PILOT INVESTIGATIONS OF SURFACE PARTS OF THREE CLOSEDLANDFILLS AND FACTORS AFFECTING THEM

JOUKO SAARELAFinnish Environment Institute, Kesäkatu 6, Helsinki, FIN, Helsinki, Finland

(∗ e-mail: jouko.saarela@ymparisto.fi)

Abstract. Aftercare of closed sanitary landfills in a major environmental problem. Rehabilitationof the landfill with vegetation and reducing leachate production are two issues that must be dealt.For this reason, Finnish Environment Institute has conducted several projects on closed landfills.This research aims at determining the physical and chemical properties of the soils at three closedlandfills in Helsinki, Finland. Research was conducted to understand the impact by studying thefollowing properties: Chemical, nutrient metal, gamma and radon analysis of surface soils of threeclosed landfills in Helsinki area.

Keywords: landfill research, landfill vegetation and rehabilitation, pilot investigation

1. Introduction

Landfill research is in many ways a new science and, and as such, it has notyet standardized investigation methods. Therefore, one of the aims of these pilotinvestigations was to test the suitability geotechnical, and environmental investiga-tions methods for landfill. Landfills can also contain many kinds of toxic materials.Therefore toxicity investigations were also conducted at the landfills. Greenbuild-ing is an important factor in preventing infiltration of precipitation into wastefill.Tests were conducted on three closed landfills in Helsinki area.

1.1. GEOTECHNICAL INVESTIGATIONS

1.1.1. Drill Tests and Soil InvestigationsAccording to the results, resistance of light multiple use drill tests varied con-siderably on all landfills at different points and they were classified according tothe drill tests from loose to tight (Tie ja vesirakennushallitus, 1970a). Difficultyto penetrate wastes, for example, pieces of concrete, made weight-sounding testsdifficult at almost all investigation points. Therefore, light multiple-use-drills werenot suitable for landfill investigations. Characteristics of surface soils determinedfrom the samples were the following: hydraulic conductivity of surface samples (0–25 cm) at Iso-Huopalahti, Mankkaa and Vuosaari landfills varied 10−6.0–10−9.0 msec−1, water content 15.3–86.9%, and dry unit weight 8.6–16.5 kN m−3.

Environmental Monitoring and Assessment 84: 183–192, 2003.© 2003 Kluwer Academic Publishers. Printed in the Netherlands.

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Figure 1. Landfills where pilot investigations where conducted.

On the Mankkaa and Vuosaari landfills, the water levels were measured in 1991from four investigation points once a month. Results were obtained only from twopoints. On the Mankkaa landfill on 3 April 1991, the water was highest, and it was110 cm from the surface of the slope. In other measure-ments, it was 117–247 cmfrom the surface of the slope. At Vuosaari, the water level was 245 cm from thesurface of the slope. Location of investigations is shown in Figure 1.

1.1.2. Frost MeasurementsThe frost depths were measured in the winters of 1991–1992 on the tops and on theslopes of the Iso-Huopalahti, Mankkaa and Vuosaari landfills. It was found that thegreatest frost depth was on the slope of the Vuosaari landfill and it was 90 cm. Onthe Mankkaa landfill the greatest frost depth was 64 cm (top) and in Iso-Huopalahtiit was 52 cm (top). Most of the measurement points had no snow as the wind hadblown it away (Saarela, 1997).

Soveri and Varjo (l977) investigated and reported maximum frost depths from1955–1975 on snow-free till areas. In the coastal area of Southern Finland, thefrost depth was 120 cm and the freezing index was between 10 000–15 000 hr◦C. During this investigation, the freezing index in the winters of 1991–1992 wasabout 9000 hr ◦C. From these results, it can be deduced that the results of thisinvestigation are much the same as the results of Ettala (l986). According to hisinvestigations, the frost depth at landfills is, on average, less than in natural areas.

PILOT INVESTIGATIONS OF SURFACE PARTS 185

This is due evidently to the decomposition of organic material, which producesheat.

It must be noted that the frost depth can vary in different landfills due to theage of the landfill, type of waste etc., which have effects on the temperature ofthe waste. The effect of the temperature of wastes on the frost depth must, ifneeded, be measured or calculated, because the new landfill technology aims e.g.to enlarge, centralize and increase the height of landfills. It can be supposed that thetemperatures of landfills are in future higher which will decrease the frost depth.

2. Greenbuilding and Environmental Investigations

In greenbuilding investigations, the nutrient content of surface soils were investig-ated by taking samples from the surface parts of the landfills and analyzing theirnutrient content. The purpose of the environmental investigations was to clarifywhether there are any hazardous chemicals in the surface of the landfill.

The investigations were done at the Iso-Huopalahti, Mankkaa and Vuosaarilandfills. All these landfills are old landfills of Helsinki area (about 20–30 yr old).Specific electrical conductivity, pH, nitrate nitrogen, phosphorus, potassium, cal-cium, magnesium and boric content of samples were analyzed in the nutrient ana-lysis. There were 11 samples from Iso-Huopalahti and 5 from the Mankkaa andVuosaari landfills. For boric analysis, 3 samples were taken from each landfill. Thenutrients were analyzed according to the Finnish standards for nutrient analysis ofsoil samples for greenbuilding described by Kähäri et al. (1987).

Radon was analyzed, because it is a common problem in Southern Finland.High radon contents are toxic for man. High radon contents of landfills preventrecreational use. Measurements were made from composite samples according tomethods described by Markkanen and Arvela (1992).

Polyaromatic compounds chlorinated phenols and are environmental poisons,which hinder the after use of landfills. They can be a problem if, for example, alandfill is taken into active after use and surface soils contain these environmentalpoisons. Then, the contaminated soils can be removed. They were measured fromcomposite samples according to the method described by Keith (1981).

On all landfills, oxygen, methane and hydrogen sulphide measurements weremade with a portable Crowcon triple 84TR measurement device. Temperature meas-urements in the surface parts of landfills were also conducted with a thermometerprobe.

2.1. NUTRIENT ANALYSIS

The nutrient content of surface soils was investigated in the laboratory from soilsamples from the Iso-Huopalahti, Mankkaa and Vuosaari landfills. Electrical con-ductivity, acidity, nitrogen, phosphorus, potassium, calcium, magnesium and boricwere analyzed.

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TABLE I

Results of nutrient analysis of the Iso-Huopalahti landfill (Viljavuuspalvelu Oy)

Investigation Specific pH (NO−3 -N) Nutrient content (mg L−1)

point electrical

conductivity

(µS cm−1) P K Ca Mg

1 220 5.1 7.2 46.0 130 1850 225

2 110 6.3 19.0 28.0 240 2650 200

3 50 5.7 2.8 2.5 105 600 100

4 60 6.1 5.8 1.9 95 72 60

5 310 5.7 18.0 70.0 580 2600 350

6 130 5.8 34.0 20.0 390 1175 90

7 30 5.6 5.0 1.0 25 200 10

8 870 6.3 38.0 24.0 170 3950 445

9 140 6.7 30.0 29.0 190 3750 300

10 560 6.4 24.0 28.0 265 3700 520

11 190 7.1 2.8 540.0 140 4000 425

Results of the analyses are shown in Table I. Results of the analyses werecompared to the Finnish recommendations on greenbuilding. Recommendationsfor nutrient additions for the landfill of Iso-Huopalahti are according those recom-mendations shown in Table II. It can be seen, for example, that samples need limedand fertilized peat, mineral soil and dolomite.

Results of boric analysis varied between 100 to 1900 µg L−1.In summary, it is very important to do nutrient analysis in the vegetation and

landscaping of landfills because soils used on the landfills are generally poor innutrients and need nutrient additions. Nutrient analyses are presented in this con-nection only from the Iso-Huopalahti landfill. Also Mankkaa and Vuosaari landfillneeds nutrient additions (Saarela, 1997).

2.2. RADON EMANATION AND POLYAROMATIC COMPOUNDS

Radon emanation was measured from composite samples from all three landfills.Results of the measurements are shown in Table III. By comparing the results ofthe measurements to typical radon emanation in loose soils in Southern Finland(Table VI), it is seen that radon emanation was on the same level as that of typicalsoils.

Polyaromatic compounds were analyzed from the composite samples. Also chlor-inated phenols were analyzed. It was seen that values were low and chlorinatedphenols were not a risk for the after use of landfills in question (Tables V and VI).

PILOT INVESTIGATIONS OF SURFACE PARTS 187

TABLE II

Recommended nutrient additions for grass and bush planting for the Iso-Huopalahti landfill(Viljavuuspalvelu Oy)

Investigation Limed and Mineral Dolomite Garden Garden Potassium

point fertilized peat soil lime Y-ferti- sulphate

(m3 100 m−2) (kg 100 m−2)

1 6 70 5 2

2 3 5

3 5 30 5 5

4 5 20 5 5

5 30

6 3 30 3 1

7 5 30 5 6

8

9 3 4 3

10 5

11 2

In points 5, 6 and 11 also Oulu saltpeter: 2, 1 and 2 kg 100 m−2, respectively, recommended.

TABLE III

Results of measurements of radon emanation. Natural radionuclides (Säteilyturvakeskus)

Landfill 226Ra 232Th 40K Em Radon emanation

(Bq kg−1) (%) (mBq hr−1 kg−1)

Iso-Huopalahti 38 (6) 35 (7) 490 (5) 8 (26)a 23 (27)7a

Mankkaa 30 (6) 37 (6) 670 (5) 26 (6)b 59 (9)b

Vuosaari 47 (6) 46 (6) 820 (5) 15 (13) 53 (14)b

( ) Percentage errors.a Room dry sample.b Moisture content 5% (weight).

3. Methane, Hydrogen Sulphide and Oxygen Measurements

Methane, hydrogen sulphide and oxygen were measured from several points of allthree landfills. There was no gas removing systems in the investigation landfills.The smell of methane was observed in some parts of all landfills and it causednausea in researchers. Methane is explosive at an at-mospheric concentration of 5–

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TABLE IV

Typical values of radon emanations in loose soils (Säteilyturvakeskus)

Natural radionuclides Typical value in loose soils

in Southern Finland

226Ra 30–80 Bq kg−1

232Th 30–80 Bq kg−1

40K 700–1500 Bq kg−1

Radon emanation, dry sample 20–100 mBq hr−1 kg−1

Moisture content 5% (weight) 40–200 mBq hr−1 kg−1

TABLE V

Results of analysis of clorinated phenols (Ympäristöntutkimuskeskus)

Landfill 2,4,6-trichlorophenol 2,4,5-trichlorophenol Penta- Dry content

chlorophenol of sample

Iso-Huopa Lahti 0.1 1.0 2.6 60.69

Mankkaa 0.6 – – 43.57

Vuosaari – – 0.9 82.66

TABLE VI

Limit values of chlorinated phenols (Ympäristöministeriö,1994)

Chlorinated phenols Typical value Value for soil

in soil to be classified

as contaminated

(qg kg) (qg kg−1)

2,4,6-trichlorophenol 2000 10000

2,4,6-trichlorophenol 2000 25000

Penta-clorophenol 400 4000

PILOT INVESTIGATIONS OF SURFACE PARTS 189

Figure 2. Field investigations at the Iso-Huopalahti landfill, investigation lines (a) and height profileand weight sounding tests on the investigation line (b). Difficult to penetrate wastes, e.g. places ofconcrete and other hard material made weight sounding tests difficult in almost all investigationpoints.

15%. The methane, oxygen, and hydrogen sulphide contents of the surface layersof the landfills were measured at several points. The methane content, at manypoints, was in the limits of explosive danger (5–15%) and oxygen content between10–20% of the volume. According to Duel et al. (1986) methane discharging sites

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Figure 3. Weight sounding tests, frost and moisture measurements on the slope of the Iso-Huopalahtilandfill. It was impossible to install groundwater tubes due to the lightness of the multiple-use drilland the difficulty to penetrate waste materials, e.g. large pieces of concrete and other hard material.

cannot be landscaped without methane removing systems. Also Neumann (l979)has stated that vegetation will not succeed properly if the level of oxygen in thesoil is lower than 12–14%. Hydrogen sulphide was detected in only one point onthe Iso-Huopalahti landfill.

Temperature measurements were also made from several points on the land-fills. The purpose of temperature measurement was to measure temperatures wheremethane erupted to the surface. In particular high temperatures (max. 46 ◦C) weremeasured at such points on the Iso-Huopalahti landfill.

According to Neumann (1979), if the temperature on the landfill is over 25 ◦C,it is not wise to landscape it. Also, high methane contents disturb the vegetation.High temperatures in the landfill cause, according to Vainio (1984), extra evapo-transpiration, and the concentration of salts and nutrients in the surface, whichcauses drying of vegetation.

4. Conclusions

According the results of this investigation the following points must be taken in theconsideration the closing of the landfills:

(1) Closing of landfills needs many kinds of field investigations in order to find itsenvironmental risks. It was seen that light multiple-use-drills were not suitablefor landfill investigations. This was due to the fact that landfills, in general,contain waste materials that are difficult to penetrate, for example, pieces ofconcrete, which make weight-sounding tests difficult.

(2) From nutrient analysis, it was seen that surface soils on landfills can be poor innutrients and they need nutrient additions. It must be taken into consideration

PILOT INVESTIGATIONS OF SURFACE PARTS 191

in the closing of landfills because good vegetation has great importance inreducing the infiltration to the wastefill. The reduction of the infiltration canover 30% of yearly precipitation with good vegetation.

(3) From the water levels, it was seen that the water table can change greatly indifferent parts of landfills and it can be far from the surface of the landfills.However, it was seen the changes of water levels are not so great that theycould cause problems to the development and the use of water balance modelof the landfill (LCAM) (Saarela, 1997).

(4) The frost depths at landfills were average less than in natural areas. This is dueevidently to the decomposition of organic material, which produces heat. Thismakes the frost protection easier and cheaper.

(5) Radon emanation was on the same level as typical radon emanation in loosesoils in Southern Finland. Values of chlorinated phenols and polyaromaticcompounds were also low. It was seen they are not an environmental risk forthe health of man in the closing of landfills.

(6) The smell of landfill gas was observed in some parts of all investigation land-fills. It, for example, caused nausea in researchers. Landfill gas can also beharmful for vegetation and afteruse, if methane-removing structures are notinstalled. It was seen that methane could be a risk to the vegetation and mancausing also explosion danger.

Results of this research were also used as background information in the develop-ing and testing the Finnish landfill cover approximation model (LCAM) (Saarela,1997).

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