Corrective Action Decision Document/Closure Report for Corrective Action Unit 274: Septic Systems, Nevada Test Site, Nevada, Rev. No.: 0

This Corrective Action Decision Document/Closure Report has been prepared for Corrective Action Unit 274, Septic Systems, Nevada Test Site (NTS), Nevada in accordance with the ''Federal Facility Agreement and Consent Order'' (1996). Corrective Action Unit (CAU) 274 is comprised of five corrective action sites (CASs): (1) CAS 03-02-01, WX-6 ETS Building Septic System; (2) CAS 06-02-01, Cesspool; (3) CAS 09-01-01, Spill Site; (4) CAS 09-05-01, Leaching Pit; and (5) CAS 20-05-01, Septic System. The purpose of this Corrective Action Decision Document/Closure Report is to provide justification and documentation supporting the closure of CAU 274 with no further corrective action. To achieve this, corrective action investigation (CAI) activities were performed from November 14 through December 17, 2005 as set forth in the CAU 274 Corrective Action Investigation Plan. The purpose of the CAI was to fulfill the following data needs as defined during the data quality objective (DQO) process: (1) Determine whether contaminants of concern (COCs) are present. (2) If contaminants of concern are present, determine their nature and extent. (3) Provide sufficient information and data to complete appropriate corrective actions. The CAU 274 dataset from the investigation results was evaluated based on the data quality indicator parameters. This evaluation demonstrated the quality and acceptability of the dataset for use in fulfilling the DQO data needs. Analytes detected during the CAI were evaluated against final action levels (FALs) established in this document. No analytes were detected at concentrations exceeding the FALs. No COCs have been released to the soil at CAU 274, and corrective action is not required. Therefore, the DQO data needs were met, and it was determined that no corrective action based on risk to human receptors is necessary for the site. All FALs were calculated using the industrial site worker scenario except for benzo(a)pyrene, which was calculated based on the occasional use scenario. Benzo(a)pyrene was detected above the preliminary action level at CAS 20-05-01; however, it was not identified as a COC because the concentration was below the FAL. As a best management practice and to ensure that future site workers are not exposed to this site contaminant for more than this decision-basis exposure duration, an administrative use restriction was established around the leachfield at CAS 20-05-01. In addition, the removal of the septic tanks and septic tank contents at CASs 03-02-01, 06-02-01, and 20-05-01 was performed