Assessing and Managing Large‐Scale Geochemical Impacts From Groundwater Replenishment With Highly Treated Reclaimed Wastewater

Abstract

Reuse of wastewater through a combination of advanced wastewater treatment (AWT) and managed aquifer recharge (MAR) is an important water management option. As an integral part of any AWT-MAR system, the geochemical compatibility of the recharged water with the targeted aquifer must be assessed to avoid groundwater quality deterioration. Although short-term field experiments may uncover potentially concerning sediment-water disequilibria, an advanced analysis is often required to understand the long-term geochemical impacts of large-scale MAR. Here, we develop and apply a pragmatic approach to upscale and verify the previously derived local-scale geochemical understanding to the spatial and temporal scale required for assessing and managing large-scale and long-term impacts resulting from the recharge of AWT-processed water. We use Australia's largest MAR scheme, in which aerobic, purified water is injected into deep, anaerobic, pyritic aquifers as an illustrative example. In this case, the local-scale understanding was derived from a comprehensive field trial and the interpretation of the data through a trial-scale high-resolution reactive transport model (RTM). Based on (i) the trial-scale RTM, (ii) new data from the early phase of the full-scale MAR, and (iii) downscaling of an existing, regional-scale flow model, we developed an upscaled RTM to assess two critical issues for the large-scale groundwater replenishment of Perth deep aquifers, that is, the sustainability of native pH buffering processes and the dynamics of fluoride release and attenuation. In a final step we illustrate how the upscaled RTM can be applied to assess how changes in the AWT affect long-term groundwater pH changes.

Mobilization of Arsenic and Other Naturally Occurring Contaminants during Managed Aquifer Recharge: A Critical Review

“…However, the water quality shifts observed under batch conditions were expected to be less pronounced during field-scale operations due to (1) oxygen supply to the aquifer being limited in injection water compared to continuous replenishment in the laboratory experiment, (2) mixing of waters from different aquifer zones, (3) prevention of metal accumulation by flushing of injection water, and (4) sediment buffering and resorption down gradient. 70,142 Later, field-scale MAR operations in the same aquifer showed that sufficient pH buffering occurred, predominantly by proton buffering at exchange sites, 143,144 and metals mobilization was not a significant concern. 144 If recharge water introduces competitive ions, contaminant desorption and mobilization can occur from sorption sites associated with Fe (oxyhydr)oxides or other minerals.…”

“…70,142 Later, field-scale MAR operations in the same aquifer showed that sufficient pH buffering occurred, predominantly by proton buffering at exchange sites, 143,144 and metals mobilization was not a significant concern. 144 If recharge water introduces competitive ions, contaminant desorption and mobilization can occur from sorption sites associated with Fe (oxyhydr)oxides or other minerals. This was observed in Bolivar, Australia, during an ASR trial, where phosphate in the injectant limited the amount of As adsorption on Fe (oxyhydr)oxides during injection, while reductive dissolution of Fe (oxyhydr)oxides caused As mobilization during the storage and recovery phases.…”

“…Laboratory incubations with sediments from an ASR site in the Leederville Aquifer, Australia, showed desorption of Ni, Co, Zn, Cd, and Pb from Fe (oxyhydr)­oxides at pH values <4.5 caused by acidity produced by pyrite and organic carbon oxidation; low concentrations of As were released and correlated to pyrite oxidation. However, the water quality shifts observed under batch conditions were expected to be less pronounced during field-scale operations due to (1) oxygen supply to the aquifer being limited in injection water compared to continuous replenishment in the laboratory experiment, (2) mixing of waters from different aquifer zones, (3) prevention of metal accumulation by flushing of injection water, and (4) sediment buffering and resorption down gradient. , Later, field-scale MAR operations in the same aquifer showed that sufficient pH buffering occurred, predominantly by proton buffering at exchange sites, , and metals mobilization was not a significant concern . In general, studies more commonly report high sediment buffering capacity due to calcite dissolution, and significant decreases in groundwater pH have not been reported during MAR.…”

Biological and Physical Clogging in Infiltration Wells: Effects of Well Diameter and Gravel Pack

“…The referenced studies investigated only the potential of SDW for clean water recharge. In practice, however, storm water (Page et al 2010;Gao et al 2014), water from ephemeral rivers (Alataway and El Alfy 2019), and treated waste water (Goren et al 2014;Sun et al 2020) are used for MAR. While storm waters contain high loads of suspended particles, treated waste waters are usually characterized by high concentrations of nutrients, bacteria, and dissolved organic matter (Icekson-Tal et al 2003;Asano and Cotruvo 2004).…”

Comparative Assessment of Methods for Coupling Regional and Local Groundwater Flow Models: A Case Study in the Beijing Plain, China

“…Since the design of the grid is very flexible, the grid refinement is no longer restricted by the shape grid and refinement area. Multi-scale models can be constructed by the USG method either when the boundary of the local model area is irregular or the hydrological stresses change in the local area might have a significant influence on the larger region [19,20]. Finer grid resolution can be used to refine the area near river channels [21,22] or only on the model top layer [23] to investigate surface and groundwater interaction.…”