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A Combined Ozone Remedy for a Mixed VOC DNAPL Source Zone
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A Combined Ozone Remedy for a Mixed VOC DNAPL Source Zone

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Background/Objectives. In 2003, 1,300 drums and over 3,000 tons of soil were excavated from a drum disposal area in New England. Residual DNAPL created a 2,500 foot long plume that includes …

Background/Objectives. In 2003, 1,300 drums and over 3,000 tons of soil were excavated from a drum disposal area in New England. Residual DNAPL created a 2,500 foot long plume that includes chlorobenzenes, toluene, and chlorinated ethenes. The plume discharges to a wetland and has led to vapor intrusion concerns at downgradient properties. Full-scale source zone remediation has been implemented to mitigate potential risks to ecological and human receptors.

Approach/Activities. Following extensive site characterization, bench-scale testing, and a successful field pilot test, the full-scale source zone remedy began in November 2010. The combined remedy approach uses physical, chemical, and biological treatment mechanisms to destroy the residual DNAPL in the vadose and saturated zones. Soil vapor extraction (SVE) and air sparging target the more volatile compounds, while in situ ozone injection (IOI) targets the less volatile compounds such as chlorobenzenes. Aerobic biological activity is also likely enhanced as a result of oxygen injection from IOI and air sparging. Three ozone injection systems deliver a total of 100 lbs of ozone per day to the subsurface; the SVE system extracts soil vapor at a rate of 650 scfm; the air sparge system continuously sparges air at 50 scfm at approximately 30 psi.

Results/Lessons Learned. Performance monitoring includes analysis of VOC concentrations in soil, soil gas, and groundwater. Quarterly low-flow groundwater sampling has shown substantial decreases in groundwater VOC concentrations relative to baseline. In the first six months of operation, 18 of the 20 monitoring wells sampled showed decreases in total VOC concentrations ranging from 14 to 97% with an average decrease of 57%. Furthermore, the mass discharge of total VOCs in groundwater from the source area has decreased from approximately 105 g/day before pilot-test start-up to less than 4 g/day. Concentrations of VOCs in soil gas are monitored in real-time by an automated soil gas monitoring system equipped with a photoionization detector (PID), and on a periodic basis with Waterloo Membrane Samplers™ that provide a speciated analysis of VOCs in soil gas. Of the 47 soil gas monitoring points that were sampled during the first six months of operation, 36 show decreasing trends in soil gas TVOC concentrations. Minimal rebound was observed in soil gas concentrations after treatment was temporarily suspended. Performance monitoring data have informed periodic system optimization to increase the efficiency of the remedy. These results indicate that the combined remedial technologies are effectively reducing source mass and mass discharge, and that the aggressive two year remedial time-frame will likely be met.

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  • 1. Combined Ozone, Air Sparge, and SVE Remedy for Treatment of a Mixed VOC DNAPL Source ZoneChapman M. Ross, G. Owen Cadwalader, Peter J. Zeeb – Acton, MA Bruce Marvin – Oakland, CA
  • 2. Presentation Outline Site Background Performance Monitoring  Methods  Results  Long-term trends Optimization Conclusions
  • 3. Site Background Former sand and gravel borrow pit in New England Removed 1,300 drums & 3,000 tons soil (up to 30 ft bgs) 18 Months into Full-Scale Treatment
  • 4. Drum & Soil Removal Ruptured Drums
  • 5. Chemical Properties of Site COCs Vapor Henrys Law Solubility Koc Pressure Constant mg/L ml/g mm Hg dimensionlesstrichloroethene 1,100 125 60 0.4cis-1,2-dichloroethene 800 50 210 0.21,1,1-trichloroethane 4,400 150 100 0.7toluene 515 300 22 0.3xylene 200 240 10 0.3chlorobenzene 500 330 12 0.131,2,3-trichlorobenzene 18 7,400 0.2 0.121,2,4-trichlorobenzene 30 9,200 0.3 0.06
  • 6. Chemical Properties of Site COCs Vapor Henrys Law Solubility Koc Pressure Constant mg/L ml/g mm Hg dimensionlesstrichloroethene 1,100 125 60 0.4cis-1,2-dichloroethene 800 50 210 0.21,1,1-trichloroethane 4,400 150 NAPL 100likely present. 0.7 7 VOCs in GW fromtoluene 515 300 22 0.3 1 to ~20% of aq. solubilityxylene 200 240 10 0.3 prior to treatmentchlorobenzene 500 330 12 0.131,2,3-trichlorobenzene 18 7,400 0.2 0.121,2,4-trichlorobenzene 30 9,200 0.3 0.06
  • 7. Potential Receptors Wetland/ Vernal Pool Drum Excavation Area Town Hall 200 100 0 200 feetVOC plume is approximately ½ mile long
  • 8. Treatment AreaPilot FullTest Scale
  • 9. Source Characterization – Soil and GW Groundwater Flow
  • 10. Source Characterization – Soil and GW Groundwater Flow
  • 11. Source Characterization – Soil and GW Groundwater Flow
  • 12. Pilot Test to Full-Scale Design Pilot Test Full-Scale Treatment Area System 2,500 ft2 10,000 ft2 Ozone 27 lb/day 100 lb/day Air Sparge 25 scfm 55 scfm SVE 300 scfm 600 scfmPilot Test (25% of source) Duration 7 months 2+ years Full-Scale
  • 13. Full-Scale Cross-SectionOzone Injection and SVE Ozone InjectionOzone and Air Sparging
  • 14. Performance Monitoring Soil Gas  Real time monitoring system: TVOC, O3, O2, CO2  Waterloo Membrane Samplers (WMSTM)  Handheld PID measurements Groundwater  Analytical laboratory data  ORP field data Shutdown Test
  • 15. Soil Gas Results – Vadose Zone TVOCs Baseline
  • 16. Soil Gas Results – Vadose Zone TVOCs 18 Months Operation
  • 17. Soil Gas Results – Vadose Zone TVOCsTVOC (ppm) Baseline Feb 2012 % ReductionAverage 794 13 98Median 112 4.9 96Maximum >10,000 101 >99 18 Months Operation
  • 18. WMSTM Soil Gas Results – Vadose Zone VOCsBaseline
  • 19. WMSTM Soil Gas Results – Vadose Zone VOCs18 Months Operation
  • 20. WMSTM Soil Gas Results – Vadose Zone VOCs Vadose zone treatment now focused on these remaining high concentration areas.18 Months Operation
  • 21. Groundwater Sampling Results – VOCs Baseline
  • 22. Groundwater Sampling Results – VOCs 18 Months Operation
  • 23. Groundwater Sampling Results – VOCs GW treatment now focused on these remaining highconcentration areas. 18 Months Operation
  • 24. Long-term Trends in GW in TCE Plume Core: LR-18S
  • 25. Long-term Trends in GW in TCE Plume Core: LR-18S 97% Reduction 99% 91%
  • 26. Long-term Trends in Capillary Fringe GW in TCB Plume Core: OZ-CAP-33
  • 27. NAPL Evaluation – Pre/Post-Treatment(Cherry and Feenstra, 1991)
  • 28. Mass Discharge of VOCs – Transect Method  6 wells  K = 15 ft/day  q = 0.045 ft/day  B = 6 to 11 ft Groundwater Flow Einarson and Mackay, 2001
  • 29. Mass Discharge of VOCs - Summary Treatment Area Mass Discharge of VOCs in Groundwater 18 months operation 18 tons of ozone injected total (pilot and full- scale)
  • 30. Optimization Efficient focused Real-time Data• SGSS Optimization treatment• ORP Probes • Automatic data processing & analysis using OptiRTC Targeting • Decision matrix for recalcitrant laboratory data analysis zones early • Remote system control Laboratory Data• Groundwater• Soil gas (WMSTM) Faster Site ClosureSee Owen Cadwalader’s presentation on OptimizationSession A5 - Wednesday 9:40 A.M (Abstract #141)
  • 31. Conclusions Decrease from 7 to 3 in number of VOCs present as NAPL 2 orders of magnitude reduction in groundwater VOC mass discharge Moderate rebound in groundwater VOCs after 6-week shutdown test (increase by 90% on average) On target to meet goal of <1 mg/L TVOC in groundwater
  • 32. AcknowledgementsCo-Authors – G. Owen Cadwalader, Peter J. Zeeb, Bruce K. Marvin (Geosyntec) Peter Shellito and Chris Martin – Geosyntec Field Crew Chapman Ross - cross@geosyntec.com