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A-1 Radionuclides Selected for Hydrogeological and Risk Assessment Modeling. .. A-5 A-2 Extremes and Statistically-Derived Boundaries and Depth-Defined Boundaries of Modeled Release Zones for Radionuclides

Justification: This Record of Technical Change (ROTC) is required to update the Corrective Action Investigation Plan (CAIP) for Corrective Action Unit (CAU) 410: Waste Disposal Trenches, Tonopah Test Range (TTR), Nevada, and allow for the proposed removal of contaminated soil from Corrective Action Site (CAS) 03-19-001, Waste Disposal Site. It is proposed that the work be completed as supplemental field activities to the CAIP/Data Quality Objectives (DQO) process and will focus on the excavation, segregation, and separation of soil, debris, and stained soil. It is anticipated that the remaining area of the CAS will be free of contamination greater than preliminary action level (PAL) concentrations and preclude the need for additional corrective actions at CAS 03-19-001. Therefore, a Corrective Action Decision Document /Closure Report (CADD/CR) will replace the planned CADD. Changes Section 4.2.5 CAS 03-19-001, Waste Disposal Site Delete paragraphs added in ROTC No. 1 for this section and replace with the following paragraphs: "Based on available analytical data from CAU 405 and previous investigation results for CAU 410, the contamination appears to extend to a depth of 9-ft bgs where FSLs were exceeded for TPH DRO. Supplemental field activities at this CAS include defining the site boundaries based on available data and sample locations identified during the previous investigation results for CAUs 405 and 410. Corrective Action Site 03-19-001 is bounded by sample No. ss4lf06 in the northwest corner, No. 41003006 in the southeast corner, and No. 41003003 in the southwest corner. The northeast boundary has not been defined. Technical Change No. 3

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