Turning contaminated mud into a road base material

Conceptual Product Design

Basis of Design

Process Systems Engineering

DelftChemTech – Faculty of Applied Sciences Delft University of Technology

Subject

Turning Contaminated Mud into a Road Base Material

Keywords

Contaminated mud, heavy metals, ground pollution, road foundation, customer values, purification, organic contaminants, road construction, sustainability.

Authors Student Number Telephone

Number J.A. Muller 9590426 +31 650216999 M.J. Moerman 9575441 +31 641500762 J.J.H. Pijpers 9675332 +31 641808687 S.W. Tummers 9845197 +31 641362629 Assignment issued: 26-01-2004 Report issued: 17-02-2004 Review date: 18-02-2004

Faculty of Applied Sciences

CPD 3303

Conceptual Product Design

Basis of Design

Turning Contaminated Mud into a Road Base Material

Authors:

J.A. Muller

M.J. Moerman

J.J.H. Pijpers

S.W. Tummers

Students at Delft University of Technology

Supervisors:

Prof. P.W. Appel

Chairman of the Chemical Engineering Department

DelftChemTech – Faculty of Applied Sciences

Delft University of Technology

P.L.J. Swinkels

Process Systems Engineering

DelftChemTech – Faculty of Applied Sciences

Delft University of Technology

Preface

This document is the basis of design (BOD) of the course Conceptual Product Design (CE3811). To the objectives of this course belong further development of teamwork and transforming the students creativity and gathered knowledge into an integrated product design.

In search of an appropriate assignment for the product design, one of the students came across an item on the ‘NOS-journaal’. In this item a contest was presented, called by the Department of Traffic and Water Management. This department has initiated a special program called ‘Wegen naar de Toekomst’ (Roads to the future). This contest ‘The Remediating Road’ is one of the initiatives of this program. The challenge of this contest is to present a design that combines two aspects. The large amounts of contaminated mud that will be available should be applied in a useful way and this should be done by using the empty space around and underneath roads in multiple ways. An underlying goal of this contest is to generate innovative ideas for purifying contaminated mud, in addition to conventional methods.

In view of the storage problem of the large amount of polluted mud that will be dredged in the future, this seemed like a very challenging assignment.

Summary

In the Netherlands, silting up of the waterways is an increasing problem. The waterways have to be maintained at a certain depth to keep navigation and water management at acceptable levels. For maintenance and sanitation, mud has to be dredged. This dredged mud is mostly contaminated and not all of it can be spread out into the environment, so it is deposited in depots. The depots are reaching their maximum capacity and more depots will have to be built if no other solution is devised for contaminated mud. A solution is to purify the mud and then use it as a construction material for roads. The goal of our project is to take heavy contaminated mud and purify it, so it can be used as construction material for roads. As the social acceptance for mud spreading and building extra depots decreases, the government plays an important role in this problem. Besides, the Dutch Government (including the Department of Traffic and Water Management, municipalities, and provinces) owns the largest part of the waterways. Processing contaminated mud will be more expensive than storing it in a depot. Under influence of interest groups, like dredging companies, the government is willing to subsidize processing of contaminated mud to prevent the building of new depots and to decrease the spread of mud over land or in surface waters. However, the processing costs should be as low as possible. As a rough guideline, the government is willing to spend 25 euro for the decontamination of 1 m3 of mud, whereas the deposition in depots costs only 10 euro per m3 mud. A global inventory of available decontamination techniques is also presented in this report. Various techniques are available, such as extraction, electro-osmotic,

microbial conversion, and several other possibilities. Which technique or combination of techniques is the most appropriate design, will be the main challenge during the remaining part of the Conceptual Product Design.

Table of Contents

2.3 GEOGRAPHICAL ORIENTATION OF POLLUTING FACTORIES ... 4

2.4 MUD PROBLEM ... 5

2.4.1 Some facts ... 5

2.4.2 Salt mud ... 5

2.4.3 Fresh mud ... 5

2.5 PROBLEMS WITH THE GOVERNMENT ... 6

2.5.1 Spreading of mud ... 6 2.5.1.1 Land ... 6 2.5.1.2 Sea ... 7 2.5.2 Financial impact ... 7 2.5.2.1 Salt mud ... 7 2.5.2.2 Fresh mud... 7 2.5.3 Results analysis ... 9

2.5.4 Responsible agencies in the dredging business ... 11

2.5.5 Overall ... 11

2.6 PROCESSING OF MUD ... 12

2.6.1 Mud becomes waterbottom ... 12

2.6.2 Mud becomes building material... 12

2.6.2.1 Sand Seperation ... 13

2.6.2.2 Dewatering, Maturing and Land Farming ... 13

2.6.2.3 Cold and Thermal Immobilization ... 13

2.6.3 Storage in Waterways, in Existing or Newly Dug “Holes” ... 13

2.6.4 Storage in Large Depots out of the Water, on Land ... 14

3 MARKET ANALYSIS ... 15

3.1 INDUSTRY ... 15

3.2 GOVERNMENT ... 15

3.3 OTHER INTEREST GROUPS ... 16

3.4 PRODUCT DEMANDS ... 18

3.4.1 Level 1: User Demands ... 19

3.4.2 Level 2: Functional Demands ... 19

3.4.3 Level 3: demands on the constructive behaviour and properties ... 21

3.4.4 Level 4: Behaviour of materials ... 22

3.4.5 Level 5: Nature of the material ... 23

3.4.6 Resolution of Building Materials ... 24

3.5 CUSTOMER VALUES ... 26

3.5.1 Summary of Customer Values ... 26

3.5.2 The government as customer ... 27

5 BASE MATERIAL ... 31

5.1 WHAT IS MUD? ... 31

5.1.1 Chemical composition ... 31

5.1.2 Physical properties related to cleaning of the soil ... 34

5.2 GOVERNMENTAL CLASSIFICATIONS ... 35

5.3 COMPARISON BETWEEN DEGREE OF CONTAMINATION OF SOIL AND USE OF SOIL AS BUILDING MATERIAL ... 36

6 PROCESS SPECIFICATIONS ... 37

6.1 QUANTIFICATION OF MUD PROBLEM ... 37

6.2 BLOCK SCHEME AND CALCULATIONS ... 38

6.3 OVERVIEW OF POSSIBLE PURIFICATION METHODS ... 39

6.3.1 Heavy metal removal techniques ... 39

6.3.2 Organic compounds techniques ... 41

7 CONCLUSION ... 42 APPENDIX TABLE OF CONTENTS ... APPENDIX – I–

1 Introduction

Each year, enormous amounts of mud have to be dredged from Dutch waterways in order to guarantee the accessibility for ships. These dredging activities are also important for water management purposes. A considerable amount of this mud is contaminated with heavy metals, mineral oil, Poly-Aromatic Hydrocarbons (PAH) or a cocktail of the aforementioned compounds. According to government regulations, this mud cannot be spread into sea or on land, as is the case with unpolluted mud. Contaminated mud has to be deposited in special depots. The problem is that the capacity of these depots is not enough to deposit all contaminated mud in the future. The construction of new depots is not favoured by the public opinion and by politics, since the storage of large amounts of polluted material is not considered as a

sustainable solution.

The contaminated mud could also be used as a founding material in certain civil engineering projects (roads, dikes, etc.) in case the pollutants have been removed from the mud. Besides removal of the contaminants, the physical structure of the mud should also be manipulated, so that it becomes usable as a founding material.

The purpose of this ‘Conceptual Product Design’ is to design a process, in which Class 3/4 mud1 is purified to such a level, that the material does not exceed the

Category 1 directives of the ‘Bouwstoffenbesluit’14. Class 3/4 mud is the most heavily polluted mud, as described by the Dutch government. The ‘Bouwstoffenbesluit’ is a document that describes the conditions that have to be fulfilled when the material is being used as founding or construction material. It is our goal to design a process, in which the pollutant concentrations are reduced as much as possible against lowest costs. As mentioned before, the contaminant concentrations may not exceed the Category 1 regulations.

In this design, only heavy metals (As, Cd, Cr, Ni, Hg, Pb and Zn), PAH’s, and mineral oils are taken into account in the decontamination steps. Removal of other contaminants like PCB (Poly Chloride Biphenyls) and OCP’s (Organo Chloride Pesticides) is not accounted for, in order to not complicate the design unnecessarily. In the transformation from polluted mud to construction material, two steps are important: removal of the contaminations and adjustment of the physical properties. The ultimate goal is to design a process in which requirements of both aspects are fulfilled against as low as possible costs.

2 Problem

Identification

This chapter will give a brief introduction of the origin of European ground pollution. The reasons for ground and water pollution will be indicated and a summary of harmful substances will be given. The different kinds of industries causing this pollution and their geographical orientation will serve as an indication for the spread of contaminants. After this orientation, the dredging will become the point of main interest. Dredging is important for mainly the water management of rivers and for the navigation. Here, the relation between the concept of dredging and the concept of pollution will become clear.

In Western Europe, more than 300.000 locations are identified as possible contaminated places. The most important reasons for ground pollution are:

 Inadequate or unauthorized dumping of waste materials  Chemical industry

 Metal industry

 Agriculture (pesticides etc.)

 River navigation (oils, exhaust gasses)  Military terrains (artillery exercises)  Mines

 Accidents

Of these reasons, the most significant pollution sources are the chemical industries and the heavy metal industries. Therefore, in the next sections, these sources will be discussed in more detail.

2.1 Chemical Industries

The worldwide production of the chemical industry since 1945 has increased

significantly and amounted for 400 million tons in 1995. Europe, as a region, is with 38% of the world turnover the biggest producer of chemical compounds in the world. The chemical industry is constantly developing new and improved products and processes, creating and serving completely new markets. These more effective substitute materials and products are used by other industries and enable them to be more efficient and productive.

Figure 1 Growth of EU chemical production, total industry, and GDP2

Figure 1 shows that over the years 1992-2002, the growth in volume of the EU chemical industry was 1.5 point above industry in general, and 1.4 percentage point above that of GDP (Gross Domestic Product).3 Appendix A shows the annual growth of the chemical industry against the total industry annual growth.

2.2 Chemical Substances

Since the beginning of the industrial revolution, chemical compounds are used intensively in various products. New chemical products are introduced to the market every year, besides the now over 100.000 chemical structures used in existing commercial chemical substances.4 A lot of these substances are disposed in the environment after their use as consumption goods, but little is known about the possible effects on humans, on the environment, and about the spread in the environment. In the seventies, people became first concerned about the possible effects of chemical compounds on the environment. Consumer goods, like foods, were the major source of exposure to harmful substances.

The heavy metals that are most harmful for public health are cadmium, mercury and lead. Heavy metals can be transported over national borders before ending up in soil, sea sediment, rivers, or in animals. In general, the concentrations have decreased since 1985. The decrease of cadmium concentrations for instance is due to rigorous

policies. The decrease of the other metals is probably due to better sewage purgation. Harmful effects on ecological systems as a result of heavy metals are usually found around melting furnaces, dumps of mine wastes and other forms of contaminated soil.

2 _{Figure is taken from the CEFIC website. Web: www.cefic.be}

3 _{CEFIC facts and figures, European Chemical Industry Council. Web:}

http://www.cefic.be/factsandfigures/level02/growthindustry_index.html

4 _{These chemical compounds were listed by the European Chemicals Bureau after an EU initiative in}

1981 in the European Inventory of Existing Commercial Substances (EINECS). Web: http://ecb.jrc.it/existing-chemicals/

Besides the heavy metals, also persistent organic pollutants (POP’s) form a reason for concern in the global environmental politics. Appendix B shows a list of some

persistent organic pollutants. Although the emissions of these POP’s have decreased, there do still exist a lot of regions contaminated with residues of formerly globally used POP’s. The concentrations of these contaminants can be measured quite easily, but the demonstration of the effects on human health remains difficult. This is because people are exposed to many substances at the same time and because the

contaminants can enter the body in different ways. These uncertainties are

strengthened by the fact that the effects can also be induced by chemicals, which exist naturally in the environment and by the fact that the time between exposure and the time at which the effects become visible can be quite long. However, it is clear that these kinds of pollution must be avoided.

2.3 Geographical Orientation of Polluting Factories

As can be seen in Figure 2, the heavy industries in Western Europe are mostly located near rivers. The pollutants that originate from these industries end up in rivers, hereby contaminating the water and the soil.

Legend

Figure 2 Geographical Orientations of Western European Industries5

The three most polluted rivers, which flow into The Netherlands, are the Maas, the Rijn, and the Schelde. Figure 2 indicates that around these rivers, a lot of heavy factories are located. These waterways have to be maintained, just as all other

waterways, because leaves, rests of plants, and agricultural land end up in rivers. Also erosion plays a significant role in the increase of the river sediment. These processes cause the waterways to become shallow and therefore the superfluous mud has to be removed. Dredging is essential for the preservation of the different functions of the

water systems. These functions are for instance navigation, water management, and recreation. But when this mud is contaminated due to the presence of the described factories, another problem arises. The next section will discuss this mud problem.

2.4 Mud Problem

In this chapter the mud problem will be addressed and possible solutions will be given. The dredged mud needs to be stored somewhere. This is a big problem, because most of the mud is contaminated and cannot be dumped everywhere. The heavily contaminated mud has to be dumped in special depots where it is stored until there is a method for cleaning the mud.

2.4.1 Some facts

The government acknowledges the problem and is willing to invest in the development of new techniques to clean mud. For the period until 2010 the government has 272 million euros in total available for the mud problem in the Netherlands.

For the period of 2002-2011 there will be 400 million cubic meter mud dredged from the rivers. About 50 percent will be fresh mud and the other half is salt mud. Most of the salt mud is not or slightly polluted so that 90% can be dumped into sea. Of the fresh mud, only 30% percent can be dumped into nature (land or surface water). The rest needs to be treated before it can be used. 50 percent of this fraction consists of mud from classes 0/1/26 (relatively clean mud).

2.4.2 Salt mud

There are two kinds of mud, one with a high salt concentration (salt mud) and one with a low salt concentration (fresh mud). Only in 5 provinces in the west of Holland salt mud is being dredged (Zeeland, Zuid-Holland, Noord-Holland, Friesland,

Groningen). The authorities responsible for these dredging activities are the

government (main waterways to seaport) and the local municipality (other waterways, including the harbours).

The salt mud that cannot be dumped into the sea needs to be dealt with. Zeeland and Noord-Holland have agreed to process a part of this contaminated mud. The part that cannot be processed is deposited in a depot. Zuid-Holland has the Slufter, with a capacity of 150 million m3, and in Zeeland the Koegorspolder is constructed, with a capacity of 7 million m3. The other provinces don’t have sufficient depot capacity. The northern provinces will even have a bigger problem when the new norms will be stated for salt mud7.

2.4.3 Fresh mud

Fresh mud is mud from fresh waterways, like rivers, channels, and harbours. Due to financial problems the fresh mud hasn’t been maintained that well. The rivers haven’t been dredged as much as needed, so there is about 70 million m3 overdue.

The fresh mud that is too contaminated for spreading on land has to be stored in depots or processed. Some of the mud is processed but the majority is deposited. The

6 _{See chapter 5.2 for details}

big problem is that there is not enough room to deposit it. And even if there is room in a depot not all categories6 of mud are allowed to be deposited in a depot. The depots have regulations on the type of mud that is allowed to be deposited. These regulations also state that mud can only come from a specific place. So if one province for

instance is not allowed to dump in a depot it has to deviate to another depot. Especially the northern provinces have the problem of a depot shortage.

2.5 Problems with the Government

The main problem with mud is that it is not clear to which legislation a processor of mud should hold. There are different laws that overlap each other regarding mud regulations. For instance, when filling a former sand mining location with mud, it is not clear whether this should be considered dumping, reuse of soil, or building. For every process there is a different law with different legislation. Other concerns are the change of the laws in depositing. In the future you have to pay more for depositing mud that can be cleaned. Also the norms for spreading mud will be sharpened. These legislation changes will bring about increasing costs.

2.5.1 Spreading of mud

In this paragraph the spreading of mud will be discussed, there are two possibilities for spreading the mud. Mud can be spread on land or in the sea.

2.5.1.1 Land

The government plays a big role in the spreading of mud on land. The government sets the bar on what is allowed to be spread. Within the legislation of today there is a shortage of locations to spread mud of classes 0/1/2 (light contaminations). The public begins to play a big role as well. The public acceptance of dumping mud on land for landfarming or maturing is decreasing. The public is frightened for crop and animal diseases, and uncertain whether mud induces unfertile ground. So this will play a role in revising the legislation. So from the public’s point of view, spreading on land is not acceptable. So for now the mud is deposited in depots. The government

acknowledged this problem and decided to treat the spreading of mud as reuse of soil and try to couple this to the rules of soil redevelopment. With this decision all fresh mud that is dumped, spread or processed will be treated equally when looking at legislation. The consequences and results of this decision for the amounts of mud that will be spread over land are not yet foreseeable. The amounts could decrease but that depends on the willingness of the mud processing industry.

2.5.1.2 Sea

The legislation is the biggest problem in the case of salt mud. In the near future the chemical compound ‘tributhyltin’ will be added to the legislation of the quality of this mud. The government ‘Rijkswaterstaat’ will implement a new toxicity test (Chemie-Toxiciteit-Toets CTT). This test will contain the maximum amount allowed values of the compounds in the mud. Tributyltin will be added to this list. Also a measure for the biological impact will be implemented. This change will result in the fact that the amount of salt mud, from the harbours, that is allowed to be dumped into sea will increase. For the northern part of the Netherlands this will result in a decrease of allowed mud depositing. This will have great consequences in the northern part of the Netherlands, because no big storage facilities have been built there to store the

contaminated mud. The total amount of salt mud will not change, only the origin of the mud.

2.5.2 Financial impact

In January 2002, the Dutch government decided to make 41 million euros available for the stimulation of mud processing. This is a one-time sum of money to stimulate the research and effort to reuse contaminated the mud. Further legislation on purified mud will change. As of 2002, mud with a sand percentage above 60% will be

considered cleanable. If this mud is deposited, it will cost more then non-cleanable mud. Between 2004-2006 this will be sharpened and mud that can be cleaned after maturing or land farming will also be considered as cleanable. This will have a great impact on the amounts of dumping.

2.5.2.1 Salt mud

For salt mud processing, dredging and dumping a total of 580 million euros is needed, the government has put aside 318 million euros. So there is a shortage of 260 million euros for the next 7 years.

Solutions for the mud that cannot be spread out are:  Filling of too deep harbours/waterways  Depots

The mud cannot be dumped in depots, because there is not enough storage capacity. Another problem with depots, due to legislation, is that there will be a geographic shift of non-dumpable salt mud.

2.5.2.2 Fresh mud

The problem with fresh mud is much more urgent than salt mud. The past years not all the mud that had to be dredged was removed, so the problem will increase within years. For a solution the government has developed scenarios. The scenarios are divided into two focuses. One focus is on the time wherein the mud is removed and the other is on the policy on removing mud. With these focuses three policies have been made and four time plans.

1. Continuing present policy

In this policy nothing changes about how the government handles mud. The legislation doesn’t change and the rules on whether it is clean or not, are not changed.

2. More destinations

the legislation has to be revised. The main idea is that the mud is reused with the most cost efficient method. The tools that will be used are that the

legislation for construction material will include a special part for mud related materials, so that the mud that has been cleaned can be used in construction. And the use of open depots will be encouraged by increasing it’s acceptance for mud of category 36. As a last tool, the mud will be dredged only in places where it is absolutely necessary.

3. Advanced processing

In this policy the majority of the mud will be processed. The processes are cold immobilization, thermic immobilization, maturing and landfarming. The depots will only be used to store the residues of the previous mentioned processes.

The problem is divided in four time plans

A. Continuing present budget

In this plan the total amount of money available for the removing of mud will be the same as now. This comes down to 2,15 billion euros in total for the period until 2010. So this will lead to a silt up of the rivers and waterways, as not all the mud can be dredged for keeping the waterways accessible.

B. Stand-still

In this plan only mud is being dredged that is ‘new’. This means that no work will be done to resolve overdue dredging or recreation dredging. This plan offers the least service, it is just enough to overcome that new overdue mud is gathered.

C. Everything in 10 years

In this plan all of the mud that has to be removed (192 million m3), due to maintenance of waterways and new mud, will be removed and processed, in the period from 2002 till 2011. In this plan no dredging is considered to remove overdue dredging.

D. Everything in 40 years

This plan stated that in 40 years all of the mud will be dredged including overdue dredging (479 million m3_{). This plan takes everything into account,}

also the mud that has to be removed in the years past 2011. This plan can be chosen if plan C can’t be reached. It is the idea that the amount to be dredged is evenly spread over the years.

2.5.3 Results analysis

To choose a scenario one should look at the amount of mud that will be dredged, the costs of dredging, what the mud’s destination is and which responsible agencies will have to invest the most effort and money. In Figure 3, the amount of fresh mud in million m3 is plotted for the different scenarios. It can be seen that in plan A the least amount of mud has to be dredged. In Figure 4 the costs for the dredging is plotted. Also in this figure you can see that plan A is least expensive. Plan A however, is not a solution; it is more a method to keep a float. This plan is not very flexible with peak amounts of mud. Plan C is very ambitious and will costs a lot of extra investment for the next 10 years. Plan D looks to be the best solution considering the amounts that have to be dredged and costs. For a sustainable solution of the mud problem it is necessary to take into account all the mud, including the overdue mud. The only plan that considers this is plan D. Therefore; we will work out this plan. The complete workout and discussing can be found in Appendix C.

Figure 3 Dredged mud in period 2002-2011 (million m3) for each scenario8

2.5.4 Responsible agencies in the dredging business

Several parties play a role in the mud business. In Figure 5 and Figure 6, the amounts and costs are plotted per party. It is understandable that the Department of Traffic and Water Management and the District Water Board have to invest the most money.

Figure 5 amount of mud in million m3 that has to be dredged per department9

Figure 6 costs in billion euros per department9

2.5.5 Overall

All these scenarios (D 1,2,3) will lead to the result that the mud will be processed. However, they do have different impacts on the environment and on the agencies involved in the mud business. The effect on the environment hygiene and on geographic impact, for the different responsible agencies, is shown in Table 1.

Table 1 environment hygiene and geographic effects (+ positive, -negative)10 Current Policy (D1) More Destinations (D2) Advanced Processing (D3)

Produced Product (tons) 0 + ++

Waste Material (m3) 0 + ++

Emission toxic materials on destination 0 - +

Used energy (MJ) 0 + --

Remaining Emission in Water system 0 - 0

(temporary) Storage 0 - +

From Figure 15 in Appendix C the conclusion can be drawn that the cheapest scenario is D2. The drawback is that this scenario has the most impact on the environmental hygiene and geographic effects (Table 1), because more mud is allowed to be spread out in nature.

For the CPD-project we will use scenario D2 as reference point, this scenario is the most sustainable and realistic from our point of view.

2.6 Processing of mud

The Dutch government has acknowledged the mud problem and plans to invest in active management of the water soil. This means that the mud will be utilized instead of dumped. The government has 4 options for processing mud.

1. Mud becomes waterbottom

2. Mud becomes building material (process step required) 3. Storage in waterways, in existing or newly dug “holes” 4. Storage in large depots out of the water, on land

2.6.1 Mud becomes waterbottom

Not all waterways silt up. In some waterways it is even necessary to raise the bottom, or to reclaim land, or form islands in a lake. This has been done in the ‘Nieuwe IJssel monding’, here mud created an artificial wet nature. Another possibility for this mud is that it can be put on the banks of rivers to create nature friendly banks, or use it for fertile soil for woods.

2.6.2 Mud becomes building material

To utilize mud in building material is a promising way to solve the mud problem. The mud then needs to obtain the physical properties that are required for building. These properties can be categorized in 5 clusters:

 Pressure absorbing (spreading) layers  (non) Constructive elevation

 (non) Constructive supplementation layers  Covering layers

 isolation layers

Figure 7, usage mud in road or dike rising

When mud is used as building material usually a process needs to take place to influence the particle size, the water content and the constructive abilities. With the choice of process the environment issues as stated in ‘het Bouwstoffenbesluit’14 need to be taken in consideration. The techniques available will be mentioned below.

2.6.2.1 Sand Seperation

With this technique, the relative clean sand fraction is separated from the ‘dirty’ sludge fraction. The contaminations in mud are concentrated in the sludge part; this is due to chemical interactions with the sludge. The separation can be done with use of gravity in a settler. The sludge fraction is lighter then the sand and in this way it will be separated. This can also be achieved with use of a hydrocycloon, this is a big centrifuge which creates a bigger gravitational field, than in a settler, by which the sludge and sand will separate. The clean sand can then be used in the different projects mentioned above. The dirty sludge needs to be stored in depots.

2.6.2.2 Dewatering, Maturing and Land Farming

These techniques are usually performed in small projects. When mud is dewatered the mud becomes concentrated. With maturing, the physical properties of the mud

change. During this process the mud will dry and oxidize to a compacter more air permeable material. The created product can be used for (constructive) elevation. Land farming is a similar process as maturing, with the exception that land farming is more intense, the mud has to be turned over periodically.

2.6.2.3 Cold and Thermal Immobilization

When the mud is immobilized by adding some kind of binding material (cement) it is called cold immobilization. This is done to improve the strength of the mud so it can be used as a construction material. When the mud is heated (> 400 C) the organic compounds burnout and sintering or melting immobilizes the inorganic compounds. This process is called thermal immobilization. The product is then artificial

granules/basalt.

2.6.3 Storage in Waterways, in Existing or Newly Dug “Holes”

In existing lakes or rivers, holes have been dug for sand mining. These holes, called wet depots, can be filled with mud, to raise the bottom. This elevation stimulates the ecosystem. At great depth the light intensity decreases rapidly and plant life is scarce. So adding the mud will increase the environmental diversity (Figure 8).

Figure 8, nature value enrichment through mud

2.6.4 Storage in Large Depots out of the Water, on Land

When it is not possible to store the mud in wet depots, artificial holes, dry depots, have been created to store the mud. These depots are most often a final stage for the mud. So it is a permanent storage, until science has found a economical way of disposing it. These depots are mostly used for the mud that is of such a high contamination that it has to be isolated from the environment.

3 Market

Analysis

In this chapter, it will be briefly repeated from which sources the contamination in mud originate. Furthermore, the role of the Dutch government and the role of other interest groups are discussed.

3.1 Industry

A major source of the pollution of Dutch water soils is the chemical and steel industry in neighboring countries. These industries are situated in Germany, Belgium and in the Northeast of France. Although their emission of pollution into the surface water has decreased considerably (thanks to more strict environmental regulations), the above industrial complexes are still a cause of contamination of the soil and water of rivers. In Holland, the port of Rotterdam is a source of pollution for the local water soils. Other sources of pollution originate from agriculture and domestic waste. The last major contributor to the water soil pollution is the shipping sector, often by releasing fuel and lubricants into the waterways. This sector is highly dependent on dredging, since they depend on the accessibility of waterways (rivers, channels, ports, etc). Emission regulations exist on national level. However, there are several

agreements between countries about pollution, river height, etc. between countries. For Holland, agreements exist for the Rijn, Maas, Schelde and Eems river. It is the responsibility of the companies to monitor their emissions. These reports are randomly checked by provincial officials.

3.2 Government

Clearly, various governmental organizations are involved in the mud problems. Below, the role of the relevant organs of the Dutch government is discussed.

One of the main interested parties of our product would be the “Ministerie of Verkeer en Waterstaat” (Department of Traffic and Water Management). This department is responsible for the accessibility of the national channels, rivers and other waterways. For this purpose, dredging operations are performed by the department, as a result of which huge quantities of contaminated mud are obtained. Furthermore, the sanitation of other sources of contaminated mud is also the responsibility of the ministry. Municipalities are responsible for local dredging activities and sanitations. These dredging activities are financed by special pollution taxes, which are imposed upon all citizens.

Most of the dredged mud is contaminated with heavy metals and organic pollutants. However, the contamination of 90% of the dredged mud is not that severe so that it may be spread without purification steps. Salt mud is spread in sea and fresh mud is spread on land, in order to raise the ground level of the Dutch polders. The main problem is the heavy polluted mud, which is denominated as class 3/4 mud by the Dutch Government. It is expected that 151 million m3 of non-disposable mud will be dredged in the period 2002-2011, of which 87 million m3 is class 3/4 mud11. The remaining non-disposable mud (64 million m3) is fresh mud, which is only slightly contaminated. However, when this mud is dredged from a waterway next to urban areas, industry, greenhouses, etc., there is no space to deposit the mud on that

11 _{AKWA, rapportnummer 01.014 Base Document Decennial Scenario Water Soils, Utrecht December}

location. This mud must be removed from the site in order to spread or purify it elsewhere.

This class 3/4 mud can either be decontaminated or be stored in special depots, which are administered by the provinces. Since the depot capacity is not sufficient to store all the mud and there exist societal objections against a continuous increase of this capacity, the problem could be partly solved by decontamination of the mud. A complicating factor is that government regulations do not allow that mud from province A is deposited in province B.

Since it is our goal to use the decontaminated mud for civil engineering purposes, the regulations for construction materials (‘Bouwstoffenbesluit’) have to be fulfilled. These regulations are made by the Department of VROM (Spatial Planning, Housing and Environment). For instance, the immission values for heavy metals in soils may not exceed a specific level, to prevent the ground water to become polluted.

At the moment, the European Union has not formulated any laws that are related to the deposition of mud, the composition of construction materials or to other related fields. These matters are regulated on a national level. However, several EU-guidelines already exist and it is expected that European laws will be defined in the future.

3.3 Other Interest Groups

The dredging companies are organized in the VBKO, an interest group for dredging, coastal and shore projects. Recently, the VBKO has complained about the

investments of the government in dredging projects. The planned investments should not be enough to realize long-term dredge policy. This lack of investments could affect the quality of the seaways in the Netherlands. The VBKO is also not very pleased by the high expenditures in mud decontamination since this lowers the available money for dredging activities. Decontamination projects are thought to be beneficial only when the total budget for dredging is increased. The organization advises to adapt the regulations for building materials, so that slightly contaminated mud can be used more easily for i.e. infrastructural projects12.

The development of technology for decontamination of mud is present within

technical design agencies and (technical) universities. The dredging companies posses a lot of practical knowledge.

After decontamination of the mud, it would be ideal to use it in infrastructural or construction works. Therefore, contractors must be willing to use the decontaminated mud. They will only do this if the physical structure of the mud is suitable for

construction purposes, if the ‘Bouwstoffenbesluit’ is not violated and if the costs of the material are comparable with regular sand. Feedback of contractors on the desired physical specifications is therefore an important matter.

Environmental action groups are also interested in the contaminated mud problem. Organizations like ‘Milieudefensie’ have brought the problems of the Ketelmeer

depot into the publicity, where 7500 kg polluted material leaked out of the depot. They question the safety of the depot and are not pleased with the presence of

recreation water facilities near the polluted mud depots. From their point of view, it is preferable to immobilize the contaminants in the mud and use it in infrastructural projects.

Finally the public opinion is an important aspect of the mud problem. This opinion is most of the times a little ambiguous. On the one hand, people don’t like it when there is a depot with contaminated mud in their backyard, but on the other hand the need for dredging projects is very clear. Decontamination of the mud is a popular option, although the costs may not become too high. The public opinion has a large influence on the policy of the government. Therefore, it is possible that various parties will try to give more publicity to the mud problem in order to influence the public opinion.

3.4 Product Demands

Before the mud can be used as building material, it has to satisfy some standards. Our primary goal is to make the mud suitable for a road foundation. The term functional demands will be used and it is derived from the fact that the foundation needs to satisfy the demands; i.e. it needs to have a certain capacity. When functional demands are made on road foundations, the type of material used is irrelevant. The most

important function of a foundation is the spreading of the load induced by the mass of the upper layers and induced by the traffic, in such a way that unacceptable

deformations are avoided. This capacity is directly coupled to the function of the foundation in a road construction.

The demands can be visualized by a pyramid. This pyramid indicates the possible relations between the demands on different levels.

Figure 9 Political pyramid of demands

The Dutch public (or the managers of a company) map out a policy for the road infrastructure, as can be seen in Figure 9. Infrastructural designs are made for the needed capacity, including environmental reports. This design must be worked out in a road structural design, where the dimensions of the hardening construction relate to the traffic load. This quite abstract political pyramid can be translated to a technical pyramid, where road structural characteristics are described. In a technical pyramid, measurable demands are indicated. In this pyramid, the next five levels are

distinguished.

 User demands;

 functional or performance demands;  constructive behaviour demands;  material behaviour demands;  nature of the material.

The technical pyramid of demands is indicated in Figure 10.

13 _{CROW, Rapport 02-08: Functionele eigenschappen wegfunderingsmaterialen, gebonden en}

Figure 10 Technical pyramid of demands

The demands on for instance level 1 require demands on level 2, etc. The description of each level will be indicated in the next sections.

3.4.1 Level 1: User Demands

The users can be broadly interpreted. They differ from actual road users (motorists, etc.), from financiers and contractors to people and agencies in the vicinity. The main demands and preferences of these users are related to:

 Capacity and availability of the road  Nuisance for the vicinity

 Safety of the road users  Comfort of the road users  Scenery insertion

 Base materials

 Environmental policy  Labour circumstances  Economics

3.4.2 Level 2: Functional Demands

The above described user demands are mostly quite vague. They have to be translated into (quantifiable) material independent demands. These functional demands have to be recorded in a way that for instance the contractor can demonstrate that he has fulfilled these demands. These functional demands relate in general to the following:

1. Feasibility

a. Technical Feasibility; the available techniques and materials must be sufficient in order to complete the road before the appointed time. b. Safety and Health; the regulations with respect to acceptable safety and

health risks must be satisfied during the construction, maintenance, reconstruction, and demolition of the road.

c. Nuisance; the nuisance during the construction, maintenance,

reconstruction, and demolition of the road must be within acceptable boundaries for the neighbourhood and the local residents.

d. Passableness; the road must be accessible during all steps of the

construction process under all environmental circumstances (like frost, thaw, precipitation, high groundwater level).

2. Safety

a. Flatness; the flatness must satisfy the stated demands. b. Stiffness; the stiffness must satisfy the stated demands.

c. Geometry; the demands of the geometry are about horizontal and vertical alignment, design of intersections, etcetera.

d. Surface properties of the road surface; besides flatness and stiffness, properties like light reflection, ‘splash-and-spray’ properties, and so on must also be considered.

3. Capacity/Availability; future developments and current road usage must be considered here.

4. Water Management; Both ground and surface water management cannot be inadmissibly influenced during the implementation process and the entire lifespan of the road.

5. Re-use

a. The possibility of the use of secondary base materials should be present.

b. The used materials should be removable after use. c. The used materials should be recyclable.

6. Environment; legislation like the ‘bouwstoffenbesluit’ indicate the environmental demands with respect to the construction of roads. The

exploitation of the materials, the construction of the road, as well as the impact on the landscape during the construction and the demolition phase are bound to regulations with respect to for instance immission values and MAC’s of contaminants. These regulations are very important in this design.

7. Economic feasibility; the costs for the construction, maintenance, and for the demolition and re-use of the road must be acceptable for the involved parties. These functional demands with respect to the road can be translated into demands concerning the foundation. In Appendix D, a table is shown where this translation is given schematically.

3.4.3 Level 3: demands on the constructive behaviour and

properties

The in section 3.4.2 and Appendix D described demands result in demands for the construction when it is loaded. The constructive behaviour is determined by measurable properties.

Table 2 relation between constructive behaviour and constructive properties Constructional Property Flexural Stiffness ● 1:1 - - Load Spreading Capacity ● 1:1 - - Elastic Deformation 1:1 ● - - Permanent Deformation 1:1 ● ● ● Crack Sensitivity ● 1:1 - - Pressure Resistance ● 1:1 - ● Moisture Resistance ● ● ● ● Frost Resistance ● ● ● 1:1

Allowance for Settling 1:1 ● ● -

Water Permeability ● ● 1:1 ●

Capillary Action ● ● 1:1 ●

Sensitivity to Frost ● ● ● 1:1

Constructional Behaviour

Deformation Strength Hydrologic Frost

1:1 = direct relation; ● = indirect relation; - = no relation.

The design criteria of a road are mostly derived from the material of the upper layer of the road. They do not give insight in the demands on the foundation. Therefore, it is necessary to define the design criteria for the foundation, which are indicated in Table 3.

Table 3 Survey of the importance of the various demands for a foundation

Demands Asphalt Concrete Elements

UF,

SF BF UF, SF BF UF, SF Bf

Bit. Hyd. Bit. Hyd, Bit. Hyd.

Fatigue Strength (●) ● ● - - - - ● ● Load Spreading Capacity ● ● ● ● ● ● - - - Permanent Deformation (●) ● - - - - ● ● - Crack Behaviour ● - ● - - ● - - - Drain Behaviour ● - - ● - - ● ● ● Integrity ● ● ● ● ● ● ● ● ●

UF = unbound foundation ● = Design criterion SF = self-binding foundation - = Not a design criterion BF = bound foundation Bit. = Bituminous bound foundation

Hyd. = Hydraulic bound foundation

3.4.4 Level 4: Behaviour of materials

The basic properties of materials can be categorized in the following groups:  Mechanical Properties - Elasticity modulus - Resilient modulus - Compression strength - Tensile Strength - Shearing strength - Creep - Cohesion

- Angle of internal friction - Grain strength  Volume Properties - Hygrical Elasticity - Thermal Elasticity - Chemical Elasticity  Durability Properties - Fatigue resistance

- Sensitivity against erosion - Sensitivity against frost - Sensitivity against liquids - Durability against frost - Durability against liquids - Chemical durability

 Contraction/use - Compressibility - Willingness of compaction - Sensitivity to segregation  Water management - Capillary action - Water permeability  Environment - Soil leaching

Appendix E shows the influence of the material properties on the constructive properties for bound foundations. Appendix F shows the same, but then for unbound foundations.

3.4.5 Level 5: Nature of the material

The demands with respect to the nature of the material concern the quality of the material. Here, chemical-mineralogical, physical, and morphological aspects are considered. Appendix G shows the basic influence of the material behaviour on the nature of the material and Appendix H shows the influence of the nature of the material on the basic material behaviour.

3.4.6 Resolution of Building Materials

The intention of the Resolution of Building Materials (‘Bouwstoffenbesluit’ in Dutch) is to prevent rocky materials from polluting the water. The rules are intended to limit the possible immision of pollutants from the building materials into the earth or the groundwater to a maximum allowable level. Also the Bouwstoffenbesluit must stimulate the use of secondary building materials. This will decrease the pressure on the environment and the use of primary building materials.

Primary building materials are materials that can be used with only a little extra processing after it has been gained from nature. Secondary materials originate from byproducts of production or purification processes.

The Bouwstoffenbesluit uses a classification, based on the question whether it is allowed to use the soil as building material. It divides the soil in four categories: 1. Clean soil:

- Soil that exceeds none of the composition values for inorganic and organic compounds, as indicated in the ‘Bouwstoffenbesluit, Bijlage1’14.

2. Category 1-building material:

- A building material that exceeds none of the composition values for organic compounds and also none of the composition values for inorganic compounds, as indicated in the ‘Bouwstoffenbesluit, Bijlage 2’14.

- It can be used in such a way that, in case there are no isolation measures taken, none of the immision values for inorganic compounds, as indicated in the literature14 will be exceeded.

3. Category 2-building material:

- A building material that exceeds none of the composition values for organic compounds and also none of the composition values for inorganic compounds, as indicated in the ‘Bouwstoffenbesluit, Bijlage 2’14.

- It can be used in such a way that, only in case there isolation measures are taken, none of the immision values for inorganic compounds, as indicated in the literature14 will be exceeded.

4. Special materials, like AVI bottom ashes.

Clean soil can be used without restrictions. For category 1-building material a

distinction is made between soil and construction material. When category 1-building material is used as soil, a minimum amount of 50 m3 should be applied. When it is used as a construction material, there are no restrictions. Use of category 1-soil must be made mention of.

Use of category 2-building material should always be made mention of. For this type of building material applies a minimum amount of 10,000 tons continuous. In road foundations a minimum amount of 1,000 tons continuous is allowed to be processed.

14 _{The Bouwstoffenbesluit is a resolution formulated by the Dutch Government on 23 November 1995,}

in which the regulations concerning the use of building materials up or underneath the soil or in the surface water are described. Web: http:// www.vrom.nl/bouwstoffenbesluit

Recently the Dutch Government has given some exemptions with respect to some immision values and the composition value of mineral oil. These new regulations can be found in the‘Temporary exemption agreement for soil and mud’15. The immision values of some compounds have appeared to be too strict. These compounds can appear in the soil by nature and therefore the immision values were exceeded even for clean soil. There has been granted exemption for the immision values of bromide, fluoride and sulphate. For antimony, molybdenum, selenium and vanadium different new standards have been determined. Also the composition value for mineral oil appeared to be too strict. Most part of the mineral oil in mud is heavy oil, while the light oil fractions are responsible for the ecotoxicity. Therefore the limiting value for mineral oils has been increased.

15 _{The temporary exemption agreement for soil and mud, 9 September 2003, Dutch Department of}

3.5 Customer Values

In the field of Chemical Product Design, it is important to consider consumer values. These values represent trends that exist in society with respect to intrinsic aspects of a product that people value. Below, an overview is given of the values that are in general important. Although our product – decontaminated mud- is not a consumer product, it is useful to define how the clean mud satisfies the needs of the involved parties. It must be noted that our product is initially meant for the Dutch market. For instance, a value like ‘Sustainable Entrepreneurship’ is appropriate for the Dutch market, but not for other parts of the world. Finally, it is argued that the Dutch government is the main customer of our product. It is briefly discussed under what conditions governmental officials take decisions and how our product should be designed to fulfil the governments desires.

3.5.1 Summary of Customer Values

Convenience

For the Dutch economy, it is important that the many waterways are well accessible. Therefore, dredging activities are needed to maintain the quality of the waterways. The shipping sector and industries that rely on supply of raw materials by ship are highly dependent on the accessibility of the waterways. Since our product adds to a structured solving of the dredging problems, it will lead to more convenience for the (commercial) users of the waterways. The same argument is valid for recreative users of Dutch waterways: they also benefit from the good conditions of rivers and lakes.

Health

The presence of large quantities of contaminated mud in waterways or depots is a potential risk for the public health. First, pollutants can diffuse from the water soil into the groundwater, where it affects agriculture, drinking water, and nature.

Furthermore, humans can be exposed to pollutants when recreating in polluted areas or when eating contaminated fish. Since it is our goal to purify heavily contaminated mud, our product will decrease these public health risks. Therefore, our product is advantageous for the Dutch population in general, which is represented in various government organs.

Personalized

This customer value is applicable to consumer goods and not at all for decontaminated mud.

Instant availability

Our product is decontaminated mud that can be used as a building material in infrastructural and building projects. In these projects, it is extremely important that contractors can rely on the supply of building materials. Delays in construction

processes are extremely expensive and therefore, contractors will search for a building material that can be supplied instantly.

As can be concluded from the above, instant or constant availability is an important feature in the decontamination process. The chance that the production process breaks down must be reduced as much as possible.

Quality Time

Quality time is a customer value that is typical for consumer products and is not applicable to decontaminated mud.

Sustainable Entrepreneurship

Our product certainly answers to the increased appeal for sustainable entrepreneurship in The Netherlands. It is irresponsible to leave the heavily contaminated mud in the water soil, since it will cause health risks for the Dutch population (besides more pragmatic arguments like the accessibility of the waterways). Furthermore, the aquatic environment can be seriously disturbed by accumulation of pollution in the food chain. Depositing the polluted mud in depots is also not a sustainable option, since it will pass the problem to future generations. On the other hand, purification of

contaminated mud corresponds to a responsible attitude towards society and environment.

3.5.2 The government as customer

From the above, it becomes obvious that many parties benefit from our product. There is not one specific group of customers, like for instance in the consumer products industry. This implies that there is not one group that pays for the product. Since many groups in society benefit from our product and it is the responsibility of the government to preserve the quality of the waterways, it seems reasonable to define the government as the main ‘customer’ of our product. It is the government that decides how contaminated mud is dealt with. Hence, it is a task of the government to

stimulate the development of purifying techniques, for instance by providing

subsidies. Hereby, the government can be seen as a customer, paying for the product benefits.

The fact that the government is the ‘customer’ in our business implies that our product must be marketed in a very specific way. Government decisions are not taken in the same way as regular consumers make their choices and, therefore, the following aspects have to be considered.

It is obvious that the government has to deal with several problems and that its financial budget is limited. Each euro that is spent on the decontamination of mud cannot be spent on i.e. social welfare. Therefore, responsible government officials will always make a consideration between the benefits and the costs, when taking measures. The logical conclusion of this reasoning is that the decontamination may not be excessively expensive. Although the government may appreciate initiatives for high-tech solutions to decontaminate mud, suchlike techniques will not be applied if they are unreasonably expensive compared to storage in depots (the conventional solution for the mud contamination problem). Thus, the demand of our customer is to reduce contaminations as much as possible at low costs. Furthermore, it would be appreciated if the solution for the mud problem could be combined somehow with other governmental responsibilities. An example is the use of decontaminated mud as a construction material of roads.

Another characteristic is the slowness with which decisions are taken by the government. Consensus between societal groups is generally aimed for and bureaucratic institutions try to achieve this in an often time consuming process. Decisions that are drastic and riskful will take more time than less complicated

measures. The government prefers simple but effective solutions that can be ‘sold’ to the public in an easy way.

Another interesting aspect is that governmental decisions are often influenced by lobbies of various groups within society. These groups range from environmental groups to industrial companies. Besides influencing the government directly, they also try influence the public opinion. Obviously, the public opinion is a powerful tool in a democracy to influence political decisions.

Concluding, the production of decontaminated mud for construction material purposes must be designed in such a way that the government is willing to implement this technique. This implies low cost, efficient processes that can be easily explained to all societal groups that are involved in the mud problem.

4 Economic

Considerations

At the moment, heavily contaminated mud is stored in a depot after dredging. The following factors contribute to the overall costs of the dredging activities16: Dredging:

 The costs of dredging vary per location, but are approximately 5 euro per m3

ex-situ mud17. Transport:

 0.11 euro/km (dredged from navigable location, this mud can be transported with ships)

 1.45 euro/km (dredged from non-navigable location, this mud has to be transported with trucks)

Offloading:

 Approximately 2 euro/m3_{, these costs are made by huge power demands of}

pumps. Storage in depot:

 10 euro/ex-situ m3 _{(governmental depot)}

 20-25 euro/ex-situ m3 _{(commercial depot)}

According to Leonard Osté (RIZA)16, the government would be willing to spend 25 euro/ex-situ m3 for processing the contaminated mud. However, this would be a directive from national politics. The budget for all dredging activities is divided by the national government between all responsible parties (provinces, municipalities, etc.). Each party decides itself how they will spend their budget. Therefore, it is imaginable that a responsible party chooses to dredge 10 km of a channel and deposits the mud in a depot, instead of dredging only 5 km and processing the mud. This could be

overcome by other regulations of the government, in which responsible parties should indicate how they want to handle their contaminated mud. Hereby, these parties are not discouraged to process their mud, because it does not proceed anymore at the expense of dredging itself.

An advantage of processing mud is that it can be sold as a construction material. When sand is used as a founding material under i.e. highways, contractors pay ± 10 euro/m3 sand18. In-situ mud consists of 0.846 ton dry material/m3. Hereby, it can be calculated that 1 m3 ex-situ mud contains 0.846/1.2 = 0.705 ton dry material. Only half of this dry material consists of a sand fraction and can therefore be used for construction purposes. The density of sand for construction purposes is roughly 1.8 ton/m3. As a rough approximation, we assume that each cubic meter of ex-situ mud can be processed into (0.705/2)/1.8 = 0.196 m3 sand. Hence, each m3 of ex-situ mud can be processed into construction material, which can be sold for roughly 2 euro ( 0.196*10). A comparison between depositing and processing the mud is given in Table 4.

16 _{Appendix J, Interview with Leonard Osté (RIZA)}

17 _{During dredging activities, mud at the bottom of a waterway (in-situ mud) is gathered by a floating}

dredge. During this process, in-situ mud is mixed with water. This results in mud with a higher water content, which is called ex-situ mud. This mud has a volume that is 1.2 times as large as the original volume

Table 4 Economic comparison between processing and deposition of contaminated mud

Indication of costs: processing mud (euro/m3) Indication of costs: depositing mud (euro/m3) Dredging 5 Dredging 5 Transport 3 Transport 3 Offloading 2 Offloading 2 Decontamination 25 Deposition in governmental depot 10 Sale of sand -2

Total 33 Total 20 Concluding, the costs for purifying contaminated mud must be in the order of magnitude of 25 euro/m3 mud. As can be seen from Table 4, the government has to spend an extra 13 euro per m3 of dredged mud, if they choose to stimulate the

purification of mud. The processed mud can be sold as a construction material, but the accompanying revenues are rather low in comparison with the overall costs.

5 Base

material

In this section a description will be given of the composition of the mud that will be used as base material. A discussion will be outlined on the different types of particles in mud, in particular their differences in particle size and in chemical composition. Also the main mechanisms that influence the purification of the mud will be

discussed. Next, an overview will be given of the classification of contaminated soil based on the degree of pollution and a comparison will be made between this classification and the demands according to the Bouwstoffenbesluit.

5.1 What is mud?

5.1.1 Chemical composition

Mud contains sediment material that is obtained from erosion processes. The soil material is deposited in various ways, for example erosion of embankments, air particulates settling onto water bodies, and clay and silt loads transported in streams and rivers.

Water acts as a carrier or as a medium where all of the soil particulates settle to form the sediment bed.

Because of the large amount of different types of elements in soil, there are various ways to classify soil. One way is a classification based on particle size and is given in Table 5.

Table 5 Classification of soil based on particle size20

Particles min. size (mm) max. size (mm)

Gravels 2.000

Sands 0.063 2.000

Silts 0.002 0.063

Clay 0.002

The ratios between the amounts of these classes for various types of soil are given in nd a fraction of lutum of 10 %.

19 _{Raymond N. Yong, Geoenvironmental Engineering, CRC Press, Boca Raton, 2001, Chapter 2.}

Table 6. In this table, information is given about the percentage of sands and gravels (>63 μm) and the percentage silts and clay-sized particles (<63 μm). The clay-sized particles are also called lutum. So moderate sandy soil has a fraction of sand and gravels of 47 %, a fraction of silt-sized particles of 37 % and a fraction of lutum of 10 %.

Table 6 Properties of different types of dredged materials21

Type of dredged material

Parameter Unity Sandy Moderate

sandy Clayish Peaty

Dry matter content (in situ) % m/m 68 56 41 35

Tdm / m3 _{in-situ 1.170 0.846 0.532 0.430}

In-situ density Ton / m3 _{in-situ 1.72 1.51 1.30 1.23}

Content fines Tdm / m3 _{in-situ 0.234 0.423 0.426 0.387}

Sand content based on mineral parts % > 63 m 80 50 20 10

Sand content based on dry matter % m/m >63 m 78 47 18 7

Min. sludge content based on dry matter % m/m < 63 m 20 47 70 63

Organic substance content based on dry matter % m/m 2 6 12 30

Lutum content based on dry matter % m/m 3 10 22 25

Another way of classifying mud is by dividing mud in different types of phases: 1. Gaseous phase; air and other gases

2. Fluid phase; water with dissolved contaminants 3. Soil

a. Soil organics:

i. Humic substances ii. Soil polysaccharides b. Inorganic crystalline:

i. Primary and secondary minerals; clay minerals

ii. Oxides and hydrous oxides of iron, aluminum and silicon iii. Carbonates, sulphates, phosphates and sulphides

c. Inorganic non-crystalline: Hydrous oxides of iron, aluminum and silicon

For the description of the transport mechanisms in soil, both the fluid phase and the soil are important. What is meant by the gaseous and fluid phase is rather

straightforward, however, the composition of the soil fractions needs some further explanation.

Soil organics originate from vegetation and animal sources. It is usually categorized in humic and non-humic material. Humic substances are defined as organics resulting from the chemical and biological degradation of non-humic materials. Non-humic compounds are organics that remain intact or are only partially degraded and contain polysaccharides of microbial origin.

Clay minerals exist in two forms, primary and secondary minerals. Primary minerals are those materials that are derived in unaltered form from their parent rocks through physical weathering processes, and cover major portions of sand and silt fractions in soils. The largest amounts of clays are secondary minerals, which are derived as altered products of physical, chemical, and/or biological weathering processes. Primarily, the clay minerals consist of silicate layers. All kinds of different crystal structures exist. They differ in the proportion in which tetrahedral and octahedral sheets occur. Clays are often negatively charged. This is due to substitution of one ion for another in the clay lattice and imperfections at the surface. The main substitutions

21 _{From Prospect. Web:}

are aluminum for silicon in the silica sheet and ions such as magnesium, iron, or lithium substituting aluminum in the aluminum sheet. These substitutions produce a characteristic charge, which is generally called a fixed charge.

Isomorphous substitution, imperfections at the surface of the clay particles and unsatisfied valence charges on the edges of particles all combine to provide a net negative electric charge.

The fact that these particles have a negative charge is very important, because all heavy metal pollutants are positively charged. The combination of a high specific surface area and significant surface charge makes the clay minerals important participants in the contaminated soil interaction process.

Most clay materials have fixed charges, but the oxides / hydrous oxides minerals, a large number of non-crystalline inorganics and soil organics, have variable charges. Their charge depends on the pH. These are called amphoteric surfaces or variable charge surfaces.

The general term ‘oxides’ refers to the crystalline form of the material. Examples of oxides are bauxites and quartz. They are all oxides, hydroxides, and oxyhydroxides of iron, aluminum, manganese, titanium, and silicon. The oxide forms of iron,

aluminum, and manganese are more dominantly present in soil, because of their low solubility in water for the general pH range in comparison with the titanium and silicon oxides.

For most oxides, the amorphous shapes of the oxides form coatings surrounding particles, which show net negatively charged surfaces.

Carbonates and sulphates are generally considered to be more soluble than silica minerals. The most abundant carbonate mineral is calcite (CaCO3). Carbonate

materials are thought to be good absorbers of heavy metals and phosphates. Gypsum (CaSO4.2H2O) is the most common of the sulphate minerals found in soils.

5.1.2 Physical properties related to cleaning of the soil

To process the base material from heavily contaminated mud to a construction material that can be used as a foundation for roads, the mud has to be purified and processed to a material that is suitable for the foundation.

In order to design these processing steps, it is important to have an idea of the most important properties. An overview of the main material properties that are important for a suitable foundation for roads has already been given in chapter 3.4. For the purification step, other properties are important.

Soil particles can be seen as porous particles, containing both micro- and macropores, with an irregular shape. Important mechanisms for purification are:

- the interactions between the soil fractions and water molecules and how they affect the interactions between soil fractions and contaminants;

- the interactions between soil fraction and contaminants and how they result in sorption and bonding between contaminants