METHOD OF INCREASING HYDROPHOBICITY OF NATIVE WATER-BEARING ZONES

Abstract

Methods for increasing hydrophobicity of native water-bearing zones or aquifers comprising the step of permanently embedding non-degradable, solid colloidal materials formed to have a particulate size of less than 10 microns. Exemplary materials include activated carbon, zeolites and hydrophobically treated clays. The particulate colloidal materials are coated with an agent to facilitate their distribution, including anionic polymers, chelating agents or combinations thereof. The materials are applied preferably by low pressure injection and are particularly effective at containing the migration of hydrocarbon contaminants, typically present as a plume, for at least several decades.

Claims

1. A method of permanently increasing the hydrophobicity of a subsurface water-bearing zone, comprising the step of embedding a non-degradable, solid, colloidal material within said water-bearing zone.

2. The method of claim 1 wherein said material is 0.1 to 10 micron diameter in size.

3. The method of claim 1 wherein said material is treated with a coating to facilitate its distribution within the water-bearing zone when the solid material is applied.

4. The method of claim 3 wherein the coating material comprises at least one anionic polymer.

5. The method of claim 3 wherein the coating material comprises at least one chelating agent.

6. The method of claim 5 wherein the coating material is formulated with a combination of at least one anionic polymer and at least one chelating agent.

7. The method of claim 1 wherein said solid material is applied by injection to the subsurface of the water-bearing zone at an injection pressure of <100 psi.

8. The method of claim 1 wherein the solid material is selected from the group consisting of activated carbon, zeolites, hydrophobically altered clays, and combinations thereof.

9. The method of claim 1 wherein the material increases the retardation factor of the contaminant by at least 50% over the native conditions of the water-bearing zone.

10. The method of claim 1 wherein the material increases the retardation factor of the contaminant by a factor ranging from one to three orders of magnitude over the native conditions.

11. The method of claim 1 wherein the desired retardation factor is first determined and the dose of said material is calculated in order to meet said desired retardation factor.

12. The method of claim 1 wherein the water-bearing zone includes a contaminant plume present in the dissolved phase.

13. The method of claim 12 wherein the contaminant plume consists of an organic contaminants selected from the group consisting of gasoline, diesel, motor oil and their constituents, chlorinated solvents including trichloroethene, tetrachloroethene, dichloroethenes, vinyl chloride, chlorinated ethanes, chlorinated benzenes, and fluorinated compounds including perfluorooctane sulfonic acid and perfluorooctanoic acid, pesticides, herbicides, organic compound-based agricultural fertilizers and combinations thereof.

14. The method of claim 7 wherein said solid material is operative to migrate a distance ranging from 5 centimeters to 5 meters from the point where said material is injected.

15. The method of claim 13 wherein said material is operative to remain in fixed position following said migration for a period of at least 30 years.

16. The method of claim 14 wherein said material is operative to remain in fixed position following said migration for a period of from 35 to 40 years.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0018] These and other features and advantages of the various embodiments disclosed herein will be better understood with respect to the following description and drawings, in which like numbers refer to like parts throughout, and in which:

[0019] FIG. 1 illustrates a simulated plume centerline concentration for tetrachloroethylene (PCE) as a plume of PCE migrates over a 35 year period under native conditions.

[0020] FIG. 2 illustrates the simulated plume centerline concentration for PCE as illustrated in FIG. 1 with the addition of a colloidal activated carbon treatment and how the same increased theretardation of the PCE plume and inhibited its migration.

DETAILED DESCRIPTION

[0021] The detailed description set forth below is intended as a description of the presently preferred embodiment of the invention, and is not intended to represent the only form in which the present invention may be implemented or performed. The description sets forth the functions and sequences of steps for practicing the invention. It is to be understood, however, that the same or equivalent functions and sequences may be accomplished by different embodiments and that they are also intended to be encompassed within the scope of the invention.

[0022] The present invention is directed to methods for permanently increasing the hydrophobicity of an aquifer in such a manner that consequently causes the retardation of the migration of hydrophobic contaminants present therein. The methods of the present invention thus advantageously facilitates the containment of such hydrophobic contaminants that would otherwise become widely dispersed within the aquifer and thus leading to more widespread contamination.

[0023] To achieve that end, the methods of the present invention deploy the use of a non-degradable, solid, colloidal material that has a high affinity for hydrophobic contaminants present in an aquifer that are further operative to be readily distributed within the aquifer under low pressure. Exemplary of such non-degradable, solid, colloidal materials include activated carbon, zeolites and hydrophobically altered clays, as well as combinations thereof, with activated carbon being a preferred material. According to a preferred embodiment, such non-degradable, solid, colloidal materials are formed to have a very fine particulate size, typically ranging from 0.1 to 10 microns, and preferably between 1-2 microns, that are further provided with surface treatment to thus enable the colloid material to distribute through soil and groundwater upon injection. To that end, such surface treatment may include treatment with an anionic or nonionic polymer, such as carboxymethyl cellulose (CMC), carrageenan, polyacrylic acid, xanthum gum, polyacrylates, polyacrylamides, co-polymers of acrylamide and acrylate, and combinations thereof

[0024] Alternatively, the particulate surface of the solid, colloidal material may comprise one or more chelating agents, which can include but not limited to citrates, phosphates, silicates, borates, sulfates, carbonates, aminocarboxylic acids and salts thereof, polyamines, and combinations thereof. In further refinements of the invention, the particulate solid, colloidal materials may be treated with both anionic or nonionic polymers and one or more chelating agents as may be desired for a particular application and/or to enhance distribution of the solid, colloidal materials in a given aquifer or water-bearing zone.

[0025] By way of example, and not in any way limiting the scope of the present invention, such colloidal materials may take the form as those disclosed in published United States Patent Application US2015/0034559 A1 entitled COLLOIDAL AGENTS FOR AQUIFER REMEDIATION, filed by Mork, et al. on Aug. 1, 2014, the teachings of which are expressly incorporated herein by reference. Any such solid, colloidal materials, however, will in all cases have a high affinity for contaminants that are not only stabilized, such as through a surface coating or other amendments, but also allow the colloidal material to effectively transport through soil and groundwater.

[0026] In use, the colloidal material will be operatively distributed via injection within the aquifer under low pressure, non-fracturing pressure, defined as less than 100 psi. Application can likewise be accomplished via other techniques well-known in the art such as gravity feed or percolation. Ideally, the solid, colloidal materials as stabilized with a surface coating will be operative to migrate into position within the aquifer a distance ranging from at least 5 centimeters to up to 5 meters from the point of introduction, depending on the characteristics of the subsurface water-bearing zone and volume of solid, colloidal materials deployed at the site of introduction into the aquifer or water-bearing zone.

[0027] Following application, the non-degradable colloidal materials will subsequently become permanently embedded on the surface of the soil or rock matrix in the aquifer and thereafter promote long-term retardation of migrating contaminant plumes for periods lasting years to decades. Advantageously, such materials can typically increase the retardation of migration plume by at least 50% over the native aquifer conditions, and in some cases by a factor of 1 to 3 orders of magnitude over the native conditions of the aquifer. In any case, the desired retardation can be calculated and then the colloidal material can be dosed accordingly to meet the desired retardation factor.

[0028] As discussed above, the solid colloidal materials will have a high affinity for contaminants, and specifically hydrophobic contaminants. Such contaminants that may be effectively treated by the methods of the present invention can include any organic contaminants that sorb to activated carbon and other sorbents used in water purification. These include all petroleum hydrocarbons, e.g. gasoline, diesel, motor oil and their constituents, chlorinated solvents including trichloroethene, tetrachloroethene, dichloroethenes, vinyl chloride, chlorinated ethanes, chlorinated benzenes, fluorinated compounds including perfluorooctane sulfonic acid and perfluorooctanoic acid, pesticides, herbicides, organic compound-based agricultural fertilizers and combinations thereof. These groundwater contaminants are listed for example and are not meant to limit the scope of the invention.

[0029] By way of illustration, and by no means meant as limiting the present invention, the following example is provided:

Example 1

[0030] Example scenario describing the increased retardation of a PCE plume through the addition of colloidal activated carbon to the aquifer. In this example, a PCE plume was modeled using a modified version of the BIOCHLOR fate and transport software with the following plume parameters:

[0031] 0.1 mg/L PCE

[0032] Model timeframe: 35 years

[0033] Seepage velocity: 100 ft/yr

[0034] foc: 0.0015

[0035] Biotransformation rate: 0.85 yr−1

[0036] Calculated retardation factor: 3

[0037] In this case the retardation factor is calculated based on the foc and the koc of PCE, and was determined to be a factor of 3. The same plume was then modeled with the addition of a colloidal activated carbon to the aquifer as follows:

[0038] Colloidal activated carbon application length: 25 feet

[0039] Colloidal activated carbon dose: 1000 mg/L

[0040] Calculated retardation factor: 394

[0041] Under these conditions, the retardation factor is calculated using the sum of native retardation factor and the factor calculated using the Freundlich isotherm parameters measured for PCE with the colloidal activated carbon. The resulting factor was determined to be 394, an increase of over two orders of magnitude over the native conditions. This is the equivalent of increasing the foc from 0.0015 to 0.3.

[0042] Graphical outputs from the modeling study are shown in FIGS. 1 and 2. The model demonstrates that under the natural aquifer conditions, represented in FIG. 1, the PCE plume would extend over 300 ft. after 35 years. In comparison, when a 25 ft. colloidal activated carbon barrier was installed at a concentration of 1,000 mg/L, the retardation factor was increased from 3 to 394, and the plume was contained for the 35-year period, as shown in FIG. 2.

[0043] Additional modifications and improvements of the present invention may also be apparent to those of ordinary skill in the art. Thus, the particular combination of parts and steps described and illustrated herein is intended to represent only certain embodiments of the present invention, and is not intended to serve as limitations of alternative devices and methods within the spirit and scope of the invention.