Marco Pola

Architecture of the western margin of the North Adriatic foreland: the Schio-Vicenza fault system

In the Italian Southern Alps, the Lombardic and Venetian chains and related foreland are separated by the Lessini-Berici-Euganei foreland block, which is unaffected by the Neogene-Quaternary shortenings. However, the Veneto-Friuli alluvial plain to the east of this foreland block has been affected by a poly-phase evolution since the Mesozoic era and represents the foreland of three surrounding chains. The area was affected by several flexural cycles related to the diachronous build-up of the External Dinarides to the east (Late Cretaceous-Late Eocene), the Eastern Southern Alps to the north (Late Oligocene-Quaternary), and the Northern Apennines to the southwest (Middle Miocene-Quaternary). The last two chains are currently active, although at different rates. The western margin of the foreland is marked by the Schio-Vicenza fault, which divides the deformed foreland (Veneto-Friuli alluvial plain) from the undeformed foreland (Lessini and Berici Mountains and Euganei Hills). The aim of this work is to unravel the architecture and evolution of this boundary using 2D seismic sections and deep wells acquired by ENI for hydrocarbon exploration. Approximately 1,000 km of seismic lines were interpreted and 10 wells were used to calibrate the seismic interpretation. Seven seismic sections that are sub-orthogonal to the main faults were selected to obtain geological cross-sections through a depth conversion process. The collected data display a complex buried fault system (Schio-Vicenza fault system) that extends with a NW-SE trend from the foot of the Prealps to the Po Delta. In the cross sections, the movement of the fault shows a vertical component with down-throw of its eastern side (hanging wall block). Some faults display a Mesozoic extensional displacement in accordance with the Mesozoic basin and swell architecture of the area. In addition, the Pliocene throw increases from the southeast to the northwest.Therefore, the Schio-Vicenza fault system can be interpreted as an inherited Mesozoic structure that reactivated during the Neogene shortening of the area. In particular, this fault system appears to have been mainly active during the Pliocene-Quaternary flexural cycle that is related to the Northern Apennines subduction, which is when the fault system accommodated a scissor movement between the Veneto-Friuli foreland and the Lessini-Berici-Euganei block.

Geostatistics as a tool to improve the natural background level definition: An application in groundwater

The Natural Background Level (NBL), suggested by UE BRIDGE project, is suited for spatially distributed datasets providing a regional value that could be higher than the Threshold Value (TV) set by every country. In hydro-geochemically dis-homogeneous areas, the use of a unique regional NBL, higher than TV, could arise problems to distinguish between natural occurrences and anthropogenic contaminant sources. Hence, the goal of this study is to improve the NBL definition employing a geostatistical approach, which reconstructs the contaminant spatial structure accounting geochemical and hydrogeological relationships. This integrated mapping is fundamental to evaluate the contaminants distribution impact on the NBL, giving indications to improve it. We decided to test this method on the Drainage Basin of Venice Lagoon (DBVL, NE Italy), where the existing NBL is seven times higher than the TV. This area is notoriously affected by naturally occurring arsenic contamination. An available geochemical dataset collected by 50 piezometers was used to reconstruct the spatial distribution of arsenic in the densely populated area of the DBVL. A cokriging approach was applied exploiting the geochemical relationships among As, Fe and NH4+. The obtained spatial predictions of arsenic concentrations were divided into three different zones: i) areas with an As concentration lower than the TV, ii) areas with an As concentration between the TV and the median of the values higher than the TV, and iii) areas with an As concentration higher than the median. Following the BRIDGE suggestions, where enough samples were available, the 90th percentile for each zone was calculated to obtain a local NBL (LNBL). Differently from the original NBL, this local value gives more detailed water quality information accounting the hydrogeological and geochemical setting, and contaminant spatial variation. Hence, the LNBL could give more indications about the distinction between natural occurrence and anthropogenic contamination.

Point dilution tests to calculate groundwater velocity: an example in a porous aquifer in northeast Italy

ABSTRACT The point dilution test is a single-well technique for estimating horizontal flow velocity in the aquifer surrounding a well. The test is conducted by introducing a tracer into a well section and monitoring its decreasing concentration over time. When using a salt tracer, the method is easy and inexpensive. Traditionally, the horizontal Darcy velocity is calculated as a function of the rate of dilution and is based on the simple assumption that the decreasing tracer concentration is proportional both to the apparent velocity into the test section and to the Darcy velocity in the aquifer. In this article, an alternative approach to analyse the results of point dilution tests is proposed and verified using data acquired at a test site in the middle Venetian plain, northeast Italy. In this approach, the one-dimensional equilibrium advection–dispersion equation is inverted using the CXTFIT model to estimate the apparent velocity inside the test section. Analysis of the field data obtained by the two approaches shows good agreement between the methods and suggests that it is possible to use the equilibrium advection–dispersion equation to estimate apparent velocity over a wide range of velocities. Editor D. Koutsoyiannis; Associate editor K. Heal

Numerical modeling to well-head protection area delineation, an example in Veneto Region (NE Italy)

The article presents an example of well-head protection area (WHPA) delineation in middle Venetian plain, using geostatistical simulation for the subsoil reconstruction, groundwater flow modeling and automatic calibration.

Natural Arsenic in groundwater in the drainage basin to the Venice lagoon (Brenta Plain, NE Italy): the organic matter's role

The aim of the article is to show the role of the redox potential and of the ammonium ion concerning the release of arsenic into groundwater from naturally occurring sources. The study is carried out on both regional and local scale. The former is performed on the area of the drainage basin to the Venice lagoon (DBVL), while the latter interests a sub-area near the Porto Marghera contaminated sites of national interest, named Agricultural west areas (AWA). The results of the work will elucidate the processes continuity at different scales.

Conceptual and numerical models of a tectonically-controlled geothermal system: a case study of the Euganean Geothermal System, Northern Italy

The Euganean Geothermal Field (EGF) is the most important thermal field in northern Italy. It is located in the alluvial plain of the Veneto Region where approximately 17*106 m3 of thermal water with temperatures of 60–86 °C are exploited annually. A regional-scale conceptual model of the Euganean Geothermal System is proposed in this paper using the available hydrogeologic, geochemical and structural data for both the EGF and central Veneto. The thermal water is of meteoric origin and infiltrates approximately 80 km to the north of the EGF in the Veneto Prealps. The water flows to the south in a Mesozoic limestone and dolomite reservoir reaching a depth of approximately 3,000 m and a temperature of approximately 100 °C due to the normal geothermal gradient. The regional Schio-Vicenza fault system and its highly permeable damage zone act as a preferential path for fluid migration in the subsurface. In the EGF area, a geologic structure formed by the interaction of different segments of the fault system in...

Mapping the variation of the potentiometric level of the Euganean thermal aquifer and relationship with the exploitation

The Euganean Geothermal Field (EGF) and its thermal water are a relevant natural and economical resource for Veneto Region (NE Italy). Approximately 14×106 m3 of hot water (temperature ranging from 65°C to 86°C) were exploited by 145 wells in 2014. The most exploited thermal aquifer is located at a depth ranging from 300 m to 600 m in fractured layers hosted within Mesozoic limestones. Six abandoned wells have been used to monitor its potentiometric level since 1975. The results show periods of level decrease followed by a recovery related to the exploitation of the thermal water. The aim of this work is to verify the reliability of the proposed model for the EGF area. Five monitoring surveys were carried out from November 2014 to November 2015 during periods of high and low exploitation. The potentiometric level of the aquifer, the temperature of the water and the flow rate were measured in approximately 130 wells. In particular, the data collected in the surveys of February 2015 (low exploitation) and April 2015 (high exploitation) were used to perform two maps of the potentiometric level. The maps are compared evidencing a general decrease of the potentiometric level from February to April in agreement with the variations observed by the continuous monitoring network. The results of this study permit to detail the areal distribution of both the potentiometric level and its variation.

Anthropic impact on thermal aquifer: the case study of the Euganean Geothermal Field (NE Italy)

The Euganean Geothermal Field represents an important natural and economical resource for Veneto region (NE Italy) and its thermal water is mainly used for balneotherapy. Approximately 170 wells exploit 14*106 m3/y of hot water (temperature from 65°C to 86°C) from rocky aquifers located at different depths. The potentiometric level of the most exploited 300-500 m deep aquifer has been monitored by a network of abandoned wells since 1975, and the exploitation has been monitored since 1979. The analysis of the level evidences an anthropic annual regime related to the touristic seasons and characterized by a decrease during spring and autumn (high rate of incoming tourists and high exploitation) and a recovery during winter and summer (low exploitation). In addition, a general increasing trend of the potentiometric level has been recorded since the 1990s and it can be related to the decrease of the exploitation. The time series showing the clearest relationship between level and flow rate is used to perform a black-box model using a Generalized Additive Model. The model estimates a natural potentiometric level of 15 m above the ground level, comparable with the level measured in a well far from the most exploited areas of the thermal field.

A local natural background level concept to improve the natural background level: a case study on the drainage basin of the Venetian Lagoon in Northeastern Italy

This study analyzes a problem related to the definition of a natural background level (NBL) for naturally occurring contaminants. Specifically, it considers the definition of an arsenic NBL in groundwater because arsenic in alluvial aquifers is a worldwide problem that causes issues in human health. Currently, the European Union (through the BRIDGE project) has suggested several methods to estimate NBLs based on the quantity and quality of the available data, providing a unique NBL value for an investigated study area. This study suggests an improvement of the NBL concept by introducing the local NBL (LNBL). LNBLs are estimated considering an indicator geostatistical approach, which takes into account both the spatial distribution of arsenic and the geochemical relationships occurring inside the aquifer. The LNBL concept aims to provide detailed spatial information of the natural background level and prevents one from defining uncontaminated water sources as contaminated water sources, and vice versa. In this study, an application of the LNBL in the drainage basin of the Venetian Lagoon is proposed.