Soil contamination and remediation
Remediation technologies
Immobilization techniques –
S/S technologies –
vitrification - capping - cut
off walls – in situ waste
containment
Solidification/Stabilization
S/S technologies uses additives or processes to
chemically bind or encapsulate contaminant
Metals, radionuclides, nonvolatile organic
compounds
Solidification/Stabilization
Solidification
Treatment that encapsulate the waste in a monolithic solid of high
structural integrity
•
does not necessarily involve chemical interactions
•
may be due to mechanical binding of the waste in the monolith
•
usually involves the reduction or elimination of free liquids in
the waste
•
Decrease mobility by decreasing the surface area exposed to
leaching or isolating waste within a capsule
•
long term integrity
Stabilization
Techniques to limit the hazard potential of contaminants by
converting them to their least soluble, toxic and mobile forms
•
may or may not change or improve the physical characteristics
•
leachability testing is typically performed to measure the
immobilization of contaminants.
•
also called fixation or chemical fixation
Solidification/Stabilization materials
Cement based S/S (portland cement, + fly ash,
bentonite)
Suitable for metals, PCBs, oils, and other
organic compound
Pozzolanic based S/S (fly ash, pumice lime kiln
dusts, aluminosilicates) forms cementitious
substances when combined with water
Applicable for metals and waste acids.
Solidification/Stabilization materials
Thermoplastic S/S (bitumen, polyethylen)
microencapsulation process, chemically
inert encapsulating material.
Applicable for metals, radionuclides and
organics.
Organic polymerization S/S (ureaformaldehyd) fly ash, pumice lime kiln dusts
Applicable for metals and waste acids.
Solidification/Stabilization
Final decision about S/S material, is done on
basis of an experiment.
Solidification/Stabilization
technologies
Mixing in-situ
Shallow mixing:
Up to 12m depth,
Mixing tool diameter up to 4m
semi-volatile compunds -> off gas hood
Cena 50 – 80 USD/m3
http://www.geocon.net/
http://www.new-technologies.org/ECT/Other/soilmixing.htm
Solidification/Stabilization
Mixing in-situ
Shallow mixing:
http://www.new-technologies.org/ECT/Other/soilmixing.htm
Solidification/Stabilization
Mixing in-situ
Shallow mixing:
http://www.geocon.net/
Solidification/Stabilization
In situ technology
Deep soil mixing
up to 40 m depth
2-4 mixing tools
Stabilizing reagents are fed
into auger
increase o soil volume ~15%
price 190 – 300 USD/m3
http://www.new-technologies.org/ECT/Other/soilmixing.htm
In situ technology
Deep soil mixing
http://www.new-technologies.org/ECT/Other/soilmixing.htm
In Situ Vitrification (ISV)
Use of heat to melt and convert the contaminated soil
into a stable glass or crystalline product
•
Organic compounds are burnt or volatilized
•
Heat is produced by electric current between two – four
graphite electrodes ~2000°C.
http://www.frtr.gov/
http://www.bnl.gov/
In Situ Vitrification (ISV)
•
•
•
•
Applicable to mixture
of contaminants
(mixture of
radionuclides, metals
and organics)
Up to 1000 tons in
one step
Volume of soil
reduces by 25-50%
Cost ~280 – 600
USD/ton soil
(depends on initial
water content)
http://www.bnl.gov/
Surface caps or covers
or silt
Surface caps or covers
Goals:
•
Prevent direct contact of human and animals
with contaminated material
•
Minimize infiltration
•
Eliminate contamination of surface water
which would otherwise contact contaminated
material
•
Prevent generation of contaminated dust or
volatilization of contaminants
http://www.bnl.gov/
Surface caps - Configuration and
materials
Source: Federal Remediation and Technologies Roundtable, February 12, 2003. 4.30 Landfill Cap
Surface caps - Configuration and
materials
VEGETATION
Purpose:
•
•
•
Erosion control
Infiltration
reduction by
Evapotranspiration
30 cm
30 cm
Characteristics:
•
•
•
Shallow rooted
plants
Low nutrient needs
Drought and heat
resistant
Source: Federal Remediation and Technologies Roundtable, February 12, 2003. 4.30 Landfill Cap
Surface caps - Configuration and
materials
TOPSOIL
Purpose:
•
•
Support vegetation
Protect underlying
layers
Characteristics:
•
30 cm
30 cm
Typically 60-cm
thick
http://www.bnl.gov/
Surface caps - Configuration and
materials
PROTECTION LAYER
Purpose:
•
•
also called biotic
barrier”
90-cm layer of cobbles
to stop burrowing
animals and deep roots
Characteristics
•
Not always included
http://www.bnl.gov/
Surface caps - Configuration and
materials
FILTER LAYER
Purpose:
•
Prevents clogging
of drainage layer
by fines from soil
layer
Characteristics:
•
May be
geosynthetic filter
fabric or 30-cm
sand
http://www.bnl.gov/
Surface caps - Configuration and
materials
DRAINAGE LAYER
Purpose:
•
•
Prevents ponding of
water on
geomembrane liner
Drains by gravity to
toe drains
Characteristics:
•
At least 30 cm of
sand with K = 10-2
cm/sec or equivalent
geosynthetic
http://www.bnl.gov/
Surface caps - Configuration and
materials
LOW K LAYER
Purpose:
•
•
Low K prevents
infiltration
of water into waste:
hydraulic barrier
Characteristics:
•
•
Geomembrane: at
least 0.5 mm thick
Compacted clay: at
least 60 cm with
K<= 10-7 cm/s
http://www.bnl.gov/
Surface caps - Configuration and
materials
GAS VENT LAYER
Purpose:
•
Needed if waste will
generate methane
(explosive) or toxic gas
Characteristics:
•
•
Similar to drainage
layer: 30 cm of sand or
equivalent geosynthetic
Connected to horizontal
venting pipes (minimal
number to maintain cap
integrity)
http://www.bnl.gov/
Liner installation
Vertical barriers
Also known as vertical cutoff barriers, vertical cutoff
walls, or barrier walls
Goals:
•
To contain contaminant
•
Redirect groundwater flow
•
To prevent contaminant spreading in the
aquiefer
Vertical barriers - Waste containment
Odčerpávání průsakové vody
Horizontální izolace
Kontainant
Těsnící zářez
Vertical barriers – Hanging barrier
LNAPL
„Zavěšená“ těsnící stěna
Nepropustné podloží (ve velké hloubce)
Containment vs. Downgradient cutoff
wall
Containment
Slurry wall encircles
and isolates waste
Downgradient
Slurry wall delays
eventual migration
or
Often combined with extraction wells
Slurry walls
Most common cut-off wall technology
Materials:
bentonite + soil (SB)
common hydraulic conductivity
K = 10-7 – 5x10-9 m.s-1
cement + bentonite (CB)
higher permeability, but also higher
compactness
SB slurry
Most common cut-off wall technology
Sharma and Reddy, 2004
Slurry wall construction
•
•
•
•
Trench excavation under slurry
Slurry overcome the active pressure of trench
walls
Backfill is placed continuously
Povrch je uzavřen betonovou hlavicí
HPV
Slurry wall construction
http://www.mp.usbr.gov/mpco/showcase/bradbury.html.
Issues in slurry walls constructions
Potential
sources of
of failure
•
•
Original direction of groundwater flow
•
•
•
Improperly
mixed backfill
(CB, SB)
Sloughing or
spalling of soils
into trench
Inadequate
bottom
excavation for
wall key
Freeze – thaw
cycles
Wet dry cycles
Alternative - sheet piles
Waterloo Barrier Inc. http://www.oceta.on.ca/
Jet Grouting
SKANSKA http://www.skanska.co.uk/skanska/templates/Page.asp?id=8581
Examples of containment
technologies used in CZ
SPOLANA A. S., NERATOVICE
Slurry walls containment (27 640m2), 110
mil CZK
KEMAT s.r.o., Skalná u Chebu (funded
by FNM)
double wall containment, inner wall done
using jet grouting (42 mil CZK)
LETIŠTĚ PRAHA RUZYNĚ
4 containments at four places 6 m3 each
standard grouting (0,5 mil CZK)
SOLETANCHE http://www.soletanche.cz/
References
Sharma, H.D., Reddy, K.R. Geoenvironmental engineering, Wiley, 2004
Domenico, P.A. a Schwarz, F.A. Physical and Chemical Hydrogeology, 1990
EMOMONITOR Chrudim, Využití biodegradačních metod při sanacích znečištění, 1997
MIT Open courseware http://ocw.mit.edu/OcwWeb/Civil-and-Environmental-Engineering/134Spring2004/LectureNotes/index.htm