Les aigües subterrànies al Maresme

The concept of the aquifer is introduced and the characteristics of subsurface rocks to form a groundwater-bearing formation are analysed in this work. The conceptual model of groundwater flow in the granitic aquifer of the Maresme and its connection with the aquifers on the coastal plains are studied, as well as the connection with the alluvial aquifers of the lower part of the La Tordera river and delta. How the water recharge takes place and how natural and artificial discharges occur are also studied. The impacts on the system caused by artificial discharges are also analysed. The analysis includes the quantitative and qualitative state of groundwater based on the water bodies defined by the Catalan Water Agency. The problem of groundwater contamination by chlorinated solvents in the aquifer of the stream of Sant Pol de Mar is presented as an example of the pressures related to groundwater quality. Finally, the origin of the Maresme geothermal manifestations (geothermal waters and springs of sparkling water), which is related to groundwater flow through deep faults and extends beyond the surficial granitic aquifer system is also studied

A new Method for determining Compound Specific Carbon Isotope of Chlorinated Solvents in Porewater

A new method for the extraction of chlorinated solvents (CSs) from porewater with dimethylacetamide (DMA) used as a solvent and the determination of δ13C by gas chromatography-isotope ratio mass spectrometry (GC-IRMS) with solid-phase microextraction (SPME) are presented. This method was used for the determination of δ13C of chloroethenes and chloromethanes. The extraction of the CSs from porewater with DMA led to a minimal loss of mass of solvent and chlorinated compounds. The accuracy of the method was verified with the analysis of the pure injected compounds using elemental analyser - isotope ratio mass spectrometry (EA-IRMS). It has been effectively applied in a study area in saturated soil samples of a pollutant source zone of perchloroethylene (PCE) and trichloroethylene (TCE). The limit of quantification of the new method was 0.034 µg/g for PCE and TCE for 10-20 g of soil sample. This new method allows for compound-specific isotope analysis (CSIA) of CSs in porewater, which can be beneficial in sites where the identification of contamination sources and the behaviour of the contaminants are not clear

Natural attenuation of pools and plumes of carbon tetrachloride and chloroform in the transition zone to bottom aquitards and the microorganisms involved in their degradation

In the transition zone between aquifers and aquitards, DNAPL pools of carbon tetrachloride and chloroform accumulate because of heterogeneity in this zone. Natural attenuation occurs at pools and plumes, indicating that remediation might be possible. The aims of the study were: i) to assess the role of heterogeneity in the natural attenuation of these compounds, ii) determine degradation processes within this zone, and iii) identify dechlorinating microorganisms. For this, groundwater concentrations, redox-sensitive parameters, CSIA isotopic and DGGE molecular techniques were used. The main findings at depth of the transition zone were: (1) the important key control played by heterogeneity on natural attenuation of contaminants. (2) Heterogeneity caused the highly anoxic environment and dominant sulfate-reducing conditions, which accounts for more efficient natural attenuation. (3) Heterogeneity also explains that the transition zone constitutes an ecotone. (4) The bacteria size exclusion is governed by the pore throat threshold and determines the penetration of dechlorinating microorganisms into the finest sediments, which is relevant, since it implies the need to verify whether microorganisms proposed for bioremediation can penetrate these materials. (5) Reductive dechlorination caused the natural attenuation of contaminants in groundwater and porewater of fine sediments. In the case of carbon tetrachloride, it was an abiotic process biogenically mediated by A. suillum, a bacterium capable of penetrating the finest sediments. In the case of chloroform, it was a biotic process performed by a Clostridiales bacterium, which is unable to penetrate the finest materials. (6) Both microorganisms have potential to be biostimulated to dechlorinate contaminants in the source and the plume in the transition zone. These outcomes are particularly relevant given the longevity of DNAPL sources and have considerable environmental implications as many supply wells in industrial areas exploit aquifers contaminated by chlorinated solvents emerging from DNAPL pools accumulated on the low-conductivity layers in transition zones

Combined use of ISCR and biostimulation techniques in incomplete processes of reductive dehalogenation of chlorinated solvents

Pools of chloroethenes are more recalcitrant in the transition zone between aquifers and basal aquitards than those elsewhere in the aquifer. Although biodegradation of chloroethenes occur in this zone, it is a slow process and a remediation strategy is needed. The aim of this study was to demonstrate that combined strategy of biostimulation and in situ chemical reduction (ISCR) is more efficient than the two separated strategies. Four different microcosm experiments with sediment and groundwater of a selected field site where an aged perchloroethene (PCE)-pool exists at the bottom of a transition zone, were designed under i) natural conditions, ii) biostimulation with lactic acid, iii) in situ chemical reduction (ISCR)with zero valent iron (ZVI) and under iv) a combined strategy with lactic acid and ZVI. Biotic and abiotic dehalogenation, terminal electron acceptor processes and evolution of microbial communities were investigated for each experiment. The main results where: i) limited reductive dehalogenation of PCE occurs under sulfate-reducing conditions; ii) biostimulation with lactic acid promotes a more pronounced reductive dehalogenation of PCE in comparison under natural conditions, but resulted in an accumulation of cis-dichloroethene (cDCE); iii) ISCR with zero-valent iron (ZVI) facilitates a sustained dehalogenation of PCE and its metabolites to non-halogenated products, however, the iv) combined strategy results in the fastest and sustained dehalogenation of PCE to non-halogenated products in comparison of all four set-ups. These findings suggest that biostimulation and ISCRwith ZVI are the most suitable strategy for a complete reductive dehalogenation of PCE-pools in the transition zone

Biogeochemistry of Plane Trees as a Tool to Detect Atmospheric Pollution

The plane tree, which is a valuable tool to detect atmospheric pollution, is one of the most common trees in European cities. Soil and leaf samplings were carried out in Barcelona and its environs (NE Spain) to establish the soil-plant relationship.Dry and ashed leaves and soils were analyzed by Instrumental Neutron Activation Analysis and Inductively Coupled Plasma-Optical Emission Spectroscopy (ICP/OES) at the ACTLABS laboratories in Ontario, Canada. Given that diesel is the main fuel used in vehicles in Europe, we sought to establish the role of diesel in atmospheric pollution. Diesel samples were obtained from service stations and analyzed after preconcentration using ICP/MS at the geochemistry laboratories of the University of Barcelona. The average content of diesel oil shows high values of Pb, Cu, Cr, Ag, Cd and Mn. High values of Pb, Cu, Au, Hg and Sb in leaves and soils were detected downtown and along main roadsoutside the city, whereas low levels of these elements were observed in rural areas

The role of ecotones in the dehalogenation of chloroethenes in alluvial fan aquifers

The presence of ecotones in transition zones between geological strata (e.g. layers of gravel and sand interbedded with layers of silt in distal alluvial fan deposits) in aquifers plays a significant role in regulating the flux of matter and energy between compartments. Ecotones are characterised by steep physicochemical and biological gradients and considerable biological diversity. However, the link between organic pollutants and degradation potential in ecotones has scarcely been studied. The aim of this study is to relate the presence of ecotones with the dehalogenation of chloroethenes. A field site was selected where chloroethene contamination occurs in a granular aquifer with geological heterogeneities. The site is monitored by multilevel and conventional wells. Groundwater samples were analysed by chemical, isotopic, and molecular techniques. The main results were as follows: (1) two ecotones were characterised in the source area, one in the upper part of the aquifer and the second in the transition zone to the bottom aquitard, where the aged pool is located; (2) the ecotone located in the transition zone to the bottom aquitard has greater microbial diversity, due to higher geological heterogeneities; (3) both ecotones show the reductive dehalogenation of perchloroethylene and trichloroethylene; and (4) these ecotones are the main zones of the reductive dehalogenation of the pollutants, given the more reductive conditions at the centre of the plume. These findings suggest that ecotones are responsible for natural attenuation, where oxic conditions prevailed at the aquifer and bioremediation strategies could be applied more effectively in these zones to promote complete reductive dehalogenation

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 place 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

Biotic and abiotic reductive dechlorination of chloroethenes in aquitards

Chlorinated solvents occur as dense nonaqueous phase liquid (DNAPL) or as solutes when dissolved in water. They are present inmany pollution sites in urban and industrial areas. They are toxic, carcinogenic, and highly recalcitrant in aquifers and aquitards. Inthe latter case, they migrate by molecular diffusion into the matrix. When aquitards are fractured, chlorinated solvents also penetrateas a free phase through the fractures. The main objective of this study was to analyze the biogeochemical processes occurring insidethe matrix surrounding fractures and in the joint-points zones. The broader implications of this objective derive from the fact that,incomplete natural degradation of contaminants in aquitards generates accumulation of daughter products. This causes steepconcentration gradients and back-diffusion fluxes between aquitards and high hydraulic conductivity layers. This offers opportunitiesto develop remediation strategies based, for example, on the coupling of biotic and reactive abiotic processes. The main resultsshowed: 1) Degradation occurred especially in the matrix adjacent to the orthogonal network of fractures and textural heterogeneities,where texture contrasts favored microbial development because these zones constituted ecotones. 2) A dechlorinating bacterium notbelonging to the Dehalococcoides genus, namely Propionibacterium acnes, survived under the high concentrations of dissolvedperchloroethene (PCE) in contact with the PCE-DNAPL and was able to degrade it to trichloroethene (TCE). Dehalococcoides genus was able to conduct PCE reductive dechlorination at least up to cis-1,2-dichloroethene (cDCE), which shows again the potential of themedium to degrade chloroethenes in aquitards. 3) Degradation of PCE in the matrix resulted from the coupling of reactive abiotic andbiotic processes¿in the first case, promoted by Fe sorbed to iron oxides, and in the latter case, related to dechlorinatingmicroorganisms. The dechlorination resulting from these coupling processes is slow and limited by the need for an adequate supply ofelectron donors

Reductive dechlorination in recalcitrant sources of chloroethenes in the transition zone between aquifers and aquitards

In the transition zone between aquifers and basal aquitards, the perchloroethene pools at an early time in their evolution are more recalcitrant than those elsewhere in the aquifer. The aim of this study is to demonstrate that the biodegradation of chloroethenes from aged pools (i.e., pools after decades of continuous groundwater flushing and dissolution) of perchloroethene is favored in the transition zone. A field site was selected where an aged pool exists at the bottom of a transition zone. Two boreholes were drilled to obtain sediment and groundwater samples to perform chemical, isotopic, molecular, and clone library analyses and microcosm experiments. The main results were as follows: (i) the transition zone is characterized by a high microbial richness; (ii) reductively dechlorinating microorganisms are present and partial reductive dechlorination coexists with denitrification, Fe and Mn reduction, and sulfate reduction; (iii) reductively dechlorinating microorganisms were also present in the zone of the aged pool; (v) the high concentrations of perchloroethene in this zone resulted in a decrease in microbial richness; (vi) however, the presence of fermenting microorganisms supplying electrons for the reductively dechlorinating microorganisms prevented the reductive dechlorination to be inhibited. These findings suggest that biostimulation and/or bioaugmentation could be applied to promote complete reductive dechlorination and to enhance the dissolution of more nonaqueous phase liquids (DNAPL)

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

The objective of our research is to identify the sequence of degradation processes leading to microbial speciation of microorganisms involved in degradation of CT and CF under natural attenuation and lactic acid biostimulation conditions. To this end, a comparative study of two types of microcosm experiments was carried out to analyze two scenarios: natural attenuation and lactic acid biostimulation. Experiments were carried out with water and sediment from a field site located at a petrochemical complex whose hydrochemical background inhibited the natural attenuation of carbon tetrachloride and chloroform. A significant result of our work was that these experiments allowed us to identify the CT abiotic degradation processes, among which the abiotic degradation induced by the biogenic activity of Dechlorosoma suillum should be noted. Although this is an abiotic degradation, the metabolism of this microorganism generates green rust precipitates, which in turn favor the abiotic reductive dechlorination of CT. Other relevant result was the identification of the biotic reductive dechlorination of CF by a bacterium of the Clostridiales order. This result presented the particularity that an apparent absence of isotopic fractionation was observed because a mixture of chloroform of different origins was produced. Our research showed that these processes were more efficient, in terms of faster degradation rates, when biostimulation with lactic acid was carried out. This biostimulation could therefore be an efficient remediation strategy at sites contaminated by chloromethanes, especially in cases where a complex pollution history results in a rich hydrochemical background that makes it difficult natural attenuation