**Office of Research and Development**

National Risk Management Research Laboratory, Ground W ater & Ecosystems Restoration Division, Ada , OK 74820



### Eva Davis, PhD US EPA
– RS Kerr Environmental Research Center 

## Thermal Remediation **in Fractured Rock** 

**January 2014** 

# In Situ Thermal Remediation **Applications** • Aggressive technologies:

– Generally applied to Source Zones to Recover NAPL • Applicable to VOCs and SVOCs • Applicable in wide variety of settings

– Simple and highly heterogeneous lithology

– Above and below water table

– Sites with surface structures

– Fractured bedrock 

### Expected Outcome in **Porous Media** • Large percentage of mass recovered • Orders of magnitude reductions in soil and groundwater concentrations • Orders of magnitude reduction in mass flux to downgradient plume • P&T or Monitored Natural Attenuation effective for downgradient plume **2**

# Mechanisms for Enhancing Recovery **of VOCs by Thermal Remediation**
• 

## Increasing the temperature:

– Increases vapor pressure • 

### For VOCs, vapor pressure increases more than an order of magnitude going from ambient temperature to 100 ° C

– Decreases viscosity of water and NAPL • 

### Most significant for viscous NAPLs

– Decreases adsorption • 

### May also increase desorption rate **3**

# For Best **Results, Heat**  **to the Boiling Point of Water** 
• 

### Boiling Point is a “Moving Target” • 

### When NAPLs are present, co - boiling lowers boiling point below that of water alone • 

### Pulling vacuum on subsurface lowers boiling point • 

### Below water table, boiling point increases due to hydrostatic pressure of water • 

### Pressure increases in low permeability rock matrix due to heating will increase the boiling point • 

### Thus, higher temperatures/somew **hat more energy required for low**  **permeability /sparsely**  **f ractured rock**  **4**

# Lab Tests on Rock Discs
• 

## More than 98% of TCE & PCE mass removed in first 24 – 25 hours of heating to 105 ° C • 

### Heating duration had a greater effect on VOC removal than temperature • 

### Thermal remediation favored by high porosities and low fraction of organic carbon **5** TCE saturated siltstone discs inside convection oven. From Lebron et al., 2012

# Challenges of Fractured Rock
• 

### Characterization of contaminant distribution and thus defining the area to be treated • 

### Moving contaminants out of low permeability matrix

– During thermal remediation, pressure buildup in low p ermeability matrix wi ll force contaminants to higher permeability zones 

### • 

### Low permeability matrix, low fracture frequency increases the boiling point of water/contaminants • 

### Ensuring capture of vapors and groundwater • 

### These are also challenges in heterogeneous porous media **6**

# Thermal Technologies
• 

## Three main technologies in use today:

– Steam Enhanced Extraction (SEE)

– Electrical Resistance Heating (ERH)

– Thermal Conductive Heating (TCH) 

## • 

## Differ in the means by which energy is added to the subsurface • 

## Life cycle assessments show that thermal technologies use less energy than conventional SVE ( Hiester and Schrenk , 2005) **7**

# Steam Enhanced Extraction
• 

## Steam injected under pressure, with continuous multiphase extraction • 

## Steam flows in fractures, heat conducted into matrix from fractures • 

## Co - air injection used to aid in upward vapor migration **8** Temperature distribution after 30 day s of steam injection into a 100 μm fracture at 50 ft depth, using 0.8 psi/ft (simulated using a modified Marx Langenheim solution; Tom Heron et al. 1999)

# Loring AFB SEE Research **Project**
• 

### Limestone Quarry where drums of wastes had been buried • 

### Complex bedrock structures with several major fracture features • 

### Sparse fracture frequency and low permeability in target area **9**

# Characterization **of the Loring Quarry**
• 

### Mapping of Fractures • 

### Coring during Well Installation • 

### Borehole Geophysics • 

### Acoustic Televiewer • 

### Methanol Extracted Rock Chip Sampling • 

### Discrete Interval Groundwater Sampling • 

### Head Measurements **10**

# Characterization **of the Loring Quarry (**  **con’t )**  • 

## Discrete Interval Transmissivity Testing • 

## Interconnectivity Testing • 

## Deep Groundwater Sampling

– Two deep angled borings under target treatment area **11**

# Loring AFB SEE Research **Project**

**Electrical Resistance**  **Tomography t**  **o monitor heating** 



### • 

### ERT seemed to show expected heat flow in fractures **12 4 October**  **2002 7 November 2002**  **19 November 2002 30 November 2002**  **Percent Difference of Conductivity Percent Difference of Conductivity**  **Percent Difference of Conductivity TC**  **- 1**  **VEA -**  **9 VEA**  **- 4**  **10.0 13.5**  **17.0 20.5**  **24.0 27.5**  **31.0 34.5** **D e** **p t** **h (** **m )**  **3.0 6.5** 

**0.0 12.1**  **24.1 Iteration**  **= 8 RMS = 9043.21%**  **38.0 Normalized**  **L2 = 30.1**  **Percent Difference of**  **Conductivity (%)**  **0.0 150**  **300 450**  **600 TC**  **- 1**  **VEA -**  **9 VEA**  **- 4**  **6.5 10.0**  **13.5 17.0**  **20.5 24.0**  **27.5 31.0**  **34.5 D** **e p** **t h** **( m** **) 3.0** 

**0.0 12.1**  **24.1 Iteration**  **= 8 RMS = 157.76%** 

**Percent Difference of**  **Conductivity (%)**  **0.0 150**  **300 450**  **38.0 TC**  **- 1**  **VEA -**  **9 VEA**  **- 4**  **6.5 10.0**  **13.5 17.0**  **20.5 24.0**  **27.5 31.0**  **34.5 D** **e p** **t h** **( m** **) 3.0** 

**Normalized L2**  **= 98.82 38.0**  **12.1 24.1**  **RMS = 1010.71% 0.0**  **600 Iteration**  **= 8**

**Percent Difference of**  **Conductivity (%)** 

**150 300**  **450 600**  **0.0 TC**  **- 1**  **VEA -**  **9 VEA**  **- 4**  **Percent Difference of Conductivity 10.0**  **13.5 17.0**  **20.5 24.0**  **27.5 31.0**  **34.5 D** **e p** **t h** **( m** **) 6.5**  **3.0**

**Normalized L2**  **= 123.30 38.0**  **0.0 12.1**  **24.1 RMS = 827.75%**  **Normalized L2**  **= 3392.89 Iteration**  **= 8**

**Percent Difference of**  **Conductivity (%)**  **150 300**  **450 600**  **0.0**

# Loring AFB Temperature **Profiles Steam flow**  **in fractures Heat conduction from**  **steam in fractures into rock matrix** 

**13**

# Loring Quarry **SEE Conclusions**

**Lori ng A**  **queous Concentrations**

0 1000 2000 3000 4000 5000 6000 7000 8000 9000

30 -Aug 2-Se p 5- Se p 8-Sep 11-Se p 14 -Sep 17-Sep 20-Se p 23 -Sep 26-Se p 29 -Sep 2-Oct 5-Oct 8- Oc t 11-Oct 14 -Oc t 17 -Oct 20-Oct 23 -Oc t 26-Oct 29 -Oc t 1-No v 6- No v 9-Nov 12-No v 15-Nov 18-No v 21 -Nov 24-Nov **Date C** **o n** **c e** **n t** **r a** **t i** **o n** **( u** **g /** **L )**  DRO (ug/L) GRO (ug/L) Sol ve nts (ug/L) Max im um Conc entrations: DRO ( ug/L): 17600 Sol ve nts (ug/L): 9540 • Steam injection could not

adequately heat the entire target area due to sparse fractures and low fracture permeability; ERH or TCH more applicable for matrix heating • All contaminant mass within 2 feet of fractures (steam in fractures put heat where it was needed) • Significantly enhanced the recovery of solvents and gasoline - and diesel - range organics in the vapor and aqueous phases **14**

# SEE Applications **in Fractured Rock**  • 

## Highly fractured rock with significant fracture permeability • 

## Where diffusion of contaminants into rock matrix is limited • 

## Characterization would include interconnectivity testing • 

## The less frequent the fractures, the more characterization needed to design injection/extraction layout • 

## Rock sampling also needed to determine injection/extraction strategy **15**

# Electrical Resistance **Heating**

**8 9**  **10 6**  **1 2**  **3 5**  **4**

**Effluent Treatment**  **System Condenser/Moisture**  **Separator Vapor Phase GA**  **C or**  **Thermox Liquid Phase GA**  **C Vapor Collection**  **Manifold Line Pow**  **er Pow**  **er Control Unit**  **Pow er**  **to Electrodes Electrode/Vapor**  **Extraction Well**  **Computer controls pow**  **er to electrodes**  **& collects subsurface**  **temperature data**  **8 7**  **9 10**  **6 1**  **2 3**  **4 5**  **7 17**  

# Electrical **Resistance Heating**  **for Remediation** 
• 

## Full scale application uses 3 phase current • 

## Alternating current applied to electrodes in subsurface • 

## Current carried between electrodes by water in pore spaces • 

## Electrical resistance of soils produces heat

**17 18**  **Electrode/V**

**ent**

**Electrode/V**

**ent Electrode/V** 

**ent Electrode/V** 

**ent Electrode/V** 

**ent** 

# How Does Electrical **Heating Work ?** 
• 

### Triangular/Hexagonal Array • 

### A typical array diameter is 20 – 40 feet • 

### Typically 100 – 600 volts applied per electrode • 

### Steam temperatures reached in ~ 3 – 6 months • 

### Electrodes also typically vapor extraction wells **Electrode/V ent** 

**18 19**  

# Electrical **Heating of Soils/Rock**
• 

## Heating dependent on electrical conductivity of water in pore space: low permeability zones often heated first due to higher cation content • 

## Works above and below water table • 

## Temperature limited to boiling point of water • 

## Contaminants collected as vapors • 

## Where groundwater flow rate is high, groundwater also extracted, can extract NAPL • 

## Challenged by flow rates greater than 1 ft/day **19**

## ERH in **Fractured Rock** 
• Very hard iron - cemented Sandstone 40 – 65 ft bgs • 1,1,2,2 - Tetrachloroethane; hydrolysis formed TCE • Rock heats at a rate similar to soils • Kluger and Beyke, 2010

**20 ERH Treatment Interval**  **Relative CVOC Conc. 3/6/06**  **2/27/06 Start**  **TM P 4 Depth**  **vs Temperature**  **0 10**  **20 30**  **40 50**  **60 70**  **80 0**  **10 20**  **30 40**  **50 60**  **70 80**  **90 100**  **110 Temperature (**  ° **C) D** **e p** **t h** **( f** **t b** **g s** **)**

**10 0** **D e** **p t** **h (** **f t** **b g** **s )**  **20 30**  **40 50**  **60 70**  **1 10**  **100 1,000**  **10,000 100,000**  **Total CVOCs (μg/kg) –**  **Log Scale 99.9% average**  **reduction S** **a n** **d s** **t o** **n e** **D e** **n s** **e S** **a n** **d Pre**  **- ERH CVOCs**  **Post -**  **ERH CVOCs Treatment Goal**  **(95% reduction)**

# Thermal Conductive **Heating**
• 

## Heater wells with temperature of ~ 700 ° C installed vertically in triangular pattern, 12 – 20 ft spacing • 

## Co - located vapor extraction wells • 

## Heat is conducted from the well into the soil, dependent on soil thermal conductivity
**21 22**  

# Thermal Conductive **Heating**
• 

### Relies on thermal conductivity of soil to heat ground

– Thermal conductivity of soils/rocks fairly uniform

– But low, ~10 - 6 

### m 2 

### /s • 

### Requires high temperature (~700 ° 

### C or greater) at point of application, close well spacing (10 – 12 ft) • 

### Triangular/hexagonal arrays • 

### Vapor extraction wells co - located with heater wells • 

### Treatment temperatures of 300 ° 

### C possible above the water table

– Can treat PCBs, PAHs
**22**

### • 

### Rock heats generally at same rate as soils **23 Te**  **mperature -**  ° **F**

# TCH in Fractured **Rock Research at NAWC Site**  • 

### Heat migration not as adversely affected by geologic heterogeneity • 

### Rock matrix heated, high groundwater flow in fractures limited treatment at fracture surfaces • 

### Co - steam injection recommended for sites with significant fracture permeability **24**

# NAWC Temperatures **during Heating Ground**  **wa ter**  **flow i**  **n fractures at**  **40 -**  **50 ft**  **bgs limited**  **heating**

**25**

# NAWC Rock Sampling
• 

### Most of the mass is adjacent to fractures • 

### Post - treatment, samples not adjacent to fractures were nondetect for TCE • 

### TCE at fractures surfaces reduced from average of 37 mg/kg to 5 mg/kg

**26 26** 

# Match Thermal Technology **to Fractured Rock Setting** • 

## Low Permeability Matrix

– Favors ERH or TCH • 

## Fracture Frequency

– High frequency favors SEE

– Low frequency favors ERH or TCH 

## • 

## Permeability of fractures

– Large groundwater flow through fractures favors SEE 

## • 

## High Permeability Fractures/Low Permeability Matrix

– Combine SEE with ERH or TCH **27**

# Questions??

• 

## davis.eva@epa.gov
• 

## (580) 436 - 8548

**28**

# References

• Hiester , U. and V. Schrenk . 2005. “In Situ Thermal Remediation: Ecological and Economic Advantages of the TUBA and THERIS Methods.” Proceedings of ConSoil 2005. Bordeaux, France. • Kluger, M., and G. L. Beyke, Electrical Resistance Heating of Volatile Organic Compounds in Sedimentary Rock, Remediation, Autumn 2010, pg. 69 - 82. • Lebron , C. A., D. Phelan, G. Heron, J. LaChance , S. Nielsen, B. Kueper , D. Rodriguez, A. Wemp , D. Baston , P. Lacombe, and F. H Chapelle, Dense Non Aqueous Phase Liquid (DNAPL) Removal from Fractured Rock Using Thermal Conductive Heating (TCH), Naval Facilities Engineering Command Contract Report CR - NAVFAC ESC Ev - 1202, August 2012. **29**