Environ. Sci. Technol. 1990, 24,559-566
Cautreels,W.; Van Cauwenberghe, - K. Atmos. Environ. 1976, 10,447-453. Giam, C. S.; Atlas, E.; Chan, H. S.; Neff, G. S. Atmos. Environ. 1980,14, 65-69. Atlas, E.;Giam, C. S. Science 1981,211,163-165. Virgin, H. I.; Hoist, A. M.; Momer, J. Physiol. Plant. 1981, 53, 158-163. Lokke, H.; Bro-Rasmussen, F. Chemosphere 1981, I O , 1223-1235.
(35) Hardwick, R. C.; Cole, R. A.; Fyfield, T. P. Ann. Appl. Biol. 1984,105,97-105. (36) Hannay, J. W.; Millar, D.J. J.Exp. Bot. 1986,37,883-897.
Received for review March 9,1989. Revised manuscript received October 31, 1989. Accepted November 16, 1989. Financial support was provided by the Swedish Environmental Protection Board.
Occurrence and Fate of Organic Solvent Residues in Anoxic Groundwater at the Gloucester Landfill, Canada Suzanne Lesage," Richard E. Jackson, Mark W. Priddie, and Peter G. Riemann
National Water Research Institute, Canada Centre for Inland Waters, Burlington, Ontario, Canada L7R 4A6 The disposal of organic chemicals in trenches at a waste disposal site near Ottawa, Ontario, Canada, has resulted in the contamination of the underlying aquifer. The organic residues measured in groundwater samples are reported and the mechanisms of contaminant transport in the aquifer discussed. Groundwater samples from monitoring wells and multilevel samplers were analysed by gas chromatography-mass spectrometry. Ultratrace quantities of chlorinated dibenzodioxins and furans were found in groundwaters directly beneath the trenches. A wide variety of volatile compounds were identified and quantitated in samples from the aquifer. The compound of greatest concern was 1,6dioxane, because of its toxicity and mobility, while that present in greatest concentration was a Freon, F113, which appeared to be very persistent, although three transformation products were identified. Introduction During the 19809, the contamination of groundwater by toxic organic chemicals became a major environmental concern in North America and Europe. Not only does this contamination directly threaten groundwater supplies used by municipal and rural populations for drinking water, but also the subsurface transport of contaminants threatens surface water supplies, such as the Great Lakes system, which are used by millions of North Americans as their potable water supply. The danger posed by such chemicals to drinking water supplies has brought about the rapid growth in contaminant hydrogeology, the passing into law of much regulatory legislation, and the creation of numerous consulting and analytical businesses. Despite a11 this activity, few substantial descriptions of the occurrence and distribution of toxic organic contaminants in groundwater flow systems have appeared in print (1-9). Only a handful of these provide a detailed account of the analytical organic chemistry of the groundwater. It is questionable whether the US. EPA priority chemicals list (10) actually defines those chemicals of greatest concern in groundwater contamination studies; furthermore, it is noteworthy that much of the unpublished information on nonpriority pollutants is thought to be flawed (11). This paper is concerned with the organic contamination of groundwater following incineration of laboratory organic solvents and wood perservatives in trenches at the Gloucester Landfill, near Ottawa, Ontario, Canada, during the period 1969-1980. This site is unique in that the hydrogeological and geochemical properties of the groundwater flow system are well-known (3, 5 ) , the wastes that were Published 1990 by the American Chemical Society
disposed in the trenches are relatively well defined, and the toxic organic chemicals of concern have been monitored intermittently over a period of 8 years by use of a dense network of hydrogeological monitoring devices concentrated in a single aquifer. The objectives of the study were (1)the identification and quantitation of toxic organic chemical residues in groundwaters beneath one part of the landfill and (2) the examination of the processes affecting the migration and fate of the identified contaminants. It is shown that the disposal and incineration of the wastes resulted in the probable formation of a series of polychlorinated dioxins and furans and the contamination of the underlying outwash aquifer by organic solvent residues and their transformation products. Furthermore, while it appears that the migration of most of these organic chemicals is governed by aqueous-phase solute transport and sorption, small quantities of nonaqueous-phase liquids may be present beneath the trenches and in the aquifer. Site Description Between 1969 and 1980, the Government of Canada disposed of hazardous wastes, principally organic chemicals from its laboratories in Ottawa, at the nearby Gloucester landfill (Figure 1). The disposal operations took place within a "Special Waste Compound", hereafter referred to as the SWC, located at the southwest corner of the landfill. These operations involved the excavation of trenches (12 m long X 3 m X 3 m) into which bottles of liquid chemical wastes were placed and subsequently combusted by detonation of explosive charges set within them. The wastes consisted of nonchlorinated solvents (56.4 m3), unspecified wood preservatives (30 m3), chlorinated solvents (8.6 m3), and smaller amounts of acidic and ferric chloride and other wastes (12). Detailed soil coring and hydrogeological testing have resulted in the identification of the five hydrostratigraphic units shown in Figure 2. Unit A, the fractured limestone bedrock, is encountered at depths between 25 and 30 m and is partly covered by a till (unit B) of relatively low hydraulic conductivity. Unit C, overlying the till and/or bedrock, is a thick (up to 25 m) sequence of silts, sands, gravel, and boulders known as glacial outwash and forms a semiconfinedaquifer beneath the landfill. This outwash is overlain by a discontinuous layer of silt, unit D. The surficial aquifer, unit E, may be up to 10 m thick and its composed of sands and gravels. The outwash aquifer, unit C, is composed mineralogically of feldspar (50+%), quartz (20%), and minor Environ. Sci. Technol., Vol. 24,No. 4, 1990 550
Sampling and Analysis Sampling. Groundwater samples were colleded during May 1988 from selected monitoring points within the monitoring well network. These points are shown in crass section in Figure 3. A set of five samples was collected from 5-cm-i.d. piezometers (denoted by 124P-128P) each completed with stainless steel screens and dedicated Teflon bladder pumps and inflatable packers (BED Environmental Systems Inc., Ann Arbor, MI), which were inflated above the well screens to contact a stainless steel pipe extension of the screen. Prior to sampling, at least three well-screen volumes were discharged to waste. The remainder of the samples were obtained from bundle-type multilevel samplers (denoted by 16M, 37M etc., ref 14) by using peristaltic pumps. Samples were collected in 25- or 40-mL amber glass vials and kept on ice until reaching the laboratory. Measurementsof pH and EH were conducted in the field using combination glass and Pt electrodes fitted into airtight flow cells (3). Dissolved oxygen was determined with an Orbisphere Laboratories (York, ME) 2606 oxygen meter. Sulfide measurements were performed by using a glass/sulfide electrode couple in acidic solution (pH < 5) under closed, continuous-flow conditions (15). Analytical Methods. Volatile organic compound analysis was carried out by following EPA method 624 (16). A Model 810 Unacon (EnvirochemInc., Kemblesville, PA) purge and trap was used to concentrate the analytes. This unit was interfaced to a Hewlett-Packard Model 5970 GC-MSD. The analytical column was a 30-m DB-624 (J&W Scientific), 0.32-mm i.d., 1-pm film thickness, directly interfaced into the source of the MSD. The gas chromatograph was cooled to -5 "C with liquid CO, to allow the analyses of the purgeable gases and programmed in two ramps to 140 OC (-5 to +35 OC at 10 'C/min and then at 4 %/mid. Difluorobenzene and chlorobenzene-d, internal standards were added to 10-mL samples immediately prior to purging. Mass acquisition was from 40 to 250 amu at 2 scans/s, but quantitation was done on extracted ions specific for each analyte, using one qualifier ion for confirmation. Analytical standards were prepared from the purest available chemicals purchased from a variety of sources. Unknowns for which no standards were available were tentatively identified by comparison of their spectra to an NBS library containing 42 000 compounds.
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amounts of mica, calcite, dolomite, and homblende. The organic carbon content of the aquifer sediments averages 0.06%. The aquifer has a mean hydraulic conductivity of m/s, a porosity of 0.30-0.35, and an average linear groundwater flow velocity of 0.05 m/day (3, 13). The groundwater temperature is in the range 9-10 "C. The groundwater flow pattern beneath the SWC is shown in Figure 2. Downward groundwater flow occurs from the surficial aquifer, unit E, to the confined outwash aquifer. Some seepage appears to occur through permeable windows in the silty confining layer, unit D. Once solutes enter the outwash aquifer, the vertical equipotential lines dictate that they are transported horizontally to the east. Monitoring of the observation well network shown in Figure 1has verified that contaminant transport is indeed in this direction (3,5).
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Environ. Sci. Technol.. Vol. 24, No. 4, 1990
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Prior to 1983, the majority of the data was obtained by using an HP7675 purge and trap interfaced to a GC-FID, with some of the analyses being confirmed on a Finnigan 4000 mass spectrometer. From 1984, a combmation of FID and Hall detectors was used, until 1987, when the GCCHLORIDE
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MSD system described above was acquired. Semivolatiles and dioxins were analysed by following the EPA 625 and 613 protocols (16), except that a 10-Lsample was extracted for dioxins. The analysis was done on a Finnigan 4000 GC-MS (17). Results and Discussion Inorganic Parameters. The distribution of chloride in plan and cross section in the outwash aquifer is shown in Figures 4 and 5, respectively. The first samples collected at the Gloucester landfill in November 1977 showed values less than 5 mg of Cl-/L in that area (see Figure 4) where concentrations are now in excess of 250 mg of Cl-/L. Background chloride concentrations in groundwaten from upgradient areas west of the SWC (e.g., 41P; see Figure 1) are less than 10 mg/L. Much higher levels occur beneath and downgradient from the SWC. The vertical configuration of the chloride plume (Figure 5) along a section extending downgradient from the SWC indicates that chloride is transported downward from the trenches within the SWC into the outwash aquifer and then downgradient to the east. The leading edge of this plume has crossed beneath the railroad tracks near Delzotto Ave. (Figure 4). This pattern of migration is consistent with the groundwater flow directions shown in Figure 2. On the basis of groundwater velocity measurements in the C'
Environ. Sci. Technol., Vol. 24, No. 4. 1990 561
Table I. Volatile Organic Compounds Present in the Outwash Aquifer, May 1988 compound dioxane diethyl ether tetrahydrofuran benzene toluene ethylbenzene o-xylene 2-ethyltoluene dichloromethane trichloromethane tetrachloromethane chloroethane chloroethene 1,l-dichloroethane 1,l-dichloroethene 1,e-dichloroethane trans-1,2-dichloroethene cis-1,2-dichloroethene l,l,l-trichloroethane l,l,Z-trichloroethane trichloroethene tetrachloroethane tetrachloroethene 1,2-dichloropropane chlorobenzene l,l,Z-trichloro- 1,Z,Z-trifluoroethane
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