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## US EPA LEACH TESTING OF CO AL COMBUSTION RESIDUES

Gregory Helms

US EPA Office of Solid Waste Washington, D.C.



### RCRA Background

EPA regulates waste management under the Reso urce Conservation and Recovery Act (RCRA). Groundwater contamination is a key waste management conc ern and has been since the beginning of the program. Leach testing has been used in our regulatory programs to help EPA make regulato ry decisions in order to determine: (1) what waste is hazardous and needs to be regulated: listings, delistings, Toxicity Characteristic (TC) regulation; and (2) (especially for inorganic wastes) what treatment is adequate: Land Disposal Restriction (LDR) treatment requirements.

TCLP is the most used leaching test de veloped by EPA and was published in a final regulation in 1990. It was the successor to the EP toxicity test. It is probably the most frequently used test because it is a regulatory test. TCLP was designed as a screening test to consider conditions that may be present in a municipal solid waste (MSW) landfill. It is acetic acid buffered to pH 5 (initial); 20:1 liquid/solid ratio; particle size reduction to 9.5 mm; equilibrium. The reason it was designed this way was because, under RCRA, EPA is required to regulate as hazardous all wastes that may pose a hazard to human health and the environment if they are mismanaged. EPA had to ask the question, if a waste is not managed in a haza rdous waste landfill, how will it be managed? The answer was that co-disposal of industrial solid waste with MSW is considered to be a plausible “worst case” management of unregulated waste. If EP A believed that a waste would cause a ground water contamination problem when placed in an MSW landfill, then EPA wanted to regulate it as a haza rdous waste. Because of its regulatory program use, TCLP is also used when it is not required. It may be used in: non-hazardous waste reuse (State Beneficial Use programs); industrial non-hazardous waste landfills; and site remediation where LDRs are not triggered (usually inplace of on-site treatment and disposal).



### EPA Science Advisory Board (SAB) Concerns Re: TCLP

The SAB/EEC commented on Agency l each testing in 1991 and 1999. The SAB expressed concern about overbroad use of the TCLP test. The SAB urged the EPA to undertake new leaching research on both occasions. The SAB urged development of tests that consider actual disp osal conditions affecting leaching and field validation of

new tests.

Technical Issues with TCLP

The SAB found that TCLP is a screenin g test that evaluates leaching potentia l under a single set of environmental conditions. EPA realizes that if you want to evaluate how a waste is actually managed, you are likely to have

conditions which are different from thos e at an MSW landfill. Under this scenario, the MSW would have initially

acidic conditions. EPA did not consider final conditions that were not considered critical and usually not known. In designing TCLP, EPA considered that conditions in the landfill would pre dominate and dictate the overall leaching conditions in a generally oxidizing environment. It wa s also considered that a relatively small proportion of industrial wastes would be co-disposed with MSW. What EPA has found in subsequent years is that for most metals, leaching is pH dependent. This means that by looki ng at a waste with a single pH, this doesn’t give you the best information. You can also get reducing conditions in the bottoms of landfills that can also affect leaching.

EPA Response to Concerns

In response to these concerns, EPA began considering alternatives to TCLP and what attributes should be investigated. As EPA began seeking approaches to be developed into reliable tests for routine use, it found that: (1) much non-TCLP testing has been research or ad hoc modifications of TCLP; (2) EPA needed defined protocols98 that are validated; validation includes inter-laboratory and field evaluations; an d (3) most existing alternatives have not been validated (particularly field validation).

The Agency has been seeking new testing approaches with: (1) better accuracy over a range of disposal conditions; (2) a better foundation in basic science (i.e. not empirical like TCLP) EPA wants to under stand from the test what parameters affect leaching and how th at effects a particular waste; (3) better applicability in environmental assessments (i.e., groundwater fate and transport modeling) ; and (4) flexibility to apply to a broad range of waste types and over a range of conditions that af fect leaching and occur in the environment.

EPA gave consideration to the factors that affect leaching like: (1) waste form (TCLP requires a particle size reduction as an initial step to obtain an equilibrium test); (2) pH (generated by the waste itself or by external conditions like co-disposal in a landfill or acid rain); (3 ) infiltration rate; (4) redox conditions; and (5) others.

EPA is trying to respond to the science advisory board so that we can find an approach where we can get validation in both the laboratory and field. EP A would like a test that can also be pr actically applied. In conducting leach tests of CCRS, EPA made regulatory determinations about TCRs in 1993 and 2000. EPA mostly relied on total concentration data, TCLP, and EP toxicity leach test results because that was what was available at the time. In going forward, EPA is likely to do regulations under subtitle D of RCRA or SMCRA that will be a performance based approach.



### Future Leach Testing of CCRs for Mercury

EPA is currently evaluating leaching from CCRs resulting from mercury em issions controls. Although the focus has been mercury, EPA has also been tes ting for arsenic, selenium , and other metals. EPA has been using a leach testing approach developed by Kosson et al. (2002) at Vanderbuilt. The Kosson Framework addresses many EPA program needs and addresses many of the SAB concerns. EPA chose this method because it considers factors known to affect leaching of metals like: (1) a range of pH values (solubility of many metal salts change with pH); several liquid to solid (L/S) ratio values (or infiltration rate); and (3) form of waste (granular, compacted, or monolithic). Because of this, EPA exp ects to obtain a better accuracy. The Ko sson approach is tiered and flexible so you can do an equilibrium test. It can test both wors t-case and more realistic cases. For small volumes, it can do conservative and cheaper testing. The outputs can be used with site conditions data to generate probabilistic leaching estimate and most appr opriately drives groundwater fate and transport modeling.

This same approach was being used for supportive consu ltation with SAB in 2003 for evaluating metals. The SAB reviewed the Kosson framework for assessment of leaching from CCRS and general waste re-use and considered the framework broadly applicable to waste assessment, especially inorganics. The SAB urged further development of relationship to field data, interpretation of data for d ecision making, and also in clude organics leaching and microbial effects on leaching. More detailed information (including the Kosse n Framework publication) is available at the SAB website: http://www.epa.gov /sab/eecconsultationonleaching.html.

In EPA’s ongoing leaching assessment of CCRs, we are eval uating class C and F fly ashes and scrubber sludges in a number of air pollution control configurations. We have generally found low leaching of mercury even with enhanced mercury controls. There has been some leachin g of arsenic and selenium. EPA has conducted extensive QA/QC performed per a QA/QC plan that uses reference fl y ash, spikes, blanks, and replicates, to ensure valid results. EPA performed laboratory mass balance study of mercury because we found initial low mercury leaching results. We were asked how we knew that the mercury was not just volatilizing. Our tests found good recovery of the mercury and we were not losing it in the glassware nor was it being volatilized. More detail can be found in the February 18, 2005 memo on “Cross Media Transfers” in the EPA public docket for the “Clean Air Mercury Rule.”



### Final Questions

Why didn’t we use TCLP for evaluation of CCRs from enhanced mercury control? This is because: (1) EPA is not making a hazardous waste determination that was done by the May 22, 2000 regulatory determination (65 FR 32214); (2) actual management conditions for CCRs are kn own; MSW co-disposal is minor, so TCLP is not99 technically appropriate; and (3) EPA is seeking an es timate of CCR leaching potential that best reflects actual

management .

Why doesn’t EPA use other existing leaching tests for CCR asse ssment? EPA found that most tests: (1) are not field validated; (2) do not try to assess environmental releases (i.e., assess leaching “under the conditions of the test”); (3) do not consider environmental conditions of waste manage ment; and (4) do not robustly support groundwater fate and transport modeling.



### References

Kosson, D.S., van der Sloot, H.A., Sanchez, F., Garrabrants , A.C. 2002. An Integrat ed Framework for Evaluating Leaching in Waste Management and U tilization of Secondary Materials. Environmental Engineering Science

, V. 19, No. 3. pp. 159-204.100