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PRIMEX TECHNOLOGIES Corrective Measures Study Workplan, EPA ID No. CAD 000 626 762 May 2000 4.2 Remediation Method for AOC #4 Excavation to a depth of approximately 4 feet bgs is proposed over an area measuring 6 feet by 6 feet, centered on AOC 4-4 (Figure 3). A portion of the existing concrete pad will be broken out and removed prior to excavation. Excavated soil will be stockpiled on VisqueenTA° and covered pending profiling for disposal off-site. One bottom and four (4) sidewall confirmation soil samples will be collected from the excavation, delivered under chain of custody to a state certified laboratory and analyzed for TPHd and 0&G. Section 6.0 of this WP describes the soil sampling and reporting procedures. The turnaround time for the confirmation soil samples will be 48 hours. If all of the analytical results are less than 1,000 mg/k\Kg, the excavation will then be backfilled with clean fill. If any of the confirmation sample results exceed 1,000 mg/Kg, an additional 2 feet of soil will be excavated from the location where the elevated concentrations were detected. Additional confirmation soil sample(s) will be collected from the bottom or sidewall as appropriate, delivered under chain of custody to a state certified laboratory and analyzed for TPHd and O&G. 5.0 SWMU #21 — CORRECTIVE MEASURES All RFI Field Investigation sample analytical results from SWMU #21 indicated concentrations of petroleum hydrocarbons exceeding 100 mg/Kg. Additional step-out samples are recommended, followed by remediation and confirmation sampling as described below. 5.1 Step-Out Sampling & Analysis at SWMU #21 Based on the results of the RFI Field Investigation, additional step-out sampling and analysis are first needed to better assess the extent of petroleum hydrocarbons impact present in soil. Seven (7) soil borings, at locations indicated on Figure 4, will be installed to approximately 15 feet bgs, or bedrock, for collecting sail samples for analysis. Sampling procedures are described in detail in Section 6 of this WP. A sample collection interval of 2'/2 feet is proposed, Solil samples from 2'/2 and 5 foot bgs will be analyzed for TPHd and 0&G. Soil samples from deeper depths will be held at the laboratory for analysis, if required. If the results from a 5-foot sample from a boring exceed 100 mg/Kg, the 7% and 10-foot samples will be analyzed on a quick turnaround (24-hour). Likewise, if a 10-foot sample exceeds 100 mg/Kg, the 12% and 15-foot samples will be analyzed on a quick turnaround (24-hour). In this manner, the vertical extent of petroleum hydrocarbons in soil will be determined. In order to assess the horizontal extent of petroleum hydrocarbons in soil, the decision to step-out an additional 5 feet will be made by the project management team in the field based on visual and analytical results form the seven borings. The step-out CHOW ENGINEERING, INC. 5