Algorithms to Pre-Process Leaching Data to Generate Source Terms 

for Modeling Landfill Leachate Migration in Ground Water 

OFFICE OF RESOURCE CONSERVATION AND RECOVERY (ORCR)

U.S. ENVIRONMENTAL PROTECTION AGENCY

WAHSINGTON, D.C. 20460

FEBURARY, 2012

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Algorithms to Pre-Process Leaching Data to Generate Source Terms for Modeling Landfill 

Leachate Migration in Ground Water

CCR leaching data for probabilistic fate and transport modeling of CCRs managed in landfills 

were provided by U.S. EPA’s Office of Research and Development (ORD) using leaching test 

methods being developed as proposed EPA Method1313,

1 Method 1314,2

and Method 1316.

3

These leaching methods are part of the Leaching Environmental Assessment Framework (LEAF) 

developed by a collaborative research effort between the U.S. EPA, Vanderbilt University, and 

Dutch and Danish partners.4These methods have not been endorsed by EPA but are currently 

under review for inclusion in EPA’s waste testing guidance document, SW-846.

5

EPA originally 

proposed using the LEAF data in its 2011 Notice of Data Availability (NODA).6 However, 

several commenters on the proposed rule and on the 2011 NODA indicated that EPA must 

consider appropriate liquid-solid (L/S) ratios and pHs to properly use the LEAF data. This 

document summarizes how EPA is considering using these data as input source terms for 

modeling landfill leachate migration in ground water in its revised risk assessment.

The ultimate goal is to use the LEAF data as a more accurate set of leachate data over time for 

EPA’s Composite Model for Leachate Migration with Transformation Products (EPACMTP). To 

do so, EPA is considering using site-specific information (i.e., coal type combusted, CCR type 

and field leachate pH) and constituent specific leaching concentrations to choose an appropriate 

Method 1313 data point. Since Method 1313 uses only a single L/S ratio, EPA is further 

considering using Method 1314 and Method 1316 data to scale the concentrations to the 

appropriate L/S ratio. Finally, EPA is considering converting the L/S partitioning curve into a 

function of leaching over time based on the recharge rates (infiltration rates) used in a given 

model simulation. EPA is considering these steps because it will provide EPACMTP landfill 

leachate inputs that are correlated to other site-specific and nation-wide inputs, and thus be more 

accurate. The steps EPA is considering using for performing such a Monte Carlo simulation are

listed below: 

1. Select a site; this provides site specific conditions such as landfill geometry, and 

precipitation and recharge rates.

2. Select the coal type combusted at the selected site. 

3. Select a CCR sample from a set of CCR samples; CCR samples vary depending on the 

type of coal combusted at the selected site and the air pollution control technology 

employed.

4. Select a chemical constituent.

 

1 Method 1313: Liquid-Solid Partitioning (LSP) as a Function of Eluate pH for Constituents in Solid Materials 

Using a Parallel Batch Extraction Procedure - http://vanderbilt.edu/leaching/downloads/test-methods/

2 Method 1314: Liquid-Solid Partitioning (LSP) as a Function of Liquid-to-Solid Ratio for Constituents in Solid 

Materials Using an Up-flow Percolation Column Procedure - http://vanderbilt.edu/leaching/downloads/test-methods/

3 Method 1316 Liquid-Solid Partitioning (LSP) as a Function of Liquid-to-Solid Ratio for Constituents in Solid 

Materials Using a Parallel Batch Extraction Procedure - http://vanderbilt.edu/leaching/downloads/test-methods/

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http://vanderbilt.edu/leaching/leaf/

5

http://www.epa.gov/osw/hazard/testmethods/sw846/index.htm

6

76 FR 63252 (available at http://www.regulations.gov/#!documentDetail;D=EPA-HQ-RCRA-2011-0392-0001) 
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5. Generate a value of pH to be used for the simulation based on the probability distribution 

reported for field observations in U.S. EPA (2009).7

6. Select the leaching concentration from the Method 1313 data that corresponds to the 

simulation pH if the sample was analyzed at that pH, or interpolate to that pH from 

available data.

a. If the simulation pH is in a washout controlled zone (i.e., where the constituent 

leached is not limited by its solubility at that pH), then initial concentration is

obtained by scaling the Method 1313 data based on Method 1314 and 1316 results

to adjust for the liquid-to-solid ratio at the sample porosity. 

7. If the simulation pH is in a solubility controlled zone (i.e., where the constituent leached 

is limited by its solubility at that pH), then the leaching concentration obtained based on 

Method 1313 need not be adjusted. Select the mass available for leaching of the species

as indicated by the maximum leachate value across full range of pH results for Method 

1313.

8. From the mass available for leaching and the leachate concentration derived in the 

previous two steps, calculate the L/S ratio (LSmax) at which the full mass available for 

leaching will have leached out (if necessary accounting for the L/S at which a constituent 

leaves the washout controlled zone as indicated by Methods 1314 and 1316).

9. The liquid-solid partitioning curve as a function of the L/S ratio can be converted to a 

liquid-solid curve as a function of time, based on a direct relationship derived in U.S. 

EPA (2006).

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In this relationship, L/S ratio reached per year is directly related to time,

site-specific information on recharge rate, landfill depth, and density of the landfill.

10. Repeat steps 5 through 9 N times for sufficient realizations of the pH to conduct risk 

assessment modeling with EPACMTP.

The general Monte Carlo simulation framework is shown in Figure 1. The framework can be 

used to generate distributions of source term for all constituents, ash concentrations, coal type 

combusted, and site characteristics.

 

7 U.S. EPA (Environmental Protection Agency). 2009. Characterization of Coal Combustion Residues from 

Electric Utilities – Leaching and Characterization Data. EPA-600/R-09/151. Office of Research and 

Development. Research Triangle Park, NC 27711. December.

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U.S. EPA (Environmental Protection Agency). 2006. Characterization of Mercury-Enriched Coal Combustion 

Residues from Electric Utilities Using Enhanced Sorbents for Mercury Control. EPA-600/R-06/008. Office of Research 

and Development. Research Triangle Park, NC 27711. February.
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Figure 1. Framework for assessing distribution of leaching source term.

Select a site

Select a coal type burned

Select a CCR sample

Select a constituent

Generate a simulation pH

Obtain leaching concentration and 

availability from CCR data table

Washout Controlled: 

Scale concentration 

based on 1314 and 1316 

Calculate LSmax 

Solubility Controlled: 

Calculate LSmax 

Convert constituent concentration to a 

function of time using L/S per year 

equations and inputs for specific sites

N times

Distribution of source term as 

a function of L/S or time