Sediment Dredging at Superfund Megasites Assessing the Effectiveness (2007) / Chapter Skim
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4 Evaluation of Dredging Effectiveness: What Has Experience Taught Us?
4 Evaluation of Dredging Effectiveness: What Has Experience Taught Us?
Pages 90-177
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From page 90... ...
The ability to maintain cleanup levels in the long term is ideally linked to the achievement of long-term risk-based goals or remedial action objectives. Appendix C presents the various sites' cleanup levels and remedial action objectives and describes whether they were achieved at individual sites.
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From page 91... ...
Insufficient time has elapsed to judge achievement of remedial action objectives in approximately one quarter of the sites. The remaining sites apparently met remedial action objectives although the extent to which those remedial action objectives achieve long-term risk reduction may not be known.
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From page 92... ...
The goal of acquiring data for this type of analysis appears relatively simple: collect and evaluate pre-remediation and post-remediation monitoring data on concentrations and effects from Superfund sites. However, obtaining this information is surprisingly difficult.1,2 For example, the post-dredging sediment concentrations at the Waukegan 1 Harbor, IL, Superfund site were of interest.
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From page 93... ...
states that "no monitoring of the water level or quality conditions in the bayou are currently conducted -- and no water quality data has been collected in the bayou adjacent to the site since the end of the source removal remedial action in 1995." However, it also states that "the swimming and sediment contact advisory remains in effect based on the sediment samples collected [by the State of Louisiana] in 1997." The 5-year review (CH2M Hill 2001)
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From page 94... ...
Some data at sites where remedial actions had been completed are archived or not readily retrievable. Thus, even when information was available to EPA it might have been inaccessible.
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From page 95... ...
In such cases, mass removal may result in risk reduction because the future
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From page 96... ...
Dredging to Reduce Risk A more complete assessment of dredging effectiveness would include evaluation of long-term risk reduction in addition to mass removal
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From page 97... ...
state that …the results show that if a remedial action is to be evaluated and the process is extended over several years, changes in background contamination must be taken into account. After a remedial action, the results need to be followed over several years to show if it has
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From page 98... ...
Marathon Battery, New York The ability to achieve remedial action objectives and long-term risk reduction with dredging was demonstrated at Foundry Cove of the Marathon Battery, NY, site. Foundry Cove is a small body of water adjacent to the Hudson River about 85 km north of New York City.
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From page 99... ...
. As summarized in the record of decision and summary to the committee, core sediment samples collected from East Foundry Cove during the remedial investigation ranged from 0.29 to 2700 mg/kg cadmium and had
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From page 100... ...
East Foundry Cove Marsh was excavated and capped; Constitution Marsh was not remediated. Source: EPA 2006a (Marathon Battery Superfund Site, May 10, 2006)
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From page 101... ...
. Post-dredging verification sampling was conducted to establish whether cleanup levels had been met.
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From page 102... ...
Note that although cleanup levels were achieved immediately after dredging, median concentrations have since fluctuated above and below the 10 mg/kg cleanup level. Figure 4-4 presents the frequency of occurrence of sediment cadmium concentrations in the period 1995-2000.
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From page 103... ...
Figure 4-5 is a summary of long-term monitoring data collected for 5 years post-dredging (AGC 2001) and shows the ratio of pre-remediation to post-remediation tissue concentrations in various plants and animals.
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From page 104... ...
. The data suggest that in at least some cases dredging can achieve and maintain reductions in sediment concentrations and body burdens of contaminants although occasional measurements of elevated concentrations complicate the interpretation of the results.
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From page 105... ...
FACTORS AFFECTING DREDGING EFFECTIVENESS A variety of factors and site characteristics influence dredging effectiveness and can limit the ability to achieve cleanup levels and remedial action objectives. However, it is generally not possible to definitively identify the specific conditions or factors that determined success or failure in a particular project.
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From page 106... ...
Site characterization and source control require a firm understanding of the nature and distribution of the contamination, any potential sources that contribute to the contamination burden in the watershed, and the processes influencing site risks and their attenuation. A strong understanding of the extent of contaminants in place and the contribution of outside sources is essential to developing an effective conceptual site model and remedial plan to eliminate or lessen contaminant exposures and risk.
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From page 107... ...
Exposure to resuspended sediments is generally transitory and ends soon after the completion of dredging. Residuals are the contaminated sediments exposed after conclusion of the dredging and can lead to longer term exposure and risks to organisms.
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From page 108... ...
Although the resuspension losses and residuals are small relative to the total mass It should be noted that the resuspended solids fraction measured down 11 stream likely underestimates the total contaminants in the water column because some dissolved releases are likely to occur from solids that remain within the dredge footprint, that is, freshly exposed and redeposited sediments.
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From page 109... ...
and by the manner in which dredging is implemented. The next section discusses the role that each of those may play in limiting dredging effectiveness on the basis of experience at specific sites where dredging was used; taken together, the experience illustrates site-specific conditions or activities that contribute to or limit dredging effectiveness.
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From page 110... ...
Reprinted with permission from the authors; copyright 2007, Battelle Press. The objective is to identify conditions under which dredging might be effectively implemented and conditions that could discourage the use of dredging because of its inability to meet desired cleanup levels or remedial action objectives.
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From page 111... ...
. The study concluded that the increases in caged fish exposed for six weeks during dredging had increases in PCB concentrations 20 to 50 times higher than those observed in the pre-dredging time frame and increases of that magnitude suggest that uptake of PCBs was affected by the release of PCBs to the water column during dredging.
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From page 112... ...
As shown in Figure 4-8, increases in water-column PCB concentration were noted downstream of the dredging operation. TSS increased in concert with PCBs at the sampling locations adjacent to the site, but downstream PCB concentrations remain high when TSS decreased back to upstream values.
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From page 113... ...
The occasional inability to close the bucket completely because of debris interference can increase resuspended solids and thus resuspension of contaminants. A more detailed depiction of the PCB concentrations in water seen approximately 0.5 miles downstream of the dredge site is presented in Figure 4-9.
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From page 114... ...
The following year, PCB concentrations in shiners decreased to levels seen prior to dredging. There was a statistically significant increase in the downstream locations, but there is insufficient information to evaluate trends associated with dredging, because only a single post-dredging monitoring period was ROPS-WCT14 Characteristic Baseline FIGURE 4-9 PCB concentrations in water samples collected approximately 0.5 miles downstream of the dredging operations in the Grasse River (NY)
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Dredging at the site took place June to October, 2005; the 2005 fish tissue sampling was in September, 2005. Source: L
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From page 116... ...
Duwamish Diagonal, Washington In the Duwamish/Diagonal CSO, WA, early-action sediment dredging project, high PCB concentrations (above the pre-dredging surface concentrations) were found in sediments in and outside the dredge prism during a pre- and post-dredging sampling program (EcoChem Inc.
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From page 117... ...
. Methods Temporal trends in fish tissue PCB concentrations and region specific effects were established based on linear regression models using monitoring year, percent lipid content, and sampling region as independent variables.
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From page 118... ...
can be used to statistically compare trends in contaminant concentrations before and after dredging and better associate changes with dredging. Fox River, Wisconsin A further illustration of the influence of sediment resuspension on dredging effectiveness can be found in various demonstration projects conducted at the Fox River, WI.
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From page 119... ...
Prior to dredging, the average PCB water column concentrations were similar upstream and downstream of the dredging area. Similar increases (24 ng/L downstream vs 14 ng/L upstream)
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From page 120... ...
BOX 4-2 Correlations between Suspended Solids and Contaminant Concentrations Although resuspension of sediment is largely viewed as the source of contaminant losses, any contaminant that partitions rapidly from the sediment to the water column will quickly cease to be related to resuspended-sediment concentrations. As shown by the Grasse River 2005 data (Figure 4-8)
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From page 121... ...
.14 The examples cited indicate that resuspension and contaminant release during dredging can limit at least short-term dredging effectiveness. Large dredging projects that may continue for years or decades are more likely to exhibit more serious problems associated with resuspension and contaminant release than the projects of shorter duration that were examined.
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From page 122... ...
As such, this portion may not be accounted for by confirmation sampling conducted to define postdredging residuals, depending upon the timing of that sampling. The presence of such residuals directly limits the ability to meet cleanup levels and may also reduce or eliminate opportunities to achieve long-term remedial action objectives.
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From page 123... ...
. Grasse River, Massena, New York At the previously discussed 1995 non-time-critical removal action in the Grasse River, Massena, NY, the average PCB concentrations in surficial sediments (upper 8 in.)
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From page 124... ...
124 Sediment Dredging at Superfund Megasites BOX 4-3 Statistical Analysis of Mercury Concentrations in Surficial Sediment, Lavaca Bay, Texas Data Surficial sediment mercury concentrations in Lavaca Bay (Alcoa 2000) before any dredging and after four sequential dredging passes were analyzed.
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From page 125... ...
Lavaca Bay Surficial Mercury Data N Pre - 13 1 - 13 - 8 CA 2 3 - 0 4 - 0 | | | | | | Pre - 6 1 - 10 - 0 NC 2 3 - 0 4 - 0 | | | | | | Pre - 5 1 - 17 - 15 AA' 2 3 - 2 4 - 0 | | | | | | Pre - 2 1 - 13 - 8 TW 2 3 - 8 4 - 12 0 10 25 50 100 140 Mercury mg/kg FIGURE 4-12 Left, mean and 95% confidence intervals of surficial mercury concentrations (mg/kg) (log base 10 scale)
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2006. Immediately following dredging at the 2005 demonstration project at the Grasse River, residual surficial sediment PCB concentrations (0-3 in.)
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From page 127... ...
and post-capping concentrations were not significantly different from averaged pre-dredge concentrations. In the Northern Near Shore, the decline in average PCB concentrations between pre-dredging and post-dredging was not statistically significant.
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FIGURE 4-13 Distribution and sample sizes for Grasse River surficial sediment PCB concentrations (mg/kg dry weight) stratified by geographic region -- Main Channel (MC)
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From page 129... ...
In one area that initially exceeded 500 mg/kg, eight additional attempts, including multiple dredge passes, were conducted to reduce sediment concentrations. Ultimately, the contractor concluded, with EPA concurrence, that attainment of target cleanup levels in this quadrant was not possible with dredging alone, and capping was instituted (BBL 1996)
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From page 130... ...
concentrations of PCBs with a peak value of 120 ppm and an average of 16 ppm." A feasibility study containing a review of experiences at sediment dredging projects (BBL 2000) states "Pre-removal surficial sediment (0-3 in.)
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From page 131... ...
. This example illustrates both the difficulty of eliminating residual sediment concentrations in the presence of debris and bedrock and the inability to achieve long-term risk reduction because of the residual unless other processes, such as sedimentation, intervene to reduce surficial sediment concentrations.
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Fox River, Wisconsin Residuals were noted at three dredging projects on the Fox River. At the 1998-1999 removal at Deposit N, sediment rested on a fractured bedrock surface, so it was not possible for a dredge to cut into a clean underlying layer.
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From page 133... ...
are considered to be among the most difficult for attaining target cleanup levels. Commencement Bay, Washington The combination of the ability to overdredge into clean sediment and the presence of sediment that has minimal debris or other obstacles stable sideslopes for the dredge area.
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From page 134... ...
In the other areas above the SQOs, natural recovery was determined to be sufficient to meet the remedial action objectives; these areas achieved SQOs in 2003. In 2004, EPA approved the Port of Tacoma's request to end further sediment monitoring (EPA 2006a [Commencement Bay–Sitcum Waterway, April 26, 2006]
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From page 135... ...
This site remains one of the few where cleanup levels were obtained by dredging alone (except in a few areas)
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From page 136... ...
and the smaller magnitude of difference between contaminated sediment concentrations and cleanup levels decrease the potential effect of dredging residuals on achieving cleanup levels. However, generated residuals are derived at least partly from the contaminated material being removed so residuals management remains a critical issue at Pacific Northwest sediment sites.
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From page 137... ...
. Dredging to complete the debris removal and achieve cleanup levels was conducted as phase 2 from November 2003 to March 2004 and from October 2004 to November 2004 (EPA 2006a [Lockheed Shipyard Sediment OU, May 12, 2006]
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From page 138... ...
Ensure Adequate Site Characterization Central to the successful implementation of any remedial action is site characterization sufficient to define a conceptual site model. A comprehensive conceptual site model should define the contaminants of concern at a site, the spatial distribution of contamination, the processes that describe the change in contamination over time, the human and ecologic exposure routes, and the significance of exposure and risk.
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From page 139... ...
Historical surface and core samples were used in conjunction with planned studies to determine the horizontal and vertical distribution of contaminants. As described in the remedial action construction report (Dalton, Olmsted & Fuglevand, Inc.
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Accurate characterization is particularly challenging in areas where contaminated sediments are underlain by uneven sub-bottom (for example, furrows, gulleys, or depressions)
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. In the previously described 2005 pilot study in the Grasse River, it also proved difficult to accurately define the thickness of contaminated sediments using available sampling techniques and protocols.
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From page 142... ...
However, characterization activities are resource intensive and can consume time and funds otherwise available for remedial activities. As a result, decisions on whether to proceed with further characterization should seek to ascertain whether additional characterization will benefit remedial effectiveness and the point at which the additional efforts provide diminishing returns.
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From page 143... ...
This issue is addressed further in the next section. Implement Source Control As pointed out by the National Research Council Committee on Remediation of PCB-Contaminated Sediments, "the identification and adequate control of sources of PCB releases should be an essential early step in the site risk management" (NRC 2001)
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From page 144... ...
In contrast, both potentially important source areas and exposed sediment contributing to risk were missed, or not appropriately evaluated, in the characterization of the Lauritzen Channel at the United Heckathorn site. Dredging did not achieve remedial action objectives at this site despite achieving cleanup goals immediately after dredging for DDT, the contaminant of concern -- apparently because of a failure to address contaminant sources or mass contributing to exposure and risk at the site.
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From page 145... ...
. To evaluate dredging effectiveness accurately on the basis of preremediation and post-remediation fish body burdens, data sufficient to estimate both a pre-dredging time trend and a post-dredging time trend are needed from representative samples of fish collected from exposure areas that are the subject of cleanup levels and remedial action objectives.
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From page 146... ...
Methods Temporal analysis of fish trends was based on linear-regression models of PCB concentrations in fish samples with monitoring year and percent lipid content as independent variables. The Box-Cox transformation (Box and Cox 1964)
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From page 147... ...
The presence of PAH-related toxicity at a site with cleanup levels based on PCBs points to the need to focus on the full range of chemicals that may be causing toxicity at a site. At the PCB-contaminated Cumberland Bay NPL, NY, site where 34 acres was dredged, quantitative remedial goals were not set.
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From page 148... ...
That will be true not only of the upstream portion of the Fox River, where dredging is being implemented, but also of downstream locations because upstream PCB releases to the water column can affect downstream conditions. A common problem in monitoring for effectiveness is focusing on the meeting of cleanup levels, especially if operationally defined, and not on the long-term remedial action objectives.
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From page 149... ...
Examination of monitoring designed to evaluate performance relative to long-term remedial action objectives, however, has not shown expected reductions in fish concentrations. As shown in Table 4-2, spottail shiner, a fish with a limited foraging range, showed no obvious increasing or decreasing trends in PCB concentrations at the site even 5 years after the end of remediation (EPA 2005a)
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From page 150... ...
of the mean. Therefore, cleanup levels ideally should be compared to the 95% UCL for monitoring data representative of the exposure area of concern that incited establishment of the cleanup level.
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From page 151... ...
. Consider Using Pilot Tests As described above, adverse site conditions may significantly limit the ability of dredging to achieve cleanup levels and remedial action objectives.
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From page 152... ...
Several dredging demonstration projects were conducted during the remedial investigation and feasibility study at the Fox River. The previously-described demonstration projects conducted in Sediment Management Units 56 and 57 (SMU 56/57)
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From page 153... ...
. In most contaminated sediment megasites, however, the scale and complexity of the sites suggest that pilot studies are appropriate and will assist in reducing limitations of dredging effectiveness.
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From page 154... ...
Best management practices are defined on an activityspecific basis and will depend upon the type of dredging and transport equipment used, the environment in which the dredging takes place, and the process "train" or sequencing of the remedial activities. There are no standardized BMPs for environmental dredging, although "lessons learned" from environmental dredging projects to date suggests that there are BMPs that will likely be applicable to many dredging projects.
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From page 155... ...
. • Eliminating bottom stockpiling of dredged material or sweeping with the dredge bucket/head.
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From page 156... ...
The importance of using contractors experienced in environmental dredging was emphasized by the remediation contractors at the Fox River SMU 56/57 dredging project: Most large dredging contractors in the United States have little or no experience with contaminated sediment projects, working pre
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From page 157... ...
Frequently, in the past, environmental dredging contractors have followed the "navigational dredging It is true that navigation projects often have less environmental controls than 25 environmental dredging projects, but navigation dredging projects typically have to comply with water quality certification and disposal requirements of the Clean Water Act or, in the case of ocean disposal, the Marine Protection, Research, and Sanctuaries Act.
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From page 158... ...
On review of the approach, the remediation project manager revised the contract mechanism for phase 2 dredging (second season) to use a time-and-materials approach and requested new bids for the work (EPA 2006a [Lockheed Shipyard Sediment OU, May 11, 2006]
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From page 159... ...
However, contracting terms and approaches that encourage contractors to focus on achieving cleanup goals and remedial action objectives are best suited for environmental dredging. These arrangements should create incentives for reducing resuspension and residual production, using best management practices, and adjusting the dredging approach to improve chances of meeting cleanup levels and result in cost savings.
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From page 160... ...
Even in favorable dredging conditions, however, some degree of residual control is usually necessary to achieve site cleanup standards and to address site remedial action objectives. Generally, control of residuals is achieved by adding backfill or thin-layer capping; this has clear advantages in
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From page 161... ...
. Remedial action objectives included reducing toxicity of surface sediments to benthic life and enhancing benthic recolonization.
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From page 162... ...
The first round of long-term monitoring in 2004 found that the remedy appeared to have met its objectives in backfilled areas; chemical concentrations were generally below sediment cleanup levels as determined from preremediation toxicity testing, survival of benthic test organisms was high, and benthic species diversity and abundance increased relative to the pre-remediation baseline and are similar to reference areas (Exponent 2005)
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From page 163... ...
o Effective design and implementation factors include − Site characterization sufficient to develop a comprehensive conceptual site model and identify adverse site conditions. − Identification and control of sources on a water shed-wide basis.
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From page 164... ...
Where unfavorable conditions exist, increased contaminant resuspension, release, and residual will tend to limit ability to meet cleanup levels and delay the achievement of remedial action objectives unless managed through a combination of remedies or alternative remedies. RECOMMENDATIONS • A remedy should be designed to meet long-term risk-reduction goals.
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From page 165... ...
o Monitoring should be conducted to demonstrate achievement of cleanup levels and to confirm that the cleanup levels achieve remedial action objectives. o Data from monitoring should be managed and stored in electronic databases accessible for further analysis.
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From page 166... ...
St. Lawrence River Sediment Removal Project Remedial Action Completion Report.
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From page 167... ...
1997. Completion Report for Marine Remedial Action on the United Heckathorn Superfund Site, Richmond, CA.
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From page 168... ...
1990b. EPA Superfund Explana tion of Significant Differences: Bayou Bonfouca.
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1996a. Groundwater Remedial Action Five-Year Review: Bayou Bonfouca Superfund Site, Slidell, Louisi ana.
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From page 170... ...
1998a. Five-Year Review Report Marathon Battery Company Superfund Site Village of Cold Spring, Putnam County, New York.
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From page 171... ...
2003b. Five-Year Review Report Marathon Battery Company Superfund Site, Village of Cold Spring, Putnam County, New York.
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From page 172... ...
Presentation at the Second Meeting on Sediment Dredging at Superfund Megasites, June 7, 2006, Irvine, CA. Fox River Group.
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From page 173... ...
2000. An evaluation of the toxicity of contaminated sediments from Waukegan Harbor, Illinois, following remediation.
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From page 174... ...
2004. Final Engineering Per formance Standards Hudson River PCBs Superfund Site, Appendix: Case Studies of Environmental Dredging Projects.
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From page 175... ...
2004. Final Interim Remedial Action Report for Site 1 -- McAllister Point Landfill, Operable Unit 4 -- Marine Sediment/Management of Migra tion, Naval Station Newport, Middletown, Rhode Island.
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From page 176... ...
2002. Record of Decision, Operable Unit 1 and Operable Unit 2, Lower Fox River and Green Bay.
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From page 177... ...
1999. Ecological Benefits of Contami nated Sediment Remediation in the Great Lakes Basin.
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