Uncontrolled landfill investigation: a case study in Athens

Mavropoulos Antonis1,Kaliampakos Dimitris2 1: National Technical University of Athens (NTUA), Researcher, Department of Chemical

Engineering, 9 Heroon Polytehniou str., Zografou 15 780, Greece 2: National Technical University of Athens (NTUA), Lecturer, Department of Mining Engineering

& Metallurgy, 9 Heroon Polytehniou str., Zografou 15 780, Greece

Abstract

Uncontrolled landfills comprise one of the most important topics as regards to Solid Waste Management (SWM) in

Greece. The enviromental impacts of these landfills are closely related to some particular characteristics, namely the

composition and quantity of the disposed solid wastes and the conditions that control the physicochemical processes

inside the waste volume, which in fact determine the rehabilitation plan . The objective of this paper is to present a

method to gain all these crucial data. The definition of the necessary information in order to have a sufficient

knowledge about the landfill processes and the choice of the appropriate overall measurements (biogas, geophysical

methods) are the key factors to transced the problem of unconformity and the absence of data, without wasting time

and money.

Introduction

Dumping on land has been one of the most wide spread methods for the final disposal of solid

wastes, since the turn of the century untill, unfortunately, now. As it was a simple task to haul solid

wastes to the edge of the town and dump them there, open dumps became a common method to

dispose solid wastes for a long period of time. From 4639 solid waste disposal sites in Greece, 3099

(66,5 %) sites are officialy recognized as uncontrolled landfills, according to the Minister of

Environment Physical Planning and Public Works (Frantzis et al, 1993).

Thus, the restoration of thousands of uncontrolled landfills in Greece is an urgent, complicated and

difficult problem to solve. The enviromental impacts of uncontrolled landfills are closely related to

specific features, for each landfill, which finally assign the restoration plan, such as:

· The composition and quantity of the disposed solid wastes.

· The conditions controlling the mechanical, biological, physical and chemical changes inside the

waste volume.

· The main physicochemical processes affecting the waste volume.

Nevertheless, usually there is lack of information or sometimes complete unawareness, as regards

to the real state within an uncontrolled landfill. It must be also noted that, uncontrolled landfills are

very uneven systems, very much depended on location, composition of wastes and the existing

climatologic conditions. So it is very difficult to overview the environmental impacts of the

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different sites according to a global rule (Little et al, 1995). Taking into account the different

hydrogeologic and geologic conditions, the topography etc., it is evident that every uncontrolled

landfill is a unique case.

This paper is based on the work carried out in the framework of the succesfull research program

«Environmental Impact Assesment and Restoration of the Kareas landfill» (1996). This project was

carried out by the NTUA (Mining Technology Laboratory). Kareas landfill overlies an abandoned

quarry and contains about 13.500.000 tons of solid wastes disposed in the years between 1970 and

1992, at a 40 hectares area, situated only a few kilometers from the center of Athens. It is,

undeniably, the greatest uncontroled landfill in Greece.

1. Defining the required information and the data resources

The dump consists of a mixture of inert wastes with Municipal Solid Waste (MSW) with unknown

proportion and composition. Thus the following questions had to be answered.

· Which is the amount of the waste?

· Which is its composition? Which is the content in MSW?

· What particular conditions mainly exist inside the waste heap? I.e.:

· Are the waste compacted and which is the compaction ratio?

· Do exist aerobic or anaerobic conditions?

· What are the values of the existing temperature and pressure?

· What are the water conditions inside the waste heap?

· What are the main physicochemical, biological and mechanical processes controlling the

landfill?

Table 1 shows the corelation, indicated by the gray cells between the required information and the

data resources employed. The term ‘‘Case History’’describes all the information related to the

landfill, such as the climatologic, hydrogeologic, geologic conditions, soil condition, topography

and type of disposal.

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Table 1: Corellation between required information and data resources

INFORMATION RESOURCES

INFORMATION Biogas Temperature Drills Geophysical Research

Laboratory Measurements

Case History

Waste amount

Waste composition

Waste volume conditions

Compaction

Air presence

Temperature and pressure

Water infiltration

COMBINATION AND CROSSING

Processes that controll the landfill

From other studies about Kareas landfill it was given that:

· No mechanical compaction of the waste had taken place. The waste were just unloaded from the

top of the quarry.

· The surrounding limestones are intensely fractured and water permeated. Inside the waste

volume, there is a lot of CaCO3, derived by the quarrys activities.

2. Measurements

2.1 Geophysical Research

Seismic Tomography and Diffraction Seismics were selected as the most appropriate methods for

the geophysical investigation of the site. The object was to detect separate layers as well as to

investigate the physical properties of the waste. The Diffraction Seismic method, used two cross

sections, about 144 m length each. The first cross section had 144 geophones in 3 groups while the

second cross section had 96 geophones in 2 groups. The distance between the geophones was 2 m

and there were 6 detonation points at each section. The Seismic Tomography method utilised two

10 m x 10 m grids, in two different areas of the quarry. 59 and 120 geophones were located at the

corresponding areas, respectively.

The main conclusions drawn from the geophysical investigation were:

· The seismic wave velocity gradient indicated a slight bedding of the disposed material generated

by the weight of the overburden.

· No negative seismic wave velocity gradient was observed, thus no considerable concentration of

pure MSW was detected. The mixture of inerts and MSW shows a remarkable homogeneity.

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2.2 Drilling Research

Twelve (12) sampling boreholes were performed (Figure 1). Field measurements and waste

sampling for laboratory analysis were carried out around and inside the boreholes. The particular

selection of the borehole location was made in order to cover as much as possible of the quarry

area. Some boreholes detected large voids inside the waste volume.

12

34

56

7

8

9

1011

12

Figure 1: Kareas landfill and the boreholes pattern: Borehole

2.3 Biogas Measurements

A GA - 94 Infrared Gas Analyser (Geotechnical Instruments) was used to measure biogas

emmisions at the upper part of the boreholes. The operation limits of this instrument are 0 - 100%

v/v about CH4, 0 - 50% v/v about CO2 and 0 - 21% v/v about O2. All the measurements were carried

out at 9o-11 o C and 78,8% relative humidity of the air (Table 2).

Table 2: Biogas measurements

Borehole CH4 (% v/v) CO2 (% v/v) O2 (% v/v) CO (ppm) Temperature (oC)

1 0.0 11.4 7.8 0.0 35

4

2 0.0 12.9 6.6 0.0 31.1

3 0.0 12.4 7.8 0.0 28

4 0.0 10.6 8.9 0.0 23.9

5 0.0 0.7 19.1 0.0 37.8

7 0.0 6.7 13.4 0.0 23.7

8 0.0 2.1 17.3 0.0 33

9 0.0 1.6 18.4 0.0 31

10 0.0 2.7 16.6 0.0 47

11 0.0 15.6 4.4 0.0 27.8

12 7.7 13.8 0.0 7.0 15.1

During the measurements, oxygen ranged between 20.3 - 20.5 % v/v in open air. No H2S was

detected. All the measurements were done in depth ranged between 3.5 and 5 m.

2.4 Laboratory analysis

Fourty two samples, grouped at each borehole location where sampling had been taken place, were

analysed. At each sample pH, BOD5, COD, organic carbon and humidity were measured (Table 3

and 4).

Table 3: Laboratory measurements of the waste samples

Borehole Depth (m)

pH Humidity (%)

Organic C (%)

BOD5 (mg/l)

COD(mg/l)

9 8.62 6.8 2.07 17.4 90.718 9.74 10.4 1.10 18.2 100.127 8.81 15.0 1.23 17.0 93.7

1 36 9.23 14.8 2.40 17.8 84.545 8.50 7.7 2.27 20.0 102.854 8.93 15.4 1.17 19.5 85.263 8.82 11.8 2.30 17.4 91.872 8.61 12.5 1.18 19.3 99.781 8.91 8.4 0.96 18.6 102.5

9 8.36 8.8 2.10 31.3 87.018 8.30 11.9 1.71 18.1 89.327 9.03 7.4 1.30 19.7 95.5

2 36 8.41 8.5 1.07 24.8 114.445 9.18 12.7 1.60 22.3 110.754 8.49 8.9 3.72 24.5 120.163 8.54 16.4 2.93 21.8 118.072 7.83 18.0 6.00 22.3 88.3

Table 4: Laboratory measurements of the waste samples

Borehole Depth (m)

pH Humidity (%)

Organic C (%)

BOD5 (mg/l)

COD(mg/l)

9 7.90 12.0 4.70 19.6 84.23 18 9.40 12.7 5.10 20.7 91.7

5

27 8.56 14.4 5.80 21.4 95.336 7.97 15.8 6.70 22.3 102.0

4 27 9.92 3.4 0.73 32.1 95.236 8.21 2.7 0.51 28.7 121.5

9 8.40 8.4 0.76 19.9 95.318 8.40 11.5 0.80 25.7 92.127 8.59 13.6 0.83 20.1 95.736 8.60 6.9 0.78 34.0 98.7

5 45 8.18 14.8 0.78 23.0 104.854 8.80 7.9 0.90 31.3 106.263 8.80 17.4 0.95 25.7 112.472 8.12 17.5 0.91 21.8 123.7

9 8.63 11.9 1.50 17.3 78.218 9.48 11.6 1.63 17.1 77.127 12.44 9.2 0.70 17.3 77.236 8.74 13.8 1.87 17.6 78.545 8.17 10.5 1.77 17.6 75.7

11 54 10.87 10.3 2.66 17.7 63.263 9.00 7.0 3.80 17.9 63.972 8.82 10.2 0.95 17.9 65.281 8.46 9.4 0.07 18.4 73.990 8.74 7.3 0.83 18.1 75.899 9.17 5.6 1.05 18.2 64.3

The laboratory measurements of organic carbon range between 0,07 and 6,7% by weight (dry

basis). BOD5 and COD are also sensibly low. It is remarkable that there is only one borehole (n.3)

where the organic carbon ranges between 4,7 and 6,7% by weight (dry basis) while at the rest the

maximum values vary between 3,7 and 3,8%.

Value dispersion is low, almost for every parameter. Keeping in mind the possibility of organic

carbon loss during the sampling and the relatively high uniformity of the measurements , organic

carbon should be ranged between 2 - 6%. To make a safe side estimation, it is finally accepted that

organic carbon is about 6%.

3. Discussion

From the above the following can be concluded:

3.1 Waste amount and composition

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Table 5 shows main characteristics of Athens MSW composition (Lekkas et al, 1991). Organic

carbon is about 30 - 31% by weight (dry basis).

Table 5: MSW composition in Athens

C 31 %

H 0,00

04 %

S 0,1

%

Ash and inerts 33,8

%

Humidity 37,5

%

The difference in the organic carbon content between the average values of Athens MSW (31%)

and Kareas landfill solid waste (maximum 6%) can be explained by both, the low (MSW/inert

waste) ratio inside the quarry and the natural reduction of the organic C.

Granted that the whole organic carbon is contained at the MSW, the MSW ratio is about 20% of the

waste weight and organic carbon is about 810.000 tons.

3.2 Waste heap conditions

The geophysical research confirmed that there is only a slight bedding of the disposed material. So

the spatial waste distribution is characterized by the waste weight. Heavy waste have tended to

move to the bottom of the quarry while light waste stayed to upper part of the heap. The presence

of many large pockets of waste (practically uncompacted) led to the formation of air passageways

and finally to almost free air circulation conditions. The waste volume contains large amounts of

water, due to the topography, the climate in the area and the high permeability of the geologic

surrounding. The CaCO3 and the water existence create an alcaline environment inside the waste

heap, also confirmed by the pH measurements (see Table 3,4). Relatively high temperatures (Table

2) were measured at many locations inside the landfill.

3.3 Physicochemical, biological and mechanical processes

Gas emissions, due to the underground migration of the biogas, are more representative of the

global physicochemical processes and not of their local occurance (Commission of the E.C., 1992,

Straka F. et al, 1993). In a single borehole methane was detected (Table 2) and no oxygen was

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measured. Also at the same location, the measured temperature was sensibly low. It is also

remarkable that in every site where CO2 was detected, the sum of measured CO2 and O2

percentages was very close to the open air O2 percentage . This indicates that the consumed O2 was

converted to CO2 and confirms the existence of free air circulation, inside a great area of the waste

heap.

As it is known the products of the anaerobic decomposition of MSW are initially carbon dioxide

and water and carbon dioxide and methane at the latest phase of the process (Luning et al, 1993),

when the initial oxygen of the compacted wastes is depleted (Tchobanoglous et al, 1977). The

products of aerobic decomposition are carbon dioxide and water, which also happen to be the

products of the first phase of anaerobic decomposition (Arigala et al, 1995, Commission of the

E.C., 1992). According to the above, it seems that anaerobic processes are located around the area

of the borehole No 12.

The anaerobic process around the borehole No 12 area is confirmed by the fact that in this area the

waste were disposed, just before the closure of the landfill. The last waste disposed at winter of

1992 and so the waste are relatively humid. Contemporary, waste were compacted because the

waste collection vehicles passed over the specific location to unload the wastes.

Three different scenarios can occur about the rest of the landfill: anaerobic decomposition (at the

first phase) or a low intensity fire inside the waste volume or aerobic decomposition.

The first scenario is quite unlike given that the disposal of MSW have stopped since 1992. Free air

circulation and no compaction of the waste, stand for the exclusion of the anaerobic

decomposition. Also, the elapsed time for the initiation of the first phase of the anaerobic

decomposition is obviously less than 4 years (Tchobanoglous et al, 1993). The scenario of a low

intensity fire, can hardly be accepted as well as the existence of such a fire is almost impossible for

a so large area, in a landfill characterised by 6% organic carbon. Thus aerobic decomposition of

MSW is the main process running inside the waste volume. The presence of relatively high

amounts of CO2 (Table 2) at some boreholes indicates that the process touches its peak while the

low values at some other boreholes indicate the end of the process. The analogy of the measured

oxygen and carbon dioxide ranges considerably, even between adjacent boreholes. This fact proves

the great unevenness and the local features of the aerobic processes.

Conclusions

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Uncontrolled landfills are a “hot spot” at SWM, because they were the most conventional (and

environmental dangerous) way of disposal for many years. Especially in Greece, the restoration of

such landfills is an extremely urgent task.

The restoration of uncontrolled landfills is a complicated scientific and technical problem, mainly

due to the lack of information and the unhomogeneity of the processes inside the waste heap.

Furthermore scientific knowledge about dumped waste behavior originates mainly from sanitary

landfilling or laboratory experiments and so it is very difficult to simulate a real uncontrolled

landfill using this knowledge.

In order to design a restoration plan, it is necessary to have an adequate knowledge at least about:

· composition and quantity of disposed solid wastes

· mechanical, physicochemical and biological changes inside the waste heap

· the main processes affecting the waste volume

The precise estimation of such required data and the complete investigation of an uncontrolled

landfill presupposes, usually, a high and not available budget. Thus, the practical question is “how

to get the maximum possible knowledge (about the landfill), in a way that guarantees a safe and

succesfull restoration, spending the minimum money?”.

The answer can be given using methods that examine and investigate the overall behavior of the

landfill, like geophysical research and biogas measurements. Such methods provide the required

data in a more representative way than the local sampling and laboratory analysis. The combination

of the resulted data is a key - point to the whole data processing.

Table 1 shows the corelation between the required information and the data resources, as they were

settled by the authors in the framework of the specific project of Kareas landfill. The outcome

summarizes to the following:

· The waste bedding is controlled by the waste weight and the presence of large uncompacted

waste pockets within the heap, which form a lot of air passageways and finally free air

circulation conditions inside the waste volume.

· The MSW are about 20% by weight of the disposed waste. The rest 80% are mainly inert waste.

· Aerobic process is the main decomposition process inside the waste volume, with the exception

of the number 12 borehole area, which is characterised by anaerobic decomposition of MSW.

The uniformity of the results derived from field and laboratory measurements, supports the

reliability of the final conclusions.

References

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Environmental Engineering, vol. 121, N.1, p. 33-44

COMMISSION OF THE E.C. (1992) Landfill gas from environment to energy, Brussels, part II, p. 121-136

Frantzis I., Agapitidis I.(1993) Στρατηγική της Τ.Α. για την διαχείριση των απορριμμάτων στην Ελλάδα (The Local

Administration Strategic for the SWM in Greece), ΕΕΤΑΑ, Athens, p.18

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