ARCHIVED REPORTS XR0003043 - Laserfiche WebLink

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• • 5,605,634 TREATMENT OF CONTAMINATED GROUNDWATER This invention relates to the treatment of contaminated groundwater. BACKGROUND TO THE INVENTION The invention is aimed at simplifying the task of placing treatment chemicals and other substances into the ground, for the purpose of treating contaminants in groundwater, in-situ. Taking the water out of the ground for treatment is not particularly difficult technically, and if the water is taken out of the ground, the treatment chemicals can be applied to the water, above ground, in a reasonably well controlled manner, in whatever quantities and concentrations are required: but taking large quantities of water out of the ground, treating the water, and putting the treated water back, is very expensive, especially when the contaminant is Of the kind that is hazardous in small traces. THE INVENTION IN RELATION TO THE PRIOR ART 2 borehole may or may not be provided with a well -casing, but in any event the borehole is open to the throughflow of groundwater passing in through from side to side of the borehole, i.e, flowing laterally across and through the bore- s hole. A length of tubing is placed in the borehole, and arrange- ments are made for circulating the substance through the tubing. Some kinds of plastic and other non -rigid materials have the property that the plastic material is not entirely 10 proof against the passage of liquids and gases. That is to say, some fluids can leak through the walls of tubes made from some kinds of plastic. The crystalline structure of the plastic is such that only a portion of the material is crystalline, and the rest is amor- 15 phous. It is the amorphous areas which can allow the diffusion of fluids, especially those having the smaller molecules. 20 It has been proposed to inject, or otherwise place, chemi- cals, nutrients, and various substances directly into the u ground, in the path of an on -coming plume of contaminated groundwater, in order that the contaminants in the water may pass through the substances. Thereby, the contaminated groundwater may be treated without taking the water out of the ground. 30 When dealing especially with treatment substances that, to be effcctive, and safe, can only be present in small traces, one of the difficulties is to inject the treatment substance evenly and smoothly, and to ensure an even dispersion of the treatment substance. In many cases, it is important that the 35 treatment substance be evenly dispersed over the whole cross-sectional area of the oncoming plume, and to avoid pockets or streaks of concentration. Some treatment substances are only effective if present in the right concentration. Too much can be toxic in itself, 40 besides being wasteful of expensive materials. Too little, and the treatment substance may be too dilute to have an effect. Of course, there aro streaks and pockets of varying concentration of the contaminants in the plume, and the ideal would be to tailor the concentration of the treatment sub- 45 stance to exactly correspond to the concentration of the contaminant; however, it has been found to be a worthwhile contribution to the efficiency of the treatment system if the treatment substance at least is dispersed over the cross- section of the plume at an even, or pre -determined, concen- 50 tration. An aim of the invention is to provide a means for injecting small traces of treatment substances into moving ground- water, in-situ, in such a manner that the concentration of the injected substances in the groundwater is smoothly and s5 evenly dispersed through the water. Another aim of the invention is to provide a system for - injecting small traces of treatment substances into moving groundwater, in-situ, in such a manner that the concentration ba of the injected substances in the groundwater can be con- trolled to tighter limits than has been possible hitherto. THE GENERAL FEATURES OF THE INVENTION 65 The invention involves the use of a borehole or well, which is formed down into the ground from the surface. The Low density polyethylene (LDPE) is a plastic which has this property of allowing many substances to diffuse through, at significantly quantifiable flow rates, LDPE hav- ing a fairly high proportion of amorphous structure. Besides, LDPE is inexpensive and readily available, and its use is preferred in the invention. Dialysis tubing may be used when large diffusion flux rates are called for. In the invention, the substance diffuses out through the walls of the diffusion tube, and enters the ground water in the borehole. The substance is then picked up by the moving groundwater, and is home downstream along with the groundwater. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS By way of further explanation of the invention, exemplary embodiments of the invention will now be described with reference to the accompanying drawings, in which: FIG. 1 is an elevational cross-section of a polluted aquifer, containing a borehole, in which the system of the invention is being used to supply treatment material; FIG. 2 is a plan view of the aquifer of FIG. 1; FIG. 3 is a diagram showing the details of the construction of a type of diffusion tube. The apparatuses shown in the accompanying drawings and described below are examples which embody the inven- tion. It should be noted that the scope of the invention is defined by the accompanying claims, and not necessarily by specific features of exemplary embodiments. FIG. I shows a borehole 20 extending vertically down into the ground from the surface 23. The .borehole is provided with a lining or casing 25. The casing 25 is provided with openings 27, through which water can pass laterally into and out of the borehole, while screens 29 keep the borehole clear of gravel and other debris. Into the borehole is inserted a length 30 of diffusion tube, comprising a length of plastic tubing. The diffusion tube 30 is placed down the borehole 20. An entry pipe 32 conveys fluid into the top or entry end 34 of the diffusion tube 30, and an exit pipe 36 takes fluid emanating from the bottom or exit end 38 of the diffusion tube 30 back out of the borehole 20. The diffusion tube lies beneath the surface 40 of ground- water present in the borehole 20. The entry and exit pipes 32,36 are brought out of the borehole, and are coupled to a circulation control unit 43, which resides outside the borehole, above ground.