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Measuring the waterbalance of a three-layer cover of a domestic waste landfill
Engineering Geology, 21 (1985) 341--347 Elsevier Science Publishers B.V., Amsterdam -- Printed in The Netherlands
341
MEASURING THE WATERBALANCE OF A THREE-LAYER COVER OF A DOMESTIC WASTE LANDFILL
H. HOTZL 1, H. NEFF 2, H. WALTER 2 and S. WOHNLICHl ~Lehrstuhl ffir Angewandte Geologie, Universitiit (TH) Karlsruhe D-7500 Karisruhe (Federal Republic o f Germany) =Erdbaulaboratorium Dr. Tropp -- Dipl.-Ing. Neff und Partner, D-6303 Hungen (Federal Republic of Germany) (Accepted for publication November 19, 1984)
ABSTRACT HStzl, H., Neff, H., Walter, H. and Wohnlich, S., 1985. Measuring the waterbalance of a three-layer cover of a domestic waste landfill. Eng. Geol., 21 : 341--347. A covering system is described that is to be installed at a domestic waste landfill to reduce the generation of leachate. The covering system consists of three parts: 1.5 m top- and subsoil, 0.5 m barrier layer and 0.3 m gas drainage layer. The waterbalance of the covering system is measured by two large-scale lysimeters (9.5 x 16.5 m) and soft moisture measurements with neutron moisture probe. INTRODUCTION T h e c o v e r i n g s y s t e m discussed is p a r t o f a c o m p l e t e g r o u n d w a t e r p r o t e c t i o n a n d r e m e d i a l s y s t e m . In a d d i t i o n t o a c o m p l e t e u n d e r g r o u n d e n c l o s u r e o f t h e site a n d its c o n t e n t s , t h e p u r p o s e o f t h e c o v e r is t o k e e p t h e a m o u n t o f l e a c h a t e g e n e r a t e d as l o w as possible. T h e r e f o r e t h e l o n g - t e r m effectiveness o f t h e c o v e r i n g s y s t e m is vital f o r m a l n t a i n a n c e costs a n d resulthtg f u t u r e e n v i r o n m e n t a l risks. T h e r e h a v e b e e n s o m e t h e o r e t i c a l a p p r o a c h e s f o r m u l t i l a y e r c o v e r i n g syst e m s , b u t t h e r e is a lack o f p r a c t i c a l e x p e r i e n c e . T h e e m p h a s i s o f t h e investig a t i o n s discussed is a i m e d o n t h e l o n g - t e r m b e h a v i o u r o f such s y s t e m s a n d the interrelationships of covering material--refuse--vegetation. SITE DESCRIPTION General o v e r v i e w T h e site is s i t u a t e d in t h e n o r t h e r n p a r t o f t h e u p p e r R h i n e Valley, West G e r m a n y . T h e geological s t r a t a c o n s i s t o f 4 0 m Q u a t e r n a r y s a n d a n d gravel u n d e r l a i d b y a m i n i m u m 1 5 - m c l a y layer. 0013-7952/85/$03.30
© 1985 Elsevier Science Publishers B.V.
342
The water table is f o u n d at a depth of 16--18 m and groundwater is used for drinking water supply at three areas around the site.
Site history The site had been used as a quarry, which was excavated to a depth of 20 m below surface. Since 1960 the quarry, then 10 m under the water table, was refilled with waste. Beginning 1968 the site was managed as controlled for domestic waste, industrial waste and inert natural material. At present the site is 30 m above surface. The total volume amounts to 14.10 s m a, with an annual disposal of 1. l 0 s m 3.
Combined groundwater protection The total groundwater protection combines a vertical barrier and covering o f the site and its contents: around the site a 15 m trench was excavated and from its b o t t o m a slurry wall down into the tightening clay layer was dug. Over the counterscarp a flexible membrane was placed. Both actions prevent contaminants from passing through into the groundwater. The whole site will be covered with a barrier system to reduce water ingress into the site and thereby to keep leachate production to a minimum. COVERING SYSTEM
From the outer edge o f the site the slopes show a gradient of 1:3 up to a height o f 30 m. The centre of the disposal is formed by a plateau. In order to grant a complete r u n o f f of surface water, to compensate expected consolidations and to control the ventilation of landfill gas the plateau was designed as a "fold-roof", several segments of 100 m latitude and varying length. In the middle o f each segment a water-canal is situated, and slopes of 2.5% rise on each flank towards gas vents (see Figs.1 and 2). The canals drain to the outside With a gradient of 1%. The covering system consists of the following three layers. Sand filterlayer. 0.3 m of sand (medium grain size) is placed above the waste. Its purpose is to gather and drain gas. Every 100 m the gas is led away by gas vents. At the same time the filterlayer m a y be used as buffer against uprising aggressive liquids. Barrier layer. A 0.5 m thick barrier layer is situated above the filterlayer. It consists of two separately consolidated layers of clay--siltmaterial compacted to a Proctor-density of 97%. After D I N 18196 (appropriate to USCS, "Unified Soil Classification System") the soil-materialsused belong to the groups TL--TM and U M (MH--CL). By using the soil-mechanical properties as criterion for the selection of the material determination and control is simplified. Vegetation support layer. The barrier layer is covered by 1.5 m sand and clay. This vegetation support layer has to provide sufficient depth of root
343
verticat cross-section -.---1% c o v e r i n g ~ e m=abt~ ~layLayer--__-;
~ N 0 t
\testingarea 0 meteorotogicalstation
100 I
200 m I
Fig.1. Location map of the landfill and testing area.
O,30m topsoil 120m subsoil 0,50m barrierlayer O,30m gas drainage tayer
Fig.2. Design of the covering system.
growth of grass and trees,as well as enough water in order to concentrate root growth in this layer. The top contains organic material ("topsoil") the underlaying 1.2 m ("subsoil") does not. The task of the vegetation support layer is to protect the barrierlayer against drying, freezing, mechanical injuries,and biologicalinjuries(plantroots and animals). RESEARCH PROGRAM
In advance o f the final covering of the landfill one "Foldroof-segment" was installed. This segment is designed as a test of the covering system,
344
to measure its effectiveness and to obtain measures for the future waste site management. In detail three different methods were used.
Large.scale lysimeter Centre of the testing area are two large-scale lysimeters each of a dimension of 9.5 to 16 m. Lysimeter I is designed to observe the watercycle of the covering system within a closed system. The vertical walls are led up to the surface. This lysimeter is divided into 10 separately measurable segments whose bulkheads inside the lysimeter end below the barrier layer. By this means random effects will be limited on the outer four segments, while the inner six segments are expected to obtain realistic measures. Contrary to lysimeter I, lysimeter II is an open element within the covering system. Its walls do n o t reach higher than 5 cm below the b o t t o m of the barrier layer. Lysimeter II gathers and measures the vertical leachate below the barrier layer without taking horizontal water movements into account. There is no inner segmentation. Lysimeter II additionally serves as dome for collecting landfill gas. For this purpose the membrane of its base is laid out with an angle of 45 ° downward. The dome forms a collection area of 300 m 2. Both lysimeters are made of a flexible membrane. Their b o t t o m is V-shaped, the slopes 5% towards the centre and additionally 5% towards the collection pit. The special design drainage filters are situated at the lowest point of each segment. They contain a gravel--sand filter of two grain sizes. The water is led into separate tubes for each segment. All tubes of both lysimeters meet in the collection pit, where the leachate is separately measured.
/L
/L
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ct
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A_
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el. A. " ~ Fig.3. L o c a t i o n map o f the testing ares o n t o p o f the landfill.
~A_
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346
Small-scale lysimeter A small-scale lysimeter has been constructed in addition to the large lysimeters. Because of its relatively low cost and the possibility of immediate construction the small-scale lysimeter has been built in advance of the testing area. This made it possible to obtain early measurements and first practical experience a b o u t the installation and effectiveness of the measuring systems. The measures obtained will be interpreted in comparison with the measurements from large-scale lysimeters, because uncontrollable random effects could falsify the small-scale lysimeter results. On the other hand, a comparison between both types of lysimeter might give reasons for the future use of small-scale lysimeters. Their low costs makes them ideal as monitoring and testing system for covering or similar systems. A
cllltK~oll pit
larlJI-$ld! lyliil~ter l
r
I
large-scale tysiraeter I I I I
I I
i
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2
1~
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e~
,i
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I~'.- - - - -
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m
Fig.4. Vertical cross-section through the testing area. A ~ f----2m
_±1
~-
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~i
_~.~~''
"1 L
1,sin---~ II
. ' ~ : I
.'~']i!~
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Fig.5. Cross-section through the small-scale lysimeter.
,
'
"
346 The small-scale lysimeter used, consists of a 2.5 m cylinder through the profile of the covering system. Its b o t t o m inclines by 10%. Leachate gathers at the drainage filter. The measuring device is located in the collection pit. The small-scale lysimeter is built up by five prefabricated armoured concrete rings with an inner diameter of 2 m. The rings are tightened by an inner coat of "Inertol". Soil moisture measurements
Measurement of soil moisture changes within the covering system is another possibility to quantify the water movement. By using a neutron probe "Wallingford IH 2" at several measuring points in the testing area, soil water contents at different depths are recorded weekly. The differences between the measurements will be used for the calculation of the water movement in dependence from vegetation, climate and soil characteristics. They will also be used for the localisation of inhomogeneous zones within the barrier layer. Meteorological measurements
Two kilometres west of the landfill site a complete range of meteorological measurements has been regularly recorded. The results from there are improved by a meteorological station on the landfill, which makes continuous measurements of humidity, temperature and precipitation. The precipitation is also measured daily at five locations on the landfill. SUMMARY Although there are some theoretical approaches as for h o w to design a multilayer covering system only few practical examples are known. The landfill discussed will be covered by such a system and simultaneously get an underground barrier for groundwater protection. The research programme for the first time uses flexible large-scale lysimeters and soil moisture measurements, for the estimation o f the water balance within the covering system, At the present time the programme is at its beginning. The experiences at the installation give hope for better measures of the factors acting on covering systems. ACKNOWLEDGEMENTS The remedial conception was the product of an interdisciplinary cooperation. It was planned by Erdbaulaboratorium Dr. Tropp--Dipl.-Ing. Neff und Partner. This paper is presented by permission of the Magistrat der Stadt Frankfurt a.M. and the Federal Department of Research and Technology, who sponsors the research project. The cooperation of each is gratefully acknowledged.
347
REFERENCES Goode, D.J., 1983. Evaluation of simplified techniques for predicting moisture breakthrough of soil liners.Proc. Nat. Conf. Management of Uncontrolled Hazardous Waste Sites,Washington, D.C., pp.161--168. J~iger, B. and Wiemer, K., 1981. MSglichkeiten der Sickerwasserminirnierung in abgeschlossenen Deponien. Verl~ngerung der NutzungsdaUer yon Deponien, Abfallwirtschaft an der T U Berlin, Band 8, pp.174--185. Sanning, D.E., 1983. Remediation of an Inoperative Municipal Waste Landfil -- Windham Landfill. Municipal Environmental Research Laboratory, Preliminary Draft, Cincinnati, 1983. Neff, H. and Walter, H., 1983. Konzeption zum Grundwassersehutz der Hausrniilldeponie Dreieich. Fortschritte der Deponietechnik, Haus der Technik, Essen. Parry, G. and Bell, R., 1983. Draft Report on Covering Systems. N A T O / C C M S Pilot Studie on Contaminated Land.
341
MEASURING THE WATERBALANCE OF A THREE-LAYER COVER OF A DOMESTIC WASTE LANDFILL
H. HOTZL 1, H. NEFF 2, H. WALTER 2 and S. WOHNLICHl ~Lehrstuhl ffir Angewandte Geologie, Universitiit (TH) Karlsruhe D-7500 Karisruhe (Federal Republic o f Germany) =Erdbaulaboratorium Dr. Tropp -- Dipl.-Ing. Neff und Partner, D-6303 Hungen (Federal Republic of Germany) (Accepted for publication November 19, 1984)
ABSTRACT HStzl, H., Neff, H., Walter, H. and Wohnlich, S., 1985. Measuring the waterbalance of a three-layer cover of a domestic waste landfill. Eng. Geol., 21 : 341--347. A covering system is described that is to be installed at a domestic waste landfill to reduce the generation of leachate. The covering system consists of three parts: 1.5 m top- and subsoil, 0.5 m barrier layer and 0.3 m gas drainage layer. The waterbalance of the covering system is measured by two large-scale lysimeters (9.5 x 16.5 m) and soft moisture measurements with neutron moisture probe. INTRODUCTION T h e c o v e r i n g s y s t e m discussed is p a r t o f a c o m p l e t e g r o u n d w a t e r p r o t e c t i o n a n d r e m e d i a l s y s t e m . In a d d i t i o n t o a c o m p l e t e u n d e r g r o u n d e n c l o s u r e o f t h e site a n d its c o n t e n t s , t h e p u r p o s e o f t h e c o v e r is t o k e e p t h e a m o u n t o f l e a c h a t e g e n e r a t e d as l o w as possible. T h e r e f o r e t h e l o n g - t e r m effectiveness o f t h e c o v e r i n g s y s t e m is vital f o r m a l n t a i n a n c e costs a n d resulthtg f u t u r e e n v i r o n m e n t a l risks. T h e r e h a v e b e e n s o m e t h e o r e t i c a l a p p r o a c h e s f o r m u l t i l a y e r c o v e r i n g syst e m s , b u t t h e r e is a lack o f p r a c t i c a l e x p e r i e n c e . T h e e m p h a s i s o f t h e investig a t i o n s discussed is a i m e d o n t h e l o n g - t e r m b e h a v i o u r o f such s y s t e m s a n d the interrelationships of covering material--refuse--vegetation. SITE DESCRIPTION General o v e r v i e w T h e site is s i t u a t e d in t h e n o r t h e r n p a r t o f t h e u p p e r R h i n e Valley, West G e r m a n y . T h e geological s t r a t a c o n s i s t o f 4 0 m Q u a t e r n a r y s a n d a n d gravel u n d e r l a i d b y a m i n i m u m 1 5 - m c l a y layer. 0013-7952/85/$03.30
© 1985 Elsevier Science Publishers B.V.
342
The water table is f o u n d at a depth of 16--18 m and groundwater is used for drinking water supply at three areas around the site.
Site history The site had been used as a quarry, which was excavated to a depth of 20 m below surface. Since 1960 the quarry, then 10 m under the water table, was refilled with waste. Beginning 1968 the site was managed as controlled for domestic waste, industrial waste and inert natural material. At present the site is 30 m above surface. The total volume amounts to 14.10 s m a, with an annual disposal of 1. l 0 s m 3.
Combined groundwater protection The total groundwater protection combines a vertical barrier and covering o f the site and its contents: around the site a 15 m trench was excavated and from its b o t t o m a slurry wall down into the tightening clay layer was dug. Over the counterscarp a flexible membrane was placed. Both actions prevent contaminants from passing through into the groundwater. The whole site will be covered with a barrier system to reduce water ingress into the site and thereby to keep leachate production to a minimum. COVERING SYSTEM
From the outer edge o f the site the slopes show a gradient of 1:3 up to a height o f 30 m. The centre of the disposal is formed by a plateau. In order to grant a complete r u n o f f of surface water, to compensate expected consolidations and to control the ventilation of landfill gas the plateau was designed as a "fold-roof", several segments of 100 m latitude and varying length. In the middle o f each segment a water-canal is situated, and slopes of 2.5% rise on each flank towards gas vents (see Figs.1 and 2). The canals drain to the outside With a gradient of 1%. The covering system consists of the following three layers. Sand filterlayer. 0.3 m of sand (medium grain size) is placed above the waste. Its purpose is to gather and drain gas. Every 100 m the gas is led away by gas vents. At the same time the filterlayer m a y be used as buffer against uprising aggressive liquids. Barrier layer. A 0.5 m thick barrier layer is situated above the filterlayer. It consists of two separately consolidated layers of clay--siltmaterial compacted to a Proctor-density of 97%. After D I N 18196 (appropriate to USCS, "Unified Soil Classification System") the soil-materialsused belong to the groups TL--TM and U M (MH--CL). By using the soil-mechanical properties as criterion for the selection of the material determination and control is simplified. Vegetation support layer. The barrier layer is covered by 1.5 m sand and clay. This vegetation support layer has to provide sufficient depth of root
343
verticat cross-section -.---1% c o v e r i n g ~ e m=abt~ ~layLayer--__-;
~ N 0 t
\testingarea 0 meteorotogicalstation
100 I
200 m I
Fig.1. Location map of the landfill and testing area.
O,30m topsoil 120m subsoil 0,50m barrierlayer O,30m gas drainage tayer
Fig.2. Design of the covering system.
growth of grass and trees,as well as enough water in order to concentrate root growth in this layer. The top contains organic material ("topsoil") the underlaying 1.2 m ("subsoil") does not. The task of the vegetation support layer is to protect the barrierlayer against drying, freezing, mechanical injuries,and biologicalinjuries(plantroots and animals). RESEARCH PROGRAM
In advance o f the final covering of the landfill one "Foldroof-segment" was installed. This segment is designed as a test of the covering system,
344
to measure its effectiveness and to obtain measures for the future waste site management. In detail three different methods were used.
Large.scale lysimeter Centre of the testing area are two large-scale lysimeters each of a dimension of 9.5 to 16 m. Lysimeter I is designed to observe the watercycle of the covering system within a closed system. The vertical walls are led up to the surface. This lysimeter is divided into 10 separately measurable segments whose bulkheads inside the lysimeter end below the barrier layer. By this means random effects will be limited on the outer four segments, while the inner six segments are expected to obtain realistic measures. Contrary to lysimeter I, lysimeter II is an open element within the covering system. Its walls do n o t reach higher than 5 cm below the b o t t o m of the barrier layer. Lysimeter II gathers and measures the vertical leachate below the barrier layer without taking horizontal water movements into account. There is no inner segmentation. Lysimeter II additionally serves as dome for collecting landfill gas. For this purpose the membrane of its base is laid out with an angle of 45 ° downward. The dome forms a collection area of 300 m 2. Both lysimeters are made of a flexible membrane. Their b o t t o m is V-shaped, the slopes 5% towards the centre and additionally 5% towards the collection pit. The special design drainage filters are situated at the lowest point of each segment. They contain a gravel--sand filter of two grain sizes. The water is led into separate tubes for each segment. All tubes of both lysimeters meet in the collection pit, where the leachate is separately measured.
/L
/L
~
A_
2.5%
0
10
A_ Oo : o ~
/L
A_ A_ ¢b_
A_ A_
A_
A_ A --~
A_
°°I ° ~ ~ = ~ ii r .... ~
2.5%
^
A_
ct
20m
A_ key: n
-g~g* bushes
A_
A_
A_
A_ ~
:!A_
el. A. " ~ Fig.3. L o c a t i o n map o f the testing ares o n t o p o f the landfill.
~A_
A_ ~
A_ A_
346
Small-scale lysimeter A small-scale lysimeter has been constructed in addition to the large lysimeters. Because of its relatively low cost and the possibility of immediate construction the small-scale lysimeter has been built in advance of the testing area. This made it possible to obtain early measurements and first practical experience a b o u t the installation and effectiveness of the measuring systems. The measures obtained will be interpreted in comparison with the measurements from large-scale lysimeters, because uncontrollable random effects could falsify the small-scale lysimeter results. On the other hand, a comparison between both types of lysimeter might give reasons for the future use of small-scale lysimeters. Their low costs makes them ideal as monitoring and testing system for covering or similar systems. A
cllltK~oll pit
larlJI-$ld! lyliil~ter l
r
I
large-scale tysiraeter I I I I
I I
i
~ ' - "
2
1~
-It
e~
,i
~s-venf - -
A' "I I I
I~'.- - - - -
I•
-": .II::"'u°"
m
Fig.4. Vertical cross-section through the testing area. A ~ f----2m
_±1
~-
J__LL:.L:_
~i
_~.~~''
"1 L
1,sin---~ II
. ' ~ : I
.'~']i!~
ii " i
J ,,,.,.
•
rIIu'~/SII
'
?
"
"
" "
"
i'
I..-- ~ ---.I
I
2m
Fig.5. Cross-section through the small-scale lysimeter.
,
'
"
346 The small-scale lysimeter used, consists of a 2.5 m cylinder through the profile of the covering system. Its b o t t o m inclines by 10%. Leachate gathers at the drainage filter. The measuring device is located in the collection pit. The small-scale lysimeter is built up by five prefabricated armoured concrete rings with an inner diameter of 2 m. The rings are tightened by an inner coat of "Inertol". Soil moisture measurements
Measurement of soil moisture changes within the covering system is another possibility to quantify the water movement. By using a neutron probe "Wallingford IH 2" at several measuring points in the testing area, soil water contents at different depths are recorded weekly. The differences between the measurements will be used for the calculation of the water movement in dependence from vegetation, climate and soil characteristics. They will also be used for the localisation of inhomogeneous zones within the barrier layer. Meteorological measurements
Two kilometres west of the landfill site a complete range of meteorological measurements has been regularly recorded. The results from there are improved by a meteorological station on the landfill, which makes continuous measurements of humidity, temperature and precipitation. The precipitation is also measured daily at five locations on the landfill. SUMMARY Although there are some theoretical approaches as for h o w to design a multilayer covering system only few practical examples are known. The landfill discussed will be covered by such a system and simultaneously get an underground barrier for groundwater protection. The research programme for the first time uses flexible large-scale lysimeters and soil moisture measurements, for the estimation o f the water balance within the covering system, At the present time the programme is at its beginning. The experiences at the installation give hope for better measures of the factors acting on covering systems. ACKNOWLEDGEMENTS The remedial conception was the product of an interdisciplinary cooperation. It was planned by Erdbaulaboratorium Dr. Tropp--Dipl.-Ing. Neff und Partner. This paper is presented by permission of the Magistrat der Stadt Frankfurt a.M. and the Federal Department of Research and Technology, who sponsors the research project. The cooperation of each is gratefully acknowledged.
347
REFERENCES Goode, D.J., 1983. Evaluation of simplified techniques for predicting moisture breakthrough of soil liners.Proc. Nat. Conf. Management of Uncontrolled Hazardous Waste Sites,Washington, D.C., pp.161--168. J~iger, B. and Wiemer, K., 1981. MSglichkeiten der Sickerwasserminirnierung in abgeschlossenen Deponien. Verl~ngerung der NutzungsdaUer yon Deponien, Abfallwirtschaft an der T U Berlin, Band 8, pp.174--185. Sanning, D.E., 1983. Remediation of an Inoperative Municipal Waste Landfil -- Windham Landfill. Municipal Environmental Research Laboratory, Preliminary Draft, Cincinnati, 1983. Neff, H. and Walter, H., 1983. Konzeption zum Grundwassersehutz der Hausrniilldeponie Dreieich. Fortschritte der Deponietechnik, Haus der Technik, Essen. Parry, G. and Bell, R., 1983. Draft Report on Covering Systems. N A T O / C C M S Pilot Studie on Contaminated Land.