WO2024079373A1 - Recirculation cell for groundwater remediation in aquifer-aquitard transition zones - Google Patents

Abstract

The invention relates to recirculation cells and decontamination methods, characterised in that they operate at low volumes and involve half cycles of filling and emptying that allow the effective treatment of pollution present in aquifer-aquitard transition zones.

Description

Recirculation cell for groundwater remediation in aquifer-aquitard transition zones

The present invention refers to the field of groundwater decontamination, more specifically to an injection-extraction cell that allows the aquifer-aquitard transition zones to be effectively decontaminated.

STATE OF THE TECHNIQUE

On a global scale, groundwater provides between 25 and 40% of drinking water (UNEP, (2003). Groundwater and its Susceptibility to Degradation. UNEP/DEWA, Nairobi). In Europe, 60% of drinking water is of underground origin (Schmidt-Thomé, P., & Klein, J. (Eds.). (2013). Climate change adaptation in practice: from strategy development to implementation. John Wiley & Sons .). The loss of quality has health and economic consequences, as it increases purification costs. Therefore, the fight against its pollution is one of the great challenges of today's society, since it puts human health and ecosystems at risk (Li, P., Karunanidhi, D., Subramani, T., & Srinivasamoorthy, K. (2021).

Groundwater decontamination has traditionally been carried out either by ex-situ techniques (often using pumping and treating systems) or by in-situ techniques.

Among the frequently used in-situ techniques are chemical remediation and bioremediation (Chen, Q., Fan, G., Na, W., Liu, J., Cui, J., & Li, H. (2019). Past, present, and future of groundwater remediation research: A scientometric analysis. International journal of environmental research and public health, 16(20), 3975). These techniques have almost always been applied separately. Among the chemical techniques, known in the English literature as in-situ chemical remediation, those that use reagents that carry out oxidation reactions (in English, In-Situ Chemical Oxidation, ISCO) are distinguished (ITRC, I. (2005) . Technical and regulatory guidance for in situ chemical oxidation of contaminated soil and groundwater, New York: Council TITaR.) and those that use reagents that give rise to reduction reactions (in English, In-Situ Chemical Reduction, ISCR), (Tratnyek). , PG, Johnson, RL, Lowry, GV, & Brown, RA (2014). remediation. In Chlorinated Solvent Source Zone Remediation (pp. 307-351). Springer, New York, NY).

In the case of ISCO techniques, one of the main known limitations is the short half-life of the reagents used (with the exception of the use of potassium permanganate). This greatly limits the migration of the reactants downstream of their injection point (Siegrist, R. L, Crimi, M., & Simpkin, T. J. (Eds.). (2011). In situ chemical oxidation for groundwater remediation (Vol. 3). Springer Science & Business Media) and also limits the treatment area, and consequently the decontamination efficiency. Furthermore, the short life of the reagents makes it difficult for them to penetrate, through molecular diffusion, to the interior of the levels of low hydraulic conductivity, where large amounts of contaminant are stored (EPA (2017): How To Evaluate Alternative Cleanup Technologies For Underground Storage Tank Sites A Guide For Corrective Action Plan Reviewers. EPA 510-B-17-003). The lack of treatment of these levels favors the existence of the so-called rebound effect once the aquifer is decontaminated (Puigserver, D. Herrero, J., Nogueras, X., Cortés, A., Parker, B. L. Playá, E. & Carmona, J. M. (2021). Biotic and abiotic reductive dechlorination of chloroethenes in aquitards.

In the case of the reagents used in ISCR techniques, one of the most common has been metallic iron (Fe ⁰ ), known as Zero Valent Iron (ZVI). It is a reagent that is applied to the medium in the form of particles of different grain sizes, from millimeter size (mm) to the size of microparticles (pm) and nanoparticles (nm) (Labeeuw, V. (2013). In Situ Chemical Reduction using Zero-Valent Iron Injection-A Technique for the Remediation of Source Zones. Machteld De Wit, OVAM, 104). These particles are injected into the medium in the form of a dispersion within an emulsion that keeps them in suspension. Depending on their size, ZVI particles present different limitations, the most important being the individual weight of these particles.

Among bioremediation techniques, two large groups are differentiated. Those based on the biostimulation of the indigenous microbial population and those based on bioaugmentation through the inoculation of non-native microorganisms, but capable of degrading contaminants in the environment, and the inoculation of indigenous microorganisms grown in the laboratory (Adams, GO, Fufeyin, PT , Okoro, S.E., & Ehinomen, I. (2015). biostimulation and bioaugmentation: a review. International Journal of Environmental Bioremediation & Biodegradation, 3(1), 28-39).

The reagents used in biostimulation are very varied, ranging from nutrients to electron donors, among others (Hussain, C. M. (Ed.). (2020). The handbook of environmental remediation: classic and modern techniques. Royal Society of Chemistry). In all cases, however, one of the problems that often arises with biostimulation is that there is the possibility of promoting microbial overgrowth of communities that do not decontaminate the compounds to be eliminated (Puigserver, D., Carmona, J. M. , Barker, J., Cortes, A., Nogueras, X., & Viladevall, M. (2011). Use of chemical and biological techniques in the remediation of sites contaminated by chlorinated solvents. Hydrological Sciences, 445-448.), or that displacements of the microbial niche are generated, which decreases decontamination efficiency (Herrero, J., Puigserver, D., Nijenhuis, I., Kuntze, K., & Carmona, J. M. (2019). Combined use of /SCR and biostimulation techniques in incomplete processes of reductive dehalogenation of chlorinated solvents. Science of the total environment, 648, 819- 829.

Furthermore, in most cases reagent injection and pollution treatments focus on decontaminating aquifers. However, the techniques used have a very low penetrability within formations of low hydraulic conductivity (aquifer-aquitard transition zones), which makes the treatment of these zones difficult, within which large amounts of contaminant are stored, especially when These are mature contamination episodes (that is, decades old since the contamination began).

The procedures usually used to place treatments and/or reagents in the contaminated environment have been based on passive methods or by creating closed injection and pumping cells in the aquifer. These treatments consist of aqueous solutions of chemicals (for example, chemical reagents) or emulsions of specific preparations (for example, of microorganisms cultured for inoculation in the medium. From now on, the aforementioned aqueous solutions and emulsions will be referred to in this document as “treatment” or “treatments”, regardless of whether they are chemical or biological treatments. Passive methods and closed injection and pumping cells are discussed in Kitanidis & McCarty (2012) (Kitanidis, PK & McCarty, PL (Eds.). (2012). Delivery and Mixing in the Subsurface: Processes and Design Principles for in situ remediation (Vol. 4).

Passive methods consist of injecting the reactants into the aquifer, allowing them to react along the flow (Rosansky, S., Condit, W., & Sirabian, R. (2013). Best practices for injection and distribution of amendments . Technical Report TR-NAVFAC-EXWC-EV-1303.). This implies that most of the reactants migrate through the most permeable levels, that is, more conductive levels (that is, with greater hydraulic conductivity), ceasing to interact with the levels of low hydraulic conductivity, where large quantities accumulate. of contaminants.

In the case of the use of closed cells (formed by wells for injecting water with treatment and/or reagents and wells for extracting treated water within the contaminated medium), the continuous injection and pumping modify the natural flow field and the flow that flows between the injection and extraction wells. This requires sufficiently permeable media that prevent the system from being dry and isolate it from the rest of the aquifer (Muller, K. A., Johnson, C. D., Bagwell, C. E., & Freedman, V. L. (2019). Review of Amendment Delivery and Distribution Methods, and Relevance to Potential In Situ Source Area Treatment at the Hanford Site (No. PNNL-29198; DVZ-RPT-0023-Rev. 0.0). Additionally, in the event that the reagents favor the generation of reducing redox conditions, these are promoted in the zone of influence of the cell. The problem arises when the degradation products generated are more toxic than the parents from which they are derived, which increases the risk to human health and ecosystems, especially when they accumulate in the environment.

There are two large groups of reagent injection systems in the environment. On the one hand, there are systems based on drilling that are equipped as injection wells that allow continuous or discontinuous injection of reagents. On the other hand, Direct-Push type techniques based on perforation of the medium and simultaneous injection of the reagents, so they are punctual injections (in space and time) and guided, but they do not allow the introduction subsequent reagents at that same point (Muller, KA, Johnson, CD, Bagwell, CE, & Freedman, VL (2019). Review of Amendment Delivery and Distribution Methods, and Relevance to Potential In Situ Source Area Treatment at the Hanford Site (No. PNNL-29198; DVZ-RPT-0023-Rev. 0.0). Pacific Northwest National Lab.(PNNL), Richland, WA (United States)).

Apart from these two groups, there are also systems capable of introducing the reagents into the medium instantly (an injection pulse), or through a passive system, such as the introduction into a well of rods of products capable of slowly releasing reagent to the medium. contact with groundwater, as is the case of ORC bars (oxygen release compound), which dissolve, releasing oxygen progressively as the groundwater flow circulates.

As can be derived from the above, in the state of the art there is still a need to have systems and procedures that allow the treatment of the large amount of pollutant mass that is accumulated inside low permeability materials ( hydraulic conductivity) thus avoiding the rebound effect mentioned above. These are, for example, the levels of low permeability (conductivity) that are interspersed at the base, in the middle or on the roof of numerous aquifers, forming the transition zones that frequently exist between the aquifers and the underlying or superjacent aquitards ( although, to a lesser extent, they can also be found in the middle of aquifers). These aquifer-aquitard transition zones are formed by numerous intercalations of centimeter-thick levels with low permeability (hydraulic conductivity) where contaminants accumulate. These intercalations are separated by more permeable (more conductive) levels, also centimeter thick. The alternation of low permeability levels (below 0.001 cm/s) and more permeable levels (between 0.001 and 0.023 cm/s) makes these transition zones jointly (i.e., globally) low permeability formations (i.e. that is, low hydraulic conductivity), that is, poorly permeable formations. However, in any case, they are part of the aquifer. Its range of overall hydraulic conductivity (i.e. global permeability) can range from 0.001 cm/s to 0.012 cm/s.

EXPLANATION OF THE INVENTION

The inventors of the present invention, after extensive and exhaustive experiments, have discovered a recirculation cell that works by filling and emptying half cycles and a decontamination procedure associated with it that allow, in an effective and surprising way, to solve the problems present in the state of the art (mentioned previously) and, therefore, decontaminate the aquifer-aquitard transition zones, located at the base, in the middle or on the roof of the aquifers.

Therefore, the recirculation cell and the procedure of the present invention are applicable and effective for the treatment of low permeability media (i.e., low hydraulic conductivity media), for example and preferably, of the aquifer-aquitard transition zone type. (Puigserver, D., et.al. (2016). Reductive dechlorination in recalcitrant sources of chloroethenes in the transition zone between aquifers and aquitards. Environmental Science and Pollution Research, 23(18), 18724-18741 ; Puigserver, D., et.al. (2020). Natural attenuation of pools and plumes of carbon tetrachloride and chloroform in the transition zone to bottom aquitards and the microorganisms involved in their degradation. Science of The T otal Environment, 712, 135679), which, although frequent. , the state of the art fails to treat effectively and causes problems such as the rebound effect and subsequent recontamination of already treated aquifers. In contrast, the cell and procedure of the present invention are, therefore, not applicable to media with very low permeability (such as aquicludes), nor to aquitards of high thickness, beyond the decimetric scale. The cell and method of the present invention are also not applicable to media of medium to high transmissivity (i.e., good aquifer media). Transmissibility is a parameter widely known in the state of the art and by those skilled in the art and which results from multiplying the permeability (that is, the hydraulic conductivity) by the water-saturated thickness of the medium of interest (which can either be a aquifer as a part of it, such as, for example, an aquifer-aquitard transition zone). Therefore, in a first aspect, the present invention refers to a recirculation cell that comprises: a) at least one extraction well that allows the extraction of water from an aquifer-aquitard transition zone; b) at least one tank to store recirculated water; c) at least one reinjection well that allows reinjection into the aquifer-aquitard transition zone of water from at least one tank to store recirculated water; and d) at least one means to supply a treatment to the aquifer-aquitard transition zone, characterized in that said cell is configured to operate in semi-cycles of filling and emptying of at least one tank to store the recirculated water, so that in the semi-cycle of filling the at least one tank to store recirculated water, water is extracted from the at least one extraction well at a flow rate of between 0.30 and 1.30 L/min for filling the said at least one tank to store recirculated water ; and in the semi-cycle of emptying the at least one tank to store recirculated water, the water from said tank is reinjected into the at least one reinjection well at a flow rate of between 0.80 and 3.80 L/min.

In a second aspect, the present invention refers to a procedure for the decontamination of an aquifer-aquitard transition zone that comprises the use of a cell of the present invention to carry out said decontamination.

As used herein, “low hydraulic conductivity level” and its plural have the meaning they commonly acquire in the state of the art, that is, layers of low permeability materials (hydraulic conductivity or permeability below 0.001 cm). /s). Although the thickness of these levels can be varied, in the context of the present invention they are thin layers.

In the present document, “poorly permeable formation” and its plural acquire the meaning that they commonly have in the state of the art and are accumulations of layers (levels) that, as far as permeability is concerned, can be homogeneous or heterogeneous ( that is, with diverse permeability values), but overall its permeability is low (not reaching the category of good aquifer - very transmissive hydrogeological formation).

As used in this document, “aquifer-aquitard transition zone” and its plural, they acquire the meaning that they commonly have in the state of the art, that is, they are formations constituted by the alternation of low permeability levels and more permeable, which makes these transition zones together be poorly permeable formations in which groundwater flow takes place along the more permeable levels, that is, along these more permeable levels, groundwater flows “by advection” (it moves by advection at low speed, as corresponds to groundwater, although in a perceptible way on the human scale); In contrast, along the low permeability levels of the same transition zone, water does not frequently move in a perceptible way at the human scale, in which case we are faced with aquicludes (advection at these levels is practically zero, that is, the speed of water movement is practically zero), although, as has been indicated, the contaminants penetrate inside, but not by advective flow of groundwater but by diffusion. molecular. An aquifer-aquitard transition zone is always a poor aquifer (compared to an aquifer of the same thickness, whose permeability will always be greater precisely because it is an aquifer). The problem is that, as explained above, when the transition zone is contaminated, the flow of groundwater through it contaminates the aquifers with which it is connected, hence the importance of achieving means that allow the decontamination of these areas, such as the cell and the process of the present invention. The range of global hydraulic conductivity (global permeability) of an aquifer-aquitard transition zone can vary from 0.001 cm/s to 0.0120 cm/s.

In this document, “aquitard” and its plural acquire the meaning that they commonly have in the state of the art, that is, it is a hydrogeological formation capable of storing water, but whose hydraulic conductivity is very low, so it transmits it with slowness. Examples of aquitards are fine sands and silts. An aquitard has a permeability (hydraulic conductivity), whose range varies from 10' ⁷ to 10' ³ cm/s.

As used in this document, “aquiclude” and its plural acquire the meaning that they commonly have in the state of the art, that is, it is a hydrogeological formation that, although it contains water in its pores, its permeability is extremely low. , so water circulates considerably slowly, so that on a human scale it can be considered impermeable. In Anglo-Saxon literature, there is a certain tendency not to use the term aquiclude, replacing it with aquitard accompanied by the value of its permeability. Examples of aquicludes are clays. An aquiclude has a permeability (hydraulic conductivity) below 10' ⁷ cm/s.

As used herein, “medium to high transmissivity media” and “good aquifer media” have the same meaning and are used interchangeably. In both cases, the meaning is that which is commonly acquired in the state of the art. Transmissivity is a hydraulic parameter that results from multiplying permeability by the water-saturated thickness of an aquifer. This parameter is indicative of the flow of water that circulates through the aquifer (and, therefore, the flow that can be extracted from it). This flow rate depends, therefore, on the permeability of the aquifer (the more permeable it is, the greater the flow rate that can be obtained) and the thickness of that aquifer (the greater the thickness, the greater the flow rate that can be obtained). The higher the value of this parameter, the better the aquifer is and vice versa. From the point of view of the flows that can be extract, transmissivity is indicative of the flow of water that circulates through the aquifer (and therefore the flow that can be extracted from it). Typical transmissivity values for good aquifers can range from 700 (medium transmissivity) to 4000 m ² /day (high transmissivity).

As used herein, “hydraulic conductivity” and its plural acquire the meaning they commonly have in the state of the art. Therefore, hydraulic conductivity is synonymous with permeability, and is a measure of the ability of a medium to transmit water through it (regardless of the thickness of that medium). Its determination in the state of the art is diverse:

1. In the laboratory through the measurement of permeability (using a laboratory permeameter) of a sample taken in the field. Very punctual representation.

2. In the field through field tests: pumping tests, slug tests, injection of tracers, etc. Very high representation of the reality of the environment.

3. In the office, through real field data (flow and hydraulic gradients). Very high representativeness.

4. Through databases of real values of rocks and sediments based on their typology and texture. High representativeness if good witnessing of subsoil rocks and sediments is carried out.

In this document, hydraulic conductivity is determined using various methods of typologies 2 and 3 and, as the testimonies from surveys are available, comparing with literature databases.

Throughout the description and claims the word "comprises" and its meanings are not intended to exclude other technical characteristics, additives, components or steps. Furthermore, the word "comprises" includes the case "consists of." For those skilled in the art, other objects, advantages and features of the invention will emerge partly from the description and partly from the practice of the invention. The following examples and drawings are provided by way of illustration, and are not intended to be limiting of the present invention. Numerical signs relating to the drawings and placed in parentheses in a claim are intended solely to enhance the understanding of the claim, and should not be construed as limiting the scope of protection of the claim. Furthermore, the present invention covers all possible combinations of particular and preferred embodiments indicated herein. BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1. Shows a schematic plan view of the recirculation cell of the present invention placed in an aquifer-aquitard transition zone to be treated.

FIG. 2. Shows a diagram of an extraction well of the recirculation cell of the present invention.

FIG. 3. Shows a diagram of a reinjection well of the recirculation cell of the present invention.

FIG. 4. Shows a diagram of a tank to store recirculated water from the recirculation cell of the present invention.

FIG. 5. Shows a schematic of a tank to store a recirculation cell treatment of the present invention.

FIG. 6. Shows a diagram of the operation of the recirculation cell of the present invention.

FIG. 7. Shows a diagram (section) of the recirculation cell of the present invention used in example 1, as well as the pretreatment applied in said example to the aquifer-aquitard transition zone to be treated.

DETAILED EXPOSITION OF IMPLEMENTATION MODES

As indicated above, in a first aspect, the present invention refers to a recirculation cell that comprises: a) at least one extraction well that allows the extraction of water from an aquifer-aquitard transition zone; b) at least one tank to store recirculated water; c) at least one reinjection well that allows reinjection into the aquifer-aquitard transition zone of water from at least one tank to store recirculated water; and d) at least one means to supply a treatment to the aquifer-aquitard transition zone, characterized in that said cell is configured to operate in semi-cycles of filling and emptying of at least one tank to store recirculated water, so that in the semi-cycle of filling of the at least one recirculated water tank, water is extracted from the at least an extraction well at a flow rate of between 0.30 and 1.30 L/min for filling said at least one tank to store recirculated water (more preferably, at a flow rate of between 0.42 and 1.25 L/min min, even more preferably, at a flow rate between 0.58 and 0.94 L/min); and in the semi-cycle of emptying the at least one tank for storing recirculated water, the water from said tank is reinjected into the at least one reinjection well at a flow rate of between 0.80 and 3.80 L/min (more preferably, at a flow rate of between 0.83 and 3.75 L/min, even more preferably at a flow rate of 1.25 L/min).

In the cell of the present invention, the at least one extraction well and the at least one reinjection well are positioned at the ends of the cell in the direction and direction of the water flow, the at least one water extraction well being located downstream and at least one reinjection well upstream.

The at least one extraction well and the at least one reinjection well preferably have a well casing.

Each of the wells of the cell of the present invention comprises at least one slotted area, more preferably a slotted area.

The slotted zone of a well (in English, screening zone, or well admission zone, regardless of whether it is an extraction or injection well) is the part of a well through which it extracts or injects water. , depending on the well in question. It is an area of variable length in which the pipe that forms the corresponding well is perforated (slotted), so that water enters the porous and permeable geological formation through said slotted area if it is a well equipped of an injection pump (therefore, reinjection well). Likewise, if it is a well equipped with an extraction pump (therefore, it is an extraction well), the water leaves the porous and permeable formation through the aforementioned slotted area. The upper part of the grooved area is at a certain depth, and the lower part of it is at a greater depth.

In the cell of the present invention, the slotted area of the at least one extraction well and the slotted area of the at least one reinjection well are located exactly in front of the aquifer-aquitard transition zone. That is, the top of both grooved zones is at the same depth as the top of the aforementioned transition zone (which is which is called the roof of that transition zone), and the bottom of both grooved zones is at the same depth as the bottom of said transition zone (what is called the base of that transition zone).

In this way, the treatment and/or reagents are injected through the entire thickness of the contaminated transition zone, and the recirculated water is extracted through the entire thickness of the extraction zone.

The recirculation cell of the present invention works in semicycles. Two half-cycles form a cycle, a half-cycle for filling the at least one tank to store recirculated water and a half-cycle for emptying the at least one tank filled with water that has been recirculated throughout the area of influence of the cell (between the roof and the base of the transition zone). Therefore, in the cell of the present invention, when water is extracted through the at least one extraction well to fill the at least one tank to store recirculated water, water is not being reinjected into the cell through the at least a reinjection well, and vice versa. That is, the filling and emptying half cycles are successive and never simultaneous. In a preferred embodiment, the filling half cycle lasts between 60 and 180 minutes; and the emptying semicycle between 20 and 90 minutes.

The extraction and reinjection flow rates in the recirculation cell of the present invention are very small. In this way, in addition to avoiding an excessive drop in levels and practically drying out the cell, above all, a very low flow speed is obtained. This low speed ensures that the chemical and biogeochemical reactions that enable the degradation of contaminants have sufficient time to occur along the path taken by the reagents or treatments inside the cell.

Therefore, in the cell of the present invention for the treatment of aquifer-aquitard transition zones, water is extracted from said zone through at least one extraction well until the filling of at least one tank to store recirculated water (semicycle of filling) and in the subsequent emptying semicycle said recirculated water will be reinjected into the at least one reinjection well and will circulate through the cell again to the at least one extraction well to be extracted in the next filling semicycle.

In the recirculation cell of the present invention, the space between the at least one extraction well and the at least one reinjection well determines or comprises the area to be treated and decontaminate and is the area through which the extracted and reinjected water and the treatment or treatments injected into the cell of the present invention will recirculate.

In a preferred embodiment, the at least one extraction well and the at least one reinjection well have the necessary length to reach the aquifer-aquitard transition zone and their respective at least one grooved zone (preferably, one) has the arrangement previously explained.

Said at least one extraction well, also preferably, has the necessary depth to be able to extract water from the aquifer-aquitard transition zone; more preferably said at least one extraction well reaches the aquifer-aquitard transition zone; Even more preferably, said at least one extraction well reaches the base of the aquifer-aquitard transition zone.

For its part, the at least one reinjection well, in a preferred embodiment, has the necessary depth to be able to reinject the recirculated water into the aquifer-aquitard transition zone; more preferably said at least one reinjection well reaches the aquifer-aquitard transition zone; Even more preferably, said at least one reinjection well reaches the base of the aquifer-aquitard transition zone.

Therefore, an expert in the field will be able to determine the necessary depth of the at least one extraction well and the at least one reinjection well based on the characteristics and situation of the aquifer-aquitard transition zone to be treated.

In a preferred embodiment, each of the at least one extraction well comprises at least one means for extracting water, more preferably a means for extracting water. Each of said at least one means for extracting water comprises at least one extraction pipe and at least one extraction pump; more preferably an extraction pipe and an extraction pump, said extraction pipe connecting the extraction well with at least one tank for storing recirculated water.

Said at least one extraction pipe preferably has at least one sampling means, more preferably one. Additionally, in a preferred embodiment, said at least one extraction pipe is thermally insulated, more preferably it is covered with thermal insulating material (califugators). Also in a preferred embodiment, the at least one extraction pump is a peristaltic pump or a submersible pump.

The at least one extraction well preferably additionally comprises a pressure sensor configured to measure the water level of the well. If the pressure sensor detects a water level below that established as the minimum water level of the extraction well, the semi-filling cycle of at least one tank will be stopped to store recirculated water (to avoid drying out of the well).

It is contemplated that the at least one extraction well additionally comprises at least one sensor for measuring one or more of the following parameters: temperature, electrical conductivity, dissolved oxygen, redox potential and pH. Preferably, the at least one extraction well comprises sensors for measuring temperature, electrical conductivity, dissolved oxygen, redox potential and pH.

Preferably, the internal diameter of the at least one extraction well is at least 100 mm, more preferably between 100 mm and 150 mm.

In a preferred embodiment, the at least one reinjection well comprises at least one means for reinjecting water. Said at least one means for reinjection of water preferably comprises at least one reinjection pipe and at least one reinjection pump, more preferably a reinjection pipe and a reinjection pump, said reinjection pipe connecting the reinjection well with at least one tank to store recirculated water.

Said at least one reinjection pipe preferably has at least one sampling means, more preferably one. Also preferably, the at least one reinjection pipe is thermally insulated, more preferably, the at least one reinjection pipe is covered with thermal insulating material (califugators).

Also in a preferred embodiment, the at least one reinjection pump is a peristaltic pump or a submersible pump.

The at least one reinjection well preferably additionally comprises a sensor pressure configured to measure the water level of said well. If the pressure sensor detects a water level above that established as the maximum water level of the reinjection well, the emptying half-cycle of at least one tank to store recirculated water will be stopped (to prevent the well from overflowing).

It is contemplated that the at least one reinjection well may additionally comprise at least one additional sensor, for example, to measure one or more of the following parameters: temperature, electrical conductivity, dissolved oxygen, redox potential and pH.

Preferably, the internal diameter of the at least one reinjection well is at least 100 mm, more preferably between 100 and 150 mm, even more preferably between 100 and 120 mm.

In a preferred embodiment, each of the at least one means for supplying a treatment to the aquifer-aquitard transition zone comprises a storage tank for the treatment (in liquid form) and a means (preferably, a pipe and a pump) for injection. of treatment in the aquifer-aquitard transition zone.

Preferably, the means for injecting the treatment into the aquifer-aquitard transition zone allows the injection of the treatment into the at least one reinjection well.

Said treatment can be any treatment known in the state of the art suitable for water decontamination. An expert in the field, depending on the type of contamination present in the aquifer-aquitard transition zone to be treated, will be able to determine if said at least one treatment is necessary and which one should be applied. It is contemplated that more than one simultaneous or successive treatment can be applied, depending on each contaminant and contaminated location. In a preferred embodiment, the cell of the present invention comprises means for supplying lactic acid, even more preferably means for supplying lactic acid and means for supplying a buffer solution (preferably sodium bicarbonate and sodium carbonate in an aqueous medium). Preferably, each of the treatments is injected at a flow rate of between 0.5 and 1.5 mL/min.

It is contemplated that the at least one tank for storing recirculated water is any tank available in the state of the art. Preferably, the at least one tank for storing recirculated water is opaque, even more preferably it is made of opaque polyethylene. In a more preferred embodiment, the at least one tank for storing recirculated water comprises a settling volume, a useful volume and a head volume (in this order, from the base to the top of the tank), the useful volume being the which is filled and emptied with water in the filling and emptying half cycles of the cell of the present invention.

What was indicated above for the tank to store recirculated water is also applicable to each of the treatment storage tanks (one or more).

It is contemplated that the cell of the present invention is configured (preferably, by means of automatic control of the operation of the cell) to carry out consecutive filling and emptying half cycles in which: a) first a semi-cycle for filling the at least one tank for storing recirculated water in which the useful volume of the at least one tank for storing recirculated water is filled by extracting water from the aquifer-aquitard transition zone to be treated by means of at least one well. extraction. b) then, in the emptying semi-cycle, the useful volume of at least one tank is emptied to store recirculated water, reinjecting the recirculated water into the aquifer-aquitard transition zone to be treated by means of at least one reinjection well, preferably together with at least one treatment.

The repetition of stages a) and b) is contemplated (that is, the filling and emptying half cycles) until the desired decontamination is obtained.

Additionally, in a preferred embodiment, the recirculation cell of the present invention comprises at least one monitoring well that includes sensors for monitoring water quality, and thus, being able to verify how the water treatment procedure is evolving. More preferably, the cell of the present invention comprises three monitoring wells: a first monitoring well located upstream of the cell; a second monitoring well located between the extraction well and the reinjection well; and a third well located downstream of the cell.

In the most preferred embodiment (combinable with any of the embodiments mentioned above), in the recirculation cell of the present invention: the at least one extraction well is an extraction well; the at least one reinjection well is a reinjection well; and the at least one tank for storing recirculated water is a tank for storing recirculated water.

As indicated above, the at least one extraction well (preferably, an extraction well) and the at least one reinjection well (preferably, a reinjection well) are positioned at the ends of the transition zone portion aquifer-aquitard to be treated (preferably, the entire aquifer-aquitard transition zone to be treated), in the direction and sense of the flow of groundwater, with at least one extraction well being located (preferably, a water extraction well underground) downstream and the at least one reinjection well (preferably, a reinjection well) upstream.

It is contemplated that if the aquifer-aquitard transition zone to be treated is very extensive, various recirculation cells of the present invention can be placed both in parallel and in series, or both at the same time (forming a regular rectangular mesh).

Preferably, in the recirculation cell of the present invention the distance between the extraction well and the reinjection well is between 4 and 8 meters, more preferably 6 meters.

In a preferred embodiment, the length of the slotted areas of the extraction well (through whose slotted area the recirculated water in the aquifer-aquitard transition zone to be treated is extracted) and of the reinjection well (through whose slotted area The recirculated water is injected and the decontamination treatments in the aquifer-aquitard transition zone to be treated) are identical to the thickness of the aquifer-aquitard transition zone to be treated. Additionally, preferably, said slotted zones are positioned just in front of the aquifer-aquitard transition zone to be treated, and both wells are aligned in the direction and direction of the flow of groundwater within the cell, with the water extraction well located downstream and the reinjection well upstream.

The recirculation cell of the present invention, due to its special structural and operating configuration (including the low flow rates at which it operates and operation in successive filling and emptying semi-cycles) allows solving the present technical problems. in the state of the art and mentioned above, as derived from the example included below. Therefore, the recirculation cell of the present invention allows the effective decontamination of media that globally (i.e., as a whole) are of low permeability (i.e., low hydraulic conductivity media). As already described above, these media are formed by the alternation of numerous levels of low permeability (each of them of thin thickness, usually centimetric); and more permeable levels, each also of thin thickness (usually centimeter). The result of this alternation of levels is a medium that is overall poorly permeable (that is, with little hydraulic conductivity), for example and preferably, of the aquifer-aquitard transition zone type.

Additionally, the recirculation cell of the present invention can be applied for the abiotic or biotic decontamination of organic contaminants (for example, halogenated solvents, hydrocarbons in general, emerging contaminants such as pesticides, pharmaceutical products, including veterinary pharmacy products, persistent contaminants , etc...). It can also be used for the decontamination of, among others, nitrate in the aforementioned transition zones.

In the state of the art there are no semi-cycle recirculation cells, since all the cells that exist are designed for contaminated aquifers (that is, very permeable geological formations), and they cannot work in contaminated, slightly permeable formations such as those for which it has been designed. designed the cell by half cycles, as previously explained. In addition, the aquifer cells operate continuously, they are made up of two wells, one for extraction and the other for reinjection, both operating continuously. Therefore, in said state-of-the-art cells, water continually enters and leaves the cell, and at high flow rates. On the other hand, the recirculation cell of the present invention works in semi-cycles and at small flow rates, otherwise the contaminated formation would remain practically dry within the poorly permeable geological formation to be treated. If this were to happen, all the mass of contaminant that would have been stored within the very low permeability levels would not be eliminated. This situation would be unsustainable, so when the cell was subsequently dismantled and the water levels recovered, the rebound effect mentioned above would take place. Furthermore, if the source of contamination is made up of a non-aqueous liquid that is denser than water, this would not be treated either, which, when were to recover the levels, it would lead to new incorporation of contaminant into the groundwater of the poorly permeable area.

As indicated above, the emptying of the at least one tank to store recirculated water coincides with the reinjection into the cell of the recirculated water through the at least one reinjection well. This reinjection is accompanied by the injection of the corresponding reagent/s or necessary treatment/s. After circulating throughout the cell, the recirculated water (and the reagents and/or treatments that have not yet been consumed, if applicable), are extracted again through at least one extraction well located downstream of the cell. reinjection. The extracted water is stored again in at least one tank to store recirculated water, to start a semi-cycle of filling that tank again. The extraction and reinjection flow rates are very small. In this way (in addition to avoiding a disproportionate drop in levels and practically drying out the cell) a very low flow speed is obtained (preferably between 0.35 and 1.40 mm/min). This low speed ensures that the chemical and biogeochemical reactions that enable the degradation of contaminants have sufficient time to occur along the path carried out by the treatments and/or reagents within the cell. In addition to this, and simultaneously with the degradation of the mass of contaminant that circulates through the most permeable levels of the treated formation, the longer residence time of the reactants due to the small flow velocity generated, makes it possible for the reagents penetrate by molecular diffusion into the levels of lowest permeability, allowing the degradation of the contaminant mass that is stored inside and avoiding the subsequent rebound effect when the most permeable levels have been decontaminated (which allows being very precise in the remediation).

As indicated above, in a second aspect, the present invention refers to a procedure for the decontamination of an aquifer-aquitard transition zone, characterized in that it comprises the steps of:

Step a): Establish at least one recirculation cell of the present invention, so that between the at least one extraction well and the at least one reinjection well the aquifer-aquitard transition zone to be treated is included or encompassed.

Stage b): Filling semi-cycle stage: Filling of the useful volume of at least one tank to store recirculated water by extracting water from the aquifer-aquitard transition zone to be treated by means of at least one extraction well.

Stage c): Empty semi-cycle stage: Next, after stage b), emptying of the volume useful of at least one tank to store recirculated water by reinjecting the water into the aquifer-aquitard transition zone to be treated by means of the at least one reinjection well, preferably together with at least one treatment.

In the procedure of the present invention, it is contemplated that steps b) and c) (filling and emptying half cycle, respectively) are repeated until the desired decontamination is obtained.

The recirculation cell of the present invention and its characteristics are in accordance with what was previously explained in the first aspect of the present invention.

More preferably, in the process of the present invention, the filling of the useful volume of at least one tank for storing recirculated water in step b) is carried out at a flow rate of between 0.30 and 1.30 L/min, more preferably at a flow rate of between 0.42 and 1.25 L/min, even more preferably at a flow rate between 0.58 and 0.94 L/min.

Also more preferably, in the process of the present invention, the emptying of the useful volume of the at least one tank for storing recirculated water in step c) is carried out at a flow rate of between 0.80 and 3.80 L/min. , more preferably at a flow rate of between 0.83 and 3.75 L/min, even more preferably at a flow rate of 1.25 L/min.

In a preferred embodiment, step b) (filling half cycle) in the process of the present invention lasts between 60 and 180 minutes; and stage c) (emptying half cycle) lasts between 20 and 90 minutes.

Therefore, in the procedure of the present invention for the treatment of aquifer-aquitard transition zones, water is extracted from said zone through at least one extraction well until the filling of at least one tank to store recirculated water (semi-cycle of filling (stage b)) and in the subsequent emptying semi-cycle (stage c)) said recirculated water will be reinjected into the at least one reinjection well and will circulate through the cell again to the at least one extraction well to be extracted in the next half-filling cycle.

In the process of the present invention, it is contemplated and preferred that, before stage a) and/or stage b), at least one pretreatment of the aquifer-aquitard transition zone to be treated is carried out. Preferably, said treatment is carried out before step a), therefore, the at least one pretreatment, preferably, is carried out before the start-up of the at least one recirculation cell of the present invention, even more preferably, before the construction of the at least one recirculation cell of the present invention. Pretreatment will depend on the nature of the contamination to be treated. In a preferred embodiment, the pretreatment is with metallic iron (Fe ⁰ ), more preferably with mZVI (microscale zero-valent iron).

In the process of the present invention, preferably, in step b), if the water level of the at least one extraction well falls below the minimum established water level, the filling half cycle is stopped. This semi-cycle is resumed when, naturally, the water level in the corresponding extraction well recovers, exceeding the water level value established as a minimum in the extraction well and a water level value (preset) is reached. in the automatic cell control) that is above said minimum value (normally, after a few minutes of natural recovery of levels in the well).

In the process of the present invention, preferably, in step c), if the water level in the at least one reinjection well rises above the maximum level established, the emptying half-cycle stops. This semi-cycle is resumed when, naturally, the water level in the reinjection well drops (because the recirculated water reinfiltrates into the aquifer-aquitard transition zone) to a depth preset in the automatic control of the cell (this depth must be the one corresponding to the natural static level of the reinjection well). At that moment (preferably, automatic cell control) the reinjection pump is started again until the useful volume of at least one tank to store recirculated water is emptied.

In the process of the present invention, as indicated above, in step c), at least one treatment is preferably injected into the reinjection well. Said at least one treatment can be any treatment known in the state of the art suitable for the decontamination of groundwater. An expert in the field, depending on the type of contamination present in the aquifer-aquitard transition zone to be treated, will be able to determine if said at least one treatment is necessary and which one should be applied. It is contemplated that more than one simultaneous or successive treatment can be applied, depending on each pollutant and contaminated site. In a preferred embodiment, this at least one treatment applied in step c) of the process of the present invention is lactic acid, more preferably together with a buffer solution (preferably sodium bicarbonate and sodium carbonate in an aqueous medium). Preferably, each of the treatments is injected at a flow rate of between 0.5 and 1.5 mL/min.

As indicated above, the recirculation cell of the present invention comprises: a) at least one extraction well that allows the extraction of water from an aquifer-aquitard transition zone; b) at least one reinjection well that allows the reinjection of water from the tank to store recirculated water in the aquifer-aquitard transition zone; c) at least one tank to store recirculated water; and d) at least one means to supply a treatment to the aquifer-aquitard transition zone, characterized in that said cell is configured to operate in semi-cycles of filling and emptying of at least one tank to store recirculated water, so that in the semi-cycle of filling the at least one recirculated water tank, water is extracted from the at least one extraction well at a flow rate of between 0.30 and 1.30 L/min for filling said at least one tank for storing recirculated water (more preferably , at a flow rate of between 0.42 and 1.25 L/min); and in the semi-cycle of emptying the at least one tank for storing recirculated water, the water from said tank is reinjected into the at least one reinjection well at a flow rate of between 0.80 and 3.80 L/min (more preferably, at a flow rate of between 0.83 and 3.75 L/min).

The recirculation cell of the present invention covers the volume of subsoil in which, within the aquifer-aquitard transition zone to be treated, the groundwater is contaminated (see FIG. 1). This volume of subsoil is contaminated because either: 1) it totally or partially contains within it a source of contamination that constantly emits contaminant to the groundwater flow, giving rise to a pollution plume, or 2) it totally or partially contains , inside a plume of pollution. In the first case, the objective of the cell of the present invention is to eliminate the source of contamination, and thus also the associated plume. In the second case, the objective is to eliminate the pollution plume that had already moved downstream from the previously eliminated pollution source.

As indicated above, if the dimensions of the contamination source and/or plume are very large (so the portion of the aquifer-aquitard transition zone that needs to be treated is also very large, according to the dimensions of the aforementioned source and/or plume), various recirculation cells of the present invention can be placed, in series or in parallel, so that, together, the entire volume of contaminating source and contaminated water to be treated is contained within the overlap of all the cells of the present invention used.

In FIG. 1, a general scheme of the recirculation cell of the present invention 1 is shown, which comprises an extraction well 2 and a reinjection well 3 positioned at the ends of the aquifer-aquitard transition zone to be treated (in dashed lines), in the direction and sense of groundwater. The direction of the arrows shows the flow of water both outside the recirculation cell 1, in solid arrows, and inside the recirculation cell 1, in dashed arrows. Therefore, extraction well 2 is located downstream and reinjection well 3 is located upstream of the recirculation cell.

The reflected flow within recirculation cell 1 and from extraction well 2 to reinjection well 3 shows the recirculated water (dashed arrows).

In the recirculation cell 1 of the present invention, the distance between the extraction well 2 and the reinjection well 3 must be determined by the person skilled in the art based on the aquifer-aquitard transition zone to be treated. However, preferably the distance between the extraction well 2 and the reinjection well 3 is between 4 and 8 meters, more preferably 6 meters.

As indicated above, the recirculation cell 1 of the present invention should preferably be provided with at least three monitoring wells (FIG. 1). All three equipped with pressure sensors to control the water level in each well, and distributed as follows: 1) A first monitoring well A 4 located at a distance of 2 or 3 meters upstream of the cell (that is, upstream of the reinjection well 3). Its objective is to monitor the contaminated water not recirculated upstream of the cell. This would be the case where recirculation cell 1 only partially encompasses a pollution source and/or a pollution plume. In these cases, as indicated above, other cells of the present invention should overlap with this one (if the final objective is the total remediation of the site).

2) A second monitoring well B 5 in the center of the cell, to monitor the recirculated water that is being decontaminated inside the recirculation cell 1.

3) A third monitoring well C 6 is located about 2 or 3 m downstream of the cell (i.e., downstream of extraction well 2). This well 6 monitors the groundwater located downstream of cell 1 and, therefore, untreated. Its function is similar to that of the cases mentioned for the first monitoring well 4 located upstream of cell 1.

These three monitoring wells, 4, 5 and 6, are equipped with pressure sensors for continuous recording of levels and physical and chemical parameters that allow continuous, real-time monitoring of the evolution of the remediation. At the same time, the monitoring well 5, and the extraction well 2, allow periodically taking samples of recirculated (and, therefore, treated) water to verify that, beyond the continuous parameter sensors, the progression of the remediation or decontamination is being carried out adequately.

In FIG. 2 shows the detail of an extraction well 2 that comprises an extraction pipe 7 that connects the extraction well 2 with the tank for storing recirculated water 8 and that, together with the extraction pump 9, allows the extraction of water and the filling the tank to store recirculated water 8 during the filling half cycle. In FIG. 2 you can also see the different layers of the terrain: Unsaturated zone (D), Aquifer (E), Aquifer-aquitard transition zone (F) and Aquitard (G). It is observed how extraction well 2 has the necessary depth to reach the aquifer-aquitard transition zone (F) to be treated. Additionally, the bold arrows show how water from the Aquifer-Aquitard Transition Zone (F) enters extraction well 2. As explained above, the slotted area 32 of the extraction well 2 has the necessary length to be located precisely between the depth of the roof of the aquifer-aquitard transition zone and the base of said hydrogeological formation to be treated.

In FIG. 2 also shows the water pressure sensor 10 intended to measure the length of the water column present in the extraction well 2, as well as other sensors 11,12,13 intended to measure other variables such as temperature, pH, dissolved oxygen. or redox potential, among others (these other sensors 11, 12, 13) measure, record and store the temporal variation of said parameters at previously set time intervals (for example, at a minute or five-minute measurement interval).

The extraction pump 9, shown in FIG. 6, is of small flow (see two flow examples included in Table 1). This flow rate, as indicated above, must necessarily be small to enable a slow underground flow rate within cell 1, which gives time for the chemical and biogeochemical reactions that transform the contaminants to take place. The extraction pump 9 is equipped with a flow control system that allows this parameter to be adjusted to the operating value considered appropriate for each case. The extraction pump can be submerged or non-submerged, but it must always be capable of lifting water at a small flow rate. If it is a peristaltic extraction pump, it is located outside the extraction well, and if it is a submerged extraction pump, its flow control system is located outside the well. In the case that the extraction pump is peristaltic, it is connected to the extraction pipe 7. The groundwater suction end (suction zone 14) of the extraction pipe 7), is below the level of security 1 (SL1). In the case of a submerged extraction pump, it is the body of the extraction pump itself that constitutes the suction zone 14 of the extraction pipe 7, being below the safety level (SL1).

The water pressure sensor 10, as indicated above, measures the level of the water column in the extraction well 2 and if said level drops to the value set as safety level 1 (SL1), the pump extraction 9 is stopped to prevent the suction zone 14 of the extraction pipe 7, through which the extraction pump 9 extracts groundwater, from running dry. To do this, the value of SL1 must be above the depth at which the aforementioned groundwater suction zone 14 is located. The SL1 value can be reached if the extraction flow rate exceeds the reinjection flow rate in the reinjection well producing a significant drop in the level in the extraction well, which drops to the value corresponding to SL1. The SL1 value can also be reached due to various circumstances (natural or anthropogenic) throughout the decontamination that cause a significant level drop in the extraction well. For example, during the start-up of the cell until an adequate extraction and reinjection flow rate is adjusted, as an anthropogenic cause. It can also happen that the level drops naturally during the summer, causing that, although the extraction flow is small, it is large enough for the level to reach the height of SL 1. A similar case, but of anthropic nature, would be that wells other than the decontamination of the present invention were put into operation and that would lower the level.

Table 1. Examples of operation of the extraction well in a recirculation cell of the present invention

In FIG. 3 shows the detail of a reinjection well 3 comprising a reinjection pipe 15 that connects the tank for storing recirculated water 8, FIG. 4, with the bottom of the reinjection well 3 and that, together with the reinjection pump 16, FIG. 6, allows the reinjection of water and the emptying of the tank to store recirculated water 8 during the emptying half cycle. In FIG. 3 you can also see the different layers of the terrain: Unsaturated Zone (D), Aquifer (E), Aquifer-Aquitard Transition Zone (F) and Aquitard (G). It is observed how reinjection well 3 has the necessary depth to reach the aquifer-aquitard transition zone (F) to be treated. Additionally, the bold arrows show how water leaves reinjection well 3 and enters the aquifer-aquitard transition zone (F).

As explained previously, reinjection well 3 has the necessary depth to reach the aquifer-aquitard transition zone to be treated. Slotted area 18 This well extends from the top of the aforementioned transition zone to be treated to the base of said zone.

In FIG. 3 also shows the water pressure sensor 17 intended to measure the length of the water column present in the reinjection well 3.

The reinjection pump 16 has a small flow rate (see two flow examples included in Table 2). This flow rate, as indicated above, must necessarily be small to enable a slow underground flow rate within cell 1, which gives time for the chemical and biogeochemical reactions that transform the contaminants to take place. The reinjection pump 16 is equipped with a flow control system that allows this parameter to be adjusted to the operating value considered appropriate for each case. The reinjection pump can be submerged or non-submerged, but must always be able to operate at a low flow rate. If it is a peristaltic type reinjection pump, it is located outside the reinjection well 3, and if it is a submerged reinjection pump, its flow control system is located outside the well.

The water pressure sensor 17, as indicated above, measures the level of the water column in the reinjection well 3, and if said level rises to the value set as safety level 2 (SL2), the pump reinjection well 16 is stopped to prevent reinjection well 3 from overflowing. That is, this water pressure sensor 17 detects or indicates that the level of the water reinjected into the reinjection well 3 is very high and there is a danger that this water will overflow over the edge of the extraction well 3 and go outside. This situation can occur if the geological formation is not capable of absorbing the reinjection flow in reinjection well 3, or if biological or abiotic plugging occurs in the slotted zone 18 in reinjection well 3 (or even in the own geological formation).

En la FIG. 3, también se observan las primera y segunda tuberías de inyección de tratamientos 19, 20. Table 2. Examples of operation of the reinjection well in a recirculation cell of the present invention

In FIG. 3, the first and second treatment injection pipes 19, 20 are also observed.

FIG. 4 shows the tank for storing recirculated water 8. Said tank 8 is preferably cylindrical and made of opaque polyethylene (or other resistant plastic). To said tank 8, as seen in this figure, the extraction pipe 7 (which comes from the extraction well 2) enters the upper part and, inside the tank, descends to an area near the base, approximately 4 centimeters below the top of the settling volume 8.1, so that it is always submerged (in this way, aeration by bubbling of the recirculated water that fills the tank is avoided as much as possible and changes in redox conditions are minimized. of this water before it is reinjected into cell 1). Through the base area of tank 8 (settling volume area 8.1), reinjection pipe 15 exits (which goes to reinjection well 3). The tank for storing recirculated water 8 has three zones, from bottom to top (from bottom to top of tank 8): a settling volume 8.1 (acts as a decanter for possible inflows of fine materials from extraction well 2, or from solid precipitates that may form during the recirculation and storage process inside tank 8; these fine materials could clog the pipes if they do not have sufficient gradient), a useful volume 8.2 and a head volume 8.3. For a 120L tank 8 (this volume is what would contain, for example, a tank 45 cm in diameter and 75.5 cm high) the settling volume 8.1 would be 25L, the useful volume 8.2 would be 75L and the head volume 8.3 would be 20L. The tank 8 has a pressure sensor 22 at the bottom to measure the water column present in the tank and, consequently, the amount or volume of water present in the tank 8 and thus be able to determine the filling and emptying half cycles. When this volume is only 25 L, it corresponds to the settling volume 8.1, it indicates that the emptying half cycle of tank 8 has come to an end (because the settling volume 8.1 has already been reached) so it is given the order to stop the reinjection pump 16, thereby stopping reinjection. At the same time, the order to start the extraction pump 9 is given and a half-cycle of filling the tank 8 begins. When the pressure sensor 22 located at the bottom of the tank 8 indicates a water column corresponding to the sum of the settling volume 8.1, 25 L and the useful volume 8.2, 75L, is the signal that the useful volume 8.2 is complete and that therefore the tank 8 is full up to 100 L. At that moment, the order is given to the extraction pump 9 is stopped in the extraction well 2, ending the filling half-cycle and, at the same time, starting an emptying half-cycle. Although the lid of the tank 8 must be perfectly closed at all times, the wall of the tank 8 has in its upper part a ventilation perforation 33 of two or three millimeters in diameter, which crosses it from side to side, and which acts as a vent to prevent vacuum from being generated in the tank during emptying and from deforming due to implosion.

FIG. 5 shows a tank for storing a treatment 21 (preferably cylindrical and made of opaque polyethylene or other resistant plastic). Said tank 21 in an area close to its base presents (area of the decantation volume 21.1) the treatment injection pipe 19 that connects the tank 21 with the reinjection well 3 and allows the treatment contained in the tank to be injected into said well 3. 21. The tank for storing a treatment 21 has three zones, from bottom to top: a reserve volume 21.1 (reagent or treatment reserve volume), a useful volume 21.2 and a head volume 21.3. For a 100L tank 21, the reserve volume 21.1 would be 15L, the useful volume 21.2 would be 75L and the head volume 21.3 would be 10L. The tank 21 is preferably provided with a visual (or electronic) device that indicates the level of reagent or treatment solution present inside (not shown in the figure). Obviously, the level indicator device must be resistant to the reagent or treatment contained in the tank 21.

Although the lid of the tank 21 must be perfectly closed at all times, the wall of the tank 21 has in its upper part a ventilation perforation 34 of two or three millimeters in diameter, which crosses it from side to side, and which acts as a vent to prevent vacuum from being generated in the tank during emptying and from deforming due to implosion.

It is contemplated that the recirculation cell 1 of the present invention has a system for sending the data captured by the different sensors that includes a central server. In this case, the evolution of the remediation or treatment can be evaluated in real time within the perimeter of the cell's zone of influence.

FIG. 6 shows a diagram of the operation of the recirculation cell 1 of the present invention. Once the recirculated water has been extracted throughout the cell through the extraction well 2, it, through the extraction pump 9 and through the extraction pipe 7, reaches the tank to store recirculated water 8, which is filled during the filling semicycle. In the case of the extraction well 2, the extraction pipe 7 is preferably equipped with a tap 30, which allows sampling to be carried out (this tap 30 is located therefore, at a point along the route of the extraction pipe 7) located immediately after leaving the extraction well 2 and before entering the tank 8). Once the useful volume 8.2 of the tank for storing recirculated water 8 has been filled, the filling half cycle is completed (and, therefore, the extraction of water from the extraction well 2 stops). At this moment the emptying semi-cycle begins in which the useful volume 8.2 of the tank is emptied to store recirculated water 8. To do this, the water is driven from the tank 8 to the reinjection well 3 by means of the reinjection pump 16 through of the reinjection pipe 15. The reinjection pipe 15 is equipped with a tap 23 that allows sampling. This cock 23 is located at a point along the route of the reinjection pipe 15 located after the tank 8 and before the reinjection pipe 15 enters the reinjection well 3.

In FIG. 6, means for the storage and injection of two treatments are also represented, which are put into operation for the injection of one or more treatments in the reinjection well 3 in the emptying half cycle (that is, together with the reinjection of water recirculated, the injection of one or more treatments occurs during the emptying semicycle). In FIG. 6, the means for the storage and injection of two treatments comprise a first tank for storing a first treatment 21 which, by means of a first injection pipe 19 and a first injection pump 24, inject a first treatment or reagent into the reinjection well 3 ; and a second tank to store a second treatment 25 that, by means of a second injection pipe 20 and a second injection pump 26, inject a second treatment or reagent into the reinjection well 3. Both the first injection pipe 19 and the second injection pipe injection 20 have a tap 27, 28 that allows sampling and verifying the operation of the injection pumps 24, 26. In this sense, in FIG. 6 has represented the case of two treatments, although there may be as many as necessary depending on the contamination to be treated. In a preferred embodiment, the first treatment is lactic acid and the second treatment is a buffer solution of sodium bicarbonate and sodium carbonate in an aqueous medium. During the time that the reinjection of recirculated water lasts, the two injection pumps 24, 26 inject directly into the reinjection well 3 a certain number of doses of each treatment through the corresponding injection pipes 19, 20. This injection is It is always carried out below the water level in the reinjection well 3. The two injection pumps 24, 26 can be peristaltic or submerged. The purpose of injecting the treatment doses in the indicated manner is that these doses of treatment solution are carried away by the water. recirculated throughout cell 1 to carry out the treatment of the aquifer-aquitard zone to be treated by dispersion and molecular diffusion.

As indicated, each of the operating cycles of the recirculation cell 2 of the present invention is formed by two successive half cycles (non-concurrent), one for filling the tank to store recirculated water 8 and another for emptying it. .

Preferably, all the pipes of the recirculation cell 1 of the present invention are covered with thermal insulating material (heaters) to prevent freezing of the water they transport in winter.

Finally, it should be noted that it is contemplated and in fact preferred that the recirculation cell of the present invention 1 presents a system for the automatic control of the cell 1 and its operation, for example, an automatic electrical control panel 29 that It receives information from all the sensors and automatically controls all the pumps of the recirculation cell of the present invention 2.

For better understanding, the present invention is described in more detail below with reference to the following non-limiting example.

Example. Pilot test of mobilization of PCE sources in the transition zone to the aquitards (aquifer-aquitard transition zone) by combining mZVI and biostimulation with lactic acid with a recirculation cell of the present invention

Materials and methods: Design and implementation of a cell of the present invention. The pilot test execution consisted of two stages. In the first stage, six mZVI injection boreholes of 8 meters depth were drilled by rotation and with continuous recovery of borehole cores following the guidelines provided by Puigserver et al. (Puigserver, D., Herrero, J., Torres, M., Cortés, A., Nijenhuis, I., Kuntze, K., ... & Carmona, JM (2016). Reductive dechlorination in recalcitrant sources of chloroethenes in the transition zone between aquifers and aquifers. Environmental Science and Pollution Research, 23(18), 18724-18741.). Injection of an aqueous emulsion of mZVI and guar gum (both food grade) was carried out in all six wells using groundwater from the drilled wells (FIG. 7 shows the location of the uncased boreholes for the injection of mZVI 31). The mZVI injection method in each well was pressure hydrostatic, always from bottom to top between 8 and 4.5 m deep. The total mass of mZVI injected was 30 kg (5 in each injection well). With the injection of mZVI in the sixth, last survey, the pilot test began. This moment is considered day zero of the test (time 0 days).

In a second stage, the recirculation cell of the present invention was activated on day 149 after the start of the test (time 149 days) to inject the lactic acid solution used in the biostimulation (FIG. 7 shows the zone of influence of this recirculation cell).

FIG. 7 shows: 7A Zone of influence of recirculation cell 1 (limited by the outermost flow lines). Location of the six untubed boreholes for the injection of mZVI 31 (from the emulsion of mZVI and guar gum) and also location of the extraction well 2 and reinjection 3 of recirculated water and lactic acid. 7B Vertical section of the uncased wells for the injection of mZVI 31 and the recirculation cell 1 of the present invention showing the extraction well 2, the reinjection well 3, the tank for storing recirculated water 8 and the tank 21 lactic acid solution. The arrows indicate the circulation of water within recirculation cell 1.

The recirculation cell of the present invention was designed to biostimulate the aquifer-aquitard transition zone to be treated. Given the low hydraulic conductivity of this transition zone, the cell was designed to operate in semi-cycles of filling and emptying a water recirculation tank to prevent the extraction well from drying out and allow time for reinjection. Furthermore, it was interesting to obtain a slow velocity of the groundwater so that the residence time of the lactic acid in the medium was long enough to favor the degradation reactions of the chloroethene.

The recirculation cell of the present invention was formed by:

1) an extraction well 2, slotted 32 in the aquifer-aquitard transition zone and equipped with a peristaltic pump that extracted flow rates ranging between 0.58 and 0.94 L/min (this well also had a pressure sensor of the water column that controlled the water level between the pre-established maximum and minimum values);

2) a tank to store recirculated water 8 that stored up to 100 L of recirculated water, which allowed the reinjection of 75 L of that water in each filling-emptying cycle; 3) two tanks 21 and 25 of 30 L capacity, each stored reagents (one tank for a lactic acid solution and the other a buffer solution composed of 80% sodium bicarbonate and 20% sodium carbonate) ;

4) both tanks mentioned in point 3 were connected to peristaltic pumps that dosed the lactic acid and the buffer solution (with flow rates ranging from 0.5 to 1.5 mL/min); and

5) a reinjection well 3.

During the pilot test in a semi-cyclical manner (for almost a year, between days 149 and 504; that is, 355 days), a total of 13.03 kg of lactic acid, specifically (S)-lactic acid, was also injected. called food grade (S)-2-hydroxypropion¡ic acid (IIIPAC). The lactic acid and the buffer solution were injected 6 m deep into the reinjection well, slotted in the upper part of the aquifer and in the aquifer-aquitard transition zone. This well was also equipped with a peristaltic pump connected to the tank to store recirculated water and the recirculated water was reinjected at a flow rate of 1.25 L/min. As in the case of the extraction well, this well was equipped with a water column pressure sensor that regulated the level between preset maximum and minimum values. If the maximum level was reached, the reinjection pump and the two dosing pumps were automatically turned off, thus preventing the spillage of reinjected water that did not have time to re-infiltrate into the well.

The monitoring network of the pilot test was made up of a multilevel well, and the two wells that made up the cell. Data on the main characteristics of the pilot test monitoring points can be found in Table 3 included below.

Table 3 Characteristics of the monitoring points of the pilot test P1 (extraction well), P2 (reinjection well). F1 UB (Solinst CMT multilevel system), three ports in the transition zone. HDPD (high density polyethylene). TEFLON™ (polytetrafluoroethylene, PTFE). Depth, (depth), Casing type, (type of casing), Diam. Int. (inner diameter of casing), Diam. ext. (casing outside diameter), Length. ran. (length of the slotted area),

Depth rank, rank zone. (Depth range of the grooved area), Length. your B. blind (length of blind pipe).

Groundwater monitoring during pilot testing and analytical methods

The pilot test began at the time corresponding to day 0 (first day of sampling), when mZVI was injected. This reagent acted only during the first 149 days. At the end of this period (day 149), the recirculation cell of the present invention was activated and the combined treatment of mZVI and biostimulation with lactic acid came into operation for a total of 355 days (i.e., until day 504, see Table 4).

Table 4. Days from the beginning of the pilot test in which groundwater samples were taken in the control network. The first sample (day 0) was taken immediately before mZVI injection. Days on which groundwater samples were also taken to identify microorganisms are marked with an "X."

Days of groundwater sampling in the control network (days from the start of the pilot test)

^end of pilot test

The procedures followed for groundwater sampling in the monitoring network are briefly described below. Before sampling and in accordance with

Puigserver et. to the. (Puigserver, D., Herrero, J., Parker, B. L, & Carmona, J. M. (2020). Natural attenuation of pools and plumes of carbon tetrachloride and chloroform in the transition zone to bottom aquitards and the microorganisms involved in their degradation .Science of The Total

Environment, 712, 135679), checkpoints were purged using a peristaltic pump connected to a field flow cell coupled to sensors for physicochemical parameters. The parameters were dissolved oxygen (DO, mg/L), oxidation-reduction potential (ORP, mV), pH, temperature (T, °C) and electrical conductivity (EC, pS/cm). Once the values of these parameters were stabilized and recorded, water samples were taken with the peristaltic pump at low flow to minimize the volatilization of VOCs (according to Puigserver, D., Cortés, A., Viladevall, M., Nogueras, X., Parker,

B. L., & Carmona, J. M. (2014). Processes controlling the fate of chloroethene emanating from DNAPL aged sources in river-aquifer contexts. Journal of contaminant hydrology, 168,

25-40). The sampling protocols used were those described by Puigserver et al. (2014).

The order of field sampling was: 1) 1 L of water (in autoclaved glass bottles) for the determination of microbial communities in groundwater (phyla and genera); This water was subsequently filtered with 0.2 micron filters and frozen at -20 °C in the laboratory according to Puigserver et al. (2020). 2) 250 mL to determine the concentrations of chloroethene, and other VOCs: dichloroacetylene (DCA), chloroacetylene (CA), and the gases ethene, ethane, acetylene and methane, 3) 250 mL to determine the 5 ¹³ C of the chloroethene, 4) 100 mL to determine the nitrogen species, Mn ²⁺ , Fe ²⁺ , sulfate, S ² ' and, finally, 5) 50 mL of water for the determination of lactate and acetate.

The samples were transported and stored at 4 °C, and in each sampling campaign the following samples were taken: 1 evaluation field sample and 1 low concentration evaluation field sample. Each sample was taken in duplicate and 1 field blank was collected, except in the case of samples intended for microbial determination, in which two blanks were collected, 1 blank of blanks and 1 blank of transport for each sample transport refrigerator, in order to guarantee the traceability and representativeness of the samples.

In the case of samples to determine chloroethene concentrations and 5 ¹³ C values of these compounds, bactericidal was added to inhibit bacterial activity during transport and storage following the protocol described in Puigserver et al. (2020). All samples were analyzed by the Environmental Hydrogeology and Global Change group of the University of Barcelona in the laboratories of the Scientific and Technological Centers of the University of Barcelona (CCiTUB), which follow the ISO 9001:2000 standard.

VOCs present in groundwater were analyzed by gas chromatography (GC) (Carlo-Erba GC8000-Top) coupled to a mass spectrometer (GC-MS) (ThermoFinnigan Fisons MD800). The compounds analyzed were perchloroethylene (PCE), trichlorethylene (TCE), cis-dichloroethylene (cDCE), trans-dichloroethylene (tDCE), 1,1-dichloroethylene (1,1-DCE), vinyl chloride (CV), dichloroacetylene, chloroacetylene and the gases ethene, ethane, acetylene and methane.

Compound Specific Isotopic Analysis (CSIA) was applied to determine the isotopic composition of VOCs and gases. For this, solid phase microextraction was used following the method described by Puigserver et al. (2014) and using Combustion Chromatography Isotope Ratio Mass Spectrometry (GC-C-IRMS).

Anion concentrations were determined by ion chromatography, following EPA protocol 9056. Mn ²⁺ , Fe ²⁺ , and S ² ' were measured by absorption spectrophotometry with a Merck Spectroquant NOVA60. Lactate, acetate and formate were determined by liquid chromatography (HPLC).

DNA extraction for the identification of the phyla and genera of microorganisms in the sampled groundwater was carried out in a sterile environment with the DNeasy Ultraclean Microbial Kit from Qiagen, with an adaptation of the first two stages, to extract the DNA from the filters . The preparation of the 16S rRNA library, sequencing and bioinformatic analysis was carried out at the Genomics Unit of the Scientific and Technological Centers of the University of Barcelona (CCiTUB). The V3V4 region of the 16S rRNA was amplified as described by Willis et al. (Willis, J., et al. (2018). Citizen science charts two major “stomatotypes" in the oral microbiome of adolescents and reveals links with habits and drinking water composition. Microbiome, 6(1), 1-17. ) using a set of modified primers V3-V4-F and V3-V4-R containing a 1-4 bp "heterogeneity spacer" that were designed to mitigate problems caused by low sequence diversity amplicons (the primers used for 16S rRNA sequencing can be found in Table 4). PCR conditions were modified: an initial denaturation at 95°C for 3 min, followed by 25 three-step cycles consisting of 95°C for 30 s, 55 °C for 30 s and 72°C for 30 s; and a final extension of 5 minutes at 72°C. Each PCR amplification was carried out with 4 μl of DNA, 0.2-pM of each forward and reverse primer. Kapa ready mix (Kapa biosystems) in a total volume of 10 pl.

After the first PCR step, the PCR products were purified, a second PCR and a second purification were performed, followed by a normalization and quantification process as described by Willis et al. (2018).

Sequencing was performed on Illumina MiSeq with 2 × 300 base pair reads using the v3 kit (Bioo Scientific) with a loading concentration of 18 pM. To increase the diversity of sequencing, 10% PhlX control libraries were introduced.

Three simulated community samples were used in this study. Two mock bacterial communities were obtained from the Human Microbiome Project BEI Resources (HM-276D and HM-277D), each containing genomic DNA from ribosomal operons of 20 bacterial species. The third mock community, ZymoBIOMICS™ Microbial Community DNA Standard (Zymo Research, catalog number D6306), is a mixture of genomic DNA isolated from pure cultures of eight bacterial strains and two fungal strains. Test DNAs were amplified and sequenced in the same way as the other experimental samples.

As derived from the results obtained (see Table 5) and those included previously, in the remediation of contamination by chlorinated solvents, the combined use of mZVI and biostimulation with lactic acid of the microbial flora of the medium through the cell The present invention resulted in an efficient method for eliminating sources of recalcitrant contamination located in aquifer-aquitard transition zones, object of the pilot test treatment.

Removal efficiencies ranging between 83% and 96% of PCE were obtained in pools located in the zone of influence of the cell within the transition zone. The degradation of this PCE was practically total, reaching harmless compounds such as ethane, ethene and CO2.

Table 5. Percentage of original PCE (the one that existed at time 0) degraded throughout the pilot test.

Claims

1. Recirculation cell comprising: - at least one extraction well that allows the extraction of water from an aquifer-aquitard transition zone to be treated; - at least one tank to store recirculated water; - at least one reinjection well that allows reinjection into the aquifer-aquitard transition zone to be treated of water from at least one tank to store recirculated water; and - at least one means to supply a treatment to the aquifer-aquitard transition zone to be treated, characterized in that said cell is configured to operate in semi-cycles of filling and emptying of at least one tank to store recirculated water, so that in the semi-cycle for filling the at least one recirculated water tank, water is extracted from the at least one extraction well at a flow rate of between 0.30 and 1.30 L/min for filling said at least one tank for storing recirculated water; and in the semi-cycle of emptying the at least one tank to store recirculated water, the water from said tank is reinjected into the at least one reinjection well at a flow rate of between 0.80 and 3.80 L/min. 2. Recirculation cell according to claim 1, characterized in that the at least one extraction well has a slotted area and because the length of the slotted area of the at least one extraction well coincides with the thickness of the aquifer-aquitard transition zone. to treat. 3. Recirculation cell according to claim 1 or 2, characterized in that the at least one extraction well has the necessary depth to be able to extract water from the aquifer-aquitard transition zone to be treated. 4. Recirculation cell according to any of claims 1 to 3, characterized in that the at least one extraction well reaches the aquifer-aquitard transition zone to be treated. 5. Recirculation cell according to any of claims 1 to 4, characterized in that the at least one extraction well reaches the base of the aquifer-aquitard transition zone to be treated. 6. Recirculation cell according to any of claims 1 to 5, characterized in that the at least one reinjection well has a slotted area and because the length of the slotted area of the at least one reinjection well coincides with the thickness of the injection area. aquifer-aquitard transition to be treated. 7. Recirculation cell according to any of claims 1 to 6, characterized in that the at least one reinjection well has the necessary depth to be able to reinject water into the aquifer-aquitard transition zone to be treated. 8. Recirculation cell according to any of claims 1 to 7, characterized in that the at least one reinjection well reaches the aquifer-aquitard transition zone to be treated. 9. Recirculation cell according to any of claims 1 to 8, characterized in that the at least one reinjection well reaches the base of the aquifer-aquitard transition zone to be treated. 10. Recirculation cell according to any of claims 1 to 9, characterized in that each of the at least one extraction well comprises at least one means for extracting water. 11. Recirculation cell according to claim 10, characterized in that each of the at least one means for extracting water comprises at least one extraction pipe and at least one extraction pump, said at least one extraction pipe connecting the at least one extraction well with at least one tank to store recirculated water. 12. Recirculation cell according to claim 11, characterized in that the at least one extraction pipe has at least one sampling means. 13. Recirculation cell according to claim 11 or 12, characterized in that the at least one extraction pipe is thermally insulated. 14. Recirculation cell according to any of claims 11 to 13, characterized because the at least one extraction pump is a peristaltic pump or a submersible pump. 15. Recirculation cell according to any of claims 1 to 14, characterized in that each of the at least one extraction well additionally comprises a pressure sensor configured to measure the water level of the well. 16. Recirculation cell according to claim 15, characterized in that if the pressure sensor detects a water level below that established as the minimum water level of the extraction well, the half-cycle of filling the tank to store recirculated water will stop. 17. Recirculation cell according to any of claims 1 to 16, characterized in that each of the at least one extraction well additionally comprises at least one sensor for measuring one or more of the following parameters: temperature, electrical conductivity, dissolved oxygen, redox potential and pH. 18. Recirculation cell according to any of claims 1 to 17, characterized in that the internal diameter of the at least one extraction well is at least 100 mm. 19. Recirculation cell according to any of claims 1 to 18, characterized in that each of the at least one reinjection well comprises at least one means for reinjecting water. 20. Recirculation cell according to claim 19, characterized in that the at least one means for reinjecting water comprises at least one reinjection pipe and at least one reinjection pump, said at least one reinjection pipe connecting the at least one well. reinjection with at least one tank to store recirculated water. 21. Recirculation cell according to claim 20, characterized in that the at least one reinjection pipe has at least one sampling means. 22. Recirculation cell according to claim 20 or 21, characterized in that the at least one reinjection pipe is thermally insulated. 23. Recirculation cell according to any of claims 20 to 22, characterized in that the at least one reinjection pump is a peristaltic pump or a submersible pump. 24. Recirculation cell according to any of claims 1 to 23, characterized in that each of the at least one reinjection well additionally comprises a pressure sensor configured to measure the water level of said well. 25. Recirculation cell according to claim 24, characterized in that if the pressure sensor detects a water level above that established as the maximum water level of the reinjection well, the half-cycle of emptying the tank to store recirculated water will stop. 26. Recirculation cell according to any of claims 1 to 25, characterized in that the at least one reinjection well additionally comprises at least one sensor to measure one or more of the following parameters: temperature, electrical conductivity, dissolved oxygen, redox potential and pH. 27. Recirculation cell according to any of claims 1 to 26, characterized in that the internal diameter of the at least one reinjection well is at least 100 mm. 28. Recirculation cell according to any of claims 1 to 27, characterized in that each of the means for supplying a treatment to the aquifer-aquitard transition zone comprises a treatment storage tank and a means for injecting the treatment into the aquifer-aquitard transition zone to be treated. 29. Recirculation cell according to claim 28, characterized in that the means for injecting the treatment into the aquifer-aquitard transition zone allows the injection of the treatment into the at least one reinjection well. 30. Recirculation cell according to any of claims 1 to 29, characterized in that the at least one tank for storing recirculated water is opaque. 31. Recirculation cell according to any of claims 1 to 30, characterized in that the at least one tank for storing recirculated water is made of opaque polyethylene. 32. Recirculation cell according to any of claims 1 to 31, characterized in that the at least one tank for storing recirculated water comprises a decantation volume, a useful volume and a head volume, the useful volume being the one that is filled and emptied. of water in the filling and emptying half cycles. 33. Recirculation cell according to any of claims 1 to 32, characterized in that it additionally comprises means for automatically controlling the operation of the cell. 34. Recirculation cell according to any of claims 1 to 33, characterized in that it is configured to carry out consecutive filling and emptying half cycles in which: - firstly, a semi-filling cycle of at least one tank is carried out in which the useful volume of the tank is filled to store recirculated water by extracting water from the aquifer-aquitard transition zone to be treated by means of at least an extraction well; - Next, in the emptying semicycle, the useful volume of the at least one tank to store recirculated water is emptied, reinjecting the recirculated water into the aquifer-aquitard transition zone to be treated by means of the at least one well. reinjection, preferably together with at least one treatment; and - Steps a) and b) are repeated until the desired decontamination is obtained. 35. Recirculation cell according to any of claims 1 to 34, characterized in that it comprises at least one monitoring well comprising sensors for monitoring water quality. 36. Recirculation cell according to claim 35, characterized in that it comprises three monitoring wells: - a first monitoring well located upstream of the cell; - a second monitoring well located between the extraction well and the reinjection well; and - a third well located downstream of the cell. 37. Recirculation cell according to any of claims 1 to 36, characterized in that the at least one extraction well is an extraction well; the at least one reinjection well is a reinjection well; and the at least one tank for storing recirculated water is a tank for storing recirculated water. 38. Recirculation cell according to claim 37, characterized in that the extraction well and the reinjection well are positioned at the ends of the portion of the aquifer-aquitard transition zone to be treated, in the direction or direction of the groundwater, the downstream extraction well and upstream reinjection well. 39. Recirculation cell according to claim 37 or 38, characterized in that the distance between the extraction well and the reinjection well is between 4 and 8 meters, more preferably 6 meters. 40. Procedure for the decontamination of an aquifer-aquitard transition zone, characterized in that it comprises the following steps: a) establish at least one recirculation cell according to any of claims 1 to 39, so that between the at least one extraction well and at least one reinjection well include the aquifer-aquitard transition zone to be treated; b) carry out a semi-filling cycle stage, filling the useful volume of at least one tank to store recirculated water by extracting water from the aquifer-aquitard transition zone to be treated by means of at least one extraction well; c) carry out an emptying semi-cycle stage, emptying the useful volume of at least one tank to store recirculated water, reinjecting the water into the aquifer-aquitard transition zone to be treated through the reinjection well, preferably together with at least one treatment; and - repeat steps b) and c) until the desired decontamination is obtained. 41. Procedure for decontamination according to claim 40, characterized in that the filling of the useful volume of at least one tank for storing recirculated water in step b) is carried out at a flow rate of between 0.30 and 1.30 L/ min. 42. Procedure for decontamination according to claim 40 or 41, characterized in that the emptying of the useful volume of at least one tank to store recirculated water in step c) is carried out at a flow rate of between 0.80 and 3.80 L. /min. 43. Procedure for decontamination according to any of claims 40 to 42, characterized in that before stage a) and/or stage b) at least one prior treatment of the aquifer-aquitard transition zone to be treated is carried out. 44. Procedure for decontamination according to any of claims 40 to 43, characterized in that if in step b) the water level of the at least one extraction well falls below the minimum water level established, the filling semicycle stops. 45. Procedure for decontamination according to any of claims 40 to 44, characterized in that if in step c) the water level in the at least one reinjection well rises above the maximum level established, the emptying semicycle stops.