A REVIEW OF THE APPLICABILITY OF VARIOUS ELUTRIATE TESTS AND REFINEMENTS OF THESE METHODOLOGIES

Transcription

1 A REVIEW OF THE APPLICABILITY OF VARIOUS ELUTRIATE TESTS AND REFINEMENTS OF THESE METHODOLOGIES Albert Vicinie 1, Michael Palermo 2 and Larry Matko 3 ABSTRACT Elutriate tests are designed to measure and predict the release of contaminants to the water column in a variety of different situations such as open water disposal, confined disposal, re-suspension at the dredging site, and other engineering applications. Common methods include the Standard Elutriate Test, the Modified or Effluent Elutriate Test, the Dredging Elutriate Test and the Illinois Supernatant Test. There are several variants of the elutriate methods, and this paper provides an overview of their intended use, applicability and comparison to assist in project design and method selection. As the laboratory and user community have gained significant experience in employing and conducting these methods since their original release, it is appropriate to discuss various aspects of the methods that require and benefit from additional clarification that should be considered in pre-project planning. Many of these aspects can result in substantial differences in the results generated and therefore impact the decisions made using these data. By increasing the awareness of these factors, assumptions and their impact on data more appropriate decisions will be possible by the user community. Keywords: Elutriate, standard elutriate, modified elutriate, dredging elutriate. INTRODUCTION The potential environmental impacts due to releases of contaminants during dredging operations or dredged material disposal operations must be considered for both navigation and sediment remediation projects. Ocean disposal of dredged material is regulated under Section 103 of the Marine Protection, Research, and Sanctuaries Act of 1972 (MPRSA), also called the Ocean Dumping Act. Disposal of dredged material in inland waters of the U.S. is regulated under Section 404 of the Federal Water Pollution Control Act Amendments of 1972 also called the Clean Water Act (CWA). The U.S. Army Corps of Engineers (USACE), the U.S. Environmental Protection Agency (USEPA), and the States have regulatory responsibilities under these laws. These regulations mandated the development of testing procedures to evaluate potential impacts, to include those due to releases of contaminants into the water column. Several elutriate test procedures were developed by USACE under a series of research programs pertaining to dredging and dredged material management to meet the regulatory requirements under both the MPRSA and CWA. The elutriate procedures have been incorporated in testing manuals jointly published by both the USACE and USEPA to include the Ocean Testing Manual (OTM) for evaluations of ocean disposal (USEPA and USACE, 1991), the Inland Testing Manual (ITM) for evaluations of disposal in waters of the United States (USACE and USEPA, 1998), and the Upland Testing Manual (UTM) for evaluations of releases from confined disposal facilities (CDFs) (USACE 2003). The elutriate test procedures were developed to support navigational dredging and disposal applications, and have been routinely applied for these projects for decades. More recently, the same test procedures have been applied in the context of sediment remediation. While the testing protocols in the OTM, ITM, and UTM provide the standardized methods used for the tests, there have been some questions regarding specific issues that occur based upon site conditions that we have identified in the discussion portion for consideration. In addition to the common base elutriate methods discussed here there are a number of regional methods that may be employed as well. The detail provided in these original source methods provide varying levels of information. In some cases interpretation of the terms or assumptions in performing the method can lead to variance in its 1 General Manager, TestAmerica Laboratories, 301 Alpha Drive, Pittsburgh, PA USA, T: , Fax: , rusty.vicinie@testamericainc.com 2 Consulting Engineer, Michael Palermo Consulting, Inc., 6409 Fayetteville Rd, Ste , Durham, NC, 27713, USA, , mike@mikepalermo.com. 3 Technical Director, TestAmerica Laboratories, 301 Alpha Drive, Pittsburgh, PA USA, T: , Fax: , larry.matko@testamericainc.com. 29

2 performance and the subsequent data generated. Several of these methods allow and encourage adaptation of the methods to reflect conditions anticipated relative to the specific site and operation involved for the more accurate generation of data. They do provide default conditions to be used in the absence of this information and, in many cases, these assumptions are conservative and may over estimate the release of contaminants and nutrients actually experienced. Likewise these methods provide general instruction for common matrices but are not exhaustive for all of the various situations that may be encountered by individual dredging operations at specific sites that impact laboratory performance of these methods used in generating analytical data and the subsequent interpretation and use of these data. By having an enhanced understanding of the background of these methods, their intended use and limitations, the user community can generate and evaluate data in the most useful manner. METHODS Overviews of common individual methods are provided below. In most cases these methods are variants and adaptations of the standard elutriate method that utilize differing ratios of solids to site water to generate the solids loading anticipated in the various operations and conditions that they are designed to represent. They also may have different settling times, geometry and they evaluate various fractions such as total and/or dissolved analytes. The methods in general do not specify traditional QA/QC measures that should be considered by the project team to better characterize the data generated and its subsequent use. The methods may be conducted with some differences if the elutriates are being generated for evaluation of water quality or water toxicity evaluations. In general elutriates for toxicity evaluation are not filtered or centrifuged. Table 1 provides a summary comparison of these tests. Application Ratio of Sediment to Site Water (typ.) Table 1. Comparison of Common Elutriate Methods Standard Elutriate Modified Elutriate / Effluent Elutriate Open Water Disposalpoint CDF effluent resulting of disposal from CDF placement 1: 4 ratio sediment to 150 g/l dry wgt. basis site water volumetric (default) a determined by displacement Dredging Elutriate Release at Point of Dredging 10 g/l dry wgt. basis Agitation Time 30 min stirring 5 min stirring 5 min stirring Aeration Time None 1 hour 1 hour Agitation Method Mechanical Mech/Aeration Mech/Aeration Settling Time (typ.) 1 hour 24 hour (default) b 1 hour Fractions analyzed Dissolved Total and Dissolved Total and Dissolved Routine Volumes of 8 Liters 20 Liters 1 Liter Sediment required Routine Volumes of 20 Liters 40 Liters 4 Liters Site Water required Typical yield of ml ml ml Elutriate/ 4 L c a. Sediment and dredging site water should be mixed to approximate the anticipated average field conditions. If estimates cannot be made, then the 150 g/l should be used b. Sediment to dredging site water should be mixed approximately equal to the expected average field inflow concentration and field retention times. If estimates can not be made based on column settling results or past data then the default settling time of 24 hr. should be used.\ c. Typical supernatant yield is 20 % of total volume for the MET & SET 30

3 Standard (Open Water) Elutriate Test -The Standard Elutriate Test (SET), sometimes referred to as the open water elutriate test, is intended to simulate the release of dissolved constituents into the receiving water column during open-water disposal of dredged material (Figure 1). The test is applicable for evaluations of direct pipeline discharges and hopper dredge discharges to open water disposal sites. The SET is also applicable to barge discharge of mechanically dredged material, although it is considered a conservative approach. The main steps of the test include mixing one part of sediment with four parts of water (by volume), agitation for a period of 30 min, a settling period of 1 hr, and finally centrifugation and/or filtration. The filtrate is considered the standard elutriate, which is then analyzed for the desired chemical parameters. This represents the dissolved fraction only, which may then be compared to applicable water quality criteria or standards, considering mixing zones as appropriate. The test can also be used to determine the total fraction of contaminants and also is intended to serve as the medium for performing water column bioassays if they are required. The SET procedure is based on a number of laboratory developmental efforts and field verification studies conducted in the 1970s under the USACE Dredged Material Research Program (Keeley and Engler1974; Lee, Lopez, and Piwoni 1976; Jones and Lee 1978). The laboratory development efforts evaluated factors which affect the results of the test to include solid-liquid ratio, time of contact, ph, dissolved oxygen concentration, agitation, particle size, handling of solids, characteristics of water and sediment, and method of solid-liquid separation. Results provided the basis for determining the testing procedures for regulatory application. The SET procedure is described in detail in both the OTM and ITM. Figure 1. Standard elutriate test. 31

4 Modified (or Effluent) Elutriate Test- The Modified Elutriate Test (MET), also referred to as the Effluent Elutriate Test (EET) is designed to simulate the quality of water discharged as effluent from a CDF and accounts for geochemical changes occurring in the CDF during active disposal operations (Figure 2). Test procedures allow for estimates of dissolved contaminant concentrations expressed in milligrams per liter of effluent and fractions of contaminants in the TSS in milligrams per kilogram suspended solids (SS) under quiescent settling conditions. The test consists of mixing a sediment sample with dredging site water to form a slurry, allowing the slurry to settle under conditions equivalent to those in a CDF, then extracting an effluent elutriate sample for chemical analysis. The default criteria for this method represents the highest solids loading of all the elutriate tests at 150 g/l dry wgt. It is mechanically agitated for 5 minutes, followed by 1 hour of aeration. The sample is then allowed to settle up to 24 hours. The supernatant separated and is analyzed for total constituents. A portion of the supernatant is then centrifuged and/or filtered to generate the dissolved fraction for analysis. The MET procedure is based on a laboratory developmental effort and field verification studies conducted by the USACE in the 1980s (Palermo 1986 and 1988; and Palermo and Thackston 1988a and b). Laboratory studies evaluated factors related to agitation methods, settling column effects, solid-liquid ratio, settling times, redox conditions, and methods of sample extraction and handling. Direct comparison of laboratory behavior with field results across a range of site conditions provided the basis for determining the testing procedures for regulatory application. Field verification studies showed that the MET/EET is a conservative predictor of CDF effluent quality. The MET/EET procedure is described in detail in both the ITM and UTM. Figure 2. Modified elutriate test. 32

5 Dredging Elutriate Test-. The Dredging Elutriate Test (DRET) procedures were developed by the USACE as a predictive tool for estimating the degree of contaminant release from sediments due to resuspension at the point of dredging. The DRET test consists of mixing sediment and site water at a total suspended solids concentration of typically 5 to 10 g/l which is considered representative of resuspended sediment as generated at the dredgehead source, aeration of the slurry for 1 hour, allowing the slurry to settle for a period of 1 hour, and analyzing the elutriate for TSS and both dissolved and total concentrations of contaminants. DRET results only apply to releases due to dredging-induced resuspension, and would not be necessarily representative of releases resulting from debris removal activities, propeller wash, spudding/anchoring activities, and other potential resuspended and dissolved contaminant loss sources. The DRET procedure was developed by the USACE under a contracted effort with the University of North Carolina at Chapel Hill (DiGiano, Miller, and Yoon 1993 and 1995). Only limited field verification studies for the DRET were performed as a part of its development, but results have shown that the DRET is a conservative predictor of contaminant release at the point of dredging for hydrophobic organics (DiGiano, Miller, and Yoon, 1993 and 1995). Illinois Supernatant Test-This is an example of one of several regional test that may be required for any hydraulically or mechanically moved material in Illinois. It is based upon Standard Methods of Water and Wastewater Analysis method 2540 (f) 20th Ed, It employs a 1:4 ratio of sediment to receiving water and a 4 hour settling time or settling times consistent with those of the placement facility. An Imhoff cone is utilized in the conduct of this test. DISCUSSION A comparison of the common elutriate methods is provided in Table 1. The volumes and yields listed are generic and should be evaluated for project specific needs but may be used as defaults and estimates in the absence of other information. As with any project involving tests that can be adapted to site specific conditions, pre-project communication, and involvement in all parties associated with the project in the study design will increase the overall quality of the project outcome. We have identified some areas for consideration to assist in these decisions. Obviously the tests identified were designed to replicate in the laboratory, certain anticipated conditions in the field, and selection of the most appropriate test is critical. Determination of constituents of concern in the generated supernatant will be analyzed and will then drive many decisions. Field collection and processing techniques and materials will need to be evaluated to ensure than contamination is not introduced, not result in analyte loss. As identified in the table above, sample quantities are significantly increased relative to bulk sediment sample collection for similar traditional determinations. The logistical challenges in addition to the volume needed, such as homogenization, collection containers used, processing time effect on holding times, shipping conditions and mechanisms should be evaluated. Often multiple elutriation devices will be needed to be set up for generation of adequate amounts of supernatant to support the analytical determinations. The collection and compositing techniques and materials should be considered relative to the project objectives. It is recommended that various procedural blanks are introduced into the overall process to monitor and assess any impact these processes may have on the overall data set. For tests that require the generation of a dissolved fraction, various techniques are available for utilization. Typically filtration using 0.45 um glass fiber filters or centrifugation is employed to generate this fraction. Filtration is normally appropriate for inorganic constituents and centrifugation for organic constituents. This is important for example, in pesticide and PCB determinations, as dissolved fractions must be free of particulates as those compounds will be highly absorbed on those particles but should not be filtered due to their tendencies to absorb onto the filer media or particles trapped by the filter. Filter material, effective pore size, centrifuge vessel material, vacuum vs. pressure filtration, centrifuge speed, duration and rotor radius employed to generate specific g, should be evaluated to ensure no bias is introduced to the data set. We recommend addition of procedural blanks into this process for evaluation. Elutriates generated for the purpose of supporting bioassay toxicity evaluations are typically not filtered or centrifuged. The solids loading within the supernatant can have a significant impact on the analytical methods employed for chemical determination. High solids may result in interferences that have an impact on reporting limits that are able to be achieved and may require modifications to address this in certain situations to meet data quality objectives. This is especially relevant to the MET/EET as it utilizes the highest solids ratio and is often employed in fresh water 33

6 conditions. It us not unusual to see a third layer in these elutriates that contains exceptionally high suspended material. While the method discusses settled fraction and supernatant it does not address this situation directly. In deciding how to treat this highly suspended fluidized phase the project objectives need to be clearly understood and communicated. The inclusion of this fluidized layer can have a significant effect in constituent concentrations and reporting limits. Likewise, not including this layer will have a significant impact on the yield of supernatant from the elutriate tests. Understanding the end use of the data generated by the MET when a third fluidized layer is encountered should be discussed. In most cases it is appropriate to include the fluidized layer as it represents likely transport of contaminants associated with the suspended solids. Extended settling time in many cases does not result in additional settling of the suspended material. It may require the collection of significantly more sediment and site water if it is determined in some situations that the use of the third fluidized layer is not appropriate for the intended use of the test data.. Yields of clear supernatant have been observed at 1-2% of total yield as an example rather than a more typical 20%. This is most typically encountered in situations that have high clay and silt content along with fresh water sites. Digital photography is encouraged to help document settling characteristics. There currently is not the ability to use one consolidated elutriate procedure for all the applications in Table 1. Dedicated research and field verification effort would be required prior to any agency endorsement of a combined procedure. CONCLUSIONS When evaluating data generated from an elutriate test, it is imperative that the data user understand which of the various elutriate methods was used to generate the elutriate. As described there are various differences in the conduct of the method and assumptions that may be made in the conduct of those methods that, while compliant with the method, may have significant impact on the data generated and the subsequent decisions made using that data. The more information that is available relative to the specific site and operation being conducted and utilized in the performance of these methods will yield the most accurate estimates of actual contaminant release during these operations. Due to the significant cost and effort of sample collection activities associated with these tests and the decisions made using the generated data, it is essential that communication among the entire project team is conducted in advance of executing these activities and methods. ACKNOWLEDGEMENTS The authors would also like to acknowledge Richard Sheets, Pat McIsaac and Tara Schlenker of TestAmerica for contributions to this article REFERENCES DiGiano, F. A., Miller, C. T., and Yoon, J. (1995). "Dredging Elutriate Test (DRET) development," Contract Report D-95-1, U.S. Army Engineer Waterways Experiment Station, Vicksburg, MS., NTIS No. AD A DiGiano, F. A., C. T. Miller, and J. Yoon Predicting release of PCBs at the point of dredging. Journal of Environmental Engineering 119(l):72-89, American Societyof Civil Engineers. Jones, R. A., and Lee, G. F. (1978). "Evaluation of the elutriate test as a method of predicting contaminant release during open-water disposal of dredged sediments and environmental impact of open-water dredged material disposal; Volume I: Discussion," Technical Report D-78-45, U.S. Army Engineer Waterways Experiment Station, Vicksburg, MS., NTIS No. AD A Keeley, J. W., and Engler, R. M. (1974). "Discussion of regulatory criteria for ocean disposal of dredged materials: Elutriate test rationale and implementation guidelines," Miscellaneous Paper D-74-14, U.S. Army Engineer Waterways Experiment Station, Vicksburg, MS., NTIS No. AD Lee, G. Fred, et al. (1978). "Evaluation of the elutriate test as a method of predicting contaminant release during open-water disposal of dredged sediments and environmental impact of open-water dredged material disposal; Volume II: Data report," Technical Report D-78-45, U.S. Army Engineer Waterways Experiment Station, Vicksburg, MS., NTIS No. AD A Lee, G.F., Piwoni, M.D., Lopez, J.M., Mariani, G.M., Richardson, J.S., Homer, D.H., and Saleh, F.,1975. "Research Study for the Development of Dredged Material Disposal Criteria", Contract Report D-75-4, Final Report, November 1975, US Army Engineer Waterways Experiment Station, Environmental Effects Laboratory, Vicksburg, MS. 34

7 Ludwig, D. D., Sherrard, J. H., and Amende, R. A. (1988). "An evaluation of the standard elutriate test as an estimator of contaminant release at the point of dredging," Contract Report HL-88-1, U.S. Army Engineer Waterways Experiment Station, Vicksburg, MS., NTIS No. AD A Palermo, M.R Development of a Modified Elutriate Test for Predicting the Quality of Effluent Discharged from Confined Dredged Material Disposal Areas. Technical Report D-86-4, U.S. Army Engineer Waterways Experiment Station, Vicksburg, MS. Palermo, M.R., and Thackston, E.L. 1988a. Test for Dredged Material Effluent Quality. Journal of Environmental Engineering, American Society of Civil Engineers, Vol. 114, No. 6, December Palermo, M.R., and Thackston, E.L. 1988b. Verification of Predictions of Dredged Material Effluent Quality. Journal of Environmental Engineering, American Society of Civil Engineers, Vol. 114, No. 6, December Palermo, M.R Field Evaluations of the Quality of Effluent from Confined Dredged Material Disposal Areas. Technical Report D-88-1, U.S. Army Engineer Waterways Experiment Station, Vicksburg, MS. USACE- ERDC, Evaluation of Dredged Material Proposed for Disposal at Inland,.Nearshore or Upland Confined Disposal Facilities- Testing Manual. ERDC TR-03-1 (UTM) USEPA, USACE, 1991.Evaluation of Dredged Material Proposed for Ocean Disposal. EPA 503/8-91/001 (OTM) USEPA, USACE, Evaluation of Dredged Material Proposed for Discharge in Waters of the U.S.-Testing Manual. EPA-823-B (ITM) CITATION Vicinie, A., Palermo, M., Matko, L., A review of the various elutriate tests and refinements of these methodologies Proceedings of the Western Dredging Association (WEDA XXXI) Technical Conference and Texas A&M University (TAMU 41) Dredging Seminar, Nashville, Tennessee, June 5-8,