Overview of ISTD and Examples of Groundwater Quality...

John LaChanceARCADIS

Overview of ISTD and Examples of Groundwater Quality Improvement Following Source Zone Treatment

Outline

• Introduction to ISTD • Primary Mechanisms• Energy Balance for ISTD Sites Below the Water Table

• Benefits of Cleaning up Source Zones• Example of Downgradient Plume Attenuation Following Source Zone Cleanup

Thanks Gorm!

ISTD/TCH* - Simultaneous application of heat via thermal conduction and vacuum extraction

Heating governed by thermal conductivity (f~3) nearly uniform

ISTD = In Situ Thermal DesorptionTCH = Thermal Conduction Heating*Offered by TerraTherm, Inc. 3

Power distribution system

Vapor treatment

Knockout pot

Blower

Water treatmentDischargeVapor cap

Heater wells

Treated vapor to atmosphere

Extraction well

Heat exchanger

Pump

Treatment area foot-print

Temperature and pressure monitoring holes

Typical ISTD Site Layout

4

ISTD is the simultaneous application of:• Heat via Thermal Conduction• Vacuum Extraction

ISTD Well FieldProcessTreatment

ElectricalEquipment

5

ISTD – Ability to go beyond the boiling point of water

NAPL

VOCs

SVOCs,Hg

6

Energy Balance Approach to Understanding The Heating and

Removal Mechanisms at ISTD Sites

Sandy fill 0-1.5 m

Bay Mud

Treatment zone0 – 6.2 m

TTZ

ISTDHeater

Horizontal SVE well

Schematic cross-section showing existing building, stratigraphy, and location of heaters and extraction wells. The water table is approximately 1.5-2 m below grade.

Example ISTD Site: Point Richmond, CA

Design ElementDesign

Specification Comment

Areal extend of Target Treatment Zone (TTZ)

836 m2

(9,000 ft2)

The TTZ is the volume inside the overall thermal well field targeted for treatment that benefits from the superposition of surrounding heaters.

Treatment Interval/Depth

0 to 6.2 m(0 to 20 ft)

Heated Interval/Depth 0 to 6.6 m(0 to 22 ft)

Extends below the bottom of TTZ to ensure sufficient heating within the TTZ, and to prevent unwanted vertical migration of contaminants.

TTZ Volume 5,097 m(6,667 cy)

Target Treatment Temperature

100°C(212°F)

Steam distillation of the PCE and other VOCs will occur at, or slightly below 100°C. This is the temperature to be achieved in the coolest locations between the thermal wells within the TTZ.

TCH Well Spacing 3.66 m12 ft

Number of TCH Wells 126

Power Input Rate 1.15 kW/m(0.35 kW/ft)

Temperature Range Within TTZ

100 to 400°C(212°F to 752°C

Higher temperatures in soil adjacent to heaters and heater-vacuum wells provides vertical pathways for steam and contaminants to migrate up from within the TTZ to the vadose zone for extraction.

Bay Mud

350 W/ft = 0.06 gpm of water removed as steam

20 ft

Sand Silt/Clay

350 W/ft = 0.06 gpm of water removed as steam

3‐4% of TTZ Volume

2‐3% of Total Energy Input

0

500,000

1,000,000

1,500,000

2,000,000

2,500,000

0 20 40 60 80 100 120 140

Energy Added ISTDEnergy Removed as SteamNet Energy Added

Energy Balance for Point Richmond Site

Days of Operations

kWhs

327 kWh per CY200 to 300 KWh per CY

typical

0%

5%

10%

15%

20%

25%

30%

35%

40%

45%

50%

55%

0

10

20

30

40

50

60

70

80

90

100

110

0 20 40 60 80 100 120 140

AVG Temp ofTTZ% of Energy toBoiling

Days of Operations

Average Tempe

rature ‐C

% of E

nergy used

for B

oilin

g

Rate of Heat‐up and Percent of Energy Used for Boiling/Steam Production

35‐45%Typical

10

30

50

70

90

110

130

0

100

200

300

400

500

600

700

0 20 40 60 80 100 120 140

PVs of Steam

Days of Operations

Average Tempe

rature ‐C

Num

ber o

f Pore Vo

lumes of S

team

Treatment Zone Heat Up and Pore Volumes of Steam Removed

Represents ~30% of the

Water in the TTZ

1 mm

[Udell et al. 1999; Alameda Point SEE demonstration]

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Add heat change state of chemicals from liquid to vapor

Even in tight clays, 500‐600 PVs of steam are removed

Boiling of NAPL below 100C

0.0

0.5

1.0

1.5

2.0

0 20 40 60 80 100

Temperature (oC)

Pres

sure

(atm

)

Water and TCE

Clean water

TCE: Pure Phase Boiling Point = 87C

Heterogeneous Azeotrope or Eutectic Point

73

15

TC-7

40

60

80

100

120

140

160

180

200

220

0 10 20 30 40 50 60 70 80

68 ft

83 ft

BP TCE-Water 73°C

BP Water 100°C

Days Since Start of Heating

Tem

pera

ture

-o F

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Mass Removal During Treatment

0.0

2.0

4.0

6.0

8.0

10.0

12.0

14.0

16.0

18.0

0 15 30 45 60 75 90 105 120 135 150

Days after Initial Startup (Jan 29, 2007)

Rem

oval

Rat

e (lb

s/hr

)

0.00

1.00

2.00

3.00

4.00

5.00

6.00

7.00

Tota

l Rem

oved

(Ton

s)

Removal Rate Total Removed

~12,000 lbs ofTCE

0.0

2.0

4.0

6.0

8.0

10.0

12.0

14.0

16.0

18.0

0 15 30 45 60 75 90 105 120 135 150

Days after Initial Startup (Jan 29, 2007)

Rem

oval

Rat

e (lb

s/hr

)

0.00

1.00

2.00

3.00

4.00

5.00

6.00

7.00

Tota

l Rem

oved

(Ton

s)

Removal Rate Total Removed

~12,000 lbs ofTCE

30 4515 60 75 90 105 120 135 1500

17

0

1

2

3

4

5

6

7

8

0 1 10 100 1,000 10,000 100,000 1,000,000 10,000,000

Soil Concentration - g/kg

Dep

th B

elow

Gro

und

Surf

ace

- m

Pretreatment - PCEPost Treatment - PCE

Bottom of Treatment Zone

Bottom of Heated Zone

Point Richmond TCH Site, CASoil PCE Concentration (g/kg)

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Confidential TCH Site, SC0

10

20

30

40

50

60

70

80

90

1 10 100 1,000 10,000 100,000 1,000,000 10,000,000 100,000,000

Location 1

Location 2

Location 3

Location 4

Location 5

Location 6

MaxPre-Treatment

ft bg

s

ND DNAPLCleanup Objective: 95% UCL of mean < 60 g.kg

Min. Soil Conc.indicative of DNAPL;foc: 0.05% - 0.1%n: 0.3-0.35

95% UCL of mean TCE conc. = 17.1 g/kg

Soil TCE Concentration (g/kg)

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Young‐Rainey STAR Center Area A, FL

0

5

10

15

20

25

30

35

40

45

1 10 100 1000 10000 100000 1000000

Soil TCE Concentration (ug/kg)

Dep

th (f

t)

Pre Operational

Interim

Post Operational

100 ug/kg- PRG, unsaturated Soil

56000 ug/kg- PRG, saturated so


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Confidential TCH Site, OH

0

2

4

6

8

10

12

14

16

18

20

1 10 100 1,000 10,000 100,000 1,000,000 10,000,000

TCE ug/kgD

epth

BG

S F

T

Confirmatory Samples

Pre-Treatment

ND

Cleanup Goal

n = 384

n = 90


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ISTD (ISTR) Can Provide Significant Mass Reductions (99% to >99.99%) in Source Zones

But What Impact Can we Expect on the Downgradient Plume?

Contaminated SitePlume

The 14 Compartment Conceptual Model of Source Zones and Plumes

Source: ESTCP/ Sale and Newell, 2011

Conceptual Model of Back‐Diffusion Sorption/desorption


Source Zone

Potential Impact of Back Diffusion on Plume Persistence Following Source Remediation

Offsite Plume

Offsite Plume


DG: Summary of common challenges to developing remedial systems

• Differences in expectations from involved parties• The possibility of large uncertainty regarding subsurface

conditions

• The fact that the most common requirement for closure (near‐term attainment of drinking water standards – maximum concentration levels or MCLs – in groundwater at all points has rarely, if ever been achieved

• The fact that finite funds are available, considering numerous social priorities.

Proposed Reasons not to Clean up Source Zones

• Downgradient plume that is a problem– Soil vapor exposure route– Drinking water receptor

• Heterogeneous geologic setting – Sands with silts and clays– Zones for diffusion and back diffusion

• Ultimate/final remedial goals (e.g., MCLs) will likely not be met everywhere

• Numerous social needs and finite funds• Why cleanup the source zone if downgradientplume and impacts will persist?

Reasons to Cleanup Source Zones• Eliminate/minimize exposure risk• Re‐establish value/use • Reduce or eliminate source feeding diffusion reservoirs in downgradient plume

• Maybe back diffusion isn’t as significant as perceived and concentrations in downgradientplume will reach ultimate final goals at some sites

Example Effects of Source Depletion on Water Quality

Source Removal Impact on Dissolved Plume

Case Study Results – In Situ Thermal Desorption

PosterJohn Bierschenk, Robin Swift, Gregg Crisp,

Tim Mahoney151 Suffolk Lane, Gardner, MA 01440 USA

Cinder Fi

Groundwater •PCE:5 μg/L•TCE:5 μg/L

Soil – Source Zone•No single sample <5.5 mg/Kg PCE•Average less than 0.56 mg/Kg PCE

System Design and Installation•~14,000 cubic yards treatment zone•Treatment depth to 30 ft bgs•257 ISTD heater wells•72 vapor extraction wells•19 multiphase extraction phase•28 temperature points•14 pressure monitoring points•Insulating vapor cover•Granular activated carbon•192 days of operation

Thermal Treatment Results

•3,100 lbs of chlorinated compounds •9,000 lbs of petroleum hydrocarbons•<$1M pilot + $2.8M full scale •Remedial goals for source area soil met•NYSDEC and NYSDOH stated ISTD “successful”

PRE‐ AND POST‐TREATMENT SOIL SAMPLES

0

5

10

15

20

25

30

0.001 0.01 0.1 1 10 100 1000 10000

Concentration (mg/Kg)

Average of Post‐Treatment Samples:

0.04 mg/Kg

Treatment Goal:Avg. Less Than0,56 mg/Kg

Average of Pre‐Treatment Samples:

125 mg/Kg

Post‐Treatment Pre‐Treatment

Lacustrine Silt

Smear Zone

Soil Fill

PCE IN GROUNDWATER

PRE THERMAL POST THERMAL

TCE IN GROUNDWATER


cis‐1,2‐DCE IN GROUNDWATER


VC IN GROUNDWATER


Remediation using ISTD and Steam – Source Removal and Plume

EffectsKnullen, Denmark

PosterSteffen Griepke Nielsen and Henrik Steffensen (NIRAS A/S,

Odense, Denmark)Gorm Heron (TerraTherm, Inc., Keene, California)

Niels Just (Region of Southern Denmark, Vejle, Denmark)

Contaminant distribution, geology and hydrogeology

Clayey till

Fill

Sand

/gravel

Target treatment zoneArea: 250 m2

Volume: 1900 m3

Treatment depth: 4‐14 m bgs

Separation tank

Building

Hydraulic head in sand/gravel

Hydraulic head in clay layer

Depth bgs

0 m / 0 ft1 m / 3 ft

11 m / 36 ft

14 m / 46 ft

PCE

Hoejby Water boar

Lindved Water board

Contaminated Site

Plume

Remediation objective: clean up source zone

Source Zones Can Generate Long Plumes Downgradient

Thermal Source Zone Treatment Included ISTD and Steam Enhanced Extraction

Mass Removal

0

2000

4000

6000

8000

10000

12000

26-06-2008

03-07-2008

10-07-2008

17-07-2008

24-07-2008

31-07-2008

07-08-2008

14-08-2008

21-08-2008

28-08-2008

04-09-2008

11-09-2008

18-09-2008

25-09-2008

02-10-2008

09-10-2008

16-10-2008

Tid

PCE

(mg/

m3)

0

1.000

2.000

3.000

4.000

5.000

6.000

I alt

opsa

mle

t kg

PCE

Total PCE Innova (mg/m³) Total PCE (kulrørsanalyser, mg/m3) I alt opsamlet PCE (kg)Total PCE (online) [mg/m3] Total PCE (grab samples) [mg/m3] PCE recovered [kg]

• Total amount of PCE recovered: 3,500 kg (7,700 lbs)• Total amount of DCE recovered: 500 kg (1,100 lbs)

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Pre‐ and Post‐Treatment PCE Concentrations in Soil

0

2

4

6

8

10

12

0.001 0.01 0.1 1 10 100 1000 10000 100000

Dep

th [m

bgs

]

PCE in soil pre treatment [mg/kg]PCE in soil post treatment [mg/kg]

Detection limit Remediation goal

Summary of Source Zone ResultsPre‐Treatment Post‐Treatment Reduction

Average concentration of PCE in soil: 340 mg/kg

Average concentration of PCE in soil: 0.5 mg/kg

1,000 fold (99.7%)

Mass discharge rate from source zone: 25 kg/yr

Mass discharge rate from source zone: 0.08 kg/yr

300 fold

Locations of Source Zone and Downgradient Monitoring Wells

PCE Groundwater Concentrations in Source Area

PCE concentrations in the source zone were reduced by a factor of 150‐2,000.

PCE Groundwater Concentrations in Plume

PCE concentrations 50 m downgradient show reductions by a factor of up to 30.

Simulated Impact of Source Remediation

Summary

• ISTD is capable of achieving 99% to >99.99% reductions in source zone concentrations/mass

• In some geologic settings this is sufficient to achieve low gw concentrations (e.g., MCLs) within and downgradient of the source area

• Sites settings favorable for this type of outcome, include:– Adequate delineation and treatment of source zone

• Sufficient vertical and horizontal characterization• Complete/thorough heating (100C)

– Insulated cover– Acceptable gw flux rates

• Robust vapor extraction0.0

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emov

al R

ate

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hr)

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~

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Summary cont.

• Sites settings favorable for this type of outcome, include:– Minimal to moderate heterogeneity

• Limited mass diffused in low permeability units (back diffusion reservoirs)

– Good conditions for natural attenuation in downgradient aquifer

• Reducing/oxidizing conditions• Thermal enhancement downgradient of treatment zone

• Presence of minerals favorable for abiotic degradation

Overview of ISTD and Examples of Groundwater Quality...

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