A soil vapor extraction (SVE) pilot test system was constructed at the solid waste management unit (SWMU) Burn Area 3 (B-3) located at Camp Stanley Storage Activity (CSSA) from February 19 to February 23, 1996. A limited, two week initial pilot test was performed (1) to determine the air permeability at the site, (2) to evaluate the influence of the extraction wells on the subsurface soil gas conditions inside the trench area and in the surrounding native limestone material, (3) to determine the emitted vapor concentrations before, during and after the test, and (4) to estimate the approximate volume (or amount) of volatile organic compounds (VOC) that can be removed from the tested configuration. The results of this testing demonstrated that an SVE system operated at the site could significantly reduce the VOC concentrations present in the trench area. The results also indicated that the subsurface soils at the site are very complex, and that it would be difficult to extrapolate the pilot test results across the entire site without the collection of additional data.

This addendum to the initial pilot test work plan (Parsons ES, 1996a) describes the additional data collection activities that will be performed at the site. The purpose of this addendum is to describe the general procedures required to further evaluate the efficiency of the SVE pilot system and to collect data for determining optimal operating parameters for the expansion and long-term operation requirements of the system to remediate VOC contamination at the site. As an addendum, this document does not reiterate the items already discussed in the plan, and focuses only on the changes that are hereby incorporated into the plan, and the important factors that assisted in the design of the expanded test system.

The primary tasks of this phase of the SVE pilot test are briefly outlined below.

1. An initial system check to evaluate the system performance, collect initial soil gas chemistry data, and determine VOC removal rates after numerous weeks of continuous air extraction.

2. Drill and sample up to 12 soil borings and install vapor extraction wells (VEWs) in each boring.

3. Collect at least five confirmation soil samples to assess the removal of volatile organic compounds (VOCs) during SVE operation from soils adjacent to the locations initially sampled during installation activities in February 1996, prior to initiating any air extraction from the existing system.

4. Monitor soil gas at each VEW and vapor monitoring point (VMP) after shutting off the extraction blower to determine recovery rates of volatile hydrocarbons in soil gas and to measure oxygen consumption.

5. Periodic testing of at least three different extraction configurations to determine the effective radius of influence of each VEW.

6. Design and install an automated timer and moisture separator drain for the blower system.

7. Prepare a technical/treatability investigation report for the SVE pilot test, including a design for a short-term (up to one year) treatability test system and a conceptual design of the full-scale treatment unit.

This addendum is organized into the same six sections as the work plan, including site conditions in Section 2, SVE pilot system expansion in Section 3, reporting requirements in Section 4, a tentative performance schedule in Section 5, and Section 6 includes the references. The specific changes and additions to pilot test procedures are primarily included in Section 3.

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