Supporting documents

1. 3 1. BRC Common Areas Soils – Closure Process Site-Wide CSM 4 Site-Wide DQOs *a Change land use Data gaps identified Sub-Area CSM  CAMU Sub-Area DQOs Sub-Area Work Plan (contains Sub-Area CSM and Sub-Area DQOs) 6 DQA 1 1 2 5 Implement Work Plan 3 4 5 Complete RA * * * * * * BRC Decision   Supporting documents Closure Plan Fail Additional excavation (per CAP) Pass Refine RA Pass NFA Determination 7 Fail Fail Link to more detail Link to notes page

2. 2. Notes Closure Process  *a *c *b 1 2 3 4 5 6 * Please refer to the Phase 3 Settlement Agreement and Administrative Order on Consent (AOC) Appendix E for additional descriptions regarding each item on the Closure Process Figure. = Deliverable which requires NDEP review and approval   = Deliverable which is considered an “evergreen” document; meaning that this document may be revised over time as additional data are collected.   = Deliverable which contains many parts and is a continuing work product (e.g.: data validation summary reports will be generated as new data are collected).   = Deliverable which represents a document or item that has been newly defined.   = Revised as requested by the NDEP or as needed. If BRC or NDEP identifies applicable changes, the specific sections of the Closure Plan or Site-Wide Conceptual Model should be resubmitted, however, it will not be necessary to resubmit the entire document.   = DQO Steps 1 and 2 should be completed at the Site-Wide level. = Work Plan implementation might involve data collection, excavation or both. = Examples include removing conservatism from a deterministic risk assessment by changing some parameter values from upper bound values to central tendency or realistic values (e.g., development of site-specific factors), or performing probabilistic risk assessment. = NDEP decision document. = Waste placement may start once the CAMU is ready to receive waste, and prior to completion of construction. Dashed lines represent possible paths back, which might be requested by the NDEP or otherwise be seen as needed.

3. Closure Process  *c *b *a *a *b * * * * * * * * * * 3. Partial List of Supplemental Documents • Site Related Chemicals Document • Background and Upgradient Conditions Documents for a variety of soil and groundwater horizons. • Dust Mitigation Work Plan • Health and Safety Plan • Perimeter Air Monitoring Plan • Field SOPs • Project QAPP • Data Validation Summary Reports (for all data sets) • Data Usability Evaluations • Evaluation of ARARs Document (may be contained in DQA) • Fate and Transport Evaluations for all media (e.g.: a variety of analytical and numerical models, as necessary)

4. Closure Process  4. Sub-Area Specific Work Sub-Area Specific Work may include a number of items. It should be noted that not all items listed below will be necessary for all sub-areas or for every iteration. v     Sub-area specific Work Plans will address data collection and the need to perform further excavation if necessary. v     Sub-area data usability evaluations. These evaluations should be completed as soon as possible. Additional evaluations will need to be completed as additional data is collected. v     Sub-area specific CSMs. A sub-area specific CSM is needed prior to the initiation of additional sampling or excavation. As excavation is completed the conditions will change and CSMs will need to be updated. In addition, as neighboring sub-areas are investigated and remediated the conditions and CSM will change. Some discussion will be needed so that the redevelopment of these sub-area CSMs is not onerous. v     On a sub-area basis DQO steps 3-7 should be considered. It is not always necessary to complete all seven steps. As work progresses the DQOs will require review. BRC will need to answer the question of whether or not they can support the decisions that are needed to be made for risk assessment. v     Modeling. Fate and transport issues may need to be addressed by analytical or numerical models. Examples of models that may need to be considered are as follows: o       VLEACH to address the soil to groundwater leaching pathway. o       Dispersion modeling for data collected from the flux chamber. o       Dust dispersion modeling to address windblown dust. v     Data quality assessment (DQA) will need to be completed on a sub-area specific basis. If this assessment passes the risk assessment can be completed. If the DQA does not pass BRC should return to the “BRC Decision” step.

5. Closure Process  5. BRC Internal Evaluations and Decisions BRC will perform internal evaluations of the confirmatory data collected (per the Statistical Methodology Document and the Corrective Action Plan) to determine a path forward. NDEP review and approval of these evaluations is not required or desired. BRC should inform the NDEP of the decision made. Examples of internal evaluations are as follows: v     Preliminary runs of the geo-statistical model to determine if additional samples or excavation is necessary. v     Preliminary runs of the risk assessment to determine if additional excavation is necessary. v     Rudimentary comparisons to ARARs to determine if additional excavation is necessary. The decisions that BRC makes here are risk-based decisions. That is, BRC will evaluate risk to the receptors identified in the CSM, and will determine if more action is required, or if the risk assessment can be evaluated with respect to DQA, and potentially for NFA determination. If BRC determines that further iteration is required, options include: refining the risk assessment (e.g., justifying different input parameters for a deterministic RA or performing a probabilistic RA); performing further excavation, which will be followed by new data collection; identifying obvious data gaps that still need to be filled; and/or, changing the land use scenario if it seems clear that the RA cannot pass without doing so. It will streamline the process if NDEP is involved in the decisions being made prior to providing the formal risk assessment deliverables.

6. Closure Process  6. Data Quality Assessment Decision Once BRC has decided that sufficient excavation and data collection has been performed to support a risk assessment, the final technical step before proceeding to completion of the risk assessment is to perform a Data Quality Assessment to verify that the project DQOs have been satisfied. This might take the form of confirming the DQOs using classical statistical techniques or it might take the form of estimating probability distributions for risk. Considerations will include: v     The geo-statistical basis for the risk assessment, if this is ultimately used. v     Background comparisons for important chemicals (risk drivers). v     Risk assessment for the different risk endpoints. EPA’s DQA guidance (EPA, G-9, Data Quality Assessment Guidance, 2006) addresses verification that DQOs have been met using the classical statistics paradigm, and provides details of statistical methods that can be used to evaluate environmental data. DQA will include exploratory data analysis, assumptions testing, statistical testing, and verification that DQOs have been satisfied. Data Quality Indicators such as representativeness and comparability can also be addressed as part of the DQA activities. Upon successful completion of the DQA, it is anticipated that BRC will complete the Risk Assessment documentation and will submit same to NDEP for review and concurrence. Note that the final NDEP review is likely to proceed more smoothly if NDEP have been involved in the decisions being made prior to providing the formal deliverables.

7. Closure Process  7. NFA Determination Once the RA has been completed, NDEP will review the final risk assessment and associated documents. Note that completion of the RA implies finalizing documentation of an RA that BRC already expects will pass, and for which NDEP has been involved in the decision process prior to receiving the formal RA deliverables Successful review and review comment responses are necessary for NDEP to support an NFA determination. Note that if NDEP does not concur with BRC’s findings then NDEP will expect that sub-area specific work will continue. BRC should inform the NDEP of the decisions made during the iterative cycle of sub-area specific work. BRC should involve the NDEP review in the decisions that are being made without providing formal Deliverables until appropriate. NDEP should review and concur with the finalized data usability evaluation, COPC selection, and EPC calculations prior to completing the risk assessment. This will streamline the review of the risk assessment and reduce the cost of unnecessary revisions of the risk assessment.

8. CAMU- AREA WORK Closure Process  *a 5 5 6 * * * * * CAMU - Area CSM Slit Trench RAS Borrow Pit HHRA Work Plan RAP Application Slit Trench ROD RAP Permit Borrow Pit HHRA Borrow Pit Excavation and CAMU Construction ( Per RAP application/ permit; Borrow Pit HHRA; CAP; and all related documents) (Per RAP permit; CAP; and all related documents) Waste Placement CAMU Closure and Post - Closure (Per RAP application & permit)

9. Glossary Closure Process  ARARs = Applicable or Relevant and Appropriate Requirements BRC = Basic Remediation Company CAMU = Corrective Action Management Unit CAP = Corrective Action Plan CSM = Conceptual Site Model DQA = Data Quality Assessment DQOs = Data Quality Objectives HHRA = Human Health Risk Assessment NDEP = Nevada Division of Environmental Protection NFA = No Further Action QAPP = Quality Assurance Project Plan RA = Risk Assessment RAP = Remedial Action Plan RAS = Remedial Alternatives Study ROD = Record of Decision SOP = Standard Operating Procedure