Manuel Viladevall

Subsoil heterogeneities controlling porewater contaminant mass and microbial diversity at a site with a complex pollution history

This study seeks to improve our understanding of the conceptual model of pollutant transport and fate in cases of DNAPL contamination at sites with a complex contamination history. The study was carried out in an unconfined aquifer of alluvial fans in the Tarragona Petrochemical Complex (Spain). Two boreholes were drilled and continuous cores were recovered in order to carry out a detailed core description at centimeter scale and a comprehensive sampling of borehole cores. The biogeochemical heterogeneity at these sites is controlled by the conjunction of lithological, hydrochemical and microbiological heterogeneities. Biodegradation processes of contaminant compounds take place not only at the level of the dissolved fraction in the aquifer but also at the level of the fraction retained in the fine, less conductive materials as shown by the biodegradation haloes of parent and metabolite compounds. Sampling the low-conductivity levels also allowed us to identify compounds, e.g. BTEX, that are the remaining traces of the passage of old contaminant plumes whose sources no longer exist. This enabled us to describe past biogeochemical processes and to partially account for the processes occurring today. Transition zones, characterized by numerous textural changes, constitute ecotones whose biostimulation could be effective in promoting the acceleration of the remediation of the multiple pollution at these sites.

Metal Mobilization and Zinc-Rich Circumneutral Mine Drainage from the Abandoned Mining Area of Osor (Girona, NE Spain)

AbstractContaminated soil and mine wastes in Spain’s abandoned Osor mining area contain Cd, Co, Pb, Zn, As, Ba, and Sb at levels that exceed Catalonia’s regulatory limits for soils of industrial use. Mine water from the Coral adit, which is the main dewatering system in the Osor area, has circumneutral pH from carbonate and silicate dissolution, and high concentrations of Fe, Mn, Ni, Pb, and Zn. Geochemical modeling showed that smithsonite and hydrozincite were possible solid phases for Zn. The Coral adit is the main source of contaminants to Osor Creek, especially Zn and SO4−2. ZusammenfassungKontaminierte Böden und Bergbaurückstände im stillgelegten Bergbaugebiet Osor in Spanien enthalten Cd, Co, Pb, Zn, As, Ba und Sb in Konzentrationen, die die Katalanischen Grenzwerte für die industrielle Nutzung überschreiten. Das Wasser aus dem Coral-Stollen, dem Hauptentwässerungssystem des Osor-Gebietes, hat einen zirkumneutralen pH infolge Karbonat- und Silikatauflösung und hohe Konzentrationen an Fe, Mn, Ni, Pb und Zn. Geochemische Modellierungen wiesen Smithsonit und Hydrozinkit als mögliche Mineralphasen für Zink aus. Der Coral-Stollen ist die Hauptquelle für die Kontamination des Osor-Baches, insbesondere für Zn und SO4−2.ResumenLos suelos contaminados y los residuos mineros de la zona minera abandonada de Osor (España) contiene Cd, Co, Pb, Zn, As, Ba y Sb a niveles que exceden los límites regulatorios de Cataluña para suelos de uso industrial. El agua de mina desde el socavón Coral, que es el principal sistema de desagüe del area, tiene pH casi neutro debido a la disolución de carbonatos y silicatos y altas concentraciones de Fe, Mn, Ni, Pb y Zn. Mediante modelos geoquímicos se mostró que smithsonita y hidrocincita eran las posibles fases sólidas de Zn. El socavón Coral es la principal fuente de contaminantes, especialmente Zn y SO4−2, para el arroyo Osor.摘要在西班牙已废弃的奥索尔(Osor)矿区,受污染土壤和矿山固废的镉、钴、铅、锌、砷、钡及锑含量已超过西班牙加泰罗尼亚(Catalonia)地区规定的工业用土壤污染界限。科拉尔(Coral)是奥索尔地区的主要疏水矿坑,排出的废水为近中性的碳酸盐和硅酸盐水,含有高浓度的铁、锰、镍、铅和锌。地球化学模拟结果显示,锌可能主要源自固相菱锌矿和水锌矿。科拉尔矿坑是奥索尔河(Osor Creek)各类污染(尤其是锌和硫酸盐)的主要污染源.

Processes controlling the fate of chloroethenes emanating from DNAPL aged sources in river-aquifer contexts.

This work dealt with the physical and biogeochemical processes that favored the natural attenuation of chloroethene plumes of aged sources located close to influent rivers in the presence of co-contaminants, such as nitrate and sulfate. Two working hypotheses were proposed: i) Reductive dechlorination is increased in areas where the river-aquifer relationship results in the groundwater dilution of electron acceptors, the reduction potential of which exceeds that of specific chloroethenes; ii) zones where silts predominate or where textural changes occur are zones in which biodegradation preferentially takes place. A field site on a Quaternary alluvial aquifer at Torelló, Catalonia (Spain) was selected to validate these hypotheses. This aquifer is adjacent to an influent river, and its redox conditions favor reductive dechlorination. The main findings showed that the low concentrations of nitrate and sulfate due to dilution caused by the input of surface water diminish the competition for electrons between microorganisms that reduce co-contaminants and chloroethenes. Under these conditions, the most bioavailable electron acceptors were PCE and metabolites, which meant that their biodegradation was favored. This led to the possibility of devising remediation strategies based on bioenhancing natural attenuation. The artificial recharge with water that is low in nitrates and sulfates may favor dechlorinating microorganisms if the redox conditions in the mixing water are sufficiently maintained as reducing and if there are nutrients, electron donors and carbon sources necessary for these microorganisms.

Temporal hydrochemical and microbial variations in microcosm experiments from sites contaminated with chloromethanes under biostimulation with lactic acid

ABSTRACT The aim of this research was to identify the sequence of degradation processes that leads to the selective enrichment of microorganisms involved in the degradation of carbon tetrachloride and chloroform under conditions of natural attenuation and lactic acid biostimulation. To this end, a comparative study using microcosm experiments was conducted to analyze these two scenarios. The authors used groundwater and sediment collected from a field site located at a petrochemical complex to create the microcosms. Chemical, compound-specific isotope and microbial analyses were performed. A significant finding of this work was the abiotic degradation of carbon tetrachloride. Another result was the identification of biotic reductive dechlorination of chloroform by a bacterium of the Clostridiales order. This study showed that biostimulation with lactic acid produced faster degradation rates of carbon tetrachloride and chloroform. Lactic acid acted as an electron donor and promoted a decrease in the concentration of other electron acceptors such as nitrate and sulfate, which competed with chloromethanes. Thus, biostimulation could be an efficient remediation strategy for sites contaminated with chloromethanes, especially when a sites complex pollution history results in chemical background concentrations that are high in compounds that could potentially reduce natural attenuation.

Biogeochemical exploration using the Thola shrub in the Andean Altiplano, Bolivia

This study concerns the implementation of the most suitable geochemical prospecting methodology to explore for gold deposits in the Andean Altiplano, Bolivia. The main gold ore deposits in this area are associated with the ‘saddle reef antimony-gold type’ in low-grade metamorphic Ordovician–Silurian siliciclastic rocks, placer gold deposits of Miocene age and epithermal gold deposits related to acid volcanic rocks of Tertiary age. An orientation biogeochemical survey was carried out over these deposits by analysing a common plant (Thola shrub) for Au, Sb and pathfinder elements. Thola is widespread and abundant in this semi-arid highland terrain and includes different families such as Compositae (Baccharis incarum/B. tola) and Solanaceae (Fabiana densa) with deep roots (>5 m) that are able to penetrate allochthonous rocks (acid tuffs) and mineralized zones. This orientation survey shows strong anomalies in gold and antimony over saddle reef antimony-gold deposits and anomalies over placer gold deposits where the bottom of the placer is exposed. High concentrations of Au and pathfinder elements were obtained in transects across acid volcanic rocks in the vicinity of abandoned mines. The Thola shrub therefore has the potential to be an excellent exploration medium throughout an area of 140 000 km2 in the Bolivian Altiplano.