Post on 14-Mar-2018
transcript
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]
14
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
16
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)
18
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)
19
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
Soil TCE Concentration (g/kg)
20
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
Soil TCE Concentration (g/kg)
21
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: ESTCP/ Sale and Newell, 2011
Source Zone
Potential Impact of Back Diffusion on Plume Persistence Following Source Remediation
Offsite Plume
Offsite Plume
Source: ESTCP/ Sale and Newell, 2011
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
PRE THERMAL POST THERMAL
cis‐1,2‐DCE IN GROUNDWATER
PRE THERMAL POST THERMAL
VC IN GROUNDWATER
PRE THERMAL POST THERMAL
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)
44
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
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 150R
emov
al R
ate
(lbs/
hr)
0.00
1.00
2.00
3.00
4.00
5.00
6.00
7.00
~
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 150R
emov
al R
ate
(lbs/
hr)
0.00
1.00
2.00
3.00
4.00
5.00
6.00
7.00
~
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