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Assessment and Remediation of Contaminated Sediments (ARCS) Program

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Assessment Guidance Document
Chapter 10

US Environmental Protection Agency. 1994. ARCS Assessment Guidance Document. EPA 905-B94-002. Chicago, Ill.: Great Lakes National Program Office.

10. Conclusions 

This document represents the culmination of several years of work, which was designed to investigate scientifically sound methods of assessing sediment contamination in Great Lakes AOCs. This work is the result of the combined efforts of the ARCS Toxicity/Chemistry Work Group, whose members represent a broad spectrum of expertise (Table 10-1). The assessment methods described in this document are intended to assist Great Lakes RAP personnel and others in answering the following questions:

The Toxicity/Chemistry Work Group surveyed the field of existing sediment assessment methods and identified those methods that showed the most promise for addressing these questions, and then demonstrated their use in studies of several Great Lakes AOCs. The selected methods integrate physical, chemical, and biological information to achieve an overall assessment of sediment contamination that is based on a preponderance of evidence from independent measurements (or observations).

The guidance provided in this document is intended to address not only the physical, chemical, and biological assessment methods themselves, but also related topics such as QA/QC considerations, the design of sediment sampling surveys, and data interpretation methods. The described assessment methods are not those required under specific regulatory programs, but are instead more generally applicable in investigations of the nature and extent of sediment contamination. Although intended for application in the Great Lakes AOCs, they may be applicable in other environments as well. Some of the methods described (e.g., the sediment toxicity tests) are applicable only in freshwater environments, while others are more generally applicable.

It is absolutely essential that any data to be collected in a sediment assessment program be of high quality when those data are likely to be used in decisions about the potential need for sediment remediation. Chapter 2 provides guidance on the essential elements of a QA/QC program. DQOs should be defined early in the planning for a sediment assessment program to ensure that all parties understand the goals of the program, to eliminate unnecessary waste of time and money, and to establish the level of data quality necessary to meet the program's goals. MQOs should then be defined in terms of detection limits, bias, precision, representativeness, comparability, and completeness. Any sediment assessment program that includes the field collection and laboratory analysis of sediment samples should include various QA/QC samples to quantitatively assess and control the error associated with the results. DQOs and MQOs should be defined in a project-specific QAPP developed prior to sample collection. Other important aspects of the QA/QC program discussed in Chapter 2 include the development of a laboratory audit program, database requirements, and data verification/validation methods.

Given that any sediment samples collected for analysis will represent but a small fraction of the total sediments of interest, it is critical that sufficient consideration be given to ensuring that those samples accurately reflect the characteristics of the sediments in the area in which they were collected. The design of field surveys of contaminated sediments is highly site-specific, and therefore detailed guidance is beyond the scope of this document. Nevertheless, Chapter 3 provides an overview of the general issues that should be considered in the design of such field surveys. Chapter 3 also describes the desirable features for sampling vessels to be used in sediment surveys and the advantages and disadvantages of available field positioning methods. The ARCS Program demonstrated the use of both sediment grab samplers and vibrocorers for the collection of sediment samples; Chapter 3 describes the advantages and disadvantages of several different types of each of these sediment samplers. Field processing methods for sediment samples are then briefly discussed, followed by a brief description of available remote sensing equipment that may provide important supplementary information for sediment surveys.

In areas where there is a paucity of data on sediment characteristics, there is often a need for a low-cost, screening-level investigation to determine whether there is sufficient sediment contamination to be of concern, and to identify areas where more detailed investigations are warranted (Chapter 4). The ARCS Program explored the efficacy of a two-phased sampling design: a set of quick, less expensive assays ("indicator analyses") was performed on the sediments collected from a large number of sediment coring stations, while detailed chemical analyses and toxicity tests were performed at a limited number of surface sediment stations throughout the study area. The indicator analyses included both those that produce a direct measure of sediment composition or contamination (i.e., metals, total and volatile solids, TOC, grain size, ammonia, and the Microtox ® test) and those that produce an indirect measure of sediment quality (i.e., conductivity, pH, extractable residue, and organohalogens) that may be related to other variables of environmental or regulatory importance. Attempts were made to define relationships between the indicator analyses and the more detailed toxicity tests conducted at a limited number of stations so that the latter could be predicted from the former, but the results were site-specific. More recent research has suggested that other screening-level analyses (e.g., fluorometry for PAHs; immunoassays for PCBs, chlorinated pesticides, and PAHs; infrared spectroscopy for petroleum hydrocarbons; TLC for semivolatile organic compounds; XRF for metals; rapid toxicity tests) are also quick and relatively inexpensive, can sometimes be performed in the field, and may be more comparable from site to site than the indicator analyses tested in the ARCS Program. These screening-level analyses may be very useful in delineating areas of high contamination that warrant more detailed investigation, while eliminating areas likely to be relatively uncontaminated.

Chemical analyses conducted under the ARCS Program were focused on application of the best currently available analytical methods (Chapter 5). The sediment samples collected for analysis presented significant problems, such as high levels of hydrocarbon contamination. This resulted in a series of recommendations for additional sample cleanup steps to overcome such analytical challenges. Routine organic and inorganic chemical analyses provide total concentrations of each contaminant in a matrix. Supplemental analyses that provide a better representation of the biologically available fraction of chemicals in a matrix may provide data that are more suitable for interpreting the risk to aquatic organisms. For example, the simultaneous extraction of metals during the extraction of AVS holds promise, but more research is required before such analyses are recommended for routine use. It is impossible to provide detailed guidance on the selection of appropriate analytes and analytical methods for all sediment assessment programs because each situation generally presents a unique combination of factors. It is recommended that the selection of analytes be based on a complete survey of the literature for previous monitoring and exploratory studies in an area of interest, as well as on available data concerning treated and untreated wastewater discharges in the drainage basin for the site. Consideration should also be given to exploratory chemical analyses. This information, in combination with the results of a screening-level investigation and best professional judgment, should provide the basis for selecting the appropriate analytes and analytical methods.

A wide variety of laboratory sediment toxicity tests were performed under the ARCS Program on samples collected from three AOCs (Chapter 6). Included were both elutriate and whole-sediment toxicity tests using various organisms (e.g., bacteria, algae, macrophytes, rotifers, cladocerans, amphipods, mayflies, and fish) and a range of acute and chronic endpoints. Sensitivity, discriminatory power, and redundancy were determined for the various tests. Based on the experience with toxicity tests in the ARCS Program, it is recommended that future sediment assessment programs include a battery of two to three toxicity tests. The use of more than one species is recommended because it reduces uncertainty and limits the probability of false positive or false negative results. At least three measured responses (i.e., survival, growth, or reproduction) should be used in integrated assessments of sediment contamination; behavior as a measured response is a fourth possible endpoint that can be considered, but tests incorporating this endpoint are less well developed. Whole sediment toxicity tests were shown to be very sensitive and provided the most realistic exposure system; exposures using elutriate samples are not recommended for routine sediment assessments. Sediment toxicity testing complements analyses of benthic community structure and physicochemical characteristics of the sediments, and is recommended for an integrated assessment of the degree of sediment contamination. Chapter 6 includes additional guidance on the selection of an appropriate battery of sediment toxicity tests from those shown to produce the most reliable and interpretable results in the ARCS Program.

Field surveys of freshwater benthic invertebrate community structure (Chapter 7) represent the third component (along with sediment chemical analyses and laboratory toxicity tests) of an integrated assessment of sediment contamination. Quantitative surveys of benthic invertebrates were conducted under the ARCS Program in three AOCs. The data were evaluated to provide guidance on the conduct of similar surveys in future sediment assessment programs for other AOCs. Based on the ARCS Program data, the following recommendations can be made: 1) benthic community evaluations provide an important complement to laboratory toxicity tests because changes in benthic communities are likely the result of long-term exposures not adequately simulated in the laboratory; 2) measurements of chemical and physical variables should be made on subsamples of the sediments from which the invertebrates are collected; 3) preliminary benthic community surveys enable an assessment to be made of the species likely to be present, and assist in the design of subsequent more detailed investigations; 4) consideration should be given to sampling with artificial substrates as well as with sediment grab samplers because of the different fauna sampled; 5) the variance in abundance estimates might be reduced by collecting and analyzing more replicate samples than used in the ARCS Program, perhaps using a smaller grab sampler; and 6) additional research is needed to evaluate the specific contaminant, biotic, and abiotic factors that control invertebrate abundance and community structure in contaminated sediments.

Although not as frequently included in assessments of sediment contamination as are investigations of sediment chemistry, sediment toxicity, and benthic invertebrate community structure, fish tumor surveys (Chapter 8) can provide valuable complementary information about biological effects of sediment contamination. Laboratory sediment toxicity tests (Chapter 6) typically focus on biological effects that are manifested within several weeks of exposure to contaminated sediments. Other biological effects, such as carcinogenesis, take a long time to develop and cannot be evaluated using short-term toxicity tests. Although it is feasible to conduct long-term tests in the laboratory that are designed to induce the development of lesions, such tests are usually prohibitively expensive. In lieu of such long-term laboratory tests, surveys of liver lesions in bottom-dwelling fishes have been shown to provide valuable evidence of damage to resident organisms potentially resulting from exposure to contaminated sediments. Chapter 8 provides guidance on the conduct of fish tumor surveys, based on the experience gained in a survey of the Ashtabula River AOC conducted under the ARCS Program. Histopathological examination of the fish by trained specialists is required to achieve accurate estimates of lesion prevalence. If there is an increased prevalence of liver lesions in bottom-dwelling fish from a specific area as compared to a reference area, there is a strong suggestion of potential adverse effects resulting from exposure to contaminated sediments. It should be recognized that movement of the fish, about which little is generally known, complicates the interpretation of exposure. In the absence of supporting laboratory studies designed to examine the effect of exposure to contaminated sediments or sediment extracts in producing lesions, apparent relationships between lesions in fish and the presence of contaminated sediments provide a body of evidence that is consistent with, but not proof of, the hypothesis of chemical causation of the lesions.

Chapter 9 provides an overview of potentially applicable data presentation and interpretation techniques that may be useful for individual sediment assessment programs. Included are examples of techniques for mapping sediment quality data, classifying sediments as "contaminated" or "uncontaminated," and ranking of sites for consideration for remediation. It is not possible to recommend specific data interpretation techniques for each and every sediment assessment program. The data interpretation techniques selected for a given sediment assessment program may be a function of the program under which the assessment is being conducted, as well as of the types of data collected and the specifics of the AOC under consideration.

The ARCS Program was working with the state-of-the-science throughout these studies. Sediment assessment is a rapidly evolving science, and advances have taken place since the field and laboratory studies described in this document were completed. Further, several valuable techniques were omitted from these studies due to budgetary concerns. Overall, this document incorporates the state-of-the-science at the present time. However, users should be aware that newer techniques and assays may supplant the recommended tests. The multidisciplinary approach described in this document will remain sound, but the latest technologies should be adopted as appropriate.


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