Download Recommended Procedures for Site Investiga

Recommended Procedures for Site Investigations of Waste Disposal Sites and Contaminated Sites in Thailand
Funded by the Ministry of Education and Research (BMBF) of the Federal
Republic of Germany (FKZ 0261218)
Bangkok, Berlin, Hannover, Cottbus 2006
For the scientific content the authors are solely responsible.
Authors: Prof. Dr. Hans-Juergen Voigt, Dr. Ursula Noell, Dr. Klaus Knoedel, Dipl.-Ing. Florian Jenn, Dipl.-Geol. Jens Radschinski, Dr. Christoph Grissemann, Dipl.-Geophys. Gerhard Lange
With contributions of: Dr. Joachim Baumann, Dr. Manfred Birke, Peter W. Boochs, Dr. Gunter Doerhoefer, Dr. Dr. Matthias Dorn, Prof. Dr. Ulrich Foerstner, Dr. Joachim Gerth, Dr. Hagen Hilse, Dr. Kurt-Heiner Krieger, Dr. Thomas Lege,
Dr. Jürgen Lietz, Prof. Dr. Rolf Mull, Dr.-Ing. Claus Nitsche, Dr. Matthias Schreiner, Dr. Andreas Schuck, Dipl.-Geophys.
Knut Seidel, M. Sc. Worawoot Tantiwanit, Dr. Hildegard Wilken, Dr. Thomas Wonik
Contact Address: Dr. Ursula Noell, Federal Institute for Geosciences and Natural Resources, Hannover, Germany,
[email protected]
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The “Recommendations for Site Investigations of Waste Disposal Sites
and Contaminated Sites in Thailand” are a product of the Thai-German
Research Project WADIS (Waste Disposal: Investigation of abandoned
landfills and proposed areas for new waste disposal sites in Thailand).
This project has been approved by the Thai Cabinet on 30th May 2000 and
has been funded by the German Federal Ministry for Education and Research (BMBF). The research work has been carried out in Thailand in
cooperation with the Department of Mineral Resources (DMR).
The WADIS Project emphasizes the application of the “Multi-Barrier
Concept” as a powerful approach to enhance the safety of waste disposal
sites. This concept follows an integrated approach and requires not only
the installation of a man-made barrier (technical barrier) to reduce the
danger of pollution but also the integration of the natural subsoil of a
waste site (geological barrier) as a safety component.
This concise summary gives a brief overview on the recommended procedures for locating new waste disposal sites and the investigation of sites
suspected to be hazardous. The main focus is the assessment of the lateral
extent and sealing qualities of the geological barrier. For this assessment
geophysical, geohydrological, geo- and hydrochemical studies are to be
performed which are described briefly in this concise summary.
The authors thank all colleagues in DMR, PCD, BGR, universities and
companies in Thailand and Germany for their contributions and discussions. The full text of these recommendations is available from the Federal Institute for Geosciences and Natural Resources (BGR) in Germany.
Table of Contents
Waste Problem and Multi Barrier Safety
Site Searching Process
Part 1: Selection of New Waste Disposal Sites
1.1. Overview Investigation
1.2. Geological Assessment
1.3. Hydrogeological Investigation
1.4. Geophysical Investigation
1.5. Geochemical and Hydrochemical
Investigation
1.6. Natural Attenuation Capability
1.7. Geotechnical Stability
Part 2: Investigation of Sites Suspected to be
Hazardous
3.1. Overview Investigation
3.2. Detailed Investigation
3.3. Geophysical Investigation
3.4. Hydrogeological Investigation
References/Further Reading
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6
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Waste Problem and Multi Barrier Safety
Initiatives to separate waste and to organize
recycling have been set up but recycling is
not for free, it can also cause contamination.
Increasing population density and industrialization is creating a high strain on the
natural environment and resources. Therefore, precautionary measures to protect the
environment and remedial actions to repair
the damages of the past have high priority.
Resources to be protected are surface water,
groundwater, soil and air. Hazards to these
resources are landfills and industrial sites as
well as mining facilities, including tailings,
conditioning plants, and smelters, oil refineries, distribution facilities and pipelines,
gas stations and other areas used by humans
(e.g. military training sites).
Waste Reduction
Waste Avoidance
Environmental protection has a high priority
on the national agenda of the Kingdom of
Thailand. The best way to avoid environmental damage due to landfill facilities is to
avoid the waste generation. We have to train
ourselves to become more aware about the
waste generation by asking whether
o a product will last,
o it can be maintained, repaired or restored as it gets older,
o there is a simpler, less wasteful alternative.
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Incineration and other waste treatment reduce the waste volume; however, waste will
still be generated. Landfill construction will
be required to deal with the incineration
ashes often containing high amounts of
harmful substances.
Efforts are made on all levels striving towards a Zero Emission Strategy (ZERI).
Until this aim is fully achieved safe landfill
construction will be necessary.
The Multi Barrier Concept
High-level standards are necessary for the
disposal of waste in order to avoid environmental damages. State of the art is the Multi
Barrier Concept (MBC) for landfills which
was introduced in Germany in 1993 under
the regulation “Technical Instructions on
Wastes from Human Settlements” (TASi).
The MBC comprises the phases of planning,
construction, operation and follow-up care
of a waste site and is based on the combined
effects of several, from each other largely
independent barriers systems. The three barriers are the landfill body, the landfill sealing and drainage system and the landfill site
(geological barrier) as shown in Figure 1.
Most importantly a landfill has to be constructed in such a way that the drainage water is collectable by free outflow from the
waste site. It is therefore of utmost importance to construct a landfill as heap and not
to fill existing pits.
The Waste as Barrier
The waste to be emplaced must comply with
a number of characteristics in order to take
on the function of a barrier. These include
having the minimum possible eluation behaviour, in other words must strongly inhibit infiltration and leachate formation,
having minimum possible toxicity as well as
long-term chemical stability. Assessment
values include not only threshold values for
toxic constituents but in particular the specification of a low content of organic components expressed as the "ignition loss". For
the most part inert wastes can only be guaranteed by way of suitable conditioning
methods (e.g. incineration, pre-composting).
In many cases the waste generated will not
comply with these characteristics. They are,
however, important to strive for. If they are
fulfilled the waste itself acts as a barrier and
the risk of environmental pollution by the
landfill is greatly reduced. It is of utmost
importance to avoid deposition of toxic material as well as fuel, batteries, and other
long lived industrial objects in combination
Figure 1: The Multi Barrier Concept
with household waste as they will cause a
lasting threat to the groundwater. Whenever
possible waste should be separated and for
the different types of waste (biodegradable,
metallic, recyclable plastics, etc) an adequate treatment is to be organized.
Technical Barrier
In terms of technical barriers, based on today’s standard, combination systems made
up of mineral seals together with plastic
membranes promise the best infiltration inhibition as the base seal. Other elements of
technical barriers comprise drainage systems offering long-term functionality
(drainage beds) and
also systems for gas
collection (gas drainage).
The base seal must be
emplaced right at the
start of the landfill
construction. Even if
the thorough study of
the geological barrier
has proven its very low
hydraulic conductivity
a technical base seal
should always be emplaced. The technical
barrier retains the
leachate for the first
years until it is chemically stabilized. The seal also enables a well
defined access to the leachate for monitoring purposes.
Only at the end of the deposition process the
decision on surface seals must be taken. Dry
cracking often results in adverse effects and
is to be avoided. Particularly clay seals bear
the risk of cracking once they dry out. New
surface seals (e.g. bitumen, capillary barriers) get currently developed with improved
characteristics.
Geological Barrier
The geological barrier holds a special position within the MBC. It in all cases comprises naturally arranged, slightly permeable, unconsolidated or consolidated rock of
several meters thickness and exhibiting a
high pollution retention capacity extending
beyond the area of the dumping site. The
existence of such a barrier is to be proven at
sites suspected to be hazardous. The following chapters describe the procedures regarded necessary for investigation of the
geological barrier. The combination of the
three barriers will result in a landfill having
the least detrimental effects for the resources water, soil and air. If the geological
barrier is insufficient technical barriers must
be constructed to fulfill its function which
will increase the landfill’s construction
costs.
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Site Searching Process
General Aspects
It is important to understand the complexity
of the process required to obtain reliable and
reproducible results for site investigation
and assessment. The steps of a scientific
landfill site search and investigations of
sites suspected to be hazardous are not a
matter of personal judgment or individual or
social preference, but are based on scientific
principles. They can be repeated since they
are generated according to well documented
procedures, and new data can be integrated
for broadening the insight. This is of prime
importance for the search of a geological
barrier, i.e. the evaluation of potential barrier properties of rocks.
The scientific character of the procedure ensures that everyone involved can agree on
the results. And if the objective is not consensus based on scientific results, nothing
else has a chance of leading to a consensus.
Acceptance of the results of a scientifically
based landfill site search process by the
public will be high and potential conflicts
can be reduced. However, it is of utmost
importance to involve all stakeholders in the
site searching process.
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Public Participation
It is important that all the steps of the site
searching process are open to the public.
Transparency, mediation between disagreeing parties, and the right to participate as an
equal partner in the discussion strengthen
the site search process. Its design as a public
process avoids the impression that a site will
or can be selected without taking the public’s opinion into consideration.
The primary aim of a site searching process
is to minimize the environmental impact of
a waste disposal site. A site is to be selected
where the least detrimental effect can be ensured with minimum costs; geological barriers are for free, technical barriers must be
paid for. And the population suffers from
the burden of an improper site selection.
The site searching process must take the regional aspects and problems, i.e. regional
planning decisions, special geological features, and economic conditions (affecting,
for example, the amount of waste produced)
into consideration.
Pragmatic Approach in Planning of
New Landfills
There are regions for which at present no
geological and hydrogeological data bases,
no “Potential Barrier Rock Maps (PBR
maps)” and/or “Groundwater Vulnerability
Map”, and in some cases no geological map
1 : 50 000 are available. In such cases a
pragmatic approach in planning a new landfill can be used. Possible waste disposal
sites are selected by political decision
and/or applying non-geoscientific criteria
(e.g. availability of public land, transport
routes). In such cases the geoscientific site
investigation and assessment must be carried out in order to make sure that inadequate sites are excluded and the most appropriate site in terms of the geological barrier is chosen.
On account of the various complicated geoscientific issues to be considered when
looking for a new landfill site or to investigate a site suspected to be hazardous professional contractors should be appointed for
these tasks. These contractors should be selected by a transparent tender process as to
reduce the risk of detrimental influence on
siting decisions to a minimum.
The necessary steps for the geoscientific investigation, although easily described in
theory, become often very complicated due
to various social and political aspects which
have to be taken into account. The following describes in a flowchart a procedure to
be followed:
The local authority responsible (LAR) should appoint a general
contractor for the site searching process or parts of this process.
This general contractor should steer through the whole process, ensure the contracting of specialists for certain detailed investigations
and should organise public participation as agreed with the local authority responsible.
LAR: Definition of initial conditions
ƒ
ƒ
ƒ
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kind of landfill (kind of waste),
planning area (e.g. district),
quantity of waste (for 25 years);
size of landfill site.
LAR in cooperation with ARP: Selection of
sites for a suitability assessment.
LAR and IR: First consultation with the IR
• advice on the basic principles,
• provision of available data.
LAR: Commissioning of overview investigation
Contractor: Conducts orientating site investigation and assessment (phase 1)
• compilation of available data for the
proposed sites,
• exclusion of unfavorable sites,
• orientating geoscientific investigations,
• comparative site assessment
If no selected
site is suitable
as a waste disposal site, LAR
should select
new sites with
the support of
IR
LAR and IR: Second consultation with the IR
•
assessment of results
LAR: Commissioning of the detailed site
investigation
Contractor: Detailed site investigation
IR: Assessment of results, possibly approval of landfill planning.
The institution responsible (IR) should be consulted at well defined
steps of the process to give advice concerning the general principles
of the site searching, to provide geoscientific data if available and
to ensure that the whole process is performed according to rules and
regulations set in the Kingdom of Thailand. It is of utmost importance that the procedures are coherent countrywide, by no ways is it
acceptable that safety requirements are adhered to only by certain
communities and not by others.
The authority for regional planning (ARP) should be consulted at
the very beginning. The Kingdom of Thailand is rapidly developing
and plans for future settlements, industries and national parks or
recreation facilities must be taken into account in the very early
phases of the site searching. Planned roads, railways and other
means of public transport, possibly having detrimental effects of the
sites safety and long term stability, need to be considered. Landfills
are long lasting facilities, the future use of the area, once the deposition is terminated, should be planned thoroughly already at the
early phases of landfill planning. Abandoned landfills, without
proper monitoring and organized future use, present an unacceptable hazard for future generations.
Specification of
further investigations if necessary
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Part 1: Selection of a New
Waste Disposal Site
1.1
Overview Investigation
The first step to select a suitable site for
landfill construction is the overview investigation. In this overview investigation firstly
the excluding criteria for landfill construction are evaluated. In the Kingdom of Thailand excluding criteria are recommended by
the Pollution Control Department (PCD)
and published in the PCD booklet
(1998/2000): “Regulation and Guideline of
Municipal Solid Waste Management”. According to these recommendations no landfill is to be constructed
1) Within the watershed areas class 1 and
class 2.
2) Within 1-kilometer distance from the
property boundary of any ancient monuments.
3) Within the 5-Kilometer distance from
any licensed and operating airport runways.
4) Within 700 meters of a potable water
well or community water treatment plant.
5) Within 300 meters of any natural or manmade body of water, including wetlands.
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6) In an area where the formation will not
provide support for the solid waste.
7) In an area subject to frequent and periodic flooding unless flood protection measures are in place.
8) Unless in an area where the normal water
table is sufficient low. In high water level
area, unless special design is provided.
Further Excluding Criteria
In addition to these criteria others have to be
taken into account, based on experience and
aimed at finding a location with least detrimental effects the environment and at
minimizing combating interests. It is
strongly recommended never to construct a
landfill
ƒ within a particular hazard prone area.
Hazards to be looked upon are floods,
earthquakes, landslides, subsidence and
tsunamis. In areas of seismic activity the
greatest possible distance to faults and
lineaments, active during holocene times,
are to be kept.
ƒ within an area of high soil quality in order to minimize combating interests.
ƒ above an aquifer bearing potable water
unless it is protected by an aquiclude of
some meters thickness.
ƒ within nature reserves, wildlife sanctuaries, areas of ecological importance and
recreation areas.
ƒ directly adjacent to quarries and mining
areas in order to avoid combating interests.
ƒ directly adjacent to main rivers and river
tributaries.
ƒ Within an area of particular high wind
speed.
Mapping
A map should be produced to visualize all
areas excluded by the criteria mentioned
above. To construct this map the following
characteristics of the investigation area are
to be gathered:
ƒ topography, land use and vegetation, settlements, industrial areas, roads and railways, other man made structures (landing strips, military areas, pipelines,
power lines, …),
ƒ precipitation, temperature, evapotranspiration, direction, velocity and intensity of
wind,
ƒ natural or man made bodies of water,
wetlands, and flood plains,
ƒ drainage (streams. rivers, any natural or
man made drainage channel),
ƒ flood-, land slide-, tsunami-, and earthquake prone areas,
ƒ soil, stratigraphy and lithology,
ƒ fault zones and lineaments,
ƒ ecological aspects: e.g., nature reserves,
protected geotopes, water protection areas.
Information for this investigation phase can
be drawn from archived material and available maps on the different topics. Remote
sensing methods are of particular help for
detecting fault zones and lineaments and the
mapping of areas prone to flooding. Areas
of former landslides can also be detected by
remote sensing methods.
Maps and data to be gathered and used
comprise but are not limited to:
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The best way to compile a map on these
characteristics is by using a Geographical
Information System (GIS). If this is not
available maps at a scale of 1:25000 are to
be drawn, where all these characteristics are
properly displayed.
topographic maps,
aerial photography,
satellite images,
geological maps,
hydrological maps,
maps on hazards and/or geological risks,
reports and expertise as well as special
literature.
A reconnaissance survey in the field must
be done in order to check the accuracy of
maps and data. A historical review of anthropogenic sites or structures is recommended and can be achieved by interviews
of time witnesses or evaluation of old aerial
photographs.
High Potential Barrier Rocks (acc. to boreholes/acc. to geological map))
Medium Potential Barrier Rocks (acc. To boreholes/acc. To geological map)
ca.4 km
Figure 2: Potential Barrier Rock Map of the Lamphun area (abbreviated after Dorn & Tantiwanit, 2002).
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1.2 Geological Assessment
First Assessment of the Potential
Barrier Properties
The most important characteristic of the
geological barrier is it’s low to very low hydraulic conductivity. Only areas where the
lithological information gives evidence for
low hydraulic conductivity should be suggested as possible sites for detailed investigations. The geological map gives the first
clue to the hydraulic conductivity, however,
field surveys are necessary to prove this. A
study on potential barrier properties of different lithologies has been performed in the
Chiang Mai area and the following scheme
has been developed (abbreviated from Dorn
& Tantivanit).
Unit
Potential Barrier
Property
high
5
6
Lithological description
Fluvial clay : clay,
silty
Natural levee silt,
very fine
Alluvial fan sand
Alluvial sand and
clay
Low terrace gravel
Colluvial formation
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High terrace gravel
none
8
9
Sandstone
Shale and mudstone
low
high
1
2
3
4
10
medium to high
none
medium to high
none
high
This scheme gives an idea in which way the
potential barrier property might be attributed to the different lithologies, but for
every geological setting an appropriate
scheme must be developed.
A map, termed Recommended Areas for
Site Investigation Map (RASIM) should be
compiled. In this map only areas with high
to very high potential barrier characteristics
and not excluded by the excluding criteria
above are to be marked. This map should
be compiled in a format readily comprehensible for the public and should be used to inform all stakeholders of the current status of
the investigation.
Detailed Investigation
The one to three areas recommended for detailed investigations due to their supposedly
high to very high potential barrier properties
must now be investigated in detail. The detailed investigation aims at the assessment
of the subsurface in terms of
ƒ structure and composition (texture, grain
size, mineral content, density, water content, possibly contamination),
ƒ strength (compressibility, shear strength),
ƒ porosity and water saturation, and
ƒ hydraulic conductivity.
The detailed investigation must not only focus on the planned landfill site but also on
its surrounding. The groundwater system of
a site might cover an area of several 10 km2,
and information about this system must be
collected. The local system to be investigated in detail usually covers an area between 0.1 and 1 km2. Relevant to site investigations is a depth range from surface to
50m depth. Deeper (up to 150m) investigations (possibly by reflection seismics) might
be necessary to better understand the regional structures (stratigraphy and tectonics)
as well as the groundwater system.
Principle Approach
The geological barrier must be as homogeneous and hydraulically impermeable as
possible in order to minimize the risk of
groundwater pollution. The principle aim of
the study is to proof these characteristics of
the planned landfills subsurface.
Below the one to three sites recommended
for detailed investigation the extension and
thickness of the rock beds (lithological
units) and their hydraulic conductivities are
determined using geological methods (geological mapping, excavations, drilling, direct push sounding, geophysical borehole
logging) in combination with geophysical
methods, remote sensing, hydrogeological
investigations, geo- and hydrochemical
analysis, determination of the retention capacity and geotechnical assessment. These
different methods are described in detail below.
The Conceptual Model
A conceptual hydrogeological model is the
basis as well as the final result of the (hydro)-geological investigation of new landfill
sites and contaminated sites. The initial
conceptual model will continually change
during the process of investigation.
For every site two steps are necessary to develop a first conceptual hydrogeological
model:
1. geological field survey and
overview surveys. All boreholes and measurement points must be plotted into this
map. The requested lateral accuracy is 1m
and the precision for the elevation should be
0.01 m for boreholes to be used as groundwater observation wells, 0.03m for gravimetry, 0.1m for seismics and 0.5 m for
geoelectrics and electromagnetics. It is
strongly advisable to mark the geophysical
profiles on the investigated site in a lasting
way.
on the refined model. Detailed geophysical
measurements might be helpful to clarify
the hydrogeological situation. Normally
drilling should be done on the geophysical
profiles in order to enable the best calibration of the geophysical measurements. It
should be considered well in advance that
drilling and geophysical profiling is performed in such a way as to enable the identification of the groundwater flow direction.
The results of the geophysical surveys are to
be used to refine the conceptual hydrogeological model. The position of the investigations wells will be decided upon based
2. analysis of existing well and borehole data.
The geological field survey must include
not only the site but must cover the surrounding area. The geology of the area is
to be assessed in terms of lithology,
stratigraphy and tectonics. Hand augering
is to be performed and the samples are to
be analyzed lithologically and stratigraphically. Water samples are to be
taken and analyzed for the hydrochemical
characteristics.
A detailed geological and hydrogeological map of the site and its surrounding is
to be compiled. This map serves as base
map for positioning of the geophysical
Figure 3: Cross section in North-South direction of the site Mae Hia in the Chiang Mai area.
Groundwater flow towards south into the canal is evident by the water table of the wells and boreholes. The waste site is within a clay rich layer thus inhibiting leaking of contaminants into the
deeper groundwater layers, as verified by hydrochemical measurements.
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1.3 Hydrogeological Investigation
These parameters have to be measured in
the field or be obtained from nearby meteorological stations.
Comprehensive knowledge of the groundwater conditions is necessary for the assessment of long-term safety of a planned
landfill site as well as the planning of effective groundwater monitoring.
It is necessary to investigate all major aquifers which could possibly provide a pathway for contaminant transport. Their hydraulic and hydrochemical parameters need
to be assessed.
Based on results of the investigation of
groundwater conditions and geological information, a hydrogeological model of the
site must be developed.
Field Investigations
Compilation of Climatic Data
There are different reasons to study the local
climatic and hydrological conditions. The
climatic conditions define the water balance
of the investigation site. The most important
parameters are precipitation, temperature,
humidity,
runoff,
evaporation
and
evapotranspiration. Precipitation not only
recharges the groundwater, but also forms
leachate in landfills and mobilizes solutes in
contaminated sites.
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Subsurface investigations, such as trenches,
boreholes and direct push technology (DPT)
soundings are necessary to get information
about:
• the geological structure,
• the lithological and stratigraphical profile,
• the spatial distribution of aquifers and
aquicludes,
• their hydraulic and geochemical properties, and
• the groundwater table and the catchment
area of the drainage basin.
It is necessary to drill wells and to sample
water, soil and rocks for laboratory analysis.
Hydraulic well tests, pumping tests,
groundwater tracer tests and continuous
groundwater level measurements are used to
investigate the hydrodynamic situation of a
site. For these investigations groundwater
monitoring wells are necessary. Therefore
drilling and well construction is an essential
part of the hydrogeological field work.
Quality monitoring wells are furthermore
the prerequisite for hydrochemical sampling. Apart from the requirements for hydrogeological site investigations, it should
be considered to use the newly constructed
wells as components of a groundwater
monitoring system.
Well Construction
Drilling and installation of wells are the
most important hydrogeological investigation methods. The construction of monitoring wells of high quality is of crucial importance for well tests and hydrochemical sampling. Important for the quality of wells are:
• clean work and proper materials,
• appropriate drilling technique,
• correct placement and length of the filter,
• sufficient clay seals, and
• suitable well dimensions for all following investigation (sampling, hydraulic
tests, etc.).
Hydrogeological Conditions
The hydrogeological conditions of a site can
be described by the following parameters:
water table, water content, direction and rate
of groundwater flow, hydraulic conductivity, and value of aquifer.
The hydrogeological situation is a significant aspect which determines the geotechnical concept of a planned landfill. The
groundwater table below the landfills base
and the mechanical properties of the geological barrier determine the level of the
landfill base.
The hydraulic conductivity (kf) of the saturated zone can be determined with various
methods. These include pumping tests, well
bore tests (slug/bail, drill-stem, water pressure and vibratory methods), and infiltration
tests.
While pumping tests are suitable for the determination of hydraulic conductivities of
aquifers, other tests (e.g. drill-stem,
slug/bail, pulse test) are also applicable in
potential barrier material with low hydraulic
conductivities.
The term infiltration describes the entry of
water into the soil through the ground surface. Lysimeters and double ring infiltrometers are devices to study the infiltration
processes.
Groundwater Dynamics
Groundwater dynamics – the temporal behavior of groundwater- as one aspect of the
hydrogeological conditions is determined by
the following parameters:
•
•
•
•
•
•
•
groundwater gradient,
direction and rate of groundwater
flow,
depth of groundwater table,
hydrodynamic dispersion,
groundwater recharge,
hydraulic interaction between aquifers, and
seepage from aquifers and surface
waters.
Water level measurements in observation
wells allow the determination of groundwater contours, groundwater flow direction,
and groundwater gradient. Furthermore, by
investigating time series of water levels and
geological information, confined and unconfined aquifers can be distinguished. Based
on the understanding of the hydrogeological
conditions at the site, derived from the
aforementioned data, the hydrogeological
model for the site can be developed.
The measurements of the groundwater levels are generally taken over longer time periods, if possible throughout a full hydrological year (i.e. comprising all seasons,
usually 1 November until 31 October) and
correlated with measurements taken over
many years from neighboring observation
wells. Only by this procedure the natural
fluctuations in the water levels and their effects on the hydraulic system can be interpreted. Civil engineering measures for the
construction of the landfill base (e.g. assessing distance to the groundwater in all seasons, required depth of the drainage system)
can be adequately planned if this information is at hand.
aquifer
filling material
filter gravel
counter filter
seal
L
d BH
F
screen
casing
water level
Figure 4: Schematic sketch of monitoring well
filter section.
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1.4 Geophysical Investigation
Geophysical measurements are necessary to
investigate the structure of the subsurface at
the site of a planned landfill and the surrounding. Geophysical methods are most
appropriate to get an overview on the layering, the depth to the different layers and
their lateral and vertical extent. In order to
proof the existence of the geological barrier
and it’s homogeneity geophysical investigations are indispensable.
Once a conceptual hydrogeological model is
developed geophysical overview measurements should be done. These aim at proofing the model and assessing the heterogeneity of the subsurface. Based on the geophysical results the conceptual model
should be refined. Furthermore detailed
geophysical measurements might be required. The location of the boreholes should
be decided upon based on the refined conceptual model.
Suitable Geophysical Methods
Many geophysical methods can be used for
the investigation of the subsurface of a
planned landfill, i.e. magnetics, gravimetry,
dc-resistivity, electromagnetics, ground
penetrating radar, reflection and refraction
seismics and Surface Nuclear Magnetic
Resonance (SNMR). In this chapter only dc14
resistivity, electromagnetics (EM) and refraction seismics will be described in more
detail. The magnetic and gravimetric methods will be described in the chapter on hazardous sites. Reflection seismics often lacks
resolution in the upper 20 m. It is used for
the investigation of the deeper subsurface, if
required. The investigation depth of ground
penetrating radar is very limited in electrical
conductive material such as clay. Both
methods have many merits and might be required in certain cases. The SNMR method
detects the free water quantitatively but and
is currently in an experimental stage.
DC-Resistivity
The direct current (dc)-resistivity method
reveals the structures and the layering of the
subsurface in terms of electrical resistivity.
To carry out dc-resistivity measurements
current is induced into the subsurface by
two electrodes (A and B) and the voltage is
measured between two other electrodes (M
and N). The investigation depth depends on
the distance between the current electrodes
A and B, the AB spacing. As a rule of
thump the investigation depth is about 1/10
of the maximum AB-spacing.
dc-resistivity measurements can be carried
out in three different ways: dc-soundings,
dc-resistivity mapping and multi-electrode
measurements. The latter are used to pro-
duce 2D-resistivity sections. These show the
structures along a profile up to a certain
depth, depending on the profile length, i.e.
maximum AB-spacing (Figure 5). Different
electrode configuration can be used, such as
Schlumberger, Wenner or Dipole-Dipole.
The most appropriate configuration depends
on the situation and can be decided upon in
advance by forward modeling.
Many geological formations with low hydraulic conductivities also show low electrical resistivities thus dc-resistivity measurements are recommended for mapping the
geological barrier properties of the subsurface. Sand and clay differ in electrical resistivity as do dry sand and water saturated
sand. Dry sand shows normally high resistivities and clay, shale and mudstone normally show low resistivities. But the resistivities often overlap, thus borehole information is required for calibration.
EM-Investigation
Electromagnetic (EM) - mapping is the
most often used method to investigate the
lateral changes in the subsurface of a
planned landfill site. The EM-method, as
does the dc-resistivity method, looks upon
the subsurface in terms of electrical resistivity. The electromagnetic waves, however,
pose certain advantages. The contact to the
ground is achieved by electromagnetic in-
duction, not by electrodes, which might be
difficult to stick into hard layers or might
not get sufficient electrical contact in loose
dry sand.
EM-measurements are often done along
profiles and the electrical resistivity is
measured. The investigation depth depends
on the frequency and the distance between
transmitter and receiver. Instruments usually
offer more than five frequencies and some
fixed transmitter-receiver distances. Mostly
measurements are carried out for investigation depths of up to 30m, deeper measurements are possible but rarely used.
Refraction Seismics
Refraction seismic looks upon the subsurface in terms of seismic velocities. An elastic wave is called refracted, if it runs at the
interface of two layers with different velocities. The refracted wave can only be recorded at the surface, if the velocity is increasing with depth. This generally happens,
if young soft sediments cover older and
harder ones, or if they cover even hard
rocks. The stronger the velocity contrast between the layers, the better the method
works. A velocity gradient inside a layer
can bias the depth of its lower layer boundary. The correlation of the seismic velocity
to lithologies is ambiguous, as is the correlation between electrical resistivity and
lithologies. Borehole information should be
used to calibrate the measurements in terms
of lithologies.
an explosion and recorded along a surface
profile by geophones. If the layers in the
subsurface are inclined, the measurements
must be done with reversed shooting, at
least with shots at the start point and at the
end point of the profile. If a subsurface layer
is expected to be curved, more shotpoints in
between are needed. The investigation depth
depends on the profile length and the geological situation (attenuation and strength of
velocity contrasts). As a rule of thump it is
about 1/5 – 1/10 of the profile length. The
required profile length and receiver distances can easily be calculated from expected velocity contrasts and depth.
The elastic waves are generated by a hammer, a falling weight, a vibrator or even by
Figure 5: dc-resistivity profile from a site consisting of a sandstone formation (reddish color, high resistivity) with interbedded mudstone layers (greenish color, low resistivity). The mudstone layer is discontinuous. Both, the geoelectrical section and the EM-Mapping (not shown), point to strong fracturing. Potable water was found in a borehole
at profile length 650 m at a depth of 30 m. This site is therefore not suggested for landfill construction due to the lack of homogeneous barrier layers.
15
1.5 Geochemical and Hydrochemical Investigation
The geochemical investigation in the study
area is primarily focused on characterizing
the complex chemical inventory of soil,
rock, stream and lacustrine sediments,
groundwater, surface water and soil gas.
In case of planning and construction of a
new landfill the geogenic background values and the anthropogenic input from former land use have to be determined for
comparison with the later changes caused
by the landfill. An hydrochemical assessment during operation and aftercare phase
of a landfill is only possible with observations of the undisturbed state (hydrochemical background).
Sampling
Proper collection of the samples is necessary to obtain exact analytical results and
thus a correct assessment of the site being
investigated. Errors made in collecting the
sample cannot be recognized in the laboratory and hence cannot be corrected afterwards.
16
Sampling of Water
Sampling and analysis of water must be
done in accordance with international standards (DIN, ISO, ASTM, EPA).
•
Groundwater samples from observation wells: DIN 38402-A13:12.85 and
ISO 5667-11:03.93
•
Preservation and handling of samples
DIN EN ISO 5667-3:0496
•
Surface water bodies DIN 38402A12:06.85
•
Standing water bodies DIN 38402A15:06.86
Normally groundwater samples are taken
from an observation well. Stagnant water
has to be removed from the well before
sampling, by purging. In the case of pumped
groundwater samples, it is important to continually record changes in the well during
the sampling (pH, electrical conductivity,
temperature, oxygen concentration, depth to
water table, and pumping rate) in order to
determine the appropriate time for taking
the sample and as documentation for the interpretation. The pumping for purging or
during sampling must be such that the resultant lowering of the groundwater table is
minimal. A submersible pump together with
a pressure-retaining bailer fulfils the practi-
cal requirements for sampling best. The
need of on-site sample analysis as well as
sample preservation measures must be assessed by the laboratory staff in accordance
with the objectives of investigation.
Sampling of soil
In geochemical site characterisation samples
of soil, rock, stream and lacustrine sediments (summarized as “soil”) are taken in
order to determine the background contents
and the location-specific properties. Soil
samples can be taken form: dug holes, percussion core drillings, trenches, piles of soil,
liner samples. The samples must be representative for a defined area and depth at a
defined time. Samples are taken for laboratory analysis of:
•
texture, structure and environmental
parameter values,
•
contents and distribution of substances,
•
physical, chemical and biological
properties,
•
migration processes of interaction between the groundwater and the sediments,
•
microbiological and geochemical
processes of natural attenuation
Water Chemistry Analysis
Soil Analysis
For the characterization of the water type
and the geogenic background of the investigation area, a spectrum of main ions and parameters should be analyzed, containing at
least:
The specific properties of a soil, the source
rock of the soil, chemical environmental parameters (pH, redox) and sorption-effective
components (organic carbon, clay mineral
content) are significant for the migration
behavior of contaminants and/or the sorption potential of the soil. They are therefore
of prime importance for the characterization
of the geological barrier.
cations: Sodium, magnesium, calcium, potassium, aluminium, manganese, iron and
silicon. ammonia.
anions: chloride, sulphate, nitrate, and hydrogencarbonate/carbonate (total inorganic
carbon).
furthermore: TOC (total organic carbon), or
DOC (dissolved organic carbon), pH-value,
electrical conductivity, oxygen content, and
redox potential.
Basic soil parameter to be analyzed:
• physical-chemical parameters
dry bulk density, hydraulic conductivity, pH-value, electrical conductivity, grain size distribution, water con-
tent, porosity , cation exchange capacity, neutralizing capacity (against
acids and bases), and shrinkage/swell
behavior of clay minerals.
• mineralogical parameters
clay mineral composition, contents of
iron compounds, and carbonates.
• chemical parameter:
organic carbon content and the main
ions in an aqueous extract..
Furthermore the methods described under
1.6. “Natural Attenuation Capability”
should be included in the assessment of soil
parameter for site characterization.
For monitoring purposes and to trace the
water quality changes during and after the
operation of the planned landfill the following components, typical for waste site influence should be included in the analysis program: boron, sum parameters (COD, BOD)
or groups of organic contaminants (e.g.
phenols, mineral oil content), heavy
metal(e.g. arsenic, cadmium, chromium,
copper, mercury, nickel, lead, and zinc)
Figure 6: Sampling of water with on site measurements and treatment.
17
1.6 Natural Attenuation Capability
Natural Attenuation
The effectiveness of the geological barrier is
based not only on geohydraulical effects
(low levels of water conductivity and diffusion) but as well on hydrochemical/biological and geochemical/-biological
processes. These determine the natural attenuation capability of soil and sediments.
Two of the most important processes of
natural attenuation are the retardation and
biodegradation of contaminants. Retardation
is synonymous with delayed transport of a
contaminant compared with the movement
of water without contaminants. Causes for
contaminant retention comprise the processes of adsorption/desorption with a transport-retarding effect. The preferred barrier
material is a clay-rich substrate of low hydraulic conductivity which, unlike any other
material, offers both low water conductivity
and a large surface for reaction with pollutants, respectively. The retardation of cations
and organic contaminants takes place primarily via sorption on fine grained mineral
and organic components. In comparison
with retardation biodegradation is the most
important process of natural attenuation because of its sustainable reduction of contaminants. Biodegradation is also effected
18
by structure and texture of soil and sediments. These determine the level of redox
potential and the availability of electron acceptors as well.
and carbonates, cation exchange capacity,
ion coating and exchangeable cations, main
ions in aqueous extractions, pH-value as
well as acid and alkali capacity.
Worst Case Scenario
For municipal landfills metal-sulfide systems (sulphide precipitation) and the formation of complexes by organic substances are
of concern. It is suggested to examine the
leachate from existing landfills for contaminants typically found in the dumped waste
of the area.
The propagation of substances from landfills takes place primarily in dissolved form.
The worst case scenario is that the substances are not retarded (adsorbed) and biodegradated in soil and sediments, respectively. If this is the case the time until the
leachate has passed through the geological
barrier depends on the barrier thickness, its
fine structure, its hydraulic conductivity, its
porosity, and the hydraulic/hydrological
boundary conditions (e.g. hydraulic gradient). This time is predictable using geohydraulic models.
Each soil or sediment has more or less natural attenuation capability. For estimation of
specific retardation and biodegradation parameters laboratory tests are necessary.
Laboratory Tests for Retardation
and Biodegradation
Only laboratory tests provide the possibility
for correlating retardation and biodegradation with the following parameters of the
barrier material (soil or sediment): Clay
mineralogical composition, content of organic carbon, contents of ion-compounds
Because of the complexity of the different
reactions between leachate and soil or sediment it is necessary to use original leachate
and uncontaminated soil or sediment from
the aquifer downstream of the landfill.
Two laboratory test methods are common
for estimation of retardation and biodegradation parameters. These are subdivided in
batch and column tests.
Batch tests are used for parameter estimation of sorption and transformation like biodegradation. Transport processes are not
considered in batch tests. These tests may
be performed on soil samples which are disturbed/undisturbed, consolidated/unconsolidated, saturated, or with a water/solid ratio
of 1 or higher. One distinguishes, in general,
between static and dynamic batch tests, depending on whether the soil and water are in
motion during the batch test. Movement in
those tests is used to accelerate the averaging process.
Column tests are used for parameter estimation of transport, retardation and exchange
between different phases like soil, air and
water. The evaluation of column test data is
based on the complete one-dimensional
mathematical migration model. Therefore
the length-diameter ratio of columns should
be greater than 5:1 (3:1 at a minimum). A
column experiment has to be performed until the output concentration of the contaminants reaches the input concentration in order to attain a break-through curve.
1.7 Geotechnical Stability
For risk assessment of waste disposal sites
knowledge about the stability of the ground
is necessary. The landfill base sealing system and the stability of the landfill body is
not to be jeopardized by settlement of the
landfill body. Current and archival aerial
photographs very often contain indications
for destabilization processes like subsidence
caused by subrosion and mining activities,
landslides and sinkholes. Terrain feature indicating destabilization processes are fracturing and jointing, subsidence of Earth surface, caves to the surface, bedding slippage
of slopes, break edges as well as tension and
relaxation indications. Stability of the landfill base and the landfill body are required
inter alia to ensure the functionality of the
seepage collection as well as the base and
surface seal.
Settlement Calculation
The calculations of the landfill settlement
can be undertaken either analytically or numerically (e.g. finite element method).
Rough settlement calculations can be performed „by hand“ and computer software is
available in many versions. However, settlement calculations ultimately always represent approximations and the results can
differ from reality to greater or lesser extent.
For the calculation the modulus of resistance (Es ) of the different layers must be determined in the laboratory on soil samples
using a compression-permeability test or
other suitable tests. Es differs for the different soil types; typical values are 10 – 80
[MN/m2] in sand and 2 - 20 [MN/m2] in
silty clay.
As far as the function of the drainage systems and the base seal of landfills are concerned, it is not only the absolute figures for
settlement of the subsurface which are critical but primarily the probability of settlement differences and the resulting stretching. The degree of settlement difference is
mainly dependent upon the properties of the
near surface beds. It is therefore of utmost
importance to investigate the homogeneity
of the planned landfills subsurface since lateral variations might be a hazard for the
landfills stability.
Settlement Time
Settlements over thick cohesive beds can
last about 100 – 200 years before they come
to an end. This is a consequence of the slow
rate of consolidation of the subsurface (as a
comparison, the operating period of the
landfill is approx. 10 years). If for example
the clay bed has a thickness of 15 m, the settlement could rise to s = 9.75 cm and the
time period could be t = 180 a.
Stability Hazards
Regretfully thick clay beds which offer effective barrier properties form particularly
unstable slopes. Furthermore, in the case of
soft substrata it is possible for deep reaching
collapse figures to occur since loads can
generate pore water overpressures which reduce the shear strength of the soil to solely
that of the cohesion fraction (angle of friction). In order to alleviate the risk of slope
failure the landfill construction must be preceded by a careful engineering study.
19
Part 2: Investigation of Sites
Suspected to be Hazardous
2.1 Overview Investigation
Old landfills, industrial sites and mining
activities are rarely located on a geological
barrier of sufficient quality. They are often a
source of pollution of water, soil and air,
thus possibly having harmful effects on humans and the environment. The objectives
of the study are to investigate those sites in
detail, to estimate their possible pollution
risk and to suggest measures for the remediation of such risk.
It is necessary to analyze the toxicity or
danger of the material, the amount of toxic
or otherwise dangerous material, the amount
of leakage/contaminant transport and to estimate the area threatened by leakage/contaminant transport. The contamination by volatile substances (gaseous phase)
and dust like particles also need to be assessed.
As far as investigation of the landfill body is
concerned, special safety regulations apply
not least because of the risk of injury or impairment to the health of the personnel and
the inadvertent carry-over of contaminants.
Investigation is made more difficult by any
inhomogeneities and instabilities of the
landfill body. A further aspect is that the
20
landfill body may cover the geological underground strata. When investigating landfill bodies the focus must be on noninvasive techniques such as remote sensing
and geophysics. Drilling work should be
used very sparingly, if at all.
The overview investigation of such sites
suspected to be hazardous is subdivided into
two parts: the overview investigation and
the detailed investigation.
First Tasks
The first step is to gather all available information (recent and historic) of the sites
suspected to be hazardous. This entails information about the former owner/user of
the site, the kind of material deposited, details on the deposition methods and the usage of the site after termination of the deposition/use of the site.
Site Typology
There are three typical examples of sites
suspected to be hazardous. These are classified as follows:
¾ industrial sites,
¾ waste deposits, and
¾ mining sites.
Site Master Data
The following data on the site are to be
gathered
¾ site location: The site and its lateral extent must be marked on a topographic
map with appropriate accuracy (±10m).
GPS measurements may be required to
ensure this accuracy,
¾ current owner and user of the site,
¾ type of waste deposition (e.g. stockpiling, heap on a slope, backfill of a quarry,
backfill of a gravel pit, etc.) and amount
of deposited waste or hazardous material,
¾ type of material deposited, its origin, and
process of waste generation (e.g. uncontaminated excavated soil, natural rocks,
minerals from mining industry, industrial
waste, hospital waste, sludge from tanneries, etc.),
¾ type of contaminants expected (e.g. water
soluble substances, gaseous and volatile
substances, inorganic substances, organic
substances, toxic substances, etc.),
¾ present use of the site, and
¾ owners of the adjacent properties.
Site Historic Data
All historic data on the site must be collected by whatever sources available.
Multitemporal aerial photographs and satellite images should be evaluated in order to
discover the site’s development and the
former land use in the area. A report should
be compiled containing the above mentioned and the following information:
¾ person(s) or company(s) responsible for
release of harmful substances,
¾ operation time of the industrial sites,
landfills or mining sites, and
¾ past use of the site.
Site Screening by Field Surveys
All indications of spreading of harmful substances by all possible pathways need to be
analyzed. This task entails site surveys for
vegetation changes, surface- and groundwater contamination, emissions of harmful
volatile substances, and any other conspicuous occurrences. Remote sensing methods
are particularly useful for parts of this study.
The following themes have to be assessed:
¾ subsidence and/or indications for land
slides and flooding,
¾ conspicuous changes (e.g. change in the
color of soil, vegetation changes, death
or illness of fishes or other species),
¾ ground- and surface
water quality on and
in the vicinity of the
site. The chemical
analysis must be
done for all substances which can be
expected to occur,
¾ seepage and/or other
drainage signs near
the site, samples are
to be taken and analyzed for all substances important to
assess the possible
risk, and
¾ smell nuisance and Figure 7: Water conductivity in the shallow wells around the Mae
harmful volatile sub- Hia Waste site in September 2002 (after Liese, 2004)
stances in the vicingeoscientific criteria. However, other criteity of the sites with appropriate tools.
ria, such as urgent economical needs, might
have to be incorporated. The current status
Site Ranking
of national and international legislation has
If there are several sites suspected to be
to be adhered to.
hazardous in an area the most dangerous
A workplan for the detailed investigation of
sites with pose urgent public health hazards
the sites must be developed.
must be outlined by applying an appropriate
ranking scheme to the sites. A stepwise investigation procedure with the least detrimental effects for the human health and the
environment must be developed. The ranking scheme has to be fully comprehensible
for all stakeholders and must be based on
21
2.2 Detailed Investigation
Aim of the detailed investigation is to examine all contaminant pathways of the most
highly ranked sites suspected to be hazardous during a comprehensive field study. The
pathways to be investigated are soil, water
and air.
Often contaminants are not easily traced.
New methods use indicators to trace the environmental effects of contaminants by analyzing occurrence, abundance and health of
most sensitive species. The most hazardous
situation occurs when food plants can tolerate high contaminant loads. Under these circumstances the contaminants can easily enter into the food chain.
Contaminant Inventory
A contaminant inventory for each site must
be established. Base for this inventory is the
information on the former use of the site
and the material deposited as already established during the orientating survey.
The contaminant inventory must specify organics, inorganics, radionuclides and microbials in the highest possible detail.
The Soil Pathway
Contaminants might be deposited on the soil
by erosion or reach the soil by leakage, by
microbial activity or by capillary transport.
The most common soil pollutants of metal22
lic (industrial) origin are Arsenic, Cadmium,
Chromium, Copper, Lead, Mercury, Nickel
and Zinc. Metal contamination can persist in
the soil for very long periods. Other contaminants which might accumulate in the
soil are pesticides, antibiotics, dioxin, endocrine disruptors and aggressive substances
such as sulphates, chlorides and acids.
Soil samples are to be taken on the site and
all areas where the pollution might have
spread by erosion, leakage, and other ways
of transport. A map on soil contaminant
spreading has to be prepared. Sampling and
analysis should be done as described in 1.5.
The Water Pathway
Ground- and surface water contamination is
of utmost concern. The main emission
pathway from landfills and contaminated
sites is the migration of leachate, carrying
contaminants into the ground, initially into
the unsaturated zone, from there into the
groundwater and then transported with the
groundwater flow into the surrounding area.
For the investigation of this pathway firstly
the ground- and surface water situation in
the area is to be established. A hydrological
and hydrogeological report on each site
should be compiled comprising:
¾ maps on the hydrological and hydrogeological situation at the site,
¾ ground- and surface water flow direction
in all surface waters and in all contaminated aquifers and the highest aquifer not
yet contaminated,
¾ runoff amount,
¾ contaminant load and concentration in all
surface waters and all aquifers,
¾ hydraulic conductivity of the aquifers,
¾ hydraulic conductivity of the aquifers,
and
¾ estimation of groundwater/surface water
interaction.
In order to assess the ground- and surface
water contamination sufficient amounts of
samples are to be taken and analyzed for all
important harmful substances and at all
places deemed adequate to assess the contamination due to the site in a comprehensive way.
The Air Pathway
The gaseous phase and dust like particles on
the site and in the vicinity must be measured
with appropriate tools. It is necessary to extrapolate the spatial area likely to be effected by these gaseous phases. Seasonal
changing wind speed and direction is to be
taken into account.
2.3 Geophysical Investigation
Geophysical investigation methods are particularly useful to determine the lateral and
vertical extent of sites expected to be hazardous and to evaluate the spreading of
harmful substances in the groundwater.
However, what can be traced by geophysical means depends on the kind of substances
deposited and leaking from the site. In addition to the dc-geoelectric method, the EMmapping and the refraction seismics, which
is explained in section one, magnetic and
gravimetric measurements, are recommended to detect buried sites and to discover the spatial extent of partly hidden objects.
Geomagnetic Measurements
Many sites expected to be hazardous contain metallic objects such as barrels, batteries, building rubbish with steel lining, cans,
metallic industrial waste, wrecked vehicles
or damaged vehicle appliances and ashes.
Those items can be detected by magnetic
measurements and an area where those
items are scattered can be mapped by the
geomagnetic method. The total magnetic
field or the magnetic vertical gradient can
be used for this study.
The measurements are done on a regular
grid covering the site and the magnetic read-
ings are plotted. Data filtering and smoothing might be necessary to reduce the data
scatter caused by ferromagnetic objects directly at the surface.
If the total magnetic field is measured the
values have to be reduced to account for the
natural magnetic field at the site. Only the
anomaly field is plotted and areas with scattered and buried ferromagnetic objects are
often obvious by strong small scale variations of the magnetic readings. The surrounding area, where the magnetic field is
only due to natural sources often shows an
only slightly varying magnetic field.
If the magnetic vertical gradient is measured
the distance between the two sensors and
the measurement height can be used for
smoothing. The values of the gradient are
plotted and the landfill often shows itself by
high negative or positive values of the vertical gradient compared to the surrounding
area, where only the natural magnetic field
exists.
Gravity Measurements
extent of a buried landfill can be discovered
by the gravimetric method.
The gravity measurements are done on a
regular grid and utmost care must be taken
to determine the elevation of every single
measurement point, the required accuracy is
< 3 cm. It is necessary to carry out the
measurements in a loop and to repeat a certain amount of readings to correct for the instrumental drift and the tidal signal. The
normal gravimetric corrections must be applied and the anomalies are plotted on a
map. The buried landfill often shows itself
as a distinct negative anomaly compared to
the surrounding having undisturbed layers.
The hope to detect buried cavities, however,
is often in vain, since they normally cause a
very small signal which remains hidden in
the overall noise of the measurements. Depending on the anticipated size of the cavity
and the density of the surrounding material
the expected signal of the cavity should be
modeled in order not to attempt hopeless
endeavors.
Most landfills contain apart from single
heavy objects loose material. The overall
density of the landfill contents may be about
1540 kg/m3 while the surrounding geological strata might have a density of 2400
kg/m3. On account of this often the lateral
23
2.4 Hydrogeological Investigation
Investigation of the groundwater situation is
one of the key objectives when exploring a
landfill or contaminated site. The groundwater is in most cases the main pathway for
the migration of contaminants.
The main objectives of the hydrogeological
investigation in the course of site searching
for a new landfill are the assessment of the
geological barrier because its proper function inhibits contaminant migration. Normally the investigation of an old site or site
suspected to be hazardous is initiated by the
occurrence of contaminants in the surrounding of the site. Therefore the objectives of
the investigation are:
• assessment of the current state of contamination,
• prognosis on the progress of contamination, and
• planning of measures for remediation.
The methods used for investigation are
similar or identical to the methods described
under 1.3, but sampling and drilling becomes even more important.
After the assessment of the hydrogeological
conditions and the groundwater dynamics,
24
in most cases it will be necessary to drill
and establish a new monitoring system by
constructing high quality monitoring wells.
These drillings and wells are important for
the determination of quality, quantity and
distribution of contaminants.
Production wells, dug wells and old monitoring wells of doubtful conditions may
only serve as indication of contamination.
Nevertheless a preliminary survey to determine whether there are any existing monitoring wells that may be suitable for integration into the planned monitoring network is
always the first step during the planning of
any monitoring program. In order to ensure
the proper functioning of monitoring wells
(e.g. no leakage), it is of utmost importance
to carry out technical in situ tests (pumping
or infiltration tests, borehole television, and
geophysical borehole logging).
tial distribution of contaminants and their
changing conditions in time can be evaluated. They are also used for groundwater table monitoring.
If the groundwater flow direction is unknown, as a first step three monitoring wells
must be installed around the contaminated
site (in a so called hydrogeological triangle)
in order to determine the local groundwater
dynamics.
Drilling Technique
The borehole drilling technique used must
suit the conditions at the site and the questions to be answered. Each method has advantages and disadvantages in relation to
the aim of investigation and the geological
conditions.
Investigation boreholes provide information
about the geological profile. They are used
to calibrate the geophysical measurements,
to identify aquifers, to take rock samples,
and to determine the depth of the groundwater table.
Drilling techniques can be divided into percussion and driving methods or into dry
methods and methods with fluid circulation.
Common methods are:
• cable tool techniques,
• percussion drilling,
• auger drilling (solid and hollow stem
auger), and
• rotary drilling.
Monitoring wells should be constructed in
such a way as to tap the different aquifers at
different depths. From these wells the spa-
Auger technique is the most desirable
method for drilling on waste or contaminated sites. Using this method the geologi-
Investigation Boreholes
cal profile of the subsurface can be evaluated by the drill cuttings. These are transported to the surface and their depth can
normally be determined as accurate as some
50 cm. The cuttings are used for grain size
analysis and for geochemical laboratory investigations (batch tests).
The hollow stem auger technology allows to
take undisturbed sediment samples and also
to install monitoring wells.
Direct Push Methods
There are two direct push methods: cone
penetration testing (CPT) and percussion
drilling. Prerequisite for the use of directpush technology is unconsolidated rock.
Different tools are used to identify the
lithology of different layers, the depth of the
groundwater table, the thickness of the capillary fringe, or to detect the distribution of
contaminants in the subsurface. There are
also tools for collecting soil, water, and soil
gas samples.
CPT tools can be used with geophysical
sensors, for example to measure:
• electrical conductivity to determine
sediment type and contaminations,
• natural gamma measurements to determine the clay content,
• neutron-neutron to determine the water
content, and
• gamma-gamma measurements to determine the density.
Geophysical logging methods provide very
detailed information about the strata. Geotechnical tools can provide a highly detailed, 3-dimensional picture of the subsurface in less time than needed by traditional
methods.
soil-gas, and groundwater samples can be
taken at selected depths.
Open direct-push boreholes provide a path
for contaminant migration. Therefore these
boreholes have to be sealed with bentonite
once the investigation is terminated.
Special tools are available for detecting
types of contaminants, e.g.:
• petroleum hydrocarbons,
• BTEX (benzene, toluene, ethyl benzene,
xylene),
• volatile organic halogen compounds
(VOC),
• PAH (polycyclic aromatic hydrocarbons), and
• Phenols.
Individual compounds cannot be identified
and the results are only semiquantitative.
Other tools are able to detect inorganic substances (e.g., heavy metals).
Sample Collection
Sample collection is also possible with direct-push technologies. When the lithology
and the type and distribution of contaminants has been determined using geotechnical and contaminant-detecting tools, soil,
Figure 8: Typical lithological log resulting from drilling.
25
References / Further Reading
ALLABY, M. (1977): A dictionary of the environment. Van Nostrand Reinhold Company, New
York.
BANNERT, M., BERGER, W., FISCHER, H., HORCHLER,
D., KEESE, K., LEHNIK-HABRINK, P., LÜCK, D.,
PRITZKOW, J. & WIN, T. (2001): Anforderungen
an Probennahme Probenvorbehandlung und
chemische
Untersuchungsmethoden
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