1. A plant for in situ decontamination of contaminated soils, comprising the following parts:- an injection well;- at least one extraction well;- a flow measuring device and a pressure measuring device;- a mobile purification plant connected to the extraction well;
characterized in that the plant further comprises- a water-ozone mixing section;- a device to measure the concentration of the dissolved ozone connected to the ozone-water mixing section;and wherein the flow measuring device and the pressure measuring device are connected on the same line as the device to measure dissolved ozone; and the - mobile purification plant connected to the extraction well is connected to the ozone-water mixing section, and comprises a device to measure the concentration of the residual ozone.

2. The plant as claimed in Claim 1,
comprising a by-pass line of the mains water on the ozone-water mixing section.

3. The plant as claimed in one of the previous claims,
comprising a section for injecting saline solution into the injection well

4. The plant as claimed in one of the previous claims,
comprising quartzite and active carbon filters downstream of the purification plant.

5. The plant as claimed in one of the previous claims,
where an ozone generator and the mains water are conveyed inside the ozone-water mixing section.

6. A process for in situ decontamination of contaminated soils, making use of a plant as claimed in claims 1 to 5, comprising the following steps:a - obtaining pressurised water to which ozone is added in the ozone-water mixing section;b - pumping the ozonated water into the injection well after passing through a flow measuring -device and a pressure measuring device, consequently obtaining hydraulic fracturing of the soil;c - drawing the same quantity of water injected in step (b) from the extraction well;d - in situ ozonation of the soil;e - conveying of the water pumped from the extraction wells to the mobile purification plant, where it is filtered on quartzite filters and subsequently by passing through active carbon filters;f - use of the gaseous ozone not solubilised in the mixing section for purification of the water extracted from the soil.

7. The process as claimed in Claim 6,
where the maximum capacity of the ozone generator is 1400 g/h.

8. The process as claimed in one of Claims 6 or 7,
where the hydraulic fracturing step (b) is implemented by feeding into the injection well a saturated saline solution composed of water and sodium chloride, as tracer to identify the fracturing conditions of the soil to be treated, monitoring and recording the variations in electrical conductivity in said soil.

9. The process as claimed in one of Claims 6 to 8,
where hydraulic fracturing takes place by injecting a quantity of saline solution between 500 and 1500 litres for a maximum time of 3 hours.

10. The process as claimed in one of Claims 6 to 9,
where in situ ozonation of the soil takes place by injecting ozonated water for a time between 100 hours and 50 days.

11. The process as claimed in Claim 10,
where the flow of ozonated water varies between 1.0 and 5.0 m3/h and has a concentration of dissolved ozone between 6 and 13ppm.

12. The process as claimed in one of claims 6 to 11,
where hydrogen peroxide is added to the ozonated water to obtain hydroxyl free radicals which optimise chemical oxidation of the pollutants present in the soil.