Drilling and Grouting for the Rehabilitation of Contaminated Areas: An Italian Case History-Paper

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The paper describes the rehabilitation of two abandoned municipal-waste landfills in former calcarenite quarries near Manfredonia, Italy. Groundwater investigations found that leachate was escaping through fractures and karst features in the underlying rock. Rather than excavating and relocating the waste, the project created an in-situ containment system.<br /><br />The design combined a grouted bottom barrier with grouted perimeter barriers, tied together and completed with a surface cap. Horizontal Directional Drilling (HDD) was used to install curved, sub-horizontal boreholes beneath the waste without penetrating it. Up to 150 m long, the holes were guided to within 0.3 m of their planned paths. A total of 565 bottom-curtain holes, drilled in two levels, treated a rock layer at least 3 m thick. The perimeter barriers used three rows of sub-vertical holes.<br /><br />Cement-based grouts sealed larger openings, while durable mineral-silicate mixes treated finer fissures. Staged injection methods and computerized monitoring controlled grout pressure, volume and flow. Verification drilling, video inspections, permeability tests and geophysical surveys assessed the completed barriers. Water tests measured 2–5 Lugeon units, meeting the design target of no more than 5.<br /><br />The landfill surfaces were reshaped and capped with HDPE membrane, geogrid, geotextile and topsoil. The completed system encapsulated the waste while leaving it in place, avoiding the environmental risks and time associated with removal. Work began in early 2010 and was completed in January 2011. The authors conclude that HDD-assisted drilling and grouting provided an innovative, cost-effective means of containing contamination with minimal disturbance to the waste.

Keywords

landfill rehabilitation

municipal waste landfill

in-situ containment

horizontal directional drilling

grouted barrier

leachate containment

karst fractures

calcarenite quarry

HDPE cap

grouting injection