Stefan Melchior

Results from 18 years of in situ performance testing of landfill cover systems in Germany.

The water balances and the long-term performance of different landfill cover systems have been measured in situ in large-scale lysimeters on the landfill Hamburg-Georgswerder, Germany since 1988. The cover systems including different barrier components for water transport were constructed with state-of-the-art technology and have been excavated at several occasions especially to inspect the structure of the barriers. For the first time, the irreversible impact of crack formation in cohesive soil barriers and geosynthetic clay barriers due to desiccation, shrinkage, ion exchange, and plant root penetration has been observed and quantified in this study. After four years of good performance, these covers began to leak between 90 and 200 mm/year (average precipitation of 860 mm/year). The hydraulic conductivity of the cohesive soil barriers increased from 2× 10−10 to 9× 10−8  m/s , the daily peaks of the leakage through the geosynthetic clay barriers from initial values around 2× 10−11  to 2× 10−7 m3 / ( m...

The Use of Capillary Barriers in Landfill Covers

Different technical systems are available to cover disposal sites. Compacted soil liners and plastic liners (high density polyethylen, HDPE) are most commonly used to construct barriers. Both systems, often used in combination, have specific advantages and disadvantages. The latter essentially are: construction controlled by weather conditions, the necessity of complicated quality assurance and test programs, high costs, un-knowns with respect to the longterm stability of the systems (e.g. aging of HDPE, dessication and shrinkage of soil liners and preferential flow along macropores). Capillary barriers, in some cases, can be more efficient and cost-effective.

Results of the Long-Term Monitoring of Different Types of Covers on the Georgswerder Landfill (Hamburg, FRG)

The long-term performance of different covers has been monitored on the Georgswerder landfill (Hamburg, FRG) since 1988. The compacted soil liners have lost their efficiency due to desiccation and shrinkage. The flexible membrane liners and an extended capillary barrier perform very well. A slight periodical desiccation due to thermally induced liquid and vaporous water transport is observed within the soil component of the composite liners (flexible membrane above compacted soil liner). The suitability of compacted soil liners in landfill covers is questioned and the use of other systems with an intrinsic controllability proposed.

Studies on the Desiccation Risk of Cohesive Soil Liners for Landfills Due to Thermally Induced Water Movement

Landfill covers and base liners are constructed according to the latest technology as combined systems with plastic liners (High Density Polyethylene, HDPE) on top of compacted cohesive soil material (often referred to as “clay liners”). In case of a failure of the plastic liner the concept of combined liners solely relies on the efficiency of the compacted cohesive soil liner.

Zur Eignung des „Hydrologic Evaluation of Landfill Performance“ (HELP) Modells der U.S.-Umweltbehörde zur Simulation des Wasserhaushalts von Deponieabdecksystemen

Bei der Abfalldeponierung und Altlastensanierung ist die Einkapselung des Deponie-korpers eine wichtige Sicherungsmasnahme. Bei der Konzeption von Oberflachenabdecksystemen spielt die Abschatzung ihres Wasserhaushalts eine wesentliche Rolle. Hierfur wurde fur die Umweltbehorde der USA das „Hydrologie Evaluation of Landfill Performance“ (HELP)-Modell entwickelt. Im Beitrag werden einige wesentliche Beschrankungen sowie einige Schwierigkeiten in der Handhabung dieses fur die USA entwickelten Modells aufgezeigt und in einem Outputvergleich Modellergebnisse anhand von Mesergebnissen der Wasserhaushalts-Testfelder auf der Deponie Georgswerder (Hamburg) uberpruft.

Studies on the Efficiency of Compacted Cohesive Soil Liners for Landfills

Since 1987 six test fields with different types of covering systems are being studied on the Georgswerder landfill in Hamburg. Besides combined systems with plastic liners on top of compacted cohesive soil liners, and an extended capillary barrier design, compacted cohesive soil liners without superjacent plastic liners are being tested. The measurements and experiments show that two years after installation the efficiency of the compacted soil liners is significantly reduced due to desiccation and shrinkage. Inspections of the liners show that a soil structure, already present at the time of installation, has become hydraulically effective during the dry summer of 1989. The measurements at the combined liner systems indicate that besides capillary rise of liquid water vaporous water movement too contributes to the desiccation. The results probably have consequences for the use of compacted cohesive soil liners without additional liners like covering plastic membranes or subjacent capillary barriers in general. In any case the structure of the liner material has to be destroyed, the individual lifts of the liner must mesh to avoid joints, and any formation of macropores and cracks has to be ruled out by technical measures.

Der Einsatz von Kapillarsperren in Deponieabdecksystemen

Fur die Oberflachenabdichtung von Deponien und Altlasten stehen verschiedene technische Systeme zur Verfugung. Am haufigsten werden verdichtete bindige Sedimente als sogenannte mineralische Dichtschichten und Kunststoffdichtungsbahnen aus Polyethylen hoher Dichte (PEHD) eingesetzt. Beide, oft auch kombiniert eingesetzte Dichtverfahren weisen spezifische Vor- und Nachteile auf. Die Nachteile liegen im wesentlichen in den hohen Anforderungen, die an die Witterungsbedingungen und die Qualitatssicherung wahrend des Einbaus zu stellen sind, in den folglich hohen Kosten solcher Systeme und in der Ungewisheit uber deren Langzeitstabilitat (Standzeiten von PEHD, Austrocknungsgefahr und Makroporenbildung in mineralischen Dichtschichten u. a.). Kapillarsperren konnen unter gewissen Rahmenbedingungen effektiver und kostengunstiger sein.

Meßdatenerfassung und -verarbeitung in einem Forschungsprojekt zur Untersuchung der Wirksamkeit mehrschichtiger Deponieabdecksysteme (Mülldeponie Georgswerder)

Im Rahmen der Sanierung der durch Dioxinfunde in ihrem Sickerwasser in die Schlagzeilen geratenen Mulldeponie Georgswerder in Hamburg werden eine Reihe von Forschungs- und Entwicklungsvorhaben zur Entwicklung von Sanierungstechniken und zur Kontrolle der Wirksamkeit der ergriffenen Sicherungs- und Sanierungsmasnahmen durchgefuhrt. Das hier vorgestellte Projekt befast sich mit der vergleichenden Untersuchung des Wasserhaus¬halts mehrschichtiger Deponieabdeckungen (Naheres in MELCHIOR und MIEHLICH, 1987 und 1989).