Section 3 - Building 90 Removal Action

The purpose of the removal action is to remove or significantly reduce the levels of VOCs present in the shallow soil material in and around Building 90. The removal activities planned for Building 90 include the characterization of contaminant mass present in the fill material, installation and operation of a subslab ventilation system, and removal of impacted soil material from specific areas west of the building.

A subslab ventilation system will be installed to remove VOCs that have accumulated in the fill material beneath the building. Following initial startup and testing of the system, CSSA and Parsons will decide if the subslab system alone will be sufficient to reduce VOC concentrations to acceptable levels or whether limited removal action beneath the building floor is warranted. Excavation of impacted soils beneath the building floor may be conducted as an alternate removal activity in the event that the subslab ventilation system proves ineffective at reducing contaminant levels. Long-term operation of the subslab system may be required if the accumulation rate of VOCs beneath the floor slab is sufficiently high.

Impacted soils along a drainline and a drainage ditch west of Building 90 will be excavated to remove soils exhibiting high levels of VOCs. If removal activities are required beneath the building, this SAP Addendum will be revised to include procedures for this activity. 

The activities to be conducted during the removal actions are summarized in the following sections. Detailed information of the Building 90 subslab ventilation system is presented in Section 3 and Section 4 of the AOC-65 Treatability Test Plan, Parsons, April 2002. Detailed information regarding the soil removal activities is presented in Section 4 of the Environmental Cleanup Plan, Parsons, April 2002.

3.1 - Building 90 Subslab Ventilation System

A subslab ventilation system will be installed to remove vapors that have accumulated beneath the building floor. The subslab ventilation system will consist of a focused SVE system that will reduce the mass of VOCs that have accumulated in the soils beneath the building as well as reduce the potential for VOC vapors to migrate into the working areas of the building. Effluent from the subslab system will be connected to the effluent of the AOC-65 SVE system and then treated using a vapor phase carbon unit. Information regarding the vapor phase carbon absorption system is included in Section 5.0. Additional information regarding the installation, startup and testing of the system is included in the following sections and in Section 4 of the AOC-65 Treatability Test Plan, Parsons, April 2002.

3.1.1   Soil Boring

Up to 12 soil borings will be performed inside Building 90 to determine the mass of tetrachloroethene (PCE) and trichloroethene (TCE) contaminants in the fill material beneath the building and to allow the construction of a subslab ventilation system. The borings will be advanced near the north vat, the suspected source vat, and other portions of the building where elevated soil gas concentrations were discovered during previous investigations. Soil analytical results will be used to determine whether removal actions beneath Building 90 are necessary or if not, identify the extent of remediation that will be required beneath the building slab. Planned soil boring locations are presented on Figure 4.1 of the Environmental Cleanup Plan, Parsons, April 2002. The analytical requirements for the Building 90 Subslab installation sampling are included in Table 1.1. Sample collection and quality assurance procedures are presented in Sections 7.2 and 9.0 of this addendum, respectively.

The fill material beneath the floor slab is anticipated to be highly-compacted gravely material, which may create difficulties with the planned sampling activities. The high compaction and presence of gravel may cause difficulties with the use of the split-spoon sampler. Additionally, drilling this material may generate significant heat that can affect the levels of VOCs in samples collected from the auger flights. Therefore, if difficult drilling conditions are encountered and representative soil samples cannot be assured, then soil samples may not be submitted for analysis. The field team lead will make the determination as to which boring samples should be submitted for laboratory analysis. In the event that difficult drilling prevents the collection of a sufficient number of soil samples to characterize the extent of impacted fill material, field screening soil gas sampling will be performed from the subslab VEWs to provide data for this assessment.

3.1.2   Vapor Extraction Wells Construction

Following completion of the soils borings conducted inside the building, Vapor Extraction Wells (VEWs) will be installed in the boreholes. The VEWs will be constructed to serve either as extraction wells or as vapor monitoring points (VMPs). Procedures for the installation of the VEWs are presented in Section 7.6 of this addendum. Detailed information regarding the design and construction the VEWs/VMPs is presented in the AOC-65 Treatability Test Plan, Parsons April 2002. 

3.1.3   Building 90 Subslab Ventilation Initial System Test

Upon completion of the installation of the Building 90 subslab system, an initial system test will be conducted. Using data collected during this initial test, an evaluation of the system effectiveness will be conducted. The initial test data will be used to determine if the system is producing adequate removal from all impacted areas, to identify areas where additional extraction wells are needed, and to evaluate the need for soil removal actions. The initial system test will include the collection of field screening and analytical soil gas samples, pressure response readings, and airflow rate measurements at specific times during the test. 

Prior to system startup, field screening and analytical soil gas samples will be collected to identify areas of high concentration and to establish a baseline for comparison of field screening results to actual contaminant concentrations. Following system startup, analytical soil gas samples will be collected at various time intervals from specific VEWs identified during the pre-startup testing. Field screening soil gas samples, pressure response, and airflow measurements will be conducted during the startup period. Sampling parameters for the field and analytical sampling conducted during the initial system check is included in Table 1.1. Soil gas sample collection procedures are described in Section 7.4 of this addendum. Detailed information regarding the initial system check for the Building 90 subslab ventilation system is presented in Section 4 of the AOC-65 Treatability Test Plan, Parsons, April 2002.

3.2 - Building 90 Removal Action

Based on previous investigation results, soils contaminated with VOCs are believed to be present under the asphalt driveway, along a drainline, and a drainage ditch west of Building 90. Soil borings will be advanced in the driveway, adjacent to the drainline, and along the drainage ditch. Soil samples will be collected from the borings to characterize the concentration and distribution of contaminants in the soils. Impacted soils will be excavated and transported off-site for disposal. Upon completion of the soil removal, the excavation will be backfilled and the asphalt driveway replaced. A summary of the soil removal activities is presented in the following sections. Additional information regarding these removal activities is included in Section 4 of the Environmental Cleanup Plan, Parsons, April 2002.

3.2.1   Soil Borings

Up to 12 soil borings will be performed outside Building 90 along the drainline, under the driveway, and the drainage ditch west of the building where releases may have o urred. Soil samples will be collected from the soil borings to characterize the concentration and extent VOCs in the soils. Analytical results of the soil boring samples will be used to determine areas requiring excavation of impacted material. Proposed soil boring locations are presented on Figure 4.1 of the Environmental Cleanup Plan, Parsons, April 2002. The analytical requirements for the Building 90 Soil Removal sampling are included in Table 1.1. Sample collection and quality assurance procedures are presented in Sections 7.2 and 9.0 of this addendum, respectively.

3.2.2   Soil Excavation Sampling

Closure certification samples will be collected from the excavation to confirm clean closure of the unit for soils. Soil samples will be collected from the sidewalls of the main portion of the excavation and will be analyzed for VOCs, ICP metals (barium, chromium, copper, nickel and zinc), arsenic, cadmium, lead and mercury. Excavation sidewall soil samples will be collected from the drainage ditch area and will be analyzed for VOCs, ICP metals (barium, chromium, copper, nickel and zinc), arsenic, cadmium, lead, mercury, PCBs and TPH. PCB and TPH analyses are included for samples collected from the ditch portion because previous data indicated low levels of both parameters. Soil samples will be collected using the surface soil sample collection procedures described in Section 7.1. Soil grab samples will be collected at intervals of one sample for every 100 linear feet of excavation sidewall.

Rock samples will be collected from the surficial bedrock material underlying the excavated soils to confirm closure of the excavation. One rock sample will be collected from the floor of the main portion of the excavation immediately west of Building 90, and will be analyzed for VOCs, ICP metals (barium, chromium, copper, nickel and zinc), arsenic, cadmium, lead and mercury. One rock sample will be collected from the excavation floor in the ditch area and will be analyzed for VOCs, ICP metals (barium, chromium, copper, nickel and zinc), arsenic, cadmium, lead, mercury, and SVOCs. No SVOC analysis is included in the sample collected from the main excavation area because of likely interference from overlying asphalt. Rock samples will be collected using the rock sample collection procedures described in Section 2.1.4 of the SAP. Selection of rock sample locations will be biased to represent portions of the excavation bottom where the highest levels of contaminants were encountered during the excavation activities.

Soil sample analytical data may be used to support regulatory closure of soil media at AOC-65. If the soil data is to be used to document closure, sample Quality Assurance/Quality Control (QA/QC) requirements should be followed. Additional information regarding the soil removal activity is included in Section 4.0 of the Environmental Cleanup Plan, Parsons, April 2002. Sample requirements and analytical parameters are included in Table 1.1.

[Next Section]