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AOC 65 Treatability Test Plan
Section 4 - SVE Treatability Testing System
The existing air permit for Building 90 will be reviewed with regard to the remediation efforts planned inside Building 90 (subslab ventilation, excavation activities, etc.) and an appropriate one-time waiver will be prepared to address potential emissions that may occur during the removal action activities. Additionally, two standard exemptions will be prepared for off-gas emissions from both the AOC 65 SVE and Building 90 subslab ventilation systems.
To reduce the regulatory burden, CSSA has requested that the extraction systems be constructed with off-gas treatment to eliminate potential for exposure to on-site workers. The standard exemptions will specify no off-gas treatment is necessary in accordance with allowable practice. However, off-gas treatment will be provided until all risk to on-site workers is eliminated.
4.2 - SVE Treatability Testing Activities
An evaluation of the potential effectiveness of the Building 90 subslab ventilation system will be completed as part of the removal action inside Building 90. SVE effectiveness testing of both the Building 90 subslab ventilation system and the AOC 65 SVE system will be completed prior to any removal of contaminated fill material underlying Building 90. This testing will determine the potential to reduce levels of VOCs in soil and evaluate whether or not subslab ventilation could effectively treat soil contamination without having to disturb the building�s floor and operations.
The initial system check of the subslab ventilation and AOC 65 SVE system will be performed at the start-up of the extraction systems. Prior to system start-up, all VEWs and VMPs will be field monitored for oxygen and TVH levels to assess static conditions. The extraction well with the highest TVH level and lowest oxygen level, indicating the highest degree of contamination, will be selected as the extraction well for the start-up test. Soil gas samples will be collected from at least six VEWs for VOC analysis by method TO-14. A correlation will be made between the TVH readings and the actual volatile concentration using the TVH field screening and TO-14 analytical results. These data comparisons will allow field TVH readings to be used to predict VOC concentrations in subsequent field tests.
The appropriate system blower will then be turned on and a vacuum will be pulled on the selected extraction wells. The system will run continuously for 4 to 8 days with collected air samples analyzed for VOCs by method TO-14. Air samples will be collected from the selected extraction well after 1 hour, 8 hours, 24 hours, 48 hours, 4 days, and possibly after 8 days of operation to assess changes in VOC removal rates over time. Pressure responses and field screening parameters (oxygen and TVH) will be measured from all available monitoring points including VMPs, nearby monitoring wells, subslab VEWs, and piezometers at 1, 2, 4, and 8 days after start-up to assess soil gas changes with time and to evaluate the radius of influence for the selected extraction well.
In addition, water levels in area piezometers will be monitored closely during initial SVE testing to evaluate possible effects on groundwater conditions.
4.2.2 Radius of Influence Testing
Following the initial system check, the system will be shut down and subsurface conditions allowed to equilibrate. Radius of influence tests will then be performed on some or all of the five remaining extraction wells. Radius of influence testing of the AOC 65 SVE system will include measurement of soil gas changes and pressure responses to assess the depth and lateral influence of each VEW.
Different configurations of extraction using the Building 90 and AOC 65 VEWs will be tested by shutting off air flow from one or more VEWs and assessing the pressure response from each VMP and existing monitoring well at the site. The results will provide initial data on preferential pathways and interconnections in the subsurface soils beneath Building 90 and at AOC 65. Following at least 2 weeks of continuous extraction, airflow measurements and VOC concentrations will again be measured at each of the VEWs. This data will be used to assess the relative impact the extraction exerted on soil gas levels by observing contaminant concentration changes at each VEW.
Additional types of testing are contemplated depending on results from the SVE study, including an extended radius of influence test and dual phase extraction pilot tests. Extended radius of influence testing will enable collection of data through several heavy rainfall events and assess the efficiency of pulsing extraction on the performance of the SVE system. Testing of dual-phase extraction (liquid and air) pilot systems, such as vacuum enhanced pumping (VEP) may also be tested so its potential effectiveness for contaminant removal may be evaluated and compared to observed SVE effectiveness. The SVE system will be designed so a pilot test VEP blower unit could be connected to the existing SVE system layout with only minor modifications.
Tracer tests may be performed to obtain more specific information regarding travel time, retardation, and flush time of VOCs in the fractured limestone beneath the site. UTSA proposes to inject a suite of tracers into up to five different nearby monitoring wells (within 200 to 300 feet from the SVE). The levels of tracers will be monitored in soil gas samples collected from SVE wells coincident with the radius of influence testing portion of the AOC 65 SVE treatability study. The tracer test results will determine flush times from the point of tracer injection to the SVE and, in turn, how big the area of influence is and how often the fractures are flushed with air. The test will also help determine NAPL, organic matter, and water content along those flow paths and enable the forecast of TCE retardation due to flow in the fractures.
Sampling conducted at AOC 65 will comply with requirements of the AFCEE QAPP, Version 3.0. Sampling and decontamination procedures will be performed in accordance with procedures set out in the Draft AOC 65 Treatability Study Sampling and Analysis Plan Addendum, Parsons, April 2002.
Analytical data collected from installation and testing of the SVE systems at AOC 65 will be analyzed by DHL Analytical, Round Rock, Texas. The project required detection limits will be below regulatory criteria. The laboratory data will be validated by a Parsons chemist in accordance with the AFCEE QAPP, Version 3.0.
Data collected as part of the Treatability Study at AOC 65 are considered screening data. Therefore, no field duplicate (FD) or matrix spike (MS)/matrix spike duplicate (MSD) samples will be collected. However, trip blanks will be collected for each day that VOC analysis samples are sent to the laboratory at a rate of one trip blank per cooler shipped.
4.4 - Operation and Monitoring
The SVE systems at AOC 65 will be operated and maintained until the Groundwater Recharge Study is complete in September 2003. Following completion of the initial system check and the radius of influence testing, Parsons will prepare an Operations and Maintenance (O&M) Plan for the AOC 65 SVE System. The plan will include recommendations for system expansion/modification, continued operation, monitoring, and maintenance of the SVE system based on site conditions, operation parameters determined during the system check, and manufacturer recommendations. Optimization testing of the SVE system will be conducted during the O&M period. A letter report summarizing O&M activities will be completed every six months until the O&M plan is prepared and approved.