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Soil pollution by petroleum products, III. Kerosene stability in soil columns as affected by volatilization
Journal of Contaminant Hydrology, 5 (1990) 37~385
375
Elsevier Science Publishers B.V., Amsterdam - - Printed in the Netherlands
SOIL POLLUTION BY P E T R O L E U M PRODUCTS, III. K E R O S E N E STABILITY IN SOIL COLUMNS AS A F F E C T E D BY VOLATILIZATION
Ts. GALIN, Z. GERSTL and B. YARON
Department of Soil Organic and Residues Chemistry, Institute of Soils and Water, Agricultural Research Organization, The Volcani Centre, Bet Dagan 50250 (Israel) (Received May 11, 1989; revised and accepted December 12, 1989)
ABSTRACT Galin, Ts., Gerstl, Z. and Yaron, B., 1990. Soil pollution by petroleum products, III. Kerosene stability in soil columns as affected by volatilization. J. Contam. Hydrol., 5: 375-385. The stability of kerosene in soils as affected by volatilization was determined in a laboratory column experiment by following the losses in the total concentration and the change in composition of the residuals in a dune sand, a loamy sand, and a silty loam soil during a 50-day period. Seven major compounds ranging between C9 and Cls were selected from a large variety of hydrocarbons forming kerosene and their presence in the remaining petroleum product was determined. The change in composition of kerosene during the experimental period was determined by gas chromatography and related to the seven major compounds selected. The experimental conditions - - air-dry soil and no subsequent addition of water - - excluded both biodegradative and leaching losses. The losses of kerosene in air-dried soil columns during the 50-day experimental period and the changes in the composition of the remaining residues due to volatilization are reported. The volatilization of all the components determined was greater from the dune sand and loamy sand soils t h a n from the silty loam soil. It was assumed t h a t the reason for this behavior was t h a t the dune sand and the loamy sand soils contain a greater proportion of large pores ( > 4.5 #m) t h a n the silty loam soil, even though the total porosity of the loamy sand and the silty loam is similar. In all the soils in the experiment, the components with a high carbon number formed the main fraction of the kerosene residues after 50 days of incubation.
INTRODUCTION
Kerosene is a petroleum product characterized by low viscosity and medium volatility in comparison with heavy and residual fuels. It is used for wick-fed illumination, spark ignition engines (mainly in agriculture), and aviation gas turbines (Goodger, 1975). Its widespread utilization may result in accidental pollution of soils along pipelines (e.g., Dibble and Bartha, 1979), under gas stations, or in the vicinity of airports. The low viscosity of kerosene makes it a potential pollutant for porous media and groundwater. Hunt et al. (1988a, b) showed that the only logical explanation for the presence of high soil concentrations of kerosene is that it exists as an immiscible phase with water
0169-7722/90/$03.50
© 1990 Elsevier Science Publishers B.V.
376
Ts. GALINET AL.
either as discrete ganglia or as lenses within the porous media. The properties of kerosene may change when this liquid penetrates the soils, due to differential volatilization of its individual components. Studies carried out in our laboratory (Acher et al., 1989; Yaron et al., 1989) on a synthetic kerosene mixture have shown that changes in the composition of the parent product (hydrocarbon mixture) occur in the soil medium. Those studies provided experimental data for such synthetic mixtures which can be used to confirm different approaches in defining the impact of volatilization on the fate and transport of petroleum products from land surfaces to groundwater (Schwille, 1984; Pinder and Abriola, 1986; Baher, 1987; Corapcioglu and Baher, 1987; Yaron, 1989). The results published to date have dealt mainly with theoretical models or with well-defined hydrocarbons mixtures. This paper reports data and the composition of industrial kerosene in dry soils as affected by volatilization. 2. MATERIALS AND METHODS
2.1. Materials 2.1.1. Kerosene Industrial aviation gas turbine kerosene composed of a large
number of hydrocarbons with carbon numbers ranging from 9 to 15 was used in the experiment. The chromatogram of the kerosene used is shown in Fig. 1. Seven major components representing 36.8% of the total kerosene were
ClO t
Ci I
CI5 I
l 5
I I0
C 14
I 15
I 20 T I M E (rain)
I 25
I 30
I 35
I 40
Fig. 1. Chromatogram of the kerosene used in the experiment. The identification of C9 to C15 components was based on the boiling point-retention time relationship of well-defined hydrocarbons.
377
SOIL POLLUTIONBY PETROLEUM PRODUCTS,III. TABLE 1 R e l a t i v e a m o u n t of m a j o r identified k e r o s e n e c o m p o n e n t s C a r b o n No.
% of t h e total
C~ C10 Cll C12 C,3 C14 C,~ Total
2.5 7.2 8.0 6.3 6.6 4.4 1.8 36.8
% of s e v e n selected hydrocarbons 6.7 19.5 21.8 17.1 18.0 12.0 4.9 100
identified on a carbon number basis by calibrating the retention time and boiling point of well-defined hydrocarbons. The carbon numbers of the selected kerosene peaks were obtained from this calibration curve, but do not imply (or refute) t h a t these peaks represent the n-alkanes of identical carbon number. The carbon numbers of the components identified by this procedure, C9 to C15, are similar to those reported in the literature (Senn and Johnson, 1985). The percentage of each component in the entire kerosene and from the total of the seven selected components is presented in Table 1.
2.1.2. Soils. The soils used in the experiment were a dune sand, a loamy sand Mediterranean red soil (Typic Rhodoxeralf), and a silty loam loessial sierozem (Typic Haplargid). Before use the soils were air-dried, ground and sieved (50 mesh). The characteristics of the soils used in the experiment are presented in Table 2. 2.2. Experimental procedure Glass columns 10 cm long and 1.5 cm wide were packed with air-dry soils to obtain a soil column of 7.5 cm. The bottom of the column was sealed with a rubber stopper provided with a glass tube (2 cm long and 0.2 cm wide) in order to allow leaching of the excess kerosene and the volatilization of the remaining liquid after the free flow of kerosene stopped. A layer of glass wool was placed on top of the pierced rubber stopper to retain the soil in the column. The apparent bulk density of the columns was 1.93gcm -3 for the dune sand, 1.55gcm 3 for the loamy sand soil and 1.47gcm -3 for the silty loam. The experiment was started with a set of 9 columns for each soil. Kerosene was applied to the top of the soil columns until saturation. The residual kerosene retention capacity of the soils, i.e. the amount of kerosene retained by the soil which, if exceeded, results in free flow of kerosene, was determined. Van Dam (1967) and Schwille (1984) call this value the "residual oil saturation", but to
0 12 16
clay 0 3 36
silt
Particle size distribution (%)
100 85 48
sand
*IAccording to the U,S.D.A. system of classification• *2Specific surface area (determined after Carter et al., 1965).
Dune sand Loamy sand Silty loam
Soils
Characteristics of the soils used in the experiment
TABLE 2
12.2 54.8 89,3
SSA .2 (m 2 g - l )
0 0,6 0,5
(%)
Organic matter
2.3 7.9 18,6
atm.
0.8 6.2 7~2
15 arm.
W a t e r retention (%)
0.3 0.8 2,5
(%)
Air-dry water content
SOIL POLLUTION BY PETROLEUM PRODUCTS, III.
379
avoid confusion this terminology was changed to '~residual retention capacity". The "residual water r e t e nt i on capacity" of the soil columns was determined in the same m a n n e r as the residual kerosene ret ent i on capacity. Preliminary experiments showed t ha t negligible differences in the residual oil and water r eten tio n capacity were found along the experimental soil columns. The top of the columns saturated with kerosene was sealed with Teflon% covered rubber stoppers and kept at 22°C for 50 days and the volatilization of the kerosene occurred only t hr ough the bottom of the columns. The total volatilization of kerosene was determined daily by weighing and the composition of the remaining residues was determined 25, 35 and 50 days after application. For the residual composition, three columns were taken from the experimental set, the kerosene was extracted from the soil and gas chromatography measurements performed. Each t r eat m ent was carried out in three replications and the results were analyzed statistically by ANOVA methods. The experimental conditions - - air-drying of the soil and no subsequent addition of water - - excluded both biodegradative and leaching losses.
2.3. Analytical procedure 2.3.1. Kerosene was extracted from the soil in a 25-mL flask by adding 10mL of a 1:1 w a t e r - c a r b o n tetrachloride mixture to 5 g of soil. The tightly closed flask, was placed in a lab or a t or y shaker for 24 h and then centrifuged (2500 r.p.m.) for 10 min. An aliquot of the carbon tetrachloride was transferred to a 25-mL screw cap flask with aluminum liner, and Na2SO4 and A1203 were added to remove water and humic material, respectively, and saved for analytical quantification. 2.3.2. Gas chromatographic determination The carbon tetrachloride extract of the soil sample was analyzed chromatographically. Aliquots (3#L) were injected into a Varian ® 3300 gas chromatograph equipped with a 30 M DB-1 ® column (i.d. 0.53mm). The analysis was performed in a temperatureprogrammed regime of 2min at 50°C, then to 120°C at 2°Cmin 1, and then to 200°C at 50°C min -1. The carrier gas was nitrogen, while hydrogen and air provided the combustion mixture for the flame ionization detector (FID); the flow rates for nitrogen, hydrogen and air were 30, 30 and 300 mL min ', respectively. The FID was connected to a Merck ®D-2000 integrator, which quantified the chromatogram peak. 4. RESULTSAND DISCUSSION
4.1. Residual kerosene retention capacity The residual kerosene r et ent i on capacity, and the residual water ret ent i on capacity of the soils used in the experiment are compared in Table 3. Both the
380
Ts. GALIN ET AL.
TABLE 3 R e s i d u a l w a t e r a n d k e r o s e n e r e t e n t i o n c a p a c i t y in t h e e x p e r i m e n t a l soil c o l u m n s Soil
Bulk density ( g c m -a)
Total p o r o s i t y .1 (%)
P o r e size d i s t r i b u t i o n (tim) *~ < 0.1
Dune sand Loam
sand Silty loam
0.1 4.5
Retention capacity (w/w) > 4.5
kerosene
water
1.93
27
3.0
8.5
88.5
11.5 + 0.4
14.4 _+ 0.7
1.47
44
14.1
18.0
67.9
23.1 + 2.0
29.0 ± 1.1
1.55
41
17.6
45.4
37.0
26.0 i 0.8
29.5 i 1.0
*~ A s s u m i n g soil particle d e n s i t y is 2.65 g cm a. .2 C a l c u l a t e d from t h e w a t e r r e t e n t i o n c a p a c i t y at ~ a n d 15 atm.
kerosene and the water r et ent i on capacity of the dune sand were ~ 50% of that of the loamy sand and silty loam soils. Those differences are expressed by the low total porosity and larger pore size of the dune sand soil. The data obtained in our column experiment are of the same order of magnitude as those reported by T h o r n t o n (1980) and Hoag and Marley (1986) for gasoline, and show the effect of soil porosity on the residual kerosene retention. It should be noted that the pore-size distribution in the loamy sand soil and the silty loam soils is quite different, despite similar total porosity values (Table 3). However, the pore size distribution did not affect the total residual kerosene retention capacity, indicating t h a t only the distribution and size of the blobs or ganglia trapped in the pores and fractures differed. 4.2. Kerosene volatilization Relative kerosene volatilization from the dune sand, loamy sand and silty loam soils are shown in Fig. 2. A significant difference (P = 0.05) was found to exist between the silty loam soil on the one hand and the dune sand and loamy sand soils on the other hand. The volume fraction of kerosene volatilized was much higher in the sand and loamy sand soils t han in the silty loam soil. Twenty days after application of the kerosene to the soils, ~ 30% of the initial amount remained in the dune sand and loamy sand soil, whereas in the silty loamy soil > 60% of the kerosene was still present. After 50 days the residual kerosene in the dune sand and loamy sand soils was 20%, and in the silty loam 35%. The volatilization of kerosene from the loamy sand and silty loam soils differed considerably, despite the fact t ha t the total porosity and the residual kerosene r eten tio n capacity of these soils are similar. This behavior may be explained by the effect of pore-size distribution in each soil as well as by the free pores in the soil system (Baver, 1959). As seen from Table 3, the dune sand
SOIL POLLUTION BY PETROLEUM PRODUCTS, III. I00
o c
381
-
80--
N
5E
o 60
w~40 z ~_ ±
0
LOAMY
SAND
~ - 2o I 00
I0
I
I
20 30 TIME (doy~)
I
I
40
50
Fig. 2. R e l a t i v e v o l a t i l i z a t i o n of k e r o s e n e from s a n d dune, l o a m y sand, a n d s i l t y l o a m s oi l s (in p e r c e n t of t h e i n i t i a l a m o u n t ) .
and loamy sand soils are characterized by 68-88% large pores ( > 4.5 pm) while the silty loam soil contains > 60% small pores ( < 4.5 pm). The mass transfer of kerosene to the atmosphere is entirely via the vapor phase, so that the mass transfer coefficient is basically an air-phase resistance term. The volatilization of the kerosene components will therefore be affected by the pore-size distribution of the soils. In the silty loam soil the volatilization is restricted by the large number of small pores, so t hat the rate of volatilization is lower than in the dune sand and loamy sand soils, which are characterized by the presence of large pores.
4.3. Stability of simulated spills of kerosene The changes in the composition of the residual kerosene in soils were followed during a 50-day period by analyzing the behavior of seven selected components with carbon numbers ranging between C 9 and C15. Table 4 shows the percent of each component remaining in soils 25, 35 and 50 days after application. Since the biological activity becomes marginal in air-dry soils (Bossert and Bartha, 1984; T. Hoepner, pers. commun., 1989) we consider t hat the volatilization is the main factor affecting the stability of kerosene. In general, the volatilization of the specified kerosene components from soils was inversely related to their carbon number. An exception was the C~5 component, which exhibited a volatilization pattern similar to t hat of the C~3 and C14 hydrocarbons. The volatilization of all seven components determined - characterized by a carbon number between 9 and 15 - - was greater from the dune sand and loamy sand soils t han from the silty loam soil. The differences between the two groups of soils are statistically significant. These results are
382
Ts. GALIN ET AL.
TABLE 4 Major kerosene hydrocarbons remaining in dry soil columns, after volatilization (% of initial amount) Components
Time (days)* 25
35
50
25
dune sand C9 C10 C1, C,2 C13 C,4 C~
35
50
25
loamy sand
5.8 10.3 17.2 30.4 43.5 58.5 46.0
1.2 3.1 7.4 20.0 36.4 47.5 39.3
0.5 1.3 3.4 12.5 31.6 47.8 39.7
4.8 8.5 15.4 22.5 46.2 65.7 40.9
35
50
n.d. n.d. n.d. n.d. n.d. n.d. n.d.
4.6 12.8 23.0 33.5 47.2 58.1 40.4
silty loam
2.1 5.4 12.0 22.0 38.4 43.3 28.0
0.7 2.8 7.2 16.1 32.7 40.2 28.5
26.7 30.4 36.1 41.1 50.2 57.8 39.8
n.d. = not determined. * After application.
40 -
DUNE SAND
r-
~~)o
0
LOAMY SAND
I0
o 4O
20 30 TIME (days)
40
50
SILTY LOAM
20
I0 1
0
I0
I
20 TIME
I
30 (days)
I
40
• C9 • C13
~
o C10 o Cl,4
• Cll ~ Cl 5
D C12
50
Fig. 3. Changes in the concentration of the major hydrocarbons (C 9 to C15) measured in the kerosene 25, 35 and 50 days after the simulated spills in dune sand, loamy sand and silty loam soils (in percent of the total of seven components).
383
SOIL POLLUTION BY PETROLEUM PRODUCTS, lII.
~8
%
--
~
DUNE SAND LOAMY SAND
x
SILTY LOAM
o-, ,.~6 -
o
54 x:
C9
C10
Cl!
C12
C13
C14
J C15
Fig. 4. Compositionof a kerosene spill 50 days after incorporation into the dune sand, loamysand and silty loam soils (ttg/g soil). in accordance with those presented previously (Fig. 2) for the total kerosene volatilization from the same soils. The differential volatilization of the kerosene components according to their carbon number results in an altered composition of the kerosene residues in soils. The remaining residues will be characterized by a larger amount of components with a high carbon number, regardless of the type of soil from which kerosene volatilization occurs. Considering the seven hydrocarbons characterized by carbon numbers C9 to C,~ as major components of kerosene, we calculated the changes in the composition of kerosene in soils. Fig. 3 shows the relative concentration of the selected hydrocarbons with carbon numbers C9 to C15 immediately after kerosene spills in soils, and 25, 35 and 50 days later. Relative composition is defined as the percent of each individual componenVof the total of seven selected hydrocarbons on the sampling date. As a general pattern, the relative concentration of the hydrocarbons with higher carbon numbers increased, since the concentration of those with smaller carbon numbers decreased. The changes in the relative concentrations of the components in the kerosene were affected by the soil properties. For example, the relative concentration of the hydrocarbon characterized by C9 decreased in 50 days from 7% to 0.2% in the dune sand, to 0.3% in the loamy sand, and to 1% in the silty loam soil (Fig. 3). The C14 hydrocarbon increased from 12% to 35% in dune sand, to 25% in loamy sand, and to 26% in silty loam soil. Since the rate of volatilization of the different components from the soils is affected by their properties (e.g., pore-size distribution) the composition of the remaining kerosene at a given time varies from soil to soil. The ultimate concentration and composition of kerosene spills in soils are controlled by the soil properties. Fig. 4 shows the amount of components C9 to C~5 found in the dune sand, loamy sand and silty loam soils 50 days after the simulated spill. The greatest amount of kerosene remaining was in the silty
384
Ts. GALIN ET AL.
l o a m s o i l w h i c h is c h a r a c t e r i z e d b y p r e d o m i n a n t l y s m a l l p o r e s . I n t h e d u n e sand and the loamy sand soils, characterized by predominantly large pores, the v o l a t i l i z a t i o n o f l a r g e f r a c t i o n s o f l o w - m o l e c u l a r - w e i g h t c o m p o u n d s is f a v o r e d a n d t h i s p r o c e s s l e a d s t o a d r a m a t i c d e c r e a s e i n t h e r e s i d u a l k e r o s e n e concentration. Differential volatilization of the individual components leads to a c h a n g e i n t h e c o m p o s i t i o n o f t h e k e r o s e n e r e s i d u e s i n s o i l s . T h e s e c h a n g e s in a d r y s o i l a r e d i r e c t l y r e l a t e d to t h e v o l a t i l i z a t i o n o f e a c h c o m p o n e n t a n d t o t h e soil properties. After a certain period of time following a kerosene application, the components with a higher carbon number are found in greater proportions. ACKNOWLEDGEMENTS This research was supported by a grant from the National Council for Research and Development, Israel, and the Deutsche Forschungs- und Vers u c h s a n s t a l t ffir L u f t u n d R a u m f a h r t e.V., K S l n - P o r t z , F . R . G .
REFERENCES Acher, A.J., Boderie, P. and Yaron, B., 1989. Soil pollution by petroleum products, I. Multiphase migration of kerosene components in soil columns. J. Contam. Hydrol., 4: 333-345. Baher, A.L., 1987. Selective transport of hydrocarbons in the unsaturated zone due to aqueous and vapor phase partitioning. Water Res., 21: 926-938. Baver, L.D., 1959. Soil Physics. Wiley, New York, NY, 489 pp. Bossert, I. and Bartha, A., 1984. The fate of petroleum in soil ecosystems. In: R.M. Atlas (Editor), Petroleum Microbiology. Macmillan, New York, NY, pp. 436-473. Carter, D.L., Heilman, M.D. and Gonzales, C.L., 1965. n-Ethylene glycol monoethyl ether for determining surface area of silicate materials. Soil Sci., 100: 356-360. Corapcioglu, M.Y. and Baher, A.L., 1987. A compositional multiphase model for groundwater contamination by petroleum products, 1. Theoretical considerations. Water Resour. Res., 23: 191-200. Dibble, J.I. and Bartha, R., 1979. Rehabilitation of oil-inundated agricultural land: a case history. Soil Sci., 128: 56-60. Goodger, E.M., 1975. Hydrocarbons Fuels. Macmillan, London, 27 pp. Hoag, G.E. and Marley, M.C., 1986. Gasoline residual saturation in unsaturated uniform aquifer materials. J. Environ. Eng., 11: 586~04. Hunt, J.R., Sitar, N. and Yolell, K.S., 1988a. Nonaqueous phase liquid transport and cleanup, 1. Analysis of mechanisms. Water Resour. Res., 24:1247 1258. Hunt, J.R., Sitar, N. and Yolell, K.S., 1988b. Nonaqueous phase liquid transport and cleanup, 2. Experimental studies. Water Resour. Res., 24: 1259-1265. Pinder, G.F. and Abriola, L.M., 1986. On the simulation of nonaqueous phase organic compounds in the subsurface. Water Resour. Res., 22: 109-119. Schwille, F., 1984. Migration of organic fluids immiscible with water in the unsaturated zone. In: B. Yaron, G. Dagan and J. Goldschmid (Editors), Pollutants in Porous Media. Springer, Berlin, pp. 27 50. Senn, R.B. and Johnson, M.S., 1985. Interpretation of gas chromatography data as a tool in subsurface hydrocarbon investigation. Proc. Petroleum Hydrocarbons and Organic Chemicals in Groundwater, Houston, TX, Am. Pet. Inst.-Natl. Water Wells Assoc., Publ., pp. 331 335. Thornton, J.S., 1980. Underground movement of gasoline in ground water and enhanced recovery by surfactants. Presented at Natl. Conf. on Control of Hazardous Material Spills, Louisville, KY, pp. 13 15.
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v a n Dam, J., 1967. The migration of hydrocarbons in a water-bearing stratum. In: P. Hepple (Editor), The J o i n t Problems of the Oil and Water Industries. Institute of Petroleum, London, pp. 55-96. Yaron, B., 1989. On the behaviour of petroleum hydrocarbons in the unsaturated zone: Abiotic aspects. In: Z. Gerstl, Y. Chen, U. Mingelgrin and B. Yaron (Editors), Toxic Organic Chemicals in Porous Media. Springer, Berlin, pp. 211 230. Yaron, B., Sutherland, P., Galin, T. and Acher, A.J., 1989. Soil pollution by petroleum products, II. Adsorption~iesorption of "kerosene" vapors by soils. J. Contam. Hydrol., 4: 347-358.
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Elsevier Science Publishers B.V., Amsterdam - - Printed in the Netherlands
SOIL POLLUTION BY P E T R O L E U M PRODUCTS, III. K E R O S E N E STABILITY IN SOIL COLUMNS AS A F F E C T E D BY VOLATILIZATION
Ts. GALIN, Z. GERSTL and B. YARON
Department of Soil Organic and Residues Chemistry, Institute of Soils and Water, Agricultural Research Organization, The Volcani Centre, Bet Dagan 50250 (Israel) (Received May 11, 1989; revised and accepted December 12, 1989)
ABSTRACT Galin, Ts., Gerstl, Z. and Yaron, B., 1990. Soil pollution by petroleum products, III. Kerosene stability in soil columns as affected by volatilization. J. Contam. Hydrol., 5: 375-385. The stability of kerosene in soils as affected by volatilization was determined in a laboratory column experiment by following the losses in the total concentration and the change in composition of the residuals in a dune sand, a loamy sand, and a silty loam soil during a 50-day period. Seven major compounds ranging between C9 and Cls were selected from a large variety of hydrocarbons forming kerosene and their presence in the remaining petroleum product was determined. The change in composition of kerosene during the experimental period was determined by gas chromatography and related to the seven major compounds selected. The experimental conditions - - air-dry soil and no subsequent addition of water - - excluded both biodegradative and leaching losses. The losses of kerosene in air-dried soil columns during the 50-day experimental period and the changes in the composition of the remaining residues due to volatilization are reported. The volatilization of all the components determined was greater from the dune sand and loamy sand soils t h a n from the silty loam soil. It was assumed t h a t the reason for this behavior was t h a t the dune sand and the loamy sand soils contain a greater proportion of large pores ( > 4.5 #m) t h a n the silty loam soil, even though the total porosity of the loamy sand and the silty loam is similar. In all the soils in the experiment, the components with a high carbon number formed the main fraction of the kerosene residues after 50 days of incubation.
INTRODUCTION
Kerosene is a petroleum product characterized by low viscosity and medium volatility in comparison with heavy and residual fuels. It is used for wick-fed illumination, spark ignition engines (mainly in agriculture), and aviation gas turbines (Goodger, 1975). Its widespread utilization may result in accidental pollution of soils along pipelines (e.g., Dibble and Bartha, 1979), under gas stations, or in the vicinity of airports. The low viscosity of kerosene makes it a potential pollutant for porous media and groundwater. Hunt et al. (1988a, b) showed that the only logical explanation for the presence of high soil concentrations of kerosene is that it exists as an immiscible phase with water
0169-7722/90/$03.50
© 1990 Elsevier Science Publishers B.V.
376
Ts. GALINET AL.
either as discrete ganglia or as lenses within the porous media. The properties of kerosene may change when this liquid penetrates the soils, due to differential volatilization of its individual components. Studies carried out in our laboratory (Acher et al., 1989; Yaron et al., 1989) on a synthetic kerosene mixture have shown that changes in the composition of the parent product (hydrocarbon mixture) occur in the soil medium. Those studies provided experimental data for such synthetic mixtures which can be used to confirm different approaches in defining the impact of volatilization on the fate and transport of petroleum products from land surfaces to groundwater (Schwille, 1984; Pinder and Abriola, 1986; Baher, 1987; Corapcioglu and Baher, 1987; Yaron, 1989). The results published to date have dealt mainly with theoretical models or with well-defined hydrocarbons mixtures. This paper reports data and the composition of industrial kerosene in dry soils as affected by volatilization. 2. MATERIALS AND METHODS
2.1. Materials 2.1.1. Kerosene Industrial aviation gas turbine kerosene composed of a large
number of hydrocarbons with carbon numbers ranging from 9 to 15 was used in the experiment. The chromatogram of the kerosene used is shown in Fig. 1. Seven major components representing 36.8% of the total kerosene were
ClO t
Ci I
CI5 I
l 5
I I0
C 14
I 15
I 20 T I M E (rain)
I 25
I 30
I 35
I 40
Fig. 1. Chromatogram of the kerosene used in the experiment. The identification of C9 to C15 components was based on the boiling point-retention time relationship of well-defined hydrocarbons.
377
SOIL POLLUTIONBY PETROLEUM PRODUCTS,III. TABLE 1 R e l a t i v e a m o u n t of m a j o r identified k e r o s e n e c o m p o n e n t s C a r b o n No.
% of t h e total
C~ C10 Cll C12 C,3 C14 C,~ Total
2.5 7.2 8.0 6.3 6.6 4.4 1.8 36.8
% of s e v e n selected hydrocarbons 6.7 19.5 21.8 17.1 18.0 12.0 4.9 100
identified on a carbon number basis by calibrating the retention time and boiling point of well-defined hydrocarbons. The carbon numbers of the selected kerosene peaks were obtained from this calibration curve, but do not imply (or refute) t h a t these peaks represent the n-alkanes of identical carbon number. The carbon numbers of the components identified by this procedure, C9 to C15, are similar to those reported in the literature (Senn and Johnson, 1985). The percentage of each component in the entire kerosene and from the total of the seven selected components is presented in Table 1.
2.1.2. Soils. The soils used in the experiment were a dune sand, a loamy sand Mediterranean red soil (Typic Rhodoxeralf), and a silty loam loessial sierozem (Typic Haplargid). Before use the soils were air-dried, ground and sieved (50 mesh). The characteristics of the soils used in the experiment are presented in Table 2. 2.2. Experimental procedure Glass columns 10 cm long and 1.5 cm wide were packed with air-dry soils to obtain a soil column of 7.5 cm. The bottom of the column was sealed with a rubber stopper provided with a glass tube (2 cm long and 0.2 cm wide) in order to allow leaching of the excess kerosene and the volatilization of the remaining liquid after the free flow of kerosene stopped. A layer of glass wool was placed on top of the pierced rubber stopper to retain the soil in the column. The apparent bulk density of the columns was 1.93gcm -3 for the dune sand, 1.55gcm 3 for the loamy sand soil and 1.47gcm -3 for the silty loam. The experiment was started with a set of 9 columns for each soil. Kerosene was applied to the top of the soil columns until saturation. The residual kerosene retention capacity of the soils, i.e. the amount of kerosene retained by the soil which, if exceeded, results in free flow of kerosene, was determined. Van Dam (1967) and Schwille (1984) call this value the "residual oil saturation", but to
0 12 16
clay 0 3 36
silt
Particle size distribution (%)
100 85 48
sand
*IAccording to the U,S.D.A. system of classification• *2Specific surface area (determined after Carter et al., 1965).
Dune sand Loamy sand Silty loam
Soils
Characteristics of the soils used in the experiment
TABLE 2
12.2 54.8 89,3
SSA .2 (m 2 g - l )
0 0,6 0,5
(%)
Organic matter
2.3 7.9 18,6
atm.
0.8 6.2 7~2
15 arm.
W a t e r retention (%)
0.3 0.8 2,5
(%)
Air-dry water content
SOIL POLLUTION BY PETROLEUM PRODUCTS, III.
379
avoid confusion this terminology was changed to '~residual retention capacity". The "residual water r e t e nt i on capacity" of the soil columns was determined in the same m a n n e r as the residual kerosene ret ent i on capacity. Preliminary experiments showed t ha t negligible differences in the residual oil and water r eten tio n capacity were found along the experimental soil columns. The top of the columns saturated with kerosene was sealed with Teflon% covered rubber stoppers and kept at 22°C for 50 days and the volatilization of the kerosene occurred only t hr ough the bottom of the columns. The total volatilization of kerosene was determined daily by weighing and the composition of the remaining residues was determined 25, 35 and 50 days after application. For the residual composition, three columns were taken from the experimental set, the kerosene was extracted from the soil and gas chromatography measurements performed. Each t r eat m ent was carried out in three replications and the results were analyzed statistically by ANOVA methods. The experimental conditions - - air-drying of the soil and no subsequent addition of water - - excluded both biodegradative and leaching losses.
2.3. Analytical procedure 2.3.1. Kerosene was extracted from the soil in a 25-mL flask by adding 10mL of a 1:1 w a t e r - c a r b o n tetrachloride mixture to 5 g of soil. The tightly closed flask, was placed in a lab or a t or y shaker for 24 h and then centrifuged (2500 r.p.m.) for 10 min. An aliquot of the carbon tetrachloride was transferred to a 25-mL screw cap flask with aluminum liner, and Na2SO4 and A1203 were added to remove water and humic material, respectively, and saved for analytical quantification. 2.3.2. Gas chromatographic determination The carbon tetrachloride extract of the soil sample was analyzed chromatographically. Aliquots (3#L) were injected into a Varian ® 3300 gas chromatograph equipped with a 30 M DB-1 ® column (i.d. 0.53mm). The analysis was performed in a temperatureprogrammed regime of 2min at 50°C, then to 120°C at 2°Cmin 1, and then to 200°C at 50°C min -1. The carrier gas was nitrogen, while hydrogen and air provided the combustion mixture for the flame ionization detector (FID); the flow rates for nitrogen, hydrogen and air were 30, 30 and 300 mL min ', respectively. The FID was connected to a Merck ®D-2000 integrator, which quantified the chromatogram peak. 4. RESULTSAND DISCUSSION
4.1. Residual kerosene retention capacity The residual kerosene r et ent i on capacity, and the residual water ret ent i on capacity of the soils used in the experiment are compared in Table 3. Both the
380
Ts. GALIN ET AL.
TABLE 3 R e s i d u a l w a t e r a n d k e r o s e n e r e t e n t i o n c a p a c i t y in t h e e x p e r i m e n t a l soil c o l u m n s Soil
Bulk density ( g c m -a)
Total p o r o s i t y .1 (%)
P o r e size d i s t r i b u t i o n (tim) *~ < 0.1
Dune sand Loam
sand Silty loam
0.1 4.5
Retention capacity (w/w) > 4.5
kerosene
water
1.93
27
3.0
8.5
88.5
11.5 + 0.4
14.4 _+ 0.7
1.47
44
14.1
18.0
67.9
23.1 + 2.0
29.0 ± 1.1
1.55
41
17.6
45.4
37.0
26.0 i 0.8
29.5 i 1.0
*~ A s s u m i n g soil particle d e n s i t y is 2.65 g cm a. .2 C a l c u l a t e d from t h e w a t e r r e t e n t i o n c a p a c i t y at ~ a n d 15 atm.
kerosene and the water r et ent i on capacity of the dune sand were ~ 50% of that of the loamy sand and silty loam soils. Those differences are expressed by the low total porosity and larger pore size of the dune sand soil. The data obtained in our column experiment are of the same order of magnitude as those reported by T h o r n t o n (1980) and Hoag and Marley (1986) for gasoline, and show the effect of soil porosity on the residual kerosene retention. It should be noted that the pore-size distribution in the loamy sand soil and the silty loam soils is quite different, despite similar total porosity values (Table 3). However, the pore size distribution did not affect the total residual kerosene retention capacity, indicating t h a t only the distribution and size of the blobs or ganglia trapped in the pores and fractures differed. 4.2. Kerosene volatilization Relative kerosene volatilization from the dune sand, loamy sand and silty loam soils are shown in Fig. 2. A significant difference (P = 0.05) was found to exist between the silty loam soil on the one hand and the dune sand and loamy sand soils on the other hand. The volume fraction of kerosene volatilized was much higher in the sand and loamy sand soils t han in the silty loam soil. Twenty days after application of the kerosene to the soils, ~ 30% of the initial amount remained in the dune sand and loamy sand soil, whereas in the silty loamy soil > 60% of the kerosene was still present. After 50 days the residual kerosene in the dune sand and loamy sand soils was 20%, and in the silty loam 35%. The volatilization of kerosene from the loamy sand and silty loam soils differed considerably, despite the fact t ha t the total porosity and the residual kerosene r eten tio n capacity of these soils are similar. This behavior may be explained by the effect of pore-size distribution in each soil as well as by the free pores in the soil system (Baver, 1959). As seen from Table 3, the dune sand
SOIL POLLUTION BY PETROLEUM PRODUCTS, III. I00
o c
381
-
80--
N
5E
o 60
w~40 z ~_ ±
0
LOAMY
SAND
~ - 2o I 00
I0
I
I
20 30 TIME (doy~)
I
I
40
50
Fig. 2. R e l a t i v e v o l a t i l i z a t i o n of k e r o s e n e from s a n d dune, l o a m y sand, a n d s i l t y l o a m s oi l s (in p e r c e n t of t h e i n i t i a l a m o u n t ) .
and loamy sand soils are characterized by 68-88% large pores ( > 4.5 pm) while the silty loam soil contains > 60% small pores ( < 4.5 pm). The mass transfer of kerosene to the atmosphere is entirely via the vapor phase, so that the mass transfer coefficient is basically an air-phase resistance term. The volatilization of the kerosene components will therefore be affected by the pore-size distribution of the soils. In the silty loam soil the volatilization is restricted by the large number of small pores, so t hat the rate of volatilization is lower than in the dune sand and loamy sand soils, which are characterized by the presence of large pores.
4.3. Stability of simulated spills of kerosene The changes in the composition of the residual kerosene in soils were followed during a 50-day period by analyzing the behavior of seven selected components with carbon numbers ranging between C 9 and C15. Table 4 shows the percent of each component remaining in soils 25, 35 and 50 days after application. Since the biological activity becomes marginal in air-dry soils (Bossert and Bartha, 1984; T. Hoepner, pers. commun., 1989) we consider t hat the volatilization is the main factor affecting the stability of kerosene. In general, the volatilization of the specified kerosene components from soils was inversely related to their carbon number. An exception was the C~5 component, which exhibited a volatilization pattern similar to t hat of the C~3 and C14 hydrocarbons. The volatilization of all seven components determined - characterized by a carbon number between 9 and 15 - - was greater from the dune sand and loamy sand soils t han from the silty loam soil. The differences between the two groups of soils are statistically significant. These results are
382
Ts. GALIN ET AL.
TABLE 4 Major kerosene hydrocarbons remaining in dry soil columns, after volatilization (% of initial amount) Components
Time (days)* 25
35
50
25
dune sand C9 C10 C1, C,2 C13 C,4 C~
35
50
25
loamy sand
5.8 10.3 17.2 30.4 43.5 58.5 46.0
1.2 3.1 7.4 20.0 36.4 47.5 39.3
0.5 1.3 3.4 12.5 31.6 47.8 39.7
4.8 8.5 15.4 22.5 46.2 65.7 40.9
35
50
n.d. n.d. n.d. n.d. n.d. n.d. n.d.
4.6 12.8 23.0 33.5 47.2 58.1 40.4
silty loam
2.1 5.4 12.0 22.0 38.4 43.3 28.0
0.7 2.8 7.2 16.1 32.7 40.2 28.5
26.7 30.4 36.1 41.1 50.2 57.8 39.8
n.d. = not determined. * After application.
40 -
DUNE SAND
r-
~~)o
0
LOAMY SAND
I0
o 4O
20 30 TIME (days)
40
50
SILTY LOAM
20
I0 1
0
I0
I
20 TIME
I
30 (days)
I
40
• C9 • C13
~
o C10 o Cl,4
• Cll ~ Cl 5
D C12
50
Fig. 3. Changes in the concentration of the major hydrocarbons (C 9 to C15) measured in the kerosene 25, 35 and 50 days after the simulated spills in dune sand, loamy sand and silty loam soils (in percent of the total of seven components).
383
SOIL POLLUTION BY PETROLEUM PRODUCTS, lII.
~8
%
--
~
DUNE SAND LOAMY SAND
x
SILTY LOAM
o-, ,.~6 -
o
54 x:
C9
C10
Cl!
C12
C13
C14
J C15
Fig. 4. Compositionof a kerosene spill 50 days after incorporation into the dune sand, loamysand and silty loam soils (ttg/g soil). in accordance with those presented previously (Fig. 2) for the total kerosene volatilization from the same soils. The differential volatilization of the kerosene components according to their carbon number results in an altered composition of the kerosene residues in soils. The remaining residues will be characterized by a larger amount of components with a high carbon number, regardless of the type of soil from which kerosene volatilization occurs. Considering the seven hydrocarbons characterized by carbon numbers C9 to C,~ as major components of kerosene, we calculated the changes in the composition of kerosene in soils. Fig. 3 shows the relative concentration of the selected hydrocarbons with carbon numbers C9 to C15 immediately after kerosene spills in soils, and 25, 35 and 50 days later. Relative composition is defined as the percent of each individual componenVof the total of seven selected hydrocarbons on the sampling date. As a general pattern, the relative concentration of the hydrocarbons with higher carbon numbers increased, since the concentration of those with smaller carbon numbers decreased. The changes in the relative concentrations of the components in the kerosene were affected by the soil properties. For example, the relative concentration of the hydrocarbon characterized by C9 decreased in 50 days from 7% to 0.2% in the dune sand, to 0.3% in the loamy sand, and to 1% in the silty loam soil (Fig. 3). The C14 hydrocarbon increased from 12% to 35% in dune sand, to 25% in loamy sand, and to 26% in silty loam soil. Since the rate of volatilization of the different components from the soils is affected by their properties (e.g., pore-size distribution) the composition of the remaining kerosene at a given time varies from soil to soil. The ultimate concentration and composition of kerosene spills in soils are controlled by the soil properties. Fig. 4 shows the amount of components C9 to C~5 found in the dune sand, loamy sand and silty loam soils 50 days after the simulated spill. The greatest amount of kerosene remaining was in the silty
384
Ts. GALIN ET AL.
l o a m s o i l w h i c h is c h a r a c t e r i z e d b y p r e d o m i n a n t l y s m a l l p o r e s . I n t h e d u n e sand and the loamy sand soils, characterized by predominantly large pores, the v o l a t i l i z a t i o n o f l a r g e f r a c t i o n s o f l o w - m o l e c u l a r - w e i g h t c o m p o u n d s is f a v o r e d a n d t h i s p r o c e s s l e a d s t o a d r a m a t i c d e c r e a s e i n t h e r e s i d u a l k e r o s e n e concentration. Differential volatilization of the individual components leads to a c h a n g e i n t h e c o m p o s i t i o n o f t h e k e r o s e n e r e s i d u e s i n s o i l s . T h e s e c h a n g e s in a d r y s o i l a r e d i r e c t l y r e l a t e d to t h e v o l a t i l i z a t i o n o f e a c h c o m p o n e n t a n d t o t h e soil properties. After a certain period of time following a kerosene application, the components with a higher carbon number are found in greater proportions. ACKNOWLEDGEMENTS This research was supported by a grant from the National Council for Research and Development, Israel, and the Deutsche Forschungs- und Vers u c h s a n s t a l t ffir L u f t u n d R a u m f a h r t e.V., K S l n - P o r t z , F . R . G .
REFERENCES Acher, A.J., Boderie, P. and Yaron, B., 1989. Soil pollution by petroleum products, I. Multiphase migration of kerosene components in soil columns. J. Contam. Hydrol., 4: 333-345. Baher, A.L., 1987. Selective transport of hydrocarbons in the unsaturated zone due to aqueous and vapor phase partitioning. Water Res., 21: 926-938. Baver, L.D., 1959. Soil Physics. Wiley, New York, NY, 489 pp. Bossert, I. and Bartha, A., 1984. The fate of petroleum in soil ecosystems. In: R.M. Atlas (Editor), Petroleum Microbiology. Macmillan, New York, NY, pp. 436-473. Carter, D.L., Heilman, M.D. and Gonzales, C.L., 1965. n-Ethylene glycol monoethyl ether for determining surface area of silicate materials. Soil Sci., 100: 356-360. Corapcioglu, M.Y. and Baher, A.L., 1987. A compositional multiphase model for groundwater contamination by petroleum products, 1. Theoretical considerations. Water Resour. Res., 23: 191-200. Dibble, J.I. and Bartha, R., 1979. Rehabilitation of oil-inundated agricultural land: a case history. Soil Sci., 128: 56-60. Goodger, E.M., 1975. Hydrocarbons Fuels. Macmillan, London, 27 pp. Hoag, G.E. and Marley, M.C., 1986. Gasoline residual saturation in unsaturated uniform aquifer materials. J. Environ. Eng., 11: 586~04. Hunt, J.R., Sitar, N. and Yolell, K.S., 1988a. Nonaqueous phase liquid transport and cleanup, 1. Analysis of mechanisms. Water Resour. Res., 24:1247 1258. Hunt, J.R., Sitar, N. and Yolell, K.S., 1988b. Nonaqueous phase liquid transport and cleanup, 2. Experimental studies. Water Resour. Res., 24: 1259-1265. Pinder, G.F. and Abriola, L.M., 1986. On the simulation of nonaqueous phase organic compounds in the subsurface. Water Resour. Res., 22: 109-119. Schwille, F., 1984. Migration of organic fluids immiscible with water in the unsaturated zone. In: B. Yaron, G. Dagan and J. Goldschmid (Editors), Pollutants in Porous Media. Springer, Berlin, pp. 27 50. Senn, R.B. and Johnson, M.S., 1985. Interpretation of gas chromatography data as a tool in subsurface hydrocarbon investigation. Proc. Petroleum Hydrocarbons and Organic Chemicals in Groundwater, Houston, TX, Am. Pet. Inst.-Natl. Water Wells Assoc., Publ., pp. 331 335. Thornton, J.S., 1980. Underground movement of gasoline in ground water and enhanced recovery by surfactants. Presented at Natl. Conf. on Control of Hazardous Material Spills, Louisville, KY, pp. 13 15.
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v a n Dam, J., 1967. The migration of hydrocarbons in a water-bearing stratum. In: P. Hepple (Editor), The J o i n t Problems of the Oil and Water Industries. Institute of Petroleum, London, pp. 55-96. Yaron, B., 1989. On the behaviour of petroleum hydrocarbons in the unsaturated zone: Abiotic aspects. In: Z. Gerstl, Y. Chen, U. Mingelgrin and B. Yaron (Editors), Toxic Organic Chemicals in Porous Media. Springer, Berlin, pp. 211 230. Yaron, B., Sutherland, P., Galin, T. and Acher, A.J., 1989. Soil pollution by petroleum products, II. Adsorption~iesorption of "kerosene" vapors by soils. J. Contam. Hydrol., 4: 347-358.