A brief presentation of methods used by EKOSYSTEM spol. s r. o. to eliminate old environmental burdens in built-up environments
EKOSYSTEM spol. s r. o. regularly provides comprehensive services in the area of eliminating old environmental burdens from soils, rock environments and groundwater, i.e., we do all the associated work, from surveying, through complete remediation techniques, to post-remediation monitoring and final evaluation. The fundamental process involves the following stages:
- Survey work, and where some information about the site contamination is at hand, possibly design and implementation of additional surveying to an extent necessary to specify the required remediation measures.
- Elaboration of a risk analysis (including application of mathematical modelling) proposing remediation targets and ways to achieve them.
- If needed, a feasibility study that specifies the required type and scope of remediation work.
- Remediation work proper employing the techniques referred to below, including project design, ongoing evaluation and final outputs.
- All forms of ongoing monitoring and additional sub-surveys.
- Post-remediation monitoring, including final evaluation of remediation work success.Other extra and specialized work related to the remediation work (expert assessment, supervision, etc.).
Our company normally does remediation work in a way that does not result in disruptions to the operation of industrial facilities. Our adherence to this requirement can be documented with references from current remediation sites; these include, among others, sites of TRANSGAS a.s. (Rozvadov, Tvrdonice, etc.), ALIACHEM a.s. – Synthesia Pardubice, and PAL International a.s. Praha-Kbely.
Techniques dealing directly with decontamination of the unsaturated zone (soil and rock environment)
Wherever technically feasible, we readily employ invasive remediation techniques, chiefly excavation of contaminated earth and rock (and demolition of contaminated structures if necessary), followed by neutralization (biodegradation in situ, composting, earth washing, etc.) and backfilling of the excavated areas with inert materials. Such remediation is very quick and effective, but only applicable on certain sites, where the excavation work cannot result in destabilization to structures or process equipment, significant restrictions on industrial production, etc.
That is why EKOSYSTEM spol. s r. o. favours in-situ remediation techniques, of which the following are particularly suitable for the purpose in question (remediation of extensive and massive contamination):
The working principle consists in exhausting the soil air using a vacuum pump and purifying it using filters, which removes volatile organic compounds, above all, from the unsaturated zone. This is typically done using specially adjusted venting boreholes or combined boreholes along with remediation pumping. An alternative to venting is “air rinsing”, where the mobility of the volatile compounds is increased by forcing compressed air down adjacent boreholes.
At present, venting is commonly used on all the sites remediated by EKOSYSTEM spol. s r. o. where volatile organic compounds are the dominant pollutant.
A variation on venting applicable to the elimination of all biodegradable substances. It consists in adding oxygen to the unsaturated zone (using a combination of air exhaust and forcing, or setting the exhaust parameters in a way that boosts the circulation of soil air in the earth), which stimulates the degradation potential of the microflora primarily present in the earth or added to the earth artificially. Nutrients can be delivered to the unsaturated zone for a more intense effect. One advantage, among others, is the easy transformation of conventional venting to bio-venting by simply readjusting the technical parameters.
We commonly use bio-venting alongside conventional venting on sites with mixed contamination.
Suitable for the removal of volatile organic compounds (our best positive experience is with removing chlorinated hydrocarbons) from groundwater and the adjacent portion of the unsaturated zone, especially where it is porous enough. This is a variation on stripping: air is forced down a specially adjusted forcing borehole, where it disperses below the groundwater level in the form of fine bubbles. They bind the volatile pollutant, which is released into soil air along with them and then exhausted through a nearby venting borehole and purified using filters. An alternative is air-sparging in so-called self-remediating boreholes, where both air forcing and exhaust are done in a single borehole of a special design.
The advantage of this method is its applicability in isolated and point sources of contamination and wherever a remediation station cannot be installed for various reasons. We have used it, among other cases, as an auxiliary remediation technique when eliminating the old environmental burden on the premises of PAL International a.s. Praha-Kbely (in combination with remediation pumping and venting).
An advanced method of eliminating contamination along the dividing line between the saturated and unsaturated zones, especially suited for removing petroleum hydrocarbons from the groundwater surface. A mobile pipe is lowered into a borehole, which sucks in (“slurps”) the contaminated layer of groundwater near its surface along with, or alternately with, soil air. Conditions for biodegradation are provided at the same time, resulting in simultaneous bio-venting (see above).
EKOSYSTEM spol. s r. o. has tested this technique successfully on the ČKD site in Praha-Vysočany, and we expect to use it routinely from now on.
Biodegradation in situ
This technique is also based on the existence of microflora with degradation capabilities in the soil and rock environments (or added there artificially); to some extent, the principle is similar to the above methods of bio-venting and bio-slurping. Groundwater pumped for remediation is enhanced with nutrients on the surface and then reabsorbed by the ground, where it stimulates the degradation potential of the microorganisms.
Biodegradation can be combined with other methods of pollutant removal as well. EKOSYSTEM spol. s r. o. employs it on selected sites, including premises of TRANSGAS a.s.
Chemical oxidation in situ
Among several variations differing in the oxidation medium (ozone, Fenton’s reagent, etc.), chemical oxidation using potassium permanganate has been tested in practice and employed in routine remediation. The chemical is forced into the rock environment in the form of a high-concentration solution by way of pressure soaking using specially designed boreholes. This achieves, above all, oxidation of chlorinated hydrocarbons in groundwater and soil, producing non-toxic or insoluble inorganic compounds (potassium chlorine, manganese oxides). These substances are no longer an environmental burden and can be left in the rock environment.
Chemical oxidation in situ has been tested successfully at VELAMOS a.s. Zlaté Hory; we are currently employing this remediation method at PAL International Praha-Kbely.
Heavy metal precipitation in situ
This technique has mostly been used in water treatment so far; its use in in-situ remediation is not very widespread as yet, but is expected to expand. Among various methods (carbonate and hydroxide precipitation, coagulation, etc.), we have tested sulphidic precipitation of chromium and nickel in practice. It is based on immobilizing the heavy metals by means of gravity soaking chemical preparations via boreholes (sodium sulphide and products based on it, in this case). The resulting precipitate remains in the ground without posing any environmental burden.
Sulphidic precipitation has been tested at VELAMOS a.s. Zlaté Hory, and we expect to employ it more widely from now on.
This is based on the simple principle of soaking into the soil and rock environment using soaking boreholes or soaking drains. The soaking is combined with remediation pumping.
Rinsing is done using:
- water; typically this is re-soaking of remediation pumping water after running it through a decontamination station;
- bio-preparations; essentially a modification of biodegradation in situ as described above;
- chemical preparations, including detergents, for example.
Rinsing, especially using treated remediation pumping groundwater, is employed on most sites being remedied by EKOSYSTEM spol. s r.o., at least as a supporting method.
Encapsulation (retention) methods in the broader sense
Besides the rarely used (technically difficult and expensive) encapsulation in the strict sense of the word, i.e., complete enclosure of the contamination cloud in an impermeable barrier, the following measures preventing the penetration of pollutants into the outside environment are commonly available:
- protective drains: a relatively versatile application (wherever a pollutant has to be prevented from spreading via groundwater); typically they are subject to remediation pumping; the advantage is that other remediation techniques can be employed at the same time (e.g., soaking of oxidation or precipitation media). EKOSYSTEM spol s r. o. has been successfully using a protective drain as part of remediating the premises of PAL International a.s., for example, where it substantially reduces the spreading of the pollutant outside the premises and into the Kbely municipal district.
- sealing walls: suitable for preventing the spreading of difficult-to-remove pollutants or rapidly preventing the migration of massive contamination clouds. We have employed them successfully on TRANSGAS a.s. sites, for example.
These are essentially sealing walls fitted with so-called reactive gateways: passages at the saturated zone level filled with metallic (zero-valent) iron. They are used in remediation of volatile organic compounds, chiefly chlorinated hydrocarbons, on specific sites with massive contamination. The advantage is the partial permeability, meaning reduced interference with the hydrogeological conditions of the site, combined with the prevention of contamination spreading.
These achieve the removal of pollutants chiefly or exclusively from groundwater, thus indirectly contributing to the decontamination of the unsaturated zone. Remediation pumping is the most widespread and most commonly employed by EKOSYSTEM spol. s r. o. Here, groundwater is pumped out, purified in a remediation station and then returned to circulation (discharged down the sewer or a suitable watercourse, or left to soak in). The most common purification devices are stripping columns and aerators (chlorinated hydrocarbons or volatile organic compounds in general), gravity separators (petroleum derivatives), and filters. The pumped water can also be decontaminated using advanced techniques such as membrane separation. EKOSYSTEM spol. s r.o. employs remediation pumping in practice on all its remediation sites.
Remediation techniques may also include taking advantage of the natural attenuation of organic substances in the rock environment. This is basically a passive remediation method. The principle consists in the recognition that the quantity of a pollutant can be spontaneously and gradually reduced, due to various factors in the rock environment, to a level that is environmentally tolerable, without the need for a remediation intervention. The application of natural attenuation therefore only requires highly targeted monitoring and ongoing evaluation. It is mostly an auxiliary method employed in parallel with the various remediation techniques described above.
The decision on which particular remediation technique (or combination of several techniques) to use is always case-by-case and follows from the specific conditions on the site in question, including notably the following:
- pollutant type;
- intensity of contamination and pollutant distribution;
- geological and hydrogeological conditions;
- spatial conditions;
- existence of limiting factors (such as underground mains, limitations due to process equipment, structures, etc.).
That is why a preliminary assessment, possibly including the need for additional surveying, always has to be made even with basic knowledge of the site and its contamination. The type and scope of remediation cannot be determined without basic knowledge of the site.