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US EPA LEACH TESTING OF COAL COMBUSTION RESIDUES 

Gregory Helms 

US EPA Office of Solid Waste 

Washington, D.C. 

RCRA Background 

EPA regulates waste management under the Resource Conservation and Recovery Act (RCRA). 

Groundwater contamination is a key waste management concern and has been since the beginning of the program. 

Leach testing has been used in our regulatory programs to help EPA make regulatory 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 developed 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 hazardous 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 EPA believed that a waste would cause a groundwater contamination problem when placed in 

an MSW landfill, then EPA wanted to regulate it as a hazardous 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 leach 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 disposal conditions affecting leaching and field validation of 

new tests. 

Technical Issues with TCLP

The SAB found that TCLP is a screening test that evaluates leaching potential 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 those 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 predominate and dictate the overall leaching 

conditions in a generally oxidizing environment. It was 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 looking 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 protocols 
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that are validated; validation includes inter-laboratory and field evaluations; and (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 understand from the test what 

parameters affect leaching and how that 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 affect 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. EPA would like a test that can also be practically 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 emissions controls. Although the focus has 

been mercury, EPA has also been testing 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 expects to obtain a better accuracy. The Kosson approach is tiered and flexible 

so you can do an equilibrium test. It can test both worst-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 appropriately drives groundwater fate and transport modeling. 

This same approach was being used for supportive consultation 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 decision making, and also include organics leaching and 

microbial effects on leaching. More detailed information (including the Kossen 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 evaluating 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 leaching of arsenic and selenium. EPA has conducted extensive 

QA/QC performed per a QA/QC plan that uses reference fly 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 known; MSW co-disposal is minor, so TCLP is not 
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technically appropriate; and (3) EPA is seeking an estimate of CCR leaching potential that best reflects actual 

management . 

Why doesn’t EPA use other existing leaching tests for CCR assessment? 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 management; 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 Integrated Framework for Evaluating 

Leaching in Waste Management and Utilization of Secondary Materials. Environmental Engineering Science, 

V. 19, No. 3. pp. 159-204. 
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