Environ. Sci. Technol. 2003, 37, 681-690
Locating and Quantifying PCB Sources in Chicago: Receptor Modeling and Field Sampling Y I N G - K U A N G H S U , †,‡ T H O M A S M . H O L S E N , * ,† A N D PHILIP K. HOPKE§ Department of Civil and Environmental Engineering and Department of Chemical Engineering, Clarkson University, Potsdam, New York 13699
Potential source contribution function (PSCF) modeling using polychlorinated biphenyl (PCB) concentrations measured in the Chicago area resolved three PCB source sectors. They were (i) the direction northwest of Chicago, (ii) the direction southwest of Chicago, and (iii) the south side of Chicago in the neighborhood of Lake Calumet. The area south of Chicago was further examined by taking upwind/ downwind samples near a landfill and sludge drying beds. Results identified the sludge drying beds and a large landfill as PCB sources to the atmosphere. Another PCB source identified in Chicago was a transformer storage yard. This site had the highest upwind/downwind concentration increments in this study (downwind PCB concentrations were more than 5 times those in the upwind air). These PCB sources were characterized in terms of inventories, emission rates, contributions, and PCB congener profiles (fingerprints). Preliminarily results indicate that the sludge may emit up to 90 kg/yr of PCBs to the air. This amount is probably not a significant contribution of PCBs to the Chicago atmosphere on the basis of dispersion modeling results and a simple box model.
Introduction Recent research has shown that ambient PCB concentrations in the urban area surrounding southern Lake Michigan (SLM) are significantly higher than in nearby nonurban areas (approximately 2-3 vs 0.5 are shown in more detail in Figure 4. This figure was subdivided into PSCF categories of 0.57-0.67, 0.67-0.86, and 0.86-1.0 with the squares indicating the highest value. As discussed above, most of the southwesterly trend with high PSCF values was probably related to increased volatilization from numerous surfaces due to higher temperatures and trailing effects. Potential source areas that remain encompass the area south of Chicago to Joliet, IL. In this region, the highest PSCF value surrounds the Lake Calumet area. This location had PSCF values equal to 1 when LMUATS and over 686
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lake data were used (Figures 2 and 3). This area is a highly industrial area that includes municipal and hazardous waste landfills, water reclamation facilities, and other industries. Additional evidence suggests that there are PCB sources in the area to the south and northwest of Chicago as shown in Figure 5. This modeling result used AEOLOS-IIT data (2) excluding three samples taken during rain events that had unusually high concentrations (14.2, 7.6, and 4.0 ng/m3) probably because of water molecules displacing the PCBs from soil and other surfaces (42, 43). These results contain most of the high potential PCB source areas that were found
TABLE 2. Potential Sources Upwind/Downwind PCB Concentrations
date
site
08/14/98 08/15/99 08/15/99 08/17/99 07/20/00 07/20/00 07/06/99 08/16/99 07/19/00 07/19/00 07/18/00 07/18/00 08/13/98 07/04/99 08/16/99 08/12/98 08/15/98 08/17/99
ComEd transformer storage yard
a
Calumet East drying beds Stickney drying beds CID landfill Indiana Harbor CDF McCook Metals
temp (°C)
wind speed (m/s)
PCB concn (ng/m3) updownwind wind
30 23 23 28 23 25 28 25 21 21 22 21 28 32 27 27 25 28
4.63 3.15 3.86 6.10 2.74 4.41 4.50 4.73 5.51 5.27 4.58 4.81 3.94 7.20 6.03 5.44 3.99 6.10
naa 1.41 1.33 na 1.21 1.53 2.87 na 1.12 0.76 2.57 1.83 na 1.93 1.23 na na na
11.89 2.11 2.73 3.29 6.49 8.07 5.47 1.94 3.19 1.82 4.54 3.90 5.13 3.99 2.47 1.34 1.61 1.79
na, not available.
FIGURE 6. ComED transformer storage yard average air PCB profile. The height of each bar indicates the average percent of the corresponding PCB congener in samples. when all of the samples were used (Figure 1) except the large southwest source trend, indicating that these three rain events occurred during southwest winds. Field Sampling. Transformer Storage Yard. The highest upwind/downwind concentration increment found in this study was between the fence lines of the ComEd transformer storage yard (Table 2). A centerline downwind sample collected in 1998 contained 11.9 ng/m3 of PCBs. Downwind samples collected in 1999 and 2000 at a distance approximately 100 m from the fence and not at the centerline (because of the wind direction during sampling and poor accessibility of this site) were smaller but still elevated. This transformer storage yard was not listed in 1999 EPA’s PCB Transformer Registration Database (44). This site had PSCF values of less than 0.5 for all of the data sets examined meaning that the total PCB contribution to Chicago air may not be significant. At this site the downwind minus upwind concentration profiles contained both low and high molecular weight congeners (Figure 6). These profiles are similar to mixtures of the commercial Aroclors used in transformers and capacitors and contain more high molecular weight congeners than typically found in ambient air.
FIGURE 7. Calumet East and Stickney municipal sludge drying beds average air PCB profile. Municipal Sludge Drying Beds. Both Stickney and Calumet East sludge drying beds were verified as PCB sources (Table 2) using upwind/downwind sampling. Variations in the increment between upwind and downwind concentrations were, in part, due to the differences in wind directions, wind speeds, ambient temperatures and types and amounts of material in the drying areas during the different events. The upwind/downwind sample set collected at the Calumet East drying beds on July 6, 1999, was taken when the wind was from the west, so the upwind sample was downwind of the west sludge drying beds and wastewater aeration facilities. As a result, the upwind concentrations were higher than the upwind samples obtained on other days. In 2000, additional sets of samples were taken upwind and downwind of the drying beds. In each case, the downwind sample was elevated over the upwind sample. On July 19 when the wind was from the north, the upwind air samples, which were downwind of downtown Chicago, have relatively low concentrations (0.76 and 1.12 ng/m3). The area including the sludge drying beds and CID landfill had PSCF values equal to 1 in all modeling results, which indicate that they may be significant contributors of PCBs to Chicago air. The downwind minus upwind PCB profiles were similar and rich in low molecular weight congeners (Figure 7). These downwind air PCB profiles are more similar to Aroclor 1242 than to the higher molecular weight Aroclors and had much lower concentrations of the high molecular weight congeners than the profiles from the transformer storage yard. CID Landfill. The CID landfill was also verified as a PCB source (Table 2). The source of these PCBs may be from both landfill gas escaping from the landfill and the wastewater sludge used as a cover. When some of the landfill appeared to be covered with freshly dried sludge from MWRDGC, downwind samples contained 5.1 and 4.0 ng/m3 of PCBs. When the landfill was covered with soil, the increment between upwind/downwind concentrations was lower, possibly because of PCB emission retardation when the sludge was covered with soil (45, 46). The CID landfill samples had similar PCB profiles to the sludge drying facilities possibly in part because the dried sludge from Stickney and Calumet East Plants has been disposed of in this landfill along with numerous other materials (Figure 8). This site had PSCF values equal to 1, indicating that it may be a significant PCB source. Other Potential Sources. PCB concentrations measured downwind of Indiana Harbor and the CDF were 1.34 and 1.61 ng/m3, respectively (Table 2). These samples were taken at a distance of less than 2 km from the lakeshore and were higher than the average concentration of 0.5 ng/m3 collected over the lake (2). They were also higher than the measureVOL. 37, NO. 4, 2003 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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FIGURE 8. CID landfill average air PCB profile. ments made at IIT during AEOLOS when the winds were from the lake direction (averaged 0.88 ( 0.44 ng/m3) (2). Both Indiana Harbor and the CDF had PSCF values equal to 1. The sample collected downwind of McCook Metals had a PCB concentration of 1.79 ng/m3 (Table 2). No upwind sample was taken. PSCF results (less than 0.5) did not identify this area as a potential PCB source. This site in McCook, IL, approximately 18 km southwest of downtown Chicago, is registered with the EPA as having the highest PCB inventory in Illinois in the 1999 PCB Transformer Registration Database (44). Sludge PCB Measurements. In July 2000, grab samples of municipal wastewater sludge were taken from different processes and stages of dryness from both Stickney and Calumet East Plants. Concentrations of PCBs in these sludge samples ranged from 0.6 to 1.0 mg/dry kg, similar to those reported by MWRDGC (47). In their report, average PCB concentrations were reported to be 0.48 mg/kg in both Stickney and Calumet East sludge ranging from not detected to 1.78 mg/kg (summation of Aroclors 1016, 1242, and 1260). Webber et al. (28) reported that the PCB content of digested sludge from Stickney Water Reclamation Plant averaged 1.4 ( 1 mg/dry kg, significantly lower than the 50 mg/dry kg reported in 1982 for Madison Metropolitan Sewerage District sludge (41). In the sludge analyzed in this study, the congener profiles were similar, and homologues were fairly evenly distributed. To measure water and PCB losses during air-drying, sludge drying experiments were performed in the laboratory. In these experiments it took less than 3 d to decrease the sludge moisture content from 75% to 12%, significantly faster than the six to eight weeks it takes in the field. The amount of PCBs lost was similar (0.74 to 0.15 mg/dry kg) and highly correlated with the moisture content (r2 ) 0.86) (50). For all eight sludge samples collected during this study:
PCB concentration (mg/dry kg) ) 0.0098 × moisture content (%) + 0.1401 (4) Since PCB biodegradation over this short time period should be negligible (48), PCB loss during this experiment was volatilization to the air. Chiarenzelli et al. (49) also measured PCB volatilization losses during air-drying, although they used sediment from a Federal Superfund Site. Under ambient conditions (20 °C, RH ) 25%) PCB losses ranged from 14% to 23%, with 8090% of the total loss occurring within the first 8 h. PCB loss was positively correlated with water loss (r2 > 0.99). Sludge PCB Inventory Estimation. The MWRDGC sludge drying beds usually contain 20 cm thick sludge with an initial moisture content ranging from 75% to 85% and a final moisture content of approximately 35%. Drying time varies 688
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from 3 to 8 weeks, depending largely on the weather conditions. At this final moisture content, the PCB concentration can be estimated to be 0.48 mg/dry kg using eq 4. A freshly centrifuged sludge grab sample from Calumet East Plant had a PCB concentration of 1.01 mg/dry kg similar to the value that Webber et al. (28) reported for digested sludge from the Stickney Water Reclamation Plant (1.4 ( 1 mg/dry kg in 1990). Using the 1.01 mg/dry kg value, PCB volatilization during drying is estimated to be 52%. If this value represents the average PCB loss in 1999 when the annual sludge production from Stickney and Calumet East drying beds was 170,685 dry tons (47), PCB volatilization from these sludge drying beds is estimated to be 90 kg/yr to the atmosphere. This estimate, based on laboratory measurements, needs to be verified in the field since volatilization in the field may be significantly different than in the laboratory. The U.S. EPA 1990 Emission Inventory of Section 112(c) (6) Pollutants (5) reported 142.9 kg/yr of PCB emitted to the air nationwide from incineration sources (the only source included in this report). The 1996 Inventory of Toxic Air Emissions (51) estimated 16.1 kg/yr of PCBs emitted to the air in Region 5, although no sources were listed for Illinois. Clearly there is a significant need to update these emission inventories. Modeling of PCB Emissions. The K-theory approach has been developed for describing short-range air dispersion from area sources of nonbuoyant toxics (52-57). Under steady conditions, transport of gases in the atmosphere may be described by
u(z)
∂ ∂c ∂c ) K(z) ∂x ∂z ∂z
(5)
if the effect of diffusion in the horizontal direction is neglected where u is the turbulent-mean wind, assumed to be in the x direction, K is the eddy diffusivity in the vertical direction (z), and c is the concentration of the transported substance. The z dependence of the wind and the diffusivity may be represented by empirically determined power laws:
u(z) ) cuzm
Kz(z) ) ckzn
(6)
where m and cu are power law coefficients of wind velocity, and n and ck are power law coefficients for the vertical eddy diffusivity. An approximate solution to eq 5 has been obtained by an integral method by Lebedeff and Hameed (52, 53). Explicit model development and parameter estimation can be found in Chitgopekar et al. (57). PCB emission rates were estimated for the sludge drying beds, the CID landfill, and the transformer storage yard with a model based on K-theory (52, 53, 57) and the EPA virtual point source model (58) (Table 3). For these calculations, the areas of the transformer storage yard and each sludge drying cell were estimated to be 91 m × 150 m and 422 m × 311 m, respectively. The size of the CID landfill covered with sludge and soil was estimated to be the same size as a sludge drying cell. Upwind/downwind concentration increments, meteorological parameters (temperatures and wind speeds) measured during sampling, and an estimated roughness of 10 cm (59) were also used. On the basis of wind speed and solar isolation measured in the field, neutral stability was assumed. Under neutral conditions, the Monin-Obukhov (M-O) lengths, L, were estimated to range between -45 and 45 m at a roughness of 10 cm (60). After multiplying by the estimated source areas, the emission rates of each source unit based on K-theory and EPA virtual point source model were found to be similar (Table 3). To determine the importance of these sources to the Chicago Region, the estimated PCB input from these sources
TABLE 3. Emission Rates Based on K-Theory and EPA Virtual Point Source Models
site
date
(down - up) wind concn (ng/m3)
ComEd ComEd Calumet East Calumet East Calumet East Stickney Stickney CID landfill CID landfill
7/20/00 7/20/00 7/06/99 7/19/00 7/19/00 7/18/00 7/18/00 7/04/99 8/16/99
5.28 6.53 2.60 2.07 1.06 2.07 1.97 2.06 1.24
were compared to the total estimated emissions to the atmosphere of Chicago. This amount was estimated with a simple box model using an average mixing height for Chicago of 800 m (61) and a wind speed range from 1.8 to 5.5 m/s (2). The width of the box is highly uncertain because only a limited number of locations were sampled but probably ranges between a maximum of 60 km (the distance between Evanston, IL, and Gary, IN) and about half of that distance. The PCB concentrations measured simultaneously at IIT and Kankakee, IL, were used to determine the concentration increment between the downwind and upwind sides of the box. At these two sites, the PCB concentration differences ranged from 0.62 to 2.98 ng/m3 when the winds were from the southwest direction (1). This increment is similar to the difference between the average PCB concentration measured at IIT-Rice campus in Wheaton, IL, in 1999 (1.01 ng/m3) and at IIT during AEOLOS in 1994 (3.26 ng/m3). Using this information in the box model indicates that between 2 and 70 kg of PCBs are entering the air within Chicago each day from various sources. These calculations suggest that between 0.03 and 8% of the emission to the Chicago atmosphere can be accounted for by the sources investigated in this study. Relevant Regulations. The CAAA regulates air emissions from mobile and stationary sources. Under the CAAA of 1990, air contaminants are designated and regulated by defining a list of 189 hazardous air pollutants including PCBs. Specific rules have not been promulgated (62). Occupational Safety and Health Administration (OSHA) permissible exposure limit for PCBs is 500 000 ng/m3 (54% chlorine, 8-h time-weighted average) (29 CFR 1910). National Institute of Occupational Safety and Health (NIOSH) recommended a maximum exposure level of 1000 ng/m3 (10-h time-weighted average) (29 CFR 1900). Ambient PCBs downwind of all identified sources were at least several orders of magnitude lower than OSHA and NIOSH recommended concentrations. Superfund cleanup levels are determined on a site-bysite basis to achieve protection of human health and the environment. For soils, the starting action level or preliminary remediation goal is 1 ppm for PCBs at sites where unlimited exposure under residential land use is assumed and 10-25 ppm for sites where industrial use is assumed (62). The highest PCB source concentration found in this study was from the Calumet East Plant centrifuged sludge at 1.01 mg/dry kg (1.01 ppm wt/wt).
Acknowledgments This work was funded in part by the Great Lakes National Program Office, Angela Bandemehr and Paul Horvatin Project Officers. We also thank Eleanor Hopke at Clarkson University, Dick Todd at IIT Rice Campus, Thomas Murphy at DePaul University, and Jeff Chiarenzelli and Jim Pagano and their research group at SUNY Oswego for all their assistance. The cooperation of the Metropolitan Water Reclamation District of Greater Chicago is greatly appreciated.
emission rate K-theory (ng m-2 s-1) 0.31-0.80 0.38-0.99 0.17-0.27 0.14-0.21 0.07-0.11 0.14-0.21 0.13-0.20 0.14-0.21 0.08-0.13
emission per cell K-theory EPA model (ng/s) (ng/s) 4 250-10 900 5 250-13 500 22 600-35 400 18 000-28 200 9 230-14 400 18 000-28 200 17 100-26 800 18 000-28 200 10 800-16 900
82 600 164 000 230 000 183 000 96 100 160 000 145 000 239 000 120 000
Supporting Information Available Two figures showing PSCF results using AEOLOS-IIT data (July 1994) and IIT-Rice 1999 data. This material is available free of charge via the Internet at http://pubs.acs.org.
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Received for review January 16, 2002. Revised manuscript received November 22, 2002. Accepted December 2, 2002. ES025531X
