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Treatment of contaminated water in clays and the like

  • US 5,641,020 A
  • Filed: 05/19/1995
  • Issued: 06/24/1997
  • Est. Priority Date: 05/20/1994
  • Status: Expired due to Term
First Claim
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1. Procedure for treating contaminated groundwater, including the steps of:

  • taking a sample of the ground containing the contaminated groundwater;

    establishing the nature of the contaminant, and selecting a suitable treatment material;

    proceeding with the following steps responsive to the selected treatment material being of the kind that will bring about a chemical breakdown of the contaminant when the contaminant is located, at a point of breakdown, in close physical proximity to the treatment material, being breakdown of the kind wherein;

    (a) the contaminant is chemically converted into a relatively non-contaminating substance, (b) the concentration of the contaminant at the point of breakdown is substantially depleted by the breakdown, and (c) the effective concentration of the treatment material at the point of breakdown is unaffected or affected only very slowly by the breakdown;

    determining the nature of the ground, and proceeding with the following steps responsive to a determination that the ground comprises large blocks of low permeability material (LPM), and the large LPM blocks are intercalated with cracks or other zones of higher permeability;

    determining the concentration (CC-i) of the contaminant at an interior point of the LPM block, located a distance L from the nearest point on the boundary of the block;

    carrying out measurements and calculations to determine the passive diffusion rate of the contaminant (PDR-C) in the LPM block, being the rate at which the concentration of the contaminant at the point changes over time as a function of the concentration gradient of the contaminant (CG-C) at that point;

    providing conditions whereby passive diffusion of the contaminant towards the boundary of the block can take place;

    proceeding with the following steps in response to a need to reduce the size, being the dimensions L, of the blocks;

    providing a fracturing fluid, comprising a mixture of the treatment material with e carrier fluid;

    establishing a concentration of treatment material (CTM-H) that can be injected into the fracks in the fracturing fluid, and forming the mixture to that concentration;

    carrying out measurements and calculations to determine the extent of the treatment area, being the area of the contaminated LPM;

    drilling boreholes at intervals over the treatment area;

    fracturing the ground around the holes, so as to form fracks, by injecting the fracturing fluid under pressure into the boreholes;

    spacing the boreholes a pitch distance apart over the treatment area such that the fracks overlap laterally;

    establishing a mathematical model, based on the PDR-C, for enabling a theoretical prediction to be made of the relationship between the distance L and the time period taken for CC-i to drop to a safe concentration (CC-safe);

    assigning an acceptable time period T for the CC-i to fall to CC-safe;

    from the model, computing the distance L corresponding to that time period T;

    forming a plurality of the fracks in the borehole, spaced a distance V apart, where V is no more than L;

    after fracturing, maintaining passive conditions in the fracks at the point of breakdown;

    wherein the passive conditions are such that, under the passive conditions, passive diffusion of the contaminant towards the boundaries of the LPM blocks takes place, substantially without the input of flow-inducing energy.

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