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PRIMEX TECHNOLOGIES • • Corrective Measures Study Workplan, EPA ID No. CAD 000 626 762 May 2000 sample locations in the former aboveground tank (now machine shop) area (location numbers SWMU21-S13 and S14) will be collected first and analyzed while the other step-out samples are being collected. If results from the center of the former tank area exceed 100 mg/Kg, step-out samples on the far side of the tank area will be added (and will be performed during the same mobilization). Likewise, the remaining step-out samples will be analyzed on a quick turnaround to determine if additional borings will be required. In this manner, the soil will be characterized in one drilling mobilization. 5.2 Corrective Measure Alternatives for SWMU #21 Given the concentrations of petroleum hydrocarbons detected at SWMU #21 and their proximity to the surface, the 'no action' alternative would not be feasible. Soil excavation is the proposed corrective measure over the in-situ remediation method, in order to expedite the closure of the area. Therefore, it is proposed that sampling and quick turnaround of analysis (e.g., 48 hours) will be performed allowing for expedited definition of the hydrocarbon-impacted soil followed by excavation of soil during the same site mobilization. 5.3 Remediation Method for SWMU #21 Based on the step-out soil sample results, performed as a part of this WP, the area and depth of excavation at SWMU #21 will be determined by the project management team. The goal of the excavation will be to remove soil impacted with concentrations of petroleum hydrocarbons exceeding 1,000 mg/Kg. An exception to the 1 ,000 mg/Kg remediation level will occur if analytical results form soil samples collected from under the former aboveground tank (AGT), now the location of the machine shop building, area indicate elevated concentrations of petroleum hydrocarbons. In this case, unless the hydrocarbons are shown to be migrating, the petroleum hydrocarbon impacted soil located beneath the AGT will be considered to be capped by the cement floor of the former AGT. The SWMU #21 excavation is not anticipated to include saturated soil as groundwater is considered to be approximately 50 feet bgs at the site. Excavated soil will be stockpiled on VisqueenTm and covered pending profiling for disposal off-site. 6.0 SAMPLING PROCEDURES Two types of soil samples will be collected during implementation of this workplan, step-out samples and confirmation samples. The analysis program will be conducted in accord with Table 1 of this WP. CHOW ENGINEERING, INC. 6