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ERA Responses to Questions

GENERAL QUESTIONS OR COMMENTS

TT1. A general comment is that this is an impressive array of data and information collected by both the EPA and GE. It clearly has been a Hercul ean effort to synthesize and reduce the amount of information down into the ERA, a nd generally, this has been done well. Two general themes that I will come back throughout my initial comments, and my overall review, is that (1) it is difficult t o follow the thought and decision processes in the ERA (so-called “transparenc y”) and (2) figures are no substitute for providing actual data. An example of the former is the inconsistent way COPCs from the Tier III are presented. That P CBs are the primary focus is clear; discerning how each of the individual endpoi nts examines PAHs, metals, dioxins and furans is inconsistent. An example of the later are the tables and figures that relate to benthic invertebrate communities and results from bioassays. The reader is asked to accept the data in bar charts (e.g. , virtually all data in Appendix D), tables of “yes/no” (Table D.3-1), or shading representing stat istical sig ni ficance (e.g., Table 4.4-5). As will be discussed under the Benthic Inv ertebrate section, not presenting a list (at least as an Appendix) of the collected spe cies by station does not allow for a good review.

Response: The issue of ensuring that the ecological risk asses sment document contains the thought and decision processes of the assessors is an important one. If there are areas that need improvement in this regard, EPA apprec iates the Panel pointing them out.

To make the document more readable and to better illustrate patterns in th e data, the ecological risk assessment makes extensive use of figures. Although fig ures are often a better communication tool than are tables, the recommendation to includ e all data in tables is appreciated and will be considered.

While it is true that the Appendices are focused on risks primarily from tPCBs (and TEQ where appropriate), there was a consistent approach app lied between Appendices, and the other COC s were screened and assessed at a level of detail proportional to their chemical hazard. With regard specifically to Appendix D, PCBs received more attention because the indications of chemic al screening, correlations with toxicity endpoints, Phase I TIE results, etc., implic ated PCBs as the dominant chemical stressors. The concentrations of other CO Cs were also assessed in various environmental media and conclusions were dra wn regarding their potential to exert adverse responses.

TT2. The ERA must completely document and present the information in a way that shows the overall decision-making process. With an impressive array of information/data comes an impressive set of work plans, Quality Assurance Project Plans, Standard Operating Procedures, individual data reports, field notes, data validation reports, etc. There is no criticism here on lack of such information, or

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that EPA has not made a good faith effort to provide those. In fact, tho se exist and the Peer Review Panel has been provided with a tremendous amount of information. Having said that, the ERA could be improved by adding a section on organization that includes a list of all the studies that have been done, and where that information can be found. I believ e a good example of the type of summary I am describing is in GE’s RCRA Facilities Investigation (RFI), Section 1.3, Overview of Housatonic River Investigation Activities.

Response: Section 1.6 (Data Sources) of the ERA briefly lists th e site-specific investigations conducted by EPA and GE that were used in the de velopment of the ERA. Tables 2.8.1 and 2.8.2 provide some greater detail. The m ost complete presentation of the information available from each study is includ ed on the two CDs provided to all Peer Review Panel members (i.e., Supportin g Information and Studies for the Housatonic River Project and Ecological Field Studies Conducted by General Electric for the Housatonic River Projec t). Detailed summaries of the data used to evaluate each assessment endpoint are provided in the associated appendices and a complete listing of all data sources is provided in Appendix L. However, EPA will consider improveme nts to this section of the report to better provide cross-references for this information.

The following 3 questions have been responded to with a single answer:

TT4: As a general organization comment, the overall Table of Contents (TOC) should be expanded to include the appendices and their subsections. Considering that the way the overall document is structured there is a great deal o f referencing to the appendices. Having a list up front would expedite the “hunt” for relevant sections.

TT5: A corollary thought is that the TOC needs a list of all CDs that accompany the ERA. This should, in my opinion, include all of the CDs that have information provided by GE. Fur thermore, I recommend that all of the CDs be located in one vo lume – and not be scattered throughout the document. I note that myself, and at leas t one other peer reviewer, went through the entire document, pu lling all the CD s, and placing them in one CD case.

TT6: A list of acronyms is missing from the TOC. I submit this is a mandatory addition for the Final ERA.

Response: The omission of the list of acronyms in the main TOC was an oversight during document production, EPA agrees that this is a necessary component of any such document. The list has been provided to the Peer Review Panel. An expanded TOC is provided in Attachment TT4, a through c, and TT5.

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BS1. The ERA focuses on aquatic biota (fish, benthic inverte brates, and amphibians) and wildlife. Noticeable by their absence are any so il-associated receptors (terrestrial plants, soil invertebrates, and soil microbia l processes). Aquatic plants are also absent as receptors. The report states that the affected area includes the riparian habitats and associated floodplains, and that the a rea along the Housatonic is one of the most biologically diverse in New England, including a number of rare plants. Given that soil-associated receptors are likely t o be exposed, are highly diverse, and may include special status species, it is unclea r to me why they were not considered. Additional justification for the evaluation of soil biota is the fact that they provide food (plants and soil inverts) and habit at structure (p lants) for many birds and mammals. So, the question is, why were terrestrial and aqu atic plants, soil invertebrates, and microbial processes not included as rec eptors?

Response: Over a period of several years preceding the Consent Degree, EPA, GE and other stakeholders discussed available information on the contaminants present at the site and the Housatonic River ecosystem, and th e assessment endpoints appropriate for the ERA . Subsequent details regarding measurement endpoints, study design and, data analysis included input from the aforementioned parties. Emphasis throughout the conceptual model and endpoint development process was on the identification of endpoints where maximum e xposure and adverse ecological effects were anticipated.

Unlike metals, it has been shown that terrestrial plants do not take up an appreciable amount of PCBs, the primary routes of exposure being through volatilization and as particulate matter (i.e. “splash” of soil after rain events). Through an evaluation of air monitoring data and the fate of the highly chlorinated environmental mixture of congeners observed at the sit e (resembling Aroclor 1260), direct uptake from soil was not considered to be an important pathway. Terrestrial soil invertebrates were collected as prey items , but were not studied directly as an endpoint because of the limited amount of in formation in the literature on effects from PCBs that would support a weigh t-of-evidence approach in determining risk. Similarly, there is little inform ation on the effects of PCBs on microbial processes.

Aquatic plants do take up PCBs through the dissolved phase. Aquat ic plants were sampled for PCBs, but primarily to support compartments in th e food chain model. Again, there is little information available on the effects of PCBs on aquatic plants, therefore they were not included as an endpoint in the ERA.

BS2. It appears that the screening phase of the ERA is being referred to as the 'Pre-ERA'. This is atypical nomenclature and is not consistent with terminology in the EPA ERA guidance. Although not a big issue, because ERA's have a large amount of specialized terminology and can be difficult to follow for professional and

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lay persons alike, creating new te rms does not facilitate improved clarity. Is there a specific reason for the new terminology?

Response: As discussed in Section 2.1, the functional requir ements of a screening-level problem formulation were achieved with the prep aration of the Upper Reach – Housatonic River Ecological Risk Assessment (W eston 1998). The purpose of the Pre-ERA in this assessment was to refine the li st of potential contaminants of concern so that a more focused assessment could be conducted for each assessment endpoint . The use of the Pre-ERA terminology was included so that a clear distinction could be made between earlier screening activities and those performed as part of this ERA.

JO1 . Have sample been taken or have studies been designed to assess mobilization of PC Bs from the upstream remediation areas on the PSA or Rest of River a reas?

Response: Under the scope of the removal ef forts, GE and EPA are conducting regular monitoring both upstream and downstream of remediation activities to ensure that there are no releases of contaminants from the area undergoing remediation. The results of these studies have shown that the remediation conducted to date has not released contaminants that could affect the Rest of River.

TL1. Why are HQs termed “probabilistic?” (Executive Summary and Page 2-17ff) HQs, introduced in the Executive Summary and discussed in Section 2, “Problem Formulation,” are not probabilistic. They are deterministic and rely on one number derived from two terms, the environmental concentration (presumably a veraged over some area) divided by an “effect level,” which could be acutely toxic (mortality) or reproductive (chronic). HQs may be used in a probabilistic approach, but only if one esti mates and incorporates the probability of exceeding “critical” environmental con centrations and the probability distribution of toxic responses , given the con centrations experienced by the target organisms (benthic, fish, amphib ian, etc.). HQ s, per se, are not probabilistic; they are a starting point from which to look for pro blem areas.

Response: Th e statement that the HQs are probabilistic was intended to refer to the wildlife HQs only. The HQs for aquatic receptors were deterministic and were calculated by dividing summary statistics (i.e., medians, means, 25th and 75th percentiles, and minima and maxima) on concentrations of tPCBs in the environment (sediment for benthic invertebrates and amphibians, tissue for fish) by the corresponding effects benchmark. HQs for TEQ were also calculated using the same approach for fish. This procedure provides some estimate of the uncertainty associated with the HQ.

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For w ildlife receptors, probabilistic HQs were calculated as follows (see Section 12.2.2.2):

• The distributions from the Monte Carlo analyses for total daily inta ke of COCs by representative species were each divided by the corresponding effec ts metrics used to estimate risks in Sections 7 to 11 and Appendices G to K. In the case of a dose-response curve effects metric (e.g., mink exposed to tPCBs), the effe cts metric was specified as a uniform distribution of dose ranging from 10 to 2 0% effect. A similar approach was used for NOAEL-L OAEL ranges (e.g., bald eagles exposed to tPCBs), field-based effects metrics (e.g., tree swallows exposed t o tPCBs), and threshold ranges (e.g., kingfishers exposed to TEQ).

• A similar approach was used with the results of the probability bounds analysis, except that the effects metric wa s specified as a distribution-free range.

• The analyses were conducted for both tPCBs and TEQ.

• Modified box-and-whisker plots were developed for each representative species in the PSA. For species with smaller foraging ranges , the analyses were conducted for different areas within the PSA. Included in the box-and-whisker plots (Figures 12.2-3 and 12.2-4) are the median HQ fro m the Monte Carlo analysis ( the thick line bisecting each box), the mean HQ from the Monte Carlo analysis (star symbol), the 25th and 75th percentile HQs from the Monte Carlo analysis (the bottom and top of each box), the 10th percentile HQ from the lower bound of the probability bounds analysis (botto m whisker), and the 90th percentile from the upper bound of the proba bility bounds analysis (top whisker).

• In addition to the above, probabilistic HQ plots were also devel oped for tree swallows exposed to tPCBs using measured concentration s in 12-day nestlings (data from Custer 2002) as an estimate of exposure. This was done to facilitate comparison of risks using the microexposure model ing approach and using measured concentrations from birds in the PSA. Ins ufficient data were available to do a similar analysis for TEQ. For the measured concentration data, an empirical histogram was specified fo r each PSA location using the available 3 years of data for the Monte Carlo p ortion of the analyses. The empirical histog rams were divided by the same threshold range as used for HQs based on the microexposure model outputs. For the probability bounds analyses, 95% Kolmogorov-Smirnov confidence limits were calculated for each empirical histogram. Both the upper and lower confidence limits were divided by the same threshold range as used for HQs based on the microexposure model outputs. Using the results of these analyses, modified box-and-whisker plots were developed as described previously (Figures 12.2-3 and 12.2-4).

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• In addition to plots developed for mink and otter exposed to tPC Bs and TEQ using the results of literature-based dose-response curve, plo ts were also developed using the results of the mink feeding study conducted by Bursian et al. (2003). In this case, the denominator was the NOAEL to L OAEL range from Bursian et al. (2003), rather than the 10 and 20% e ffects doses from the literature-based dose-response curve. Otherwise, the approach was as described above. The results are shown in Figures 12.2-3 and 12 .2-4.

For w ildlife species other than tree swallow, mink and river otter, it was not possible to derive field-based or feeding study-based HQs because the required data were not available.

TL2. A critique of HQs is that they, like any derived vari able (Green, 1979), do not account for the separate variances associated with numerator and denominator. To phrase this as a que stion: How are the individual (= River Segment) variances of the effect co ncentrations and the exposure concentrations ta ken into account in using HQs?

Response: For aquatic receptors, the denominator for these anal yses (i.e., the effects benchmark, or MATC) was deterministic, and no var iance in the denominator was accounted for.

For wildlife, it was assumed in the exposure portion of the HQ calculation assumed that there was spatial and temporal averaging of expos ure over long periods of time. That is, predators would not feed on the most or least-contaminated prey item day after day for mo nths at a time. Thus, for wildlife, the mean concentration in prey was used as input to the exposure analyses. Because there was uncertainty as to the value of the mean due to sample s ize and other issues, this uncertainty was included in the analyses (e.g., by using t he 95% UCL on the mean in the Monte Carlo analyses or the distribution-free r ange from the LCL to the UCL in the probability bounds analyses).

TL3. Overall, do the results of the Monte Carlo analysis truly represen t variance in distribution of PCBs in sediments among River Segments? Do th ey reflect a combination of variability and uncertainty? This question derives from the extensive use of statistical re-sampling (Monte Carlo) analyses in this ERA. Such analyses ha ve their value, yet underlying variance in metr ics (such as sediment PCB concentrations) are missing. In the case of linking biological responses to sediment concentrations, the variance or heterogeneity in PCB mass in different sediments may be very important. In reading Sections 2 and Attachment 2.1, I found it very difficult to get an idea of the variance associated with sediment PCB concentrations in any reach. Is there a way to describe the heterogeneity of PCB concentrations in Housatonic sediments within each River Segment? Were sediments sampled in proportion to the types of substrates (depositional, erosional, reach) present in the Housatonic River Segments?

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Response: As indicated in the response to Question TL-1, Monte C arlo analyses were not conducted for aquatic receptors, the only receptors for w hich sediment exposure was considered. The summary statistics calculated for con centrations of COCs in sediment for the probabilistic HQ analyses fo r benthic invertebrates and amphibians were based on actual data and thus reflect variability only.

Concentrations of COCs in sediment were not considered in the wildlife exposure analyses, only concentrations in diet.

However, the heterogeneity in PCB concentrations even within a partic ular sediment type is clearly demonstrated in Figure 3.2-3, generated from the 12 repl icates sampled as part of the Sediment Quality Triad approach. In this effort, 12 replicate 6-in2 samples were collected immediately adjacent to each other from v isually similar sediments and tPCB concentrations were found to range over as much as two orders of magnitude in an area of perhaps a square meter or less. Additional information on the variability encountered when sampling across all sediment types, by riv er mile within the PSA, is demonstrated in Figure 4-19 in the RFI.

TL4. Why are there no statements concerning statistical power in this E RA? To this end, there are several sections of the ERA that state “no difference” between PCB concentrations in sediments or tissues (see sections>>>>>>>). When there are no differences found, it is imperative that a statement accompany the conclusion, indicating the power of the test (Sokal & Rohlf (1990), Quinn & Keogh (2002), many other stat refe rences). For exa mple, what percentage difference would it make in sediment PCB conce ntrations to be able to statistically determine differences in PCB concentration (15%?, 25%?, 80%?, more?). Stat istical power is a function of the relative differences among means and in sa mple size.

Response: The question appears to relate to some of the t-tes ts reported in ERA Section 3 and Appendix D (Benthic Invertebrates). The results of pairwise comparisons of the contaminated stations to the negative control a nd reference stations were provided in the ERA in the interest of completeness. However, the basis for the derivation of MATC values in the ERA was not f ounded upon NOAELs and LOAELs resulting from these statistical tests of significance. Instead, other approaches, such as EC20 and EC50 (effect-size based) measures and general linear modeling were applied to determine threshold effect levels. EPA agrees that standard significance tests are limited by stati stical power considerations. In addition to “relative differences among means a nd in sample size,” the other factors that contribute to statistic al power are the significance level (α), and the magnitude of variation within treatments. The “lines of evidence approach,” which considered concordance of outcomes across individual toxicity endpoints, and an emphasis on effect size (rather than statistical significance), are a reliable method for establishing effects thresholds. In a few cases, statistical comparisons were made among tissue types or across sampling locations for a given medium. These tests were few in number and were not an essential part of the overall analyses or risk conclusions.

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In the wildlife sections, no statistical tests were conducted reg arding PCB concentrations at different sites or at different times. This qu estion is not applicable to this portion of the ERA as concentrations of concern were evaluated in diet, not sediment.

TL5. Beginning with Figures 2.5-2, -3, -4, and continuing throughout t he ERA, why are the River Segments portrayed in the figures as if they were equi-dista nt from each other? It would be better (in my opinion) to use River Mile (as in Figures 2.5-12, 13), as the perception of changes in concentration (“rates of decline”) are deceptive when c ategorical data (e.g., Station IDs) are presented as continuous (e.g., River Miles). If Segment ID is to be used, then the downstream statio ns should be distributed on the X-axis in the correct scale. An example of where the Stations are depicted with a “dramatic” increase in downstream fines is fou nd in Figure 3.2-2. If the stations were presented as River mile on the X-ax is, the increase in f ines would not appear so steep.

Response: EPA appreciates the Panelist’s recommendations for im provement of the ERA document. Although some figures, i.e., those showing sedime nt parameters, could be reformatted to show each segment (Reach) to scale according to river miles, this could not be done for floodplain soil parameters. Soil data in the floodplain is not assigned a unique river mile because a single point in the floodplain could be linked to many different river mile points due to meandering. This is particularly problematical for locations at greater distances from the river, where points along t he river for as much as a half-mile, or more, may be equidistant to the sample location.

TL 6. This questions holds for the sediment data downstream in the Housatonic (Station 10 or high er). What is the power of the analyses indicating “low” concentration s of PCBs in Riv er Segments 10 or higher (downstream, in CT)? In addition, to the m ean, median, hig h and low concentrations, what is the skew?

Response: The assessment of "low" PCB concentrations in Housatonic River sediments in CT, i.e., in Reaches 10 through 16, was based on a visual examination of the data and a qualitative assessment of the CT concentrations compa red with those further upstream in Massachusetts (particularly in Reach 9, a 26 mile length of the river), notably sediment concentrations in the PSA. Because the state ment was not based on statistical hypothesis testing there is no assoc iated "power" of the analysis.

TL7: In our tour of the Housatonic River on October 30, we saw numerous paper or pulp mills along the river. The pulp mills may be producing confounding influences (e.g., dioxins, chloramines, etc.). As stated, this ERA does not consider multiple chemicals in the sediments, except for the Ah-active chemicals. How has the ERA dealt with the confounding influences of the pulp mills? Do they present confounding influences?

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Response: Although pulp mills were common in Massachusetts, including along the Housatonic River, shortly after the industrial revolution, there are cu rrently no pulp mills discharging to the river. There are a number of paper mills, many of which are smaller operations specializing in 100% cotton fiber and/or other high-q uality papers. There was a concern in designing the studies that the influence of thes e, and perhaps other industrial sources, could confound the studies, therefore the m ajority of the studies, with the exception of the reference areas, were located within th e Primary Study Area (PSA). The only industrial sources or mills located upstrea m of the PSA are those of the Crane Paper Company in Dalto n. Sampling of the river between Dalton and the PSA conducted over the last several years indicates no or minimal contamination of the river and its sediments due to this source.

A review of the NPDES permit conditions for all permitted paper mill d ischarges into the Housatonic River indicated that all of these wastewater discharges are monitored for conventional parameters (and a limited number for metals) an d there is no indication that any of these mills discharge organic contaminants. Many of these discharges are also monitored via whole-effluent toxicity testing, which would indicate if any toxic contaminants were being discharged in amounts th at could affect the results of this risk assessment.

VF14. With respect to evaluating the presence or absence of harm (Menzie et al. 1996, p. 293) I would interpret th e term ‘undetermined’ to indicate that the measurement endpoint was either not measured for the particular site/sample or that for some other reason that it was not possible to determine whether or not there was harm. Is this the way that the term ‘un determined’ was used in the present ERA? Or was it also used in cases w here evidence was conflicting or inconclusive? In cases for which harm was ‘undetermined’ i s it possible to esti mate a magnitude of harm?

Response: The term “undetermined”, as used in the risk analysis sum mary tables in Sections 3 to 11, was used to indicate that it was not possible to dete rmine whether there was evidence of harm, for the measurement endpoint being con sidered (e.g., field study, modeled exposure and effects, etc). The term “undeterm ined” was not used in cases where evidence was conflicting or inconclusive. In thes e situations, it was indicated in the discussion that the conclusions regarding risk (i.e., low, intermediate or high) were termed “uncertain” (see top of page 7-86 for an example statement). In cases for which harm was “undetermined”, it is nevertheless possible to estimate magnitude of harm. For example, some field studies could rule out intermediate or high harm, but could not rule out harm altogether. Such studies would not be able to determine harm (i.e., would be termed “undetermined”), but could specify low magnitude of harm (i.e., unknown if harm is occurring but, if it is, the magnitude of harm is low).

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VF15. The comment by NOAA raised concerns about the risk definit ions (e.g., for piscivorous mammals). For example, they suggest that following the definitio ns used a 90% effect observed 40% of the time would not be defined as high. They also questioned whether thes e were prob bilities or proportions of a population. Please clarify these issue a s.

Response: While one could in theory draw a line that passes b elow the high risk criterion (i.e., probability of 20% or greater effect is greater th an 50%) and then passes through the point defined by NOAA above, in practice this is highly unlikely to occur. As evidence of this point, every single instance in the report (see Sections 9 and 10) where the probability of 90% effect or grea ter was equal to greater than 40%, risk was classified as high. In cases where the risk curve passed close to the high risk criterion (e.g., figures 9.5-11, 10.5-1 to 10.5-4), probabilities of 90% or greater effect were always very low (


Waide and TFH Allen. 1986. A Hierarchical Concept of Ecosystem s. Princeton University Press, Princeton, NJ), there was little knowledge to be gained by assessing population-level effects for these species. Likewise, for other species (e.g., mink, river otter), risk to individuals in the PSA was high based on the weight of evidence, therefore, locally-exposed populations would also be at high risk.

VF20. According to Menzie et al. 1996, the WOE approach, whether quantitative or qualitative should ’elucidate the risk assessor’s thought process’. They also e mphasize that when a qualitative WOE approach is used that ‘it is extremely important for the risk assessor to d ocument the rationale for the relative weight given to each attribute’. Where is/are the best plac e(s) in the documentation to find an explicit statement of the rationale used?

Response: In Appendices D through K, the tables that describe the weighting of measurement endpoints include the rationale for how each attribute was weighted, as well as the overall endpoint weighting.

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EXECUTIVE SUMMARY

The follo wing 2 questions have been responded to with a single answer:

TT7. Highlight box – fir st bullet. Recommend listing what are the COCs in the PSA. I also recommend that since this is the very first call out of both acronyms, they get defined here.

TT8: Personal preference is that I think the use of text boxes – i n the current format – are distracting and do not necessarily make inform ation access easier for the reader. For example, in this first highlight box I believe the reader would be bet ter served by having a summary as a separate section in paragraph form, and reserve use of the text box to capture and explain what “high”, “moderate”, and “low” risks means. To re iterate, an observational bias – not at all a critique.

Response: EPA appreciates the input from the Panelist and will consider formatting issues after the Panel deliberations have been completed.

TT9. Page ES-11, “Assessment Endpoint” text box. Not-withstanding previous comments about text boxes (this is not necessary here), a recommendation is that the ass essment en dpoints be restructured so that the biological group is list ed first. I.e., “Be nthic invertebrate community structure….”, “Fish survival, growth and rep roduction”. Agreed this is somewhat trivial, but in communicat ion with the general public the important consideration is the receptor group first.

Response: EPA appreciates the input from the Panelist and will consider formatting issues after the Panel deliberations have been completed. As a point of clarification, the receptor groups had been called out in Figure ES-3 on the previous page.

TT10. Page ES-12, Line 5, “weight-of-evidence” approach. Here may be an example of how a text box could be used to generally explain what WOE is. More of an issue of risk communication – but to the general public, WOE is not an obvious term.

Response: The recommendation to highlight this discussion even further through the use of a text box is appreciated and will be considered. The weight-

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of-eviden ce approach is briefly described at the bottom of page ES-12 and top of page ES-13.

TT11: General question that will come up again under problem formu lation. Was the Menzie et al approach to the ERA an ARAR for conducting the overall investigation? If so, then the Executive Summary should point o ut that the ERA was conducted in accordance with procedures prescribed by the State of Ma ssachusetts. If not – comment is reserved for Problem Formulation Section.

Response: The Menzie et al (1996) approach to conducting a Weight of Evidence analysis is not an ARAR, nor is the Massachusetts Contingency Plan, which suggests the use of a weight of evidence approach .

The following 2 questions have been responded to with a single answer:

TT12: Recommend that the ES be carefully examined for statements such as “not predicted to be catastrophic” (Page ES-16, lines 20 – 21, 23). In this case, “catastrophic” is not defined, and these types of sta tements are inflammatory.

TT15: On page ES-31, line 13, the term “significant” risk is use d. What that intentional? It doesn’t appear to refer to statistical significan ce. In which case it may be worth considering only using “significant” where statistica l testing has been applied.

Response: The Executive Summary is intended for a less-technical audience and was therefore written with somewhat less rigorous review of the ty pe of “value-laden” terms identified by the Panelist. EPA appreciates and con curs with the Panelist’s comments, however, and will consider these recommend ations in the context of other comments received following the public Peer Revie w meeting.

TT13. Could the various summaries for the Assessment Endpoints be written with more detail and be supported by factual information from the various appendices (see previous absence of data comment). The paragraph written for piscivorous mammals makes a clear, unambiguous statement concerning mink health when fed fish from the PSA. With perhaps the exception of benthic invertebrates, where the data are to conflicting to be of much value (see below), similar statements can be constructed for the other receptors of interest. The “Omnivorous and Carnivorous Mammals”, for example, could be strengthened if some population data examples were included.

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Response: With executive summaries, there is always a deba te as to how much detail should be included. The executive summary for the ER A document is already 50 pages long. Thus, additional detail should be add ed only if it significantly improves the document. Nevertheless, the recommen dation to add more factual information to support the summaries of the risk ass essments for each of the assessment endpoi nts is a good one. As with other recommendations, however, EPA will wait until completion of the Peer Review before deciding upon the appropriate course of action.

TT14: Could the ES be strengthened by inclusion of more population -based data? Not-withstanding the previous comment related to transparency on the GE studies, while th e presentation of Hazard Quotients in Figures ES4 through ES-7 is good, by not including population-based data in the ES, it provides the appearance that the ER A is an HQ-based decision process. Something not intended, bu t apparently con cluded.

Response: EPA concurs that the Executive Summary (ES) in its current form could be misinterpreted to indicate that the ERA is based primari ly on the HQ approach, which wa s not the intention. Figures ES4 through ES7 were included in the ES to summarize the risk to ecological receptors in a graphic manner that could be readily grasped by the readers that the ES was intended to reach. EPA appreciates the recommendation and will reconsider this approach in the context of other review comments.

The following 2 questions are answered by one response:

RS1 . p. ES-1: Please explain the statement shown below. In my experien ce the finding of “ unacceptable risk” is a risk-m anagement decision, and is not the subject of an ERA. The ERA seeks to quantify, where possible, the magnitude of the risk and the cause of it, but does not reach a conclusion as to the acceptabilit y or unacceptability of the level of risk .

Total PCBs and other COCs in the PSA of the Housatonic River pose unacceptable risks to some assessment end points.

RS9 . P. ES-50: See previous comment / question for page ES-1.

Weight-of-evidence assessments indicated that aquatic life and wildlife in the Primary Study Area of the Housatonic River are experiencing unacceptable risks as a result of exposure to tPCBs and other COCs.

Response: As the Panelist notes, the acceptability or unacceptability of risk was often considered to be a decision to be made solely by risk managers rather than risk assessors. This can be a straightforward issue in the circumstances of a Human Health

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Risk Assessment because, when the risks are put in context of the es tablished EPA risk range and the noncancer HQs the answer is relatively clear, but th is becomes more problematic for ecological risk assessments because of the lack o f such criteria. In EPA’s 1999 “Ecological Risk Assessment and Risk Management Principles for Superfund Sites”, the second question posed in the guidance require s that the risk assessors and risk managers discuss the risks and communicate the infor mation clearly with regard to the acceptable or unacceptable risks. This has occurred within the five-step SMDP process, and is put forward for consideration in the Peer Review Process, which could then suggest alternative conclusions for EPA’s consideratio n.

RS2. p. ES-16: Please clarify statements where TEQ is used in lieu of a more correct description of the PCBs (or congeners) in ques tion. TEQ is a concept, thus exposure to the concept is not the same as exposure to the particular COPC. This may be a matter of semantics or grammar, but using TEQ in lieu of the particular PCB o r congener in question does not appear to be an appropriate approa ch.

Insectivorous Birds—The WOE results for exposure of insectivorous birds to tPCBs are presented in Table ES-4, and for exposure to TEQ in Table ES-5.

Response: The Panelist is correct that TEQ, or 2,3,7,8 – TCDD Toxic Eq uivalence, is a concept that refers to the sum of the toxicity of the various PCB, diox in, and furan congeners that have the same mode of toxicity as 2,3,7,8 – TCDD. The de termination of toxic equivalence in the Housatonic River ERA is explained in detail in Appendix C.10. EPA believes it is clear from the document that TEQ is used in the context of the ERA to refer to the combined toxicity of those congeners which act in a dioxin-like manner (typically referred to as the coplanar congeners), expressed as an equivalen t concentration of 2,3,7,8 – TCDD through the use of toxic equivalence factors. This terminology is commonly used in the scientific literature by a wide variety of investigators.

RS3. p. ES-16: Please explain the level of confidence in modeled studies such that the modifier “would” is used rather than “could”. What is the scientific bas is for making this claim ?

In addition, a population model was constructed for wood frogs to deter mine whether effects from PCBs on individual wood frogs influence the populations with in the PSA. A 10-year simulation, both with and without the effects of PCBs, was conduc ted. The model demonstrated that effects observed in the toxicity studies would result in population-level impacts.

Response: The term “would,” indicating a high level of certainty, is used to refer to the results of the population model in a limited sense, i.e., internal to the model itself, not necessarily to the degree of certainty of the various inputs to the model, including the results of the toxicity studies. The population model is stochastic in the sense that it calculates probabilities of certain outcomes, in this case certain levels of impact to wood

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frog populations, based on the inputs provided. It is deterministic, how ever, in that if presented with the same inputs the model always returns the same results. The population modeling study is described in detail in Attachment E.3, in which it is clear tha t the model is based on a number of assump tions, including the assumption that the effects observed in the toxicity studies are in fact occurring.

RS4. p. ES-21: Please explain the toxicological basis for the state ments shown below – what is the toxicological rela tionship between Ah-receptor-regulated enzyme induction and the observation of jaw lesions ? If there is no to xicological or mechanistic association of the two, please so state.

Further, the jaw lesion study indicated that erosion of the j aw occurs at even lower doses and exhibits a dose-response relationship. Such effects could eventually lead to starvation. The occurrence of jaw lesions coincides with the induction of Ah-receptor-regulated enzymes (ECOD and EROD) also in a dose-response manner.

Response: The observed jaw lesions and enzyme induction were two separate components of the mink toxicity study in which effects followed a clear dose-response pattern. No toxicological or mechanistic association between t hese two effects is implied, other than they are both an effect of exposure to PC Bs. Recent studies have established the relationship between jaw lesions and PCB/TEQ exposure. Several studies have shown that the jaw lesion id entified as hyperproliferation of squamous epithelium is indu ced by 3,3',4,4',5-pentachlorobiphenyl (PCB 126) in ranch-raised mink, and that the lesions caused by PCB 126 may be neoplastic (Beckett et al. 2003a). A recent study also demonstrated that wild mink in the Kala mazoo River basin, which have TE Q concentrations in their livers similar to those that caused jaw lesions in ranch-raised mink, also have jaw lesions (Beckett et al. 2003b). The severity of the lesion in wild mink was related to the hepatic TEQ concentrations (Beckett et al. 2003b). The technical appendix (Appendix I) dealing with the mink toxicity study discusses these effects in separate sections

RS5. p. ES-22: Please explain the scientific basis for the discrepancy between results of studies conducted by EPA and GE as shown in Tables ES-8 and ES-9.

Response: Appendix I, Sections I.4.2.2 and I.4.4 describe the EPA and GE piscivorous mammal field studies, their findings, and limitations. A discussion is presented regarding the weight given to each measurement endpoint and an explanation for the values in Tables ES-8 and ES-9.

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RS6. p. ES-25: Please explain the scientific basis for combining the two risk estimates as discu ssed below. If this is common practice, was it done for other receptors and other estimates?

The risk for a dult bald eagles exposed to TEQ was low; however, risk to bald eagle eggs ex posed to TEQ was high. These two risk estimates were combined to yield intermediate risk to bald eagles.

Response: As discussed in Section 2.9 and elsewhere in the ERA, the risk characterization is based on the Massachusetts Weight of Evidence Workg roup approach (Menzie et al, 1996). In this WOE approach, concordance among risk esti mates for eachmeasurement endpoint is evaluated and combined into a single estimate of risk for the endpoint, as was done for bald eagles in the ex ample above. As discussed in ERA Section K.4, the lack of concordance between risks to adults and to eggs resulted in an overall assessment of intermediate risk for this endpoint. This combination of risk estimates was done for numerous other endpoints throughout the ERA.

RS-7. p. ES-31: Please explain the scientific basis for how estimating HQs is equivalent to an observation of significant risk, or that risk is occurring.

As explained in the text, benchmarks (MATCs – maximum accep table toxicant concentrations) were derived for some assessment endpoints to represent th e contaminant concentration beyond which ecologically significant effects would reasonably be expected. No “safety factors” were incorporated into these MATCs. Admittedly, as with all approaches to determining risk, this approach involves a degree of unce rtainty, but the HQ approach itself is commonly used and well documented. By this definition, and considering the lack of any safety factor in the MATCs used, concentrations in ex cess of the benchmark, i.e., HQs exceeding 1.0, indicate that risk is expected.

RS8. p. ES-39: Please explain the scientific basis for the use of a factor of “4” to adjust the MATC for trout. Why not 2 or 10 or 7 ?

Furthermore, there are other trout species found downstream of the PS A (e.g.,brown trout) for which sensitivity has not been assessed. Given that some trout spe cies have been documented to have greater sensitivity of PCBs and dioxins, relative to t he warmwater species considere d in the development of the 49 mg/kg tPCB warmwater MATC, a factor of 4 was applied in recognition of these potential interspecies differences. Therefore, a tissue MATC of 12 mg/kg tPCBs (whole body, wet weight) was derived for trout.

Response: The scaling factor of 4 used to extrapolate the MATC developed for warmwater fish to trout species is based on both site-specific studies and the scientific literature. The approach is described in ERA Section F.4.6.2, and in the response to Question JO32, below.

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INTRODUCTION & PROBLEM FORMULATION

TT16. Page 1-11, Lines 4 – 6. A table of all of the COPCs would be helpful here. Wh ich volatiles, PAHs, semivolatiles and metals.

Response: Tables of media-specific COPCs are provided in Section 2.4 and Appendix B (Pre-ERA), Tables B-145 through B-148.

TT17. Is the intent of the ERA to focus solely on PCBs with perhaps c onsideration of dioxin/furans, or are all COPCs considered? What are the COP Cs does not appear to be treated in a consist ent and clear manner. If the Consent Decree for the Housatonic River is for PCBs, than this should be the sole focus of the ERA, and made clear within the introduction. This appears to be the case for the RFI, in which GE makes the following statement:

Response : The definition of the Rest of River in the Consent Decree is that:

“Rest of the River” or “Rest of River” shall mean the Housatonic River and its sediments and floodplain areas downstream of the confluence of the East and West Branches of the Housatonic River, including backwater s, except forActual/Potential Lawns, to the extent that such areas are areas to which Waste Materials that originated at the GE Plant Area have migrated a nd which are being investigated and/or remediated pursuant to this Consent Decre e.

Many contaminants were detected, some at elevated levels, at the G E Plant Area. Although PCBs and dioxins/furans were known to be the contaminan ts of primary concern within the study area because they were found in the non-a queous phase liquid (NAPL) adjacent to the river, the Pre-ERA (Appendix B) evaluation was conducted to identify other COPCs that should be included in the ERA as appropriate for each assessment endpoint. Several contaminants, in addition to PCBs and dioxins/furans, remained as COPCs in sediment and surface water after completion of the Pre-ERA and those additional COPCs were further evaluated for inclusion as COCs in the appropriate assessment endpoint discussions. However, none of these other COCs were found to be risk drivers for these endpoints.

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ERA Responses to QERA Responses to Quuestionsestions

TT18. Was a Biological and Technical Assistance Group (BTAG) assist in the Problem Formulation stage? If so, what agencies were involved, and how was the pro ccess condu ted?

Response: EPA, NOAA, USFWS, CTDEP, MFWS and MADEP were active participants in the RCRA negotiations with GE for the ERA to be performed by GE under the Corrective Action Permit process. Many of these people were BTAG team members as well, however the EPA Regional policy at the time was that the BTAG did not formally participate at RCRA sites. The selection of assessment endpoints for the ERA was based primarily on the discussion between all parties on the scope of the ERA.

TT19. Is there a discussion of the potential for “conventional” parameters to pose risks – particularly to benthic infauna in either the Screening Level ERA or the Baseline ERA? Ammonia in sediments has been important in other river systems (e.g., Ohio, Fox, Missouri, Mississippi), as are sources of phosphorus leading to eutrophication. Have any data ever been collected to address this potential issue in sediments? Conventional water quality parameters were collected, as noted in the RFI (see below), but I could not find a similar treatment for sediments. There is some acknowledgement of ammonia in the TIE, but I could not find this anywhere else. Would EPA please comment on this?

Response: The majority of the sediment samples that were collected were analyzed for tPCBs, TOC and grain size. Approximately 10% of all the sediment samples collected were analyzed for PCB congeners and homologues, Appendix IX SVOCs, organochlorine pesticides, dioxins/furans and inorganics. The analysis of “conventional” parameters in sediment (such as ammonia, DO, pH). was limited primarily to samples collected for the sediment toxicity testing that was conducted by Dr. Allen Burton and his staff at Wright State University. Surface water was analyzed for many of these parameters and results of these

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analyses indicate that levels of conventional parameters are within acceptable norms and are not expected to contribute to observed or predicted risk.

TT20. The conclusion of Section 2.4 lists the COPC, which inc ludes PCBs, dibenzofurans, 16 PAHs, 4 – 11 metals, depending upon the reach/geom orphological type. Section 2.5 discusses Fate and Transport of Contaminant Stresso rs, and states immediately that the focus is PCBs and dioxi n/furans. Would EPA please provide a succinct rationale for this focusing, please? There is no issue with that decision, onl y in the tra nsition to that expression in Section 2.5.

Response: Although a number of contaminants in sediments remained as COPCs after the Pre-ERA (Appendix B), the potential risk associated with these contaminants based on comparison to benchmarks was very low relative to the potential risk associated with PCBs and dioxins/furans. This determination was subsequently supported by the additional screening evaluation s that were conducted (for specific assessment endpoints) to develop the final lis t of COCs.

TT 21. To be sure all good things are noted -- the discussion in the RFI related to PCB distribution is very good, concise, and helpful. Much of that was adapted for the ERA, but I found the treatment in the RFI to be very good.

Response : EPA agrees that the RFI provides a good discu ssion of the data from the various sampling programs which were conducted for the Rest of River.

TT 22: Why was a detection limit of 500 ppb tPCBs selected f or this site? Par ticularly when ecological risk values for sediments are as low as 60 p pb?

Response: The detection limit of 500 ppb (0.5 ppm [mg/kg]) wa s for the field screening laboratory only. Use of the field screening laboratory in the project allowed for the collection and analysis of large numbers of sedi ment samples, the majority of which were above 0.5 mg/kg tPCB in the PSA, to better document the extent of contamination. For quality control purposes, five percent o f the samples analyzed by the field laboratory were also analyzed in a standard fix ed laboratory with a detection limit of 0.02 mg/kg; if the field laboratory reported a non-detect and the fixed laboratory returned a detected result or a non-detect at the lower detection limit the fixed laboratory result was retained in the project database.

TT23. Why was a 15 cm surface sediment interval selected? Is this backed up by biological studies and/or Sediment Profile Imaging to show biological activity to this depth for benthic infauna?

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Response: The majority of the sediment samples had to serve many purposes for the Supplemental Investigation, including use not only in the ERA b ut also in the HHRA and Modeling Study. It was determined that the interval th at would best serve these interests was 6 inches, or 15 cm. Although no sed iment profile imaging was done, evaluation of deep core samples taken along the river showed that the sediments are reworked, often at depth.

TT24: Would you please refer me again to where the spatial averagi ng methods used for Figures 2.5-5 through 2.5-11 are documented? BTW, these are very good and informat iv e figures. Why weren’t similar constructs done for in-water sed iments?

Response: The approach followed for the spatial weighti ng of tPCB concentration in floodplain soils is detailed in Appendix C.3 (ERA Volume 4). Spatial weighting was not conducted for river sediments beca use the data collected for the project indicate that concentrations in these sediments vary greatly on very small spatial and temporal scales, and it was felt that presenting figures similar to those constructed for the floodplain would imply a stability and permanence in sediment PCB concentrations that is not supported by the data.

TT 25: Page 2-42, lines 6 – 8. A reference to how the congener data col lected do not sup port degradation as a major removal process is needed here. Is tha t the Bedard and May 1996 reference?

Response: The conclusion that degradation is not a major rem oval process was based on the data collected in the current EPA study, in combination with a review of the literature, including the Bedard and May 1996 paper as well as other work conducted by Bedard on Housatonic River sediments. That conclusion is documented in Appendix C.7 to the ERA, and EPA agrees that a reference to that Appendix at this point in the document would have been helpfu l. EPA will consider this revision along with all comments received following the Peer Review meeting.

TT27. As a corollary to the question above, would EPA please discuss why a pelagic invertebrate pathway was not included as part of the ERA?

Response: During the assessment endpoint development process that included representatives from the regulatory agencies, trustees, and GE, it was determined that the pelagic invertebrate pathway was of lesser concern that than the benthic community pathway because PCB concentrations in waterborne particulate and surface water were much lower than those found in sediment and pore water.

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TT28. The ERA discusses “risk hypothesis” on page 2-57, line 5, a nd “testable hypotheses” on page 2-59, line 31. The use of hypotheses requires fo rmulation of specific statements which can be tested with specific data and defin ed statistical limits. The Assessment and Measurement Endpoints in Tables 2.8.1 a nd 2.8.2 are very qualitative statements. Would EPA discuss the term “hypotheses” as used in the ERA, and indicate what was intended? If specific, testable hyp otheses exist, wou ld EPA please point those out?

Response: In each assessment endpoint section and correspondin g appendix, a conceptual model is presented. As stated on page 2-54, "the conc eptual model presents a series of working hypotheses regarding how the stresso r might affect ecological components at the site". While testable hypotheses are not explicitly stated in the text of the ERA, EPA believes that the conceptual mod els presented throughout the ERA achieve the same objective. On page 2-57, it is further stated that "the primary question to be asked by the risk hypothes is is 'what probabilities are associated with effects of differing magnitudes as a result of exposure of the assessment endpoint to the COPC'?" This question is the one that is addressed in each of the assessment endpoint sections and corresponding appendic es.

TT29. As a general comment, other than the issue relating to pelagic vs. benthic invertebrates and hypothesis testing, the receptors, assessment endpoints, and measurement endpoints appear to be appropriate to the Housatonic River.

Response : Comment noted.

TT30. Why was the Menzie et al (1996) “Weight of Evidence Appro ach” selected for use in this ERA? While using WOE is a commonly accepted practice for eco logical risk assessments, the process developed for the Massachusetts Dep artment of Environmental Protection is not commonly applied. Co uld EPA also exp lain how the weightings were assigned for each of the receptors an d endpoints? The se are very subjective, so how/who defined and quantified that is ve ry important to o ur understanding of the process.

Response: The Menzie et al. (1996) approach was developed by the Massachusetts Weigh-of-Evidence Workgroup and is frequently u sed at RCRA and CERCLA sites in Massachusetts and in other New England states. This approach was recently used in the ERA conducted at the Portsmouth Naval Shipyard and published in Environmental Toxicology and Chemistry (Johnston et al, 2002). This approach is flexible, and allows for the development of quantitative or qualitative weight-of-evidence assessment.

Detailed justification for the overall weights assigned to each line of evidence associated with a specific assessment endpoint is provided in the Weight-of-

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Evidence Analysis portio n of the Risk Characterization section in each of the assessment endpoint appendices.

VF13. There seems to be some debate as to the quality of some of the fie ld studies (in particular a couple of the vertebrate (e.g., bird, shrew) studies performed b y GE). There appear to be concerns that some of the studies did not have suffic ient statistical power for detecting effects. Were any formal power analyses performed on any of the field stud ies and if so is it possible to get access to the results?

Response: No power analyses were included in the reports provide d to EPA for the wood frog, short-tailed shrew, or belted kingfisher studies cond ucted by GE. However, a power analysis was provided for the GE American robin stu dy (see Tables 4 through 8 in the Robin Productivity study), and is mentioned in the ET&C publication of the short-tailed shrew study. EPA performed power analyses in the design of the studies; these analyses can be found in the appendices to the SIWP (Weston 2000). For the field surveys (conducted by EPA and GE), a p ower analysis was not appropriate.

VF 16. Table 2.9-1 (Problem Formulation) – please explain how the totals were calc ulated?

Response: Table 2.9-2 provides a description of the attributes us ed to evaluate each measurement endpoint considered a s part of the ERA. A thorough discussion of the thought process that went into the actual qualitative weights assigned to each attribute for each measurement endpoint is provided in the specif ic assessment endpoint section and associated appendix. An overview of the general criteria used to weight each attribute can be found in the Menzie et al.(1996) paper tha t was provided to each Peer Review Panel member (see Table 2).

An overall measurement endpoint value of low to high was assigned based upon a review of all indiv idual attribute weights. All attributes were considered of equal importance, and the total endpoint values were determined using best professional judgment based upon the values assigned for each of the attributes. Th e rationales for these weightings were included in each Appendix in the ERA.

BENTHIC INVERTEBRATES

TL8. The “conservative benchmark” used for this ERA and the HQs is a threshold effect concentration (TEC) of 0.0598 mg PCB/kg sediment (MacDonald et al. 2000). The document needs to explain why this TEC has been selected. Are the data sets not sufficient in this ERA (combined with data collected on earlier GE-sponsored studies) to calculate a

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“Housatonic specific” TEC (this also applies below for SQ Gs)? In my opinion, there needs to be further explanation of why this TEC is thought to be protective.

Response: The conservative benchmark was used in the initial phase of the analysis to confirm the extent of contamination of concern specifically for this assessment endpoint, and was not relied upon in a quantitative manner s ubsequently.

The site-specific analyses were sufficient to develop “Housatonic spec ific” threshold concentrations, and only these site-specific values were applied in the de velopment of MATCs. The scre ening criteria for aquatic media (e.g., the MacDonald TEC) were also reported for informational purposes, but these were not ap plied in the establishment of MATCs.

For example, the benthic invertebrate tPCB sediment threshold of 3 mg/kg was developed from analysis of site-s pecific toxicity and benthic community structure data. This value was compared against the range of sediment quality criteria from the literature (to provide context), and it was found that the site-specific threshold fell toward the upper end of the range of criteria.

The summary hazard quotients depicted for aquatic receptors in Section 12 were based only on site-specific MATCs, and only the site-specific values w ere applied in extrapolations to downstream areas.

TL 9. As stated above, it would make spatial comparisons of the PCB concen trations in the sediments easier, if River mile locations were included with Segment Numbers (or develop a tabl e relating Rivermile to Station number and then use river mile) for the benth ic community and the toxicity testing samples (examples include Figs 3.2-3, -4, and –5).

Response: Table D.2-1 provides the relationship of river mile to s tation number for the benthic Triad s tations. Note, however, that PCB concentrations measured in the benthic community and toxicity testing samples were not based on random sampling of the PSA. Instead locations were chosen a priori to span the range of PCB concentrations found in the PSA to facilitate dose-response evaluat ions. Caution should be used in inferring PSA spatial trends from these locations. A depiction of spatial pa tterns in sediment concentrations can be found in Figure 3.2-3 in the ERA and in Figure 4-19 in the RFI.

TL10. As stated on Page 3-18, lines 8ff, there is considerable variance in PCB distribution in the surficial sediments. Are there data describing the variances (including skew and in addition to data presented in Figures 3.2-3 and 3.2-4) in sediment PCB concentrations within each station?

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Response: ERA Figures 3.2-3 and 3.2-4 present the PCB concentra tion data from the benthic commu nity grab samples and the sediment samples located adjacent to the benthic toxicity stations.

Additional summary statistics were calculated in response to this qu estion for the benthic community grab samples (mean, median, variance, skew, kur tosis, etc.) and the results are presented in Attachment TL3 to these resp onses. The raw data are also included in the attachment in the spreadsheet labeled “data”. Concentrations that were non-detect were assigned the detection limit value for the calculations.

Raw data that were used for the development of Figure 3.2-4 are also provided in Attachment TL3.

TL 11. Have the Risk Assessors used a canonical correspondence analysis to determine the association of critical benthic fauna with specific station physical/chemical data?

Response: Statistical approaches other than canonical correspond ence analysis (CCA) were used to relate benthic responses to chemistry/physical v ariables. CCA identifies linear combinations of the variables from two sets of data that have the strongest correlations. The statistical approaches used in the ERA were simpler techniques (e.g. graphical tools, ANOVAs and regressions) and pro vided similar information as would have been obtained by canonical correspond ence analysis. Habitat parameters were examined and substrate was identified as the parameter that may have confounding effects on the benthic community analysis ( see ERA Section D.3.7.8); therefore, data were separated to either the fine o r coarse-grained grouping to minimize the effect of substrate in further analyses. Carrying out multi-dimensional scaling (MDS) based on six benthic metrics provided simple graphic al displays to show station similarities. The ANOVAs conducted to identify differe nces between reference and contaminated stations (in terms of total abundance or taxa richness) provided statistical support to observations made from the MDS plots.

TL 12. The discussion on benthic taxa does not have great depth or clarity in key details of the data used. Phrased as a question: Why are the benthic organism abundances, distributions, and associations not analyzed more fully?

Response: There were two main approaches to the evaluatio n of benthic community assemblages. One approach evaluated the overall compo sition of the community in terms of taxonomic “indicators” such as abundance, richness, and various other metrics. The other approach was more specific and investigated distributions of specific “keystone” taxa.

The ERA emphasized the broad level analysis (first approach). Although indicator organisms (such as EPT abundances) were assessed, the approach taken was to conduct a combined evaluation of the various metrics using multivariate methods.

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Accordingly, the predominant statistics tools in the benthic ER A are multivariate approaches such as rank analysis, multidimensional scaling, and cluster analysis.

To further address the Panelist’s concerns, an additional multiple lin ear regression analysis was performed of the abundance of keystone benthic taxa v s. physical (% fines) and chemical (tPCB level) data from each sampling site was c onducted (see Attachment TL12 - T ext.doc and “Attachment TL12 - Figures and Data) to examine the relationship between benthic abundance, percentage of fines and total PCB concentrations in sediments.

Despite the apparent lack of differences in benthic invertebrate commun ity structure at reference and contaminated fine-grained substrate sites (see ERA ), subsequent analyses show differences among invertebrate taxa in their sensitivity to PCBs. When invertebrate abundance data were subjected to a multiple linear regre ssion analysis that considered both substrate type (% fines) and total PCB concen tration, it was apparent that while the abundance of many taxa was largely determined by the amount of fines in the substrate, some taxa, particularly chironomids, are s ensitive to the presence of PCBs, and they are present in reduced numbers or absen t at sites with elevated PCB concentrations. In contrast, taxa such as worms, sphaer iid clams, and most snails appear to be relatively insensitive to PCBs. The results of the field studies vis a vis the relative sensitivities of taxa to PCBs are confirmed by the results of the laboratory studies conducted for the Housatonic River study, in whic h chironomids were found to be sensitive to PCBs, but oligochaete worms were fou nd to be less sensitive.

TL13. For the Housatonic River itself (fish) and for organisms relying on the benthos, benthic organisms are at the base of the avian, fish and mammalian food webs. It would appear to me that the benthos should have a more intensive analysis than has be en presented in this textual material. A more complete consideration of benthic results (for example, dominant species, EPT index values, even a more simplistic analysis of the var iation between “course-grained ” and “fine-grained” species associations would substantially enhance the determination of risk.

Alth ough there is a statement on Page D-31 o f the Appendix on Benthic Endpoints about the “low power,” there should be a quantitative statement of what the power is. To re-phrase as a que stion, “What is the statistical power of the functional group analysis – a nd the other ben thic analyses?”

Response: “Functional group analysis” is understood in this context to mean the analysis of invertebrate community responses using metrics that relate to the functional groups of the organisms in question.

Benthic community data were primarily analyzed using approaches other than hypothesis testing and power analysis. The MDS analyses are visual tools that did not involve hypothesis testing and therefore power analyses were not necessary or

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possible. For the ANOVAs conducted to test for differences between the reference and contaminated sites for fine or coarse-grained sediments for total a bundance and taxa richness, no retrospective power analyses were conducted. However, since significant differences were identified based on comparisons between the references and contaminated sites (e.g. significant results for the coarse gra ined sediment stations), this indicated th at the study design had sufficient power for some situations. In cases where no statistical significant result was identified, this may have been due to insufficient statistical power.

To investigate the situations where no statistical differences in summary metrics were observ ed, additional investigations were conducted at a more detailed taxonomic level. These studies are referenced in responses TL11 and TL12 and summarized in Attachment TL12 - Text.doc and Attachment TL12 - Figures and Data to these responses).

TL14. Sediment Toxicity: From Page 18, Burton’s report in the “Supporting Information” disc, states: “sediment samples were collected using a standard core tube. The core tube was used to take five separate 4- to 5-cm-deep sediment samples from each of the lo cations where in situ toxicity testing took place. A composite of five separate sediment por tions was then homogenized in a sterilized stainless steel bowl and placed in 8-oz amber jar s. Portions of each sediment sample were either used for chemical analysis of total PCBs or shipped to Wright State University (WSU) on ice for laboratory testing.” Is it understoo d by the Risk Assessors that this dilutes the COCs? Given the heterogeneity of PCB cont amination of sediments, and the micro-ha bitat variances in distribution, taking an “average” by lumping five sediment cores has the high probability of diluting the COCs. Further, is it und erstood by the Risk Assessors that the variances reported under this scenario des cribe “how well the sediments were mixed in the steel bowl and have nothing to do wit h variances associated with COC distribution (and the resultant potential for exp osure) in the original sediments?

Response: Taking an “averag e” by homogenizing five sediment cores does not dilute the COCs, but it does reduce the potential for measuring an extreme (either high or low) concentration value and then incorrectly assuming that conce ntration to be representative of the exposure concentration for the in situ testing. Because of the known small-scal e spatial and temporal variability in sediment concentrations in the PSA, the sampling technique used provides a more representative exposure concentration for the in situ testing location.

It is unclear what the Panelist means by the “variances reported under this scenario”; the document does not report such variances, which are not known because only the single composite concentration was measured and not the individual concentrations in the five sediment cores.

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TL15. As stated above, this reviewer is concerned with the confounding effe cts of the pulp mills on benthic community dynamics. In consideration of the multiple (alb eit low-level) COCs in the more downstream stations, were any empirical sediment qu ality criteria derived? Given the importance of simultaneous exposure to multiple contam inants at many stations, is there an overall evaluation of reference or do wnstream stations that summarizes all contaminants used to calculate an empirical SQG? Has there been an asse nssment of a y “median effects range” (ERM) for the Housatonic River?

Response: Sediment quality criteria for PCBs were derived b y empirically relating the exposure concentrations to effects observed in the toxicity t ests performed within the PSA and at the reference sites. Empirical criteria for o ther COCs were not derived, since these COCs were: (a) not significantly correlated with toxicological responses, and/or (b) not identified as a causal agent in the TIE, and/or (c) posed low toxicological hazard based on screening to conservative sediment quality values.

TL 16. What are some of the changes in benthic species (or dominant grou p) abundances dow nstream? What are the means, skew, variances of individual “keystone” tax a?

Response: “Keystone taxa” are assumed to be those taxa that have a central role in maintaining the ecological functions in an ecosystem. Mean abunda nces, standard errors, and skewness of all invertebrate taxa vs. sampling stations h ave now been ca lculated and are included in Attachment TL16 to these responses.

A summary of the supplemental analysis of individual taxa, and relationships to substrate and PCBs, in presented in Attachment TL12 - Text.doc and Attachm ent TL12 - Figures and Data”. Raw benthic community data are provided i n Attachments TT1.

TL 17. On Page 3-14, line 19, the text states that the median concentrations w ere chosen as the measure of central tendency for data collected at the same time, same place. Presumably, this avoids bias in temporal variability. Does it? How do we know?

Response: It is not the choice of the median over some other mea sure of central tendency that avoids temporal bias, but rather the collapsing of multiple measurements made at a single place and time into a single data point. Using, for example, the mean as the central tendency measure would have similarly avoided temporal bias, but the median is the more appropriate measure based on the known skewed distribution typically encountered with environmental data. The method ensures that the central tendencies are not dominated by a large number of data points collected at the same time. This provides a more equal balance among various studies relevant to the toxicity tests.

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TL18. Given the key importance of the benthos for this ERA, it is critical (in my opinion) to fully describe the temporal and spatial variances in benthic species distributions and relate them to the mi cro -spatial variance in PCB concentrations.

Response: There are many variations in microhabitat characteristics that chang e both in space and time, and over both small and large scales, in t he PSA. For example, the influence of large woody debris, seasonal instream vegetat ion, and storm events all serve to alter the PCB distribution, and possible the biota dis tribution, in an uncontrollable framework. EPA agrees that is would be useful to kno w more about the temporal and spatial patterns of benthic macroinvertebrate abundanc e in the river, and to be able to relate these patterns to the small-scale spatial pa tterns of PCB concentration, and that this would allow more accurate characterization of the extent of the risk posed by PCBs to sediment-dwelling invertebrates. Howe ver due to the difficulties that would exist in developing a robust and implementabl e study design and time and budget constraints, such an ambitious study objec tive was not established, but rather a more limited, yet achievable objective was s elected. EPA believes that the available data are sufficient to concl ude that the abundances of certain taxa are negatively affected by elevated sediment PCB concentrations. A summary of the supplemental analysis of individual taxa, and relationships to substrate and PCBs, is presented in Attachments TL12 - Text.doc and TL12 - Figures and Data. These additional analyses may help to address the Panelist’s comment.

TL19. Were the results in Table 3.3-1 compared using logistic regression of endpoints? In a table of “pairwise statistical tests,” the chances are that among the 1 4 X 15 ( = 210) pairwise comparisons that the conclusions of 10 comparisons (Type I error, at alpha = 0.05) will be wrong . It is very critical (in my opinion) to include a statement of the “power of the test ” here: What percentage difference among mean responses is required f or the tests to be a ble to determine differences among means? Another way to calculate the se data would be t o look at “time to effect” and compare acute and/or chronic survival among the stations.

Response: Probit analysis (a technique similar to logistic regression ) was used to analyze the benthic toxicity data. Probit regression was used when appro priate (i.e. the Chi-square goodness-of-fit-test did not reject the probit model at an α of 0.05) to estimate EC20s and EC50s. Otherwise, the Trimmed Spearman-Karbe r method was used to estimate ED50s. Summary tables of the EC20 and EC50 estimate s are provided in ERA Tables D.3-5 to D.3-6 for the different organisms.

For parametric analyses, the minimum significant difference (MSD ) percentages relative to the control are provided in Attachment TL19 to these responses. For survival, the percentage differences ranged from 13.5 – 34.1% except for 48-h Daphnia, which was 69.8%. The MSD percentage relative to the control for reproduction and weight endpoints ranged from 9.8 – 79.5%. No minimum significant differences were calculated for comparisons based on nonparametric methods.

Results based on the comparison of the responses from the negative control/references to contaminated sites are used to generate the LOAEL and NOAEL by ordering the

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station based on the measured total PCB concentration at each con taminated site. However, the NOAELs do not provide a good basis for regulatory acti on for reasons outlined in Chapman et al. (1996) and Chapman et al. (1997). Instead p oint estimates of specified effect sizes (e.g. EC20 and EC50) are recommended be cause of their improved consistency, higher reliability and lower variability. In the ERA, the point estimates are used rather than NOAELs or LOAELs in the development of thresholds for the Risk Characterization.

TL20. In my opinion, Figure 3.3-15 is so broad as to be meaningless. It w ould be muchpreferable to treat the six metrics individually. To phrase it in a question, were the benthic data treated on the basis of proportionality among substrates? Were depositional communities wi thin stations compared among stations (versus “lumping” over all types of s ubstrates)?

Response: The proportionality of samples among substrates was rec ognized as an issue, insofar as the highest PCB concentrations were recorded in sand y (i.e. coarse-grained) vs. silty (i.e., fine-grained) su bstrates. A multiple linear regression approach was used to address the compounding effect of substrate on benthic invertebrate abundance. Because substrate characteristics varied within sites as w ell as among sites, the effect of percent fines on invertebrate abundance was examined for individual sampling sites, as opposed to stations.

Overall, the sampling design for the benthic community grabs was not d irected towardthe evaluation of intra-station substrate variations. This approach was selected in an effort to reduce the amount of inter-habitat variability among the sa mples, which would have introduced additional variance into the data set. At each sampling location, the 12 b enthic grabs were placed within an area that was visually homogeneous in substrate composition. Therefore the particle size distributions and TOC concentrations were relatively constant across the 12 replicate s within each station. The grain size distribution data in Attachment TT38 to th ese responses illustrate this, and also indicate the similarity of exposed stations to ref erence stations in terms o f substrate type.

TL 21. The shaded ovals in Figure 3.3-16 “lead the witness.” If they have no meaning, they sho uld not be shaded. What do the MDS axes imply for the benthic commu nities? What are the communalities? Which chemical/physical characteristics influen ced most the spe cies distributions?

Response: The MDS axes were driven most by the abundance and richness differences observed across samples. In terms of evaluating chemical versus physical influences on benthic assemblages, please consult the supplemental analyses included with these responses as Attachment TL12 - Text.doc and “Attachment TL12 - Figures and Data. In summary, some taxonomic groups were affected most significantly by physical substrate (i.e., particle sizes, TOC) whereas other taxa were affected most by

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PCB concentrations. Several species were affected by an interaction between these factors. These findings are consistent with the conclusions presente d in the ERA, which suggest that sensitive species are affected by PCB concentration even after the influences of habitat and substrate are considere d.

The following two questions are answered by one response:

TT26. Would EPA comment on the ERA’s definition of a benthic in vertebrate as “organisms that reside in, or are in direct contact with, Housatonic Riv er sediment? Within the problem formulation the conceptual site model for ecological ris k assessment shows cladocerans and ostracods as “pelagic”, and mussels and ins ect larvae as “benthic”. In reviewing the Ecological Characterization report many o f the species listed are not what would be considered sediment-dwellers. While there is l ittle argument over chironomids, oligochaetes, and m ussels, the dragonfly and damselfly species listed in Table 2-5 and 2-6, along with the species listed in Table 2-7 of th e Ecological Characterization report are more likely to be associated with submerged and emergent aquatic vegetation.

For example, Potamogeton is reported within the pools systems. From my own work in high prairie ponds and lakes in Wyoming, the EPT and Odanata speci es are found associated with the pondweed, while only oligochaetes and chironomids in the mud. Those were lacustrine systems and the carbon biomass that support fish and bird populations comes not from sediment dwelling infauna, but from the insects epiphytic on the aquatic macrophyte community. Carbon flow in these systems come s from what might be more appropriately considered as epiphytic organisms, whose exp osure to PCBs is not from sediments, but from water and from sequestered PCBs in forage or prey. The fact that these were collected using funnel traps, and not sediment grab sam ples, suggest that these collected organisms were indeed not in the sediment. As the Benthic Invertebrate section (Appendix D) did not supply specific species lists, it is hard to determine what is/is not “in” the mud. This is an important concept to defi ne and defend upfront, and one that may be appropriate for the peer reviewers to take up and discuss. The inference in the ERA is that all insects are benthic invertebrates, a nd that direct counts of infauna in sediments (for which we were not provided data) or in-lab exposure to sediments is the appropriate assessment and measurement endpoint.

TT 32. As noted previously, the issue of what is the definition of “benthic in vertebrates” is imp ortant to this as a measurement and assessment endpoint. Since direc t exposure to sed iment is the measurement endpoint, narrowing the scope to include those organisms in con tact with sediment is important.

Response: In the context of the ERA, benthic invertebrates refer to invertebrates that are exposed via sediment and pore water uptake pathways. These organisms include “infauna” and “epifauna” but exclude “water column invertebrates”. The organisms collected in the benthic grab samples and D-net samples were either infauna or epifauna (primarily the former), because most of these samples were collected in very

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shallow water (several inches) it was possible to confirm that most o rganisms were dwelling below the sediment surface, at least at the time of collectio n. In several instances, large odonates were completely within the sediment and only exposed during sieving. Only the most downstream benthic sampling lo cation, at the headwaters of Woods Pond and the Threemile Pond reference site included any living plants, therefore it was not possible for invertebrates collected at the other 11 locations to be truly epiphytic.

The concentrations of PCBs in water column invertebrates are predicted to be lower than benthic invertebrates. The risk assessment for benthic fauna should therefore be protective of all invertebrates.

TT31. The Ecological Characterization appendices for the River are very nice work. Wit hin Appendix A.1, Section 3.1.3 on vernal pools, the last sentence reads “These data, som e of which are also presented in the text, refer to overall…”, an d then ends. Enquiring minds want to know what it refers to.

Response: …observations made while performing surveys for amph ibians. Good eyes!

TT 33. The “COCs that screened through to the risk assessment for benthi c invertebrates wer e tPCBs, several metals, several polycyclic aromatic hydrocarbons (PAHs) and dibe nzofuran”, but Section 3 and Appendix deals almost exclusively with tP CBs. Would EPA explain why the other COCs are not treated in the same way in these sectio ns.

Response: Other COCs were screened and ass essed in Appendix D at a level of detail proportional to their chemical hazard. PCBs received more attention because the indications of chemical screening, correlations with toxicity endpoin ts, Phase I TIE results, etc., implicated PCBs as the dominant chemical stressor s. The concentrations of other COCs were also assessed in various environmental media and conclusions were drawn regarding their potential to exert adverse responses.

TT 34. Would EPA explain the thought process that determined that 13 benth ic grabs and 7 bioa ssay stations would be representative of the 10 miles of River under conside ration?

Respo nse: The study designs of the benthic community study and the toxicity testing are provided in Appendices A.13 (pages A.13-4 and A.13-5) and A.14 (pages A.14-1 and A.14-2), respectively, to the Supplemental Investigation Work Plan (Weston 2000). As described in these work plans these studies were not designed to be representative of 10 miles of river, but rather to span the range of PCB concentrations within soft-bottom substrate in the PSA. In addition, the number of toxicity testing stations was limited by the capacity of the Wright State University laboratory.

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TT35. Would EPA explain more clearly using either “a combined data set” and/or the “sin gle most synoptic chemistry value” for evaluating concentration-response re lationships?

Response: As discussed in the response to TL3 above, substantial sm all-scale variability in PCB concentrations in sediments was observed at the bent hic sampling locations. For the benthic community grabs, the sampling design incorporated sufficient replication (i.e., 12 grabs over an area about the size of a t able) that the variation could be adequately described. However, the measurements ma de during the toxicity testing program did not have replication, and therefore these single measurements are uncertain estimates of the actual exposure concentrations for the test organisms. In the face of this uncer

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