title: Fate of arsenic, phosphate and ammonium plumes in a coastal aquifer affected by saltwater intrusion.
abstract: A severe groundwater contamination with extensive plumes of arsenic, phosphate and ammonium was found in a coastal aquifer beneath a former fertilizer production plant. The implementation of an active groundwater remediation strategy, based on a comprehensive pump and treat scheme, now prevents the migration of the dissolved contaminants into the marine environment. However, due to the site's proximity to the coastline, a seawater wedge was induced by the pumping scheme. Additionally the groundwater flow and salinity patterns were also strongly affected by leakage from the site's sewer system and from a seawater-fed cooling canal. The objective of this study was to elucidate the fate of arsenic and its co-contaminants over the site's history under the complex, coupled hydrodynamic and geochemical conditions that prevail at the site. A detailed geochemical characterisation of samples from sediment cores and hydrochemical data provided valuable high-resolution information. The obtained data were used to develop various conceptual models and to constrain the development and calibration of a reactive transport model. The reactive transport simulations were performed for a sub-domain (two-dimensional transect) of an earlier developed three-dimensional flow and variable density solute transport model. The results suggest that in the upper sub-oxic zone the influx of oxygenated water promoted As attenuation via co-precipitation with Al and Fe oxides and copper hydroxides. In contrast, in the deeper aquifer zone, iron reduction, associated with the release of adsorbed As and the dissolution of As bearing phases, provided and still provides to date a persistent source for groundwater pollution. The presented monitoring and modelling approach could be broadly applied to coastal polluted sites by complex contaminant mixture containing As.
authors.affiliation: Department of Earth Sciences, "Sapienza" University, Rome, Italy.
authors.forename: N
authors.initials: N
authors.lastname: Colombani
authors.affiliation: Department of Physics and Earth Sciences, University of Ferrara, Ferrara, Italy. Electronic address: mtm@unife.it.
authors.forename: M
authors.initials: M
authors.lastname: Mastrocicco
authors.affiliation: CSIRO Land and Water, Private Bag No. 5, Wembley, WA 6913, Australia; School of Earth and Environment, University of Western Australia, 35 Stirling Hwy, Nedlands, WA 6009, Australia; National Centre for Groundwater Research and Training (NCGRT), Flinders University, GPO Box 2100, Adelaide, SA 5001, Australia.
authors.forename: H
authors.initials: H
authors.lastname: Prommer
authors.affiliation: Department of Earth Sciences, "Sapienza" University, Rome, Italy.
authors.forename: C
authors.initials: C
authors.lastname: Sbarbati
authors.affiliation: Department of Earth Sciences, "Sapienza" University, Rome, Italy.
authors.forename: M
authors.initials: M
authors.lastname: Petitta
mesh_terms: D000537:Aluminum Oxide / Q000737:chemistry; D064751:Ammonium Compounds / Q000032:analysis*; D001151:Arsenic / Q000032:analysis* / Q000737:chemistry; D011232:Chemical Precipitation; D004784:Environmental Monitoring / Q000379:methods; D005290:Ferric Compounds / Q000737:chemistry; D060587:Groundwater / Q000032:analysis* / Q000737:chemistry; D062070:Hydrology / Q000379:methods; D008962:Models, Theoretical; D010710:Phosphates / Q000032:analysis*; D054712:Salinity; D012623:Seawater; D014874:Water Pollutants, Chemical / Q000032:analysis* / Q000737:chemistry
chemical_list: D064751:Ammonium Compounds; D005290:Ferric Compounds; D010710:Phosphates; D014874:Water Pollutants, Chemical; C000499:ferric oxide; D000537:Aluminum Oxide; D001151:Arsenic
keywords: Arsenic; Coastal aquifer; Groundwater pollution; Reactive transport modelling