Clamshell vs. Backhoe Excavation of Permeable Reactive Barriers

Abstract

Problem statement: Permeable Reactive Barriers (PRBs) were one of the most widespread solutions for the remediation of contaminated aquifers. Although, a variety of excavation methods had been developed, backhoe (hydraulic excavators) were commonly used for the construction of PRBs in North America. Approach: In Europe, the most common method of slurry excavation was with a hydraulic grab and crane. The aim of this study was to compare clamshell and backhoe excavation techniques and to describe the installation of a full scale PRB using a crawler crane equipped with a hydraulic grab. Results: Backhoes had been used on a larger number of PRB installations and permit a rapid rate of excavation and generally require less skill to master. Long stick backhoes were capable of digging as deep as 30 m. Instead, clamshell excavators require more skill to use, but were able to excavate to a depth of more than 70 m, with a high degree of precision. Two similar case studies were presented to compare the relative merits of the two excavation techniques. Conclusion/Recommendations: The first describes a funnel and gate system excavated by long stick backhoe, in the US, whose longest gate is 0.73 m thick, 68 m long and up to 13 m deep. The latter is a 0.6 m thick, 120 m long and 13 m deep continuous PRB, excavated by crane mounted grab to remediate a chlorinated hydrocarbons plume, in Avigliana, near the city of Torino, in Italy. Comparison of the two techniques is performed on the availability of instrumentation, excavation power and precision, potential for cost savings.

Support Tool for Identifying In Situ Remediation Technology for Sites Contaminated by Hexavalent Chromium

“…The PRBs are technically and economically sustainable if the depth of the installation does not exceed 25 m from g.l. [69][70][71][72]. Aquifers with high hydraulic conductivity are difficult to treat with this type of installation, because the reactive layer must have permeability of at least an order of magnitude greater than the aquifer to intercept effectively the contaminated plume.…”

Biochar/Biopolymer Composites for In-Situ Groundwater Remediation

“…Recently, new in-situ adsorption processes have been developed based on injectable colloidal activated carbon (CAC) stabilized by humic acids and carboxymethylcellulose (CMC) [14,15]. This approach allows remediation at greater depths in that digging a trench at great depths (over 30 m) is significantly more complex than drilling [16]. However, implementing CAC in in-situ remediation approaches remains niche due to challenges in distributing the colloid effectively without clogging porous media.…”