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A predictive laboratory study of trace organic contamination of groundwater: Preliminary results
Journal of Hydrology, 67 (1984) 223--233 Elsevier Science Publishers B.V., Amsterdam -- Printed in The Netherlands
223
[2] A PREDICTIVE L A B O R A T O R Y S T U D Y OF TRACE ORGANIC CONTAMINATION OF GROUNDWATER: PRELIMINARY RESULTS
S.R. HUTCHINS and C.H. WARD
National Center for Ground Water Research, Rice University, Houston, TX 77251 (U.S.A.) (Received February 10, 1983; accepted for publication March 5, 1983)
ABSTRACT Hutchins, S.R. and Ward, C.H., 1984. A predictive laboratory study of trace organic contamination of groundwater: preliminary results. J. Hydrol., 67 : 223--233. A previous study at Rice University demonstrated that trace organic compounds in primary and secondary effluents treated in rapid-infiltration systems are detected in associated groundwaters. However, a direct cause-and-effect relationship was not established, since background data on trace organics in the groundwater were not available. Field studies on a rapid-infiltration site currently under construction at Fort Polk, Louisiana, U.S.A., have indicated that characteristic trace organics are mostly absent from groundwater underlying the site. Therefore, a laboratory study was undertaken to investigate the potential for groundwater contamination by trace organics during operation of this system. Four columns were packed with topsoil obtained from one of the basins at the site. Unchlorinated secondary effluent was also obtained from the site and used as feed solution for the columns. The columns were operated on a 2-day inundation--12-day drying cycle to parallel design operation of the rapid-infiltration system. Feed solution and column effluents were monitored for 22 trace organics by reverse-ion search using capillary gas chromatography--mass spectrometry. By the end of the second inundation cycle, 14 target trace organics consistently found in the feed solution were also detected in the column effluents. However, significant reductions (% reduction) in concentrations were noted for p-dichlorobenzene (100%), tetrachloroethylene (90%), and 2(methylthio)benzothiazole (94%) in the first inundation cycle, and also for p-dichlorobenzene (84%), tetrachloroethylene (84%), acetophenone (67%), 2-(methylthio) benzothiazole (98%), and dibutyl phthaiate (75%) in the second inundation cycle. These preliminary results indicate that groundwater contamination at the Fort Polk rapid-infiltration site can occur once the system begins operation, although concentrations of specific trace organics may be significantly reduced.
INTRODUCTION Land application offers a practical and economical method for the treatm e n t o f d o m e s t i c w a s t e w a t e r . I t i n v o l v e s t h e u s e o f p l a n t s , t h e soil s u r f a c e , a n d t h e soil m a t r i x t o r e m o v e m a n y w a s t e - w a t e r c o n s t i t u e n t s . O f t h e c o m m o n l a n d - t r e a t m e n t m e t h o d s a v a i l a b l e , r a p i d i n f i l t r a t i o n is t h e m o s t
224
advantageous in terms of total land required and the application rates possible. In rapid infiltration most of the applied waste water percolates through the soil and the treated effluent eventually reaches the groundwater. Removal of the waste-water constituents by the filtering and of the variability of waste-water composition, soil characteristics, and oxygen demand, and fecal coliforms are almost completely removed in most cases (U.S.E.P.A., 1977). Phosphorus removals can range from 70 to 90%, depending on the physical and chemical characteristics of the soil. Nitrogen removals are generally poor unless specific operating procedures are established to maximize denitrification. In contrast, little research has been done on the fate and transport of trace organics in these systems. Trace organics are operationally defined here as those compounds, amenable to gas chromatography, which can adsorb to and be extracted from XAD ® resins, and range in concentration from a few nanograms per liter up to several micrograms per liter. Once these c o m p o u n d s migrate away from the more bioactive surface soils, they can persist for long periods of time in groundwater due to the absence or reduction of degradation, volatilization, and transformation processes present in surface waters. A previous study at Rice University has shown that several trace organics c o m m o n in waste water are transported through rapid-infiltration systems and can be found in the associated groundwaters (Tomson et al., 1981}. In addition, a survey of several land-treatment operations in the U.S.A. has revealed that there are characteristic trace organics present in waste water which can generally be found in groundwaters receiving the infiltrate, in spite of the variability of waste-water composition, soil characteristics, and treatment regimes at different sites (Table I). These organics, of industrial origin, are found in many domestic products, and hence are c o m m o n in municipal waste waters. The absence of these compounds in local groundwaters hydrologically unaffected b y rapid infiltration suggests that land treatment is a direct source of trace organics in groundwater. However, due to the absence of background trace organic data at the sites surveyed, it cannot be conclusively stated that the groundwaters were free of these c o m p o u n d s prior to operation of the rapid infiltration systems. A 78-acre (31.57ha) rapid infiltration site currently under construction at Fort Polk, Louisiana, U.S.A., may provide a means of obtaining direct evidence of groundwater contamination and allow for the study of trace organics through the groundwater system. The site was designed to provide tertiary treatment for the 5.2 MGD (7.2" 106 m 3 yr.- 1) unchlorinated secondary effluent from the South Fort Polk sewage-treatment plant. Six polyvinyl chloride (PVC) monitoring wells have been placed around the landtreatment area and sampled on two occasions for trace organics using a modification of the resin adsorption--extraction procedure described previously (Tomson et al., 1979). Two separate analyses o f the secondary effluent at the treatment plant revealed the presence of numerous trace organics, including several candidates from Table I. A list of 22 "target trace organics"
225
TABLE I Wastewater trace organics in groundwaters at land application sites .1 Trace organic
Fort Devens, Mass, U.S.A.
Boulder, Colo., U.S.A.
Lubbock, Texas, U.S.A.
Phoenix, Ariz. U.S.A.
Tetrachloroethylene Toluene Xylene m-Dichlorobenzene p-Dichlorobenzene Naphthalene
0.63 0.02 1.14 0.56 -0.20 0.03 0.19 0.87 0.15 1.40
n.q,*2 _,3 NQ 0.05 0.50 0.22 1.51 0.11 0.34 --
n.q. n.q. n.q. -n.q. n.q. n.q. -n.q. --
2.13
--
0.07 0.02 0.05 0.05 0.07 0.03 -0.01 0.02 0.03 0.05
1.57 0.09 -1.40
0.53 0.48 2.38 0.11
--n.q. n.q.
0.06 0.01 0.73 0.13
2,6-Di-t-butyl-p-benzoquinone Dimethyl phthalate Diethyl phthalate 2-(Methylthio) benzothiazole Benzophenone p -( 1,1,3,3-Tetramethylbutyl ) phenol N-Butylbenzenesulfonamide Dibutyl phthalate Bis (2-ethylhexyl) phthalate
* 1 Units in btg 1-1. n.q. ----compound detected and verified but not quantitated. .3 Compound not detected.
*2
p r o v i d e d t h e d a t a base f o r t r a c e organic a n a l y s e s o f t h e field site a n d t h e c o l u m n s t u d y . T h e initial field-site s t u d y s h o w e d t h a t t h e g r o u n d w a t e r was f r e e o f t h e t a r g e t t r a c e organics a t t h e l i m i t o f d e t e c t i o n a n d in f a c t c o n t a i n e d f e w t r a c e organics a t all. T h e r e f o r e , a l a b o r a t o r y c o l u m n s t u d y was u n d e r t a k e n t o investigate t h e p o t e n t i a l f o r g r o u n d w a t e r c o n t a m i n a t i o n b y the rapid-infiltration system once operation began.
MATERIALS AND METHODS
Soil columns T o m i n i m i z e a d s o r p t i v e a n d leaching e f f e c t s , t h e entire c o l u m n s y s t e m was c o n s t r u c t e d o f T e f l o n ® a n d glass. F o u r c o l u m n s w e r e c o n s t r u c t e d o f 1 2 2 × 7 - c m I.D. P y r e x @ t u b i n g a n d e q u i p p e d w i t h T e f l o n @ s t o p c o c k s . T h e columns were then silyated, cleaned with methanol and methylene chloride, a n d h e a t e d a t 4 0 0 ° C f o r a p e r i o d o f 2 hr. C o l u m n caps w e r e c o n s t r u c t e d f r o m 7 . 6 ~ m O.D. T e f l o n @ r o d a n d t a p p e d w i t h t h r e e t~ -in. N P T inlets. T h e c o l u m n s w e r e p a c k e d in t h e f o l l o w i n g m a n n e r : a 0.3-g p l u g o f s i l y a t e d glass w o o l was i n s e r t e d a b o v e t h e s t o p c o c k f o l l o w e d b y 1 5 0 g o f T e f l o n ®
226 TABLE II Characteristics of Fort Polk rapid-infiltration basin topsoil used in column study Parameter Soil pH Buffer pH Organic matter Cation exchange capacity Sand Silt Clay Soil texture Nitrate-nitrogen Phosphorus (Bray 1 NaCHO3) Sodium Potasssium Magnesium Calcium Sulfate-sulfur Zinc Manganese Copper Iron Boron
Analytical result* 5.5 pH units 6.7 pH units 0.4% dry weight 5.6 meq per 100 g soil 67:6% dry weight 8.6% dry weight 23.8% dry weight sandy clay loam 3 9 46 40 40 200 52 0.2 2.6 0.1 3,0 0.5
* All units in mg l-1 (ppm) unless otherwise expressed. boiling chips (Chemplast) which had been cleaned by S o x h l e t e x t r a c t i o n w i t h m e t h y l e n e chloride. A final plug o f 5.0 g silyated glass wool was placed on t o p o f t h e T e f l o n ® boiling chips. T o p s o i l was o b t a i n e d f r o m o n e o f t h e basins at t h e field site; soft characteristics are given in Table II. T h e soft was p a c k e d in its natural state (8.8% m o i s t u r e c o n t e n t ) w i t h o u t sieving. Rocks, organic debris and soft aggregates greater t h a n 3.5-cm d i a m e t e r were discarded. T h e c o l u m n s were packed, using glass rods, b y stepwise a d d i t i o n o f 1.0-cm i n c r e m e n t s o f soil. T h e soil was d i s t r i b u t e d g e n t l y across t h e cross-sectional area w i t h care t a k e n t o minimize breakage o f t h e soil aggregates. Packing c o n t i n u e d until a soft core length o f 107 c m was o b t a i n e d . T h e e f f l u e n t ends o f t h e c o l u m n s w e r e t h e n fitted with T e f l o n C h e m f l u o r ® c o n n e c t o r s (Chemplast) and ~ - i n . T e f l o n ® t u b i n g a n d c o n n e c t e d t o reservoirs c o n t a i n i n g a k n o w n a m o u n t o f resin~extracted w a t e r ( R E water). RE w a t e r was o b t a i n e d b y passing d e i o n i z e d w a t e r t h r o u g h a c o l u m n o f t y p e APA ® 12 × 4 0 mesh g r a n u l a t e d activated c a r b o n (Calgon) and t h e n t h r o u g h a m i x e d b e d c o l u m n o f A m b e r l i t e ® XAD-2, XAD-4, X A D - 7 a n d XAD-8 resin ( R o h m & Haas). T h e c o l u m n s w e r e saturated in an u p w a r d s d i r e c t i o n b y gravity feed in step i n c r e m e n t s o f 5.0 c m e v e r y 1 2 h r . T h e c o l u m n s were t h e n c o n n e c t e d t o feed reservoirs a n d o p e r a t e d via a Mariotte siphon t o m a i n t a i n a c o n s t a n t h e a d o f 3 c m o n t h e soil (Fig. 1).
227
STERILE AIR
TEFLON
C A P S ......
.......
INLET
CONSTANT
HEAD.
p
FEED
SOLUTION
RESERVOIR
GLASS
WOOL.
TEFLON
CHIPS XAD-4
STOPCOCK
............
""
RESIN
Fig. 1. Soil column design schematic. Secondary effluent (feed solution) enters the soil column by gravity and a constant level ~ maintained on the soil drying flooding cycle by Mariotte siphon. Trace organics are adsorbed onto XAD4 resin column and analyzed after flooding cycle has been completed.
Feed reservoirs were constructed from 4-1 amber glass jugs and sealed with Teflon® caps. Lines connecting the columns to the feed reservoirs, air supply, and resin columns were ]~-in. Teflon®. The columns were then wrapped with a l u m i n u m foil to prevent light entry and algal growth. The ambient temperature of the incubator was adjusted to 20°C. Connections were made to deliver the feed solution to the reservoirs by gravity from a storage reservoir maintained at 4°C. The feed solution, unchlorinated secondary effluent obtained from the site, was transferred into 50-1 glass carboys using a Teflon® and stainless-steel pump, transported back to the laboratory, and stored at 4°C. The columns were operated on a schedule identical to the design schedule for the Fort Polk rapid-infiltration site. This schedule involved a 2-day flooding--12-day drying cycle in which the average infiltration rate would be 46 cm/week. Due to an initial rapid infiltration of the feed solution, infiltration rates for the columns varied from 56 to 78 cm/week. Flooding was
228 initiated by applying air pressure to the Mariotte siphon. Once effluent began eluting from the columns, the flow rate was restricted to 1 . 2 " 1 . 7 ml min.- 1 with the effluent needle valve. At the end of the 2~lay flooding period, the siphon was broken and the columns were allowed to drain at normal speed. The effluent was collected to measure the total eluted volume, After the feed solution had drained to the top of the soil, sterile air flow was initiated to the column headspace at 15--20 cm a min." 1 to give an air volume turnover of once every 13.5--18,0min. Air was maintained on the columns during the entire drying period and disconnected just prior to the next inundation cycle. Sampling for trace organics occurred from the time o f the first appearance of column eluate to the point at which the siphon feed to the columns was disconnected.
Trace organic analysis: sampling Trace organics were concentrated and analyzed by a modification of the resin extraction m e t h o d described previously. Amberlite® XAD-4 resin was cleaned by sequential Soxhlet extraction with methanol, acetonitrile, diethyl ether and methanol for 24hr. each, and stored under methanol. Resin columns were constructed from 8.0 × 1 . 3 ~ m I.D. Pyrex ® tubing with the ends constricted to 0.8 cm. The columns were cleaned with methylene chloride, silyated, rinsed with methanol, and heated at 400°C for at least 12 hr. prior to packing. A silyated glass wool plug was inserted in one end of the column and it was filled with a methanol slurry of XAD-4 resin corresponding to ~ 9 . 0 cm 3. The resin columns were placed in a Soxhlet extractor and extracted for 24 hr. each with methylene chloride and methanol just prior to use. A silyated glass wool plug was inserted into the top inlet and the methanol was flushed from the column with 200 ml RE water. The resin columns were then packed in ice, sealed from light, and connected to the soil columns with Chemfluor® connectors and Teflon® tubing. Once eluate had begun to appear at the effluent end of the soil columns during an inundation cycle, the sampling valve was closed and the soil column effluent was directed through the resin with a minimum introduction of air. The average flow rate through the resin was 1 . 6 m l m i n . -1 , or ~ 1 0 . 7 bed volumes per hour. Once the sampling was complete, the columns were sealed with Teflon® caps and stored in the dark at 4°C until t h e y could be processed.
Trace organic analysis: extraction and analysis All extraction glassware was rinsed with methylene chloride before use. The resin and the glass wool plugs were transferred t o 25-ml separatory funnels with a small a m o u n t of RE water. The water was then drained from the funnel with nitrogen pressure and 10 ml methylene chloride was added. The separatory funnels were handshaken for 2 rain. each a n d the solvent was
229 allowed to penetrate into resin for an additional 20 min. The solvent was drained into a second sepamtory funnel and the resin extraction was repeated. The combined extracts were then drained into concentration vessels, taking care n o t to drain any of the aqueous phase. Concentration vessels were constructed b y fusing the lower 2-ml end of a 15-ml graduated centrifuge t u b e o n t o a 25-ml r o u n d - b o t t o m flask. A small Teflon ® boiling chip was added with the internal standards, deuterated naphthalene and deuterated anthracene. A Vigreaux column was attached and the extract was concentrated to ~ 0.5--1.0 ml over a steam bath. At this point acetone was sprayed over the outside of the concentration vessel to allow the condensing solvent to wash the inside. The extract was further concentrated to 100 ~ 1 b y nitrogen gas. A 100-~1 syringe was used to adjust the final volume and transfer the extract to storage vials with Teflon®-lined septa. Samples were initially analyzed on a Tracor ~ 560 gas chromatograph using capillary columns with flame ionization detectors. Operating parameters were as follows: injection port temperature, 270°C; detector temperature, 300°C; oven temperature, 50°C for 4min., programmed to 270°C at 8°Cmin. -1 . A SP2100 ® fused silica column 50 m in length was used with a flow rate of 1.0 ml min. -1 for capillary work. Identification and quantitation b y reverse-ion search was done using a Finnigan ® 4 0 0 0 gas chromatograph-mass spectrometer. Quantitation was done b y the use of internal and external standards using both the base-ion intensity and the peak area generated in the reconstructed ion chromatogram. Since it was noted that there was essentially no difference in results between the t w o methods, the baseion intensity m e t h o d was chosen for routine work. Statistical analysis
Since trace organic concentrations have been f o u n d to follow a lognormal distribution in some effluents (McCarty et al., 1979), the data were logtransformed to approximate equal variances for parametric testing. The fraction o f trace organics removed by the column, termed the percent reduction, was calculated b y dividing the average concentration of that comp o u n d from all f o u r columns (where detected) b y the concentration measured in the input and subtracting from 100%. The percent reductions were evaluated using the two-tailed Student's t-test with the significance level set at 0.05. The test was designed to determine whether changes in average concentrations of c o m p o u n d s in the feed solution and the column effluents were significant when compared to the variations in concentrations encountered from column to column. RESULTS AND DISCUSSION Table III presents data from the second inundation cycle showing the concentrations o f 22 target trace organics in the feed solution and in the
23O TABLE III Trace organic concentrations in feed solution and column effluents for second inundation cycle No.
1 2 3 4 5 6 7 8 9 10
11 12 13 14 15 16
17 18
19 20 21 22
Target trace organic
Tetrachloroethylene m-Xylene, p-xylene o-Xylene Benzaldehyde p-Dichlorobenzene Cineole Acetophenone Fenchone Linalool Naphthalene ~-Terpineol Carvone Triacetin Skatole o-Phenylphenol Diethyl phthalate 2-(Methylthio) benzothiazole Benzophenone Dibenzothiophene N -Butylbenzenesulfonamide Dibutyl phthalate Bis (2~ethylhexyl) phthalate
Feed solution
Column effluent* I
(pg1-1 )
(#g1-1 )
1.10 0.062 0.042 0.060 0.24 0.019 0.28 0.068 . . . 0.042 . . . . . . . 0.094 . . . -0.19 1.34 0,13 0.004 0.11 0.45 2.51
0.18 -+ 0.030 0.062 + 0.012 0.043 + 0.009 0:052 -+ 0.015 0.042 + 0.015 -- .2 0.095 -+ 0.028 0:059 -+ 0,012 . 0.055 -+ 0.021 . .
.
. ....
.
. 0,26 + 0.070 0:043 -+ 0.037 0.077 -+ 0.042 -0.15 + 0.033 0:12 -+ 0.053 1.35 + 1.50
• l Average of four columns -+ standard deviation. • 2 Compound not detected. soil c o l u m n effluents. N o t all o f t h e target trace organics were c o n s i s t e n t l y p r e s e n t in t h e feed s o l u t i o n d u r i n g the c o u r s e o f t h e s t u d y . C o m p o u n d s such as cineole, linalool, a - t e r p i n e o l , c a r v o n e a n d t r i a c e t i n a p p e a r to be readily b i o d e g r a d a b l e a n d disappeared f r o m t h e feed s o l u t i o n d u r i n g storage at 4°C. O t h e r c o m p o u n d s such as skatole, o - p h e n y l p h e n o l a n d d i b e n z o t h i o p h e n e were p r e s e n t in such trace a m o u n t s t h a t q u a n t i t a t i o n was o f t e n difficult. O f t h e 1 4 t a r g e t t r a c e organics r e m a i n i n g , e a c h , w i t h t h e e x c e p t i o n o f p < l i c h l o r o b e n z e n e , was d e t e c t e d in t h e c o l u m n effluents b y t h e e n d o f t h e first i n u n d a t i o n cycle. A t the e n d o f t h e s e c o n d i n u n d a t i o n c y c l e all these c o m p o u n d s were c o n s i s t e n t l y d e t e c t e d in t h e c o l u m n effluents, a l t h o u g h several were significantly r e d u c e d in c o n c e n t r a t i o n b y passage t h r o u g h t h e soil c o l u m n s . S o m e o f t h e t r a c e organics a p p e a r e d t o be in higher c o n c e n t r a t i o n s in the c o l u m n effluents t h a n in t h e f e e d s o l u t i o n being applied t o t h e c o l u m n s . A l t h o u g h t h e possible f o r m a t i o n o f these c o m p o u n d s in t h e soil c o l u m n c a n n o t be dismissed, it is m o r e p r o b a b l e t h a t
231 TABLE IV Summary data from first tw o inundation cycles Target trace organic
Tetrachloroethylene m-Xylene, p-xylene o-Xylene Benzaldehyde p-Dichlorobenzene Acetophenone Fenchone Naphthalene Diethyl phthalate 2-(Methylthio) benzothiazole Benzophenone N-Butylbenzenesulfonamide Dibutyl phthalate Bis ( 2 ~ t h y l h ex y l ) phthalate
First inundation cycle
Second inundation cycle
percent reduction .1
significance of treatment .2
percent reduction
significance of treatment
90 + 3 25 -+ 16 4+ 100 -+ 0 + + + +
removal no change addition no change removal addition addition addition addition
84 -+ 2 36 + 13 % 8 -+ 29 84 -+ 6 67 -+ 10 + + +
removal no change no change no change removal removal no change no change no change
94 -+ 7 19 + 31
removal no change
98 -+ 3 44 +- 34
removal no change
% 42 -+ 31
no change no change
475 + 12
no change removal
÷
no change
69 -+ 60
no change
,1 Values in percent -+ standard deviation; + indicates that the concentration was greater in the column effluent than in the feed solution. *2 Statistical interpretation o f the results of the treatment process at the 5% significance level.
they are contaminants of the soil or were introduced during the soil column construction. It may also be that the higher organic load in the resin column sampling the feed solution induced limited biodegradation on the resin, even though the column was contained in an ice bath to minimize the process. This would lead to a lower estimate of the concentration in the feed solution. Consistent reductions in concentrations during both inundation cycles were noted only for tetrachloroethylene, p~lichlorobenzene, and 2-(methylthio)benzothiazole (Table IV). The mechanism of removal of these compounds cannot be ascertained based upon the simple design of this study. Retardation of these compounds in the soil by reversible adsorption cannot be the sole removal mechanism, since partition theory predicts that these trace organics should have migrated through the column at the time of the second inundation cycle. Other researchers using pure solutions of concentrations several orders of magnitude above those employed in this study have found that 81 + 16% of tetrachloroethylene and 63 + 4% of p
232 P e r c e n t Reductiorl 0
50
100
Te rachtoroethylene ~-'.'.','~::i:f~ m-Xylene, p-Xylene !
'
11
12
12 ::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::: ::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::
:::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::
A c e t o p h e n o n e !1:::::.::: :.:.:~. • .~;~:::::~:::::::: :¢::::¢,:,:,:.:.:::.:-:.::::::::::: : :~:~:~:;::::;:::;::::~s~;::::i:!:~:;:;:;::::::::::::~:::::::::::::~:::::::::::::::::::::::::::::::::::::: :::::::::::::::::::::: 2 Fenchone !1
Nal3hthalene ! 1 D,ethyl Phthalate ! 1 2 - ( M e t h y , , o ) b e n z o t h a,ol~' ~;:;:~;::i~:~
i1
Benzophenone
N-But ylbenzenesulfonamide
12
~
DIbutyl Phthalate ~:.:.:.:,:+:.:,:.:.: .:.:.:.:+:.:.:.:.:;:.:~:.:.:->:~.:.>:.:.:.:+:+:.:-:-'..:.: ~.~.~.~+~:;~;:;~;~;~+~.:.~.~....~.~.~.~.~::::::::::::::::::::::::::::::::::::::::::::: :+:~.£;£+.-::: ;::! 2 B~s(2 -Ethylr~exyl)Phthalate
1
12
Fig. 2~ Treatment efficiency of soil columns with target trace organics. Bar graph units are in percent. Numbers to the right of the bar graphs refer to first and second inundation cycle. Bars which are shaded illustrate that percent reduction is significant at the 5% significance level.
and dibutyl phthalate were significantly removed only in the second inundation cycle. If microbial degradation is responsible, then it may be that a finite amount of adaptation time is required before these compounds can be partially assimilated. However, these preliminary data are too few to validate such a conjecture. Of primary interest is the observation that several of the target trace organics were relatively unaffected by the treatment process in spite of the fact that some are readily biodegradable at higher concentrations under optimum conditions (Fig. 2). These compounds would be predicted to migrate into the groundwater during operation of a rapid infiltration system, as has indeed been observed for a number o f these trace organics in similar systems.
CONCLUSIONS
The column study is still in progress; effects of microbial i n a c t i o n s on the fate and transport of these trace organics will be assessed in the near future. These preliminary remits show that several trace organics present
233 in waste w a t e r are capable o f migrating t h r o u g h t h e soil profile i n t o groundw a t e r , a l t h o u g h s o m e m a y b e significantly r e d u c e d in c o n c e n t r a t i o n b y t h e process. Based u p o n t h e a b o v e s t u d y , it can be p r e d i c t e d t h a t o p e r a t i o n o f t h e rapid-infiltration site at F o r t Polk, Louisiana, U.S.A., can c o n t r i b u t e a variety o f c o n t a m i n a n t t r a c e organics t o t h e g r o u n d w a t e r .
ACKNOWLEDGEMENT This w o r k was s u p p o r t e d b y C o o p e r a t i v e A g r e e m e n t No. C R 8 0 6 9 3 1 - 0 w i t h t h e U.S. E n v i r o n m e n t a l P r o t e c t i o n A g e n c y .
REFERENCES McCarty, P.L., Argo, D.G. and Reinhard, M., 1979. Treatment R & D/Operations. Syrup. on Water Reuse, March 25--30, 1979, Washington, D.C. Tomson, M.B., Hutchins, S.R., King, J.M. and Ward, C.H., 1979. Trace organic contamination of ground waters: methods for study and preliminary results. Int. water Resour. Assoc., April 23--27, 1979, Mexico City, Proc. 3rd World Congr. on Water Resources, 8 : 3701--3709. Tomson, M.B., Dauchy, J., Hutchins, S.R., Curran, C., Cook, C.J. and Ward, C.H., 1981. Ground water contamination by trace level organics from a rapid infiltration site. Water Res., 15: 1109--1116. U.S.E.P.A. (U.S. Environmental Protection Agency), 1977. Process design manual for land treatment of municipal wastewater. U.S. Environ. Prot. Agency, Washington, D.C., EPA 625/1-77-008. Wilson, J.T., Enfield, C.G., Dunlap, W.J., Cosby, R.L., Foster, D.A. and Basmin, L.B., 1981. Transport and fate of selected organic pollutants in a sandy soil. J. Environ. Qual., 10: 501---506.
223
[2] A PREDICTIVE L A B O R A T O R Y S T U D Y OF TRACE ORGANIC CONTAMINATION OF GROUNDWATER: PRELIMINARY RESULTS
S.R. HUTCHINS and C.H. WARD
National Center for Ground Water Research, Rice University, Houston, TX 77251 (U.S.A.) (Received February 10, 1983; accepted for publication March 5, 1983)
ABSTRACT Hutchins, S.R. and Ward, C.H., 1984. A predictive laboratory study of trace organic contamination of groundwater: preliminary results. J. Hydrol., 67 : 223--233. A previous study at Rice University demonstrated that trace organic compounds in primary and secondary effluents treated in rapid-infiltration systems are detected in associated groundwaters. However, a direct cause-and-effect relationship was not established, since background data on trace organics in the groundwater were not available. Field studies on a rapid-infiltration site currently under construction at Fort Polk, Louisiana, U.S.A., have indicated that characteristic trace organics are mostly absent from groundwater underlying the site. Therefore, a laboratory study was undertaken to investigate the potential for groundwater contamination by trace organics during operation of this system. Four columns were packed with topsoil obtained from one of the basins at the site. Unchlorinated secondary effluent was also obtained from the site and used as feed solution for the columns. The columns were operated on a 2-day inundation--12-day drying cycle to parallel design operation of the rapid-infiltration system. Feed solution and column effluents were monitored for 22 trace organics by reverse-ion search using capillary gas chromatography--mass spectrometry. By the end of the second inundation cycle, 14 target trace organics consistently found in the feed solution were also detected in the column effluents. However, significant reductions (% reduction) in concentrations were noted for p-dichlorobenzene (100%), tetrachloroethylene (90%), and 2(methylthio)benzothiazole (94%) in the first inundation cycle, and also for p-dichlorobenzene (84%), tetrachloroethylene (84%), acetophenone (67%), 2-(methylthio) benzothiazole (98%), and dibutyl phthaiate (75%) in the second inundation cycle. These preliminary results indicate that groundwater contamination at the Fort Polk rapid-infiltration site can occur once the system begins operation, although concentrations of specific trace organics may be significantly reduced.
INTRODUCTION Land application offers a practical and economical method for the treatm e n t o f d o m e s t i c w a s t e w a t e r . I t i n v o l v e s t h e u s e o f p l a n t s , t h e soil s u r f a c e , a n d t h e soil m a t r i x t o r e m o v e m a n y w a s t e - w a t e r c o n s t i t u e n t s . O f t h e c o m m o n l a n d - t r e a t m e n t m e t h o d s a v a i l a b l e , r a p i d i n f i l t r a t i o n is t h e m o s t
224
advantageous in terms of total land required and the application rates possible. In rapid infiltration most of the applied waste water percolates through the soil and the treated effluent eventually reaches the groundwater. Removal of the waste-water constituents by the filtering and of the variability of waste-water composition, soil characteristics, and oxygen demand, and fecal coliforms are almost completely removed in most cases (U.S.E.P.A., 1977). Phosphorus removals can range from 70 to 90%, depending on the physical and chemical characteristics of the soil. Nitrogen removals are generally poor unless specific operating procedures are established to maximize denitrification. In contrast, little research has been done on the fate and transport of trace organics in these systems. Trace organics are operationally defined here as those compounds, amenable to gas chromatography, which can adsorb to and be extracted from XAD ® resins, and range in concentration from a few nanograms per liter up to several micrograms per liter. Once these c o m p o u n d s migrate away from the more bioactive surface soils, they can persist for long periods of time in groundwater due to the absence or reduction of degradation, volatilization, and transformation processes present in surface waters. A previous study at Rice University has shown that several trace organics c o m m o n in waste water are transported through rapid-infiltration systems and can be found in the associated groundwaters (Tomson et al., 1981}. In addition, a survey of several land-treatment operations in the U.S.A. has revealed that there are characteristic trace organics present in waste water which can generally be found in groundwaters receiving the infiltrate, in spite of the variability of waste-water composition, soil characteristics, and treatment regimes at different sites (Table I). These organics, of industrial origin, are found in many domestic products, and hence are c o m m o n in municipal waste waters. The absence of these compounds in local groundwaters hydrologically unaffected b y rapid infiltration suggests that land treatment is a direct source of trace organics in groundwater. However, due to the absence of background trace organic data at the sites surveyed, it cannot be conclusively stated that the groundwaters were free of these c o m p o u n d s prior to operation of the rapid infiltration systems. A 78-acre (31.57ha) rapid infiltration site currently under construction at Fort Polk, Louisiana, U.S.A., may provide a means of obtaining direct evidence of groundwater contamination and allow for the study of trace organics through the groundwater system. The site was designed to provide tertiary treatment for the 5.2 MGD (7.2" 106 m 3 yr.- 1) unchlorinated secondary effluent from the South Fort Polk sewage-treatment plant. Six polyvinyl chloride (PVC) monitoring wells have been placed around the landtreatment area and sampled on two occasions for trace organics using a modification of the resin adsorption--extraction procedure described previously (Tomson et al., 1979). Two separate analyses o f the secondary effluent at the treatment plant revealed the presence of numerous trace organics, including several candidates from Table I. A list of 22 "target trace organics"
225
TABLE I Wastewater trace organics in groundwaters at land application sites .1 Trace organic
Fort Devens, Mass, U.S.A.
Boulder, Colo., U.S.A.
Lubbock, Texas, U.S.A.
Phoenix, Ariz. U.S.A.
Tetrachloroethylene Toluene Xylene m-Dichlorobenzene p-Dichlorobenzene Naphthalene
0.63 0.02 1.14 0.56 -0.20 0.03 0.19 0.87 0.15 1.40
n.q,*2 _,3 NQ 0.05 0.50 0.22 1.51 0.11 0.34 --
n.q. n.q. n.q. -n.q. n.q. n.q. -n.q. --
2.13
--
0.07 0.02 0.05 0.05 0.07 0.03 -0.01 0.02 0.03 0.05
1.57 0.09 -1.40
0.53 0.48 2.38 0.11
--n.q. n.q.
0.06 0.01 0.73 0.13
2,6-Di-t-butyl-p-benzoquinone Dimethyl phthalate Diethyl phthalate 2-(Methylthio) benzothiazole Benzophenone p -( 1,1,3,3-Tetramethylbutyl ) phenol N-Butylbenzenesulfonamide Dibutyl phthalate Bis (2-ethylhexyl) phthalate
* 1 Units in btg 1-1. n.q. ----compound detected and verified but not quantitated. .3 Compound not detected.
*2
p r o v i d e d t h e d a t a base f o r t r a c e organic a n a l y s e s o f t h e field site a n d t h e c o l u m n s t u d y . T h e initial field-site s t u d y s h o w e d t h a t t h e g r o u n d w a t e r was f r e e o f t h e t a r g e t t r a c e organics a t t h e l i m i t o f d e t e c t i o n a n d in f a c t c o n t a i n e d f e w t r a c e organics a t all. T h e r e f o r e , a l a b o r a t o r y c o l u m n s t u d y was u n d e r t a k e n t o investigate t h e p o t e n t i a l f o r g r o u n d w a t e r c o n t a m i n a t i o n b y the rapid-infiltration system once operation began.
MATERIALS AND METHODS
Soil columns T o m i n i m i z e a d s o r p t i v e a n d leaching e f f e c t s , t h e entire c o l u m n s y s t e m was c o n s t r u c t e d o f T e f l o n ® a n d glass. F o u r c o l u m n s w e r e c o n s t r u c t e d o f 1 2 2 × 7 - c m I.D. P y r e x @ t u b i n g a n d e q u i p p e d w i t h T e f l o n @ s t o p c o c k s . T h e columns were then silyated, cleaned with methanol and methylene chloride, a n d h e a t e d a t 4 0 0 ° C f o r a p e r i o d o f 2 hr. C o l u m n caps w e r e c o n s t r u c t e d f r o m 7 . 6 ~ m O.D. T e f l o n @ r o d a n d t a p p e d w i t h t h r e e t~ -in. N P T inlets. T h e c o l u m n s w e r e p a c k e d in t h e f o l l o w i n g m a n n e r : a 0.3-g p l u g o f s i l y a t e d glass w o o l was i n s e r t e d a b o v e t h e s t o p c o c k f o l l o w e d b y 1 5 0 g o f T e f l o n ®
226 TABLE II Characteristics of Fort Polk rapid-infiltration basin topsoil used in column study Parameter Soil pH Buffer pH Organic matter Cation exchange capacity Sand Silt Clay Soil texture Nitrate-nitrogen Phosphorus (Bray 1 NaCHO3) Sodium Potasssium Magnesium Calcium Sulfate-sulfur Zinc Manganese Copper Iron Boron
Analytical result* 5.5 pH units 6.7 pH units 0.4% dry weight 5.6 meq per 100 g soil 67:6% dry weight 8.6% dry weight 23.8% dry weight sandy clay loam 3 9 46 40 40 200 52 0.2 2.6 0.1 3,0 0.5
* All units in mg l-1 (ppm) unless otherwise expressed. boiling chips (Chemplast) which had been cleaned by S o x h l e t e x t r a c t i o n w i t h m e t h y l e n e chloride. A final plug o f 5.0 g silyated glass wool was placed on t o p o f t h e T e f l o n ® boiling chips. T o p s o i l was o b t a i n e d f r o m o n e o f t h e basins at t h e field site; soft characteristics are given in Table II. T h e soft was p a c k e d in its natural state (8.8% m o i s t u r e c o n t e n t ) w i t h o u t sieving. Rocks, organic debris and soft aggregates greater t h a n 3.5-cm d i a m e t e r were discarded. T h e c o l u m n s were packed, using glass rods, b y stepwise a d d i t i o n o f 1.0-cm i n c r e m e n t s o f soil. T h e soil was d i s t r i b u t e d g e n t l y across t h e cross-sectional area w i t h care t a k e n t o minimize breakage o f t h e soil aggregates. Packing c o n t i n u e d until a soft core length o f 107 c m was o b t a i n e d . T h e e f f l u e n t ends o f t h e c o l u m n s w e r e t h e n fitted with T e f l o n C h e m f l u o r ® c o n n e c t o r s (Chemplast) and ~ - i n . T e f l o n ® t u b i n g a n d c o n n e c t e d t o reservoirs c o n t a i n i n g a k n o w n a m o u n t o f resin~extracted w a t e r ( R E water). RE w a t e r was o b t a i n e d b y passing d e i o n i z e d w a t e r t h r o u g h a c o l u m n o f t y p e APA ® 12 × 4 0 mesh g r a n u l a t e d activated c a r b o n (Calgon) and t h e n t h r o u g h a m i x e d b e d c o l u m n o f A m b e r l i t e ® XAD-2, XAD-4, X A D - 7 a n d XAD-8 resin ( R o h m & Haas). T h e c o l u m n s w e r e saturated in an u p w a r d s d i r e c t i o n b y gravity feed in step i n c r e m e n t s o f 5.0 c m e v e r y 1 2 h r . T h e c o l u m n s were t h e n c o n n e c t e d t o feed reservoirs a n d o p e r a t e d via a Mariotte siphon t o m a i n t a i n a c o n s t a n t h e a d o f 3 c m o n t h e soil (Fig. 1).
227
STERILE AIR
TEFLON
C A P S ......
.......
INLET
CONSTANT
HEAD.
p
FEED
SOLUTION
RESERVOIR
GLASS
WOOL.
TEFLON
CHIPS XAD-4
STOPCOCK
............
""
RESIN
Fig. 1. Soil column design schematic. Secondary effluent (feed solution) enters the soil column by gravity and a constant level ~ maintained on the soil drying flooding cycle by Mariotte siphon. Trace organics are adsorbed onto XAD4 resin column and analyzed after flooding cycle has been completed.
Feed reservoirs were constructed from 4-1 amber glass jugs and sealed with Teflon® caps. Lines connecting the columns to the feed reservoirs, air supply, and resin columns were ]~-in. Teflon®. The columns were then wrapped with a l u m i n u m foil to prevent light entry and algal growth. The ambient temperature of the incubator was adjusted to 20°C. Connections were made to deliver the feed solution to the reservoirs by gravity from a storage reservoir maintained at 4°C. The feed solution, unchlorinated secondary effluent obtained from the site, was transferred into 50-1 glass carboys using a Teflon® and stainless-steel pump, transported back to the laboratory, and stored at 4°C. The columns were operated on a schedule identical to the design schedule for the Fort Polk rapid-infiltration site. This schedule involved a 2-day flooding--12-day drying cycle in which the average infiltration rate would be 46 cm/week. Due to an initial rapid infiltration of the feed solution, infiltration rates for the columns varied from 56 to 78 cm/week. Flooding was
228 initiated by applying air pressure to the Mariotte siphon. Once effluent began eluting from the columns, the flow rate was restricted to 1 . 2 " 1 . 7 ml min.- 1 with the effluent needle valve. At the end of the 2~lay flooding period, the siphon was broken and the columns were allowed to drain at normal speed. The effluent was collected to measure the total eluted volume, After the feed solution had drained to the top of the soil, sterile air flow was initiated to the column headspace at 15--20 cm a min." 1 to give an air volume turnover of once every 13.5--18,0min. Air was maintained on the columns during the entire drying period and disconnected just prior to the next inundation cycle. Sampling for trace organics occurred from the time o f the first appearance of column eluate to the point at which the siphon feed to the columns was disconnected.
Trace organic analysis: sampling Trace organics were concentrated and analyzed by a modification of the resin extraction m e t h o d described previously. Amberlite® XAD-4 resin was cleaned by sequential Soxhlet extraction with methanol, acetonitrile, diethyl ether and methanol for 24hr. each, and stored under methanol. Resin columns were constructed from 8.0 × 1 . 3 ~ m I.D. Pyrex ® tubing with the ends constricted to 0.8 cm. The columns were cleaned with methylene chloride, silyated, rinsed with methanol, and heated at 400°C for at least 12 hr. prior to packing. A silyated glass wool plug was inserted in one end of the column and it was filled with a methanol slurry of XAD-4 resin corresponding to ~ 9 . 0 cm 3. The resin columns were placed in a Soxhlet extractor and extracted for 24 hr. each with methylene chloride and methanol just prior to use. A silyated glass wool plug was inserted into the top inlet and the methanol was flushed from the column with 200 ml RE water. The resin columns were then packed in ice, sealed from light, and connected to the soil columns with Chemfluor® connectors and Teflon® tubing. Once eluate had begun to appear at the effluent end of the soil columns during an inundation cycle, the sampling valve was closed and the soil column effluent was directed through the resin with a minimum introduction of air. The average flow rate through the resin was 1 . 6 m l m i n . -1 , or ~ 1 0 . 7 bed volumes per hour. Once the sampling was complete, the columns were sealed with Teflon® caps and stored in the dark at 4°C until t h e y could be processed.
Trace organic analysis: extraction and analysis All extraction glassware was rinsed with methylene chloride before use. The resin and the glass wool plugs were transferred t o 25-ml separatory funnels with a small a m o u n t of RE water. The water was then drained from the funnel with nitrogen pressure and 10 ml methylene chloride was added. The separatory funnels were handshaken for 2 rain. each a n d the solvent was
229 allowed to penetrate into resin for an additional 20 min. The solvent was drained into a second sepamtory funnel and the resin extraction was repeated. The combined extracts were then drained into concentration vessels, taking care n o t to drain any of the aqueous phase. Concentration vessels were constructed b y fusing the lower 2-ml end of a 15-ml graduated centrifuge t u b e o n t o a 25-ml r o u n d - b o t t o m flask. A small Teflon ® boiling chip was added with the internal standards, deuterated naphthalene and deuterated anthracene. A Vigreaux column was attached and the extract was concentrated to ~ 0.5--1.0 ml over a steam bath. At this point acetone was sprayed over the outside of the concentration vessel to allow the condensing solvent to wash the inside. The extract was further concentrated to 100 ~ 1 b y nitrogen gas. A 100-~1 syringe was used to adjust the final volume and transfer the extract to storage vials with Teflon®-lined septa. Samples were initially analyzed on a Tracor ~ 560 gas chromatograph using capillary columns with flame ionization detectors. Operating parameters were as follows: injection port temperature, 270°C; detector temperature, 300°C; oven temperature, 50°C for 4min., programmed to 270°C at 8°Cmin. -1 . A SP2100 ® fused silica column 50 m in length was used with a flow rate of 1.0 ml min. -1 for capillary work. Identification and quantitation b y reverse-ion search was done using a Finnigan ® 4 0 0 0 gas chromatograph-mass spectrometer. Quantitation was done b y the use of internal and external standards using both the base-ion intensity and the peak area generated in the reconstructed ion chromatogram. Since it was noted that there was essentially no difference in results between the t w o methods, the baseion intensity m e t h o d was chosen for routine work. Statistical analysis
Since trace organic concentrations have been f o u n d to follow a lognormal distribution in some effluents (McCarty et al., 1979), the data were logtransformed to approximate equal variances for parametric testing. The fraction o f trace organics removed by the column, termed the percent reduction, was calculated b y dividing the average concentration of that comp o u n d from all f o u r columns (where detected) b y the concentration measured in the input and subtracting from 100%. The percent reductions were evaluated using the two-tailed Student's t-test with the significance level set at 0.05. The test was designed to determine whether changes in average concentrations of c o m p o u n d s in the feed solution and the column effluents were significant when compared to the variations in concentrations encountered from column to column. RESULTS AND DISCUSSION Table III presents data from the second inundation cycle showing the concentrations o f 22 target trace organics in the feed solution and in the
23O TABLE III Trace organic concentrations in feed solution and column effluents for second inundation cycle No.
1 2 3 4 5 6 7 8 9 10
11 12 13 14 15 16
17 18
19 20 21 22
Target trace organic
Tetrachloroethylene m-Xylene, p-xylene o-Xylene Benzaldehyde p-Dichlorobenzene Cineole Acetophenone Fenchone Linalool Naphthalene ~-Terpineol Carvone Triacetin Skatole o-Phenylphenol Diethyl phthalate 2-(Methylthio) benzothiazole Benzophenone Dibenzothiophene N -Butylbenzenesulfonamide Dibutyl phthalate Bis (2~ethylhexyl) phthalate
Feed solution
Column effluent* I
(pg1-1 )
(#g1-1 )
1.10 0.062 0.042 0.060 0.24 0.019 0.28 0.068 . . . 0.042 . . . . . . . 0.094 . . . -0.19 1.34 0,13 0.004 0.11 0.45 2.51
0.18 -+ 0.030 0.062 + 0.012 0.043 + 0.009 0:052 -+ 0.015 0.042 + 0.015 -- .2 0.095 -+ 0.028 0:059 -+ 0,012 . 0.055 -+ 0.021 . .
.
. ....
.
. 0,26 + 0.070 0:043 -+ 0.037 0.077 -+ 0.042 -0.15 + 0.033 0:12 -+ 0.053 1.35 + 1.50
• l Average of four columns -+ standard deviation. • 2 Compound not detected. soil c o l u m n effluents. N o t all o f t h e target trace organics were c o n s i s t e n t l y p r e s e n t in t h e feed s o l u t i o n d u r i n g the c o u r s e o f t h e s t u d y . C o m p o u n d s such as cineole, linalool, a - t e r p i n e o l , c a r v o n e a n d t r i a c e t i n a p p e a r to be readily b i o d e g r a d a b l e a n d disappeared f r o m t h e feed s o l u t i o n d u r i n g storage at 4°C. O t h e r c o m p o u n d s such as skatole, o - p h e n y l p h e n o l a n d d i b e n z o t h i o p h e n e were p r e s e n t in such trace a m o u n t s t h a t q u a n t i t a t i o n was o f t e n difficult. O f t h e 1 4 t a r g e t t r a c e organics r e m a i n i n g , e a c h , w i t h t h e e x c e p t i o n o f p < l i c h l o r o b e n z e n e , was d e t e c t e d in t h e c o l u m n effluents b y t h e e n d o f t h e first i n u n d a t i o n cycle. A t the e n d o f t h e s e c o n d i n u n d a t i o n c y c l e all these c o m p o u n d s were c o n s i s t e n t l y d e t e c t e d in t h e c o l u m n effluents, a l t h o u g h several were significantly r e d u c e d in c o n c e n t r a t i o n b y passage t h r o u g h t h e soil c o l u m n s . S o m e o f t h e t r a c e organics a p p e a r e d t o be in higher c o n c e n t r a t i o n s in the c o l u m n effluents t h a n in t h e f e e d s o l u t i o n being applied t o t h e c o l u m n s . A l t h o u g h t h e possible f o r m a t i o n o f these c o m p o u n d s in t h e soil c o l u m n c a n n o t be dismissed, it is m o r e p r o b a b l e t h a t
231 TABLE IV Summary data from first tw o inundation cycles Target trace organic
Tetrachloroethylene m-Xylene, p-xylene o-Xylene Benzaldehyde p-Dichlorobenzene Acetophenone Fenchone Naphthalene Diethyl phthalate 2-(Methylthio) benzothiazole Benzophenone N-Butylbenzenesulfonamide Dibutyl phthalate Bis ( 2 ~ t h y l h ex y l ) phthalate
First inundation cycle
Second inundation cycle
percent reduction .1
significance of treatment .2
percent reduction
significance of treatment
90 + 3 25 -+ 16 4+ 100 -+ 0 + + + +
removal no change addition no change removal addition addition addition addition
84 -+ 2 36 + 13 % 8 -+ 29 84 -+ 6 67 -+ 10 + + +
removal no change no change no change removal removal no change no change no change
94 -+ 7 19 + 31
removal no change
98 -+ 3 44 +- 34
removal no change
% 42 -+ 31
no change no change
475 + 12
no change removal
÷
no change
69 -+ 60
no change
,1 Values in percent -+ standard deviation; + indicates that the concentration was greater in the column effluent than in the feed solution. *2 Statistical interpretation o f the results of the treatment process at the 5% significance level.
they are contaminants of the soil or were introduced during the soil column construction. It may also be that the higher organic load in the resin column sampling the feed solution induced limited biodegradation on the resin, even though the column was contained in an ice bath to minimize the process. This would lead to a lower estimate of the concentration in the feed solution. Consistent reductions in concentrations during both inundation cycles were noted only for tetrachloroethylene, p~lichlorobenzene, and 2-(methylthio)benzothiazole (Table IV). The mechanism of removal of these compounds cannot be ascertained based upon the simple design of this study. Retardation of these compounds in the soil by reversible adsorption cannot be the sole removal mechanism, since partition theory predicts that these trace organics should have migrated through the column at the time of the second inundation cycle. Other researchers using pure solutions of concentrations several orders of magnitude above those employed in this study have found that 81 + 16% of tetrachloroethylene and 63 + 4% of p
232 P e r c e n t Reductiorl 0
50
100
Te rachtoroethylene ~-'.'.','~::i:f~ m-Xylene, p-Xylene !
'
11
12
12 ::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::: ::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::
:::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::
A c e t o p h e n o n e !1:::::.::: :.:.:~. • .~;~:::::~:::::::: :¢::::¢,:,:,:.:.:::.:-:.::::::::::: : :~:~:~:;::::;:::;::::~s~;::::i:!:~:;:;:;::::::::::::~:::::::::::::~:::::::::::::::::::::::::::::::::::::: :::::::::::::::::::::: 2 Fenchone !1
Nal3hthalene ! 1 D,ethyl Phthalate ! 1 2 - ( M e t h y , , o ) b e n z o t h a,ol~' ~;:;:~;::i~:~
i1
Benzophenone
N-But ylbenzenesulfonamide
12
~
DIbutyl Phthalate ~:.:.:.:,:+:.:,:.:.: .:.:.:.:+:.:.:.:.:;:.:~:.:.:->:~.:.>:.:.:.:+:+:.:-:-'..:.: ~.~.~.~+~:;~;:;~;~;~+~.:.~.~....~.~.~.~.~::::::::::::::::::::::::::::::::::::::::::::: :+:~.£;£+.-::: ;::! 2 B~s(2 -Ethylr~exyl)Phthalate
1
12
Fig. 2~ Treatment efficiency of soil columns with target trace organics. Bar graph units are in percent. Numbers to the right of the bar graphs refer to first and second inundation cycle. Bars which are shaded illustrate that percent reduction is significant at the 5% significance level.
and dibutyl phthalate were significantly removed only in the second inundation cycle. If microbial degradation is responsible, then it may be that a finite amount of adaptation time is required before these compounds can be partially assimilated. However, these preliminary data are too few to validate such a conjecture. Of primary interest is the observation that several of the target trace organics were relatively unaffected by the treatment process in spite of the fact that some are readily biodegradable at higher concentrations under optimum conditions (Fig. 2). These compounds would be predicted to migrate into the groundwater during operation of a rapid infiltration system, as has indeed been observed for a number o f these trace organics in similar systems.
CONCLUSIONS
The column study is still in progress; effects of microbial i n a c t i o n s on the fate and transport of these trace organics will be assessed in the near future. These preliminary remits show that several trace organics present
233 in waste w a t e r are capable o f migrating t h r o u g h t h e soil profile i n t o groundw a t e r , a l t h o u g h s o m e m a y b e significantly r e d u c e d in c o n c e n t r a t i o n b y t h e process. Based u p o n t h e a b o v e s t u d y , it can be p r e d i c t e d t h a t o p e r a t i o n o f t h e rapid-infiltration site at F o r t Polk, Louisiana, U.S.A., can c o n t r i b u t e a variety o f c o n t a m i n a n t t r a c e organics t o t h e g r o u n d w a t e r .
ACKNOWLEDGEMENT This w o r k was s u p p o r t e d b y C o o p e r a t i v e A g r e e m e n t No. C R 8 0 6 9 3 1 - 0 w i t h t h e U.S. E n v i r o n m e n t a l P r o t e c t i o n A g e n c y .
REFERENCES McCarty, P.L., Argo, D.G. and Reinhard, M., 1979. Treatment R & D/Operations. Syrup. on Water Reuse, March 25--30, 1979, Washington, D.C. Tomson, M.B., Hutchins, S.R., King, J.M. and Ward, C.H., 1979. Trace organic contamination of ground waters: methods for study and preliminary results. Int. water Resour. Assoc., April 23--27, 1979, Mexico City, Proc. 3rd World Congr. on Water Resources, 8 : 3701--3709. Tomson, M.B., Dauchy, J., Hutchins, S.R., Curran, C., Cook, C.J. and Ward, C.H., 1981. Ground water contamination by trace level organics from a rapid infiltration site. Water Res., 15: 1109--1116. U.S.E.P.A. (U.S. Environmental Protection Agency), 1977. Process design manual for land treatment of municipal wastewater. U.S. Environ. Prot. Agency, Washington, D.C., EPA 625/1-77-008. Wilson, J.T., Enfield, C.G., Dunlap, W.J., Cosby, R.L., Foster, D.A. and Basmin, L.B., 1981. Transport and fate of selected organic pollutants in a sandy soil. J. Environ. Qual., 10: 501---506.