Docket Report EPA Region 8, Solid and Hazardous Waste ConocoPhillips Billings Refinery, Billings, Montana D elisting Petition

RE: Risk Evaluation for M anagement in a Subtitle D Landfill

The Environmental Protection Agency (EPA) and the ConocoPhillips Bill ings Refinery used t he Delisting Risk Assessment Software (DRAS) version 3 .0.34 to evaluate the petitio ned waste. Both EPA and ConocoPhillips entered s ite

- specific parameters into DRAS including maximum annual waste volume and maximum observed total and l eachate concentrations of hazardous constituents in the waste. EPA used Region 8 specific target cancer and hazard levels (1x10 - 6

excess aggregate cancer risk, hazard index of 0. 1) to evaluate the waste and ConocoPhillips ran the DRAS program at the model default hazard levels of 1x10 - 5 excess aggregate cancer risk, and hazard index of 1.0. EPA independently ran the DRAS at the same hazard levels as ConocoPhillips to confirm their results. Identical risk assumptions and model inputs produced identical outp uts for both t he ConocoPhillips and EPA DR AS model runs ; the ConocoPhillips program output is attached.

In addition to the lower target risk levels EPA Region 8 set the DRAS nominal total limits to 1

, 000 mg/kg rather than the DRAS model default of 10,000 mg/kg (1%). Because this is a potential multiyear delisting Region 8 felt the lower target risk limits were appropriate. Use of a nominal upper total concentration of 1

, 000 mg/kg also defines a maximum nominal TCLP limit, since the latter can be no more t han 1/20 th the total value to conform to the TCLP analytical procedure using a 20 :1 dilution of a solid sample. This result s in several compounds having TCLP concentration limits of 50 mg/L

. Constituents that were analyzed in the ConocoPhillips samples but are not a preloaded in the DRAS model were evaluated at the nominal limit of 1000 mg/kg , resulting in a TCLP limit of 50 mg/L.

. Some geological considerations of prevalence as well as known potential risks were taken into
account. The nominal upper limi t for barium and zinc was set at 10,000 mg/kg due to low overall toxicity and higher natural abundance. For beryllium, cadmium and mercury with high toxicities and low prevalence, low overall total limits (25

- 50 mg/kg) were chosen. Arsenic is the only cons tituent that did not meet the target risk criteria for TCLP. For arsenic a risk level of 10 - 5 ; HQ=1.0, was selected as an appropriate limit and one that is very constraining (roughly twice the current maximum). This limit will maintain levels close to the present. Two additional constituents, naphthalene and 1,4

- dioxane, have DRAS limits set at 10 - 5 ; HQ=1.0, to allow for future variability in analytical detection limits.

If the allowable risk levels exceed the RCRA definitions of characteristic hazardous levels (flammability, corrosivity, reactivity and especially toxicity) the latter levels prevail. Hazardous concentration limits for toxicity (40 CFR 261.24) are based on TCLP analysis. Concentration limits for nine constituents are based on the TCLP limi ts for RCRA hazardous toxicity characteristics found in 40 CFR 261.24.

The aggregate cancer risk and hazard index for the petitioned waste me e t the criteria set by Region 8

. The risk analysis estimated the t otal aggregate canc er risk from constituents de tectedin the waste to be 6.32 x 10 - 6

. The risk analysis estimated i ndividual constituent cancer risks

well below EPA Region 8 ’s target of 1 x 10 - 6 . With the exception of arsenic, individual cancer risks ranged from 10 - 8 to 10 - 13 . Arsenic total cancer ris k is estimated to be 5.24 x 10 - 6

. F urthermore, the analysis estimated t otal aggregate hazard index (a sum of hazard quot ients) from constituents detected in the waste to be 0.0 37 6 , well below EPA Region 8 ’s target of 0. 1.

Note that the final aggregate calculation does not agree with the final table Aggregate Risk and Hazard Quotient Results from DRAS ver sion 3.0. T he Agency noted a problem with aspects of the DRAS version 3.0 aggregate calculation related to the handling of non

- detects. The calculatio n was redone o n a spreadsheet and is attached

.