G-servis Praha spol. s r.o.
G-servis Praha is fully equipped to carry out orders focused on the sanitation of the rock environment and groundwater. The method and scope of the sanitation is based on the facts ascertained within the scope of implementation and an evaluation of the previous survey works.
THE FOLLOWING CHAPTERS SHOW THE MOST COMMON METHODS FOR SANITATION INTERVENTION IN LOCATIONS WITH EXISTING ECOLOGICAL BURDENS:
“EX SITU” METHODS
The “ex situ” principle consists in the removal of the primary (for instance, an underground tank for propellant fuels) and secondary (contaminated soil) sources of donation of pollutants from the area of interest. Disposal is performed by selective excavation of the contaminated soil and its transport to a permitted decontamination facility, where it is decontaminated in compliance with the approved technological procedures and applicable legislation.
“IN SITU” METHODS
During application of "in situ" methods, the sanitation technological procedure is applied in a non-destructive manner directly to the rock environment or groundwater.
PUMP AND TREAT
The most common method of groundwater disposal is the pump and treat method. The contaminated groundwater is pumped and transported via a pipe system to the sanitation unit. After decontamination, the pre-treated water is discharged into the sewer or returned to the rock environment through infiltration boreholes.
THE FOLLOWING METHODS MAY BE USED FOR DECONTAMINATION OF GROUNDWATER:
Gravitational separation – This method uses the different densities of the fluids. It is used to displace the phase of the pollutant on the water surface (petroleum products) or on the bottom of the separating tank (chlorinated hydrocarbons).
Sorption – A sorption unit may be installed as the next cleaning stage after the gravitational level. The filling consists of hydrophobic materials (loose staple fibres, webs, fabrics), capable of binding the petroleum products (Fibroil, etc.). The sorption stage may also be an activated carbon filter (wet sorption).
Stripping (intensive aeration) – This method is used in the cleaning of pumped groundwater contaminated by volatile substances (light fraction of the petroleum products, BTEX, Cl-U). The pollutant, converted to the gaseous phase, is mostly captured on an activated carbon filter or biofilter. The principle of this method is described in detail in the Water Treatment chapter.
VENTING (VACUUM EXTRACTION)
This is used for sanitation of a rock environment contaminated by volatile organic substances. The principle consists in the sub-pressure pumping of contaminated soil air (volatile pollutants) from a network of venting boreholes. The extracted contaminated soil air is filtered at a sanitation station.
The principle of this method is the sub-pressure entrainment of oil-phase droplets from the groundwater surface. Due to the sub-pressure, a negative depression cone is created in the collector (elevation of the groundwater level), with a greater thickness of the oil phase.
In this method, the air is bubbled directly through the groundwater collector. Just like in the case of the intensive aeration method, the volatile substances change from a liquid to a gaseous form. The gaseous phase is subsequently extracted by a system of combined or venting boreholes.
The following may be classified as new and progressive technologies: Evaluation of natural attenuation (RNA). The principle of this method is an assessment of the “real capability of nature to cope with contamination by itself”. Based on this complicated enumeration, it is possible to either choose an optimal sanitation method or leave the location to self-cleaning processes.
For contamination of groundwater by Cl-U, or some heavy metals, it is possible to use the in-situ application of physicochemical and biological reagents.
The application of colloidal or chip iron (reactive barriers) – The principle of this method is the reaction (reductive dechlorination) of zerovalent iron molecules of chlorinated hydrocarbons.
Application of potassium permanganate – Application of KMnO4 as a strong oxidation reagent to groundwater leads to the quick destruction of Cl-U (without hazardous intermediate products).
Dosing of organic substrate – Another method is dosing of an organic substrate (molasses, whey) into groundwater. This method of biological reductive dehalogenation is an inexpensive and relatively effective method.