R&D Technical Report P1-500/1/TR The likely medium to long-term generation of defects in geomembrane liners Environment Agency Likely medium to long-term generation of defects in geomembranes 1 The Environment Agency is the leading public body protecting and improving the environment in England and Wales. It’s our job to make sure that air, land and water are looked after by everyone in today’s society, so that tomorrow’s generations inherit a cleaner, healthier world. Our work includes tackling flooding and pollution incidents, reducing industry’s impacts on the environment, cleaning up rivers, coastal waters and contaminated land, and improving wildlife habitats. Published by: Authors: Environment Agency Needham, A., Gallagher, E., Peggs, I., Howe, G. & Norris, J. Rio House EDGE Consultants UK Ltd, in association with I-Corp International Waterside Drive, Aztec West Inc., Nottingham Trent University and RAPRA Technology Ltd. Almondsbury, Bristol BS32 4UD Tel: 01454 624400 Fax: 01454 624409 Statement of use: This report presents a review of the processes and rates of ISBN: 1 84432 180 0 geomembrane degradation reported from laboratory and field studies. It reviews landfill monitoring data and research © Environment Agency, January 2004 from related fields to predict future rates of defect generation in geomembrane liners, for use in risk and performance All rights reserved. This document may be reproduced assessment of new landfill sites. This report should be used with prior permission of the Environment Agency. in conjunction with the Agency’s guidance on hydrogeological risk assessment for landfills and LandSim This report is printed on Cyclus Print, a 100% recycled v2.5+. stock, which is 100% post consumer waste and is totally chlorine free. Water used is treated and in most cases Environment Agency project manager: returned to source in better condition than removed. Jonathan Smith, EA Science Group: Air, Land & Water R&D Technical Report P1-500/1/TR Environment Agency Likely medium to long-term generation of defects in geomembranes 2 CONTENTS EXECUTIVE SUMMARY .................................................................................................................. 6 Acknowledgements ........................................................................................................................ 7 1 INTRODUCTION ..................................................................................................................... 8 1.1 OBJECTIVES .........................................................................................................................8 1.2 GEOMEMBRANES BARRIERS ................................................................................................8 1.3 DEFECTS IN GEOMEMBRANE LINERS ...................................................................................9 1.4 SCOPING STUDY.................................................................................................................10 1.5 OUTLINE OF THE REPORT...................................................................................................10 1.6 HOW TO USE THE REPORT .................................................................................................11 2 LITERATURE AND DATA REVIEW PROCESS ................................................................. 12 2.1 LITERATURE SOURCES.......................................................................................................12 2.2 SOURCES OF DATA ON ELECTRICAL LEAK LOCATION SURVEYS .........................................13 2.3 SOURCES OF DATA ON LANDFILL TEMPERATURES .............................................................13 3 GEOMEMBRANE LINERS................................................................................................... 14 3.1 BARRIERS...........................................................................................................................14 3.2 THE STRUCTURE AND PROPERTIES OF POLYETHYLENE FOR GEOMEMBRANE LINERS ......15 3.2.1 The structure of polyethylene.................................................................................15 3.2.2 Structural properties of polyethylene geomembranes........................................18 4 POLYETHYLENE DEGRADATION MECHANISMS........................................................... 20 4.1 TYPES OF DEGRADATION....................................................................................................20 4.2 OXIDATIVE DEGRADATION MECHANISMS ............................................................................22 4.3 ANTIOXIDANTS AND CARBON BLACK STABILISERS .............................................................26 4.4 ANTIOXIDANT DEPLETION ...................................................................................................28 5 LABORATORY STUDIES INTO OXIDATIVE DEGRADATION ......................................... 31 5.1 INTRODUCTION ...................................................................................................................31 5.2 TEST METHODS TO ASSESS DEGRADATION........................................................................31 5.2.1 Oxidative Induction Time.........................................................................................32 5.2.2 Molecular weight.......................................................................................................34 5.2.3 Tensile properties .....................................................................................................34 5.2.4 Stress crack resistance............................................................................................34 5.2.5 Crystallinity ................................................................................................................34 5.2.6 Polymer structure......................................................................................................35 5.2.7 Chemiluminescence.................................................................................................35 5.3 ARRHENIUS MODELLING.....................................................................................................35 5.4 ASSESSING TIME FOR LONG-TERM GEOMEMBRANE DEGRADATION...................................39 5.4.1 Hsuan and Koerner (1995 and 1998)....................................................................40 5.4.2 Sangam (2001).........................................................................................................43 5.4.3 Müller and Jakob (2003)..........................................................................................48 5.5 REVIEW OF LABORATORY RESEARCH INTO GEOMEMBRANE DURABILITY...........................56 5.5.1 Geomembrane materials.........................................................................................56 5.5.2 Test duration..............................................................................................................57 Environment Agency Likely medium to long-term generation of defects in geomembranes 3 5.5.3 Exposure medium and ageing temperature.........................................................57 5.5.4 Thickness effects......................................................................................................58 5.5.5 Absolute OIT values.................................................................................................59 5.5.6 Location of the OIT specimen.................................................................................60 5.5.7 Activation energy......................................................................................................60 5.5.8 Three stage degradation process ..........................................................................61 5.5.9 Selecting the liner service temperature.................................................................62 5.5.10 Conclusions on HDPE geomembrane durability laboratory testing ..............62 6 DURABILITY OF POLYETHYLENE LINERS IN FIELD APPLICATIONS ........................ 65 6.1 REPORTED FIELD PERFORMANCE ......................................................................................65 6.2 REVIEW OF REPORTED FIELD PERFORMANCE ...................................................................67 6.3 EXPOSURE CONDITIONS .....................................................................................................68 6.3.1 Temperatures at the liner.........................................................................................68 6.3.2 Ultraviolet radiation ..................................................................................................76 6.3.3 High energy radiation...............................................................................................77 6.3.4 Availability of oxygen................................................................................................77 6.3.5 Exposure to leachate ...............................................................................................79 6.3.6 External mechanical stresses.................................................................................82 7 STRESS CRACKING............................................................................................................ 83 7.1 INTRODUCTION ...................................................................................................................83 7.2 TESTING..............................................................................................................................85 7.4