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.

1. Combined Ozone, Air Sparge, and SVE
Remedy for Treatment of a Mixed VOC
DNAPL Source Zone
Chapman 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 Henry's Law
Solubility Koc
Pressure Constant
mg/L ml/g mm Hg dimensionless
trichloroethene 1,100 125 60 0.4
cis-1,2-dichloroethene 800 50 210 0.2
1,1,1-trichloroethane 4,400 150 100 0.7
toluene 515 300 22 0.3
xylene 200 240 10 0.3
chlorobenzene 500 330 12 0.13
1,2,3-trichlorobenzene 18 7,400 0.2 0.12
1,2,4-trichlorobenzene 30 9,200 0.3 0.06

6. Chemical Properties of Site COCs
Vapor Henry's Law
Solubility Koc
Pressure Constant
mg/L ml/g mm Hg dimensionless
trichloroethene 1,100 125 60 0.4
cis-1,2-dichloroethene 800 50 210 0.2
1,1,1-trichloroethane 4,400 150 NAPL 100likely present.
0.7
7 VOCs in GW from
toluene 515 300 22 0.3
1 to ~20% of aq. solubility
xylene 200 240 10 0.3
prior to treatment
chlorobenzene 500 330 12 0.13
1,2,3-trichlorobenzene 18 7,400 0.2 0.12
1,2,4-trichlorobenzene 30 9,200 0.3 0.06

7. Potential Receptors
Wetland/
Vernal Pool
Drum
Excavation
Area
Town Hall
200 100 0 200 feet
VOC plume is approximately ½ mile long

8. Treatment Area
Pilot Full
Test 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 scfm
Pilot Test (25% of source) Duration 7 months 2+ years
Full-Scale

13. Full-Scale Cross-Section
Ozone Injection and SVE
Ozone Injection
Ozone 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 TVOCs
TVOC (ppm) Baseline Feb 2012 % Reduction
Average 794 13 98
Median 112 4.9 96
Maximum >10,000 101 >99
18 Months Operation

18. WMSTM Soil Gas Results –
Vadose Zone VOCs
Baseline

19. WMSTM Soil Gas Results –
Vadose Zone VOCs
18 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 high
concentration 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
Closure
See Owen Cadwalader’s presentation on Optimization
Session 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. Acknowledgements
Co-Authors – G. Owen Cadwalader, Peter J. Zeeb,
Bruce K. Marvin (Geosyntec)
Peter Shellito and Chris Martin –
Geosyntec Field Crew
Chapman Ross - cross@geosyntec.com