• Abstract and Figures
• Public Full-text

Hudson River PCBs Site EPA Phase 1 Evaluation Report Addendum Prepared for: US Environmental Protection Agency, Region 2 and US Army Corps of Engineers, Kansas City District Prepared by: The Louis Berger Group, Inc. April 2010 Table of Contents INTRODUCTION TOPIC 1: WATER COLUMN LOADS DURING AND AFTER DREDGING 1-A PCB CONCENTRATIONS AT THE FAR-FIELD STATIONS: POST- DREDGING VS BASELINE 1-B NEAR-FIELD PCB RELEASE MECHANISM STUDY 1-C NEAR-FIELD PCB TRANSECT STUDY 1-D PCB FATE AND TRANSPORT IN THE FAR-FIELD DURING DREDGING TOPIC 2: CAUSES OF RESUSPENSION DURING PHASE 1 DREDGING TOPIC 3: REDISTRIBUTION OF CONTAMINANTS DURING DREDGING TOPIC 4: FORECASTS OF DREDGING RELATED IMPACTS AND RELATED RISK 4A FORECAST OF PCB LOADS DUE TO DREDGING COMPARED TO NATURAL ATTENUATION 4-B PREDICTION OF IMPACTS ON FISH TISSUE CONCENTRATIONS IN THE LOWER HUDSON RIVER DUE TO DREDGING TOPIC 5: SCOW UNAVAILABILITY AND ITS IMPACT ON PRODUCTIVITY TOPIC 6: UNDERESTIMATION OF DEPTH OF CONTAMINATION AND ITS IMPACTS ON THE PROJECT 6-A POST-DREDGING CORE LOCATION TREATMENTS AND THE NEED FOR MULTIPLE RESIDUAL PASSES 6-B RELEVANCE AND CONSEQUENCES OF UNCERTAINTY IN MEASUREMENTS OF THE DEPTH OF CONTAMINATION TOPIC 2 ATTACHMENT: CONDITIONS ASSOCIATED WITH WATER COLUMN PCB CONCENTRATIONS: THOMPSON ISLAND DAM 2009 Hudson River PCBs Site Page i The Louis Berger Group, Inc. EPA Phase 1 Evaluation Report – Addendum April 2010 INTRODUCTION INTRODUCTION This Addendum to the EPA Phase 1 Evaluation Report presents information compiled in response to requests and questions submitted by the Peer Review Panel after its introductory meeting in February 2010. This Addendum also includes several evaluations referenced in EPA’s Phase 1 Evaluation Report but not yet completed at the time of its release. The contents of this Addendum corroborate and supplement the conclusions presented in the report, support EPA’s proposed changes to the Engineering Performance Standards (with certain adjustments which are discussed below or which will be explained at the Peer Review Deliberation Meeting), and help demonstrate that the dredging operation can be modified in a number of respects to obtain significant improvements over the Phase 1 performance. The Addendum is a series of independent discussions organized under six Topics to provide a logical sequence of information. The findings are summarized below: 1. Water Column PCB Loads During and After Dredging - The release of PCB non-aqueous phase liquid (NAPL) from the dredging areas is influencing the resuspension monitoring results; however, it is difficult to accurately quantify its impact. The presence of NAPL is consistent with the high dissolved PCB concentrations detected in combination with low TSS concentrations. Changes observed in homolog patterns between near and far-field samples can be attributed to gas exchange of lighter, more volatile PCBs with the atmosphere during transport downstream. TSS data do not support attribution of resuspension monitoring results to releases and subsequent transport of suspended sediments. GE’s resuspension data interpretation and analysis do not incorporate these findings. 2. Causes of Resuspension - The most significant factors affecting resuspension are not simply the mass removed and river velocity. A group of six factors comprises the key “resuspension drivers”: mass and volume removal, vessel traffic, exposure of recently disturbed dredging residuals to flow, backfilling processes, and bucket closure. 3. Redistribution of Contaminants - Resuspension impacts are not exclusively tied to the creation and transport of suspended solids releases from the dredging area. As discussed in Topic 1, TSS data do not support the conclusion that significant amounts of sediment were redistributed beyond the dredging areas. Sediment trap data analyses advanced in the GE Phase 1 report lack a robust baseline data set, and were also impacted by tug traffic; they are therefore not reliable and the co-located cores used by GE as surrogates for this analysis are not adequate to support their assertions. 4. Forecasts of Dredging-Related Impacts and Related Risk – EPA has revised the analysis set forth in Appendix I-G of EPA’s Phase 1 Evaluation Report to improve the predictions of PCB loads at Waterford. The reanalysis used PCB concentration instead of loads, since a better correlation could be developed for concentrations to evaluate the recovery. The analysis indicates that a dredging release of approximately 500 kg of Tri+ PCB, as measured Hudson River PCBs Site Page 1 The Louis Berger Group, Inc. EPA Phase 1 Evaluation Report – Addendum April 2010 at the Waterford far-field station, provides net benefit to the river compared to MNA. While the load standard will continue to be based on a 1 percent net loss of PCB mass removed (approximately 2000 kg Total PCBs or 667 kg Tri + PCBs), the goal will be to minimize the dredging-related release of Tri+ PCB to 500 kg (as measured at Waterford) over the life of the project (including both Phase 1 and Phase 2). Support for the adoption of control levels derived from the 1 percent net loss figure is provided by consideration of the impact on fish tissue concentrations and project risks in both the Upper and Lower Hudson River. Analysis was performed to estimate the impact of dredging-related PCB release on fish tissue concentrations in the Lower Hudson River for the expected duration of dredging and the brief period immediately beyond. The Farley-FISHRAND models were run for Upper Hudson loads that correspond to the upper end of the proposed revisions to the Resuspension Standard. The impacts predicted here are similar to those noted in the supporting documentation for the Record of Decision. This analysis indicates that the proposed range of revisions to the allowable load standard for the Lower Hudson would not have any measurable long term impacts to the recovery of fish tissue concentrations and therefore would not pose any additional long term risks to Hudson River fish-consuming populations in the Lower Hudson. 5. Scow Unavailability and Its Impact on Meeting Performance Standards - Dredging project implementation can and should be enhanced during Phase 2. The lack of availability of empty scows (due to only partial filling and limited unloading capacity) created a greater adverse impact on dredging productivity than did resuspension concerns. It also increased boat traffic and the length of time CUs were left open, both of which contribute to resuspension. The addition of a second unloading station and the addition of a minimum of another 0.5 foot of dredged material to each scow will be necessary to facilitate achievement of the Phase 2 dredging productivity targets. 6. Underestimated Depth of Contamination: the Need for Multiple Dredging Passes – EPA shows that GE’s use of SSAP cores is incorrect and causes an underestimate of PCB mass removed during Phase 1 dredging. Most of the additional dredging was required to address underestimation of the depth of contamination (DoC). Since the additional dredging was generally not conducted to capture dredging residuals but rather inventory, the addition of a designed overcut to the first dredging pass during Phase 2 will reduce the number of dredging passes required and increase efficiency. An overcut is needed to address uncertainty in coring data and the dynamic nature of the sediment bed. These findings corroborate EPA’s belief that Phase 2 of the dredging remediation can be accomplished in a way that achieves the benefits ascribed in the ROD, with some modifications to the EPS and the dredging project design, and that it can consistently meet EPA’s proposed engineering performance standards for Phase 2. Hudson River PCBs Site Page 2 The Louis Berger Group, Inc. EPA Phase 1 Evaluation Report – Addendum April 2010 Below is a summary of each of the Topics presented in the Addendum. Also discussed below is a recent decision by EPA relating to the Halfmoon and Waterford public water supplies, and the implications of that decision for the use of the 500 ng/L water column standard. The low detected TSS concentrations, combined Topic 1 is an examination of the water with high dissolved concentrations in the near- column loads observed during and field studies, indicate that release of PCB NAPL after the 2009 Phase 1 dredging and an is influencing the resuspension monitoring analysis of various studies regarding results (although the impact cannot be accurately water column PCB and TSS loads that quantified). EPA’s evaluations of GE’s water were conducted by GE. column studies found that near-field releases were dominated by PCBs in the dissolved phase, and that the data do not support GE’s conclusions that the oil phase observed near the dredging operations represented only small, ephemeral amounts of PCBs. A 2-phase partitioning model as used by GE is not applicable in the presence of NAPL and will incorrectly identify the PCB partitioning as being in equilibrium. Since the NAPL was not explicitly characterized and is not appropriately represented in GE’s model, its overall impact on the dissolved phase concentrations cannot be quantified. If the NAPL is as concentrated as oil found at the Fort Edward Plant Site former 004 Outfall #5-58-004 (GE, 2008), even a small droplet can significantly alter the PCB concentration of a water sample. At the Fort Edward outfall, PCB concentrations of 255 to 1,240 ppm (more than six orders of magnitude – a million times - greater than concentrations in typical baseline river water samples) were detected in oil that is similar to the oil which is the source of the NAPL in the river. The dynamics of TSS and PCB loads in the near-field are highly variable due to the impacts of dredging and related activities being conducted in the river. For this reason, samples collected by GE along near-field transects can only be used to represent conditions during a relatively short duration immediately preceding sample collection.

Load more

  211

Copy Link