Amélie Cavelan
email: amelie.cavelan@univ-lorraine.fr

Fabrice Golfier

Stéfan Colombano

Hossein Davarzani

Jacques Deparis

Pierre Faure

A critical review of the influence of groundwater level fluctuations and temperature on LNAPL contaminations in the context of climate change

Keywords: Light non-aqueous phase liquids, Groundwater, Dissolution, Biodegradation, Volatilization

ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

Introduction

Over the last century, the development of chemical and petroleum industries has led to numerous accidental spills of petroleum products that have greatly affected the long-term quality of groundwater [START_REF] Güler | Organic (Hydrocarbon) Contamination: Nonaqueous Phase Liquids[END_REF]. Light non-aqueous phase liquids (LNAPLs), are one the most common source of groundwater pollution [START_REF] Rivett | An Illustrated Handbook of LNAPL Transport and Fate in the Subsurface[END_REF]. When released, LNAPLs redistribute by migrating through the saturated (SZ) and unsaturated zone (USZ) and interacting with groundwater. Redistribution of LNAPL and partitioning of its components cause significant groundwater and soil pollutions [START_REF] Huntley | Persistence of LNAPL sources: relationship between risk reduction and LNAPL recovery[END_REF][START_REF] Lee | NAPL pool dissolution in stratified and anisotropic porous formations[END_REF][START_REF] Mccarthy | Transport of volatile organic compounds across the capillary fringe[END_REF][START_REF] Mobile | Multicomponent NAPL Source Dissolution: Evaluation of Mass-Transfer Coefficients[END_REF][START_REF] Nambi | Mass transfer correlations for nonaqueous phase liquid dissolution from regions with high initial saturations[END_REF][START_REF] Oostrom | A review of multidimensional, multifluid, intermediatescale experiments: Flow behavior, saturation imaging, and tracer detection and quantification[END_REF][START_REF] Patterson | Quantification of vapor intrusion pathways into a slab-on-ground building under varying environmental conditions[END_REF]. Several petroleum LNAPL compounds are carcinogenic (e.g., benzene) affecting plants, microorganisms, animals, and human health, and making groundwater unsuitable for both agriculture and drinking water supply. Remediation of LNAPL contaminated sites can be prolonged and expensive since LNAPL fuels and oils are usually a complex multi-component mixture with variable physical properties [START_REF] Newell | Light Nonaqueous Phase Liquids[END_REF]. The processes controlling LNAPL remobilization and degradation at contaminated sites are numerous and the relation between them is not always clear [START_REF] Garg | Overview of Natural Source Zone Depletion: Processes, Controlling Factors, and Composition Change[END_REF][START_REF] Sookhak Lari | Natural source zone depletion of LNAPL: A critical review supporting modelling approaches[END_REF]. Better understanding the controlling factors of LNAPL mobilization and remediation processes became, therefore, a major scientific goal these last decades [START_REF] Alazaiza | LNAPL saturation distribution under the influence of water table fluctuations using simplified image analysis method[END_REF][START_REF] Benioug | Interaction between biofilm growth and NAPL remediation: A pore-scale study[END_REF][START_REF] Chen | Influencing Factors of BTEX Volatilization[END_REF][START_REF] Dobson | Effect of water-table fluctuation on dissolution and biodegradation of a multi-component, light nonaqueous-phase liquid[END_REF][START_REF] Ismail | Influence of Water Table Fluctuation on Natural Source Zone Depletion in Hydrocarbon Contaminated Subsurface Environments[END_REF][START_REF] Mcalexander | Influence of Ambient Temperature, Precipitation, and Groundwater Level on Natural Source Zone Depletion Rates at a Large Semiarid LNAPL Site[END_REF]Sookhak Lari et al., 2016b, 2020;[START_REF] Sun | Transient water table influence upon Light Non-Aqueous Phase Liquids (LNAPLs) redistribution: laboratory and modelling studies[END_REF][START_REF] Werner | The influence of water table fluctuations on the volatilisation of contaminants from groundwater. Groundwater Quality: Natural and enhanced restoration of groundwater polltuion[END_REF][START_REF] Zeman | Temperature impacts on anaerobic biotransformation of LNAPL and concurrent shifts in microbial community structure[END_REF].

Numerous laboratory, modeling, and field studies have demonstrated that seasonal or pumpinduced groundwater level fluctuations may affect LNAPL migration and redistribution [START_REF] Davis | Characterizing the distribution of dissolved and residual NAPL petroleum hydrocarbons in unconfined aquifers to effect remediation[END_REF][START_REF] Lenhard | Testing an analytical model for predicting subsurface LNAPL distributions from current and historic fluid levels in Monitoring Wells: A preliminary test considering hysteresis[END_REF][START_REF] Lenhard | Evaluating an analytical model to predict subsurface LNAPL distributions and transmissivity from current and historic fluid levels in groundwater wells: comparing results to numerical simulations[END_REF][START_REF] Lenhard | A practical tool for estimating subsurface LNAPL distributions and transmissivity using current and historical fluid levels in groundwater wells: Effects of entrapped and residual LNAPL[END_REF][START_REF] Steffy | Numerical simulations and long-column tests of LNAPL displacement and trapping by a fluctuating water table[END_REF][START_REF] Steffy | A field study of the vertical immiscible displacement of LNAPL associated with a fluctuating water table[END_REF], component dissolution rates [START_REF] Davis | Characterizing the distribution of dissolved and residual NAPL petroleum hydrocarbons in unconfined aquifers to effect remediation[END_REF][START_REF] Kechavarzi | Two-dimensional laboratory simulation of LNAPL infiltration and redistribution in the vadose zone[END_REF][START_REF] Lekmine | Dissolution of multi-component LNAPL gasolines: The effects of weathering and composition[END_REF][START_REF] Lenhard | A constitutive model for air-NAPL-water flow in the vadose zone accounting for immobile, non-occluded (residual) NAPL in strongly water-wet porous media[END_REF][START_REF] Mobile | Multicomponent NAPL Source Dissolution: Evaluation of Mass-Transfer Coefficients[END_REF][START_REF] Teramoto | Field data and numerical simulation of btex concentration trends under water table fluctuations: Example of a jet fuel-contaminated site in Brazil[END_REF], volatilization [START_REF] Davis | Measurement and Modeling of Temporal Variations in Hydrocarbon Vapor Behavior in a Layered Soil Profile[END_REF][START_REF] Guo | Influence of Fluctuating Groundwater Table on Volatile Organic Chemical Emission Flux at a Dissolved Chlorinated-Solvent Plume Site[END_REF][START_REF] Illangasekare | Vapor intrusion from entrapped NAPL sources and groundwater plumes: Process understanding and improved modeling tools for pathway assessment[END_REF][START_REF] Mccarthy | Transport of volatile organic compounds across the capillary fringe[END_REF][START_REF] Picone | Sensitivity analysis on parameters and processes affecting vapor intrusion risk[END_REF][START_REF] Qi | Influence of groundwater table fluctuation on the non-equilibrium transport of volatile organic contaminants in the vadose zone[END_REF][START_REF] Soucy | Bubble-Facilitated VOC Transport from LNAPL Smear Zones and Its Potential Effect on Vapor Intrusion[END_REF][START_REF] Werner | The influence of water table fluctuations on the volatilisation of contaminants from groundwater. Groundwater Quality: Natural and enhanced restoration of groundwater polltuion[END_REF][START_REF] Zhang | How Does the Periodic Groundwater Table Fluctuation Impact on Chlorinated Vapor Intrusion? Geofluids[END_REF], or biodegradation [START_REF] Dobson | Effect of water-table fluctuation on dissolution and biodegradation of a multi-component, light nonaqueous-phase liquid[END_REF][START_REF] Gupta | Assessment of LNAPL in Subsurface under Fluctuating Groundwater Table Using 2D Sand Tank Experiments[END_REF][START_REF] Ismail | Influence of Water Table Fluctuation on Natural Source Zone Depletion in Hydrocarbon Contaminated Subsurface Environments[END_REF][START_REF] Rainwater | Enhanced in situ Biodegradation of Diesel Fuel by Cyclic Vertical Water Table Movement: Preliminary Studies[END_REF]. These works showed that fluctuating groundwater 3 level conditions and/or soil moisture changes affect the vertical dispersion and redistribution of the LNAPL compounds at the capillary fringe, modifying their release into the environment. However, the dynamic nature and the intensity of groundwater level variations may change significantly in the coming decades in response to climate change [START_REF] Goderniaux | Large scale surface-subsurface hydrological model to assess climate change impacts on groundwater reserves[END_REF][START_REF] Green | Beneath the surface of global change: Impacts of climate change on groundwater[END_REF][START_REF] Jarsjö | Projecting impacts of climate change on metal mobilization at contaminated sites: Controls by the groundwater level[END_REF][START_REF] Smerdon | A synopsis of climate change effects on groundwater recharge[END_REF]. Depending on local climatic conditions, more intense groundwater level fluctuations may occur over the next century in response to variations in rainfall intensity and frequency and the increasing use of water resources [START_REF] Christensen | A summary of the PRUDENCE model projections of changes in European climate by the end of this century[END_REF]IPCC, 2014;[START_REF] Nygren | Changes in seasonality of groundwater level fluctuations in a temperate-cold climate transition zone[END_REF].

This context may strongly impact the LNAPL mobilization, the contamination lifetime, and the risk for receptors. Moreover, an increase in a few degrees in the mean surface and groundwater temperature is also expected (IPCC, 2014). This phenomenon may affect temperature-dependent mobilization and (bio)degradation processes [START_REF] Knauss | The aqueous solubility of trichloroethene (TCE) and tetrachloroethene (PCE) as a function of temperature[END_REF][START_REF] Mcalexander | Influence of Ambient Temperature, Precipitation, and Groundwater Level on Natural Source Zone Depletion Rates at a Large Semiarid LNAPL Site[END_REF][START_REF] Yadav | Biodegradation of Toluene Under Seasonal and Diurnal Fluctuations of Soil-Water Temperature[END_REF][START_REF] Zeman | Temperature impacts on anaerobic biotransformation of LNAPL and concurrent shifts in microbial community structure[END_REF], further modifying the LNAPL constituents partitioning and release into air and groundwater.

Here we review and link literature primarily from the last two decades to form a basis for the possible evolution of all the processes affecting LNAPL mobility, partitioning, and (bio)degradation in the context of climate change. We focus mainly on the two factors that may have the most significant effect on LNAPL: groundwater level variations and temperature changes. A better understanding of likely transitions in the magnitude of the dominant processes provides a basis for better management and mitigation of the risks associated with LNAPL contaminated sites.

Historical View

LNAPL features

Petroleum LNAPLs (e.g., diesel, gasoline, crude oil) can be long-term persistent sources of groundwater and soil pollution that reach the SZ and USZ upon release. The LNAPL is characterized by a hydrophobic and non-ionic nature in the presence of water and exhibits a lower density than water.

While LNAPL can correspond to a single chemical compound such as benzene, it is often a complex mixture of several hundred components with different chemical properties [START_REF] Güler | Organic (Hydrocarbon) Contamination: Nonaqueous Phase Liquids[END_REF]Gupta et al., 4 2019). Branched and n-alkanes (mainly <C25), cycloalkanes, alkenes, cycloalkenes, acetylenes and, BTEX (benzene, toluene, ethylbenzene, xylenes) are common LNAPL components.

LNAPL mobility, partitioning process, and biodegradation

After the release of LNAPLs into the subsurface, the mobile phase infiltrates downward through the soil porosity (Fig. 1i). During migration through the USZ, a significant part of the pollution can be trapped as residual LNAPL ganglia by capillary forces or sorbed to soil grains. Many of these components have a high vapor pressure and can directly volatilize into soil gas to form potentially harmful VOC emissions [START_REF] Mccarthy | Transport of volatile organic compounds across the capillary fringe[END_REF][START_REF] Nambi | Mass transfer correlations for nonaqueous phase liquid dissolution from regions with high initial saturations[END_REF][START_REF] Patterson | Quantification of vapor intrusion pathways into a slab-on-ground building under varying environmental conditions[END_REF]. If a sufficient volume of LNAPL is released, mobile LNAPL can reach and accumulate at the water table (Illangasekare et al., 1995;[START_REF] Powers | An experimental investigation of nonaqueous phase liquid dissolution in saturated subsurface systems: Transient mass transfer rates[END_REF][START_REF] Powers | An experimental investigation of nonaqueous phase liquid dissolution in saturated subsurface systems: Steady state mass transfer rates[END_REF] (Fig. 1i). Mobile LNAPL then propagates laterally in the direction of decreasing hydraulic gradient in the capillary fringe, forming residual lenses [START_REF] Schroth | Geometry and position of light nonaqueousphase liquid lenses in water-wetted porous media[END_REF]. Mobile and residual LNAPL provide a source of soluble hydrocarbons to water infiltrating through the soil and to surrounding groundwater, forming a dissolved plume of LNAPL constituents (Fig. 1i, [START_REF] Huntley | Persistence of LNAPL sources: relationship between risk reduction and LNAPL recovery[END_REF][START_REF] Lee | NAPL pool dissolution in stratified and anisotropic porous formations[END_REF][START_REF] Mobile | Multicomponent NAPL Source Dissolution: Evaluation of Mass-Transfer Coefficients[END_REF]. Mechanical dispersion and diffusion combined with the advective groundwater flux then lead to the transverse migration of dissolved phase constituents, increasing the risks to receptors (e.g. drinking water supply) where groundwater is discharged [START_REF] Picone | Toluene biodegradation rates in unsaturated soil systems versus liquid batches and their relevance to field conditions[END_REF][START_REF] Wilson | Intrinsic bioremediation of jet fuel contamination at George Air Force Base, in: Intrinsic Bioremediation[END_REF]. It remains complex and challenging to predict the evolution of these LNAPL contaminated environments over time, and the effectiveness of remediation techniques [START_REF] Newell | Light Nonaqueous Phase Liquids[END_REF].

The native microorganisms of the soil also contribute to these variations in degrading LNAPL components [START_REF] Ortega-Calvo | Roles of bacterial attachment and spontaneous partitioning in the biodegradation of naphthalene initially present in nonaqueous-phase liquids[END_REF][START_REF] Zeman | Temperature impacts on anaerobic biotransformation of LNAPL and concurrent shifts in microbial community structure[END_REF]. The diversity of the microbial community, microbial processes, and thus hydrocarbon components biodegradation is complex and strongly varies with depth along with redox conditions, electron acceptors' availability, and LNAPL composition [START_REF] Garg | Overview of Natural Source Zone Depletion: Processes, Controlling Factors, and Composition Change[END_REF][START_REF] Sookhak Lari | Natural source zone depletion of LNAPL: A critical review supporting modelling approaches[END_REF]. Biodegradation mediated by microorganisms often follows a redox succession: aerobic, anaerobic respiration, fermentation, or methanogenesis [START_REF] Garg | Overview of Natural Source Zone Depletion: Processes, Controlling Factors, and Composition Change[END_REF][START_REF] Gupta | Assessment of LNAPL in Subsurface under Fluctuating Groundwater Table Using 2D Sand Tank Experiments[END_REF][START_REF] Irianni-Renno | Comparison of bacterial and archaeal communities in depth-resolved zones in an LNAPL body[END_REF]. Works to identify the nature of the microorganisms and the mechanisms controlling bacterial activity are in progress (Bruckberger et al., 5 2021) and there is no doubt about their major contribution to the LNAPL natural attenuation rates [START_REF] Rivett | An introduction to natural source zone depletion at LNAPL sites[END_REF].

Effect of groundwater table variations at LNAPL sites

Under 'steady-state' water table conditions, dissolution, volatilization processes, and transverse migration of the dissolved LNAPL constituents are relatively limited because of the small vertical dispersion, and the slow diffusion of dissolved LNAPL compounds [START_REF] Chompusri | LNAPL redistribution on a fluctuating water table: column experiments[END_REF]Dobson et al., 2007;[START_REF] Gupta | Assessment of LNAPL in Subsurface under Fluctuating Groundwater Table Using 2D Sand Tank Experiments[END_REF][START_REF] Huntley | Persistence of LNAPL sources: relationship between risk reduction and LNAPL recovery[END_REF][START_REF] Lenhard | A constitutive model for air-NAPL-water flow in the vadose zone accounting for immobile, non-occluded (residual) NAPL in strongly water-wet porous media[END_REF]. Retention and mobility of LNAPL in a saturated porous medium depend on the saturation of each phase in the USZ (air, water, LNAPL). Hysteresis effect strongly driven by the variations of the water table level often occurs, as the mobile LNAPL phase moves vertically along with the groundwater fluctuations [START_REF] Gatsios | LNAPL transmissivity as a remediation metric in complex sites under water table fluctuations[END_REF]ITRC, 2018;[START_REF] Kemblowski | Hydrocarbon Thickness Fluctuations in Monitoring Wells[END_REF][START_REF] Steffy | Numerical simulations and long-column tests of LNAPL displacement and trapping by a fluctuating water table[END_REF]. Within the mobile LNAPL phase, the LNAPL saturation is high and water is restricted to smaller pores and exhibits a low relative permeability (Fig. 3). When the water table drops, the mobile LNAPL moves down with the water table level (Figs. 1ii, 3ii, Ballestero et al., 1994;[START_REF] Steffy | Numerical simulations and long-column tests of LNAPL displacement and trapping by a fluctuating water table[END_REF], causing the redistribution of the LNAPL and the reconfiguration of the partitioning of LNAPL components between the different phases. A part of the LNAPL remains as discontinuous residual LNAPL ganglia in the USZ [START_REF] Charbeneau | LNAPL Distribution and Recovery Model. Distribution and Recovery of Petroleum Hydrocarbon Liquids in Porous Media[END_REF][START_REF] Jeong | An analytical model for predicting LNAPL distribution and recovery from multi-layered soils[END_REF][START_REF] Kechavarzi | Two-dimensional laboratory simulation of LNAPL infiltration and redistribution in the vadose zone[END_REF][START_REF] Kemblowski | Hydrocarbon Thickness Fluctuations in Monitoring Wells[END_REF][START_REF] Lenhard | A constitutive model for air-NAPL-water flow in the vadose zone accounting for immobile, non-occluded (residual) NAPL in strongly water-wet porous media[END_REF]. The most volatile and soluble compounds of the LNAPL can volatilize or be leached by successive water infiltration and contribute to the evolution of the dissolved plumes [START_REF] Kechavarzi | Two-dimensional laboratory simulation of LNAPL infiltration and redistribution in the vadose zone[END_REF]. The subsequent rise of the water table (Fig. 1iii, 3ii-iii) results in upward redistribution of mobile LNAPL, leaving behind some immobile entrapped LNAPL droplets in the SZ [START_REF] Charbeneau | LNAPL Distribution and Recovery Model. Distribution and Recovery of Petroleum Hydrocarbon Liquids in Porous Media[END_REF][START_REF] Lenhard | Estimation of free hydrocarbon volume from fluid levels in monitoring wells[END_REF]. The zone of the water table and LNAPL fluctuation is often called the smear zone. During successive drainage/imbibition phases, the effect of capillary pressure, as well as the trapping of fluids in the SZ and USZ, continuously modify the water flow paths (Sookhak Lari et al., 2016a). These hysteresis effects accompanied by additional LNAPL-water interactions (groundwater and rainwater) favor the mobilization of the contaminants [START_REF] Parker | A model for hysteretic constitutive relations governing multiphase flow: 1. Saturation-pressure relations[END_REF]Van Geel and Sykes, 1997).

Hence, seasonal or pump-induced groundwater level fluctuations often lead to (i) significant 6 redistribution and spreading of the pollutants through the water table fluctuation zone (Fig. 1), (ii) a decrease in the average LNAPL saturation and mass of the mobile LNAPL remaining afterward (Fig. 3, [START_REF] Charbeneau | LNAPL Distribution and Recovery Model. Distribution and Recovery of Petroleum Hydrocarbon Liquids in Porous Media[END_REF][START_REF] Kemblowski | Hydrocarbon Thickness Fluctuations in Monitoring Wells[END_REF][START_REF] Lenhard | A constitutive model for air-NAPL-water flow in the vadose zone accounting for immobile, non-occluded (residual) NAPL in strongly water-wet porous media[END_REF][START_REF] Lenhard | Estimation of free hydrocarbon volume from fluid levels in monitoring wells[END_REF][START_REF] Newell | Light Nonaqueous Phase Liquids[END_REF][START_REF] Reddi | Mass loss from LNAPL pools under fluctuating water table conditions[END_REF]Van Geel and Sykes, 1997), and (iii) a decrease in LNAPL recovery yield.

Effects of groundwater table and temperature variations on LNAPL behavior

Impact of climate change on groundwater

Climate and groundwater flow systems are in constant dynamic balance. Changes in surface hydrological processes and vegetation cover in response to fluctuations of temperature and precipitation patterns expected in the coming decades will impact the magnitude and the quality of groundwater recharge. In consequence, groundwater levels will also be impacted [START_REF] Illangasekare | From Pore to the Field: Upscaling Challenges and Opportunities in Hydrogeological and Land-Atmospheric Systems[END_REF][START_REF] Taylor | Effect of temperature on sorption equilibrium and sorption kinetics of organic micropollutants -a review[END_REF]. In most of the world, the IPCC predicts by the end of the century significant global warming, a decrease in precipitations in the mid-latitudes, and more intense and frequent extreme events (heatwaves, droughts, heavy precipitations, [START_REF] Ipcc | Global Warming of 1[END_REF]. The mean surface temperature of the globe is expected to increase from 1.5°C to 2°C by 2100. However, the temperature can locally lead to much stronger variations (up to 9°C), this is why higher temperature variabilities were considered in this work.

It has been shown that the mean shallow groundwater temperatures mimic variations of mean surface temperature [START_REF] Menberg | Observed groundwater temperature response to recent climate change[END_REF][START_REF] Taylor | Shallow groundwater temperature response to climate change and urbanization[END_REF]). An increase in the local surface temperature from 12°C to 20°C should, therefore, lead to a similar increase in mean shallow groundwater temperatures. This may significantly impact groundwater quality [START_REF] Menberg | Observed groundwater temperature response to recent climate change[END_REF][START_REF] Taylor | Shallow groundwater temperature response to climate change and urbanization[END_REF] but also the soil moisture content, the microorganisms' activity, and thus, the LNAPL degradation [START_REF] Mcalexander | Influence of Ambient Temperature, Precipitation, and Groundwater Level on Natural Source Zone Depletion Rates at a Large Semiarid LNAPL Site[END_REF][START_REF] Zeman | Temperature impacts on anaerobic biotransformation of LNAPL and concurrent shifts in microbial community structure[END_REF] and mobilization [START_REF] Margesin | Biodegradation and bioremediation of hydrocarbons in extreme environments[END_REF][START_REF] Picone | Sensitivity analysis on parameters and processes affecting vapor intrusion risk[END_REF][START_REF] Wilson | Intrinsic bioremediation of jet fuel contamination at George Air Force Base, in: Intrinsic Bioremediation[END_REF].

The intensity and the temporal distribution of precipitation are expected to change around the world (IPCC, 2014). Precipitation is likely to be less frequent from spring to autumn in most parts of the world but will be probably more intense during winter [START_REF] Dams | Spatio-temporal impact of climate change on the groundwater system[END_REF][START_REF] Goderniaux | Modeling climate change impacts on groundwater resources using transient stochastic climatic scenarios[END_REF]Goderniaux et al., , 7 2009)). In Europe (except in Scandinavia), a global decrease in the mean daily precipitations up to 23% in summer, and an increase of 12.3% in winter is expected [START_REF] Christensen | A summary of the PRUDENCE model projections of changes in European climate by the end of this century[END_REF]. On the contrary, the duration and the intensity of meteorological droughts are expected to increase, as well as the frequency and intensity of extreme precipitation events (+ 25% in Europe by 2100, IPCC, 2014). These changes will affect both the dynamics and the quality of groundwater recharge, leading probably to an intensification of groundwater level variations, an increase in the capillary fringe thickness, and the occurrence of extremely high or low groundwater heads. More intensive pumping rates may also contribute to more rapid and intense variations in groundwater levels. In the southern aquifers of the western United States, the total recharge may decline by 20% by 2100 [START_REF] Meixner | Implications of projected climate change for groundwater recharge in the western United States[END_REF]. In Europe, a global decrease in groundwater heads of 8 m can locally occur [START_REF] Dams | Spatio-temporal impact of climate change on the groundwater system[END_REF][START_REF] Goderniaux | Modeling climate change impacts on groundwater resources using transient stochastic climatic scenarios[END_REF][START_REF] Goderniaux | Large scale surface-subsurface hydrological model to assess climate change impacts on groundwater reserves[END_REF]. Moreover, the rise in the mean surface temperature may cause an increase in irrigation and evapotranspiration rates enhancing decreased groundwater heads, especially during summer and drought events [START_REF] Green | Beneath the surface of global change: Impacts of climate change on groundwater[END_REF]. Such intensification of the groundwater-table fluctuations and global decrease in the mean groundwater heads may favor the trapping and spreading of the LNAPL across the smear zone, causing a greater exposure of the contaminant to attenuation and partitioning processes.

The next section, therefore, proposes to summarize current knowledge on the global effect of groundwater level fluctuations and temperature on LNAPL behavior to discuss the potential evolution of LNAPL contaminated sites in this context.

LNAPL source zone mobility, partitioning, and depletion

The composition and physical-chemical properties of the LNAPL are temperature-dependent.

Higher temperatures decrease the interfacial tensions, the viscosity, and the density of the LNAPL, modifying the distribution and the diffusion rate of the organic contaminants through the soil [START_REF] Colombano | In Situ Thermal Treatments and Enhancements: Theory and Case Study[END_REF][START_REF] Sleep | Thermal variation of organic fluid properties and impact on thermal remediation feasibility[END_REF]. A higher temperature also decreases the LNAPL soilwater partition coefficients and LNAPL/water interfacial tension, favoring LNAPL mobility [START_REF] Imhoff | Evaluation of thermal effects on the dissolution of a nonaqueous phase liquid in porous media[END_REF][START_REF] Sleep | Thermal variation of organic fluid properties and impact on thermal remediation feasibility[END_REF] and decreasing residual LNAPL saturations [START_REF] Davis | Effect of temperature and pore size on the hydraulic properties and flow of a hydrocarbon oil in the subsurface[END_REF][START_REF] Philippe | Experimental study of the temperature effect on two-phase flow properties in highly permeable porous media: Application to the remediation of dense non-aqueous phase liquids (DNAPLs) in polluted soil[END_REF][START_REF] She | The effect of temperature on capillary pressure-saturation relationships for air-water and perchloroethylene-water systems[END_REF][START_REF] Sinnokrot | Effect of temperature level upon capillary pressure curves[END_REF]. The vapor diffusion coefficient of gas also increases with temperature [START_REF] Davis | How heat can enhance in-situ soil and aquifer remediation: important chemical properties and guidance on choosing the appropriate technique[END_REF][START_REF] Knauss | The aqueous solubility of trichloroethene (TCE) and tetrachloroethene (PCE) as a function of temperature[END_REF][START_REF] Schroth | Geometry and position of light nonaqueousphase liquid lenses in water-wetted porous media[END_REF]. In the context of climate change, 8 the earth's surface temperature could locally increase from 12°C to 20°C. The effect of this increase in temperature on the main properties and partitioning coefficients of oil and LNAPL compounds were calculated based on the available data of the literature and gathered in Tab. 1. The oil viscosity decreases up to 41% over this temperature range, increasing the LNAPL mobility (Tab. 1). On the contrary, the variation of the LNAPL density, soil-water partition coefficients, and LNAPL/water interfacial tensions appear to be negligible over this range of temperatures [START_REF] Gaito | LNAPL remediation technology bench-scale testing report[END_REF][START_REF] Imhoff | Evaluation of thermal effects on the dissolution of a nonaqueous phase liquid in porous media[END_REF][START_REF] Sleep | Thermal variation of organic fluid properties and impact on thermal remediation feasibility[END_REF]. Ten Hulscher and Cornelissen (1996) revealed that a decrease by 2-3% of the equilibrium sorption constant can be expected under this range of temperatures for most organic pollutants, probably favoring their desorption and remobilization into the air and water and making them more available for degrading microorganisms [START_REF] Mcalexander | Influence of Ambient Temperature, Precipitation, and Groundwater Level on Natural Source Zone Depletion Rates at a Large Semiarid LNAPL Site[END_REF][START_REF] Wilson | Intrinsic bioremediation of jet fuel contamination at George Air Force Base, in: Intrinsic Bioremediation[END_REF]. However, a striking opposite effect is, nevertheless, observed for BTEX (Tab. 1, [START_REF] David | Variation with temperature of octanol/water partition coefficient for the homologous series from benzene to propylbenzene[END_REF].

The effect of temperature on the sorption trends of the contaminants remains thus, difficult to predict, especially because no information is available about the variations in Koc (carbon-water partitioning coefficient) and Kow (octanol-water partitioning coefficient) for the other LNAPL compounds in the investigated range of temperature (Tab. 1). A better understanding of these sorption processes between 10-20°C is, therefore, required since they may significantly limit or delay the spreading of the dissolved constituents [START_REF] Prommer | Modelling of physical and reactive processes during biodegradation of a hydrocarbon plume under transient groundwater flow conditions[END_REF]. Calculations based on the literature data compilation show that such an increase in temperature may, nevertheless, strongly increase the saturated vapor pressure of most LNAPL compounds from 25% to 45% (Tab. 1), highly modifying their volatilization rates. In the light of these results, it is clear that the expected temperature rise will probably greatly increase gas and VOC surface emissions, and to a less extent the LNAPL mobility through the soil.

Changes in groundwater level also affect LNAPL volatilization and VOC emissions [START_REF] Guo | Influence of Fluctuating Groundwater Table on Volatile Organic Chemical Emission Flux at a Dissolved Chlorinated-Solvent Plume Site[END_REF][START_REF] Illangasekare | Vapor intrusion from entrapped NAPL sources and groundwater plumes: Process understanding and improved modeling tools for pathway assessment[END_REF][START_REF] Mccarthy | Transport of volatile organic compounds across the capillary fringe[END_REF][START_REF] Picone | Sensitivity analysis on parameters and processes affecting vapor intrusion risk[END_REF][START_REF] Qi | Influence of groundwater table fluctuation on the non-equilibrium transport of volatile organic contaminants in the vadose zone[END_REF][START_REF] Soucy | Bubble-Facilitated VOC Transport from LNAPL Smear Zones and Its Potential Effect on Vapor Intrusion[END_REF][START_REF] Werner | The influence of water table fluctuations on the volatilisation of contaminants from groundwater. Groundwater Quality: Natural and enhanced restoration of groundwater polltuion[END_REF]. Rise and fall successions of the groundwater table level cause the shortening or the lengthening of gas transport pathways from the dissolved LNAPL plume to the surface (Fig. 1, [START_REF] Guo | Influence of Fluctuating Groundwater Table on Volatile Organic Chemical Emission Flux at a Dissolved Chlorinated-Solvent Plume Site[END_REF] and enhance mass transfers towards the dissolved LNAPL plume and the soil gas phase [START_REF] Mccarthy | Transport of volatile organic compounds across the capillary fringe[END_REF]. When the groundwater table level decreases, the soil water enriched in dissolved LNAPL components is partially drained (Fig. 1ii). The dissolved LNAPL constituents in pore water are progressively exposed to an air phase, favoring the transfer of volatiles constituents to the vapor phase [START_REF] Mccarthy | Transport of volatile organic compounds across the capillary fringe[END_REF][START_REF] Qi | Influence of groundwater table fluctuation on the non-equilibrium transport of volatile organic contaminants in the vadose zone[END_REF]. This increases VOC emissions and vapor intrusion risks, especially for shallow aquifers [START_REF] Illangasekare | Vapor intrusion from entrapped NAPL sources and groundwater plumes: Process understanding and improved modeling tools for pathway assessment[END_REF][START_REF] Mccarthy | Transport of volatile organic compounds across the capillary fringe[END_REF][START_REF] Picone | Sensitivity analysis on parameters and processes affecting vapor intrusion risk[END_REF][START_REF] Qi | Influence of groundwater table fluctuation on the non-equilibrium transport of volatile organic contaminants in the vadose zone[END_REF][START_REF] Thomson | A numerical investigation into factors affecting gas and aqueous phase plumes in the subsurface[END_REF][START_REF] Werner | The influence of water table fluctuations on the volatilisation of contaminants from groundwater. Groundwater Quality: Natural and enhanced restoration of groundwater polltuion[END_REF]. Additionally, groundwater fluctuations can promote the advective transport of soil gases, accelerating the transport of the vapor phase through the USZ and their release into the atmosphere [START_REF] Qi | Influence of groundwater table fluctuation on the non-equilibrium transport of volatile organic contaminants in the vadose zone[END_REF][START_REF] Soucy | Bubble-Facilitated VOC Transport from LNAPL Smear Zones and Its Potential Effect on Vapor Intrusion[END_REF]. During the rise of the groundwater, the increase in the soil water saturation reduces the soil gas/LNAPL interfacial area, reducing gas diffusivities and volatilization. Hence, low VOC emissions are sometimes temporarily observed [START_REF] Petri | Effect of NAPL source morphology on mass transfer in the vadose zone[END_REF][START_REF] Yoon | Effect of water content on transient nonequilibrium NAPL-gas mass transfer during soil vapor extraction[END_REF]. However, while the drop in the water table level can create a "suction effect" limiting the flow of the gas, the upward movement of groundwater creates a "piston effect", pushing the soil gases enriched in VOC towards the surface (Fig. 1iii, [START_REF] Boyle | Guidance on evaluation of development proposals on sites where methane and carbon dioxide are present[END_REF]. The air trapped at this moment with LNAPL ganglia in the smear zone below the water table creates a three-phase LNAPL/air/water system (Fig. 1iii, [START_REF] Lenhard | A constitutive model for air-NAPL-water flow in the vadose zone accounting for immobile, non-occluded (residual) NAPL in strongly water-wet porous media[END_REF][START_REF] Fry | Retardation of dissolved oxygen due to a trapped gas phase in porous media[END_REF]Van Geel and Sykes, 1997;[START_REF] Williams | Oxygenation of anoxic water in a fluctuating water table system: an experimental and numerical study[END_REF][START_REF] Charbeneau | LNAPL Distribution and Recovery Model. Distribution and Recovery of Petroleum Hydrocarbon Liquids in Porous Media[END_REF][START_REF] Dobson | Effect of water-table fluctuation on dissolution and biodegradation of a multi-component, light nonaqueous-phase liquid[END_REF], further promoting the transfer of entrapped and dissolved LNAPL constituents toward the vapor phase in the early time after the upward movement of groundwater (Fig. 1iii, [START_REF] Soucy | Bubble-Facilitated VOC Transport from LNAPL Smear Zones and Its Potential Effect on Vapor Intrusion[END_REF]. Given these studies, an intensification of the groundwater fluctuations will enhance volatilization. A global decrease in the average water table level in response to climate change will increase the global thickness of the USZ, probably favoring the exposure of the LNAPL constituents to volatilization processes and the enrichment of the soil gas in VOC. This may also significantly increase the exposure of the residual LNAPL compounds to the leaching/weathering process by infiltrated meteoric water. The modification of the dynamic moisture conditions induced by the infiltration of meteoric water resulting from rainfalls or irrigation causes the leaching/the desorption and the downward aqueous transport of LNAPL constituents (Lee et al., 2001;[START_REF] Newell | Light Nonaqueous Phase Liquids[END_REF]. The increase in this leaching process may affect the chemical and the physical properties of the residual LNAPL in causing a faster depletion in the most soluble constituents. However, the contribution of this process also closely depends on the intensity and frequency of precipitation events 10 and will thus probably suffer severe local and temporal modifications in response to the expected change in precipitation patterns and heavy precipitation frequency (IPCC, 2014). Previous studies showed that the mobile LNAPL phase can be more subject to adsorption into the smear zone as the water level fluctuates, preventing the soluble contaminants to be washed away by groundwater level fluctuations [START_REF] Wilson | Intrinsic bioremediation of jet fuel contamination at George Air Force Base, in: Intrinsic Bioremediation[END_REF][START_REF] Yang | Lab-based investigation of enhanced BTEX attenuation driven by groundwater table fluctuation[END_REF]. However, the influence of groundwater level fluctuations and temperature on sorption was too poorly documented to conclude.

Dissolved LNAPL plume

Higher temperatures increase the aqueous solubility of the LNAPL [START_REF] Margesin | Biodegradation and bioremediation of hydrocarbons in extreme environments[END_REF]. However, the aqueous solubility of most LNAPL components evolves only slightly over the 10-20°C temperature range, and in different ways (Tab. 1). The effect of temperature will thus probably remain limited since the water solubility of LNAPL remains low between 0 and 20°C (Tab. 1). On the contrary, the increase in Henry's law constant of the LNAPL compounds by up to 51% is expected in this range of temperature (Tab. 1), which will probably greatly favor the volatilization of most of the dissolved LNAPL constituents.

Under fluctuating water table conditions, spatial-temporal variations of the dissolved LNAPL constituents concentrations and the plume thickness are generally observed as a function of the increase and decrease in the groundwater level [START_REF] Davis | The variability and intrinsic remediation of a BTEX plume in anaerobic sulphate-rich groundwater[END_REF]. Below the water table, the entrapped LNAPL ganglia form a thin continuous film of molecular thickness at the interface between gas and water in these three-phases systems [START_REF] Fenwick | Three-dimensional modeling of three phase imbibition and drainage[END_REF]. These films exhibit higher LNAPL-water interfacial areas more available for dissolution than in a classical LNAPL/water system [START_REF] Bradford | The entrapment and long-term dissolution of tetrachloroethylene in fractional wettability porous media[END_REF][START_REF] Shojib | Dissolution of Trapped Light Non-Aqueous Phase Liquid in the Presence of Trapped Gas[END_REF]. This results in the faster dissolution of the entrapped LNAPL compounds under fluctuating groundwater table conditions [START_REF] Shojib | Dissolution of Trapped Light Non-Aqueous Phase Liquid in the Presence of Trapped Gas[END_REF]. Moreover, the advection is the dominant transport pathway for the dissolved LNAPL constituents under fluctuating groundwater conditions [START_REF] Gupta | Assessment of LNAPL in Subsurface under Fluctuating Groundwater Table Using 2D Sand Tank Experiments[END_REF]. This enhances the depletion of the LNAPL source zone with the preferential dissolution of the most soluble compounds, leading to a more rapid decrease in the LNAPL source zone's longevity [START_REF] Dobson | Effect of water-table fluctuation on dissolution and biodegradation of a multi-component, light nonaqueous-phase liquid[END_REF][START_REF] Gupta | Assessment of LNAPL in Subsurface under Fluctuating Groundwater Table Using 2D Sand Tank Experiments[END_REF]. However, this leads also to faster transport and spreading of the dissolved LNAPL constituents in groundwater along the vertical and the horizontal 11 direction [START_REF] Davis | The variability and intrinsic remediation of a BTEX plume in anaerobic sulphate-rich groundwater[END_REF][START_REF] Gupta | Assessment of LNAPL in Subsurface under Fluctuating Groundwater Table Using 2D Sand Tank Experiments[END_REF][START_REF] Wilson | Intrinsic bioremediation of jet fuel contamination at George Air Force Base, in: Intrinsic Bioremediation[END_REF]. The pollution thus reaches a more distant location, creating a larger polluted plume [START_REF] Gupta | Assessment of LNAPL in Subsurface under Fluctuating Groundwater Table Using 2D Sand Tank Experiments[END_REF][START_REF] Sarikurt | Sherwood correlation for dissolution of pooled NAPL in porous media[END_REF][START_REF] Zhou | Response of the microbial community to seasonal groundwater level fluctuations in petroleum hydrocarbon-contaminated groundwater[END_REF].

Despite a probably limited effect of the higher temperatures on the contaminants' aqueous solubilities, more intense groundwater level fluctuations will probably greatly increase the water/air/LNAPL interfaces, favoring the spreading and the enrichment of the groundwater dissolved plume in LNAPL constituents in the climate change context. The increased contribution of the leaching of residual LNAPL droplets in the USZ, may also further contribute to the dissolved plume, especially for recent or not yet stabilized LNAPL, still rich in soluble compounds. Nevertheless, the correlation between the amplitude and the frequency of the water level variations and the enrichment of the dissolved and gaseous phase in LNAPL compounds is not clear enough [START_REF] Davis | The variability and intrinsic remediation of a BTEX plume in anaerobic sulphate-rich groundwater[END_REF][START_REF] Eichert | [END_REF][START_REF] Mcalexander | Influence of Ambient Temperature, Precipitation, and Groundwater Level on Natural Source Zone Depletion Rates at a Large Semiarid LNAPL Site[END_REF]. It remains, therefore, difficult to predict to which extent a rise or a drop of the water level of a known amplitude can affect dissolution and volatilization processes.

Yet, understanding today the effect of the amplitude of these fluctuations (when they exist) on the LNAPL plume behavior on different sites could, therefore, help us to better predict the effects of climate change. The spatial variability between monitoring wells in the same site suggests that other effects may be at work such as local variations in the hydrogeological properties of the soil (soil heterogeneities), or in the height of water table variations. The low spatial and temporal resolution of field studies does not allow the conclusions to be drawn.

Natural source zone depletion

It has been demonstrated that the rise of temperature favors the (bio)degradation of the organic pollutants [START_REF] Askarani | DISSERTATION THERMAL MONITORING OF NATURAL SOURCE ZONE DEPLETION[END_REF][START_REF] Dagois | Climatic influence on mobility of organic pollutants in Technosols from contrasted industrial activities[END_REF][START_REF] Margesin | Biodegradation and bioremediation of hydrocarbons in extreme environments[END_REF][START_REF] Mcalexander | Influence of Ambient Temperature, Precipitation, and Groundwater Level on Natural Source Zone Depletion Rates at a Large Semiarid LNAPL Site[END_REF][START_REF] Yadav | Biodegradation of Toluene Under Seasonal and Diurnal Fluctuations of Soil-Water Temperature[END_REF][START_REF] Wilson | Intrinsic bioremediation of jet fuel contamination at George Air Force Base, in: Intrinsic Bioremediation[END_REF][START_REF] Zeman | Temperature impacts on anaerobic biotransformation of LNAPL and concurrent shifts in microbial community structure[END_REF]. [START_REF] Askarani | DISSERTATION THERMAL MONITORING OF NATURAL SOURCE ZONE DEPLETION[END_REF] demonstrated that monitoring subsurface temperature is a viable technique to resolve LNAPL attenuation rates for LNAPLs since both factors are correlated. Toluene biodegradation rates have been shown to double for every 10°C increase in temperature [START_REF] Yadav | Biodegradation of Toluene Under Seasonal and Diurnal Fluctuations of Soil-Water Temperature[END_REF]. At higher temperatures, the permeability of the microbial cell membrane of LNAPL-degrading microorganisms is greater, 12 favoring the uptake of nutrients and organic components [START_REF] Corseuil | Potential biomass limitations on rates of degradation of monoaromatic hydrocarbons by indigenous microbes in subsurface soils[END_REF][START_REF] Zeman | Temperature impacts on anaerobic biotransformation of LNAPL and concurrent shifts in microbial community structure[END_REF]. The toxicity of the contamination is also reduced for the microorganisms since the low molecular weight compounds are more easily and quickly volatilized at higher temperatures [START_REF] Davis | How heat can enhance in-situ soil and aquifer remediation: important chemical properties and guidance on choosing the appropriate technique[END_REF].

Comparison between experiments under steady-state and fluctuating water levels showed that successive rises and drops of the water level and the ensuing partitioning of LNAPL components strongly modify the LNAPL biodegradation rates [START_REF] Dobson | Effect of water-table fluctuation on dissolution and biodegradation of a multi-component, light nonaqueous-phase liquid[END_REF][START_REF] Gupta | Assessment of LNAPL in Subsurface under Fluctuating Groundwater Table Using 2D Sand Tank Experiments[END_REF][START_REF] Ismail | Influence of Water Table Fluctuation on Natural Source Zone Depletion in Hydrocarbon Contaminated Subsurface Environments[END_REF][START_REF] Rainwater | Enhanced in situ Biodegradation of Diesel Fuel by Cyclic Vertical Water Table Movement: Preliminary Studies[END_REF]Van De Ven et al., 2021). Experiments by [START_REF] Rainwater | Enhanced in situ Biodegradation of Diesel Fuel by Cyclic Vertical Water Table Movement: Preliminary Studies[END_REF] revealed that a column subjected to cyclic water table variations (15 cm of variations each 48 h) exhibit 15% less residual fuel contamination after 9 weeks than a static water level column. The extent of the anaerobic/anoxic zones depends on redox conditions and the availability of electron acceptors, which suffer spatial and temporal variations as a function of the rises and drops of the groundwater level [START_REF] Rezanezhad | Water table fluctuations and soil biogeochemistry: An experimental approach using an automated soil column system[END_REF][START_REF] Sinke | Effects of a fluctuating water table: column study on redox dynamics and fate of some organic pollutants[END_REF]Van De Ven et al., 2021). Variations of the water table level also temporarily affect soil moisture, modifying the oxygen diffusion rates in the vadose zone, and thus aerobic biodegradation processes. This affects the biodegradability of the organic pollutants and the ensuing gaseous emissions [START_REF] Davis | Measurement and Modeling of Temporal Variations in Hydrocarbon Vapor Behavior in a Layered Soil Profile[END_REF][START_REF] Dobson | Effect of water-table fluctuation on dissolution and biodegradation of a multi-component, light nonaqueous-phase liquid[END_REF][START_REF] Gupta | Assessment of LNAPL in Subsurface under Fluctuating Groundwater Table Using 2D Sand Tank Experiments[END_REF]Van De Ven et al., 2021;[START_REF] Zhou | Response of the microbial community to seasonal groundwater level fluctuations in petroleum hydrocarbon-contaminated groundwater[END_REF]. More generally, successive groundwater level variations naturally enhance (i) the diffusion of oxygen [START_REF] Dobson | Effect of water-table fluctuation on dissolution and biodegradation of a multi-component, light nonaqueous-phase liquid[END_REF][START_REF] Gupta | Assessment of LNAPL in Subsurface under Fluctuating Groundwater Table Using 2D Sand Tank Experiments[END_REF][START_REF] Haberer | Oxygen transfer in a fluctuating capillary fringe[END_REF][START_REF] Lenhard | A constitutive model for air-NAPL-water flow in the vadose zone accounting for immobile, non-occluded (residual) NAPL in strongly water-wet porous media[END_REF][START_REF] Vorenhout | Automated and continuous redox potential measurements in soil[END_REF], (ii) the renewal of micronutrients through the soil and the water column by advective transport [START_REF] Rezanezhad | Water table fluctuations and soil biogeochemistry: An experimental approach using an automated soil column system[END_REF][START_REF] Schimel | Microbial stress-response physiology and its implications for ecosystem function[END_REF], (iii) the evacuation of the reaction by-products accumulated during biodegradation [START_REF] Nyer | In situ treatment technology[END_REF], (iv) the functional diversity and flexibility of microorganisms themselves [START_REF] Zhou | Response of the microbial community to seasonal groundwater level fluctuations in petroleum hydrocarbon-contaminated groundwater[END_REF]. This naturally enhances the biochemical and microbial dynamics, leading to higher microbial degradation rates of the dissolved, entrapped, and residual organic contaminants [START_REF] Dobson | Effect of water-table fluctuation on dissolution and biodegradation of a multi-component, light nonaqueous-phase liquid[END_REF][START_REF] Fry | Population structure of microbial communities associated with two deep, anaerobic, alkaline aquifers[END_REF][START_REF] Rezanezhad | Water table fluctuations and soil biogeochemistry: An experimental approach using an automated soil column system[END_REF][START_REF] Suthersan | Contemporary management of sites with petroleum LNAPL presence[END_REF]. This process is further accentuated by the important spreading of the mobile LNAPL and dissolved LNAPL compounds across the soil and the water column, making the LNAPL compounds more available to the microorganisms [START_REF] Dobson | Effect of water-table fluctuation on dissolution and biodegradation of a multi-component, light nonaqueous-phase liquid[END_REF][START_REF] Gupta | Assessment of LNAPL in Subsurface under Fluctuating Groundwater Table Using 2D Sand Tank Experiments[END_REF][START_REF] Zhou | Response of the microbial community to seasonal groundwater level fluctuations in petroleum hydrocarbon-contaminated groundwater[END_REF]. The intensification of groundwater fluctuations in response to climate change may thus conduce to greater 13 availability of carbon and nutrients to soil microorganisms, sustaining biodegradation of the LNAPL.

The global decrease in the mean groundwater heads and the ensuing increase in the USZ thickness may also favor the exposure of the residual LNAPL phase to the air, favoring aerobic LNAPL (bio)degradation processes.

It seems, therefore, relatively clear that an increase in temperature by a few degrees and an intensification of water table level fluctuations will be beneficial to the activity of the microorganisms at most contaminated sites, favoring the natural attenuation of contaminations. While this may reduce the risks associated with the residual and mobile LNAPL phase, this may, however, enhance surface emissions (mainly CO2 and CH4) (Fig. 1ii, iii, [START_REF] Mayer | Soil and Groundwater Contamination: Nonaqueous Phase Liquids[END_REF][START_REF] Amos | Investigating the role of gas bubble formation and entrapment in contaminated aquifers: Reactive transport modelling[END_REF][START_REF] Sihota | Methane emissions and contaminant degradation rates at sites affected by accidental releases of denatured fuel-grade ethanol[END_REF]. Indeed, the important source of gas resulting from the biodegradation of the dissolved LNAPL constituents in groundwater may also promote the ebullition of gas bubbles in the SZ [START_REF] Amos | Investigating the role of gas bubble formation and entrapment in contaminated aquifers: Reactive transport modelling[END_REF][START_REF] Rezanezhad | Water table fluctuations and soil biogeochemistry: An experimental approach using an automated soil column system[END_REF][START_REF] Sihota | Methane emissions and contaminant degradation rates at sites affected by accidental releases of denatured fuel-grade ethanol[END_REF]. This generates important vertical gas bubble flow from the groundwater at the origin of advection-dominated conditions in the USZ [START_REF] Soucy | Bubble-Facilitated VOC Transport from LNAPL Smear Zones and Its Potential Effect on Vapor Intrusion[END_REF]. However, this "bubble-facilitated VOC transport" may probably have a limited impact on VOC emissions on the surface as many of these VOCs are likely to be degraded by the increased bacterial activity. Nevertheless, this could contribute to an increase in CO2 and CH4 surface emissions. These attenuation rates may, therefore, be faster in the coming decades at most of the contaminated sites.

Intense biodegradation of the dissolved LNAPL constituent also sustains high concentration gradients, maintaining high dissolution processes over time [START_REF] Davis | The variability and intrinsic remediation of a BTEX plume in anaerobic sulphate-rich groundwater[END_REF]. This may contribute to the faster natural attenuation of the contamination but without lowering the concentration of the dissolved compounds in the early years after the contamination [START_REF] Dobson | Effect of water-table fluctuation on dissolution and biodegradation of a multi-component, light nonaqueous-phase liquid[END_REF][START_REF] Gupta | Assessment of LNAPL in Subsurface under Fluctuating Groundwater Table Using 2D Sand Tank Experiments[END_REF].

Moreover, above certain concentrations that depend on the bacterial strains and organic species, LNAPL components become toxic for the microorganisms, reducing the efficiency of biodegradation (Gupta et al., 2019). In some areas where important concentrations of dissolved LNAPL components are released, the biodegradation rates may thus remain limited. The biodegradability of certain LNAPL compounds exhibits also spatial-temporal variations depending on the availability of more easily biodegradable organic species and the accommodation time of the microbial community to the less biodegradable and 14 toxic compounds [START_REF] Sinke | Effects of a fluctuating water table: column study on redox dynamics and fate of some organic pollutants[END_REF]. This incubation time varies greatly between LNAPL compounds [START_REF] Wiedemeier | Technical Protocol for Implementing Intrinsic Remediation with Long-Term Monitoring for Natural Attenuation of Fuel Contamination Dissolved in Groundwater[END_REF]. The extent of the effect of climate change on biodegradation rates may thus be very inconsistent across sites. Finally, the changes in the mass of the dissolved LNAPL constituents and the availability of electron acceptors are decreasing with the increasing sorption phenomenon (up to -30%) under a fluctuating water level. This may impact biodegradation rates [START_REF] Prommer | Modelling of physical and reactive processes during biodegradation of a hydrocarbon plume under transient groundwater flow conditions[END_REF].

A better understanding of the effects of climate change on these sorption effects is therefore crucial.

However, this implies a better integration of the soil properties at sites including composition, sorption capacity, and soil heterogeneities. This is all the more important since the presence of soil heterogeneities (i.e. more or less compacted layers) influences not only sorption processes but also soil moisture contents, and gas diffusivities [START_REF] Davis | Measurement and Modeling of Temporal Variations in Hydrocarbon Vapor Behavior in a Layered Soil Profile[END_REF]. These expected effects of climate change on LNAPL contaminated sites are summarized in Tab. 2.

Cases of different climatic conditions and contaminated sites properties

Global climate models often give inconsistent predictions for precipitation patterns and groundwater recharge [START_REF] Goderniaux | Modeling climate change impacts on groundwater resources using transient stochastic climatic scenarios[END_REF][START_REF] Meixner | Implications of projected climate change for groundwater recharge in the western United States[END_REF][START_REF] Smerdon | A synopsis of climate change effects on groundwater recharge[END_REF]. Hence, uncertainties remain related to the difficulty to predict the effect of climate change on groundwater resources. There is a lack of knowledge about the future evolution of precipitations and extreme events' frequency and intensity and their consequences on the hydrological cycle, the anthropic activity (especially water consumption), and groundwater resources [START_REF] Meixner | Implications of projected climate change for groundwater recharge in the western United States[END_REF][START_REF] Smerdon | A synopsis of climate change effects on groundwater recharge[END_REF].

Furthermore, the effect of climate change on LNAPL may vary locally as a function of specific sites properties but also between arid, cold, or humid coastal environments, where different precipitation and groundwater recharge patterns are expected in the coming decades [START_REF] Christensen | A summary of the PRUDENCE model projections of changes in European climate by the end of this century[END_REF]IPCC, 2014;[START_REF] Meixner | Implications of projected climate change for groundwater recharge in the western United States[END_REF]. This paragraph, therefore, proposes to discuss the possible effects of climate change on LNAPL with different climatic conditions. These expected effects of climate change on LNAPL contaminated sites under these particular climatic conditions are summarized in Tab. 3

Cold regions

In cold environments (such as boreal environments), the environmental factors consist in low temperatures (<8°C), low soil nutrient contents and availability, and excess water distribution (rainfalls > 900 mm/year) which is often responsible for low soil oxygen diffusivities [START_REF] Rayner | Petroleum-hydrocarbon contamination and remediation by microbioventing at sub-Antarctic Macquarie Island[END_REF]. Hence, natural volatilization, dissolution, and biodegradation of petroleum hydrocarbons are generally reduced to nearly negligible rates [START_REF] Boethling | Environmental persistence of organic pollutants: guidance for development and review of POP risk profiles[END_REF][START_REF] Rayner | Petroleum-hydrocarbon contamination and remediation by microbioventing at sub-Antarctic Macquarie Island[END_REF]. Hydrocarbon pollutants can, therefore, remain for long periods and be more damaging to the environment [START_REF] Boethling | Environmental persistence of organic pollutants: guidance for development and review of POP risk profiles[END_REF]. In the climate change context, these areas could experience greater global warming than the rest of the world (+5 to +9°C, IPCC, 2014). Moreover, the increase in winter precipitations (+ 30-50%, [START_REF] Christensen | A summary of the PRUDENCE model projections of changes in European climate by the end of this century[END_REF]IPCC, 2014) and the reduction of the snow cover and soil frost can be expected to enhance the groundwater recharge, leading to a rise in groundwater levels in winter [START_REF] Okkonen | A conceptual approach for assessing the impact of climate change on groundwater and related surface waters in cold regions (Finland)[END_REF]. On the contrary, warmer temperatures will enhance evapotranspiration rates, leading to a decrease in groundwater recharge and heads in summer [START_REF] Okkonen | A conceptual approach for assessing the impact of climate change on groundwater and related surface waters in cold regions (Finland)[END_REF]. This may have several consequences on LNAPL. The increased temperature and snowmelt and decreased frost may contribute to oxygen-rich water inputs [START_REF] Okkonen | A conceptual approach for assessing the impact of climate change on groundwater and related surface waters in cold regions (Finland)[END_REF], enhancing the LNAPL-degrading microorganism's activity and biodegradation rates. Increased spreading of LNAPL across the soil and groundwater can be expected due to more intense water table fluctuations. The warmer temperatures will increase LNAPL viscosity (except for older contaminations where all soluble and volatile compounds have already been remobilized; in this case, the change will be minimal) and LNAPL compounds volatility and solubility (to a less extent). This may enhance the transfer of LNAPL constituents to the dissolved and the gaseous phase, decreasing the contamination lifetime. For example, the vapor pressure of benzene increases up to 70% between 5°C and 15°C [START_REF] Sanemasa | Solubility measurements of benzene and the alkylbenzenes in water by making use of solute vapor[END_REF]. It is also conceivable that more frequent flooding events and surface-water intrusion occur from wetlands, increasing the risk of groundwater exposure to new contaminations.

Arid and semi-arid zones

Arid and semi-arid areas are characterized by specific extremes environmental conditions, including highly variable temperatures and important water table level and soil moisture content dynamics. These conditions are generally favorable to the mobilization and the biodegradation of the 16 LNAPL [START_REF] Mcalexander | Influence of Ambient Temperature, Precipitation, and Groundwater Level on Natural Source Zone Depletion Rates at a Large Semiarid LNAPL Site[END_REF][START_REF] Wilson | Intrinsic bioremediation of jet fuel contamination at George Air Force Base, in: Intrinsic Bioremediation[END_REF]. In the context of climate change, these arid regions are expected to become drier and warmer (IPCC, 2014). The expected increase in temperature (+4 to +7°C, IPCC, 2014) may lead to a net rise in the evapotranspiration rate, a strong decrease in soil moisture content, and a significant increase in the pressure on the groundwater resources for drinking water, agricultural of industrial activities [START_REF] Meixner | Implications of projected climate change for groundwater recharge in the western United States[END_REF][START_REF] Taylor | Effect of temperature on sorption equilibrium and sorption kinetics of organic micropollutants -a review[END_REF]. At the same time, the drop in precipitation in spring and summer and the declining snowpack (the major part of the water table recharge in mountainous areas) may drastically reduce the groundwater recharge [START_REF] Meixner | Implications of projected climate change for groundwater recharge in the western United States[END_REF]. Hence, a decrease in groundwater recharge up to -30% is expected in some arid lands by 2100 (e.g. San Pedro Basin AZ, Sonora Mexico, [START_REF] Meixner | Implications of projected climate change for groundwater recharge in the western United States[END_REF]. Several consequences may, therefore, be expected for existing LNAPL contaminated sites: (i) greater spreading of LNAPL across both the USZ and the SZ due to global fallings water levels and greater level variations tied with the encroachment catchment areas of pumping wells; (ii) greater volatility of LNAPL compounds and an increase in VOC emissions in response to higher temperatures and LNAPL/air surface areas in the SZ. The extremely hot temperatures in summer may also decrease nucleic acids, proteins, and the enzyme activity of soil microorganisms [START_REF] Corseuil | Potential biomass limitations on rates of degradation of monoaromatic hydrocarbons by indigenous microbes in subsurface soils[END_REF]. The increase of droughts may dry the soil out, preventing the development of LNAPL-degrading microorganisms [START_REF] Dagois | Climatic influence on mobility of organic pollutants in Technosols from contrasted industrial activities[END_REF]. More intense drought events and heatwaves may thus take over the microbial population from the soil in these areas, decreasing significantly the LNAPL natural attenuation rates.

The expected increase in extreme precipitation events' frequency and intensity may also lead to an increasing number of floods (IPCC, 2014). These events may accelerate riverbank erosion and damage LNAPL transport infrastructures, and storage tanks, causing important new LNAPL spills. For example, Colorado has more than 5,900 oil and gas wells within 500 feet of the state's rivers and streams. In 2013, severe flooding occurred, damaging more than 2,650 oil and gas facilities (wells and storage tanks), resulting in the spill of approximately 48.250 gallons of oil and condensate in the environment.

Humid coastal areas

Many LNAPL spills occurred in coastal environments [START_REF] Gupta | Assessment of LNAPL in Subsurface under Fluctuating Groundwater Table Using 2D Sand Tank Experiments[END_REF][START_REF] Gupta | Groundwater pollution by emerging industrial pollutants and its remediation techniques[END_REF][START_REF] Rice | California leaking underground fuel tank (LUFT) historical case analyses[END_REF]. In coastal regions, groundwater tables often suffer highly dynamic conditions due to tidal effects.

These environments are particularly vulnerable to climate change. In the climate change context, the sea level is expected to rise (1,7 mm/year) from 0.43 to 0.84 m by 2100 due to thermal expansion, melting ice sheets and glaciers, and land water storage changes (IPCC, 2014). Most coastal areas -are supposed to become wetter due to the increase in precipitations by the end of the century [START_REF] Christensen | A summary of the PRUDENCE model projections of changes in European climate by the end of this century[END_REF]IPCC, 2014). These phenomena are already at work. Between 1991 and 2012, coastal regions of the USA recorded an increase in precipitation and extreme precipitation events of 5-15% and 5-71% respectively (USGCRP, 2014). The sea levels have risen by approximately 15 cm since 1960 in the western USA, and are now rising about 3,3 cm per decade (USGCRP, 2014). The increasing sea level and the more frequent extreme precipitation and storm frequency and intensity are expected to cause more frequent floods, which may greatly contribute to coastal erosion (IPCC, 2014). These phenomena may have important consequences on LNAPL contaminations. First, the recharge of adjacent coastal aquifer systems and average groundwater heads are expected to increase in coastal humid environments (IPCC, 2014). This may significantly reduce the vadose assimilation space, or even totally submerge residual LNAPL contaminants by groundwater flooding. This may limit VOC emissions but favor the dissolution and the dilution of LNAPL compounds in groundwater. It may also promote the spreading and the transfer of the dissolved contaminants and the mobile LNAPL to the sea or connected rivers. This may, however, decrease soil gas diffusivities. The rise of the sea level can also increase salt-water intrusion into groundwater (IPCC, 2014), impacting the microorganisms' activity and the biodegradation rates of LNAPL components [START_REF] Rezanezhad | Influence of Salinity and NAPL Composition on Sulfate Application in the Contaminated Subsurface Systems[END_REF]. Moreover, most of the petroleum refineries and industries are located in coastal regions across the world (e.g of the California coast, USA [START_REF] Rice | California leaking underground fuel tank (LUFT) historical case analyses[END_REF]. Therefore, the floods caused by the rising sea level, heavy precipitations, and storms are expected to significantly damage infrastructures [START_REF] Rahimi | Compound Inundation Impacts of Coastal Climate Change: Sea-Level Rise, Groundwater Rise, and Coastal Watershed Precipitation[END_REF] such as petroleum industries' storage or transportation facilities. Thus, despite the precautions taken to better manage the risk of possible new spills or to stabilize existing contaminations in the last decades, new soil and groundwater contamination may occur.

Conclusions and perspectives 18

Predicting the effect of climate change on groundwater is complex and often limited to very local scales and particular climatic conditions. Climate change predictions on LNAPL sites are thus uncertain and depend on these inconsistent various numerical models. However, according to current global predictions, the higher amplitude of groundwater table variations and higher temperatures will probably increase biodegradation processes, the LNAPL mobility, and spreading across the smear zone, favoring the release of LNAPL compounds to the atmosphere and groundwater but decreasing the LNAPL mass and its longevity. Outcomes will, nevertheless, vary greatly across arid, cold, or humid coastal environments, where different effects of climate change are expected. For example, the expected drop of the water table levels and soil moisture contents may decrease biodegradation rates in arid lands, where extreme temperatures and droughts events are expected. In coastal areas, higher precipitations and groundwater levels may lead to the submersion and the dilution of the LNAPL compounds in groundwater and connected rivers. In colds areas, warmer temperatures may significantly increase the mobility of LNAPL, dissolution, and volatilization processes. The particularities of each site, need, therefore, to be considered.

Another difficulty comes from the differences between experimental, numerical, and field studies carried out on LNAPL, where the time scale, the amplitude of groundwater level variations, the porous medium type vary greatly between studies (Tab. 4, 5, Garg et al., 2017;[START_REF] Lari | Incorporating hysteresis in a multi-phase multicomponent NAPL modelling framework; a multi-component LNAPL gasoline example[END_REF][START_REF] Sookhak Lari | Natural source zone depletion of LNAPL: A critical review supporting modelling approaches[END_REF]. There are relatively few field studies (28%) compared to laboratory experiments and numerical modeling (Tab. 4). However, laboratory experiments and numerical works are simplified models that neglected the soil composition and heterogeneities, the LNAPL chemical complexity (Tab. 5), or the amplitude of water table fluctuations. Although these properties are specific to each site, they can generate discrepancies between field observations and the results of numerical models or laboratory experiments. The amplitude of water table fluctuations may control the evolution of dissolved LNAPL constituents' concentration [START_REF] Teramoto | Field data and numerical simulation of btex concentration trends under water table fluctuations: Example of a jet fuel-contaminated site in Brazil[END_REF], soil moisture content, gas diffusivity, and thus, VOC fluxes [START_REF] Qi | Influence of groundwater table fluctuation on the non-equilibrium transport of volatile organic contaminants in the vadose zone[END_REF]. Variations in soil grain sizes, composition, or compaction determine the permeability which is one of the main parameters affecting rainfall infiltration, thermal-physical effective parameters, the migration path, the plume velocity, the entrapment, LNAPL saturation 19 distribution in the soil, gas soil moisture content, gaseous phase pathways, and gas diffusivities [START_REF] Davis | Measurement and Modeling of Temporal Variations in Hydrocarbon Vapor Behavior in a Layered Soil Profile[END_REF][START_REF] Huntley | Persistence of LNAPL sources: relationship between risk reduction and LNAPL recovery[END_REF]Illangasekare et al., 1995b;[START_REF] Lehmann | Dynamics of Fluid Interfaces and Flow and Transport across Material Interfaces in Porous Media-Modeling and Observations[END_REF][START_REF] Powers | Non-aqueous phase liquid dissolution in heterogeneous systems: Mechanisms and a local equilibrium modeling approach -Powers -1998 -Water Resources Research -Wiley Online Library[END_REF][START_REF] Qi | Influence of groundwater table fluctuation on the non-equilibrium transport of volatile organic contaminants in the vadose zone[END_REF][START_REF] Sarikurt | Sherwood correlation for dissolution of pooled NAPL in porous media[END_REF][START_REF] Sun | Transient water table influence upon Light Non-Aqueous Phase Liquids (LNAPLs) redistribution: laboratory and modelling studies[END_REF]. The behavior of an organic component in the single-component conditions of laboratory experiments and numerical models is not always representative of the behavior of the complex LNAPL mixtures present at most contaminated sites due to the interactions existing between different organic species that may affect the solubility of each compound [START_REF] Lekmine | Dissolution of multi-component LNAPL gasolines: The effects of weathering and composition[END_REF][START_REF] Vasudevan | Effect of compositional heterogeneity on dissolution of non-ideal LNAPL mixtures[END_REF]. This highlights the necessity of replacing the current compartmentalized vision of these three-phase systems with more dynamic/real-time monitoring of LNAPL integrated approaches that consider the full complexity of these contaminated sites.

Finally, the evolution of environmental standards and regulations over the last decades has led to a dramatic reduction in LNAPLs releases (ITRC, 2018b(ITRC, , 2009)). Remediation efforts and precautions taken on industrial sites have stabilized and/or reduced the evolution and mobilization of the LNAPL compounds [START_REF] Askarani | Thermal estimation of natural source zone depletion rates without background correction[END_REF]. Many of these LNAPL sites will be only slightly affected by a slight increase in surface and groundwater temperature or higher water level variations. On the other hand, for coastal or riverside sites, the increased risk of flooding associated with rising sea levels and the frequency and intensity of extreme events could compromise these efforts and lead to the formation of new sources of contamination. A better understanding of these risks may help to prevent and mitigate their impacts. Understanding the effects of climate on current and future contaminated sites could therefore have great environmental and economic benefits.

FiguresFig. 1 .

 1 Figures

Fig. 2 .

 2 Fig. 2. Dominant processes involved in the LNAPL biodegradation and compounds partitioning between

table fluctuations :

 fluctuations (i) initial water table level during the oil spill; (ii) low water table level (dry season); (iii) high water table level (wet season). VOC: volatile organic carbon.

Tables

  Tab. 1. Main properties and partitioning coefficients of oil and different LNAPL components between a temperature of 12 and 20°C. Summary of the main expected global effects of the increase in temperature and groundwater table fluctuations on the LNAPL mobility, the dissolved plume, and natural attenuation rates under the climate change context. Increased short-term risks• Decreased long-term risks Tab. 3. Summary of the main expected effects of climate change on LNAPL contaminations under specific climatic conditions.

	Vapor pressure (mmHg) a 14.0 17.0 55.9 64.9 15.6 18.4 4.3 5.1 92.1 105.9 25.0 29.5 0.50 0.60 58.0 67.2 201.8 229.2 Henry's law constant (atm.m 3 /mol) 20.0 75.1 21.7 6.2 121.4 34.7 0.71 77.5 259.6 3.05E-03 3.38E-03 3.94E-03 4.60E-03 (Staudinger and Roberts, 2001) 12.0 Ref. 50.4 (Willingham et al., 1945) 13.9 (Pitzer and Scott, 1943) 3.8 (Pitzer and Scott, 1943) 83.8 (Willingham et al., 1945 22.4 (Carruth and Kobayashi, 1973; Willingham et al., 1945) 0.45 (Carruth and Kobayashi, 1973) 52.5 (Li et al., 1973) 185.0 (Willingham et al., 1945) 3.41E-03 3.79E-03 4.42E-03 5.14E-03 (Staudinger and Roberts, 2001) 3.99E-03 4.43E-03 5.15E-03 5.97E-03 (Staudinger and Roberts, 2001) 0.905 0.99 1.14 1.30 (Abraham and Matteoli, 1988) 1.20 1.33 1.54 1.77 (Abraham and Matteoli, 1988) 5.15 (Clough, 2014) 0.11 0.12 0.13 0.15 (Ashworth et al., 1988) 9.03E-02 9.81E-02 0.11 0.13 (Hansen et al., 1993) Solubility in water (mg/L) 1589.5 1581.7 1585.6 1597.3 (Sanemasa et al., 1982) 510.6 512.9 516.5 520.1 (Sanemasa et al., 1982) 156.6 157.4 158.7 160.0 (Sanemasa et al., 1982) 10.4 10.5 9.4 10.6 b 2.1 2.1 2.2 2.3 (Nelson and De Ligny, 1968) 9.0E-03 (Clough, 2014) 86.7 88.0 81.2 70.0 (Budantseva et al., 1976; Pierotti and Liabastre, 1972) 341.1 341.7 304.8 249.0 (Pierotti and Liabastre, 1972) Log Koc (L/kg) 1.88 1.89 1.91 1.92 (Sabljić et al., 1995) c 2.28 2.30 2.31 2.33 (Sabljić et al., 1995) c 2.34 (Sabljić et al., 1995) 3.34 ECHA d Dynamic viscosity (cP) 33,5 29,0 23,7 19,6 (Sleep and Ma, 1997) f Interfacial tension of oil-water system (mJ/m²) 44.3 43.8 43.1 42.4 (Sleep and Ma, 1997) g a Calculated using Antoine Equation Parameters using data of the cited references. Temperature (°C) Benzene Toluene m-Xylene n-Hexane n-Heptane n-Decane Cyclohexane Cyclopentane Benzene Toluene m-Xylene n-Hexane n-Heptane n-Decane Cyclohexane Cyclopentane Benzene Toluene m-Xylene n-Hexane n-Heptane n-Decane Cyclohexane Cyclopentane Benzene Toluene m-Xylene Hexane Oil (Voltesso 35) Oil (Voltesso 35) b Calculated from Henry's law constant and the vapor pressure. c Calculated from the log Kow after the equation of Sabljić et al. (1995): log Koc=0.81* log Kow+0.10. dc d European Chemicals Agency (ECHA): https://echa.europa.eu/fr/information-on-chemicals. The data of each parameter and compound at the different temperatures were determined according to the data available in the respective references. e Calculated after the equation of Sleep and Ma (1997): ρoil= 0.8610-1.1750*10 -4 *T-2.7738*10 -6 *T² f Calculated after the equation of Sleep and Ma (1997): ln µoil = 24.306-1.767*l0 4 /T-3.366*l0 6 /T² g Calculated after the equation of Sleep and Ma (1997): γoiI= 47.226-0.244*T Tab. 2. Main effects of the increase in temperature from 12 to 20°C Main effect of more intense groundwater level variations Global expected effect of climate change LNAPL source zone mobility, partitioning, and depletion • Decreased LNAPL viscosity (up to 41%). • Sorption? • Increased saturated vapor pressures (up to 45%) • Greater spreading of the LNAPL across the SZ and USZ • Greater exposure of the LNAPL to the air, meteoric water, and groundwater • Accelerated diffusion and advective transport of soil gas • Increased global LNAPL mobility • Increased leaching of the residual LNAPL by infiltrated meteoric water • Increased volatilization from the mobile, residual LNAPL • Increased VOC surface emissions Dissolved plume • Low variation of the LNAPL compounds solubility • Increased Henry's law constant (up to 51%) • Greater LNAPL-meteoric and groundwater interfacial areas • Easier dissolved phase transportation by advection • Increased residual and entrapped LNAPL constituents' dissolution • Increased dissolved groundwater plume concentration • Greater spreading of the dissolved plume in groundwater • Increased volatilization from the dissolved phase Natural attenuation • Increased uptake of nutrients and organic components by microorganisms • Increased microorganisms' activity • Greater availability and renewal of carbon, oxygen, and micronutrients through the soil and the water column • Better evacuation of the reaction by-products accumulated during biodegradation • Greater functional diversity and flexibility of • Increased LNAPL biodegradation and attenuation rates • Increased gaseous (CO2, CH4) surface emissions • Decreased LNAPL source zone longevity • Maintains strong dissolution processes Main expected effect of climate change by 2100 a Main expected effect of climate change on LNAPL Cold regions • Low temperatures (<8°C) • Low soil nutrient contents and availability • Excess water distribution (rainfalls> 900 mm/yr) • Low soil oxygen diffusivities • Very low LNAPL volatilization, dissolution, and biodegradation • Increased temperature (+5-9°C) and rainfalls (up to +50%) • Reduced snow cover and soil frost • Increased groundwater recharge, and heads in winter • Increased evapotranspiration, decreased groundwater recharge, and heads in summer • Increased groundwater level fluctuations • Higher oxygen inputs and diffusion in the soil and water • Strongly enhanced soil microbial activity • Strongly increased LNAPL viscosity, volatility, and solubility • Increased spreading of the pollution in the soil and water • Strongly enhanced LNAPL biodegradation • Higher VOC emissions and dissolved pollutants concentrations • Strongly decreased pollution longevity Arid/ semi-arid zones • Highly variable and extremes temperatures (-10°C-60°C) • Scarce but intense rainfalls (mean rainfalls: 185-550 mm/yr) • Important water table level and soil moisture content fluctuations • High LNAPL mobilization and biodegradation • Increased temperature (+4-7°C) • Decreased snowpack and precipitations in spring and summer • Strongly increased evapotranspiration and groundwater use • Strongly decreased groundwater recharge (up to -30%) and heads • Increased groundwater level variations tied with the encroachment catchment areas of pumping wells • Strongly decreased soil moisture content and soil microbial activity • Increase extreme precipitation events and floods frequency and intensity • Increased LNAPL/air surface areas in the SZ • Increased LNAPL compounds volatility and VOC emissions • Increased spreading of the pollution in soil • Decreased LNAPL biodegradation • Increased risks of new LNAPL spills due to damage LNAPL transport and storage infrastructures during floods • Main current properties a Humid • High groundwater table • Increased sea level (0.43-0.84 • Increase LNAPL/water microorganisms coastal dynamic due to tidal mm/yr) due to thermal expansion, surface contact
	areas	Heptane effects		2.38 melting ice sheets, glaciers, and	ECHA • Increased pollutants
		Decane		4.16 land water storage changes	ECHA dissolution and dilution in
		Cyclohexane		• Increased precipitations (+10-	groundwater, connected
		Cyclopentane		2.53 20%) and extreme precipitation	ECHA rivers, and sea
				Log Kow events (+10-50%)		• Modification of some
		Benzene	2.20	2.21 • Increased coastal erosion, flood 2.24 2.25	(David and Moldoveanu, 2019) pollutants biodegradation rates
		Toluene	2.69	2.71 events frequency, and intensity 2.73 2.75	(David and Moldoveanu, 2019) due to changes in water
		m-Xylene		3.20 • Increased coastal aquifer and	(Sabljić et al., 1995) salinity, soil moisture content,
		Hexane		groundwater heads	3.90	(Hansch et al., 1985) (25°C) and the oxygen diffusivity
		Heptane		4.66 • Increase salt-water intrusion and	(Miller et al., 1985) (23°C) • Increased risks of new
		Decane		groundwater salinity	5.01	(Coates et al., 1985) LNAPL spills due to damage
		Cyclohexane				3.44	(Hansch et al., 1985) (25°C) of coastal LNAPL transport
		Cyclopentane				3.00	(Hansch et al., 1985) (25°C) and storage infrastructures
					Density (g/cm 3 )		during floods, storms
		Oil (Voltesso 35)	0.859	0.859	0.858	0.858	(Sleep and Ma, 1997) e
							34 35

a Predictions from IPCC (2014),

[START_REF] Meixner | Implications of projected climate change for groundwater recharge in the western United States[END_REF]

,

USGCRP (2014)

.

Acknowledgments

This work was supported by the French PIA project "Lorraine Université d'Excellence", reference ANR-15-IDEX-04-LUE, and the BRGM (the French Geological Survey). The authors would like to thank Lorraine University and the BRGM. This work is included in the scientific program of the GISFI Science of the Total Environment 806 (2022) 150412 https://doi.org/10.1016/j.scitotenv.2021.150412 20 research consortium dedicated to the knowledge and the development of remediation technologies for degraded and polluted lands (Groupement d'Intérêt Scientifique sur les Friches Industrielleshttp://www.gisfi.univ-lorraine.fr).

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. 37 Tab. 4. Main research papers from 1993 to 2021 focusing on the effect of temperature or groundwater table fluctuations on the LNAPL transport and mobilization sorted according to the studied process and the scientific approach.

Main process

References Scientific approach Dissolution, transport, sorption 38 Tab. 5. Main relevant LNAPL laboratory experiments on soil columns and numerical studies from 1993 to 2021 sorted according to the complexity of the porous media and LNAPL source composition used.

LNAPL composition LNAPL mixture complexity

Commonly used compounds References

One component Toluene, n-heptane, n-decane, or n-pentane [START_REF] Chompusri | LNAPL redistribution on a fluctuating water table: column experiments[END_REF][START_REF] Gupta | Assessment of LNAPL in Subsurface under Fluctuating Groundwater Table Using 2D Sand Tank Experiments[END_REF]Gupta and Yadav, 2020;[START_REF] Ismail | Influence of Water Table Fluctuation on Natural Source Zone Depletion in Hydrocarbon Contaminated Subsurface Environments[END_REF][START_REF] Picone | Toluene biodegradation rates in unsaturated soil systems versus liquid batches and their relevance to field conditions[END_REF][START_REF] Shojib | Dissolution of Trapped Light Non-Aqueous Phase Liquid in the Presence of Trapped Gas[END_REF][START_REF] Sinke | Effects of a fluctuating water table: column study on redox dynamics and fate of some organic pollutants[END_REF][START_REF] Soucy | Bubble-Facilitated VOC Transport from LNAPL Smear Zones and Its Potential Effect on Vapor Intrusion[END_REF][START_REF] Steffy | Numerical simulations and long-column tests of LNAPL displacement and trapping by a fluctuating water table[END_REF]Van Geel andSykes, 1997, 1994;[START_REF] Yadav | Biodegradation of Toluene Under Seasonal and Diurnal Fluctuations of Soil-Water Temperature[END_REF][START_REF] Yang | Lab-based investigation of enhanced BTEX attenuation driven by groundwater table fluctuation[END_REF] 2-4 components BTEX, n-hexadecane, methylnaphthalene, [START_REF] Chen | Influencing Factors of BTEX Volatilization[END_REF][START_REF] David | Variation with temperature of octanol/water partition coefficient for the homologous series from benzene to propylbenzene[END_REF][START_REF] Dobson | Effect of water-table fluctuation on dissolution and biodegradation of a multi-component, light nonaqueous-phase liquid[END_REF][START_REF] Teramoto | Field data and numerical simulation of btex concentration trends under water table fluctuations: Example of a jet fuel-contaminated site in Brazil[END_REF][START_REF] Vasudevan | Effect of compositional heterogeneity on dissolution of non-ideal LNAPL mixtures[END_REF]2014 > 4 components Fuel, isoparaffinic solvent, or mineral oils. [START_REF] Alazaiza | LNAPL saturation distribution under the influence of water table fluctuations using simplified image analysis method[END_REF][START_REF] Kechavarzi | Two-dimensional laboratory simulation of LNAPL infiltration and redistribution in the vadose zone[END_REF][START_REF] Lekmine | Dissolution of multi-component LNAPL gasolines: The effects of weathering and composition[END_REF][START_REF] Rainwater | Enhanced in situ Biodegradation of Diesel Fuel by Cyclic Vertical Water Table Movement: Preliminary Studies[END_REF][START_REF] Sun | Transient water table influence upon Light Non-Aqueous Phase Liquids (LNAPLs) redistribution: laboratory and modelling studies[END_REF] Porous media composition Porous media complexity Type