## 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, 20122

Algorithms to Pre

- Process Leaching Data to Generat e Source Term s for Modeling Landfill Leachate Migration in Ground Water

CCR l eaching data for probabilistic fate and transport modeling of CCR s managed in landfills

w ere provided by U.S. EPA ’s O ffice of R esearch and Development (ORD) using leaching test methods being developed as proposed EPA Method 1313

, 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. 4 These 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 term s 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 convert ing 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

. T he 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 rate s

.

2. Sel ect 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 Partition ing (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.e du/leaching/downloads/test

- methods/

4 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 )3

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 sampl e 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 scal ing the M ethod 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 b ased 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 av ailable for leaching and the leachate concentration derived in the previous two steps, calculate t he L/S ratio ( LS max ) at which the full mass available for leaching will have leach ed out (if necessary accounting for the L/S at which a constituent leaves the washout controlled zone as indicated by Method s 1314 and 1316 )

.
9. T he liquid

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

- solid curve as a functio n of time

, based on a direct relationship derived in U.S. EPA ( 2006)

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

- specific information on recharge rate, landfill depth, an d 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 f or all constituent s, 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. Dec ember.

8 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.4 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 LS max Solubility Controlled : Calculate LS max

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