Analysis of Release from Single-Shell Tank at Hanford

RAC was tasked with carrying out an independent evaluation of the fate and transport of releases of hazardous chemicals and radioactive materials from Hanford’s single-shell tank system and the subsequent environmental and health risks associated with past and potential future releases. The project sought to address concerns of the Washington Office of the Attorney General and the Washington Department of Ecology over delays on the part of the U.S. Department of Energy in the remediation schedule that increased the likelihood of additional releases and associated risks to the environment and human health. It was anticipated that RAC’s work product would be used to provide technical support for ongoing litigation that sought to accelerate the rate of cleanup of the single-shell tanks.

The scope of work consisted of tasks leading up to the potential preparation of an expert report and the provision of expert testimony at discovery depositions and before the court. These tasks included a review of project documents, the characterization of contaminant source terms, flow and transport modeling in both the vadose zone and aquifer, and assessment of the projected risks. RAC published a technical report and also provided training to Department of Ecology personnel on groundwater transport modeling and dose assessment.

The independent modeling conducted by RAC included source term screening and unsaturated and saturated flow and transport modeling. Iodine-129 and Cr were identified as key radionuclides and chemicals. Concentrations of I-129 and chromium in the aquifer where it discharges to the Columbia River were well below regulatory limits of 1 pCi L–1 and 48 μg–1, respectively. Near the source, I-129 and Cr concentrations would likely exceed the regulatory limit.


Investigation of Deposition Velocities and Atmospheric Transport Models Used in Radiological Safety Assessments

RAC was contracted by U.S. Department of Energy to investigate the default deposition velocity used in the MELCOR Accident Consequence Code System (MACCS) as applied to a safety analysis of the Waste Treatment and Immobilization Plant at the Hanford Reservation. As part of this investigation, RAC compared the MACCS atmospheric transport model (a Gaussian Plume Model) with Lagrangian puff atmospheric transport models that are capable of assessing transient releases in a spatially variable meteorological wind field. RAC was invited to present their findings to the Defense Nuclear Facilities Safety Board.

RAC concluded that the default deposition velocity used in MACCS was too high, but other conservatisms in the atmospheric transport model more than compensated for the difference in doses using a lower deposition velocity.


J.E. Till, A.S. Rood, C.D. Garzon, and R.H. Lagdon. 2014. “Comparison of the MACCS2 Atmospheric Transport Model with Lagrangian Puff Models as Applied to Deterministic and Probabilistic Safety Analysis.” Health Physics, 107, 213-230.


Audit of Los Alamos National Laboratory for Compliance with the Clean Air Act

RAC was asked by the Department of Justice to perform a series of technical audits of Los Alamos National Laboratory for compliance with the Clean Air Act, 40 CFR 61, subpart H. The project was initiated by a lawsuit filed by Concerned Citizens for Nuclear Safety (CCNS) against the U.S. Department of Energy and the former director of Los Alamos National Laboratory. Settlement of the suit required that the audits be performed by an organization agreed to by all parties, and RAC was chosen as the independent auditor.

The first audit began in 1997 and evaluated compliance for the year 1996. Most significantly, RAC determined that LANL did not meet certain regulatory and technical requirements and was not in compliance with 40 CFR 61, subpart H, for 1996. However, it was considered unlikely that the Laboratory exceeded the 10 millirem per year dose standard prescribed in the regulation.

A second audit was conducted in 2000, and it was concluded that LANL was in compliance with 40 CFR 61, subpart H for the year 1999. Most notably, the audit team commended the Laboratory for addressing the findings of the first audit and for the concerted effort that was put forth during the audit to make it an open, thorough, and responsive process. Credit for this achievement was also due to CCNS, who, as a citizens’ organization, helped initiate the audit and design its format.

A third audit was conducted in 2002 when it was concluded that LANL was in compliance with 40 CFR 61, subpart H for the year 2001. RAC’s audit team noted that LANL made significant changes to improve the compliance program over the period of the audits, many in response to recommendations made within the audit reports. This was the third audit of its kind, and the audit team concluded there were no substantive deficiencies requiring corrective actions that justified a fourth audit under the Consent Decree. Therefore, RAC considered that all audit requirements under the Consent Decree were met and that the process was completed.

Final Report on 1st Audit (Adobe PDF)
Final Report on 2nd Audit (Adobe PDF)
Final Report on 3rd Audit (Adobe PDF)