Investigations at several low, medium, and high priority SWMUs at CSSA are currently taking place as described in Sections 1 through 6 of this work plan. This addendum is added as Section 12 to the work plan. The work proposed at the twelve Areas of Concern (AOCs) and one Solid Waste Management Unit (SWMU) are similar investigative activities that have been performed routinely at CSSA. The same methodologies and project controls established during previous work (Sections 1 through 4) are still valid for this addendum.

This addendum (Section 12 only) describes investigations and closure activities to be carried out at twelve AOCs (35, 36, 37, 38, 39, 40, 41, 42, 43, 50, 65, 66), and investigations/closure activities at one additional medium priority SWMU (B-9). The locations of these sites are shown in Figure 12.1. A brief description of each of the sites addressed in this addendum is provided in Table 12.1:

Table 12.1 - Sites Included in this Addendum

This document was prepared by Parsons Engineering Science (Parsons ES) for CSSA under the U.S. Air Force AETC Contract F41689-96-D-0710, delivery order 5068, dated September 30, 1999. This section is an addendum to the RL17 work plan (Sections 1 through 4). It describes the scope of investigation and closure activities at the additional AOCs and SWMU.

12.1 - Description of DO 5068 Study

12.1.1   Purpose

The objectives of the work at the twelve AOCs (35, 36, 37, 38, 39, 40, 41, 42, 43, 50, 65, 66) and the SWMU B-9, are similar to the objectives listed in Section 1. In short, the overall objectives are to collect sufficient data to determine if each of these sites can be closed; and if possible, to close them. If the AOCs and the SWMU meet RRS1 closure requirements, an effort will be made to obtain certified closure from the TNRCC. A detailed description of the closure standards and their associated requirements is provided in Section 2.2.

12.1.2   Scope of DO5068 Work

This addendum describes the following tasks:

12.2 - Rationale and Methodology

The following sections describe the rationale and methodology of the additional field actions at sites. Section 2.3 includes a general description of the field investigation.

12.2.1   Field Efforts

The field efforts to be conducted at the thirteen sites addressed in this addendum are summarized in Table 12.2 below.

Table 12.2 - Summary of Field Efforts, DO5068 Work Plan Addendum

The procedures for field sampling will follow those described in Section 2 of the work plan, the FSP (Parsons ES, 1996a), and the DO5068 FSP addendum. Media to be sampled include those listed in Table 12.3 below.

Table 12.3 - Summary of Field Sampling, DO 5068 Work Plan Addendum

The number of samples to be collected at each site is described in the site-by-site descriptions. Sample collection and handling techniques will follow the Sampling Analysis Plan (SAP) for SWMU Closures at Camp Stanley Storage Activity (Parsons ES, 1996a) and the DO5068 FSP addendum. Analytical techniques will follow procedures described in Test Methods for Evaluating Solid Waste, U.S. Environmental Protection Agency, SW-846 and Version 3.0 of the HQ AFCEE QAPP (AFCEE, 1998).

Four types of field quality control (QC) samples will be collected during the investigative effort. QC samples to be collected include equipment blanks, field duplicate samples, trip blanks, and matrix spike/matrix spike duplicate (MS/MSD) samples. Sample descriptions, identifications, and frequencies required are described in detail in the SAP (Parsons ES, 1996a).

12.2.3   Geophysical Surveys

For AOCs 35, 42, 43, and SWMU B-9, Parsons ES will perform geophysical surveys to locate and delineate potential buried wastes. The geophysical surveys will include both EM and GPR survey tools. The electromagnetic survey will utilize a Geonics EM31 instrument with datalogger capability to measure both in-phase and quadrature signals. The GPR instrument is an SIR-2 equipped with a 300 megahertz (mHz) antenna.

Prior to the survey, each site will be gridded and staked to establish survey lines. The EM31 survey will range from 20 to 50-foot grids, dependent upon the survey size and terrain. The GPR survey will be conducted along grid spacings ranging from 10 to 20 feet. The corners of each site grid will be surveyed with the CSSA global positioning system (GPS) receiver. The size of each survey area is as follows:

12.2.4 Subsurface Soil Borings

If geophysical anomalies are identified during those surveys discussed in Section 12.2.3, soils borings will be drilled at AOCs 35, 42, and 43 to a maximum depth of 10 feet each. Two samples will be collected from each boring in accordance with the sampling and analysis plan addenda. Anticipated sampling depths are at the depth of the detected anomaly and the total depth of the boring. The following table lists the number of borings, samples, and analytical parameters for each site:

At sites were no subsurface anomalies are detected by the geophysical surveys, soil borings and subsurface sampling may be replaced by surface sampling as the closure activity. Such changes to the SOW will require a contract modification before new work can proceed. Cost savings realized by the reduction of scope at these sites may allow for some additional work at other AOCs.

12.2.5   Surface Soil Sampling

For AOCs 36, 38, 39, and 40, Parsons ES will collect a maximum total of 80 surface samples (not including QA/QC) from a maximum depth of 2 feet below grade. The four sites are adjacent to each other at the northern end of the inner cantonment area, as shown in Figure 12.1. The following table lists the approximate size of each AOC:

For AOCs 36, 39, and 40, the sampling areas are predominantly long and rectangular, therefore samples will be spaced equally across the length of the site. However, AOC 38 is large (35 acres), and will require a grid coordinate system for an accurate dispersion of the sampling locations. Samples will also be collected from "hot spots" identified during prior soil gas work at the AOCs. It is expected that approximately three to four days will be required to establish the sampling locations. Samples will be collected using stainless steel hand trowels or hand augers in accordance to the SAP addenda. Each sampling location will be surveyed using the CSSA GPS receiver. At AOC 65, the concrete floor will be cored and two soil samples will be collected from the area beneath the former PCE vat.

Support for field activities will include collection of surface soil samples, analyzing the samples for trichloroethene (TCE), dichloroethene (DCE) isomers, and tetrachloroethene (PCE), and updates to the Environmental Encyclopedia hard copy, hyperlinks and GIS database. The DCE isomers are 1,1-DCE, cis-1,2-DCE, and trans-1,2-DCE.

12.2.6   Soil Gas Sampling

Soil gas surveys will be performed at three adjacent AOCs (37, 41, and 66) located just north of Well 16 and the inner cantonment fenceline as show in Figure 12.1. The size of each AOC is as follows:

The soil gas survey will be established as one contiguous grid of sampling points over the three sites (25.5 acres). The sampling effort established on a 100-foot grid is expected to yield no more than 140 individual sample locations. Only one soil gas sample will be collected per grid node. The effort will consist of approximately three to four days of establishing the sampling grid, followed by ten days of sample collection and analysis.

Past soil gas work has demonstrated that the bedrock is relatively shallow, and that the probes typically cannot be driven beyond four to six feet below grade. Samples will be obtained in Tedlar bags under a vacuum, and analyzed by a portable field GC for benzene, toluene, ethylbenzene, xylenes, PCE, TCE, and cis-1,2-DCE. The corners of the soil gas survey will be surveyed with CSSA’s GPS receiver.

12.3 - Reporting Requirements

This section provides the reporting requirements for the AOC and SWMU closure activities provided for in this work plan. All reports will be submitted to the appropriate agencies as well as the appropriate contracting authorities.

An Informal Technical Information Report (ITIR) will be prepared and submitted to CSSA and AFCEE. The ITIR will include all analytical data, including QC results and cross-reference table.

Technical/closure reports will be prepared in accordance with state closure requirements and upon completion of activities for the investigated sites. These technical reports will discuss field activities, investigative and analytical results, and conclusions and recommendations for each SWMU listed for investigation.

In order to close an AOC or SWMU, a final report will be submitted to the TNRCC demonstrating compliance under the appropriate risk reduction standards. The report shall include, but is not limited to, the following documentation:

Certification by an independent engineer, registered in the State of Texas, that the closure plan procedures were followed and compliance of the appropriate closure standard was met.

If investigative activities conclude that a site cannot be closed under RRS1 standards, a technical summary report will be prepared in lieu of a closure report. The technical summary report will present the investigation findings and analytical results. The report will identify which closure criteria were not met, as well as outline viable options and recommendations for future closure work. Additionally, remedial alternatives which may mitigate or isolate those constituents that exceed closure criteria will be identified.

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