Performance of a PRB for the Remediation of Acidic Groundwater in Acid Sulfate Soil Terrain

Computers and Geotechnics

Pathirage

Rowe

et al. 2014

Self Cite

This study focuses on coupling geochemistry with geo-hydraulics to enable time-dependent modelling of the remediation of acidic groundwater using an alkaline permeable reactive barrier (PRB). Chemical clogging due to secondary mineral precipitates reduces the porosity and hydraulic conductivity of the reactive medium. The governing equations are incorporated into commercial numerical codes, MODFLOW and RT3D. An original algorithm was developed for RT3D to simulate geochemical reactions occurring in the PRB. The results and the model predictions are in agreement, confirming that the hydraulic conductivity reduction due to mineral precipitation occurs at the start of permeation and continues until halfway through the testing phase. This study focuses on coupling geochemistry with geo-hydraulics to enable time-dependent modelling of the remediation of acidic groundwater using an alkaline permeable reactive barrier (PRB). Chemical clogging due to secondary mineral precipitates reduces the porosity and hydraulic conductivity of the reactive medium. The governing equations are incorporated into commercial numerical codes, MODFLOW and RT3D. An original algorithm was developed for RT3D to simulate geochemical reactions occurring in the PRB. The results and the model predictions are in agreement, confirming that the hydraulic conductivity reduction due to mineral precipitation occurs at the start of permeation and continues until halfway through the testing phase.Keywords: acidic groundwater, chemical clogging, permeable reactive barrier, mineral precipitation, transport modelling 2 IntroductionAcidic groundwater generated from acid sulfate soil (ASS), which occupies over 200,000 This head will be the input into MODFLOW which in return will be used to couple the groundwater flow with reaction kinetics in RT3D. User-defined module facilitated in RT3D was used to feed the geochemical algorithm into the numerical codes. This model is beneficial for practising engineers and scientists who have to deal with ASS especially in coastal areas of Australia. Laboratory column experiments were carried out under constant flow of 1.2 mL/min (millilitres per minute) using a Masterflex peristaltic pump (Fig. 2). Two simultaneous column experiments were run as suggested by [29] one for sampling and one to take pressure readings. The purpose of running two simultaneous columns instead of one column was to eliminate the impact of sampling activities on the pressure in the column [29]. The pressures at the onset were measured for both columns using pressure transducers at both ends which were almost the same. The input and environmental conditions were maintained the same for both columns, so the pressure readings calculated at each port was assumed similar to the respective sampling port at the same height in the other column. Methodology Laboratory column experimentsThe crushed recycled concrete used in this study was a waste material discarded after the demolition of old concrete structures. The particle size of crushed concre...

“…4). This is probably due to the OH -being in equilibrium during the depletion of carbonate minerals [16]. The experimental and predicted values of pH along the column are shown in Fig.…”

Section: Resultsmentioning

confidence: 98%

Section: Resultsmentioning

confidence: 99%

Coupled hydro-geochemical modelling of a permeable reactive barrier for treating acidic groundwater

Computers and Geotechnics

Pathirage

Rowe

et al. 2014

Self Cite

“…While long-term monitoring has revealed that the PRB has maintained a groundwater pH from alkaline to neutral (pH 10.0-7.2) and Al and total Fe below average concentrations of 2 and 0.5 mg/L respectively inside the barrier, a slow decrease in performance due to armouring of the recycled concrete caused by the precipitation of Al-and Fe-oxy/hydroxide minerals has been observed (Indraratna et al, 2010). Laboratory column experiments and geochemical modelling showed a reduction of 50% in the actual ANC of the reactive media compared to its theoretical ANC (Regmi et al, 2011b).…”

Section: Introductionmentioning

confidence: 99%

“…Over time, precipitates occupy the pore spaces between the recycled concrete within the PRB, reducing its porosity and hydraulic conductivity. However, field observations and modelling have shown that in many cases this loss of porosity and hydraulic conductivity occurs at relatively low rates (ITRC, 2011), which is the case for the pilotscale PRB as currently indicated by steady piezometric head (Indraratna et al, 2010).…”

Section: Introductionmentioning

confidence: 99%

Permeable reactive barrier rejuvenation by alkaline wastewater

Banasiak

Environmental Geotechnics

Lugg

et al. 2015

Self Cite

Chemical armouring of recycled concrete in a permeable reactive barrier (PRB) used for the neutralisation of acidic groundwater in acid sulfate soil terrain significantly decreases its acid neutralising capacity (ANC) by approximately 50% compared with its theoretical ANC. A long-term column test was conducted under simulated field groundwater conditions to assess the re-conditioning of armoured recycled concrete aggregates with alkaline wastewater, with the aim to restore and enhance the ANC and longevity of the PRB. The benefits of alkaline wastewater injection included sharp but short enhancement of the recycled concretes' ANC, as indicated by an increase in effluent pH (pH 3 to 7·7) and alkalinity (0 to 21·6 mM CaCO3) and a reduction in oxidation reduction potential (ORP,. While the results showed that the alkaline wastewater did not significantly reduce chemical armouring, it aided in the liberation of lodged mineral precipitates between concrete aggregates, reducing the severity of chemical and physical clogging. Batch tests demonstrated that, when exposed to acidic water, the ANC of recycled concrete pre-conditioned with alkaline wastewater was enhanced as indicated by higher pH, lower ORP and greater release of calcium (Ca2+) and alkalinity, compared to non-pre-conditioned concrete.

“…They commonly consist of a trench filled with reactive material selected to treat contaminants of concern. Research has just begun in Australia to investigate the use of PRBs to treat acidic groundwater from ASS (Waite et al, 2002;Indraratna et al, 2010). This paper outlines the findings of current research on the application of a PRB utilizing recycled concrete for the remediation of ASS in the Shoalhaven Floodplain of southeast NSW, Australia.…”

Section: Introductionmentioning

confidence: 99%

Permeable Reactive Barrier (PRB) Technology: An Innovative Solution for the Remediation of Acidic Groundwater from Acid Sulphate Soil (ASS) Terrain

Banasiak

2012

GeoCongress 2012

Self Cite

The remediation of acidic groundwater contaminated with potentially toxic metals such as aluminium (Al) and iron (Fe) resulting from the oxidation of sulphidic materials in acid sulphate soils (ASSs) is a challenging geo-environmental problem that requires innovative engineering solutions. In low-lying coastal floodplains, the remediation strategies of groundwater manipulation (e.g. fixed-level weirs) and tidal buffering (e.g. two-way modified floodgates) are not feasible due to the risk of flooding during heavy rainfall events and their inability to prevent pyritic oxidation. In view of this in 2006, the first pilot subsurface permeable reactive barrier (PRB) using recycled concrete for the remediation of acidic groundwater (~ pH 3) was employed in ASS terrain in southeast New South Wales, Australia. While monitoring has confirmed the PRB has successfully neutralized the acidic groundwater to ~ pH 7.3 and removed ~ 95% of Al and Fe, this technology is not without its challenges. These have included the: (1) selection of the appropriate reactive material; (2) elucidation of the mechanisms involved in the neutralization of the acidic groundwater; (3) chemical armouring and possible clogging of the recycled concrete by Al and Fe oxy/hydroxide precipitates; and (4) thus, uncertainty regarding the longevity of the PRB. This paper will present details on the screening process of reactive materials, the installation of the PRB, the column experiments simulating the flow of acidic groundwater through the PRB for the determination of the predominant neutralization reactions occurring within the PRB, the long-term performance of the PRB and the current research strategy for determining its longevity.