Maria Clementina Caputo

Impact of a very low enthalpy plant on a costal aquifer: a case study in Southern Italy

The interest in the low-enthalpy geothermal resources is growing, owing to its wide availability, and the possibility of overcoming the problems related to energy storage. Among the low-enthalpy plants, the installation in coastal areas of the open-loop groundwater heat pump (GWHP) systems, that use groundwater as the geothermal fluid, is particularly attractive because of the presence of shallow aquifers. Nevertheless, these aquifers are often affected by seawater intrusion, so strict monitoring before GWHP installation is needed to check the feasibility of the plant. This work reports a detailed quali-quantitative characterization of a costal aquifer, in Southern Italy, for its exploitation as a very low enthalpy geothermal resource. The main groundwater parameters were monitored to assess the groundwater suitability to be used as geothermal fluid. A long-term pumping test, simulating the designed open-loop GWHP system, was performed to evaluate its potential impact on seawater intrusion. The results revealed that the open-loop GWHP plant do not affect the quali-quantitative equilibrium of the studied coastal aquifer. Furthermore, the study demonstrated that the used methodological approach is proper for the early assessment of the feasibility of the GWHP plant without affecting the seawater intrusion processes, and with minimum impact.

Geophysical and hydrological data assimilation to monitor water content dynamics in the rocky unsaturated zone

In recent years, geophysics is increasingly used to study the flow and transport processes in the vadose zone. Particularly, when the vadose zone is made up of rocks, it is difficult to install sensors in the subsurface to measure hydrological state variables directly. In these cases, the electrical resistivity tomography (ERT) represents a useful tool to monitor the hydrodynamics of the infiltration and to estimate hydraulic parameters and state variables, such as hydraulic conductivity and water content. We propose an integrated approach aimed at predicting water content dynamics in calcarenite, a sedimentary carbonatic porous rock. The uncoupled hydrogeophysical approach proposed consists in 4D ERT monitoring conducted during an infiltrometer test under falling head conditions. Capacitance probes were installed to measure water content at different depths to validate the estimations derived from ERT. A numerical procedure, based on a data assimilation technique, was accomplished by combining the model (i.e., Richards’ equation) with the observations in order to provide reliable water content estimations. We have used a new data assimilation method that is easy to implement, based on the ensemble Kalman filter coupled with Brownian bridges. This approach is particularly suitable for strongly non-linear models, such as Richards’ equation, in order to take into account both the model uncertainty and the observation errors. The proposed data assimilation approach was tested for the first time on field data. A reasonable agreement was found between observations and predictions confirming the ability of the integrated approach to predict water content dynamics in the rocky subsoil.

Calibration of a New Device to Measure Water Content of Rocks

The vadose zone, which extends from the soil–atmospheric interface to the capillary fringe of the water table, is a fundamental part of the hydrologic cycle. It controls how the precipitation splits into infiltration, surface runoff, evapotranspiration, groundwater recharge; it regulates the storage, transfer, filtering, adsorption, retard and attenuation of solutes and contaminants before these reach the groundwater.

Field Measurement of Hydraulic Conductivity of Rocks

Groundwater often represents the main and most precious source of drinking water supply for the population. In recent decades, overexploitation, uncontrolled anthropogenic actions and continuous reduction of rainfall, due to climate change, led to a depletion of the water resource by affecting both its quantity and quality. The scientific community pays attention to this particular environmental issue in order to implement effective strategies for the safeguarding, protection, and remediation of the aquifers. Over the last decade, considerable efforts have been made to develop methodologies and techniques aimed at improving knowledge of the processes that are based in the unsaturated zone or vadose zone—the portion of the soil above the groundwater level—within which flow and transport processes occur. In this portion of subsoil, in fact, important physicochemical phenomena take place, which regulate the environmental balance of the hydrogeological system, such as the ability to store water and transport it into the ground below. It also has a natural protective function as a filter for any potential pollutants carried by fluids circulating in the solid matrix before reaching the groundwater. The knowledge and the understanding of the processes that take place in the unsaturated zone are, therefore, essential for groundwater management and protection, to evaluate the recharge rate and assess groundwater vulnerability. In particular, the measurement and monitoring of the unsaturated hydraulic properties are very important, even though it is difficult and expensive (Castiglione et al., 2005). The methods and techniques developed are designed to investigate the unsaturated flow process in the soils. When the vadose zone consists of rock, rather than soil, technical aspects increase the difficulties in several ways (Bogena et al., 2007; Kizito et al., 2008). Usually, different kinds of probes are used to monitor the water infiltration in soils: the Time Domain Reflectometry (TDR) (Jones et al., 2004; Robinson et al., 2003), the Frequency Domain Reflectometry (FDR) and multi-sensor capacitance probes (Baumhardt et al., 2000; Seyfried et al., 2004) are used to measure the water content in the subsurface, while tensiometers measure water pressure (Masbrucha & Ferre, 2003). These devices are hard to utilize in the rocks, mainly because the probes are brittle. Therefore it is difficult to install them, as there needs to be good contact between the rock and the sensor to reduce the uncertainty of the measurements due to the gap effects. Field studies, set up to measure hydraulic conductivity, have employed infiltrometer tests under different conditions, but they have rarely been performed directly on the outcropped rock, owing to the difficulty of