Regulatory agencies are developing chemical concentration-based sediment quality criteria for use in the regulation of dredging projects. Gaining popularity in criteria development is any of a number of "co-occurrence" approaches, such as the AET, the Long and Morgan ER-L and ER-M values, and the MacDonald PEL values. These approaches are founded in the compilation of data on the total concentrations of selected contaminants measured in a group of sediments and some measure of a biological "effect" associated with those sediments, irrespective of the cause of the "effect." The US EPA has developed an equilibrium partitioning-based sediment quality criteria approach for some types of contaminants. It assumes that the concentration of a contaminant in the interstitial water of a sediment can be reliably estimated based on the chemical characteristics of the sediments and that the estimated concentration in the interstitial water can be related to water quality. There are significant deficiencies in the technical foundations and implementation of these and other chemical concentration-based approaches for establishing sediment quality criteria for the regulation of dredging projects. The technical foundation, assumption, and implementation issues associated with currently proposed chemical concentration-based sediment quality criteria development approaches are critically reviewed.
Introduction
In the early 1970's the Federal Water Quality Administration, an agency preceding the US EPA, developed the "Jensen criteria" for regulating dredging projects. Those criteria specified maximum bulk sediment content of a few selected parameters that are sometimes measured in domestic wastewater sludges,
such as total Kjeldahl nitrogen, total volatile solids, chemical oxygen demand, and several heavy metals. If a sediment contained one of those constituents in concentrations above the criteria values, it was considered polluted and unacceptable for open water disposal. Even when the Jensen criteria were adopted it was already well-known that the total concentration of a contaminant in sediment was a poor measure of its potential biological effects, a fact that rendered the Jensen criteria technically invalid and inappropriate for regulating dredging projects. Nevertheless, those criteria and approaches similar to them based on total concentrations of contaminants in sediments, were used to regulate dredging of chemically contaminated sediments, and resulted in the large-scale waste of public funds in dredging projects. This caused the US Army Corps of Engineers (US ACE) to obtain funds from Congress to conduct the Dredged Material Research Program (DMRP). The DMRP was a $30 million, five-year effort conducted through the US ACE Waterways Experiment Station at Vicksburg, MS; one of its primary objectives was the development of regulatory approaches for contaminated dredged sediments to more reliably and appropriately regulate dredging projects than the Jensen criteria.
Through the DMRP significant advancements were made in the evaluation of dredged sediments, advancements that were founded upon the understanding of the aquatic chemistry and aquatic toxicology of sediment-associated contaminants, and focused on assessing potential impacts of those contaminants on water quality/beneficial uses of water. In the past few years, however, there has been a resurgence of zeal for bureaucratic expedience in judging the "quality" of sediment based on the chemical analysis of selected parameters in sediment, albeit at the expense of technical merit and relevance to water quality. There has been a virtual disregard of the fundamental controlling influence of aqueous environmental chemistry over the impact of bulk chemical composition of sediments, as well as the findings of substantial research into the topic.
Impacts of Chemical Contaminants in Dredged Sediment
In the development of the DMRP it was recognized that there are two principal areas of concern associated with chemical contaminants in dredged sediments. One is the potential release of contaminants from the dredged sediment to the watercolumn at the dredging site and/or at the dredged sediment disposal site. The other is the introduction of toxic/available forms of contaminants to the dredged sediment disposal site that could represent long-term threats to aquatic life and other designated beneficial uses of the disposal-site waterbody. Sediment evaluation approaches were developed through the DMRP to address both of those issues.
Elutriate Test
The elutriate test is a sediment leaching procedure developed by the US ACE to assess the potential for release of contaminants from dredged sediment to the watercolumn at the dredged sediment disposal site. Its design was based on the conditions to which dredged sediments are exposed and the influence of the key physical and chemical factors that control the release of contaminants from sediment solids. The elutriate test procedure involves the mixing of one volume of sediment with four of water for one hour followed by settling, all under oxic conditions similar to those which would occur at a dredged material disposal site. The supernatant, "elutriate," is then characterized by measuring dissolved/available constituents and the laboratory toxicity of the elutriate to appropriate test organisms.
The senior author and his associates published several comprehensive reports devoted to the development of the elutriate test and their intensive laboratory and field evaluation of its reliability for assessing the potential water quality impacts of chemical contaminants released to the watercolumn associated with dredged sediment disposal (see Jones and Lee, 1978). A summary of the key findings of that work was published by Lee and Jones (1984); Lee and Jones (1992) presented an updated discussion of the water quality impacts of sediment-associated contaminants as related to waterway dredging and dredged sediment disposal.
The key to appropriate use of elutriate test results in the evaluation of the potential impacts of dredged sediment-associated contaminants on disposal site water quality is the proper consideration of the concentration--duration of exposure relationship that watercolumn organisms could experience at the dredged sediment disposal site. The approach that is currently used is to compare US EPA water quality criteria concentrations for selected parameters, or state standards, to estimates of contaminant concentrations that would be present at the edge of a mixing zone at the disposal site. Those estimates are made using the elutriate test results and US ACE approaches for estimating the dilution that occurs at dredged sediment disposal sites. However, the US EPA water quality criteria and standards equivalent to them are based on chronic (long-term) exposure of organisms to contaminants. Because of the short duration and episodic nature of open-water dredged sediment disposal operations, and the typical high-energy conditions at disposal sites, watercolumn organisms at the edge of a disposal-site mixing zone would not receive a chronic exposure to released contaminants.
Toxicity Tests
A well-recognized advantage of appropriate toxicity testing is that it assesses not only the potential toxicity of regulated contaminants that are commonly a focus of water quality studies, such as heavy metals, chlorinated hydrocarbon pesticides, selected other organics, ammonia, etc., but also the potential toxicity of the unknown, unregulated non-conventional contaminants present in the dredged sediment. To address the assessment of longer-term impacts that may be associated with open-water disposal of contaminated sediments, and in conjunction with the elutriate test development and evaluation discussed above, the senior author and his associates developed and evaluated a dredged sediment toxicity test. The test involved placing watercolumn or epibenthic test organisms in settled elutriates for a four-day period in order to assess whether there was any significant aquatic organism toxicity associated with the dredged sediment that could be detrimental to the designated beneficial uses of the waterbody at the dredged sediment disposal site.
The test system that included the settled sediment allowed the test organisms to be exposed to contaminants in the settled sediments as well as to contaminants that may be released to the watercolumn during the elutriation of the sediments. While the elutriation does dilute the sediment/interstitial water volume by a factor of four and acute test endpoints (organism death) were used, the exposure conditions of the test are significantly more severe than those which epibenthic organisms would typically encounter at a dredged material disposal site following a disposal operation. Normally much greater dilution is available at the disposal site sediment/water interface than that provided in the test conditions.
The results of the authors' and their associates' work on toxicity testing, chemical analyses, and field evaluation were presented by Lee et al. (1978) and Jones and Lee (1978), and summarized by Jones and Lee (1988). They found that many US waterway sediments near municipal/industrial centers contained contaminants that caused acute toxicity to test organism under the test conditions. Typically 10 to 50% of the test organisms (grass shrimp for marine waters and daphnia for fresh waters) were killed in the four-day test period. However, it was clear that while sediments highly contaminated with potentially toxic chemicals typically showed some toxicity to test organisms under the test conditions, the toxicity manifested was far less than that which would have been expected if any significant fraction of the potentially toxic chemicals in the sediments were present in the sediments in toxic-available forms. The toxicity found was not related to the total concentrations of chemicals in the sediment.
Dredged sediment toxicity tests have become a key component of the current US EPA and US ACE procedures for evaluating and regulating disposal of contaminated dredged sediment. While there are some technical deficiencies in some of the recommended procedures and protocols, fundamentally they provide direct biological effects information on the potential toxicity of the suite of chemical contaminants and physical conditions associated with redeposited dredged sediments.
It was clear in the late 1970's from the results of the elutriate test evaluation and toxicity testing that, except for ammonia, there was little release of the conventionally regulated contaminants to the watercolumn and that the potentially toxic contaminants present in the sediments were essentially all in non-toxic, unavailable forms. This finding was consistent with expectations from the aqueous environmental chemistry of sediment-associated contaminants and with previous findings reported in the literature, that particulate forms of contaminants are largely non-toxic/unavailable and that the total sediment concentrations are a poor measure of potential impact of sediment-associated contaminants. Recent studies of the US EPA and others on equilibrium partitioning of contaminants in sediments has further documented that particulate forms of contaminants, such as heavy metals, various organics, etc., are non-toxic/unavailable to adversely impact water quality either at the dredging or dredged sediment disposal site.
Significance of Ammonia in Dredged Sediments
Ammonia was about the only contaminant of potential water quality concern that was released from dredged sediments in elutriate tests. In subsequent review of the data, the authors determined that for the set of samples examined, the toxicity found in the elutriate test bioassays could be attributed to the ammonia released during the testing (Jones and Lee, 1988). While there are situations where ammonia released during dredged sediment disposal could cause toxicity to watercolumn organisms at the disposal site, typically there is sufficient dilution at disposal sites that the ammonia released would be of no significance to watercolumn water quality. There is, however, a significant potential for ammonia toxicity to benthic and epibenthic organisms that are in contact with sediment interstitial waters. Jones-Lee and Lee (1993) have recently reviewed the information on the water quality significance of ammonia in sediments.
There are many sediments that are toxic to certain forms of aquatic life due to ammonia, hydrogen sulfide, or low dissolved oxygen conditions in the sediment. At some locations these chemicals are present naturally in sediments in toxic amounts and are not associated with input from the activities of man. However, in most areas, particulate and dissolved biodegradable organic carbon, particulate organic nitrogen, and nitrogen and phosphorus which serve as nutrients for planktonic and attached algae and other aquatic plants, from point- and non-point-source discharges/runoff contribute to the oxygen demand in the sediments. The oxygen demand of materials in the sediments leads to low dissolved oxygen, which, in turn, is conducive to the formation of hydrogen sulfide through sulfate reduction, and the accumulation of ammonia in sediments.
Recent and Current Regulatory Efforts
Despite the incontrovertible evidence in theory and practice that the impact of sediment-associated contaminants cannot be reliably estimated from the total concentrations of chemical contaminants in sediments, the US EPA and regulatory agencies in several states are now attempting to develop chemical concentration-based sediment quality criteria for use in regulating waterway dredging projects. The two principal approaches being used are based on "co-occurrence" and "equilibrium partitioning."
Co-Occurrence-Based Values
A number of investigators have compiled information on the concentrations of specific chemicals in sediments, by contaminant, and the results of some type of assessment of biological response to those sediments. The "toxic responses" reported are responses to the wide variety of contaminants that can be present in a sediment, and not necessarily a response to the specific contaminant being considered. Thus, independent of the cause of the biological response, the same degree of response was associated with the concentration of each individual chemical contaminant measured in a sediment. Tables of such "co-occurrences" of the concentration of a chemical and a "response" have been developed (e.g., by Long and Morgan, and MacDonald) and have formed the foundation of what are termed "co-occurrence" approaches. For a given chemical, the sediments are ranked by concentration and presented with the associated assessment of the "effect" of the sediments, measured in any number of ways, without consideration of what conditions or contaminants were causing or influencing the "effect." In regulatory applications, "co-occurrence" information has been used albeit incorrectly, to establish various "effects threshold" values based on statistical manipulation. Fundamental, but refutable, presumptions made are that there is a causal relationship between the concentration of each contaminant considered in a sediment and the water quality impact of that sediment (as were bulk sediment criteria), and that the "effect" reported for each sediment was caused independently by each of the measured chemical contaminants in that sediment.
Examples of co-occurrence applications are the "Apparent Effects Threshold" (AET), the ER-L and ER-M values developed from Long and Morgan's 1990 data presentation, and the "Probable Effects Levels" (PEL) values derived from MacDonald's 1992 co-occurrence compilations. If a sediment contains a chemical in concentrations above the AET, ER-M, PEL, or similar value, the sediment is considered by some regulators or in proposed regulations to be polluted, and to require special consideration such as "remediation," alternate methods of dredged sediment disposal, or additional control of discharges of the chemical to the waterbody. While administratively simple to implement, this approach is not technically valid for assessing the potential impact of sediment-associated contaminants and thus should not be used to regulate the dredging of contaminated sediments; it does not reliably consider the aqueous environmental chemistry of chemicals in aquatic sediments as they may impact aquatic life-related beneficial uses of waterbodies. Lee and Jones-Lee (1994) recently reviewed significant technical deficiencies in the use of co-occurrence-based sediment quality criteria to evaluate and manage contaminated sediments.
Advocates of the AET approach for the evaluation of sediment quality in the Puget Sound, Seattle, WA area often claim that the use of the AET approach has been found to be highly successful in regulating dredging projects. The fact that the AET approach has been used ("successfully applied") to make management decisions, does not mean that the approach is reliable or appropriate. A critical examination of how AET has been used in regulating waterway dredging projects in that area shows that it is not a reliable basis upon which to determine the potential water quality significance of chemical contaminants in sediments as they may impact dredged sediment disposal. Sediments that pass the AET screen used and are thus exempt from further testing, could readily be toxic or otherwise significantly adverse to aquatic life at a dredged sediment disposal site due to contaminants present in the sediment that are not considered in the AET evaluation. Those sediments that do not pass the AET screen are subject to the more technically reliable biological effects-based testing in accord with US EPA and US ACE (US EPA and US ACE, 1991) procedures. It would be far more reliable and cost-effective to forego the unreliable AET screen and proceed directly with appropriate biological effects-based testing to determine whether measured, as well as unmeasured, contaminants in sediments are potentially toxic to aquatic life. Further discussion of the technical deficiencies of using AET and other co-occurrence-based approaches such as those that evolved out of the Long and Morgan ER-L and ER-M values and MacDonald PEL values is provided by Lee and Jones-Lee (1994).
Equilibrium Partitioning
The US EPA is attempting to overcome the fundamental lack of technical validity of co-occurrence and other total chemical concentration-based approaches for developing sediment quality criteria by "normalizing" the concentrations of sediment-associated chemicals based on selected sediment characteristics. For the "equilibrium partitioning" approach that the US EPA is attempting to develop for this purpose it is assumed that the concentrations of selected non-polar organic contaminants in a sediment's interstitial water can be reliably estimated based on the total concentrations of the contaminants and the sediment's organic carbon content. In making that assumption, it is presumed that the only significant detoxification reaction for the non-polar organic chemicals that occurs in sediments is the sorption of those chemicals on particulate organic carbon in the sediment. The equilibrium partitioning approach also assumes that there exists a valid relationship between the calculated concentrations of contaminants in a sediment's interstitial waters and the water quality impact of those contaminants in the overlying waters.
In February 1993 the US EPA released draft sediment quality criteria for selected non-polar organics using "equilibrium partitioning" for normalization (US EPA, 1993). In the application of that approach the Agency assumed that if the calculated concentration of a dissolved chemical in the interstitial water exceeds the water quality criterion for that parameter, the chemical will be toxic to aquatic life associated with the sediments. As discussed by Lee and Jones-Lee (1993), the US EPA's "equilibrium partitioning" for non-polar organics, and similarly the acid-volatile-sulfide (AVS) normalization for heavy metals, are not valid for developing sediment quality criteria. Their use will likely result in the over-regulation of sediments containing contaminants for which there are criteria, and could under-regulate those containing certain chemicals for which there are no criteria.
Some attempt to downplay the technical deficiencies of the equilibrium partitioning and "co-occurrence" approaches by claiming they will be used only for "screening" of sediments. However, it is imperative that a "screening" approach must be technically reliable. It cannot be assumed that an unreliable value or approach is "conservative." (See Lee and Jones-Lee (1993) for further discussion of this issue.)
Biological Effects-Based Dredged Sediment Regulatory Approaches
The purpose for developing and implementing sediment quality criteria is to prevent adverse biological effects from being caused by chemical contaminants in sediments. The key to achieving this goal is the technical validity of the criteria and their implementation for assessing potential impacts of sediments and for assessing improvements in beneficial uses of waters that can be brought about by "remediation" approaches. Advocates of co-occurrence-based approaches and the US EPA's equilibrium partitioning-based approaches for regulating dredged sediment are attempting to return to the bureaucratic simplicity of the "Jensen criteria era" of the early 1970's, without due regard for technical validity. While chemical concentration-based approaches provide numeric values by which regulatory agencies and others can superficially but readily comply with regulatory requirements, they do not provide reliable information for assessing impacts of contaminants on water quality at dredging or dredged sediment disposal sites. Owing to their inherent unreliability, their use, as a "screening" tool, in conjunction with other valid or invalid approaches, or on a stand-alone basis, will provide unreliable and misleading information for regulation.
The demonstrated lack of technical validity of chemical concentration-based approaches mandates that they not be used for regulating dredging projects. Instead, appropriate, direct, and technically sound biological impact assessment approaches that evolved from the DMRP studies of the 1970's should be followed. Lee and Jones (1992), Wright (1992) and Wright et al. (1992) have discussed the importance of using what are in fact biological effects-based criteria/standards for regulating dredging projects. Rather than trying to estimate the toxicity of a contaminant in sediments using unreliable chemical concentration-based methods, it is far more reliable and cost-effective to measure toxicity directly using appropriately conducted dredged sediment toxicity tests such as some of those described by the US EPA and US ACE (1991). Further, rather than trying to estimate bioaccumulation of contaminants in sediments using chemical concentrations or even laboratory-based biological uptake methods, it is far more reliable and cost-effective to determine whether excessive concentrations of contaminants of concern exist in the tissue of appropriate types of organisms at the dredging site, and at disposal sites, if any, that have received sediments dredged from the region of concern. Such biological effects-based measurements provide information that can potentially be used reliably to regulate dredging projects.
Care must be exercised in interpreting biological effects data to avoid unjustified over-regulation. It should never be assumed that "statistically significant" toxicity measured in a toxicity test of a sediment is a demonstration of "ecologically or water quality-significant" impacts. Sediments in many waterbodies that support very good or outstanding aquatic life resources such as sportsfisheries and commercial fisheries, contain contaminants from natural or anthropogenic sources that can cause toxicity in laboratory tests. One of the greatest deficiencies that exist today in regulating contaminants in aquatic systems is the lack of understanding or proper consideration of the coupling between laboratory test results or some other "biological impact" assessment and the water quality/beneficial uses of the particular waterbody. The finding of "impacts" in a laboratory test should not be the trigger for regulation, or for the requirement of alternative methods of disposal, but rather an indication that the significance of those findings for the site-specific dredging and disposal conditions needs to be investigated. Such studies will likely be highly cost-effective in identifying those situations in which the disposal of a particular chemically contaminated sediment at a particular location that is not now an ecologically sensitive area will be detrimental to the water quality of the region, i.e., the numbers, types, and characteristics of desirable organisms in the area. It cannot be presumed that alternative disposal approaches that may be required because of a sediment's failing a screening or testing procedure will be more protective of environmental quality.
Appendix
Jones, R. A. and Lee, G. F., "Evaluation of the Elutriate Test as a Method of Predicting Contaminant Release during Open Water Disposal of Dredged Sediment and Environmental Impact of Open Water Dredged Materials Disposal, Vol. I: Discussion," Technical Report D-78-45, US Army Engineer Waterways Experiment Station, Vicksburg, MS, August (1978).
Jones, R. A. and Lee, G. F., "Toxicity of US Waterway Sediments with Particular Reference to the New York Harbor Area," In: Chemical and Biological Characterization of Sludges, Sediments, Dredge Spoils and Drilling Muds, ASTM STP 976 Am. Soc. Test. & Mat., Philadelphia, PA pp. 403-417 (1988).
Jones-Lee, A. and Lee, G. F., "Potential Significance of Ammonia as a Toxicant in Aquatic Sediments," In: Proceedings First International Specialized Conference on Contaminated Aquatic Sediments: Historical Records, Environmental Impact, and Remediation, IAWQ, Milwaukee, WI, pp. 223-232, June (1993).
Lee, G. F. and Jones, R. A., "Evaluating the Water Quality Significance of Dredged Sediments," In: Dredging and Dredged Material Disposal, Proc. ASCE Conference, pp. 1050-1061 (1984).
Lee, G. F. and Jones, R. A., "Water Quality Aspects of Dredging and Dredged Sediment Disposal," In: Handbook of Dredging Engineering, McGraw Hill (1992).
Lee, G. F., and Jones-Lee, A., "Sediment Quality Criteria: Numeric Chemical- vs. Biological Effects-Based Approaches," Proceedings of Water Environment Federation National Conference, Surface Water Quality & Ecology, Anaheim, CA, pp. 389-400, October (1993).
Lee, G. F., and Jones-Lee, A., "'Co-Occurrence' in Sediment Quality Assessment," Submitted for publication. Available as a pre-print report of G. Fred Lee and Associates, El Macero, CA, July (1994).
Lee, G. F., Jones, R., Saleh, F., Mariani, G., Homer, D., Butler, J., and Bandyopadhyay, P., "Evaluation of the Elutriate Test as a Method of Predicting Contaminant Release during Open Water Disposal of Dredged Sediment and Environmental Impact of Open Water Dredged Materials Disposal, Vol. II: Data Report, Technical Report D-78-45, US Army Engineer Waterways Experiment Station, Vicksburg, MS, August (1978).
US EPA, "Technical Basis for Deriving Sediment Quality Criteria for Nonionic Organic Contaminants for the Protection of Benthic Organisms by Using Equilibrium Partitioning," US EPA Office of Water, EPA-822-R-93-011, Washington, D.C., September (1993).
US EPA and US ACE, "Evaluation of Dredged Material Proposed for Ocean Disposal (Testing Manual)," EPA-503/8-91/001, US EPA and US Army Corps of Engineers, Washington, D.C. (1991).
Wright, T., "Evaluation of Dredged Material for Open-Water Disposal: Numerical Criteria or Effects-Based?" IN: Handbook of Dredging Engineering, McGraw-Hill, New York, pp. 9.59-9.67 (1992).
Wright, T., Engler, R., and Miller, J., "Effects-Based Testing and Sediment Quality Criteria for Dredged Material," IN: Water Quality Standards for the 21st Century, EPA 823-R-92-009, pp. 207-216, December (1992).
Key Words:
dredging, contaminated sediments, criteria, regulations
Disposal Criteria for Contaminated Dredged Sediment
G. Fred Lee, Ph.D, P.E., D.E.E. and Anne Jones-Lee, Ph.D.
G. Fred Lee & Associates
El Macero, California
Review of Background of Current Disposal Criteria
Problems with Current Approaches
Future Problem Areas
Evolution of Current Criteria
Prior to 1970's - Used Most Economical Methods of Disposal
Early 1970's - FWQA Developed "Jensen" Criteria
Bulk Sediment Analysis of Dredged Sediment - Sewage Sludge Characteristics
COD, Volatile Solids, TKN, Oil & Grease
Hg, Pb, Zn - Less than Crustal Abundance
Obviously Technically Invalid When Developed
Known at That Time: No Relationship between Total Concentrations of Constituents & Impact on Water Quality
Jensen Criteria Impetus for US ACE to Obtain $30 million for 5-yr Dredged Material Research Program (DMRP)
DMRP
Developed Elutriate Test to Assess Release of Chemical Constituents at Open Water Disposal Site
