An Approach To Evaluating

Hazardous Waste Combustion Residues For Delisting



Joseph Nixon and Jerry Drake

Compliance Strategies & Solutions, Inc.






Residues from hazardous waste combustion units (e.g., ash, spent lime, scrubber water, etc.) are often classified as listed hazardous waste under the regulations implementing the Resource Conservation and Recovery Act (RCRA).  As listed hazardous wastes, combustion residue management remains subject to stringent and costly regulations from the point of generation through the ultimate point of disposal.  The U.S. Environmental Protection Agency’s (hereafter, EPA) streamlined hazardous waste delisting petition process has allowed several hazardous waste combustion facilities to greatly reduce their regulatory and financial burdens by re-classifying listed combustion residues as non-hazardous wastes, even though the residues are derived from waste streams that carry multiple waste codes.  To illustrate how other facilities may be able to reduce their regulatory and financial burdens, this paper will review the pre-petition waste evaluation process that a facility used to determine if a delisting petition was a viable option for its combustion residues.  In addition, this paper will identify potential candidates, the timeframe, and the projected costs for the delisting petition process administered by the EPA Regional Offices and State Agencies.




The RCRA regulations contain provisions that allow the petitioning of the governing Agency to exclude or “delist” a listed hazardous waste from the universe of regulated hazardous wastes.  These provisions are provided in 40 CFR 260.20 and 260.22.  For many years delistings were considered virtually unachievable and economically unfeasible.  On March 23, 2000, however, the EPA published a guidance document on delisting entitled EPA RCRA Delisting Program Guidance Manual for the Petitioner (hereafter, Delisting Guidance).1  This guidance document has provided a streamlined framework that, when followed, can provide significant regulatory relief to the successful petitioner.  By delisting a listed hazardous waste, RCRA regulated entities benefit by minimizing their cost, liability, and regulatory burden.


To successfully delist a particular waste stream, the generator must demonstrate to the Agency that the waste stream does not meet the criteria for which it was listed, exhibit any characteristics of hazardous waste, or exhibit any other factor that could cause it to be hazardous.  This demonstration must be supported by waste analysis data that accurately characterizes the physical and chemical composition of the waste stream.  Upon receipt of the data, the Agency will evaluate the waste stream to determine if future management of the waste has the potential to threaten human health or the environment. 


A major component of the Agency’s risk evaluation involves the performance of a delisting risk assessment using the Delisting Risk Assessment Software (DRAS). The DRAS is an Agency tool that computes chemical-specific exit values or “delisting levels” based on the default cancer risk level of 1 x 10-5 (i.e., 1 in 10,000) and a noncancer hazard index of 0.1.  Waste streams with constituent concentrations that do not exceed the delisting levels are prime candidates for the streamlined delisting process.


Petitioners, who want to determine if a waste stream meets the delisting levels may use the DRAS to evaluate the potential risk posed by the waste stream before submitting a delisting petition.  The following sections of this paper present a review of a pre-petition waste evaluation strategy that a petitioner has used to support a decision to pursue a delisting petition.




Anyone who is considering pursuing a delisting petition should have a sound basis for determining that the waste stream is worthy of the time and resources that will be invested in preparing the petition.   A petitioner can gain a higher level of confidence in a waste’s potential for delisting by implementing a pre-petition evaluation strategy.  The components of such a strategy include:



Further discussion of each component of the preliminary evaluation strategy is provided in the following sections of this paper.


Evaluating Existing Data


Owners and operators of hazardous waste combustion facilities are required to characterize combustion residues to determine if they are RCRA hazardous wastes.  This characterization must be supported by process knowledge and/or waste analysis data maintained in the facility’s operating record.  Facilities with existing waste analysis data may use that data to discern which waste streams generated at the facility are unlikely to be potential candidates for delisting.  For example, combustion residues for which existing data indicate that the waste exhibits the toxicity characteristic due to high concentrations of leachable metals will likely have a low probability of success in the delisting program without further treatment (e.g., stabilization).  


While existing data may be useful to screen out waste streams from further delisting consideration, the petitioner should use extreme caution in making a decision to pursue a delisting petition based solely on existing waste analysis data.  In most cases, existing data will have been collected for purposes other than delisting, and the data is not likely to address all analytical or quality assurance/quality control (QA/QC) requirements of the delisting program.   For example, a common concern with existing waste analysis data is that the minimum detection limits are often too high.  Detection limits that are too high may falsely indicated that the waste stream is a good candidate for delisting.  The petitioner may then make the mistake of relying on the existing data to make a decision to pursue a delisting petition.  However, when new data is collected to support the delisting petition, the Agency may require detection limits that are lower than the detection limits in the existing data.  Consequently, the delisting data may identify constituent concentrations in the waste stream that exceed the delisting levels computed by the DRAS.  Existing data, therefore, should be used with caution when making a decision to pursue a delisting petition.  For many waste streams, it may be necessary to collect additional preliminary data to support a more rigorous preliminary risk evaluation.


Collecting Additional Preliminary Data


Prior to performing a preliminary evaluation on the waste stream, the petitioner should consider collecting additional preliminary waste analysis data.  The data should closely resemble the data requirements necessary to support the delisting petition.  Most importantly, the data should be representative of the waste stream and should be based on the lowest possible detections limits for the constituents of concern.  As a general guideline, data for the preliminary evaluation should address the following:



As mentioned, the detection limits for the constituents of concern should be sufficiently low such so that the detection limits for individual analytes do not exceed the delisting levels that will be calculated by the DRAS.  For most analytes, the detection limits should be less than, or equal to, the practical quantitation limits provided in Appendix IX to 40 CFR 264.  Data that meet these criteria and closely resemble data required for the delisting petition will better serve the preliminary risk assessment component of the pre-petition evaluation strategy.  The data will also provide the petitioner with a more realistic view of the waste’s potential for delisting.


Performing a Preliminary Risk Evaluation


Once a petitioner has obtained data that is representative of the waste stream, a preliminary risk evaluation should be performed using EPA’s DRAS.  DRAS v 2.0 was released by EPA in April 2002, and is designed to determine whether a waste qualifies as “not characteristically toxic” for the purpose of delisting.2


Each risk evaluation performed using the DRAS is based on a waste disposal scenario in either a landfill for solid wastes or a surface impoundment for liquid wastes.  The DRAS computes chemical-specific exit values or “delisting levels” based on the default cancer risk level of  1 x 10-5 and a noncancer hazard index of 0.1.   The constituent concentrations of the specific waste stream should not exceed the established delisting levels.  In determining the allowable constituent concentrations for a petitioned waste, the DRAS sets two delisting levels for each constituent: 1) a total concentration delisting level, and 2) a leachate concentration delisting level.  The total concentration delisting level is the maximum allowable concentration of a constituent in the whole waste.  The total concentration of each constituent in the waste should not exceed the total concentration delisting level.  The leachate concentration level is the maximum allowable concentration of a constituent in leachate derived from the waste using the TCLP.  The TCLP concentration of each waste constituent should not exceed the leachate concentration delisting level.


The DRAS back-calculates a delisting level for each waste constituent and each exposure pathway that the delisting program addresses.  The DRAS generates leachate concentration delisting levels for all groundwater exposure pathways (ingestion of groundwater, dermal absorption while bathing with groundwater, and inhalation of groundwater volatiles while showering) and for two of the air inhalation exposure pathways (inhalation of volatiles from a landfill and inhalation of volatiles from a surface impoundment).  The DRAS generates total concentration delisting levels for the remaining air inhalation exposure pathways (inhalation of particulates from a landfill), the surface water exposure pathways (ingestion of surface water and ingestion of fish), and the soil ingestion exposure pathway.


To develop the final leachate concentration delisting level for a waste constituent, the DRAS calculates the constituent’s pathway-specific leachate concentration delisting levels for the groundwater pathways and the two relevant air exposure pathways, and then selects the lowest of the pathway specific values as the final leachate concentration delisting level.  Similarly, to develop the final total concentration delisting level for a waste constituent, the DRAS computes pathway-specific values for the relevant pathways, and then chooses the lowest as the final total concentration delisting level.


For carcinogenic waste constituents, delisting levels are computed using a moderately conservative default target risk level of 1 x 10-5.   For noncarcinogenic waste constituents, delisting levels are based on a moderately conservative default Hazard Quotient (HQ) of 0.1.  The default risk level and the HQ values provide an order of magnitude of safety above the established target risk level of 1 x 10-4 for carcinogens and the established Hazard Index (HI) of 1.0 for noncarcinogens.  The delisting levels for each waste constituent are the maximum concentrations (total and TCLP) allowed for the constituent in the petitioned waste, which are based on the most sensitive exposure pathway.  If the concentration of each constituent in a petitioned waste is less than the total concentration delisting level, and if the TCLP concentration for each constituent is less than the leachate concentration delisting level, the waste may qualify to exit the hazardous waste management program.  No single constituent concentration in the waste or TCLP concentration should exceed its delisting level.3


Having performed a preliminary risk evaluation using the DRAS, a petitioner can proceed with the delisting petition process with an increased level of confidence that the waste will be excluded from RCRA regulations as hazardous waste.  However, before submitting the delisting petition, the petitioner must attend a pre-petition scoping meeting with the Agency and execute an Agency-approved Sampling and Analytical Plan.


Meeting With the Agency


A petitioner who is confident in the preliminary risk evaluation results and wants to continue pursuing a delisting petition will need to attend a pre-petition scoping meeting with the Agency.  In general, the purpose of the meeting is to discuss with the Agency the nature and extent of site-specific information that must be included in the delisting petition.  The meeting also provides an opportunity for the petitioner to seek clarification on issues such as the minimum sampling and analytical requirements that will be acceptable to the Agency.


The petitioner should prepare for the meeting by developing written responses to the Pre-Petition Scoping Meeting Checklist items provided in Appendix D of the Delisting Guidance.1  This information includes:



Developing and Executing an Agency-Approved Sampling and Analytical Plan


The next component of the pre-petition evaluation strategy is developing and executing an Agency-approved sampling and analytical plan.  The purpose of the sampling and analytical plan is to define a list of constituents of concern and generate representative data to support the delisting petition.  The objectives of the plan should include:



The sampling and analytical plan is a necessary part of the pre-petition evaluation process, because it will guide the petitioner in the collection of data that the Agency will use as a basis for granting a delisting petition.  The petitioner will also benefit from implementing the Sampling and Analytical Plan, because the analytical data to be collected will provide the petitioner an opportunity to re-evaluate the risks posed by the waste before the petition is submitted to the Agency.


Re-evaluating Risks Based on Data to be Included in the Delisting Petition


Before a petitioner proceeds with developing and submitting a delisting petition, the preliminary risk evaluation should be repeated using the data that will support the delisting petition in the DRAS.  This last component of the pre-petition evaluation strategy will provide the petitioner with another opportunity to ensure that the waste constituent concentrations do not exceed the delisting levels or raise irresolvable issues during the Agency’s review of the delisting petition.





Hazardous waste combustion residues are often regulated as listed hazardous waste if they are derived from the treatment of listed hazardous wastes.  However, for well-operated combustion units, the residues are not likely to exhibit the same physical and chemical characteristics as the listed hazardous wastes that were burned in the unit.  As a result, combustion residues generated by units that routinely burn the same waste stream may qualify as potential candidates for delisting.  Such residues can include: ash, spent lime, spent carbon, scrubber waters, baghouse dust, and wastewater treatment sludges.  These same wastes may not be good candidates for delisting when they are generated by commercial and on-site hazardous waste combustion units that burn highly variable wastes from different sources.




According to the EPA’s streamlined delisting process outlined in the Delisting Guidance, a final Agency decision on a delisting petition typically takes about 180 working days after a complete petition is submitted.  During this period, the Agency will perform a technical review of the delisting petition, and the petitioner will have to respond to any minor deficiencies identified by the Agency.  If major deficiencies are identified by the Agency, the petition will be denied by the Agency or required to be withdrawn by the petitioner.  After all minor deficiencies have been addressed to the Agency’s satisfaction, a Federal Register notice will be published to provide a 30-45 day public comment period on the delisting petition.  If public comments are received, they must be addressed and incorporated into a subsequent Federal Register notice announcing the Agency’s final decision on the delisting petition.




For each delisting petition submitted to the Agency, the petitioner will incur costs associated with gathering the necessary data and preparing the petition.  These costs may be as high as $80,000 to $100,000, but can be substantially less.4  If the delisting effort is successful, the return on the petitioner’s investment will result in significant hazardous waste management cost savings.




A prospective petitioner can gain a significant degree of confidence in a waste’s ability to be delisted by following the pre-petition evaluation strategy outlined in this paper.  Each component of the strategy should be implemented by a prospective petitioner to minimize irresolvable issues that may arise after the petition is submitted.   If the outcome of the preliminary evaluation strategy indicates a favorable delisting scenario (i.e., that the waste does not exceed delisting levels), the delisting program can serve as a streamlined process to exclude the hazardous waste from RCRA Subtitle C regulations.




1.  U.S. EPA, EPA RCRA Delisting Program Guidance Manual for The Petitioner, March 23, 2002.

2.  U.S. EPA, User’s Guide for the U.S. EPA Region 6 Delisting Risk Assessment Software (DRAS), April 2002.

3.  U.S. EPA, RCRA Delisting Technical Support Document, May 2000.

4.  U.S. EPA, RCRA Hazardous Waste Delisting: The First 20 Years, June 2002.