Delineation of Landfill Migration Boundaries Using Chemical Surrogates Danlel R. Thielen," Patricia S. Foreman,+ and Abram Davis Technology Center, Occidental Chemical Corporation, Grand Island, New York 14072
Robert Wyeth RECRA Research, North Tonawanda, New York
14120
A purgeltrap procedure for the determination of monochlorobenzene and monochlorotoluene at the 10 ng/g level in soil is described. The advantages of a heated and stirred vessel for sample preparation are demonstrated. This method was applied to samples from the Hyde Park landfill site in Niagara Falls, NY, and the results were used to define chemical migration around the landfill. Graphical representation of this migration is illustrated with both two- and three-dimensional plotting techniques. This study is a first phase in the development of a remedial plan for the Hyde Park landfill. The introduction of chemicals into the environment may occur as a result of spills, process effluents, or releases from landfills. The need to monitor and control these releases, especially at landfill sites no longer in operation, has prompted the investigation of ways of monitoring chemical migration. Particular emphasis is now being placed on chemical migration in groundwater and surface water. Generally, chemical migration patterns and chemical distribution in groundwater are followed by use of tracers added to the system or by surrogates representing the compound classes having the greatest environmental impact at a site. Compound classes having the highest aqueous mobility are chosen initially to define the outer migration boundaries. Industrialized areas have thus been studied with haloforms (1, 2 ) , chlorophenols (2, 3), or polynuclear aromatic hydrocarbons ( 4 ) . The evaluation of groundwater movement and quality has been studied by addition of tracers such as fluorinated organic acids (5-7). In landfill studies it is appropriate to use those compounds known to be present and having sufficient water solubility to define migration boundaries. Such chemicals as chloroalkanes and alkenes (8),benzene (9), and alkyl aromatics (IO) have been demonstrated to be useful as surrogates. A variety of volatile priority pollutants found in municipal solid landfills has also been reported (11). It is often necessary to define past migration of chemicals in ground-water or surface water by analysis of soil since a water phase may not be present. This paper describes methodology for soil analysis using monochlorobenzene (MCB) and monochlorotoluene (MCT) as surroPresent address: Hercules Research Center, Wilmington, DE 19899. 0013-936X/87/0921-0145$01.50/0
gates to define past migration away from the Hyde Park landfill area located in Niagara Falls, NY. This surrogate study is used as a first-phase screening and is supplemented by further chemical analysis at the boundary. Experimental Section Soil was collected by coring to specified depths. Core sections from predetermined depths then were packed into prewashed wide-mouth jars that were sealed with Teflon-lined caps. Care was taken to minimize air space above the soil by packing each jar to the lid. Samples were immediately stored at 4 "C. Water used for preparation of blanks and samples was prepared from distilled water that was further purified by passage through ion-exchange and charcoal cartridges (Mil&& System, Millipore Corp., Bedford, MA). The water was prepurged with ultra-high-purity nitrogen prior to use. The purity of the water was checked by analysis of blanks that were prepared in the same manner as samples, No interferences were evident at the method detection limits of 10 ng/g. Gas chromatography was performed on a HewlettPackard Model 5840 gas chromatograph equipped with a flame ionization detector and a 7672A autosampler. The column was a 10 ft by 2 mm i.d. glass column packed with 10% SP-2100 on 80/100-mesh Supelcoport. Column temperature was held at 40 "C for 5 min and then programmed at 5 deg/min to 150 "C, where it was held for 5 min. Carrier gas was helium at 40 mL/min flow rate. Temperatures of the injection port and detector were held at 250 "C. Sample injection size was 3 pL. Retention times for monochlorobenzene, o-chlorotoluene, and p-chlorotoluene were 11.11, 15.45, and 15.65 min, respectively. Since total monochlorotoluene concentrations were desired, no attempt was made to affect complete isomer separation. An all-glass purge/trap concentration system, similar to that described by Hertz, et al. (12), was used. It consisted of a 250-mL, three-neck round-bottom flask fitted with three thermometer adaptors. The center adaptor held an adsorption tube while the other positions were taken by a thermometer and a disposable pipet that extended to just above a magnetic stir bar. The entire assembly was placed in a heating mantle that was supported by a magnetic stirrer. The assembly was constructed to accommodate a large sample (20-30 g) as well as sufficient water to form a slurry. The large-sample capacity of the flask
0 1987 American Chemical Society
Environ. Sci. Technol., Vol. 21, No. 2, 1987
145
enabled adjustment of method sensitivity by varying sample size. Adsorption tubes used for this study were 100-mg/50-mg activated charcoal tubes as detailed by NIOSH method P&CAM 127 (13). The sample apparatus was leak-checked prior to addition of any sample. The apparatus was assembled, the charcoal adsorption tube placed in the center position, and a helium line connected to the disposable pipet. The helium line included a precalibrated rotameter with which the flow was set. Helium flow was measured at the outlet of the adsorption tube and compared to the flow set at the rotameter. All joints were tightened until the flows were equal. All ground-glass joints were sealed with Teflon sleeves. After the system was sealed, a single joint was opened, and a 20-30-g soil sample was quantitatively weighed into the extraction assembly. A total of 100 mL of purified, prepurged water was then added to the vessel and the joint resealed. Helium flow in the system was rechecked, the magnetic stirrer started, and the heating mantle turned on. The sample was purged for 20 min following attainment of a 70 "C system temperature. After sample purging, the charcoal tube was removed, and front and back portions of the tube were emptied into separate 1-mL autosampler vials. Extraction of the charcoal was done by shaking for 60 s with 0.5 mL of carbon disulfide. System blanks and spikes were prepared with soil that did not contain the analytes of interest. Spiking solutions were prepared in acetone a t a high concentration, and a minimum of solution was used as a spike to avoid any system changes from acetone. All results are reported on a dry weight basis. Moisture content of samples was determined from weight loss by oven drying in a 1-g aliquot of sample at 110 "C for 18 h.
Results and Discussion Methodology. Purge/trap techniques usually rely on a Tenax or Tenax-silica gel trap that is thermally desorbed onto the chromatographic column. The sample purge/trap unit and chromatograph are combined into an integrated system. While this procedure has proven highly effective for water, it precludes multiple, simultaneous sample preparation. An increase in productivity was realized by setting up a series of the described purge systems and running them concurrently. Use of charcoal tubes with carbon disulfide desorption gives the additional advantage of using an autosampler for unattended analysis. We have realized a 2-3-fold increase in sample throughput using this arrangement. The ability to easily transport charcoal tubes makes remote sample preparation a possibility as well. Many soil samples, and, in particular, core samples, are compressed and tightly bound by clay. The clay not only acts as an adhesive to bind the matrix tightly together but also provides adsorptive sites. Soil must be prepared for analysis so that any entrained organics become accessible to the sample treatment used. Physical breaking of agglomeration by drying is possible but may result in loss of any volatile organics. This method uses a sufficient volume of water to form a suspension, which eliminates soil clumping, Vigorous sample stirring and heating aids in release of purgable organics. An increase in temperature of a sample undergoing head-space analysis results in a shift of solute distribution coefficient toward the vapor phase. Thus, quantitative removal of solutes from an aqueous slurry during dynamic head-space purging can be carried out in a progressively shorter time period as temperature increases. On the other hand, water vapor pressure is also increasing, and trapping efficiency begins to decrease due to water entrainment in 146
Environ. Sci. Technol., Vol. 21, No. 2, 1987
40 30
50
60
70
80
90
Temperature ("C)
Figure 1. Effect of sample temperature on recovery. Monochlorobenzene is represented by the solid line. Monochlorotoiueneis represented by the dashed line.
Table I. Effect of Purge Rate and Purge Time % recovery
purge time, min
MCB
MCT
Part A 10" 200 30"
73 84 91
52 69 83
Part B lob
206
86 95
71 88
aPurge rate IO mL/min. bPurge rate 20 mL/min.
the trap. A reasonable compromise between time, temperature, and solute recovery must, therefore, be considered. In this study, monochlorobenzene (MCB) and monochlorotoluene (MCT) were used as surrogates. Figure 1 shows recovery data for MCB and MCT at various temperatures with a 20-min purge time and a 20 mL/min flow rate. Both plots show an increase in recoveries with temperature increase. At 70-80 "C, recovery drops as a result of water vapor saturation Qf the solid adsorbant. Recovery maxima occur in the 60-80 "C range with 70 "C selected as optimum for this study. Relative standard deviations of 8.9% and 7.8% were obtained for recoveries of MCB and MCT, respectively, under the conditions described above with a 70 "C purge temperature. Table I shows purge rate and purge time effects on recoveries of MCB and MCT. Recovery values represent averages over a range of 0.2-22 pg added to approximately 20 g of soil (10 ppb to 1ppm). Table IA shows the increase in recoveries as purge time increases (using a purge flow of 10 mL/min and a temperature of 70 "C). To reduce sample preparation time, the purge rate was increased to 20 mL/min, and Table IB shows that comparable recoveries can be obtained in 20 min (using an 80% recovery criteria). Higher purge rates were not attempted because of concern over leakage due to higher system back pressure on the purge vessel. Purge times stated were measured after the purge temperature had been reached. Environmental Monitoring. The determination of MCB and MCT was applied to Bloody Run Creek, which runs near and away from the Hyde Park chemical disposal area in Niagara Falls, NY. Soil corings were made a t various distances downstream from the disposal site. At each sampling point, corings were made at the center point
580
1
I I
.el
578L
1
I
1
I
I
I
I
1
50
40
30
20
10
0
10
20
30
Distance from Center of Ditch (Feet)
__
Figure 2. Cross-sectional diagram of chemical migration. Overlaid concentration values represent total MCB and MCT in pg/g.
a
1175
Figure 4. Surrogate migration at Hyde Park disposal site. Solid line represents the landfill boundary. Dashed line represents the outer migration boundary as defined by sampling along the lettered vectors. Both MCB and MCT data are included.
Table 11. Soil Analysis Recovery Data-Monochlorobenzene and Monochlorotoluene
average SD relative % SD n
P
Depth (Ft.)
Depth (Ft.) Figure 3. Three-dimensional plot of monochlorobenzenemigration: (a) view away from the landfill; (b) view toward the landfill.
of the creek and at transverse distances to the center line of the creek. Samples of the corings were then taken at various depths. In this way, information was generated for chemical migration away from the site, away from the creek bed, and into the soil. Movement of MCB and MCT away from the disposal site has been graphically presented in two ways: crosssectional diagrams and three-dimensional plots. Figure
critical value for F to critical value for t
blank Hyde non Hyde Park Park MCB MCT MCB MCT
Hyde Park MCB
MCT
87.88 14.43 16.42
76.13 16.54 21.73
89.05 11.24 12.63
91.23 16.58 18.17
112.67 26.85 23.83
89.67 12.77 14.24
16
16
22 1.65 2.18
22 1.00 2.32
9 3.46 2.64
9 1.68 2.64
0.28 1.69
2.78 1.69
3.03 1.71
2.20 1.71
QA
=Blank Hyde Park soil and Hyde Park QA soil vs. non Hyde Park soil.
2 shows a cross-sectional plot where transverse distance of a ditch is plotted against height in feet above sea level. The concentrations of the chemical are overlaid to give a visual representation of chemical dispersion at that point. A series of such plots taken at points moving away from the site gives a reasonable overview of chemical migration. Three-dimensionalcontour plotting provides a complete visual representation of monochlorobenzene movement as shown in Figure 3. The entire length of ditch is plotted as a function of depth and concentration. In this instance, the data from the center line of the ditch are shown. Depletion of surface concentration can be seen and is probably due to evaporative or leaching effects. Also, a rapid decrease in concentration is noted as distance increases from the source. Depth profiles are also apparent and indicate depth of highest concentration as well as ultimate depth of chemical migration in soil. The ability to graphically represent these concentration profiles by viewing them from the source (Figure 3a), as well as looking back at the source (Figure 3b), provides insights that are not apparent when tabular data are considered. This migration monitoringconcept has also been applied to the Hyde Park disposal site itself. Vectors radiating from the site in all directions were chosen, and soil was analyzed at increasing distances. The points at which the surrogate compounds were less than 10 ng/g were considered the outer migration boundaries. This migration is illustrated in Figure 4. The described procedures have been in use for 4 years, and sufficient quality assurance data have been generated to validate the method. Table I1 shows recovery and statistical data for three separate recovery studies. These Environ. Sci. Technol., Vol. 21, No. 2 , 1987
147
include recoveries from soils taken at and away from the Hyde Park area (designated blank Hyde Park soil and non Hyde Park soil, respectively), which were expected to be free of MCB and MCT, as well as recoveries from quality assurance spikes of Hyde Park soils (designated as Hyde Park QA) made during the sampling program. Non Hyde Park soil was used during method development and initial validation and was considered to be a base-line data set for later quality assurance studies. Hyde Park soil data were part of a routine 10% spike program used during plume definition studies. All spiking studies were done at the action level of 10 ng/g. The mean recoveries for both Hyde Park soil spikes are higher than that of the base-line data set. Recovery populations from the quality assurance program are not equivalent to base-line data as shown by t test data. The lone exception is the MCB data for the “blank” Hyde Park soil spikes. These data would suggest that there was residual, although originally undetected, MCB and MCT in Hyde Park samples. These findings are not unexpected since spiking was done at the action level and the disposal area is known to contain these chemicals. The precision of these recovery measurements, as measured by F tests, shows that they are equivalent to the base-line data. The lone exception is the MCB data for Hyde Park QA spikes. Apparently, these soil samples are likely to contain residual MCB. This is also shown by the high mean recoveries of MCB in these samples. The ability to obtain a homogeneous sample may also play a role since the Hyde park QA recoveries were corrected for residual MCB and MCT. Generally speaking, the purge method described gives good recoveries and is limited only very close to the action level of 10 ng/g, where residual levels of MCB and MCT begin to affect accuracy and precision. These effects are not considered to be prohibitive since the procedure is designed for screening purposes. Chemicals of greatest concern in terms of toxicity, bioaccumulation, etc. are often not the best choices for mi-
148
Environ. Sci. Technol., Vol. 21, No. 2, 1987
gration boundary determination. Once a boundary study is completed, it is necessary to further analyze the outermost samples for persistent or toxic chemicals to assure that complete coverage has been attained. In the case of this Hyde Park study, additional analyses are currently being performed and data being submitted to the New York State Department of Environmental Conservation and the EPA in support of a remedial plan. Registry No. MCB, 108-90-7; MCT, 25168-05-2.
Literature Cited (1) Fogelqvist, E; Josefsson, B.; Roos, C. Environ. Sci. Technol. 1982, 16(8), 479-482. (2) Josefsson, B. J. Chromatogr. 1983, 279, 119-123. (3) Wegman, R. C. C.; van den Brock, H. H. Water Res. 1983, 17, 227-230. (4) Sporstml, S.; Gl0s, N.; Lichtenthaler, R. G.; Gustaveen, K. 0.;Urdal, K.; Oreld, F.; Skel, J. Environ. Sci. Technol. 1983, 17, 282-286. (5) Davis, S. N.; Thompson, G. M.; Bentley, H. W.; Stiles, G. Ground Water 1980, 18, 14-23. (6) Stetzenbach, K. J.; Jensen, S. L.; Thompson, G. M. Environ. Sci. Technol. 1982, 16(5),250-254. (7) Bowman, R. S. J . Chromatogr. 1984, 285, 467-477. (8) DeLeon, I. R.; Maberry, M. A.; Overton, E. B.; Raschke,
C. K.; Remele, P. C.; Steele, C. F.; Warren, V. L.; Laseter, J. L. J. Chromatogr. Sci. 1980, 18, 85-88. (9) Ramsad, T.; Nestrick, T. J. Bull. Environ. Contam. Toxicol. 1981,26,440-445. (10) Pojasek, R. B.; Scott, M. F. ASTM Spec. Tech. Publ. 1981, NO.760, 217-224. (11) Sabel, G. V.; Clark, T. P. Waste Manage. Res. 1984, 2, 118-130. (12) Hertz, H. S.; Cheder, S. N.; May, W. E.; Gump, B. H.; Enaginio, D. P.; Cram, S. P. NBS Spec. Publ. (U.S.) 1974, No. 409. (13) NIOSH Manual of Analytical Methods;U S . Government Printing Office: Washington, DC, 1977; Vol. 1, Method P&CAM 127.
Received for review January 27,1986. Accepted August 14,1986.
