The document discusses surface covers used for remediation of contaminated sites. Surface covers, also called caps, involve placing a physical barrier over contaminated materials to prevent infiltration of water and transfer of contaminants. An effective cap must meet several functional requirements such as minimizing infiltration, enhancing runoff, and withstanding long-term stresses. Caps usually involve multiple layers, with the number and type of layers depending on site conditions and waste characteristics. Common layer materials include topsoil, geosynthetics, clay, and drainage materials. Design considerations for caps include slope stability analyses and drainage/leachate management. Construction must ensure layers are properly installed and sealed to perform as designed.

1. Remediation of
contaminated
sites -
Surface
Cover S.Bivin Ebenezer
M.E Environmental
Engineering and
Management
1962003

2. Introduction
▰ Remediation or cleanup of many contaminated sites may be technically impossible,
financially unviable, cost-ineffective, impossible to complete within a given time frame,
and/or unnecessary when the risk posed to public health and the environment is
acceptably low
▰ Containment of the subsurface contamination zone using physical barriers may be viable
option, it is classified under In-situ containment system
▰ Surface caps, also called covers or surface barriers, are similar to landfill final cover
▰ Covers are used to prevent infiltration of precipitation, thereby minimizing the generation
of leachate
▰ Caps also prevent transfer of contaminants to the atmosphere, reduce erosion, and
improve aesthetics
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3. ▰ The type of cap depends primarily on the nature of the waste, site
conditions, and the likelihood of extended maintenance of the cap
▰ Caps may range from a
╺ one-layer system - only vegetated soil,
╺ complex multilayer - system of soils and geosynthetics,
▰ Caps may be used as an interim or final remedial measure.
╺ Interim cap - to minimize the generation of leachate until a better
technique is selected
╺ Final cap - finial remediation action where wastes masses are too large
to excavate and remove or unrealistic costs etc.
3
Types

4. a) Must minimize infiltration
b) Must act as hydraulic barrier
c) Must enhance surface runoff
d) Must prevent surface erosion
e) Must withstand long term settlements
f) Must withstand long term slope stability
g) Must withstand surface exposure to loads and
environmental conditions
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Functional requirements of covers

5. 1. Cofiguration and
materials

6. 1. Surface layer
2. Protection layer
3. Drainage layer
4. Barrier layer
5. Gas collection layer
6. Foundation layer
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Configuration of a multilayered cap
From top
to the
bottom

7. 7
Cross-section of surface cover

8. ▰ Function :
╺ To separate the underlying components of the caps form the ground surface
╺ To grow vegetation
╺ To minimize temperature and precipitation extremes in the underlying
layers.
▰ Materials used :
╺ Topsoil, geosynthetic erosion control material overlying topsoil, cobbles, and
paving materials have all been used for the surface layer in a cap.
╺ Top soil is most commonly used layer , excessive erosion is the problem,
which can be prevented by placing geosynthetic erosion control material
over the top soil
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1. Surface layer

9. ▰ Functions:
╺ To store water that has infiltrated the cap until the water is later
removed by evaporation or transportation,
╺ To protect the waste physically from animals or roots,
╺ To minimize the possibility of human intrusion.
╺ To protect underlying layers in the cap from excessive wetting/
drying, which could cause cracking of some materials.
Material used :
╺ Soil is the most commonly used material
╺ In many cases, the surface and protection layers are combined to
form a single topsoil layer.
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2. Protection layer

10. ▰ Functions:
╺ To reduce the head of water on the underlying barrier layer, which minimizes
percolation of water through the cap
╺ To drain the surface water infiltrated from the overlying protection and surface
layers, which increases the water storage capacity and helps to minimize
erosion of these layers.
╺ To reduce pore water pressures in the cap materials, which improves slope
stability.
▰ Mostly used:
╺ Sand, gravel, geonet with a geotextile filter, and geo composite
╺ Geotextile may be used as a filter between the vegetative/protective layer and
the drainage layer
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3. Drainage layer

11. ▰ Function:
╺ Minimizes percolation of water through the cap by impeding infiltration through it
and by promoting storage or drainage of water in the overlying layers
╺ Restricts the upward movement of any gases or volatile constituents
▰ Mostly used:
╺ Soil, clay and geomembranes(less permeable than clay),Geosynthetic lay
liners(GCLs)
╺ Other barriers such as soil-bentonite, fly ash –bentonite-soli mixtures
superabsorbent geotextiles, sprayed on geomembranes and soil particle binders
╺ A geotextile may used over the geomembrane as a protective layer to prevent
mechanical damage such as tear, puncture, overstressing.
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4. Barrier layer

12. ▰ Function:
╺ Transfer of gas to collecting points for venting or flaring or
concentration
╺ Serves as foundation layer and should be strong enough to
support the overlying layers and construction equipment
▰ Mostly used materials:
╺ Granular materials and piping
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5. Gas collection layer

13. ▰ Function:
╺ Foundation layer for the cap
╺ Should be strong enough to support the overlaying layers
and construction equipment.
▰ Used materials:
╺ Sand or gravel, soil ,recycled and reused waste
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6. Foundation layer
Note:
Not all the layers are needed at all sites. It depends on the Site specification factors such
as local availability and cost of cover materials, desired function of the cover, the nature of the wastes
being covered ,local climate ,site topography ,hydrogeology and projected future uses of the site.

14. 14
Without gas vents With gas vents

15. Layer Primary function Potential materials
Surface layer Separating underly, protection against erosion
Reduce temperature and moisture extremes in
underlying areas
Topsoil (vegetated),geosynthetic
paving material
Protection layer Store infiltration water before removal,
separate waste against humans ,animals and
vegetation, protect against wetting and drying,
freezing and thawing
Soil, cobbles, recycled or reused
waste (e.g. ,fly ash ,bottom ash,
paper mill sludge)
Drainage layer Reduce water head on barrier layer, reduce
uplift pressure on overlying layers
Sand or gravel, geo composite
,recycled and reused waste
Hydraulic barrier layer Impede water percolation through cap, restrict
outward movement of gases from waste
Compacted clay, Geomembrane,
GCL ,recycled asphalt
Gas collection layer Collect and remove gases Sand or gravel , Geocomposite
,geotextile ,recycled and reused
waste
Foundation layer Foundation for the cap, especially during
construction
Sand or gravel ,recycled waste

16. 16
Geomembrane
Geonet
Geonet
Geogrid

17. ▰ Determination of global waste stability
╺ Evaluating whether a waste mass will remain stable under all potential loading conditions
▰ Underlying waste settlement analysis
╺ Evaluating the potential for foundation and waste materials to consolidate under the loading
conditions of cap
▰ Slope stability analysis of the cap system
╺ Determining the its potential for failure
▰ Drainage analysis
╺ Prevent built up of hydraulic head on low permeability cap layer
▰ Leachate management analysis
╺ Evaluation of the characteristics of the leachate and their treatment mechanisms
▰ Gas management analyses.
╺ Evaluation of proposed gas collection well designed based on waste characteristics.
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Design factors to be considered

18. ➢ The base layer, which may be a gas collection layer, overlies the waste mass.
➢ The low-permeability layer, such as the clay component of the barrier layer, is
constructed over this base layer.
➢ The clay is spread and compacted until the desired thickness is achieved
➢ Each layer is scarified to remove and trace of any smooth surface, which exhibit
binding between it and the next layer
➢ The top layer is compacted and rolled smooth so that the geomembrane can be
laid on it with direct and uniform contact
➢ A geomembrane should be laid without wrinkles, If the vents are present they
should be carefully attached to geomembrane to prevent tearing
➢ The effect of air temperature and seasonal variation on the geomembrane should
be taken into account.(expansion and contraction should be taken into account)
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Construction

19. ▰ A geotextile may be laid on the surface of the geomembrane to protect it
from damage by overlaying materials, particularly coarse and sharp
granular material are to be used in the overlaying drainage layer
▰ The drainage layer may be either a granular soil with high permeability or
a geosynthetic drainage grid or geonet sandwiched between two porous
geotextile layers
▰ Another geotextile may be put on the top of the drainage layer to prevent
clogging of the drainage layer by soil from above. Fill soil and topsoil are
then applied, and the topsoil is seeded with grass or other vegetation.
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Cont….

20. Overview:
▰ The Australian Government owns several parcels of land on the Cox
Peninsula that had been used for over 70 years for maritime,
communications and defense purposes.
▰ There were several sites across the land which contained a range of waste
materials including building rubble from Cyclone Tracey ,Asbestos was also
located in some buildings that were on the site.
▰ A range of contaminants, including asbestos, that were present at the site
were treated through a combination of removal from site and on-site
management via an engineered containment cell.
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Case Study – Cox Peninsula Remediation2

21. ▰ There was extensive contamination across a wide area both below and at
ground level, including significant quantities of asbestos, and pesticides,
heavy metals and polychlorinated biphenyls (PCBs) detected above safe
levels at many sites.
21
Contt…
Location Cox Peninsula, Northern Territory
Types of asbestos Asbestos cement sheeting debris
Volume 28,000 m3 of contaminated soil, including asbestos, lead, PCB and
pesticides

22. ▰ The demolition and removal of existing structures, including
recycling of waste where possible
▰ The treatment of soils containing Polychlorinated biphenyls and
pesticides via a thermal desorption unit
▰ The placement of ACMs and other inert wastes, including
materials currently stored within shipping containers on site, into
an engineered containment cell .
▰ Rehabilitation of the remediated areas and ongoing monitoring
of the containment cell
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Remediation plans

23. ▰ There were three elements to the management of asbestos on the site.
1. The remaining buildings and structures on the site needed to be demolished.
2. The asbestos conduit below the ground was dug up by an excavator.
3. The contaminated soil located in the various tip sites on the Commonwealth land was excavated to
remove the contaminated materials
▰ A Permanent containment cell was constructed on the site to encapsulate the contaminated materials which
measures approximately 100mX100m and a depth of 8 m.
▰ The area was excavated below ground and the base was lined with low permeability membranes
▰ A collection system was installed to collect liquid that may leach out of the waste over time.
▰ The containment cell was designed to mitigate leachate generation and to minimize leachate escaping.
▰ Once the containment cell was filled ,cap made of low permeability membrane clay layer was constructed
over the top of the cell to encapsulate the materials
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Removal methodology

24. 24
Rehabilitation of site
Containment cell

25. ▰ Geoenvironmental Engineering: Site remediation,waste containment, and
emerging waste management technologies- Hair .D Sharma, Krishna
R.Reddy
▰ Geoenvironmental Engineering (Environmental Geotechnology): Landfills,
Slurry Ponds & Contaminated Sites Prof. Manoj Datta Department of Civil
Engineering Indian Institute of Technology, Delhi
▰ Remediation technologies for contaminated sites - Albert T. Yeung
▰ Australian Government – Asbestos safety and Eradication agency Nov -
2017
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Reference:

26. Thank
you!!!
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