1. A composition for stabilization and encapsulation of acid tar with Total Petroleum Hydrocarbons (TPH) values below 200,000 mg / kg and Dissolved Organic Carbon (DOC) below 1000 mg / kg dry matter characterized in that it comprises in mass percentages:

- emulsifying detergent: 1-4%

- calcium oxide: 3-8%

- magnesium oxide 0.1-2%

- bentonite: 1-2.8%

- sand: 2-5%

- cement 3-20%

- hardening additives 1%

- absorbent 1 % - 5%

- sodium hydroxide 1% - 10%

-sodium metasilicate 0.3-0.8% the rest up to 100% being the acid tar subject to stabilization.

2. The composition for stabilizing and encapsulating acid tar according to claim 1 , characterized in that the emulsifying detergent is 1%, calcium oxide is 8%, magnesium oxide 0.1%, bentonite is 1%, sand is 2%, cement is 3%, absorbent is 1%, sodium hydroxide is 1%, sodium metasilicate 0.3%.

3. The composition for stabilizing and encapsulating acid tar according to claim 1 , characterized in that the emulsifying detergent is 3.5%, calcium oxide is 3%, magnesium oxide 0.2%, bentonite is 2%, sand is 5%, cement is 5%, absorbent is 1%, sodium hydroxide is 1%, sodium metasilicate 0.5%.

4. The composition for stabilizing and encapsulating acid tar according to claim 1 , characterized in that the emulsifying detergent is 4%, calcium oxide is 7%, magnesium oxide 0.3%, bentonite is 2.8%, sand is 3%, cement is 8%, absorbent is 1%, sodium hydroxide is 1%, sodium metasilicate 0.8 %.

5. A process for stabilizing and encapsulating acid tar with Total Petroleum Hydrocarbons (TPH) values below 200,000 mg / kg and Dissolved Organic Compound (DOC) below 1000 mg / kg dry matter, characterized in that it comprises the following steps:

- Step 1: removal of surface water from tar pits, which is collected through drainage systems and sent to a treatment plant, before a stabilization procedure.

- Step 2: Batches are delimited within the tar pit; the acid tar in the first batch is excavated and then mixed and homogenized in an acid tar treatment plant connected to a gas capture station.

- Step 3: The value of DOC, TPH, pH and metal concentrations of the homogenized tar of the first batch is calculated, in order to determine the correct stabilization recipe.

- Step 4: A suction hood is installed at the drilling / mixing / dosing plant for absorbing and treating the emissions during the works, avoiding their release into the atmosphere.

- Step 5: Neutralization of the acid tar in situ by mixing of acid tar and soil contaminated from a first working area with CaO 3-8%, MgO 1-2% , NaOH 1 - 10%, absorbent 1 - 5% and metasilicate 0.3 - 0.8%), depending on the chemical composition of the tar, calculated by the analyses performed in the previous step; a neutralizing composition is applied over the entire depth of soil contamination by mixing up and down vertically, for several times, in the mixing tanks, also for homogenizing the resulting composition both vertically and horizontally.

- Step 6: Encapsulation of the tar and contaminated soil from the first work area, neutralized in the previous step; for encapsulation, emulsifying detergent 1-4%, bentonite 1 - 2.8%, cement 3 - 20%, sand 2 - 5%, hardening additives 1% are applied, depending on the chemical composition of the tar calculated by the analyses performed in the previous step; the composition having the role of neutralization is applied over the entire depth of soil contamination by mixing up and down vertically, for several times, in the mixing tanks, also for homogenizing the resulting composition both vertically and horizontally.

- Step 7: Storage of tar stabilized in situ, in the initial tar pit, prepared by waterproofing with geomembranes and by installing of a water drainage installation.

- Step 8: Covering / closing the site, can begin and unfold sequentially, with the stabilization of a work area and the creation of another by moving sheet piles, thus systematically reducing the areas in tar pit exposed to surface water penetration and rainfall; - After treating the tar in the first work area, the procedure is repeated one at a time for the tar in each of the following work areas;

- The drainage installation is installed for the collection of rainwater in some tanks, for its analysis and treatment, in case pollutant concentration above the maximum allowed values occurs.

6. The process for stabilizing and encapsulating acid tar according to claim 5, characterized in that, said sheet piles are mounted to create a first, second and third working areas isolated from the rest of the tar pit, when the tar has a non- homogeneous composition, the work areas being created successively from the outside to the inside of the tar pit.

7. The process for stabilizing and encapsulating acid tar according to claim 5, characterized in that said sheet piles are used for sectioning the tar pit when the tar mass is developed as a compact block, followed by emptying two volumes of the tar pit, one being used for crushing and mixing in the additives, and the other for resetting the stabilized and encapsulated material.