Design Considerations for Large Diameter Auger Soil Mixing with Steam and Zero- Valent Iron for Remediation of Chlorinated VOCs

Transcription

1 Design Considerations for Large Diameter Auger Soil Mixing with Steam and Zero- Valent Iron for Remediation of Chlorinated VOCs David Hanley, Geosyntec Consultants Jeff Ahrens, Geosyntec Consultants Fifth Conference on Innovative Environmental Assessment and Remediation Technology April 23-24, 2014 Kennesaw State University

2 LDA-Steam/ZVI Technology Overview 2 Used with permission from FECC, Inc.

3 LDA-Steam/ZVI Technology Overview Steam Hot Air Zero-Valent Iron (ZVI) Organic Vapors Extracted Steam Extracted Hot Air Treatment Emission Source Area 3

4 Presentation Overview Outline Technology overview Applicability, advantages and limitations Design considerations Site Layout Thermal treatment ZVI treatment Data acquisition/management Treatment decision logic Key Themes Contact of treatment with contaminants Adaptability of technology based on real-time data 4

5 LDA-Steam/ZVI Technology Overview Full scale treatment completed at a handful of sites Design completed for several sites, pending implementation Developing technology still in need of refinement, research 5

6 Applicability Appropriate for sites with large, high concentration source areas High contaminant mass Non-aqueous phase liquids Not cost effective for small treatment volumes Heterogeneous soils Ability to focus on high-concentrations zones within treatment area 6

7 Technology Advantages Effective in heterogeneous source zone and low permeability layers ZVI serves as polishing step to address back-diffusion Ability to treat multiple contaminants Relatively short treatment duration No long term operation and maintenance costs Adaptable treatment based on VOC monitoring results 7

8 Technology Limitations Not appropriate for every site Lower cost alternatives possible as sites with shallow impacts, smaller source areas Aboveground structures and buried utilities limit implementation Not practical in bedrock High capital cost Energy intensive (500-1,000 kw) Water intensive (1,500 gal/hr) Effective on limited classes of contaminants e.g. VOCs, SVOCs, petroleum hydrocarbons 8

9 Comparable Technologies Technologies to address high-concentration source zones in deep, heterogeneous soils LDA-Clay Immobilization/ZVI LDA-Excavation Electrical Resistance Heating (ERH) EZVI Injection In situ bioremediation In situ chemical oxidation 9

10 Treatment Areas Treatment area typically defined by groundwater concentration e.g. Source area with TCE > 10 mg/l Treatment zones established within treatment area Based on depths and concentrations of contamination Different treatment protocols in each zone 10

11 11 Example Boring Layout

12 Cell Layout No overlap Gaps between borings Full overlap 17% overlap On interior borings 12

13 Treatment System Components Used with permission from FECC, Inc. 13

14 Thermal Treatment Steam, hot air pumped into soil through auger during mixing Target temperature determined by contaminant properties Drill rate approximately 1-4 ft/min (slower during first pass) Balance drill advancement rate and steam delivery to achieve desired temperature Compound PCE TCE cis-1,2-dce VC Boiling Point 250ºF 189ºF 140ºF 7.9ºF 14

15 Off-gas treatment 15 Blower moves off-gas from shroud through treatment units Conditioning unit cools gas, removes water vapor and particulates Contaminant destruction carried out in oxidizer (thermal or chemical) Activated carbon used as backup, or as primary treatment for smaller projects Liquids require additional treatment Used with permission from FECC, Inc.

16 ZVI Treatment Granular ZVI delivered as slurry with guar gum, water Mixed in batch tanks and pumped down kelly bar Delivered during final auger pass following thermal treatment Introduction of oxygen during mixing impacts iron demand Concentrations from around % of soil mass Dosing based on iron demand Determined from FID/GC response during thermal treatment >1000 pounds of iron per boring typical 16

17 Data Acquisition and Management Key parameters continuously measured Depth Steam temp, flow rate Compressed air temp, flow rate Off-gas temp, flow rate Off-gas composition Flame ionization detectors and gas chromatographs continuously monitor off-gas Real-time data allows for adaptive treatment implementation based on results 17

18 Treatment Data Steam and Hot Air Injection ZVI Injection 18 Used with permission from FECC, Inc.

19 19 Used with permission from FECC, Inc. Treatment Data

20 20 Used with permission from FECC, Inc. Treatment Data

21 Decision Logic Pilot test can be used to develop decision logic for fullscale implementation Perform additional passes based on reduction in FID/GC concentrations Temperature targets ZVI Dosing based on initial pass FID/GC reading Treatment plan can be altered during implementation 21

22 Decision Logic Example First Pass Thermal Treatment Completion Criteria ZVI Treatment FID < 500 ppm Minimum 2 passes Maintain 150º Final pass TCE < 100 ppm 0.5% iron 500 FID 1000 ppm Minimum 2 passes Maintain 160ºF Focused treatment intervals Final pass FID < 500 ppm 1% iron FID > 1000 ppm Minimum 4 passes Maintain 160ºF Focused treatment intervals 90% FID reduction Or 120 minutes 2% iron 22

23 Additional Considerations Preparation Utility clearance is critical Site demolition, clearing, grading Well abandonment Initial survey Establishment of work zones Electrical connection requirements Post-remediation Soil, groundwater sampling Subsurface temperatures Used with permission from FECC, Inc. 23

24 LDA-Steam/ZVI Summary Key design considerations Site suitability Boring layout/spacing determination Effects on site-specific contaminants Treatment decision logic Key benefits Treatment delivery, contact with contaminants Real-time monitoring, adaptability of treatment 24

25 David Hanley Geosyntec Consultants Used with permission from FECC, Inc. 25