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Environmental Cleanup Plan for AOC 65
Section 4 - Removal Action
The purpose of the removal action is to excavate soil material with high VOC levels from AOC 65. Excavating the most contaminated areas will help reduce the amount of contaminants that migrate to the groundwater and surrounding areas. Another aspect of the removal action is installation of a subslab ventilation system in Building 90. The subslab ventilation system will act similarly to a soil vapor extraction system and will expedite reduction in the mass of accumulated VOCs beneath the building, as well as minimize any possible adverse impacts from soil vapors entering Building 90.
Planning for the removal action will include determining the extent of excavations to be performed and securing the necessary approvals to proceed with the removal action (e.g., permitting). Required approvals will include the State Historical Program Office (SHPO) for modifications made to the building. Air permitting issues regarding Building 90 must also be resolved with the TNRCC. Detailed scopes of work will be prepared for drilling, analytical, and removal action subcontractors. The statement of work (SOW) for the removal action will include engineering specifications for temporary control measures and building restoration that will require CSSA approval.An investigation, described below in section 4.3 will be performed to provide a more reliable estimate of contamination in fill materials beneath Building 90 and along drain lines and ditches outside Building 90. Data collected during the investigation and subsequent subslab ventilation system installation and testing will be used to assess whether excavation inside Building 90 would be cost effective or whether the desired objective of reducing contamination to safe levels can be met with the ventilation system alone. The areal limits and depth of any excavations to be performed will be determined based on results of the investigation, plus the waste classification profile will be integrated into the SOW for the removal action subcontractor.
Soil borings will be advanced by hollow-stem auger inside Building 90. The finished concrete floor will be cored in the appropriate locations to provide access for soil boring activities. The soil borings will be located around the solvent storage pit and other areas with potentially high contaminant levels. Twelve soil borings are planned at the tentative locations shown in Figure 4.1. These locations were chosen based on results of the soil gas survey (Draft Soil Gas Survey Technical Report, Parsons, August 2001) and the previous sampling efforts conducted as part of the RFI (Draft AOC 65 RFI Report).4.2.1.1 State Historical Program Office
Building 90 at CSSA is considered an historic building. If it is determined that soil beneath the building needs to be excavated and portions of the building�s floor or other structures such as the outer dock need to be removed and later rebuilt, then Parsons will consult the SHPO and obtain any requisite permits and approvals.
The existing air permit for Building 90 will be reviewed with regard to general applicability with consideration of the planned remediation efforts. Appropriate modifications to the existing air permit will be made. Standard exemptions will be prepared for the subslab ventilation system and the SVE treatability testing system. Parsons will prepare and submit the appropriate documents to the TNRCC on behalf of CSSA and respond to any air permitting issues that arise. Since the standard exemptions must be obtained prior to the start of operations, data from the previous studies will be used to estimate removal rates. The standard exemptions will assume that no off-gas treatment is necessary; however, in accordance with a request from CSSA, activated carbon treatment systems will be installed until the protection of on-site workers is assured.
Up to an additional 12 soil borings will be advanced by hollow-stem auger in areas outside Building 90. The exterior borings will focus on the drainage ditch near the abandoned drain outfall. The exterior boring locations, shown in Figure 4.1, were chosen to provide information regarding the volume of contaminated soils to be excavated.
All soil borings will be advanced until refusal is encountered (estimated to be less than 10 feet deep). One soil sample will be collected from each of the borings and analyzed for VOCs. Sample methodology and quality control procedures are described in the AOC 65 Treatability Test Plan (SAP). Analytical results from the soil borings will help to further define the limits of the planned excavation(s), and should provide a relatively accurate estimate of the total mass of VOC contamination in soils.
The soil borings inside Building 90 will be completed as combination vapor monitoring points/subslab ventilation wells. Each well will be equipped with a valve and sample port to allow soil vapor samples to be collected. Each well will also include a riser to the ceiling rafters that will be manifolded to an extraction blower, located on the east side of the building, to enable ventilation (extraction) of the subslab fill material. This completion design will enable each VEW to be utilized as an extraction well or as a VMP.
The soil borings in areas outside Building 90 will be plugged to land surface with a cement and bentonite mix. Completion of borings completed in the asphalt parking lot west of Building 90 will include a two-inch thick layer of asphalt patch at the surface.
4.3.3 Calculation of Contaminant Mass
Analytical results from the soil boring samples will be used to estimate the contaminant mass in the soil and fill material underlying Building 90. The data will also be used to prepare contaminant concentration contours, which can be used to differentiate specific areas under the slab where removal actions should be implemented. Using depth information from the soil borings and concentration contours, the volume of soil with varying levels of contaminants will be calculated. The volume of soil multiplied by the average contaminant concentration yields the estimated mass of that contaminant in the soil.
Areas with high contaminant concentrations, and thus high contaminant mass, will be targeted for excavation or more intensive VOC reduction through subslab ventilation, while areas with lower concentrations might be selected for more passive treatments. The contaminant mass data and the results of the subslab ventilation system study will be used to determine whether soil removal beneath the building is necessary or whether subslab ventilation alone will effectively treat the soils. This strategy will assist in selecting the appropriate remedial actions that should effectively remove source areas while minimizing unnecessary disruption of operations inside Building 90 and ensuring cost-effectiveness.
4.4 - Building 90 Subslab Ventilation Study
An evaluation of the potential effectiveness of the subslab ventilation system will be completed as part of the removal action inside Building 90. Testing of the ventilation system will be completed prior to any excavation beneath Building 90 so that VOCs in the fill material can be ventilated prior to floor removal and to determine whether subslab ventilation as the sole remedy applied at the site could effectively treat the contamination without disturbing the building�s floor and operations.
Testing of the subslab ventilation system will include measurement of pressure response and soil vapor concentrations of oxygen, carbon dioxide, total volatile hydrocarbons (TVH), and VOCs. Most of the testing will be conducted with direct-read field instruments, with readings recorded on an electronic notepad. Up to six samples will be collected for offsite lab testing prior to initiating any ventilation activities. The same locations will be sampled periodically after initial treatment to assess the effectiveness of treatment and removal of vapors under the building.
4.5 - Implementation of Removal Action
4.5.1 Building 90 Removal Actions
Based on results of previous investigations, it has been anticipated that any removal action inside the building will concentrate on the now-abandoned solvent storage pit and surrounding areas. The area to be excavated is preliminarily estimated to be 40 feet by 40 feet with an average depth of 5 feet, for a total of approximately 300 cubic yards of material.
If VOC levels present in fill material can be adequately reduced through subslab ventilation, excavation of fill materials beneath Building 90 and the concomitant removal of the solvent storage vat and flooring may not be necessary. Parsons will prepare a comparative evaluation based on the soil boring samples and results of the subslab ventilation study to determine if any excavation activities are warranted.
If undertaken, excavation work inside Building 90 would include removal of the citrus cleaner storage container located on a metal plate above the abandoned solvent storage pit. The outer dock of Building 90 might also be removed to facilitate better access to the excavation areas inside the building. Temporary wood walls with plastic lining will be constructed around the removal action area inside Building 90 and negative pressure airflow will be established to prevent unnecessary exposure to CSSA employees. One personal air monitoring station will be set up inside the excavation area and two stations will be set up inside the building outside the sealed temporary walls, to ensure that the engineering controls are effective.
Parsons anticipates that all removal work can be performed in Level D personal protective equipment and will coordinate with building operations so that most work is conducted during off-hours, such as evenings and weekends. The excavation equipment will remove as much material as reasonable given bedrock at 5 feet below grade and limited accessibility of removal action equipment. A mini-excavator will be used inside the building to remove the concrete pit, portions of the floor, and fill material. The excavated material will be handled and disposed of as determined by waste characterization testing. Confirmation samples will be collected for VOC analysis following completion of the excavation activities.
4.5.2 Removal Actions Outside Building 90
The exact locations and extent of excavations to be performed outside Building 90 will be determined from results of the exterior soil borings. It is anticipated that asphalt and soil will be excavated along the abandoned drainpipe and the drainage ditch in the vicinity of the drainpipe outfall.
There are at least 20 gutters from Building 90 currently piped underneath the existing asphalt drive which discharge to the drainage ditch. Portions of the gutter system below the asphalt will also be excavated as part of the removal actions outside Building 90. Drainage from the gutters will be rerouted after completion of the removal actions so that drainage from the building gutters will be diverted from VOC source areas and disturbed recharge zones. Runoff diversion to the southwest or eastern side of the building is being considered.
All removal work will be performed in Level D personal protective equipment. The excavated material will be handled and disposed as determined by waste characterization testing. Confirmation samples will be taken from the drainpipe excavation and from the ditch. Depending on the size of the excavation, at least two samples will be collected to represent each excavated segment of pipe or ditch, or one sample for each 500 ft2 exposed area. Sampling methodology and quality control are described in the SAP addenda (Draft AOC 65 Treatability Study Sampling and Analysis Plan Addendum, Parsons, April 2002).
After completion of any excavation work inside Building 90, the excavation will be backfilled and the concrete floor and outer dock will be rebuilt. The solvent storage pit, however, will not be rebuilt and will be replaced with a concrete floor. The citrus cleaner storage container will be reinstalled once the floor has been rebuilt.Steel casing and screen, which may be used in subsequent subslab ventilation remedial efforts inside Building 90, will be installed horizontally within the excavation prior to backfilling and rebuilding the floor. This casing will be plumbed with access along the western wall or through the wall to the exterior loading dock to enable ventilation or injection of amendments to enhance contaminant removal from beneath the slab. As practical, plumbing from the horizontal wells will be manifolded to the subslab ventilation system. After installation of the casing, the excavation will be backfilled to grade with clean soil.
Prior to excavation activities, Parsons will perform an engineering evaluation of the concrete floor and the outer dock and will include these specifications in the SOW for the reconstruction subcontractor. Parsons personnel will also provide construction quality assurance and oversight. As-built engineering drawings will be prepared to document the post-remediation conditions.
Following excavation of the drain line and ditch, these areas will be backfilled with clean soil and graded. The areas will then be resurfaced with asphalt to facilitate drainage away from the building toward the open fields around Building 90. An engineering evaluation will be performed and bid specifications will be prepared for the backfill and replacement of the asphalt. Construction quality assurance and oversight will also be provided by Parsons personnel. As-built engineering drawings will be prepared to document the post-remediation conditions.
An engineering plan will be prepared to remove the gutters and drain pipe from under the asphalt drive and reinstall an alternative drainage system so that drainage from the building gutters will be diverted to the southwest or eastern side of the building where it will flow into the storm drain system.