Frequent Questions about the Delisting Risk Assessment Software (DRAS)

On this page:

• Can I use DRAS to delist waste for disposal/treatment options other than surface impoundments or landfills? 
• What chemicals should include when I run DRAS?
• What should I do when detection levels for non-detected entries exceed the delisting limits?
• How do I assess Toxicity Characteristic Leaching Procedure (TCLP) or leachability in liquid waste samples?
• Should I use the maximum, median, or mean concentration to enter into DRAS?

Can I use DRAS to delist waste for disposal/treatment options other than surface impoundments or landfills? 

RCRA policy contains a “conditional delisting” element designed to ensure that delisted wastes are managed in a manner consistent with the risk evaluation that supports the delisting decision (Cotsworth 1998). This risk evaluation includes reasonable worst-case management scenarios of disposal in an unlined landfill or surface impoundment. The DRAS models these two scenarios because it is extremely difficult to project all other potential management scenarios that can occur once the waste is delisted.  Models for landfill and surface impoundment scenarios do not predict risks resulting from exposures to wastes that are managed in other non-disposal scenarios, including treatment prior to disposal, uses constituting disposal and other recycling practices.  To reduce this uncertainty, delistings should apply to wastes managed in the type of unit modeled in the delisting risk assessment.

What chemicals should I include when I run DRAS?

The delisting regulations at 40 CFR Part 260.22 consistently cite that additional constituents other than those for which the waste was listed must be evaluated.  Part of the reasoning for this is the original listings were not meant to be inclusive of all possible hazards.  For example, listed hazardous waste K088 - spent potliners from primary aluminum reduction – was originally listed for complexes of cyanides (261 Appendix VII).  However, when treatment standards were later promulgated for K088 under the Land Disposal Restrictions (LDR) EPA found cause to require treatment for 25 additional constituents including 13 polycyclic aromatic hydrocarbons (PAHs), 11 heavy metals and fluoride. 

EPA encourages petitioners to evaluate a broad range of potential waste constituents to meet this requirement, such as from a list of any chemical or raw material that enters the waste-generating process.  This could include information from Safety Data Sheets or historical analytical data.

What should I do when detection levels for non-detected entries exceed the delisting limits?

EPA requires an Agency-approved Quality Assurance Project Plan (QAPP) to check that laboratory reporting limits (RLs) are at or below the maximum allowable concentrations from DRAS 4 using target cancer risk and hazard quotient levels set by the delisting regulatory authority and facility-specific information such as the annual volume of waste generated.  If this process results in RLs that are not below DRAS 4 maximum allowable concentrations, we consult with our analytical chemist to consider these possible resolutions:

1. Select a commonly available analytical method with a lower RL. For example, lower RLs for metals are typical of SW846-Method 6020, compared to Method 6010.  If that doesn't work:
2. Ask the question "Do you expect the constituent to be present in the waste?"
   1. If so, look for more sophisticated analytical approaches such as GC/MS with Selected Ion Monitoring (SIMs) etc.
   2. If not, consider accepting the higher detection limit.  You may want to increase the supporting information required to justify that the constituent is not likely to be present.

To assess the potential risk or hazard from a waste constituent that may be present below the RL and reported as not detected, DRAS 4 can calculate risk based on the RL.  The user can select to run this calculation at the RL or at half the RL as the constituent concentration.  This calculation can serve as a quality check on the risk assessment by comparing aggregate risk and hazard estimates that include non-detects to risk calculations based on detected values alone.

How do I assess Toxicity Characteristic Leaching Procedure (TCLP) or leachability in liquid waste samples?

In the conduct of the TCLP test, free liquids in a sample are removed and reserved and only the solids are subject to the leaching procedure. After leaching, the reserved free-liquids are added back to the leachate before analysis. This means that a 100% liquid sample would be analyzed "as is" (as there are no solids to leach) essentially the same as a "totals" analysis.

Should I use the maximum, median, or mean concentration to enter into DRAS?

The selection of the most appropriate data for input to DRAS is best determined in consultation with the regulatory authority for your delisting decision. For delistings decided by the federal delisting program, EPA typically uses the maximum value of all samples for each individual waste constituent. We have no objection to using statistical parameters; however, we rarely have enough data points to allow for a robust statistical analysis. The more robust the statistical analysis, the more likely we may consider values toward the mean, median, or an upper bound. Poor datasets, with too few observations or nonconforming distributions, will require consideration of upper-bound or maximum values for DRAS. The overall quality of the data must also be considered when selecting data for input. We currently recommend that a prospective petitioner work with us in the case of federal delistings, or their delisting regulatory authority, to develop an appropriate quality assurance project plan including sampling and analytical methodologies and strategies prior to sample collection.