SITE INFORMATION AND CORRESPONDENCE_1985-1997

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5 feet below ground surf ee.The screens were installed adjacent to each other, perpendicular to the direction hw a11i of flow. As shown in Figure 1, the field site consisted .Ew-t 1 Z] 4 of lines of monitoring points or wells oriented along the natural ground water flow direction. Samples were col- lected + 9+ -upgradient and downgradient of the oxygen RKGD + o+ • Oct ORC-CONCRETE LINE source within each line (briquet or pure powder). Two + ++ • AL AQUIFER LINE lines were used as controls to determine the benzene + • PL PENCIL LINE and toluene degradation behavior at the site in the absence of ORC. P•n<il. .EW-2 The experiment was designed to be interpreted after +.onif.,wg P.mt ...ming ..II steady-state concentration distributions were achieved . ..11 0.0 10 tm) or approached,i.e.,similar to the methods typically used oto• ..II .<r..n to interpret laboratory column tests of transformation reactions. Thus, a significant difference between the Figure 1. Site plan and monitoring locations. steady-state distributions for benzene and toluene downgradient of an ORC source and that downgradient of the comparable position in the control line could be taken as evidence of enhancement of transformation of the two compounds by the ORC source. This simple OCL-1 OCL- OCL-3 OCL-A comparative approach assumes that other solute trans- 0.0 port processes are similar along the flowpaths to be I Ii compared (advection, dispersion, and sorption), an assumption that seems warranted in the relatively homo- geneous Borden Aquifer.Since sorption and retardation V. of benzene and toluene are known to be slight in the 10 o„n Borden Aquifer (Barker et al. 1987), it was expected that the primary limit to the approach to steady state would be the acclimation of the native microorganisms to the injected substrates. Background samples were collected from a drive a.a point sampler located approximately 4 m upgradient of the source wells. The transport of the organic solutes 0.0 0.5 1.0 1.5 2.01m1 was monitored along lines of monitoring points('/4-inch stainless steel sampling points with a 1-inch screen) and Figure 2. Cross section of the site along the ORC-Concrete drive points (1-foot stainless steel screens) placed Line. approximately 4 feet below the ground surface. As stated previously, the lines of monitoring points and those prepared with cement only (concre and wells were oriented along the expected natural- briquets). The ORC-concrete briquets containe gradient flow direction. However, to minimize effects approximately 20 percent by weight ORC powder. Tl of temporal variations in the gradient due to snowmelt briquets were placed in two well screens installed in and other localized factors, two parallel lines of sheet- manner similar to that used for the source wells. Tl piling were driven 5 feet into the ground on both sides well screen in the Concrete Line contained concre of the field setup. As an additional method to maintain- briquets.Its purpose was to serve as a reference for tl a constant flow direction,two extraction wells were used ORC-Concrete Line, within which the well screen w- to extract ground water at approximately 1.5 gallons per filled with CIRC-concrete briquets. Figure 2 shows minute (gpm) each; the extraction rate and well Iota- cross section of the site along the ORC-Concrete Lir tions were selected based on 2-D modeling results. Water table elevation data were not collected during Pencil Section the experiment. Given the very small average regional gradient (0.0043), the low pumping rate (1.5 gpm per In one section gr the site, rows of app "pencil extraction well), and the short distance between moni- were placed in the ground, st a depth of approximate in toring points (approximately 40 to 50 cm along a moni- s feet. The pencils were installed by driving a ]r sa toring line), the absolute value of the head differences steel casing into the ground,jetting out the interior sat between the available monitoring points would have with water, and pouring 350 mL of an approximate been on the order of,or smaller than,the error inherent 60 percent vol/vol ORC water slurry into the emp in the head measurements. casing. The casing was then removed using a jack, aI another 150 mL of ORC slurry were added to fill t Briquet Section hole. As shown in Figure 1, pencils were installed Two types of briquets were used: those prepared rows perpendicular to the direction of flow. Each pen with cement mixed with ORC(ORC-concrete briquets), was approximately 6 inches away from the nearest pen 122 is WINTER 1994 GWMR