others (1994) suggested the presence of a contaminant plume at Site 1062 (fig. 1). Thirty-three ground-water samples were collected from 24 locations. On-site analysis detected BTEX compounds in ground water from nine locations, with total BTEX concentrations ranging from 53 to 55,997 /^g/L. Concentrations generally decreased rapidly with increasing lateral distance from the former UST area. At three of the locations where BTEX compounds were detected, TPH-GRO also were detected in concentrations ranging from 323 to

u.s. geological survey open file report/open-file report

Assessment of petroleum-hydrocarbon contamination in the surficial sediments and ground water at three former underground storage tank locations, Fort Jackson, South Carolina, 1995