Technology Status Report: In Situ Flushing - CLU-IN

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In Situ Flushing Project Summaries GWRTAC Case Study Database GWRTAC ID: FLSH0078 Project Name: PPG Plant, Lake Charles, LA City: Lake Charles State/Province: LA Primary GWRTAC Personal Communication Source (Name/Organization): Report(s)/Publication(s) (GWRTAC Source): "Surfactant-Enhanced DNAPL Remediation at a Highly Heterogeneous Site", John Fountain, Geology Department, State University of New York at Buffalo, presented May 6, 1998 at GWRTAC/U.S. EPA TIO "Advances in Ground-Water Remedation Conference", San Francisco, CA Project Summary: The following text was excerpted from "Surfactant-Enhanced DNAPL Remediation at a Highly Heterogeneous Site", John Fountain, Geology Department, State University of New York at Buffalo, presented May 6, 1998 at GWRTAC/U.S. EPA TIO "Advances in Ground-Water Remedation Conference", San Francisco, CA: At the PPG Plant in Lake Charles, Louisiana, a site with known DNAPL (primarily dichloroethane - EDC) contamination, a pilot test was undertaken to effect DNAPL source zone remediation. The site is underlain by a thick sequence of interbedded clays and thin sands of fluvial-deltaic and marine origin (Holocene and Pleistocene aged Beaumont or Prarie Formation). The site hydrostratigraphy is thus complex, and a regional aquifer (Chicot Aquifer) is present at depth. The surfactant field test was conducted in 1997-1998, only in the shallowest water-bearing unit, the "10 foot sand", which had been consistently found beneath the site at about 10 feet bgs. DNAPL was likely present in the sand layer based on cone penetrometer testing and analysis of groundwater samples collected from monitoring wells. The DNAPL primarily consists on dichloroethane, or EDC. A sand layer at 20 feet was also contaminated. Grain size analysis showed that a one foot sand zone was present at 10.5 feet bgs, and another foot of silty sand was present beneath this one foot sand zone. Permeameter tests on core samples revealed hydraulic conductivities ranging from 6 x 10-3 cm/sec in sand to
In Situ Flushing Project Summaries GWRTAC Case Study Database The surfactant field test was conducted in a 12 x 15 foot sheet piling cell. The 20 foot sand zone was pressurized to minimize the potential for DNAPL mobilization. Three injection wells and three withdrawl wells were installed within the test cell in a line-drive pattern. A partioning tracer test conducted indicated tht only 50% of the test cell was swept in the 30 day duration of the test, suggesting that the low permeability zones apparently occupied about half of the target zones. DNAPL satuaration was oonly about 0.4% at the conclusion of the tracer test, indicating approximately 6 gallons of EDC were present within the test cell. Surfactant blending was undertaken by considering the following: An anionic surfactant would be needed to minimize sorption by the clay; The high (8,700 mg/L) solubility of EDC; and, Low interfacial tension systems were not desired. The surfactant linear alkylbenzene sulfonate was selected as surfactant sorption batch and column tests showed low sorption. Interfacial tension was 1.3 dynes/cm, and the critical micelle concentration was 0.044%. The surfactant was injected from February through June 1997, and water circulation continued through December 1997. The injection rates dropped dramatically soon after surfactant injection began; this was believed to be due to a clay plug formed around the injection well. A total of approximately 2,500 gallons was injected, which was less than one total pore volume, and equivalent to about two "effective pore volumes". Based on breakthrough curve analysis for the surfactant and a conservative tracer, nearly all of the flow through the test cells was through high permeability paths near the center of the cell. Breakthrough curves potted by volume were nearly identical for the surfactant and a conservative tracer, indicating limited sorption effects occurred. Soil cores were taken near monitoring and extraction wells. In high permeability zones, cores revealed low EDC concentrations to the top of the clay. Cores from the corners of the test cell, in low permeability zones, revealed higher EDC. The highest EDC levels in otherwise "clean" cores occurred at the top of the clay unit, signifying apparent diffusion into the clay. Significant EDC was found at all levels in the base clay. Conclusions made from this project include the following: Other than well development problems, surfactant system worked well in clayey units; Apparently all units where breakthrough occurred were cleaned of DNAPL; EDC was persistent in clay, reflecting a combination of diffusion and flow (strong downward gradient exists at site); The significance of fractures at the site within the clay is to be determined. Also, it was concluded that: Heterogeneities slow the remediation process; Behavior in complex systems waas as predicted from model based on tracers; The persistance of EDC in the clay units suggest significant residual would always be present; and Clear definition of objectives are required to determine if this technology will be appropriate for a given site. Report(s)/Publication(s) (Additional Information Sources): "Surfactant-Enhanced DNAPL Remediation at a Highly Heterogeneous Site", John Fountain, Geology Department, State University of New York at Buffalo, presented May 6, 1998 at GWRTAC/U.S. EPA TIO "Advances in Ground-Water Remedation Conference", San Francisco, CA Ground-Water Remediation Technologies Analysis Center Operated by Concurrent Technologies Corporation Appendix - Page 155 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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