Liquid purification or separation – Processes – Including geographic feature
Reexamination Certificate
2000-03-22
2001-08-14
Simmons, David A. (Department: 1724)
Liquid purification or separation
Processes
Including geographic feature
C210S758000, C210S170050, C405S128350, C405S263000, C588S249000
Reexamination Certificate
active
06274048
ABSTRACT:
This invention relates to the treatment of contaminated groundwater, especially groundwater contaminated with DNAPL contaminants, such as PCE, C
2
Cl
4
, or TCE, HC
2
Cl
2
. The DNAPL (dense, non-aqueous-phase liquid) is present in the aquifer through which the groundwater passes. Generally, the DNAPL is present in the aquifer because the DNAPL has been spilled onto the ground surface from an industrial or commercial facility, and has soaked down into the ground.
The DNAPL existing in the subsurface as an immobile oily liquid causes the groundwater flowing by or through the DNAPL zones to pick up dissolved contaminants that are carried with the flowing groundwater to form a contaminant plume. Hence, the subsurface overall polluted zone comprises the DNAPL zone and the plume caused by the DNAPL zone.
The spill might have arisen due to a one-time accident that released a quantity of the DNAPL onto the ground; or the spill might have originated as a long-term continuing leakage from a pipe or storage tank; or the spill might even have arisen because the DNAPL was deliberately dumped onto the ground at a disused corner of the property.
DNAPLs such as those mentioned above are commonly used for cleaning metal components in manufacturing industries, as well as for dry-cleaning clothes. Once in the ground, the DNAPL can be expected to persist for decades, or even centuries. Groundwater pollution caused by DNAPLs exists at many thousands of industrial and other sites, both active and abandoned.
To achieve permanent remediation of the polluted subsurface zones, both the DNAPL and the dissolved and sorbed contamination should be removed and destroyed.
BACKGROUND TO THE INVENTION
It is known that organic solvents such as chlorinated ethenes and other DNAPL substances can be broken down by exposure of the DNAPL substance to a strong oxidant.
It is also known to treat groundwater contaminated with chlorinated ethenes in-situ, i.e the contaminated groundwater is treated in the aquifer through which the groundwater is passing.
Conventionally, the treatment has been done by flushing, i.e by injecting the oxidant into the ground upstream of the contaminant, and drawing water out downstream, the intention being to pass the oxidant over and through the contaminated zone, and thereby bring about the destruction of the contaminant.
The oxidation reaction transforms the chlorine component of the contaminant into a harmless chloride salt. The resultant chloride, as produced by the oxidation reaction, may be ignored, at least in the small concentrations that are produced.
Oxidants that have been used conventionally to break down chlorinated ethenes include hydrogen peroxide, and permanganate, such as potassium permanganate. As mentioned, these substances have been injected upstream and drawn off downstream, the intention being to promote a flushing action. But conventional flushing, as a way of remediating DNAPL contaminants, is inefficient, and can be incomplete. The invention is aimed at promoting the breakdown reaction, for example the oxidation reaction, in a way that is substantially more efficient, and more economical, than flushing.
The invention is aimed at causing destruction of the contaminants in whatever form they occur in the ground, whether they are in the DNAPL form, sorbed on soil particles or dissolved in the groundwater. In the invention the treatment chemical in liquid form, that is substantially denser than water such as a permanganate solution for oxidation of the contaminants, is injected into the aquifer from a borehole so as to react with the contaminants. While the treatment liquid is being injected, it spreads out quickly into the aquifer to form a discrete zone extending from the borehole. The borehole used for the injection allows the treatment fluid to enter the aquifer only in a specified discrete open interval along the vertical extent of the borehole. For example, this open vertical interval may be 0.5 meters long. Thus, as the treatment liquid is injected through the open interval under gentle or moderate pressure, it forms a disc-like or ellipsoid-like zone substantially in the lateral direction in the aquifer. As the episode of applied injection pressure for the zone comes to an end, the treatment solution in the aquifer begins to spread laterally and also sink downward because of the effect of the density of the treatment solution and, as this spreading and sinking occurs, the treatment chemical also spreads because of molecular diffusion. Hence, these spreading processes cause the treatment chemical to invade a much larger volume of the aquifer than occurs during the injection period. To achieve the full advantage of this invasion, a period of time much longer than the injection period must pass to allow the spreading caused by density and diffusion to become complete or nearly so. As the treatment solution comes into contact with contaminants, it reacts with the contaminants to cause destruction of contaminant molecules. As this destruction occurs, treatment solution is consumed. The treatment chemical can also be consumed by reactions with the geological materials or other natural constituents in the aquifer. In some circumstances the mass of treatment solution put into the aquifer during the episode is not sufficient to destroy all of the contamination in the injected and invaded zones and therefore, another injection episode at or near this location may be needed. This second injection episode should occur after the invasion resulting from the first injection episode is complete or nearly so. Additional injection episodes may be needed to complete the desired degree of cleanup of the treatment zone. Thus, the full treatment of the targeted volume of aquifer may be achieved with only one injection episode or more episodes.
An aim of the invention is to provide versatility of treatment types, including its use to treat a specific layer or lens of contamination that has been found during investigations of the site. It also can be used to treat portions of an aquifer in which contaminant occurrence is known or suspected but the exact locations have not been determined. In the first type of use of the invention, the treatment may be focused towards a specific layer or lens-like zone of contamination. In contrast, in the second type of use, the invention may be used to enable the treatment chemicals eventually to invade the full volume of aquifer where treatment is desired but the whereabouts of the contaminants in this volume is not known in any detail.
Thus, the invention may be used to blanket a targeted volume of aquifer so that the treatment chemical will reach whatever contamination occurs in the volume. An important advantage of the invention is that the injection of the treatment liquid to form the immediate disc-like or ellipse-like zones in the aquifer is designed to occur in a manner that causes very little pushing away or displacement of the contaminated groundwater existing in the volume of aquifer being treated. After the injection period the spreading by density and diffusion causes no substantial displacement. This is much different from the flushing approach in which the treatment solution is forced by injection and, perhaps also by pumping of other wells nearby, to flow through the entire zone of the intended treatment zone. This is because the application of injection pressure is continual. It is particularly important, while blanketing the aquifer zone, to avoid pushing the contaminated groundwater out in front of the injected liquid because the water that is pushed out in front of the treatment liquid cannot then be treated. The systems as described herein avoid this excessive pushing-away of the contaminated water because when using the systems, two or more of the injected disc-like zones are formed in each borehole, one below the other, so that an initial gap or space exists between the disc-like zones. The gaps are substantially larger than the vertical heights of the injected discs after the injection period. The gaps are then filled in by
Cherry John Anthony
Nelson Matthew David
Parker Beth Louise
Anthony Asquith & Co.
Lawrence Frank M.
Simmons David A.
University of Waterloo
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