ABSTRACT:

Prior to the mid 1980s, asphalt barriers were primarily used to control water seepage from facilities such as ponds, impoundments and earth dams. Asphalt was applied as hot-sprayed buried asphalt membranes and as asphalt concrete for the barrier layers. The establishment of rules for hazardous and solid waste landfill designs focused the industry toward composite liners consisting of geomembranes and compacted soil. However, in the mid-1980s, resurgence into the use of asphalt concrete for waste isolation was initiated by the US Department of Energy in their quest for very-long-term (1000+ years) hydraulic barriers for radioactive and mixed waste sites. Existing data demonstrate that asphalt concrete barriers and fluid-applied asphalt layers can provide extremely low hydraulic conductivities (<1x10–11 cm/s). On-going research results show that asphalt may have the robust properties for a service life approaching 1000 years. Field demonstration of the attributes of asphalt concrete barriers through test pads and monitored prototypes can answer the question of equivalency or superiority of asphalt concrete barriers for waste isolation.

INTRODUCTION

Asphalt containing materials have been used for hydraulic barriers for ages, possibly more than 5000 years (Freeman et al. 1994, Kays 1977, Asphalt Institute 1976). Hot-sprayed buried asphalt membranes have been used for lining water containment structures and controlling seepage through dams for about the last 60 years (Creegan and Monismith 1996, Hickey and Jones 1968, Smith 1962). Over the last 30 years, asphalt concrete has been used for hydraulic barriers and in some cases for liners for waste containment facilities (Asphalt Institute 1976). However, with the initiation of landfill composite (geomembrane + compacted soil) liner systems for waste disposal have dominated new and expanded facilities. Most regulations allow for site-specific or alternative liner designs provided they meet environmental performance criteria set forth in the rules.

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