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Soil Vapor Extraction Test Report for SWMU B-3
Section 3 - Treatability Study Methods
The purpose of this section is to summarize the activities that were performed by Parsons ES during the December 1996 installation and spring 1997 testing of the expanded SVE system at SWMU B-3, and the spring 2000 re-sampling effort. The first activity was the siting and construction of 12 additional VEWs to complement the initial six-VEW SVE Pilot test system. The completed and expanded treatability test system consists of 18 VEWs and six VMPs. All VEWs are manifolded to the single extraction blower located on site, but the valve to VEW-06 was shut for the duration of the treatability study because it is located outside of the primary target area designated for remediation of VOCs. Soil samples were collected during system expansion to characterize the pre-study conditions of the soil contamination and to further delineate the actual extent of VOC contamination present in the main SWMU B-3 trench area prior to the implementation of remedial actions.
The 1997 study activities were initiated immediately following the installation of the expanded test system. The testing activities were generally performed in accordance with the protocols detailed in the Addendum to SVE Test Work Plan for SWMU B-3 (Parsons ES, 1996e) with exceptions noted in the discussions of the specific testing methodology. The January 1997 system check was performed to assess the removal rates of the pilot system after prolonged operation and to determine baseline hydrocarbon concentrations for use in the hydrocarbon recovery test. The system was shut down immediately following the initial check, and soil gas throughout the site was monitored to determine the time required for hydrocarbon and oxygen/carbon dioxide levels to return to near static levels in the soil gas. To complete the testing activities, three multiple configuration tests (MCTs) were performed on different extraction configurations of six VEWs per MCT to determine contaminant mass removal and radius of influence exerted from VEWs in each configuration, and to measure the rate of removal during each MCT to determine if pulsing extraction could improve removal rates compared to continuous operation. The data from these testing activities were designed to complement the data already collected during the initial 1996 pilot testing activities, which are discussed in Section 2.
In April 2000, a resampling effort was conducted due to improper practices by the analytical laboratory used during analysis of the treatability study samples collected in December 1996. This effort involved the collection of soil samples from the 12 VEW soil borings performed in December 1996 (VEW07 through VEW18). Samples collected from the pilot test drilling activities were analyzed for VOCs and metals by Chemron and were determined to be acceptable. The data collected during the installation of the expanded treatability system were analyzed by ITS Laboratory in
Other samples analyzed by ITS and, therefore, of questionable accuracy, were the air samples collected during performance tests of the system and the 1997 confirmation soil samples collected to assess VOC reductions in site soils. Since it would be virtually impossible to duplicate the exact conditions when the air samples were originally collected, resampling of these tests was not performed. Additionally, the confirmation soil borings were completed in 1997 to assess system performance after six months of operation and are therefore "time sensitive". Since the 1997 data clearly indicated that VOC reductions were occurring in the deeper soils near the VEWs, resampling from these locations was not performed.
3.2 - System Construction Activities
3.2.1 Expanded System and Design
The as-built expanded SVE system layout is presented in Figure 3.1. The 12 new VEWs were installed in the landfill trench limits to allow maximum VOC removal capacity in future full-scale applications in the SWMU B-3 source area. This area was considered the critical cleanup area because it acts as a continuing source area for VOC migration into surrounding fractures in the bedrock formation. The addendum specified VEW locations and established a grid based on the observations made during construction of the 1996 pilot test VEWs and the target clean-up area determined from soil gas survey data. The grid listed ten primary locations for VEWs and five alternate locations. If a primary location was determined to be located outside the main trench area, or in an area with relatively minimal contamination, then an alternate location was selected to replace it.
Only two of the four VEWs originally intended for installation in the northern portion of the trench were constructed because the contamination observed during drilling was significantly less in VEW-07 and VEW-08 than in borings located to the south of the initial pilot system. The VEWs planned for the northern portion of the trench were replaced by two additional boreholes in the grid line north of the initial pilot test system layout. Both alternates on the northern portion of the trench were also selected to complete the expanded test system layout. Based on the high permeability findings of the first phase of the pilot test, a spacing between new VEWs of approximately 25 feet was used for the expanded pilot test system inside the trench. No multi-depth VMPs were installed during this phase of construction.
The additional VEWs were manifolded together to the pilot test SVE blower with individual control valves to turn on and off the vacuum to each VEW. The new VEWs were connected to the system using 1.5-inch and 2-inch diameter PVC casing. The only modification to the pilot system was the manifolding of 12 additional VEWs to the existing pipe network. The instrumentation diagram in Figure 2.10 is applicable for this expanded system, except for the 12 new VEWs added to the manifold. The layout of the manifold piping for the expanded extraction system is shown on Figure 3.1. The blower specifications are described in Section 2.4.2 of this report. Each VEW was 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.
An automated moisture separator drain was designed and procured for installation to the blower system once the future operating parameters and schedule have been selected. No other changes were made to the vacuum blower. The existing one blower system was determined to be sufficient for full-scale SVE implementation at the site. The installed blower is a Gast Regenair R5 Series Model R5325A-2 regenerative blower. This blower is capable of providing 160 cfm flow at 65 inches of water-column vacuum. The blower consists of a 2.5 horsepower (hp) electric motor that is rated for continuous-duty service. Average vacuum applied to the VEWs during the pilot testing of the expanded system was 25 to 50 inches with the average vacuum measured at the blower about 50 inches. This vacuum was successful at maintaining steady flow rates from each VEW. The maximum flow measured from any of the 6 VEW tests was 104 cfm.
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. The automated drain system to be installed is designed to release liquids from the separator when they reach a preset level, and then restart the blower once the moisture separator has been drained.
3.2.2 Well Construction Procedures
Drilling and VEW construction activities began on
The boreholes were drilled with continuous flight hollow stem augers with continuous split spoon sampling. The VEWs were installed in the 8-inch borehole created by the augers. The augers were removed from the borehole prior to well construction because of adequate integrity of the borehole formation. The VEWs were constructed using 2-inch-diameter, schedule 40 threaded and coupled PVC casing. The VEWs were screened with 0.032-inch factory slotted PVC screen. The well annulus was gravel packed from the bottom of the screen to approximately 0.5 foot above the top of the screen with number 6-9 silica sand. Approximately 2 to 3 feet of 1/4-inch bentonite pellets were 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 3.2.
At least one soil sample was collected from each VEW boring to provide additional characterization data for calculating more reliable contaminant mass estimates. Soil sample collection procedures and the analytical program employed for the additional characterization of the SWMU B-3 trench are described in Section 3.2.3 of this report.
3.2.3 Soil Sample Collection and Analytical Program
Soil samples were collected during drilling of the 12 additional VEWs for chemical and geotechnical analysis from December 26 to
Confirmation soil borings were drilled approximately 3 feet south of existing VEW and VMP locations. Sample depths of confirmation samples were selected to correspond to sampling depths from the 1996 initial sampling. Confirmation samples were only analyzed for VOCs. Results of confirmation soil sample analysis are intended to provide data on the VOC reductions that have occurred during the past year of partial SVE operation. The analytical methods that were performed on the soil samples are summarized in Table 3.1.
At least one sample for VOCs and metals analysis was collected from every VEW boring drilled in December 1996 (VEW07 through VEW18). The supervising geologist selected the most contaminated sampling intervals using field screening methods (Photovac 2020 instrument readings and visual observations). Geotechnical samples were collected using
Quality control (QC) samples were collected throughout this project in accordance with the approved Quality Assurance Project Plan (QAPP) (Parsons ES, 1996d). All sample analyses were reviewed by a Parsons ES data validator. An analytical informal technical information report (ITIR), prepared for this treatability study, is included as Appendix A of this report. The numbers and types of QC samples are summarized in Table 3.3 for each sampling event.
Decontamination procedures followed those detailed in the �Sampling Analysis Plan for SWMU Closures� (Parsons ES, 1996d). Soil cuttings were monitored during sampling activities to identify suspected hazardous wastes. All soil cuttings were placed in clean 55-gallon US Department of Transportation (DOT) approved drums, although no indications of significant contamination were observed during the routine screening. Analytical data from the initial pilot test sampling and the more recent characterization sampling were also evaluated to determine if any of the investigation-derived waste (IDW) is potentially hazardous or has special disposal requirements.
A composite sample of soil cuttings was collected on
Upon receipt of validated IDW characterization data which were composited from soils above 30 TAC �335 Subchapter S RRS 2 soil/air and ingestion standards for an industrial site (SAI-Ind), proper IDW classification as specified in 30 TAC �335 subchapter R was determined. The results and disposition plans for the IDW is discussed in Section 4.6.
Rinse fluids were temporarily containerized during the active drilling and decontamination activities. The field screening effort consisted of using a Photovac 2020 photoionization meter to identify soils which have recordings of ambient air concentrations greater than 50 parts per million (ppm) VOC. No soil cores had 50 percent of the total retrieved core with readings greater than 50 ppm and visual observations did not suggest that soils were contaminated, so decontamination fluids were determined to be nonhazardous. In accordance with the approved addendum work plan, these fluids were poured onto the ground within the source area where the decontamination fluids were generated at the conclusion of the drilling activities. Miscellaneous debris was double-bagged and placed in a general refuse dumpster at CSSA.
3.3 - Treatability Study Activities
Several types of treatability tests were performed to collect data to complement the data already collected during the initial pilot testing activities. These tests are described in this in the order they were performed. The tests include:
The January 1997 system check of the existing operational system after at least two weeks of continuous air extraction,
Determination of the time required for hydrocarbon levels in the soil gas to stabilize after shutting down the system, and
Three separate MCTs to monitor for subsurface pressure and soil gas influence.
No air permeability tests were performed during this phase of the pilot test because the localized permeability of soils is not a critical factor for assessing the potential performance of the blower. Also, because of the complex subsurface interconnections, the accuracy of the air permeability data can not be relied on for use in determining conceptual design parameters for full-scale operation of SVE at the site.
After construction of the additional VEWs, a system check was performed on the 1996 pilot test configuration which was extracting from VEW-01, VEW-02, VEW-04, and VEW-05. This check was performed after the blower had operated continuously for at least two weeks and sporadically since
A pressure influence test was performed while the existing SVE system was operating using magnehelic pressure gauges. This test demonstrates which portions of the main SWMU B-3 trench, including those portions represented by new VEWs, are directly influenced by extraction from the existing SVE system. Different configurations of extraction using the existing four VEWs were tested by shutting off air flow from one or more VEWs and then assessing the pressure response from each VEW and VMP at the site. The results of this test were used to determine which portions of the subsurface trench are directly affected by extraction at each of the initial pilot test VEWs. This data was also used to design the subsequent multiple configuration tests using the additional VEWs at the site. The results also provided data on preferential pathways and interconnections in the subsurface soils at SWMU B-3.
Soil gas concentrations were also measured at each of the VMPs and VEWs not included in the extraction configuration to assess potential indirect influence of the four‑VEW configuration test system on soil gas concentrations in the treatment area of the trench. Data from the hydrocarbon recovery test, which is described in Section 3.3.2, can be evaluated to determine if soil gas concentrations in different portions of the trench have been affected by extraction using the initial configuration. After extraction was discontinued for the beginning of hydrocarbon recovery testing, soil gas concentrations were monitored at each VEW and VMP to determine the time required for the soil gas to return to near static conditions (with relatively little change between periodic measurements). This data can also be used to determine which VEWs and VMPs were most effected by extraction by determining the relative changes in soil gas concentrations at the monitored points over time.
Prior to discontinuing extraction from the initial four-VEW configuration, air flow measurements and VOC concentrations were also measured at each of the extracting VEWs. This data is used to assess the relative contribution of air flow and the hydrocarbon removal rate from each VEW in the pilot test configuration. This data can be compared to pilot test data to determine if the VOC removal rate has been significantly reduced by the continuous, long-term operation of the pilot test configuration. Soil gas samples from each of the VEW manifold lines were collected and field screened for VOCs, and all four VEWs were sampled for laboratory analysis. A sample was also collected from the air effluent (or exhaust) line at the blower for laboratory analysis to estimate the cumulative emissions from the SVE system after prolonged continuous operation. The emissions data can also be compared to the pilot test emission data to determine if the rates of VOC removal have been substantially reduced.
3.3.2 Hydrocarbon Test Recovery
Prior to shutting off SVE operation, soil gas chemistry data was collected from all of the VEWs and VMPs not connected to the existing pilot system. This data was used to establish baseline hydrocarbon and oxygen levels for the hydrocarbon recovery/respiration test at the site. The primary objective of the hydrocarbon recovery test was to determine the time (number of days) required for the soil gas to reach equilibrium or stable concentrations. The recovery time is also important in determining whether idling the SVE system periodically can improve VOC removal (such as in a pulsed extraction sequence). Oxygen and carbon dioxide were also measured to assess the rate of biological degradation occurring in hydrocarbon contaminated soils. To estimate the biodegradation rates of hydrocarbons in the trench area, a stoichiometric relationship for the mineralization of specific hydrocarbons is used, along with the oxygen utilization rates (decrease in oxygen over time) observed at each monitoring point.
The hydrocarbon recovery time was also important in scheduling the MCTs so that stable soil gas conditions were present prior beginning each MCT. The hydrocarbon recovery test was performed for 24 days, with testing performed after 1, 2, 4, 8, 12, 16, 20, and 24 days following system shutdown.
Soil gas samples were also collected in Summa canisters to assess the production of biological degradation indicator compounds over time. This data provides information regarding 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 was collected for the above mentioned parameters immediately after the system was shut off to establish baseline concentrations. A second sample was collected when the oxygen levels dropped to between 10 to 15 percent oxygen (after approximately 20 hours) to provide data for assessing the rate of volatilization from soils. A third sample was collected when oxygen concentrations dropped below 5 percent (after approximately 28 hours) to determine the quantity of breakdown products prior to the system turning anaerobic. A fourth sample was collected after TVH levels had stabilized and the soil system had apparently reached equilibrium (after approximately 8 days). A fifth sample was collected prior to reinitiating extraction to verify steady state conditions (after 27 days) and to measure the concentrations of contaminants and/or breakdown products that had accumulated in the soil gas. To gather additional data on the production of biodegradation breakdown products, a sixth sample was collected after the MCT-1 test was complete and the system had idled for 24 days. This sixth sample was necessitated because ethane, methane, and ethylene were not analyzed for in the fourth or fifth samples collected, so a steady state sample was needed to compare relative concentrations of these products to the samples collected after only two days of system shut down. The results and conclusions from this testing are presented in Section 4.3. The general results indicate that biodegradation is occurring in the subsurface soils at SWMU B-3.
3.3.3 Multiple Configuration Testing
In addition to the 1997 system check planned for the pilot test SVE system, three different MCTs were performed using six VEWs per test to assess influence of different configurations on the ability to extract VOCs from different portions of the subsurface soils. The first test was performed following completion of the hydrocarbon recovery test. The VEWs involved in the first test were selected based on the findings of the initial pilot testing and the 1997 system check. The selected wells were located in the portion of the SWMU B-3 trench that exhibited the least response to extraction from the initial system extraction test. VEWs selected for the second test included the six VEWs that were not tested during the initial pilot test or the first MCT. VEWs selected for the final test were those VEWs that exhibited the greatest VOC removal rates and greatest flows during the previous testing activities.
The first and second extraction events (MCTs) were performed over a test period of 14 days. After completing each of the first two MCTs, the system was shut down for at least 24 days prior to initiating the next testing event. Twenty-four days was the length of time determined by the hydrocarbon recovery test for soil gas to return to near static conditions. The third MCT (MCT-3) was performed over a test period of 28 days to assess the long-term reduction in VOC removal rates observed from the VEWs most likely to be used in full-scale SVE operation at the site. Each test was performed using six VEWs in each configuration.
The first MCT (MCT-1) extracted from VEW-07, VEW-08, VEW-12, VEW-15, VEW-17, and VEW-18. The primary reason for selection of these VEWs is that they were the monitoring points that exhibited the least pressure response from the continuous extraction of the initial four-VEW pilot system. In addition, VEW-15 was the only monitoring point that did not experience a significant change in the soil gas conditions during the hydrocarbon recovery test after shutting off the system. Obvious odors and elevated total volatile hydrocarbon levels were encountered in only two of the selected VEWs during drilling with no significant indications of contamination encountered in VEW-07, VEW-08, VEW-17, or VEW-18. However, these perimeter VEWs were included in MCT-1 to provide information about the influence that these areas may exert on other portions of the trench.
The second MCT (MCT-2) included VEW-09, VEW-10, VEW-11, VEW-13, VEW-14, and VEW-16. The objective of MCT-2 was to evaluate the influence of six VEWs that were not included in either the initial pilot test or MCT-1, and that appeared to be located outside the direct influence of VEWs utilized in MCT-1. For determination of direct influence, the changes in oxygen, carbon dioxide, and TVH levels were evaluated. The VMPs that were influenced most by the VEW configuration were those points that experienced the greatest changes in soil gas chemistry. The expected responses from an influenced VMP are increases in oxygen, decreases in carbon dioxide, and decreases in TVH. These changes ensue from displacement of existing soil gas with ambient air pulled in from the surface or adjacent to contaminated soils. VEW-03 and VEW-04 are the only two VEWs that exhibited all three of these changes. With the exception of VEW-03, only six VEWs remained that were not included in either the initial test or MCT-1, so those six VEWs were tested during MCT-2.
The third MCT (MCT-3) included VEW-03, VEW-04, VEW-08, VEW-10, VEW-12, and VEW-15. The results of the previous configuration tests were used to select the appropriate VEWs. The objective of the third test was to evaluate the influence of six VEWs that are the best candidates for extracting VOCs from subsurface soils. The evaluation includes direct influence of VEWs as well as extraction potential. For determination of direct influence, pressure responses and changes in oxygen, carbon dioxide, and TVH levels were evaluated. For determination of TVH extraction potential, the total mass (in pounds) of TVH was evaluated for each of the VEWs during MCT-1 and MCT-2. VEW-03 and VEW-04 exhibited significant responses during both MCT-1 and MCT-2 and, therefore, were included in the MCT-3 configuration. In addition, VEW-08, VEW-10, VEW-12, and VEW-15 were selected due to their potential for contaminant removal.
The procedures for performing each MCT included three primary tasks with different objectives. The first task was monitoring soil gas hydrocarbon concentrations and flow from each extraction well over time to determine the mass removal rates relative to other monitoring locations. The second task was the collection of soil gas chemistry (field screened) and pressure response data from each of the VEWs and VMPs not included in the extraction configuration to assess the influence of the configuration on subsurface soil gas. The third task was the collection of emissions data over the operations time of each configuration. Each of these procedures are briefly described below.
Prior to beginning extraction, soil gas chemistry data were collected at all VEWs and VMPs to establish baseline concentrations. Once extraction was initiated, the flow from each VEW was measured and adjusted as necessary to maintain approximately uniform flow from each well. Air flow rates were measured and soil gas samples were collected from each VEW for field screening of total hydrocarbons. These measurements and sample collection activities were performed on a periodic schedule such that measurements were made after the flow rates were initially optimized, after approximately six hours of extraction, 24 hours after extraction, and 2, 4, 8, and 14 days after extraction. For MCT-3, the measurements were continued after 20, 24, and 28 days after beginning extraction from the test configuration. Only screening analyses with field instruments were performed except during the 1997 system check discussed in Section 3.3.1. During this test, soil gas samples were also collected from the four VEWs in the pilot test configuration for confirmatory laboratory analysis.
Influence of each VEW configuration was determined based on changes observed in soil gas chemistry over time and pressure responses observed in non-extraction wells and VMPs. Monitoring for soil gas chemistry changes during multiple configuration testing was performed on the same schedule as the flow and VOC measurements described in the previous paragraph (15 minutes, 6 hours, then 1, 2, 4, 8, 14, 20, 24, and 28 days after beginning extraction). Prior to shutting of the blower at the end of each MCT, the configuration was modified to determine the relative influence that individual VEWs in a configuration contribute to the overall influence of a particular configuration. This was performed by shutting off flow to all but one VEW and measuring pressure responses at all other VEWs and VMPs. This single VEW testing was repeated until all VEWs in the multiple VEW test configuration were tested.
Emissions data were collected during each MCT to estimate VOC emission rates of each configuration. The concentration of VOCs detected in the emission samples are used to estimate the mass of VOCs removed. These samples were collected over time from the inlet line located just prior to the moisture separator. Following initiation of extraction from each VEW configuration, emission samples were collected for laboratory analysis after approximately 15 minutes, 6 hours, 24 hours, 48 hours, 96 hours (4 days), 336 hours (14 days), and, for MCT-3, 672 hours (28 days). Emission samples were collected on the same schedule as the soil gas screening described in the preceding paragraphs. Emissions data on days 8, 20, and 24 were only screened using field instruments.