6/12/2012

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Greg Beyke, PE

VP –Technology Development

TRS Group, Inc.

thermalrs.com

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Electrical Resistance Heating

Treatment of VOCs in groundwater, soil, and

sedimentary bedrock.

Concentration reductions of 95% to 99.9%

are commonly achieved with four to eight

months of operation, with no rebound.

TRS offers guarantees of remediation

effectiveness for soil, rock, and groundwater.

6/12/2012

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SOLVENT

SAND

CLAY

BEDROCK

WATER TABLE

GROUNDWATER FLOW

PCU

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GAC

Filter

Sheet piles

Angled

Horizontal

Electrode

Types

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ERH Surface

Equipment

Steam Condenser

500 kW PCU

Operating

Electrode

Photo

Courtesy of

Brown and

Caldwell

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Why Electrical

Resistance Heating?

Steam is produced in-situ

Heating is uniform with no bypassed regions

Equally effective in the vadose, saturated

zone, and sedimentary bedrock

Heating is rapid yet gentle

No soil desiccation

Preferentially heats tight soil lenses and

DNAPL hot spots

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Boiling Temperature and

Dalton’s Law

• A substance boils when its vapor pressure is equal to

the ambient pressure

TCE 87 C PCE 121 C

Water 100 C

TCE/Water 73 C PCE/Water 88 C

TCE/Water 2:1 PCE/Water 1:2

What about the vadose zone?

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In-Situ Steam

Generation

Low permeability lens

Electrode Electrode

Current flowing between electrodes heats soil directly.

Zooming in on

this region.

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In-Situ Steam

Generation

Low permeability lens

Reductive dehalogenation creates a “halo” of chloride ions in CVOC hot spots

DNAPL

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In-Situ Steam

Generation

Uniform soils would lead to parallel ERH current lines – but soils aren’t uniform.

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In-Situ Steam

Generation

Low permeability lenses and CVOC hot spots attract current.

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In-Situ Steam

Generation

Steam bubbles form more quickly at NAPL due to interfacial tension and reduced

boiling temperatures. Typically form 500-1000 pore volumes of steam in situ.

Regions with higher current

density heat slightly more quickly.

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TRS Patented Adaptive Electrode

TRS backfill contains

zero valent iron (ZVI)

CVOC – ZVI reaction produces

conductive chloride ions

DNAPL or

high CVOC

concentrations

Automatically

boosts power

in CVOC

regions

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Why Electrical

Resistance Heating?

Because steam is produced in-situ, ERH is more

tolerant of heterogeneity than any other remediation

technology.

It doesn’t matter if:

The subsurface is clay

The subsurface is gravel

The subsurface is interbedded clay and gravel

The subsurface is vadose, perched water, or saturated

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Heating Weaknesses

• Peat or high organic carbon – granular activated

carbon is used to adsorb VOCs because of the

bonding between them*

• Oil or grease as a co-contaminant (Raoult’s Law)*

• “Pancake sites” (big area, thin depth) – minimum 10ft

treatment interval

• Fuel sites – other options and tend to be pancakes

ERH Weaknesses

• Landfills – ERH is more uniform in natural materials

• Fractured igneous rock – no experience yet

• ERH chases CVOC contamination (strength?)

* Weakness shared with other in situ technologies.

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Reasons to Heat Low

Volatility NAPLs

Reduce NAPL viscosity

Reduce NAPL specific gravity – change

DNAPL to LNAPL

Steam bubble floatation

Thermally enhanced bioremediation polish

Strip out the more volatile and toxic

components, leaving an inert and non-mobile

soil particle stain

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NAPL Viscosity

0

500

1000

1500

2000

0 20 40 60 80 100 120

Temperature (oC)

Vis

cosity (

cS

t)0

5

10

15

20

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Creosote Heavy oil

SVOC

SVOC graph

courtesy of

Dr. Gorm Heron

Absolute Viscosity of VOCs

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

10 20 30 40 50 60 70 80 90 100

deg C

cP

water

TCE

PCE

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Steam Bubble

Floatation

“Life preserver” of small bubbles lift NAPL to groundwater surface.

NAPL NAPL

Or small bubbles break away and lift NAPL droplets.

Bubbles are more likely to

form at the NAPL/water

interface.

NAPL droplet

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Electrical Resistance

Heating

HEATED ZONE

Electrodes with

co-located VR Wells

2. Steam generation is uniform

through the heated zone

1. Soil particles act as

electrical resistors

70 V to

300 V

Safe

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Dry Cleaner – Fair

Lawn, NJ

• PCE in Soil, Sandstone, and Groundwater

• Treatment area 6000 ft2, depth 0.5 to 26-ft

bgs, 5,000 yd3

• Glacial till with fractured sandstone bedrock

at 16 ft bgs

• GAC for vapor treatment

• Baseline: Up to 288 mg/kg PCE in soil

• Remedial goal: PCE

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Average Temperatures

during Heat-up Avg Temp

Nearby Mixed Soil and Bedrock Site

-30

-25

-20

-15

-10

-5

0

10 20 30 40 50 60 70 80 90 100 110

Temperature (C)

Dep

th (

bg

s)

9/14/07

9/21/07

9/28/07

10/5/07

Sed

imen

tary

Bed

rock

So

il (

silt

y s

an

d)

PCE Concentration in Soil

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99.95% Reduction

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PCE in Groundwater

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Coming Attraction –

Edgemere, NY

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Coming Attraction II –

Newtown, CT

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Polishing

Mechanisms

• Hydrolysis of Halogenated Alkanes

– Compounds such as TCA have a hydrolysis half-life of less than one day at

steam temperatures.

• Iron Reductive Dehalogenation

– Steel shot used as electrode backfill provides an iron source for reductive

dehalogenation (iron filing wall)

• Temperature Accelerates Reactions

– The above reaction rates are increased by factor of thousands at 100°C

(Arrhenius Equation)

• Bioremediation by Thermophiles

– Dehalogenating bacteria Dehalobacter, Desulfuromonas, and

Desulfotomaculum prefer 40-80°C

– Dehalogenating bacteria Dehalococcoides prefer 30°C

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Hydrolysis Water Substitution Reaction Hydrolysis Rates of Selected Halogenated Alkanes

0.01

0.10

1.00

10.00

100.00

40 50 60 70 80 90 100 110 120

Temperature (°C)

hyd

roly

sis

ha

lf-l

ife a

t p

H 7

(d

ay

s)

methylene chloride

1,2-DCA

1,1-DCA

carbon tetrachloride

EDB

1,3 dichloropropane

1,1,2,2 TeCA

1,1,1-TCA

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Microbe Counts Average of Three Wells

1.0E+04

1.0E+05

1.0E+06

1.0E+07

1.0E+08

1.0E+09

heterotrophic (all microbes)

@ 8-10 ft

petrophilic (hydrocarbon

degrading) @ 8-10 ft

heterotrophic (all microbes)

@ 12-14 ft

petrophilic (hydrocarbon

degrading) @ 12-14 ft

prior to ERH

1 day after ERH

3 months after ERH

10x increase

100x increase

5x increase

46x increase

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Natural Organic Carbon (Humic Material)

Epikarst site – Springfield, MO

MW B2MW B5

MW C4MW E5

average

pre-ERH

post-ERH

190

160

250

160

190

8

34

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0

50

100

150

200

250

Dissolved

Organic

Carbon

(mg/l)

Monitoring Wells

Effect of ERH on Groundwater Dissolved Organic Carbon

41 times

higher

100 mg/l DOC is

a common goal

for emulsified oil

injections.

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>5’

Dee

pe

r Tre

atm

en

t Zo

ne

Plastic natural

gas line above

treatment zone

(OK)

Concrete or clay

sewer line

(OK)

Steel MW in treatment zone

(OK - requires a sealed cap

and may require grounding)

Treatment extends to

within 2 feet of floor

(OK - engineering controls

to keep floor cool)

Steel

water

main

(OK)

Electrical cables in

treatment zone

(OK - may need derating)

Phone

or fiber

optic

(OK)

Steel

natural

gas line

(OK)

EFFECTS OF ERH ON BURIED UTILITIES AND BUILDING INFRASTRUCTURE

Sh

allo

w T

rea

tme

nt Z

on

e

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Electrical Resistance Heating uniformly heats the subsurface and

removes VOCs from all soil types, both above and below the

water table. Good for your “tough sites”.

Questions?

Greg Beyke

Thermal Remediation Services

(615) 791-5772

thermalrs.com