Leonardo Piccinini

Assessing transmissivity from specific capacity in an alluvial aquifer in the middle Venetian plain (NE Italy)

Defining aquifer permeability distribution accurately over large areas is often debated in hydrogeology. The operational efforts to calculate hydraulic conductivity with classical aquifer tests are significant; however, accurate knowledge of permeability areal distribution is fundamental both from a hydrogeological and a modeling standpoint. This paper presents an empirical relationship between the transmissivity (T) and the specific capacity (SC) values obtained from experimental aquifer and well tests. All experimental values were obtained from 50 mm wells in middle Venetian plain artesian gravel aquifers. Many other authors have presented empirical relationships between T and SC, but most are related to fissured/karst aquifers, and only a few concern alluvial porous aquifers. Analysis of the T vs. SC relationship standardized residuals shows that a linear relationship produces statistically significant normal residuals compared with an exponential relationship.

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.

Groundwater Modeling of Fractured Aquifers in Mines: The Case Study of Gavorrano (Tuscany, Italy)

In this paper, we describe the hydrogeological problems related to the closure of the mine at Gavorrano (Tuscany, Italy). The geological and geo-structural settings of the Gavorrano area affect the groundwater flow systems and their chemical composition; hence, the settings also affect the chance and modalities to rehabilitate and re-utilize these water resources. This paper reports the results of studies, analyses of existing data and the consequent implementation of preliminary numerical models with particular reference to the effects of controlled water recovery and the complex measures required for stopping dewatering. The study incorporates recent data and the available historical records in an analysis of the hydrodynamic impact of water recovery and an assessment of the consequences of water recovery for water resources restoration. The applied numerical simulations have been demonstrated to be a promising and effective tool for planning and managing the future applications of groundwater recovery in the Gavorrano mining area. Using these applications, it will be possible to implement mitigation measures and types of re-use that consider thermal, chemical and discharge features.

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.