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Abstract "Heft 43"

Freiburger Bodenkundliche Abhandlungen

Schriftenreihe des

Institut für Bodenkunde und Waldernährungslehre

der Albert-Ludwigs-Universität Freiburg i.Br.
Schriftleitung: P. Trüby

Heft 43

Norbert Wolsfeld

Bodenphysikalische Eignung mineralischer Oberflächenabdichtungssysteme
für Monodeponien der Stahlindustrie

(Feldversuche zur Beurteilung der Leistungsbeiträge mineralischer
Konvektionssperren und einer zielgerichteten Rekultivierung an der
Systemleistung von Oberflächenbarrieren)

Freiburg im Breisgau 2005

ISSN 0344-2691


The main target of this investigation was to verify to what extend by-products or residues of iron and steel industries can be used as efficient sealing materials for the capping of in house landfills (mineral mono-landfills) of this branch of industry with properties deviating from typical domestic waste landfills.

Field tests in 12 lysimeters with 200 m2 surface area each have been carried out to monitor the most interesting water balance parameters of surface- runoff, drainage flow and percolation ratio. Thus the following lysimeter test fields have been es-tablished:

• 6 test fields with single-layer sealing Systems based on alternative mineral sealing materials,

• 3 test fields with various restoration thicknesses and

• 3 test fields with common sealing Systems as references.

Additionally the most important meteorological data have been measured next to the test fields. The evaluation comprised the efficiency of the sealing compounds, the individual contribution to the System achievement of the restoration and the total efficiency of the complete sealing Systems in their development during the investigation period of 32 month.

The sealing effect of the alternative sealing mixtures is based on grain size opti-mised mixtures of different mineral by-products of the iron and steel production. In addition, some kind of seif compaction process induced by precipitation of CaCO3 in CO2- and water conducting pores can be observed in sealing mixtures based on calcarous steelwork slags.

Mixtures of ladle slag and blast furnace sludge achieved k-values of 3,6*10"9 m/sec after emplacement and compaction in the lysimeter. The seif compaction process effected k-values of 5*10"" m/sec within 32 month. For the sealing mixture of ladle slag : blast furnace sludge 1:1 w/w, the 95 %-fractile of the k-values calcu-lated for n = 976 monitoring days reached 1,9*10-10 m/sec. The complete sealing System with a restoration layer of 100 cm thickness showed a percolation quantity of only 2,05 l/m2 and a ratio of 0,13 % of the total atmospheric precipitation of 1562 l/m2.

Silica gel- and sewage sludge amended electric arc furnace slag showed k-values of 1,9* 10"8 m/sec after emplacement in the lysimeter. However the water conductivity decreased to k-values of 5,9*10"" m/sec within the monitoring period. Dur-ing the whole period of 32 months the k-values remained below the 95 %-fractile of k = 3*10"'° m/sec. The complete sealing system with a restoration layer of 100 cm thickness achieved a percolation quantity of 2,50 l/m2 (= 0,16 % of the precipitation input).

By Substitution of 50 % of the natural clay in a conventional clay liner by blast furnace sludge a sealing material with a water conductivity coefficient of k = 1,4* 10"9 m/sec could be generated. Despite of variations of the water conductivity in-between k = 3,6 * 10"10 and l,7*10"10 m/sec dependent on water content for the observed years of 2002 to 2004, the 95 %-fractile of k = 1,6* 10"9 m/sec was en-sured. The complete sealing System with a 100 cm thick restoration layer showed a percolation quantity of 13,5 l/m2 and a ratio of 0,86 % of the total precipitation input of 1562 l/m2.

In comparison, the Standard sealing system based on a kaolinitic clay liner reached after emplacement and compaction k-values of 9,3*10"" m/sec and a 95%-fracf:le of the k-values calculated forn = 976 monitoring days of k= 1,8*10"" m/sec.

The measurement of the water balance of complete top sealing Systems provided conclusions to the individual contribution of the restoration to the system results.

It could be shown that a restoration with a loosely piled up 100 cm thick soil layer had a loss of 85 % of the precipitation input by evapotranspiration taking the aver-age of the monitored period and variations examined. Under the same conditions a 200 cm thick restoration layer achieved even 94 % of evapotranspiration loss.

Thereby, in all restoration variations a double-layer restoration soil was used con-sisting of a silty and partly loamy sand with approximately 23 % coarse grain frac-tion serving as main soil layer and silty sand with high humus content as topsoil.

By using the correlation between water content and pF-values to derive pore size equivalents it could be demonstrated that the loose piling up retained the coarse pore structure of the restoration soil. Furthermore the total pore volume increased significantly in-between march 2003 and August 2004 from 41 % to 45 % in 25 -45 cm soil depth.

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