3.1 - Selection of Test Site

No changes.

3.2 - Extraction Well Design

The primary focus of this phase of the SVE pilot test will be to determine how the preferential pathways influence the ability of the SVE system to extract VOC contaminants from all portions of the B-3 trench. This will be accomplished by evaluating the radius of influence exerted on the soil gas by extracting air using different configurations of extraction wells. Additional data will be collected to evaluate the measured VOC removal rates and the concentrations of contaminants that may be discharged to the atmosphere using each different configuration. Tests will also be performed to assess the removal rates from individual VEWs so the contribution of VOC removal achieved from each well can be estimated, and to determine the idle time required for VOC concentrations to return to static levels. All of this data will be compiled and evaluated to design the expansion of the existing SVE system and to determine the operating parameters to optimize remediation of VOCs in the B-3 trench. The existing SVE system layout is shown on Figure 3.1.

Up to 12 VEWs will be placed within the B-3 landfill area as shown on Figure 3.2. Ten locations have been identified as primary locations and five have been tentatively identified as alternate locations. It is intended to install VEWs at each of the primary VEW locations, and to select the appropriate alternate locations based on the observations made during construction of the primary VEWs. All of these VEWs will be placed within the landfill trench limits to allow maximum VOC removal capacity in the future full-scale applications in the B-3 source area. If a primary location is determined to be located outside the main trench area, then an alternate may be selected to replace it. At least one soil sample will be collected from each VEW boring to provide additional characterization data for calculating more reliable contaminant mass estimates. Based on the high permeability findings of the first phase of the pilot test, a spacing between new VEWs of at least 20 feet is planned for the expanded pilot test system due to the greater permeability inside the trench. No multi-depth VMPs are planned for this phase. The existing VMPs and VEWs not utilized during an air extraction event should be sufficient to monitor subsurface influence at the site.

The additional VEWs will be manifolded to the existing blower with individual control valves, as was done during the initial pilot testing. Each additional VEW will be constructed with a pressure monitoring port so that it can be used to measure pressure response and soil gas chemistry when not being utilized as an extraction well. The flexibility of the system design will allow extraction from any or all of the VEWs and collection of data from those VEWs and all VMPs not involved in the extraction process.

The VEW borings will be drilled to approximately 16 to 20 feet below ground surface (bgs) and screen will be placed from the bottom to approximately 7 to 9 feet bgs. The total depth of each boring will depend on the depth that bedrock is encountered. The supervising geologist will select the appropriate depth and screened interval for each VEW based on the lithology encountered. Since the greatest contaminant levels were detected in soils immediately above the underlying limestone, each VEW boring will be extended one foot into the top of the limestone to allow the extraction well to be screened across the most contaminated interval. The top of the screened interval will not be set less than 7 feet bgs to minimize potential of short-circuiting to the surface.

The borehole will be advanced by continuous flight hollow stem augers with continuous split spoon sampling. The VEWs will be installed in an 8-inch borehole if the borehole integrity allows the augers to be removed prior to construction. The construction. Construction materials will be the same as those specified in the February 1996 SVE work plan (Parsons ES, 1996a). VEWs will be constructed using 2-inch-diameter, schedule 40 threaded and coupled polyvinyl chloride (PVC) casing. The VEWs will be screened with 0.032-inch factory slotted PVC screen. The well annulus will be gravel packed from the bottom of the screen to approximately 1 foot above the top of the screen with appropriate sized gravel pack (for 0.032-inch slot screen, number 6-9 or 4-10 silica sand is appropriate). The slot size and grain sizes specified above were chosen to maximize air flow into the well. The supervising geologist has the option of selecting a smaller screen size if conditions encountered justify the change. Approximately 2 to 3 feet of bentonite pellets or Benseal will be placed above the gravel pack in each VEW, with tap water poured into the annulus to hydrate the bentonite. A typical VEW construction diagram is presented in Figure 3.3.

The VEWs will be manifolded together with individual control valves to turn on and of the vacuum to each VEW. Each VEW will also be constructed with a pressure monitoring port, so that it can be used to measure pressure response when not being utilized as an extraction well. The flexibility of the system design will allow extraction from any or all of the VEWs and collection of data from the VEWs and VMPs not involved in the extraction.

3.3 - Pressure-Monitoring Point Design

No additional pressure-monitoring points will be installed.

Soil samples will be collected during drilling of the 12 additional VEWs for chemical and geotechnical analysis. The analytical protocol for soil samples collected for the SVE pilot test will consist of analysis for VOCs and metals to establish baseline contaminant concentrations and to estimate the total mass of contaminants present and potential vapor concentrations. In addition, at least five confirmation soil samples will be collected at locations adjacent to the first phase soil sampling locations. Confirmation soil borings will be drilled within 5 feet of existing VEWs and VMPs. Confirmation samples will be analyzed for VOCs only. The results will provide data on the VOC reductions that have occurred during the past year of partial SVE operation. Table 3.1 is a summary of the analyses to be performed.

At least one sample for VOCs and metals analysis will be collected from every VEW boring drilled. The supervising geologist will select the most contaminated sampling intervals using field screening methods. Geotechnical samples will be collected from up to ten of the VEW borings for physical property testing. The on-site supervising geologist will select geotechnical sampling depths to provide data on the different lithologic zones that are encountered. Geotechnical testing that will be performed on all geotechnical samples include soil moisture, bulk density (porosity), permeability, total organic carbon, and particle size distribution (see Table 3.2). Table 3.3 summarizes the number of soil and soil gas samples that will be collected for each type of analysis during each sampling event.

Decontamination will follow the procedures in the Sampling Analysis Plan for SWMU Closures (Parsons ES, 1996d).

All sampling activities will be monitored for air contaminants, and generated investigation-derived waste (IDW) will be field screened to identify any suspected hazardous wastes. IDW suspected to be contaminated, through field screening observations or analytical data interpretation, will be placed in clean 55-gallon US Department of Transportation (DOT) approved drums. The IDW will be characterized for disposal in accordance with applicable EPA and TNRCC regulations.

Field screening and monitoring equipment such as HNu^TM PID, HMX 271^TM combustible gas indicator, and Sensidyne^TM one-stroke pump and colorimetric tubes will be used during drilling and sampling activities. Field screening techniques will consist of using the HNu^TM PID or other appropriate monitoring device to periodically monitor the breathing zone, drill cuttings, borehole and undisturbed core samples. Headspace analysis of soil samples retrieved with a core sampler during drilling will also be tested. All readings made with the monitoring equipment will be recorded either in the field logbook or directly on the field boring logs. The frequency of air monitoring for the investigative activities is defined in the project health and safety plan.

Soils and rock cuttings will be generated through subsurface sampling activities (drilling). Upon receipt of validated analytical data which identifies soils above 30 TAC �335 Subchapter S RRS2 soil/air and ingestion standards for an industrial site (SAI-Ind), proper IDW classification as specified in 30 TAC �335 subchapter R will be determined. The classified soils will then be placed into approved DOT 55-gallon containers, properly labeled, and disposed at an appropriate authorized off-site disposal facility. However, if the soils are below 30 TAC �335 subchapter S RRS2 SAI-Ind values, they will be removed from their containers and placed near the borings from which they were derived.

In accordance with project field sampling plan, hexane and methanol will be used in addition to Alconox and clean water for decontamination of all field sampling equipment. Rinse fluids will be containerized for proper disposal. The field screening effort will consist of using a HNu� PID or other applicable monitoring devices to identify soils which have recordings of ambient air concentrations greater than 50 parts per million (ppm) VOC. If 50 percent of the total retrieved core has recordings greater than 50 ppm or visual observations suggest that soils may be contaminated, decontamination fluids will be containerized and sampled for proper waste characterization. If collected decontamination fluids are determined nonhazardous, they will be poured onto the ground within the source area where the decontamination fluids were generated. Hazardous decontamination fluids will be properly handled and disposed of at an authorized off site facility.

For miscellaneous debris, Parsons ES intends to double bag and deposit the IDW in the site dumpster.

3.4 - Vacuum Blower, Piping, and Instrumentation

The existing SVE pilot test blower will be used for the expanded pilot test system. The only modifications will be the manifolding of up to twelve additional wells and the installation of an automated timer and drain.

An automated timer and moisture separator drain will be designed and installed on the blower system following completion of the last multiple configuration test. The timer will be set at intervals that maximize VOC removal. No other changes will be made to the vacuum blower. It is anticipated that one blower will be sufficient for full-scale SVE implementation at the site. A temporary shelter will be constructed around the blower to protect its components to allow maintenance personnel easy access to the blower�s gauges and measurement ports.

New VEWs will be connected with the same type of piping as the existing wells.

The existing SVE system includes a moisture separator with a manual drain. The moisture separator has approximately 15 gallons of capacity. An evaporation pan has been placed at the outlet to allow for temporary containment of moisture drained from the moisture separator. An automated timer will be installed to shut the blower off in accordance with the prescribed pulse schedule, and the automated drain will release liquids from the separator when they reach a preset level.

3.5 - Operation and Monitoring

Several discrete tests will be performed to collect data to complement the data already collected during the initial pilot testing activities. These tests are described in this section in the order they are planned. The tests include:

After construction of the additional VEWs, and initial system check will be performed. This check will be performed after the blower has operated continuously for at least two weeks. The testing will include pressure response testing at all VEWs and VMPs not connected to the six VEWs of the existing pilot test system to determine influence throughout the test area, and to determine VOC removal rates from the existing VEW system during operation. The objectives and procedures for these tests are briefly described below.

The influence test will be performed while the existing SVE system is operating using magnehelic pressure gauges. This test will demonstrate which portions of the B-3 trench, including those portions represented by new VEWs, are influenced by extraction from the existing SVE system. Different configurations of extraction using the existing six VEWs will be tested by shutting off air flow from one or more VEWs and assessing the pressure response from each VEW and VMP at the site. The results of this test will be used to design the subsequent multiple configuration tests using the additional VEWs constructed at the site. The results will also provide initial data on preferential pathways and interconnections in the subsurface soils of B-3.

Following at least two weeks of continuous extraction, air flow measurements and VOC concentrations will be measured at each of the six VEWs manifolded to the existing blower system. This data will be used to assess the relative contribution of air flow and hydrocarbon removal achieved at each VEW. Soil gas samples from each of the VEW manifold lines will be collected and field screened for VOCs and at least four samples will be collected in Summa canisters for laboratory analysis. A sample will also be collected from the air effluent (or exhaust) line at the blower for laboratory analysis to estimate the emissions from the SVE system after a specified time of continuous operation (at least two weeks). This data can be compared to the pilot test emission data to determine if the levels rates of VOC removal have been substantially reduced.

Prior to shutting off SVE operation, soil gas chemistry data will be collected from all of the VEWs and VMPs not connected to the existing pilot system. This data will be used to establish baseline hydrocarbon and oxygen levels for the hydrocarbon recovery/respiration test at the site. The objective of the hydrocarbon recovery test is to determine the time required for the soil gas hydrocarbon levels to reach equilibrium or stable concentrations. The recovery time is critical in determining the amount of time a system will need to idle to maximize VOC removal for a pulsed extraction sequence. Oxygen and carbon dioxide will also be measured to assess the rate of biological degradation occurring in hydrocarbon contaminated soils. The hydrocarbon recovery time is also important in scheduling the multiple configuration tests so that stable conditions are present in the dormant soils at the beginning of each test.

The hydrocarbon recovery test will be performed for at least 20 days, with tentative testing scheduled for 2, 4, 8, 12, 16, and 20 days following system shutdown. The test will be continued at 8 day intervals if the hydrocarbon levels in the soil do not equilibrate in the 20-day test period.

In addition to the hydrocarbon recovery test, soil gas samples will be collected in Summa canisters to assess the production of biological degradation indicator compounds over time. These values will be evaluated to predict the relative biodegradation of the chlorinated compounds TCE and PCE, based on the breakdown byproducts cis-1,2-DCE, vinyl chloride, methane, ethane, and ethene. One soil gas sample will be collected for the above mentioned parameters immediately after the system is shut off to establish baseline concentrations. A second sample will be collected at between 10 to 15 percent oxygen to provide data for assessing the rate of volatilization from soils. A third sample will be collected when oxygen concentration drop below 5 percent to determine the quantity of breakdown products prior to the system turning anaerobic. A fourth sample will be collected after TVH levels have stabilized and the soil system has apparently reached equilibrium. The last sample will be collected prior to reinitiating extraction to evaluate any changes in soil gas composition after reaching steady state conditions.

In addition to the initial configuration testing planned for the existing SVE system, three other multiple configuration tests are planned to assess influence of different configurations on the ability to extract VOCs from different portions of the subsurface soils. The first test will be performed following completion of the hydrocarbon recovery test. The VEWs involved in the first test will be determined based on the findings of the initial pilot testing and the initial system check. The focus will be on the wells located in the portion of the B-3 trench that exhibited the least response to extraction from the initial system extraction test. For the second and third test, the VEWs selected for extraction will depend on results of the previous tests and will focus on data needs.

The first extraction event (multiple configuration test) will run for approximately 28 days prior to system shut down to monitor changes in VOC emissions from the blower exhaust for at least a one month period. After completing the first multiple configuration test, the system will be shut down for a length of time as determined by the hydrocarbon recovery test. The air extraction events for the second and third multiple configuration tests are anticipated to last 12 days. The shut down time between these testing events will remain consistent with the hydrocarbon recovery period. Following the final testing event, the system will be shut down one last time to install an automated moisture separator and operations timer. The system will be restarted following automation and will be set to the recommended operating rotation and schedule.

Each test will be performed with up to six VEWs. Prior to beginning extraction, soil gas chemistry data will be collected at all VEWs and VMPs to establish baseline concentrations. Once extraction is initiated, the flow from each well will be measured and adjusted as necessary to maintain approximately uniform flow from each well. Soil gas samples will be collected from each line and field screened for total hydrocarbons. Soil gas samples from only the first multiple configuration test will be collected in Summa canisters for laboratory analysis. Vacuum pressures at each extraction well will also be measured to assess the relative resistance to flow from the formation at each VEW. Influence of each VEW configuration will be determined based on changes observed in soil gas chemistry over time and pressure responses observed in non-extraction VEWs and VMPs.

Monitoring for soil gas chemistry changes during the multiple configuration test will be performed on a schedule slightly modified from that used for the hydrocarbon recovery test (on days 0, 1, 2, 4, 8, 14, 20, and 28). The second and third tests well be discontinued following the 14-day measurements. The schedule may also be revised for the second and third multiple configuration test, based on the findings of the first test. After the soil gas has stabilized and the final emission sample has been collected, the configurations will be modified to determine the effect of certain wells exert on particular area of the trench. This can be performed by shutting off flow to all but one VEW and measuring pressure responses at all other VEWs and VMPs. This single VEW testing will be repeated until all VEWs in the multiple VEW test configuration have been tested.

Emissions data will also be collected during each multiple configuration to estimate VOC emission rates and the VOC removal efficiency of each configuration. These samples will be collected over time from either the inlet line or from the blower exhaust. Following initiation of extraction from each VEW configuration, emission samples will be collected for laboratory analysis after approximately 15 minutes, 6 hours, 12 hours, 24 hours, 48 hours, and even 336 hours (14 days). Emission samples may be collected for additional screening analysis on a more frequent schedule (to include days 4 and 8). The laboratory analysis schedule for emission samples will be modified as appropriate, based on results of field screening or previous testing events.

3.6 - Air Emissions

Generally, most SVE systems involve very low air pollution emissions rates allowing them to be exempted, as outlined in 30 TAC 116.211, under Standard Exemption 68. Accordingly, the existing SVE system at CSSA operates under a standard exemption. However, the exemption will not explicitly apply to the upgraded system. Therefore, the exemption may need to be modified to include use of more than six VEWs (current exemption) for an upgraded system. The multiple configuration tests will not employ more that six VEWs, so an exemption modification is not required, unless soils data indicate greater VOC concentrations in other portions of the B-3 trench than were encountered during the installation of the existing system. The TNRCC will be notified of the construction of additional VEWs and testing, but an exemption modification is not planned until the final full-scale system is designed.

No changes. The Work Plan estimated emissions from the system under worst-case conditions (i.e., all VOCs in the surrounding soils would be extracted).

A standard exemption was filed with the TNRCC in April 1996 that contains all of the necessary calculations and site data for obtaining the emission exemption (Parsons ES, 1996b). The calculations were prepared based on data collected during the initial pilot testing activities in March 1996.

3.7 - Data Analysis

No changes.

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