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SAP Addendum Specific to Field Sampling Plan for Subsurface Soil Boring Activities at AOC-65 and AOC-67 under AETC DO 5084
Section 2 - Soil Gas Survey Overview
Soil gas surveys will be performed at two adjacent AOCs (65 and 57) located within the southwest quadrant of CSSA. AOC 57 is approximately 65 acres in size, and AOC 65 is approximately 5 acres in size. AOC 65 is located primarily inside Building 90 and extends approximately 100 feet from the building in all directions. The total area to be surveyed is approximately 70 acres.
The soil gas survey will be established as one contiguous grid of sampling points covering the area. The sampling effort will be established on a 100-foot grid throughout AOC 57, and will tighten to 25-foot grids in the vicinity of Building 90 (AOC 65) or other areas identified as potential hot spots within the 70-acre tract. The combined sampling grids are expected to yield approximately 600 individual sample locations. Only one soil gas sample will be collected per grid location. The effort will consist of establishing the grid, and performing the systematic sample collection followed immediately by analysis by the mobile laboratory.
Past soil gas work has demonstrated that the soil/bedrock is relatively shallow, and that the probes typically cannot by driven below 4-6 feet below grade. A geoprobe rig will be used to drive (hammer) the probes into the ground, and to retrieve the probes after the soil gas sample has been extracted. A pneumatic hammer and jack will be used to drive and retrieve rods in areas not accessible to the geoprobe rig. Samples will be obtained in Tedlar� bags under vacuum, and analyzed by a field gas chromatograph for benzene, toluene, ethylbenzene, xylenes (BTEX), vinyl chloride, PCE, TCE, trans-1,2-DCE, and cis-1,2-DCE. The parameter vinyl chloride was added to the SAP for this specific survey, and the calculation of total hydrocarbons was removed from the SAP for this specific survey. In accordance with the SAP, each sample will also be field screened for oxygen and explosive gases (lower explosive limit) using a direct read instrument, such as an HMX 271 explosimeter.
Each of the grid points will be surveyed with a GPS receiver with one-meter accuracy. A Parsons ES chemist will perform one on-site laboratory audit during the initial week of testing (a one-time, one-day audit) to evaluate the performance of the mobile laboratory. In addition, electronic data will be managed as described in this plan addendum on a daily basis during the active testing periods.
2.1 - Procedures for Sampling Activities
No modifications are needed to the soil gas sample collection methodology described in the SAP. A geoprobe rig equipped with a hammer and hydraulic lift will be utilized to drive the soil gas probes into the ground. The hydraulic lift will assist with partial removal of the probes to allow sample collection, and complete removal of the soil gas probe rods after sample collection is complete. A pneumatic hammer and jack will be utilized in portions of the grid where access for the geoprobe is limited (such as on slopes). The geoprobe rig is equipped with a concrete bit, and will be used to cut access through asphalt and concrete in the paved portions of the grid.
2.2 - Contaminants of Concern and Analytical Methods
The contaminants of concern include the BTEX compounds, vinyl chloride, TCE, PCE, trans-1,2-DCE, and cis-1,2-DCE. The mobile laboratory will analyze these compounds using modified SW846 method 8021. Preliminary sample results, quality control data, method detection limits (MDLs) and reporting limits (RLs) will be reported electronically on a daily basis to the Parsons ES chemist in charge of receipt and management of the data. Complete data packages in ERPIMS format will be submitted to Parsons ES within 14 days of the sample collection date for validation and verification.
Soil gas samples will be analyzed with a gas chromatograph (Shimadzu GC-14A) equipped with a photoionization detector (PID) as the primary detector and a Hall electrolytic conductivity detector as the secondary detector. Results from the PID are used for quantitative determination. The Hall detector is used for confirmation of chlorinated compounds only.
The chromatographic column used for analysis is DB-624 (3mm), 75 meters long, 0.53 mm id megabore. This column was selected for use since it is able to separate the compounds targeted for analysis and allows for a relatively rapid analysis time. The standard operating procedures for implementing modified SW846 method 8021 are provided in appendix B of this addendum.