Magnetic resonance imaging of enhanced mobility of light non aqueous phase liquid (LNAPL) during drying of water wet porous media

Effects of fluid composition in fluid injection experiments in porous media

Experiments on fluid flow in porous media, using fluids loaded with solids of various grain sizes, have been conducted in a modified Hele-Shaw setup. This setup utilised weakly cemented porous media with specific hydraulic and mechanical properties. Fluid injection in coarse granular media with clean or low-concentration fine particles, results in infiltration only, with pressure close to the material tensile strength, while injection in finer granular material causes damage alongside infiltration, with the fluid pressure still close to the material tensile strength. When larger particle sizes or higher particle concentrations are used in the mixture, the fluid travels further within the porous medium, primarily influenced by the grain size of the granular medium. In the latter case, the Darcy flow equation with an effective permeability term can be employed to determine the pressure differential. For the largest particle sizes included in the fluid, the equation is still applicable, but the effective permeability requires adjustment for particle size within the fluid rather than the granular medium. This is crucial when the injection point is locally clogged. The experiments show that fracturing conditions are controlled by different mechanisms. Dimensional and statistical analysis was used to classify the injection pressures to regimes predicted by fracturing theory or by Darcy law with modified effective permeabilities. The findings show that both the material properties and fluid composition are important designing parameters.

Groundwater and soil contamination by LNAPL: State of the art and future challenges

Contamination by Light Non-Aqueous Phase Liquids (LNAPL) represents a challenge due to the difficulties encountered in its underground assessment and recovery. The major risks arising from subsoil LNAPL accumulation face human health and environment, gaining a social relevance also in the frame of a continuously changing climate. This paper reports on a literature review about the underground contamination by LNAPL, with the aims of providing a categorization of the aspects involved in this topic, analyzing the current state of the art, underlying potential lacks and future perspectives. The review was focused on papers published in the 2012-2022 time-interval, in journals indexed in Scopus and WoS databases, by querying "LNAPL" within article title, abstract and/or key words. 245 papers were collected and classified according to three "key approaches" -namely laboratory activity, field based-data studies and mathematical simulations- and subordinate "key themes", so to allow summarizing and commenting the main aspects based on the application setting, content and scope. Results show that there is a wide experience on plume dynamics and evolution, detection and monitoring through direct and indirect surveys, oil recovery and natural attenuation processes. Few cues of innovations were found regarding both the use of new materials and/or specific field configuration for remediation, and the application of new techniques for plume detection. Some limitations were found in the common oversimplification of the polluted media in laboratory or mathematical models, where the contamination is set within homogeneous porous environments, and in the low number of studies focused on rock masses, where the discontinuous hydraulic behavior complicates the address and modeling of the issue. This paper represents a reference for a quick update on the addressed topic, along with a starting point to develop new ideas and cues for the advance in one of the greatest environmental banes of the current century.

Experimental investigation of light non-aqueous phase liquid mobilization in filled fractured network media

With the increasing requirement of international energy security, oil storage projects have been constructed in large numbers, but leaking petroleum-based contaminants are threatening the soil and groundwater environment. In order to assess the environmental risk of petroleum-based contaminants, an experimental apparatus was designed and developed to monitor the concentration and pressure variations of light non-aqueous phase liquid (LNAPL) in filled fractured network media. The mobilization mechanism of LNAPL was investigated by theoretical analysis and laboratory experiments; the pressure balance relationships at different interfaces were investigated. When the experimental model was unsaturated, the dynamic processes of concentration and pressure at different locations in filled fractures were explored. When the groundwater level was raised to 35 cm, the cumulative height of LNAPL (H_L) was a function of the density of LNAPL, interfacial tension, interfacial contact angle, aperture of fracture, porosity, and particle diameter of filling and H_L21 > H_L22. The final concentrations of H21, H22, H25, H26, and H27 were 0.467, 0.458, 0.026, 0.062, and 0.041 mg/mL, respectively. Subsequently, the effect of the particle diameter of filling sand on LNAPL mobilization was further discussed, the concentration of each point in the fractures increased with the increase of the particle diameter of filling sand, and its peak decreased with the increase of the burial depth. The response time of pressure at each point was advanced and the peak of pressure dynamic curve increased as the particle diameter of filling sand increased. The peak pressure heads of H12 and H13 were 22.360 cm and 25.332 cm respectively when the particle diameter of filling was 0.5-1.0 mm. The Spearman analysis results between LNAPL concentration and time showed a significant correlation (≥ 0.879, [Formula: see text]). Research results characterized the existence and mobilization of LNAPL in filled fractured network media from the perspectives of concentration and pressure, which could provide a reference for the study of the leakage and migration mechanism of LNAPL.

Analysis of the LNAPL Migration Process in the Vadose Zone under Two Different Media Conditions

This study focused on the processes of free infiltration, precipitation displacement, and natural attenuation of the LNAPL under the condition of near-surface leakage. Sandbox experiments were performed to explore the migration characteristics of LNAPL in the vadose zone with two media structures and the influences of the soil interface on the migration of LNAPL. The results indicate that the vertical migration velocity of the LNAPL infiltration front in medium and coarse sand was 1 order of magnitude higher than that in fine sand and that the LNAPL accumulated at the coarse–fine interface, which acted as the capillary barrier. Displacement of precipitation for LNAPL had little relationship with rainfall intensity and was obviously affected by medium particle size, where coarse sand (40.78%) > medium sand (20.5%) > fine sand (10%). The natural attenuation rate of the LNAPL in the vadose zone was related to the water content of the media; the natural attenuation rate of fine sand was higher. This study simulated the process of the LNAPL leakage from the near surface into the layered heterogeneous stratum, improved the understanding of the migration of the LNAPL under different stratum conditions, and can provide support for the treatment of LNAPL leakage events in the actual site.