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Environmental Cleanup Plan for AOC 65
Section 6 - Soil Vapor Extraction Treatability Study
The treatability study will focus on evaluating the effectiveness of SVE as a remedial action to address contamination at AOC 65. The study will be designed to assess the effective radius of influence of the VEWs installed in the vicinity of Building 90. The treatability study will also be used to quantify the estimated mass of PCE and TCE that can be removed by an SVE system installed at the site. Activities to be conducted during the study are described in the AOC 65 Treatability Test Plan, Parsons, April 2002.
A one-time waiver for the existing air permit for Building 90 will be prepared to include potential releases at Building 90 during the removal actions. Additionally, two standard exemptions will be prepared to address the soil vapor extraction systems installed inside Building 90 and west of the Building. Since the standard exemption must be obtained prior to the start of operations, data from the previous studies will be used to estimate removal rates. In addition, the standard exemption will assume that no off-gas treatment is necessary; however, in accordance with a request from CSSA, an activated carbon treatment system will be utilized until the protection of on-site workers is assured.
Six VEWs will be installed for use in the AOC 65 SVE Treatability Study. Additionally, 24 VMPs will be installed at six locations to monitor performance of the SVE system. The six VEWs are proposed for installation on both sides of Building 90, with most installed on the west side near the abandoned drain line that exits the building in the vicinity of the solvent storage pit. The VEWs will be installed at depths ranging from 30 to 150 feet to allow the flexibility of venting from different depths. The exact VEW locations, depths, and screened interval placement and design will be based on the geophysical data and site conditions noted as field activities progress. Additional information regarding extraction well depths will be provided by results of the extraction packer test performed during installation of the piezometers for the groundwater recharge study (see Section 5.4).
The VEWs will be manifolded together to a regenerative blower installed near an existing electrical panel on the west side of Building 90. The VEWs will have individual control valves to control the vacuum at each VEW. Each VEW will also be constructed with a pressure monitoring port so it can be used to measure pressure response when not being utilized as an extraction well. The flexibility of the system will allow extraction from any or all of the VEWs and collection of data from the VEWs not involved in the extraction.
The vacuum blower system will contain a moisture separator drain and will be fitted with an activated carbon treatment unit to ensure the safety of workers in the vicinity of Building 90. A temporary shelter (blower housing) will be constructed around the blower to protect its components and allow maintenance personnel easy access to the blower�s gauges and measurement ports.
The 24 multi-depth VMPs will include up to four distinct 10-foot screened intervals per boring and will extend to a maximum depth of 100 feet bgs. The 24 VMPs will be installed at six locations on both sides of Building 90, with most installed on the west side near the abandoned vat area, drain line, and drainage ditch.
6.4 - SVE Treatability Study Activities
The initial system check of the AOC 65 SVE system will be performed AT start-up of the extraction system. Prior to system start-up, all VEWs and VMPs will be field monitored for oxygen, carbon dioxide, and TVH levels to assess static conditions. The extraction well with the highest TVH and carbon dioxide levels, 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. Using the TVH field screening results and TO-14 analytical results, a correlation will be made between the TVH readings and the actual volatile concentration. These data comparisons will allow field TVH readings to be used to predict VOC concentrations in subsequent field tests.
The system blower will then be turned on and a vacuum will be pulled on the selected extraction well. 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 after start-up. Pressure responses and field screening parameters (oxygen and TVH) will be measured from available monitoring points to assess soil gas changes and evaluate the radius of influence for the selected extraction well. Pressure responses and field screening parameters will be collected from VMPs, nearby monitoring wells, subslab VEWs, and piezometers at 1, 2, 4, and 8 days after start-up.
6.4.2 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 the measurement of soil gas changes and pressure responses to assess the depth and lateral influence of each VEW.
Different configurations of extraction using the 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 wells at the site. The results will provide initial data on preferential pathways and interconnections in the subsurface soils 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. These 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 effectiveness of pulsing extraction on performance of the SVE system. Testing of dual-phase extraction (liquid and air) pilot systems, such as vacuum enhanced pumping may also be evaluated for effectiveness compared to observed SVE performance. The SVE system will be designed so a pilot test vacuum enhanced pumping blower unit can be connected to the existing SVE system layout with only minor modifications.
A tracer test may also be conducted at the site to obtain more specific information regarding travel time, retardation, and flush time of VOCs in the fractured limestone beneath the site. A suite of tracers will be injected into selected 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. The tracer test results will determine the flush times from the point of tracer injection to the SVE system 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 non-aqueous phase liquid, organic matter, and water content along those flow paths and enable the forecast of TCE retardation due to flow in the fractures.
Four soil gas samples will be collected from the main system exhaust of the test blower to measure removal rates and assure compliance with the standard exemption and to estimate attainable removal rates from an operational SVE system.
6.5 - Operation and Maintenance
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 O&M Plan for the AOC 65 SVE System. The plan will include recommendations for 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 test system will be continuous during the O&M period.