ENVIRONMENTAL REVIEWS & CASE STUDIES
Hudson River PCB Dredging: Midcourse Assessment and Implications Regarding Possible Project Continuation Versus Termination
Robert A. Michaels, Uriel M. Oko
Phase 1 of Hudson River dredging fractionally reduced the amount of polychlorinated biphenyl (PCB)-contaminated sediment remaining in the river bottom, but greatly increased its downstream transport, as “clamshell” dredge buckets leaked more material than they retained. Clamshells were especially inefficient at capturing liquid PCBs and PCBs adsorbed to silt and fine sediment. Material that was removed, therefore, was relatively coarse, and contained relatively little PCB. Volume reduction was achieved only at the expense of massive mobilization of liquid, colloidal, and adsorbed forms of PCB, spreading contamination to previously uncontaminated river areas. We estimate that Phase 1 increased the surface area of contaminated riverbed by at least 3 orders of magnitude, from about 50 dredged acres to many square miles. PCB entry into ecosystems, water, and air depends upon the surface area of contaminated sediment newly exposed to scouring from the riverbed, causing further downstream transport, especially in high-flow events over years or decades. Indeed, Phase | contravened EPA’s benefit criterion by mobilizing PCB at a higher rate than would occur naturally, without dredging, over the planned seven-year project duration. If dredging is to continue, therefore, Phase 2 must assure health risk acceptability and net benefit compared with no action/no dredging. Further, EPA’s benefit criterion must be revised to account for impacts of PCB mobilization to ecosystems and
air, not just resuspension to water. Finally, Phase 2 must
doi:10.1017/S1466046610000529
increase the scope and duration of environmental monitoring to enable more reliable warning of harm in real time, and project evaluation over decades. We recommend that EPA consider for Phase 2 such technologies as coffer damming, vacuum dredging, and dredging within enclosures to minimize sediment resuspension; mobilization of liquid, colloidal, and adsorbed forms of PCB; and PCB entry into ecosystems and air. If Phase 2 cannot assure health risk acceptability and comply with a revised benefit criterion, we recommend that EPA terminate the dredging project. Environmental Practice 12:377-394 (2010)
he General Electric Company (GE) has completed
Phase 1 of United States Environmental Protection Agency (US EPA)-mandated dredging of polychlorinated biphenyls (PCBs) from 27 selected hotspots along a 40-mile stretch of the Hudson River, starting near Fort Edward, New York (GE, 2010a,b; US EPA, 2010). The project, which may constitute the largest remedial action in the history of the Superfund Act of 1976 [Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA)], is divided into two phases. It is to be implemented over seven years, with a cost estimated at nearly a billion US dollars. Phase 1 was started and completed in 2009 (year 1), though its objectives remain uncompleted. Year 2 (2010) is being spent evaluating Phase 1 and planning Phase 2, which encompasses a projected five-year period.
All parties agree that Phase 1 mobilized much PCB, significantly more than planned (GE, 2010a,b; US EPA, 2010a). PCB mobilization results in entry of mobilized PCB into ecosystems and environmental media, including the atmosphere, with consequential human exposure via all major routes: inhalation, ingestion, and dermal. Airborne PCB,
Affiliation of authors: Robert A. Michaels, PhD, CEP, President, RAM TRAC Corporation; Schenectady, New York. Uriel M. Oko, PhD, PE, President, Recycle Management, Glenmont, New York.
Address correspondence to: Robert A. Michaels, PhD, CEP, President, RAM TRAC Corporation, 3100 Rosendale Road, Schenectady, NY 12309; (phone) 518-785-0976; (e-mail) ram@ramtrac.com.
© National Association of Environmental Professionals 2010
Hudson River PCB Dredging 377
like waterborne PCB, also may enter ecosystems (e.g., Buckley and Tofflemire, 1983). Planning for dredging Phase 2, therefore, must be informed by the reemerging issue of PCB toxicity to humans and other species.
Toxic effects exerted by PCB have been documented most extensively in animal studies, with probable significance for people. However, PCB effects on people also have been studied extensively [e.g., see Agency for Toxic Substances and Disease Registry (ATSDR), 2000; Baibergenova et al., 2003; Bertazzi et al., 1987; Carpenter, 1998, 2005; Carpenter et al., 2003, Chase et al., 1982; Choi et al., 2003; Colombi et al., 1982; Emmett, 1985; Emmett et al., 1988a,b; Fischbein, 1985; Fischbein and Wolff, 1987; Fischbein et al., 1979, 1982, 1985; Hennig et al., 2002; Kimbrough, Doemland, and LeVois, 1999a,b; Lawton, Ross, and Feingold, 1986; Lawton et al., 1985a,b; Lucier, 1991, Maroni et al., 1981a,b; Meigs, Albom, and Kartin, 1954; Slim et al., 1999; Smith et al., 1982; StehrGreen et al., 1986; Taylor, Stelma, and Lawrence, 1989], including many studies associated with adverse human health effects. Effects include higher incidence of low-birthweight infants among residents of zip codes of PCB disposal sites (Baibergenova et al., 2003) and, more recently, higher hospitalization rates for coronary heart disease in zip codes with PCB contamination (Carpenter, 2005). PCBs are classified as animal carcinogens and as probable human carcinogens (ATSDR, 2000).
Occupational studies suggest that PCB inhalation adversely affects the human respiratory system (Emmett, 1985; Emmett et al., 1988a,b; Fischbein et al., 1979; Lawton, Ross, and Feingold, 1986; Smith et al., 1982; Warshaw et al., 1979), though such studies have been unable to exclude reliably causation by other occupational toxins to which simultaneous or sequential exposure might have occurred (ATSDR, 2000). Occupational studies also have suggested other adverse health effects of PCB, including gastrointestinal, hepatic, and dermal effects (Alvares et al., 1977; Baker et al., 1980; Bertazzi et al., 1987; Chase et al., 1982; Colombi et al., 1982; Emmett, 1985; Emmett et al., 1988a,b; Fischbein, 1985, Fischbein et al., 1979, 1982, 1985; Kimbrough, Doemland, and LeVois, 1999a,b; Lawton, Ross, and Feingold, 1986; Lawton et al., 1985a,b; Maroni et al., 1981a,b; Meigs, Albom, and Kartin, 1954; Ouw, Simpson, and Siyali, 1976; Smith et al., 1982; Warshaw et al., 1979). Accordingly, as part of planning for the dredging project, GE was required to adhere to EPA-approved limits on PCB concentration in air and water.
Our assessment of Phase 1 implementation of the Hudson
River dredging project is informed by our findings that the project was justified by EPA based upon numerous errors,
378 Environmental Practice 12 (4) December 2010
all in the dredging-friendly direction, and our conclusion that these consistent errors amounted to pro-dredging bias on the part of EPA (Michaels and Oko, 2007). We evaluated EPA's baseline Hudson River health risk assessment (HRA) (US EPA, 1999, 2000a,b) and found it to be biased toward keeping PCBs in sediments that would be removed by dredging. The HRA did this by systematically misquantifying parameters, most essentially underestimating PCB movement from sediments to water and from water to air. EPA excluded from its analysis all monochlorinated and dichlorinated PCB congeners, which EPA subsequently estimated at about one third of total PCB mass in the river, and also excluded liquid PCB oils, dissolved and colloidal PCB, as well as PCB adsorbed to fine particles, such as clay and silt. GE Site Evaluation and Remediation Program Manager John G. Haggard on April 9, 2010, orally reported that half of the resuspended PCB in the dredging project was found to be dissolved; and half was in particulate form, which would include colloidal PCB. Consistent with this view, Paquin (2001) reported, “PCB in colloidal form constitutes the most mobile form of PCB in water, being affected only minimally by settling, physical retention or adsorption. Concentrations of PCB-like compounds in water can be much higher in colloidal form than in suspended solids or in dissolved form, and can be much more difficult to intercept through physico-chemical means” (p. 2). The dissolved and particulate phases of PCB measured in Hudson River dredging Phase 1 are quantified in Figure 5.3-14 of GE’s Phase 1 Evaluation Report (Figure 1 here), which shows them to be roughly equal. GE’s report states in the Key Findings section, “The PCB mass was mostly in dissolved form, although particulate phase PCBs were an important factor in resuspension” (GE, 2010b, p. 77).
EPA included silt-adsorbed PCB, but overestimated the rate at which it would settle out of the water column by inappropriately basing the settling rate on Stoke’s law. Stoke’s law applies to massive spherical particles that drop like marbles through a viscous medium. Flat clay particles settle more slowly with a longer path length and residence time than do spherical, or roughly spherical, particles. Dissolved and colloidal forms of PCB do not settle. None of these forms of PCB settle as Stoke’s law would predict.
EPA's baseline HRA omitted electrostatic charges on clay particles that separate them, preventing agglomeration and maintaining clay in suspension; EPA also assumed that particles never “reflect” back into the water column after settling, likewise underestimating PCB concentrations in water (Shavit et al., 2003). Also omitted was PCB codistillation, in which PCBs at low bulk concentrations in river
Particulate Phase
+1.2 Sandard Effor fo the Mean
Fevl Fev ev eve? vt
Aver: ight Percent 41 2 ad ea ie Mean 8 T sbosrrsesrifesersresitirrs
= o putiesitirees
123 4 5 6 Tf 8 8 10 Homolog
Figure 1. Comparison of average composition for dissolved and particulate PCBs downstream of the Hudson River Phase 1
dredging area. Source: GE (2010b).
water preferentially distribute to the air-water interface, greatly accelerating PCB transfer from water to air (Harza, 1992; Integrated Atmospheric Deposition Network, 2000). EPA cited its own empirical data showing more rapid PCB water-to-air transfer (US EPA, 2000a,b) but, professing to disbelieve the empirical data, reduced the effect of these data on the HRA: EPA reduced the water-to-air transfer coefficient for PCBs by averaging in modeled PCB transfer coefficients that were orders of magnitude lower than the empirical findings because the modeled values ignored codistillation. Finally, EPA omitted PCB release into the atmosphere from hot water in cooling towers in communities along the Hudson River. Water at cooling-tower temperatures may release PCB into the air more than 10 times faster than rates determined from the surface of cold water and multiple orders of magnitude more rapidly than predicted by EPA’s cold-river models.
Together, EPA’s procedures reduced airborne PCB concentrations from above to below de minimis concentrations. This in turn eliminated the requirement (NYS DEC, 1997) for EPA’s HRA [and other HRAs (such as PSEG, 2001)] to quantify inhalation risks posed by airborne PCBs. These HRaAs, therefore, “considered” airborne PCBs, but erroneously attributed zero (de minimis) health risk to them.
Our assessment is appropriately conservative. In the context of error and the aforementioned pro-dredging bias for
the dredging decision-making process (US EPA, 2006), “conservative” means being careful to err on the side of agreement with EPA rather than on the side of exaggerating EPA’s troubling methodological shortcomings and the consequences thereof (Michaels and Oko, 2007). Notwithstanding this troubling context, our assessment adopts two premises long advocated by EPA:
1. The scope of issues to be considered during the interphase period, as defined by EPA, explicitly excludes consideration of terminating the project and thereby abandoning Phase 2.
2. If dredging is to proceed to Phase 2, the manner in which it will be conducted minimally must assure conformity with EPA’s criterion that net benefit must be achieved compared with no action/no dredging.
Three major issue areas most essentially are addressed in our assessment, and should be considered during the interphase period:
1. the possible need to modify dredging in Phase 2,
2. the possible need to modify the benefit criterion in Phase 2, and
3. the possible need to modify the monitoring program in Phase 2.
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Our assessment addresses technical and policy issues within these three major issue areas.
Methods
Our analysis is based upon activities including conducting site visits to observe and photograph dredging, visiting EPA's field office in Fort Edward, interviewing EPA and GE personnel and contractors, analyzing dredging data, attending public meetings, and examining scientific and technical reports. Our analysis adopts the methods of HRA, critical evaluation of scientific information sources (e.g., GE, 2009, 2010a—c; Gruendell et al., 1996; Michaels and Oko, 2007; United Nations Environment Programme, 2003; US EPA, 2010a—c) and objective scientific peer review. The latter are not a priori methods, and they are not described in detail here. Rather, they consist of the diverse methods that are generally typical of peer review by scientists seeking to remain objective. Most essentially, these methods consist of our own disciplined, critical evaluation of the scientific merit with which numerous methods were selected for use and applied prior to dredging, during dredging Phase 1, and after Phase 1. The scope of our assessment therefore includes our own peer review of GE and EPA methods, findings, and conclusions, such as those reported orally in public meetings, and in written public communications on GE (2010c) and EPA (2010b,c) Web sites for Hudson River dredging, and more formally in GE (2010a,b) and EPA (2010a) draft and final reports published for consideration by the public, specific interested parties, and members of the Hudson River dredging project’s Peer Review Panel. Members of the public and other readers of our assessment can judge for themselves whether and to what degree we succeeded in applying the methods of HRA and of peer review objectively. We hope that we have done so completely.
Findings Possible Need to Modify Dredging in Phase 2
Mobilization of PCB-tainted sediment
A major discrepancy exists between sediment mobilized in Phase I of GE’s EPA-mandated Hudson River PCB dredging project versus the much smaller amount of sediment mobilization measured and reported by GE (2010a~-c) and EPA (2010a—c). Sediment mobilization as reported by GE and EPA refers to the amount that is “resuspended” by
380 Environmental Practice 12 (4) December 2010
dredging, and monitored miles downstream of the Phase I dredging area, almost all of which is located near Roger’s Island, some 7 miles from the monitoring station. As EPA has reported, however, most dredged sediment falls back to the river bottom in the trench or near the spot from which it was dredged initially. Thus, the preponderance of mobilized sediment remains on the river bottom, still mobile, but unrecorded in GE or EPA sediment mobilization data ... hence the “sediment mobilization discrepancy.”
The sediment mobilization discrepancy represents more than merely a difference between a measured and an actual parameter value. Rather, it represents a fundamental inconsistency in EPA’s past justification of the need to dredge versus EPA’s current characterization of the performance of the dredging project in Phase 1. The need for dredging was justified by the mobility of sediments in PCB “hotspots” requiring, according to EPA, their removal by dredging. Indeed, a small but persistent trickle of buried PCB moving downstream was documented from PCB hotspots (e.g., see US EPA, 2006), of which 27 were selected for remediation via dredging.
In contrast, in the new context of actual dredging in Phase 1, EPA dramatically has altered its concept of mobility. Mobility in the dredging project is newly quantified by the lightest-weight fractions of PCB-tainted sediments measured resuspended in the water at the Thompson Island Dam about 7 miles downstream of the preponderance of Phase I dredging, further downstream at Lock 5, and still further downstream at Waterford [see US EPA's illustration (20104), reprinted as Figure 2 here].
EPA’s altered terminology, referring to mobilized sediment as sediment “loading” or “resuspension” estimates, confuses the issue. These parameters quantify only near-term mobilization and ignore the reality that all of the sediment that falls back to the riverbed also is “mobilized,” in the original sense of that term as used by EPA to justify dredging. That is, it is mobilized because it can enter riverine ecosystems and can reenter the water column via physical, chemical, and biological processes. Examples include, respectively, scouring under turbulent high-flow river conditions, dissolution, and microbial metabolism. Mobilized sediment also can be transported by migrating organisms, such as fish and birds, and can enter the air in communities directly from river water or from heated sources (cooling towers; Michaels and Oko, 2007) used to control industrial processes, such as in factories and power plants.
450 |
Total: 437
400 |
350 |
300 5
250 |
200 }----
150 4
Net Total PCB Cumulative Load (kg)
100 5
50 4
Total: 269
1% Mass Removed (200 kg)
117 kg Annual Load Limit Total: 151
Thompson Island
LockS Waterford
Far-field Stations
Figure 2. Resuspension of sediment particles bearing trichlorinated to decachlorinated PCB measured at three stations miles
downstream of Phase 1 dredging. Source: US EPA (20104).
Quantifying mobilization of PCB-tainted sediment
We initially estimated that 80% of sediment disrupted by dredging was mobilized rather than transferred to barges. This estimate was based upon the size, shape, and operation of typical 5-cubic-yard dredge buckets that open to a width of 15 feet; that is, enclosing 15 feet of river bottom to a design depth of about 1.5 feet, and then close to a width that we visually estimate at about 3 feet (zero feet at the bottom, wider higher up). We observed that, as the buckets close, they compress their contents, squeezing inward and upward about 12/15ths (80%) of the sediments that were initially enclosed within their jaws.
These buckets also were found to leak excessively because of obstructions in the river bottom that prevent their complete closure (Figure 3). Obstructions preventing bucket closure include stones, automobile tires, tree branches, bottles and cans, and construction debris such as concrete and boards. During closure, enclosed sediments are compressed from an open-jaw width of about 15 feet to a
closed-jaw width of zero feet at the bottom (maybe about 3 feet in average width from the bottom nose of the bucket to the top of its sediment load). As dredge buckets are open at the top, this “squishing” forces out a slurry of sediment and water. Leakage of incompletely closed buckets drops material onto the river surface (Figure 4). Our 80% mobilization estimate was approximate at best, in part because not all buckets were of 5-cubic-yard capacity (see Table 1, the inventory of dredge buckets used in Phase 1).
We now have quantified the mobilization parameter more reliably by using GE’s “bucket files” (GE, 2010a). GE’s bucket files are computer registers recording each closure of a dredge bucket in each delineated 5-acre work unit [Certification Unit (CU)]. The Phase I dredging area consisted of 18 CUs and about 90 acres, but dredging actually occurred at just 10 CUs, or about 50 acres. Analysis of these GE files revealed that the preponderance of sediment disturbed by dredge buckets was left in mobile form on the river bottom, not placed in waiting barges. We related the number
Hudson River PCB Dredging 381
Figure 3. Dredge buckets should close completely before lifting their sediment load, but they leak excessively because obstructions prevent complete closure. Hudson River dredging site, July 28, 2009.
of bucket closures in each CU to separately reported information about the volume of sediment placed in barges in each CU. This analysis is summarized in Table 2, in which all bucket closures in all CUs are summed.
As Table 2 indicates, the preponderance of dredged material was not barged, but mobilized. The exact fraction mobilized depends upon the capacity of the dredge buckets that were used. The dredge bucket capacity in turn depends upon the maximum capacity of each bucket and the depth of its bite into the sediment, both of which were variable because three bucket sizes were used (Table 1), and sometimes they did not penetrate to their full design depth; for example, if they struck a boulder or construction debris. The standard bucket capacity was 5 cubic yards with a design penetration depth of 18 inches. The five 5-cubic-
382 Environmental Practice 12 (4) December 2010
yard buckets were used routinely, notwithstanding that more 1-cubic-yard buckets (seven) were available for standby use in sensitive spots, especially near shore. The project also had one 2-cubic-yard bucket (Table 1). We further assume that the design penetration depth was typically the target depth, so the overall average bucket capacity probably was close to 5 cubic yards.
As Table 2 shows, Phase I dredging pulled out 286,006 cubic yards of sediment (actually a slurry of sediment and river water), which went into barges (topped by a layer of water). The dredge buckets closed 221,521 times, producing an average load of 1.29 cubic yards per bucket load that was transferred to waiting barges (including the water). The amount of sediment to be rail-shipped to Texas is less, because sediments must be dried before loading. Even using
Figure 4. Dredge closure forces a slurry of sediment and water upward through the open top of the bucket, and leakage of incompletely closed buckets drops material onto the river surface. Hudson River dredging site, July 28, 2009.
Table 1. Summary of bucket volume, by dredge
Bucket volume
Dredge name Dredge type (cubic yards) 320-09 320 1 320-10 320 1 320-11 320 1 320-12 320 1 320-13 320 1 320-14 320 1 320-16 320 1 345-07 345 2 385-02 385 5 385-03 385 5 385-04 385 5 385-05 385 5 385-06 385 5
Source: General Electric (2010a,b, Appendix N, Table N-1).
the larger figure as the estimate of barged “sediment,” however, the amount barged still is only 26% of an assumed 5-cubic-yard average bucket capacity, or 32% of a 4-cubic-yard capacity, or 43% of a 3-cubic-yard capacity.
That means that the amount of sediment that was mobilized was 74% if the average bucket capacity is assumed to be 5 cubic yards, 68% if 4 cubic yards, and 57% if 3 cubic yards. Under any of these assumptions, the preponderance of material was mobilized, not barged, and still more was
Table 2. Sediment retention vs. mobilization in Phase 1 of Hudson River polychlorinated biphenyl (PCB) dredging, based upon automated recording of dredge bucket closures*
221,521 286,006
Number of dredge bucket closures”
Volume of sediment removed, transferred to barges
[cubic yards (yd?)]
1.29 Volume of sediment removed per bucket closure
(yd?/bucket load)
Sediment load retained in bucket vs. mobilized . . .< ... assuming average bucket capacity = 5 yd>
25.8 Percent retained and barged 74.2 Percent mobilized
... assuming average bucket capacity = 4 yd? 32.3 Percent retained and barged 67.7 Percent mobilized
... assuming average bucket capacity = 3 yd? 43.0 Percent retained and barged 57.0 Percent mobilized
* Additional sediment was mobilized when buckets impacted the river bottom but failed to close; these bucket rejection events were unrecorded. Mobilized sediment may be removed by future dredging if it falls back to the bottom at a location that is within a dredging prism.
> Data acceptance criterion: depth is below 119-foot elevation.
© Bucket capacity is 5, 2, or 1 yd°; design penetration depth is 18 inches for a s-yd? bucket.
Source: Tabulated values represent results of our analysis of General Electric (2010b) Phase 1 dredging project data, most notably GE’s bucket files (Appendix G, Table G-1).
mobilized when dredge buckets descended to the river bottom, but failed to close (termed bucket rejection). Some of the mobilized sediment, however, might have been dredged again, and a further fraction removed from the river, if the sediment fell back to the river bottom within a “prism” slated for future dredging.
We regard our best sediment mobilization estimate as 74% for the 5-cubic-yard-capacity bucket typically used. That estimate is a minimum, as it excludes sediment that is disrupted by dredge buckets when they crash to the bottom but fail to close because of obstructions such as boulders or construction debris. These factors bring the mobilization fraction closer to our initial, independent estimate of 80%, though we can quantify reliably only the 74% minimum estimate, which therefore is only approximate if viewed as a total mobilization fraction.
The mobilized fraction of sediment, therefore, conservatively amounts to about 1,100,000 cubic yards, which is approximately 3.7 million metric tons (tonnes), assuming a dredged sediment specific gravity of about 2.6 compared with water (Gruendell et al., 1996). Yet, EPA’s illustration
Hudson River PCB Dredging 383
(Figure 1) reports 437 kg resuspended sediment load at Thompson Island, 269 kg at Lock 5, and 151 kg at Waterford. Ignoring obvious double counting, EPA reports 857 kg of mobilized “resuspended” sediment, which is drastically less than 744 million kg. Thus, EPA’s figures exclude nearly all mobilized sediment. EPA simply has ignored the preponderance of sediment mobilization, and PCB mobilization, in evaluating the performance of the dredging project in Phase 1, notwithstanding that the persistent mobility of dissolved, colloidal, and fine-particle-adsorbed PCB originally constituted for EPA a central rationale for specifying the dredging remedy for the Hudson River PCB Superfund site.
Downstream PCB deposition
PCB in dredged, redeposited sediments is more mobile than was the case in the original buried state, which ironically is the physical state that EPA’s strategy of capping dredge prisms has sought to restore. From the river bottom, resting sediment piles produced by Phase I dredging gradually (perhaps over years) can and will erode. Some sediment will travel downstream, to be measured by GE in the EPA-mandated “resuspension” monitoring program. Indeed, on March 28, 2010, recently analyzed Hudson River water samples were reported to harbor PCB levels nearly five times higher than the federal drinking-water standard of 500 parts per trillion (ppt). This news reasonably could have been anticipated. The episode was reported to have been caused by scouring of PCB-tainted sediments from the river bottom during a “high flow” event, in which river flow past Thompson Island increased from 5,000 cubic feet per second (CFS) to a peak of 36,000 CFS (e.g., see US EPA, 2010b,c).
We also note two Key Findings in GE’s Phase 1 Evaluation Report (2010b, p. 77):
¢ Dredging activities caused previously buried PCBcontaining sediments to migrate downstream and settle on the surface of the river bottom, where they became bioavailable. PCB concentrations in downstream sediment traps ranged from approximately 24 to 126 mg/kg Total PCBs, with an average of 61 mg/ kg, and downstream sediment cores of previously sampled areas showed an average increase of three times pre-dredging concentrations. These and other lines of evidence show that dredging caused widespread redistribution of PCB-containing sediments on the surface of the river bottom.
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¢ These re-deposited sediments continued to release PCBs to the river well after the completion of dredging activities [emphasis added].
Demonstrably, as already shown, residual sediments disturbed by dredging are mobile, along with their PCB load. If a full dredge bucket averages 5 cubic yards, then just about a quarter of dredged sediment was transferred to barges. Some of the remainder must flow downstream with the current. The rest falls back to the river bottom, where it exists as loosely agglomerated piles of dredge spoils, including clay and mud. River currents, as illustrated by the high-flow event previously described, erode this material gradually back into the water column, from which PCBs may enter the air and ecosystems, including migrat-
ing fish and birds.
As the river again slows to its normal flow rate, some scoured, resuspended PCB-tainted sediment will settle (redeposit) downstream. As EPA’s illustration shows (Figure 2), the amount of resuspended sediment diminishes from upstream to downstream, documenting (and roughly quantifying) redeposition (roughly, as dilution also must have contributed to the decrease).
Significance of downstream deposition
Downstream deposition of river sediment involves a wide spectrum of particle sizes. Clamshell dredges preferentially capture the coarse particles: sand and rocks that have relatively little surface area. In other words, clamshell dredges preferentially leave behind relatively small particles, having the greatest surface area, on which the greatest amount of PCB is adsorbed. Dredges preferentially capture the relatively small fraction of the PCBs that are adsorbed on sand and rocks. To illustrate, consider PCB adsorption to carbon (McDonough, Fairey, and Lowry, 2008). PCB affinity for carbon is high, on average about 500 ng/m?, which reasonably might be expected also to approximate PCB affinity for Hudson River rocks and smaller particles, such as clay and mud.
If the carbon is formed into a cube, its surface area is six times the face of the cube. If the cube then is divided into finer cubes, the total surface area increases, as does PCB adsorption onto the smaller cubes. A cubic particle with a 0.01-cm side presents a surface area of 0.0006 cm? for adsorption, whereas the same amount of particulate matter divided into 1,000 smaller particles, each with a 0.0001-cm (1 mm) side, presents an aggregate surface area of 0.6 cm?, 1,000 times greater. That is still a coarse particle. If the
cube, however, is subdivided finely enough (say, to the micrometer range), its surface area becomes so large that the material acquires a new name based upon its propensity to adsorb substances such as PCBs: activated carbon, or activated charcoal. Gram for gram, fine or ultrafine Hudson River particles in the size range that is preferentially mobilized by dredging can and will adsorb PCBs in amounts that are millions of times higher than adsorption onto coarse particles, just as activated carbon adsorbs PCBs more efficiently than does a coarse block of carbon.
Upon closure of clamshells, these fine, PCB-laden particles preferentially leak into the water column, which carries many of them downstream. These particulates eventually settle. Repeated action of the dredges causes this moving front to become increasingly concentrated with PCBs.
Clamshell buckets, as already described, tend to exert not only a mobilizing effect on sediment, but also a particle resorting (or classification) effect, which constitutes one burden of PCB dredging. Moving the pontoon-mounted dredge platform and clamshell downstream effectively constitutes chasing a moving, increasingly concentrated PCB front to previously uncontaminated river areas. Depending on water-flow velocity, this can be a few hundred feet or many miles downstream of the dredge.
Perhaps the dredge type that is most damaging to the environment is pontoon-mounted backhoe/excavator dredges, of the type used in Phase I. Underwater bucket closure compresses the contents, forcing much water and sediment out of the open top of the dredge bucket, preferentially dispersing relatively fine particulates into the flowing water column (Figure 4). These relatively small particulates are slowest to settle and most susceptible to downstream migration. To prevent such migration, other types of dredges could be used. Those that suck up the bottom sediment with water to be discharged into hoppers for sedimentation and/or treatment might be most effective. The process of dredging-induced gradual sediment resuspension followed by downstream flow and redeposition illustrates that, most essentially, four insidious processes are under way:
1. PCB spreading, 2. PCB entry into Hudson River ecosystems, 3. PCB resuspension increase in high-flow events, and
4. PCB storage increase in Hudson River ecosystems.
PCB spreading. One insidious process is spreading of PCB from sectors of the river bottom dredged in Phase 1 to undredged sectors downstream. In the long term, PCB movement from sediments to river water, ecosystems, and air depends upon the surface area of contaminated river bottom, not on the volume of buried (nearly all immobile) PCB... and the area of river bottom that is contaminated is increasing due to dredging. Dredging in Phase 1 was intensively concentrated in a relatively small area (somewhat over half of the full 90 acres included in Phase 1), so dredging affected a high fraction of the river bottom in the Phase 1 area. This cannot be the case in Phase 2. Most of the river bottom on which resuspended PCB-tainted sediments will settle is not scheduled for dredging in Phase 2. As a result, PCB will continue to spread and redeposit over a gradually increasing area of river bottom, nearly all of which is not scheduled for dredging, ever.
PCB entry into Hudson River ecosystems. As the area of river bottom affected by redeposition of mobilized PCBtainted sediments increases, PCB will enter river ecosystems beyond the Phase 1 area. These will include detritus ecosystems and ecosystems involving the higher trophic levels, from primary producers (phytoplankton and rooted plants) to herbivores (such as carp), primary carnivores (zooplankton and some fish), and secondary and tertiary carnivores (including some large fish, amphibians, reptiles, and mammals).
Already, GE and EPA have reported fivefold increases in PCB concentrations in fish tissue (GE, 2010b; US EPA, 2010a), but these bioconcentration data represent a misleading underestimate of the degree of increase. The data reflect analysis of muscle tissue of fish (filets), whereas PCB levels in organs (especially fish liver) may be 2-3 orders of magnitude higher. Some people, especially American Indians, consume fish organ meats. Fish also are consumed in their entirety by microbes and by predators other than humans. Thus, the PCB load entering Hudson River ecosystems from dredging is grossly underestimated by data on PCB concentrations in fish filets.
PCB resuspension increase in high-flow events. As the area of river bottom affected by downstream movement of mobilized PCB increases, the effectiveness of increased river flow at suspending redeposited PCB-tainted sediment will increase, even if the scouring efficiency remains constant for any particular current speed. This is because the scouring efficiency, whatever it is quantitatively, will affect a larger area of the river bottom. In ad-
Hudson River PCB Dredging 385
dition, the scouring efficiency may increase for any given river flow rate because relatively low-mass particles will be the ones preferentially transported downriver from the Phase 1 area. This also suggests that the duration of river flow-induced exceedances of the 500-ppt federal drinkingwater standard for PCB may increase, as the fraction of river bottom contributing to the exceedances increases. Monitoring data (US EPA, 2010b,c) suggest that such highflow events may occur with a frequency in the range of once to 10 times per year.
PCB storage increase in Hudson River ecosystems. The aforementioned processes can be expected to alter the distribution of PCB originally confined to 27 hotspots slated for dredging to a wider, and widening, river sector. This sector will continue to expand and, along with it, the fraction of Hudson River ecosystem area affected by PCB will increase. These riverine ecosystems will relate to mobilized PCB-tainted sediments originating from dredged hotspots as a pollutant source to a pollutant sink.
This phenomenon was documented (for example, by Carson, 1962) in a famous case study involving the chlorinated pesticide DDT, which closely resembles PCB both structurally and dynamically (though PCB is somewhat more water-soluble and less long-lived in ecosystems). The uses of DDT and PCB differ, but dissemination of DDT (and its breakdown products DDE and DDD) to the environment of Clear Lake, California, to control midges (the Clear Lake “gnat”) is analogous to dissemination of PCB to the Hudson River. PCB and DDT for many decades have been disseminated to ecosystems globally, so much so that discerning their effects experimentally has been difficult for lack of unaffected control ecosystems. DDT and PCB, which have co-occurred in environmental samples for many decades, are similar structurally:
32 2.3 at cl ory Ten JV ; PCBs DDT
Indeed, their structures are so similar that, until the 1960s, only DDT was discerned analytically in environmental samples, resulting in ecological effects of DDT and PCB together being attributed solely to DDT. Structural analogues often exert similar toxic and environmental effects [termed structure-activity relationships (SARs)]. The possible consequences of spreading PCB more widely in the Hudson
386 Environmental Practice 12 (4) December 2010
River are worthy of considering in light of the Clear Lake (and global) experience with DDT. In Clear Lake, significant residues of DDT were not found, as DDT is nearly water-insoluble. This negative finding, however, proved to be misleading, as the biota of Clear Lake proved to be a major sink for DDT, which dramatically bioconcentrated, bioaccumulated, and biomagnified in its ecosystems.
By these processes, DDT (and related chlorinated hydrocarbons) exerted significant effects from which global ecosystems are just now recovering. For example, bald eagles and peregrine falcons were threatened with extinction because DDT thinned their eggshells, causing drastic population declines. Similarly, dredging-induced mobilization of PCB-tainted sediments reasonably may be expected to reintroduce PCB into receptive ecosystems, thereby setting back the clock for river recovery by four decades, during which PCB may be reburied as it was before being dredged this past year in Phase 1.
Possible Need to Modify the Benefit Criterion in Phase 2
Contravention of the benefit criterion
The EPA illustration reproduced earlier (Figure 2) documents contravention of the benefit criterion. GE and EPA used mid-Phase 1 data to attempt dredging modifications in real time to restore adherence to the benefit criterion. These efforts succeeded at reducing PCB resuspension, but not to a degree sufficient to restore adherence to the benefit criterion, as shown in Figure 2. These facts have been widely acknowledged (most notably, see GE, 2010b; US EPA, 2010a) and will not be amplified here.
Flaws of the benefit criterion
The benefit criterion allows no increase in downstream transport of resuspended sediment for the duration of the dredging project. Instead, under the benefit criterion, downstream transport may be increased by dredging in the short term, but only in amounts that will be offset by future decreases over the longer term, meaning the project duration. This benefit criterion is illogical for two reasons:
1. It assumes incorrectly that downstream transport of PCBladen sediments will stop when dredging stops in six or seven years. This assumption has been refuted by the observed decades-long mobility of PCB, even when buried beneath the river bottom. Dredged sediment that is re-
doi:10.1017/S1466046610000529
deposited onto the river bottom likewise will erode into the water column and travel downstream, along with its adsorbed PCB load, for decades to come. The rate of erosion, however, will be significantly increased (with contaminated riverbed surface area) compared with the low rate that EPA used to justify dredging.
2. It assumes incorrectly that potential dredging impacts consist of nothing more than downstream transport of resuspended sediment, whereas this appears to constitute a relatively minor contributor to total potential dredging impacts, even when considered only during the restricted dredging period of five or six more years. Maintaining a stringent resuspension performance standard, even if it could be met, still allows harm from entry of PCB from tainted sediments deposited on the river bottom into river ecosystems, including migrating birds and fish, and into the air that is breathed by people living in river communities.
Possible Need to Modify the Monitoring Program in Phase 2
Liquid PCB oils
EPA reported at a public meeting in the Hudson River town of Fort Edward, New York, on August 19, 2009, that GE clamshell dredges had started to encounter liquid PCB oils in dredging prisms (see also GE, 2010b,c; US EPA, 2010a,b). This development is worthy of note because pure PCB oils [1,000,000 parts per million (ppm)] must be viewed in an entirely different, more ominous context than river sediments harboring PCBs in the low-ppm concentration range. Mobilizing liquid PCB oils via dredging is commensurately more serious than mobilizing sediments bearing PCBs in the low-ppm range as originally anticipated.
EPA later acknowledged [for a magazine article (Brickley, 2009)] that the project recently had discovered sheens of liquid PCB oil on the river surface, “an indication, the EPA said, that the river floor contained not only contaminated silt, but more potent pockets of pure PCB oil—and that the dredging is releasing the oil into the river water.” EPA, however, placed a relatively benign spin on this news: “It’s not really affecting dredging, that’s why we’ve taken those mitigation measures to, you know, to counteract the sheens.” Counteracting microscopically thin PCB sheens visible on the river surface, however, fails to address the real challenge: counteracting remnant pools of originally disposed liquid PCB oils of unknown, potentially large volume in trenches beneath.
PCB sheens on the river surface constitute evidence of the presence of liquid (near pure) PCB and constitute yet another source of airborne PCB not addressed in any EPA assessment of risks to health potentially posed by sediment dredging at PCB hotspots in the Hudson River. These PCB sheens cannot have originated from desorption from sediments, because a sheen is a continuous monomolecular layer of liquid PCB. Their observation, therefore, raises the question of whether they might be expected to arise from underlying sediments bearing PCBs in merely the ppm range, or whether they must originate from more massive pools of liquid PCB oils at the river bottom as originally suggested by EPA.
Can bottom sediments form surface sheens via some upward PCB migration process? Three factors suggest not:
1. PCBs chemically bound to sediments for decades are unlikely to become unbound, especially as liquid PCB oil;
2. if they did become unbound, they also would have to become concentrated from the low-ppm range at the river bottom to near purity at the surface, which is unlikely to occur in a flowing, turbulent river; and
3. PCB oils are denser than water, so they would be expected to sink, not to rise from the bottom, unless physically forced upward, or lifted; just a small fraction of more-water-soluble PCB congeners might reach saturation in the water, and may appear as a sheen on the river surface.
PCB liquids include more than 200 types, or congeners, varying in their degree and pattern of chlorination (with from 1 to 10 chlorine atoms per PCB molecule). Each congener has a unique density, but bulk density of commercial PCBs of the types disposed to the Hudson River (known as Aroclors, manufactured from approximately 1930 to 1979) are reported to have a density of about 1.5 grams per milliliter [g/ml (Gruendell et al., 1996)], which is 1.5 times the density of water.
The most probable origin of PCB liquids forming surface sheens, in our view and apparently also in EPA’s view (based upon oral statements), is that dredge buckets massively disrupt them from pools of liquid PCB oils formed in sediment low points (depressions) following original disposal from land-based facilities or ships. These bottom pools gradually might have become covered with debris and sediments. The onset of dredging may be forcing the liquids upward toward the surface as dredge jaws expose them and close around them. This process is visible for
Hudson River PCB Dredging 387
sediments (which have tightly bound PCBs that would not be expected to form sheens) and reasonably would apply as well to liquid pools (which would be expected to form surface sheens).
Sediments and PCB oils that are not forced upward by closing dredge jaws might be retained within dredge buckets, and physically lifted. These materials would be subject to leakage during their ascent to the surface and beyond. These dual processes of disruption by squishing and by lifting reasonably would be expected to generate PCB liquids and PCB sheens at the surface, as PCBs are chemically attracted to surfaces, including to the air-water interface in rivers.
EPA's report of encountering PCB liquids seems, at least in retrospect, unsurprising given the history of past PCB disposal into the river in the form of liquid PCB oils from land-based facilities and from ships. Given this history, why did EPA adopt the clamshell method of dredging, thereby failing to prepare for this seemingly expectable eventuality? Its actuality casts further doubt on the wisdom of EPA having prescribed clamshell dredging rather than vacuum dredging, or no dredging, for remediation of the Hudson River PCB Superfund site.
One objection to the liquid-pool hypothesis that must be addressed is that PCB concentrations in downstream water samples have not revealed PCB oils or concentrations high enough to suggest their presence upstream. The heavier-than-water density of PCBs, however, would be expected to cause them to hug the river bottom as they move downstream. They would not be expected to register in surface or mid-depth water samples taken 5-7 miles downstream.
In planning dredging Phase 2, EPA (and GE) are faced with the quandary of whether to
1. mobilize PCB oils by continuing clamshell dredging, even though the dredge buckets cannot retain the oils efficiently,
2. allow the PCB oils to be mobilized by river currents washing over the now-exposed pools,
3. institute vacuum dredging or dredging within enclosures, or
4. stabilize the oils by covering them over again.
388 Environmental Practice 12 (4) December 2010
Monitoring for waterborne PCB
Waterborne PCB in the Hudson River, including water in dredge buckets and barges, constitutes the primary source of airborne PCB. Indeed, EPA studied the relationship of waterborne PCB in a cold river to airborne PCB 1 m above the river surface (US EPA, 2000a,b). That study produced the EPA benchmark termed the level of concern (LOC) for airborne PCB of 0.08 jg/m3, which is the air level estimated to be generated by waterborne PCB at EPA’s maximum contaminant level (MCL) for PCB of 500 ppt.? Generated primarily by dredging, waterborne PCB therefore should be measured where dredging occurs ... but that was not done in Phase 1. Instead of sampling at Rogers Island, water was sampled, and waterborne PCB measured, near Thompson Island, about 7 miles downstream of Rogers Island. As a result, waterborne PCB concentrations at dredging sites are anyone’s guess, specifically determined by anyone’s guess about the applicable dilution factor that occurs as dredge-mobilized material travels 5-7 miles downstream.
Monitoring for airborne PCB
Just as waterborne PCB concentrations at dredging locations are anyone’s guess, airborne PCB concentrations at dredge sites also are anyone’s guess, in part because airborne PCB monitoring at dredging platforms in Phase 1 consisted of personnel monitoring with sensitivity to the Occupational Safety and Health Administration’s occupational standard of 1,000 g/m? for airborne PCB (see the next section). Airborne PCB was monitored primarily by two portable air samplers set up adjacent to each dredge platform, on opposite banks of the river.
These samplers recorded 24-hour average concentrations of airborne PCB. Three problems undermined the usefulness of these monitors. First, personnel engaged in dredging are exposed to aerosols generated at the dredge platform, which reasonably would be expected to fall back to the river surface before reaching the monitors on shore, except when wind speed is adequate to transport them as far as the shore and when wind direction is aimed at a portable monitor. In those cases, of course, only one monitor would record the PCB, because the wind would be blowing away from the monitor on the opposite shore. Second, wind direction varies, so each air monitor would be pumping air that originated from 360°, not primarily from the direction of the dredge platform to which it is adjacent. This is illustrated in Figure 5, in which gray arrows represent air originating from the dredge platform, and the preponderance of black arrows represent air originating from other directions.
by ud OR
17 We
yf \ A ye
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Figure 5. PCB entry into air was quantified in Phase 1 via portable on-shore monitors (M) placed on opposite shores adjacent to each dredge unit. Gray arrows represent air originating from the dredge platform; the preponderant black arrows represent air originating from all other directions. Only average airborne PCB concentrations therefore are recorded. Peak airborne PCB concentrations that may be sampled are not reported because they are mixed with air from originating from all directions over a 24-h period.
Figure 5 also illustrates how, as the dredge platform moves downstream, the angle from which PCB might impinge on the portable monitor increases. Thus, a time series should show increasing airborne PCB concentrations as the surface area of dredged river increases. This observation actually cannot be made, however, because GE procedures call for moving each portable air monitor downstream with its adjacent dredge platform, so no monitor remains to record evolving airborne PCB concentrations at any former dredge site. Indeed, as the area of dredged river surface increases to its maximum, the concentration of airborne monitors per acre of dredged river declines in direct proportion because no monitors are added to cover the increased area of dredged river.
This gives rise to the third problem: PCB volatilization might not reach a steady state until long after the portable air monitors are withdrawn downstream with the dredge platforms. Indeed, PCB release from the river surface might not reach steady-state rates until long after completion of Phase I. By then, portable monitors would have been withdrawn, not only to points downstream, but altogether. In short, the monitors are withdrawn before they can characterize the evolution of PCB release to the air over the remaining six-year planned life of the project and beyond.
Indeed, as the acreage of dredged river increases, the number of monitors per acre declines, but the fraction of river
surface contributing to air levels over the river and on shore increases . . . never to be measured because the monitors that could have measured these evolving levels were withdrawn from service. EPA could require a permanent array of air monitors to capture the evolution of PCB release levels as the fraction of river bottom that has been dredged increases and as PCB-tainted sediments are restratified by physical, chemical, and biological processes of degradation, mobilization, and eventual release to ecosystems and the atmosphere.
One strategy to rectify this egregious situation might be effective: examining meteorology data to determine the fraction of time when wind direction was toward a portable air sampler on shore. If the fraction of time was, say, 1%, then the airborne concentration from the point of origin (the dredge platform) would have been at least 100 times higher than the concentration reported by the sampling unit (we say “at least” because the sampling unit would not have recorded PCB-bearing aerosols that had precipitated back to the river surface before reaching shore). We do not know whether the required meteorology data are available.
Personnel monitoring for exposure to airborne PCB
A major concern associated with PCB dredging relates to risks potentially posed to human health (Michaels and Oko, 2007). Apart from participation of people as ecosystem components at the top of the food chain is the issue of airborne PCB, which is derived from PCB released to the water, and which is monitored only at great distance from dredge sites, as discussed earlier. To help elucidate this issue, EPA could demand delivery of the results of personal monitoring samples taken on dredge platforms, minus confidential employee-identifying information. These samples generated the only data of which we are aware that reflect airborne PCB levels produced by dredging, at the location of dredge platforms. These samplers, unfortunately, operated with sensitivity to the occupational airborne PCB limit of 1,000 g/m, which is over 9,000 times higher than EPA’s residential limit of 11 wg/m3. If any of these samples were positive, that fact should be disclosed. EPA, however, indicated that the personal monitoring data belong to GE, and GE indicated that the data belong to its contractors. Information of possibly critical concern to the public has been “compartmentalized” thereby, out of public view. Reason exists to demand these data, because some personnel monitoring samples might be positive, even at the high threshold of detection.
Hudson River PCB Dredging 389
Indeed, EPA data relating PCB in water to PCB in air suggest that air levels must be excessive at dredging platform locations. EPA quantified the relationship between PCB concentrations in water from a cold river and in air 1 m above the river surface (US EPA, 2000a,b). For each microgram per liter (that is, for each 1,000 ppt) of PCB in river water, PCB concentrations in air (in szg/m3) were reported to be a minimum of 0.02, a median of 0.09, a mean of 0.15, and a maximum of 0.40 g/m? (Michaels and Oko, 2007; US EPA, 2000a,b). When waterborne PCB reaches EPA’s 500-ppt stop-dredging benchmark, airborne PCB 1 m above the river would be expected to be at about the mean observed value, 0.08 g/m. Significantly, that concentration also is EPA’s airborne PCB level of concern (LOC). Measurements of waterborne PCB, revealing exceedances of the 500-ppt benchmark, were taken 5~7 miles downstream of dredging locations. Waterborne PCB concentrations at locations of dredge platforms must be higher, perhaps thousands of times higher than at locations miles away (ppm rather than ppt) or even millions of times higher (parts per thousand rather than trillion) where liquid PCB oils have been encountered. These massively higher waterborne concentrations imply massively higher airborne concentrations at dredge platform locations.
Potential occupational exposure at dredging platform locations also might be significantly greater than that implied by EPA’s published relationship of waterborne PCB to airborne PCB. This is because the original EPA data relating airborne levels of PCB over a cold river to the source PCB levels in the river water do not account for dredge buckets in the Hudson River billowing sediments to the river surface as they close, and then lifting sediments and water above the surface, where leakage drops sediments and water violently onto the river surface. These processes must produce abundant droplets (aerosols) of various sizes, all containing PCBs, whereas air samples above river water in EPA’s original data did not include this source of airborne PCB. So, for occupationally exposed individuals, the relationship of PCB levels in water to levels in air must be significantly worse, exposing them to inhalable PCBs that are volatilized, as well as to PCBs that are aerosolized. That unhealthy process happens yet again when the dredges swing their retained load over the barges and drop them again, this time in their entirety, producing yet another burst of PCB entry into the air in the form of vapors and aerosols near dredge platform personnel.
Though airborne PCB concentrations in the dredging cor-
ridor would seem to be higher than EPA’s stop-dredging standards as explained earlier, the nearest measurements
390 Environmental Practice 12 (4) December 2010
are taken on shore rather than on location (see the previous section). EPA established a stop-dredging standard of 0.11 g/m} for airborne PCB in residential zones and of 0.26 g/m} for airborne PCB in commercial zones. Indeed, EPA ordered GE to stop dredging on multiple occasions, when the waterborne level was =500 ppt and presumably the air level was about =o.08 wg/m>.
Conclusions and Recommendations
Conclusions
Risks to human health potentially posed by airborne pathways of exposure to PCB under dredging and nondredging scenarios were neither assessed objectively nor compared. Water monitoring miles downstream of dredging to measure sediment loading or “resuspension” is inadequate to characterize PCB mobilization. Air monitoring using portable air samplers on shore is inadequate to quantify either residential or commercial exposure to airborne PCB. Results of personal air monitoring of GE dredging personnel remain undisclosed, therefore failing to satisfy the legitimate public interest in gaining access to this unique source of data on airborne PCB levels at dredge platforms. Levels of airborne PCB probably were higher than suggested by available data, and possibly unsafe.
EPA’s emphasis on PCB sheens observed during dredging, rather than on the possibly substantial source pools of liquid PCB hidden from view in the river bottom, is misplaced. Dredged material treated and shipped to Texas represents a small fraction of the total mobilized in the river by clamshell dredges. This modest removal has been achieved at the cost of drastically increasing the surface area of contaminated river bottom. We estimate that Phase 1 increased the surface area of contaminated downstream riverbed by at least 3 orders of magnitude, from about 50 dredged acres to many square miles.
Impacts of dredging will increase with increasing surface area of contaminated river bottom. EPA, however, primarily has quantified Phase 1 performance based upon the mass and volume of contaminated dredge spoils removed from hotspots beneath the relatively small Phase 1 dredging area. Hudson River PCB dredging, therefore, is making exposed people into experimental subjects, and riverfront communities into apt subjects of epidemiology studies that may continue for generations to come.
Recommendations
Risks to human health potentially posed by airborne pathways of exposure to PCB under dredging and nondredging scenarios should be assessed objectively and compared via correction of prior EPA assessments before authorization is given to implement Phase 2. Acceptability of risks to human health potentially posed by dredging must be adopted as a precondition for undertaking Phase 2 of the project. Phase 2 also must increase the scope and duration of environmental monitoring to enable more reliable warning of harm in real time, and project evaluation over decades.
Water and air monitoring, including personal monitoring, should occur together at dredge platforms. Results of personal airborne exposure monitoring of GE dredging personnel to PCB should be made available to the public, minus confidential personal information, as has been the case with other project data. Permanent arrays of air and water samplers are needed to verify or refute EPA’s prior safety claims, and to protect public and environmental health. The sources of PCB sheens, and the composition and volume of the possible source pools of PCB, should be investigated and, if possible, their relationship to originally disposed PCB liquids determined. Strategies to manage possibly rich sources of PCB liquids that dredge buckets disrupt and fail to hold must be developed to prevent mobilization of highly concentrated liquid PCB, and assure compliance with the benefit criterion.
Technologies should be considered for use in Phase 2, such as coffer damming, hydraulic dredging, and dredging within enclosures to minimize PCB mobilization, resuspension, and PCB entry into ecosystems and the air. Vacuum dredging, in which water, sediment, and rocks are captured without dispersing fine particles into the water column, may be the best method. The pontoons could be equipped with sedimentation basins in which flocculates that bind fine particulates can be added to the slurry. The slurry then should be filtered on site to return clean water into the river. Alternatively, the pontoons could move their entire load into the treatment plant, where proper treatment can be applied and the water returned to the river.
Note Added in Support
An official Hudson River PCB Dredging Peer Review Panel advisory to EPA released its final report (Peer Review Panel, 2010) approximately two months after we submitted our manuscript to Environmental Practice. The Peer Review
Panel report must be interpreted in light of prohibitive EPA instructions regarding its allowable scope:
The Peer Review panel will not evaluate whether the Remedial Action [dredging] will, or may, achieve the human health and/or environmental objectives of the ROD [EPA's Record of Decision under the Superfund Law], nor will the Peer Review panel evaluate whether Phase 2 should be implemented. (p. 3, emphasis added)
The report nonetheless is informative about these issues, stating implicitly that which it was prohibited from saying explicitly: Phase 2 cannot be completed feasibly and safely in the allotted five-year time frame remaining using available data, models, and criteria for success:
There is a very real need to set an allowable load limit for the Hudson River dredging project, but neither the data nor tool(s) needed to do so currently exist. To that end, the project must develop a set of models that incorporate hydrodynamics, sediment transport, fate and transport of PCBs, and bioaccumulation of PCBs in the Upper Hudson River (from Fort Edward to Troy Dam). (p. 36)
Notwithstanding two decades of EPA planning, prerequisite data and models were lacking at project onset, including the amount of PCB in the river. Further, requisite data were not collected in Phase 1, nor were requisite models developed. Dredging, therefore, might require years longer to be completed safely:
Since the total volume to be removed is not known, it is not reasonable to project what the annual production would be based on a 5-year schedule for Phase 2. (pp. 75, 76)
and, therefore,
the 5-year productivity criterion should be dropped to provide more flexibility to complete the work in a manner that protects the integrity of the project and its risk reduction objectives. (pp. v, 78, emphasis added)
The Panel also found the following:
Phase 1 showed that the 2004 EPS [Engineering Performance Standards] for Resuspension, Residuals, and Productivity were not met individually or simultaneously during Phase 1 and cannot be met under Phase 2 without substantive changes. EPA and GE proposed changes to the EPS but the Panel finds that the new proposed standards from either party would not contribute to the successful execution of Phase 2. (pp. iii, 84, emphasis added)
Notes
1. Calculation: 286,006 cubic yards (yd) of sediment barged in Phase 1, per GE bucket files (Table 2)
Hudson River PCB Dredging 391
X 1.31 m? per yd? = 373,795 m? = 3.74 X 10" cm? barged
X 2.6 g/cm? density = 9.72 X 10" g = 9.72 X 108 kg
= 9.72 X 10° metric tons barged
= 26% (= 0.26) of dredge-disturbed sediments (dredge spoils); 9.72 X 10° metric tons barged/o.26
= 3.7 X 10° metric tons mobilized = 3.7 million tonnes
2. Under the Federal Safe Drinking Water Act of 1974 (amended in 1986 and 1996), water levels are enforced at the MCL, but regulators must strive toward the more stringent MCL goal (MCLG), if feasible. The MCLG is zero for carcinogens such as PCB. That raises the issue of whether, and under what circumstances, permitting dredgingassociated increases of PCB levels in water is legal, even if the increased levels will remain within the 500-ppt MCL.
3. The “many square miles” estimate is based upon EPA and GE monitoring data that show resuspended dredge spoils at sampling locations miles downstream, at which resuspension refers specifically to dredgingassociated increments above the measured predredging background (Figure 2). The northernmost sample location was at Thompson Island, which is about 7 miles downstream of Rogers Island and about 5 miles downstream of the southernmost extent of the dredged area (at Griffith Island). Additional sampling points were further downstream of dredging, most notably including Waterford, about 40 miles downstream. Except for the dissolved and colloidal fractions (about half), resuspended material is subject to settling to the river bottom. Our estimate is conservative because the river bottom area receiving these sediments is many square miles, just counting the 40-mile stretch from the dredged area to Waterford, but it is a lot more considering that the material continues downstream to the Troy Dam and beyond, eventually to New York City and the ocean, over 100 miles downstream. Indeed, according to Key Findings in GE’s Phase 1 Evaluation Report (General Electric, 2010b) “downstream sediment cores of previously sampled areas showed an average increase of three times pre-dredging concentrations. These and other lines of evidence show that dredging caused wide-spread redistribution of PCB-containing sediments on the surface of the river bottom” (p. 77).
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Submitted July 7, 2010; revised September 22, 2010; accepted October n1, 2010.
Publication citation
Michaels, RA; and Uriel M. Oko. Hudson River PCB dredging: mid-course assessment, and implications regarding possible project continuation vs. termination. Environmental Practice, 12(4):377-94, December 2010;