The abandoned antimony-mines of SE Sardinia: impact on surface waters

This study investigates the impact of abandoned Sb-mines on the Flumendosa River, which is the most important water resource in southern Sardinia. Hydrogeochemical surveys carried out in 2005 and 2006 indicated a significant impact of waters flowing out from adits, slag, tailings and waste materials on surface waters. The contaminated waters show alkaline pH, and high dissolved SO4, Sb and As (up to 1900, 9.6 and 3.5 mg/L, respectively). Although the flow rates of drainages from the mining area are usually low (in the range of < 0.1 to 1 L/s), the contribution to dissolved concentrations of Sb in the streams downstream of mines is high. Sampling under high flow conditions in the Flumendosa River before the confluence with the contaminated streams showed Sb concentrations below the limits established by the guidelines of World Health Organization for drinking water (i.e. 20 g/L), while downstream of the confluence dissolved Sb was 32 g/L. Contamination in the Flumendosa extended 16 km, and attenuation (15 g/L Sb) was only observed close to the Flumendosa mouth

Comparison of Pre- and Post-Remediation Stream Water Chemistry in the Arsenic-Contaminated Baccu Locci Mine Watershed (Italy): Preliminary Data

AbstractEnvironmental issues related to past mining activities have become the subject of public interest only in the last 20-25 years. Consequently, experience related to the mitigation and control of environmental pollution in mining areas is a recent development. The existing methods of remediation are often partially ineffective, especially when applied without an in-depth geochemical and mineralogical study of the site. This paper reports on preliminary data concerning the effect of remediation actions in an arsenic-contaminated mine watershed (Baccu Locci mine – Italy) a few months from its completion. The persistence of the pre-remediation conditions raises some doubt on the effectiveness of the undertaken remediation actions, even if more time is certainly needed to reach a new environmental steady state. Much remains to be learned about mistakes and successes of mine site remediation, and the monitoring of the Baccu Locci area represents an opportunity to acquire new fundamental knowledge on this issue

Enargite by XPS

X-ray photoelectron spectroscopy was used for characterizing the enargite surface. Freshly cleaved samples were analyzed at liquid nitrogen temperature. Enargite is a copper arsenic sulfide of formula Cu3AsS4; it is used as a minor ore of copper. Enargite is a potential source of arsenic and may create environmental problems through the release of toxic elements upon oxidatio

Testing indirect methods to infer hydraulic conductivity in streambed sediments: preliminary results

Hydraulic conductivity, grain-size parameters, empirical approach, Kozeny-Carman model

CHEMICAL SIGNATURE OF GROUNDWATER IN COVER OVERLYING DULUTH COMPLEX NI-CU-PGE DEPOSITS, NE MINNESOTA

The U.S. Geological Survey initiated a project in 2015 aimed at evaluating geochemical exploration methods for covered deposits in the northern Midcontintent Rift, employing both site-scale studies and regional geochemical databases. A first group of groundwater samples was collected from unconsolidated material overlying the Spruce Road, Wyman Creek, and Skibo deposits in the Duluth Complex to determine effective sampling methods, characterize the groundwater chemical signature of these deposits, and determine chemical evolution along flow paths. Twenty-seven samples were collected from mini-piezometers at depths <5 m and analyzed for major and trace element chemistry and stable isotopes of water. Ten samples were also analyzed for groundwater age tracers, including noble gases, 3H, He isotopes, and chlorofluorocarbons. Site conditions presented challenges for deriving well-constrained specific ages. However, samples could be sorted into the following age categories by employing multiple tracers: <0.5 yr; 0.5 to 2 yr; 2 to 10 yr; and 15 to 30 yr. Cu and Ni concentrations over the deposits range from <0.5 to 150 μg/L and from <1 to 348 μg/L, respectively, and are commonly elevated above background. Cu and Ni are negatively correlated with pH (range of 5.7 to 8.6), probably due to progressively more adsorption on negatively charged mineral surfaces at higher pH. The pH also increases with groundwater age, likely due to weathering of abundant mafic minerals. As a result, Cu and Ni concentrations generally decrease with increasing age. These results suggest that pH provides an important limit on Cu and Ni mobility in the groundwater system, which must be taken into account in designing geochemical exploration approaches. In addition to site-scale work, a regional groundwater chemical database was compiled from available USGS (NWIS) and state databases. Initial examination reveals both geogenic and anthropogenic metal anomalies, and spatial analyses are ongoing

Numerically Enhanced Conceptual Modelling (NECoM) applied to the Flumendosa Plain groundwater system (SE Sardinia, Italy)

The alluvial aquifer of the Flumendosa delta plain, in south-eastern Sardinia (Italy), is overexploited for drinking and agriculture purposes and it is subjected to ongoing sea water intrusion phenomena. In a context of progressive quali-quantitative deterioration of groundwater resources, development of a sustainable management plan and, eventually, effective remediation actions require a deep understanding of the investigated system. A systematic review of dataset collected from literature, integrated with new field hydrogeological and geochemical data, is performed to improve the knowledge of the aquifer system. Despite the large amount of processed data, many aspects require further investigations. In this frame, a fast-running steady state groundwater flow numerical model is developed as a tool for testing the preliminary assumptions, to address the main uncertainties, and to optimize the acquisition of new field data. The adopted approach follows the methodology proposed by Lotti et al. (2021) for the development of a Numerically Enhanced Conceptual Model (NECoM). Geometrical discretization of the numerical model is based on results of the 3D hydrogeological reconstruction of the plain area (Arras et al. 2019); simulation of main inflows and outflows, water exchange between surface water bodies and groundwater, irrigation and drinking water withdrawals is performed through the implementation of general head boundaries (GHB), river (RIV), and well (WEL) packages, respectively. Results from the application of the Soil Water Balance code (Porru et al. 2020) are used as input for simulating the average recharge from precipitation. Lateral recharge from the Paleozoic basement is also simulated. More than 4000 heads observations from about 350 wells and piezometers are used as targets in the calibration process; weights are assigned to deal with the high heterogeneity of the dataset quality. RIV and GHB conductance, irrigation well yields, direct and lateral recharge, and hydraulic conductivity are set as parameters in the calibration process. Due to the high sensitivity of some parameters, different calibration cycles are performed; hydraulic conductivities and lateral recharge are then calibrated in the last cycle. Model results show that the hydrogeological conceptualization used for implementing the numerical model can reproduce the main general features of the piezometric head field. According to field observations, the Flumendosa river shows losing conditions in the western part of the plain and next to the river mouth, while gaining conditions occur in its central part; gaining conditions are also observed along the abandoned branches of the Flumendosa river, also known as foxi. Moreover, mass balance analysis show that the Flumendosa river represents the main recharge input of the whole groundwater system, providing an average inflow of about 4.3 Mm3/year. Nevertheless, several local incongruencies with the observed data were precious to highlight the effects of unknown variables such as agricultural extraction wells, the hydrogeological role of the bedrock or the water exchange between surface and groundwater bodies. The discrepancies, rather than the agreements, provided useful direction for the detection of new data to be collected to capture the salient information needed for a proper water resource management

Le acque sotterranee: uso sostenibile di una risorsa invisibile

Le risorse idriche sotterranee assicurano in Italia circa l’84% delle acque potabili, originano acque minerali e termali, e contribuiscono all’approvvigionamento dei fabbisogni irrigui e industriali. La ricchezza quantitativa e qualitativa delle acque sotterranee del nostro Paese è funzione del suo assetto geologico. Questa risorsa generalmente invisibile, ma resa visibile da studi ed indagini idrogeologiche, è strategica per la vita del pianeta e quindi per assicurare il futuro dell’umanità e degli ecosistemi. In questa nota viene fornita una panoramica sulla disponibilità delle risorse idriche sotterranee in Italia, confrontandola con il fabbisogno idrico per gli usi antropici e discutendo la sostenibilità dei prelievi di acque sotterranee

Modellistica geologica e idrogeologica tridimensionale per la valutazione quali-quantitativa delle risorse idriche sotterranee

Management of groundwater systems requires efficient modeling tools to evaluate the available resources and to define the water balance. The value of these instruments depends on the accuracy of geological and hydrogeological conceptual model. As part of a research project aimed at assessing Groundwater Resources in strategic aquifers of Sardinia, it was tested a methodology for quantitative and qualitative study of groundwater resources, based on the use of three-dimensional geological and hydrogeological modeling. The aim of this research is to provide a tool to support the decision-making process in water resources management and assessment, applicable in different hydrogeological settings. . The pilot study area is the porous Quaternary alluvial aquifer of the Cixerri Valley. The valley, located in the South-Western Sardinia, is an East-West oriented syncline linked to the tertiary tectonics, bordered by Paleozoic metamorphic and sedimentary formations and filled by tertiary and quaternary alluvial. The methodology can be summarized in three main phases. The first involved the construction of a Geodatabase (DB), where geological and hydrogeological data (geological maps and cross sections, geophysical data, wells and borehole logs, piezometric levels, hydrogeological parameters and geochemical features) were cataloged During the second phase a 3D geological model of the shallow Cixerri aquifer has been built. The data collected in the DB were validated and used for the construction of geological sections orthogonal and parallel to the fold axis. The interpolation of alluvial horizons of each sections help us to create the bottom surface of the alluvial aquifer. The third phase, currently being implemented, involves the construction of a hydrogeological 3D model and the estimation of the volume of the aquifer

Geochemistry, stable isotopes and statistic tools to estimate threshold and source of nitrate in groundwater (Sardinia, Italy)

In the European Union, nitrate vulnerable zone (NVZ) should be designed for the mitigation of nitrate (NO3−) contamination caused by agricultural practices. Before establishing new NVZ, the sources of NO3− must be recognized. A geochemical and multiple stable isotopes approach (hydrogen, oxygen, nitrogen, sulfur and boron) and statistical tools were applied to define the geochemical characteristics of groundwater (60 samples), calculate the local NO3− threshold and assess potential sources of NO3− contamination in two study areas (hereafter Northern and Southern), located in a Mediterranean environment (Sardinia, Italy). Results of the integrated approach applied to two case study, permits to highlight the strengths of integrating geochemical and statistical methods to provide nitrate source identification as a reference by decision makers to remediate and mitigate nitrate contamination in groundwater. Hydrogeochemical features in the two study areas were similar: near neutral to slightly alkaline pH, electrical conductivity in the range of 0.3 to 3.9 mS/cm, and chemical composition ranging from Ca-HCO3− at low salinity to Na-Cl− at high salinity. Concentrations of NO3− in groundwater were in the range of 1 to 165 mg/L, whereas the nitrogen reduced species were negligible, except few samples having NH4+ up to 2 mg/L. Threshold values in the studied groundwater samples were between 4.3 and 6.6 mg/L NO3−, which was in agreement with previous estimates in Sardinian groundwater. Values of δ34S and δ18OSO4 of SO42− in groundwater samples indicated different sources of SO42−. Sulfur isotopic features attributed to marine SO42− were consistent with groundwater circulation in marine-derived sediments. Other source of SO42− were recognize due to the oxidation of sulfide minerals, to fertilizers, manure, sewage fields, and SO42− derived from a mix of different sources. Values of δ15N and δ18ONO3 of NO3− in groundwater samples indicated different biogeochemical processes and NO3− sources. Nitrification and volatilization processes might have occurred at very few sites, and denitrification was likely to occur at specific sites. Mixing among various NO3− sources in different proportions might account for the observed NO3− concentrations and the nitrogen isotopic compositions. The SIAR modeling results showed a prevalent NO3− source from sewage/manure. The δ11B signatures in groundwater indicated the manure to be the predominant NO3− source, whereas NO3− from sewage was recognized at few sites. Geographic areas showing either a predominant process or a defined NO3− source where not recognize in the studied groundwater. Results indicate widespread contamination of NO3− in the cultivated plain of both areas. Point sources of contamination, due to agricultural practices and/or inadequate management of livestock and urban wastes, were likely to occur at specific sites