Assessment of optimum width and longevity of a permeable reactive barrier installed in an acid sulfate soil terrain

Abstract

Removal of contaminants from groundwater using permeable reactive barriers (PRBs) is a cost-effective and popular engineering solution used throughout the world. Dissolved pollutants in groundwater are removed through geochemical processes that make PRBs effective for different types of contaminants. In achieving this, it is vital to determine the optimum width of the PRB to allow adequate residence time within the barrier and to establish its longevity. For this purpose, both field monitoring and geochemical modelling were conducted for a trial PRB located in the Shoalhaven Floodplain, south of Wollongong in Australia. In this study, the optimum PRB width is evaluated numerically, based on the neutralization effectiveness, i.e., when acidic groundwater travels through the alkaline PRB. A model developed previously has been extended considering the residence time, reaction kinetics, mineral precipitation–induced reduction in porosity and hydraulic conductivity, influent concentrations of the contaminants, and groundwater flow velocity. Longevity of the PRB is determined with respect to groundwater flow rates and amount of reactive material consumed.

Funnel and Gate Permeable Reactive Barrier Configuration for Contaminated Groundwater Remediation – Designing, Installation, and Modeling: A Review

“…The key regulating elements for longevity are the groundwater flow rate and the amount of reactive media consumed [58]. The reactive materials either immobilize or transform the pollutants (biologically or abiotically), such that treated groundwater flowing down the PRB's hydraulic gradient shouldn't endanger water resources or other receptors [59].…”

Passive removal of sulphate and heavy metals from acid mine drainage using sewage sludge and fly ash

“…The higher the k value, indicating a better sulphate reduction. This value of rate constant will be used for barrier thickness calculation in column test [25].…”

Chemical clogging of granular media under acidic groundwater conditions

“…show rapid clogging of columns within six months, in a prototype (real-life) field PRB this translates to several years when applied to field conditions using geochemical computational models incorporating the field dimensions. For instance, Pathirage and Indraratna (2014) found that the longevity of a pilot scale PRB (filled with recycled alkaline concrete aggregates) was greater than 15 years when transformed from 1D column dimensions to those of the field trial with a width of 1.2m. The Authors have modified the model for limestone, which was calibrated with the current data.…”

“…Nevertheless, chemical clogging of the PRB granular assembly baffles the reactivity and treatability of filter grains due to encrustation of reactive media surfaces and accumulation of secondary mineral precipitates within the voids. Even partial clogging by chemical precipitates affects the groundwater flow paths through the PRB, hence, soil properties such as porosity and hydraulic conductivity are substantially reduced (Li and , Indraratna et al, 2014b, Pathirage and Indraratna, 2014. Moreover, the longevity of the PRB is also decreased even before the desired treatment is achieved.…”