Technology Status Report: In Situ Flushing - CLU-IN

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In Situ Flushing Project Summaries GWRTAC Case Study Database visits, predesign analysis, Modflow analysis, tracer test analysis, surfactant selection and optimization, surfactant recovery design, and fate transport analysis. The project was conducted within an eight month (including three weeks of actual flushing) period including procuring regulatory approval for injection. Laboratory Methods and Results The target chemicals included benzene, toluene, ethylbenzene xylenes (BTEX) and total petroleum hydrocarbons (TPH). Surfactants selected for laboratory testing were screened using the following criteria. Toxicity and biodegradability Potential enhancement of contaminant removal Potential for economic reuse and recovery of the surfactant/cosolvent Sorption of the surfactant/cosolvent onto the soil matrix Potential for the surfactant/cosolvent to remove mixed wastes (i.e., solvents, hydrocarbons, and cationic metals Resiliency of the surfactant/cosolvent (i.e., how the surfactant resists subsurface chemical reactions The following surfactants met the first three criteria listed above: DOWFAX* 8390, anionic Tween 80, nonionic STEOL CS-330, anionic SD-4, anionic with solvent Additional testing was conducted to determine which surfactant best met the above criteria for the site specific conditions. The following are detailed descriptions of the procedures followed for each laboratory method utilized in the surfactant screening process. Surfactant Precipitation. The objective of surfactant precipitation tests was to quantify the precipitation boundaries of the surfactants under investigation and to determine whether the phase boundary is crossed due to ionic composition (ionic surfactants) or ground water temperature (nonionic surfactants) of the system. Precipitation (phase separation) assays were conducted using 120 ml glass vials with 100\~ml of solution in each vial. The ionic strength of the ground water was varied by addition of excess multivalent ions to assess precipitation of anionic surfactants; the ground water temperature was varied to assess phase separation of the nonionic surfactants. Only one set of samples was mixed and allowed to equilibrate at each target temperature. Surfactant concentrations were varied from 0.1 to 50 times the CMC for assessing phase separation. All the listed surfactants, with the exception of SD-4, demonstrated resistance to precipitation in the presence of salts. As a result, the SD-4 was eliminated from further consideration. Surfactant Sorption. Surfactant sorption was assessed in batch systems by contacting solutions of varying surfactant concentrations with a constant mass of soil from the site. The experiments utilized 5 g of soil with 25 ml of surfactant solution with equilibration times of at least 24 hours. Upon centrifugation for solids\_liquid separation, aliquots of the supernatant were analyzed for the Ground-Water Remediation Technologies Analysis Center Operated by Concurrent Technologies Corporation Appendix - Page 142 of 164 Copyright GWRTAC 1998 Revision 1 Tuesday, November 17, 1998
In Situ Flushing Project Summaries GWRTAC Case Study Database equilibrium surfactant concentration via HPLC. The mass of surfactant sorbed was determined by mass balance (with appropriate controls to account for other losses). At least duplicates of each sample were conducted. The results showed that the STEOL exhibited the least amount of sorption while the Tween exhibited the highest (refer to Appendix A). Sorption for the STEOL was extremely low, averaging 0.004 g surf/g soil. Contaminant Solubilization (includes mobilization systems). The objective of the solubilization tests was to quantify the solubilization potential of surfactants for the NAPL from the site. Contaminant solubilization was assessed in batch systems (40 ml EPA vials) by contacting an excess of the NAPL with solutions of varying surfactant concentrations (ranging from CMC/10 to 20x CMC) in site ground water. Aqueous NAPL concentrations were analyzed using a Gas Chromatograph (GC). Surfactant concentrations were analyzed using a high performance liquid chromatograph (HPLC). In this test, the STEOL and the Tween produced similar results (maximum of 7000 ppm TPH), exceeding the solubilization observed for DOWFAX* (maximum of 5500 ppm TPH). As part of the solubilization study the surfactant/ NAPL solution is shaken and centrifuged. During shaking, both the Tween and STEOL formed a "gel" phase with the NAPL solution. The resulting "gel" was white and relatively stable; the gel took several hours to disperse. This phenomena was not observed in the samples containing DOWFAX*. The tests were repeated for all three surfactants with similar results. Any gel phase generated could potentially be broken chemically or thermodynamically. However, gel mitigation was not within the scope of this project. Contaminant Extraction Column Studies. Column studies were conducted in glass liquid chromatography columns (2.5 cm diameter by 15 cm length). A time-controlled fraction collector was utilized to collect discrete effluent samples for GC or HPLC analysis. The surfactant/cosolvent concentrations for each system were selected based on predicted performance. The surfactant/cosolvent solutions were prepared using native groundwater and conducted at 15 C. Hydraulic flows rates through the column were determined prior to flushing with the surfactant solution. During surfactant flushing the following parameters were monitored continually: flow, injection rate, and pressure drop. Each effluent sample was checked for free phase NAPL and NAPL concentrations in the effluent. Flushing was continued until an asymptotic level of removal was achieved. STEOL was selected for column evaluation since it demonstrated the lowest sorption and highest solubilization potential during batch testing. The DOWFAX* was also selected for screening since it was the only surfactant that did not form a "gel" phase when mixed with the NAPL. Since there is an abundance of NAPL at the location, and the groundwater extraction system is relatively turbulent, "gel" formation is probable. As is illustrated by breakthrough curves, the DOWFAX* demonstrated better solubilization enhancement than the STEOL. However, better recovery of the STEOL was observed (92%) versus the DOWFAX* (88%). There was no significant increase in pressure drop across the column in either test. All of the surfactant systems tested demonstrated promise for application in this study. The Tween and the STEOL exhibited a higher solubilization potential than the DOWFAX* in the batch tests. The STEOL demonstrated significantly lower batch sorption results than the Tween or the DOWFAX*. However, during the batch solubilization tests both the STEOL and the Tween repeatedly formed a "gel" phase after agitation. This phenomenon was not observed with the Ground-Water Remediation Technologies Analysis Center Operated by Concurrent Technologies Corporation Appendix - Page 143 of 164 Copyright GWRTAC 1998 Revision 1 Tuesday, November 17, 1998
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Technology Status Report Technology
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ABSTRACT This technology status rep
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LIST OF TABLES Table Title Page 1 I
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1.0 INTRODUCTION / PURPOSE OF STATU
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a laboratory-scale project. As illu
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3.1 Flushing Solutions 3.0 ANALYSIS
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(approximately eight) full-scale pr
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Table 1. In Situ Flushing - Summary
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Table 3 In Situ Flushing - Geology
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Table 4 In Situ Flushing - Recovere
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Full-Scale/Commercial 26% Figure 2.
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Site Remediation 25% Figure 4. In S
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NAPL Removal 34% Figure 6. In Situ
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Figure 8. In Situ Flushing - Distri
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Number of Projects 35 30 25 20 15 1
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Number of Case Studies 45 40 35 30
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25 ft and 50 ft and 10 ft and 100 f
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Unconfined Aquifer 65% Figure 16. I
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In Situ Flushing Project Summaries
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Technology Status Report: In Situ Flushing - CLU-IN

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