Methods for stabilizing heavy metal containing material for disposal in saturated zone

1. A method for storing in a saturated zone a leaching-stabilized heavy metal-containing matrix that leaches heavy metal at no more than a preselected level, the method comprising the steps of:

determining pH, adsorption-coprecipitation potential and oxidation-reduction potential of the heavy metal-containing matrix;

determining pH, adsorption-coprecipitation potential and oxidation-reduction potential and flux of the pore water;

treating a heavy metal-containing matrix with at least one of an agent for controlling pH, an agent for controlling oxidation-reduction potential, and an agent for controlling adsorption-coprecipitation in an amount sufficient to form the leaching-stabilized heavy metal-containing matrix; and

flowing an agent for increasing the acid neutralization capacity (ANC) of the stabilized matrix into contact with the stabilized matrix, the flowing agent being provided in an amount sufficient to increase the permanence of the stabilized matrix to a preselected level.

2. A method for storing in a saturated zone a leaching-stabilized heavy metal-containing matrix that leaches heavy metal at no more than a preselected level, the method comprising the steps of:

placing the leaching-stabilized matrix in a saturated zone, wherein the matrix is spaced apart from an agent for increasing the acid neutralization capacity (ANC) of the stabilized matrix, and wherein the matrix is also spaced apart from an agent for controlling oxidation reduction potential (ORP) of the matrix; and

flowing an amount of the agent for increasing the ANC sufficient to increase the permanence of the stabilized matrix to a preselected level into contact with the stabilized matrix, and wherein the stabilized matrix is also contacted with an amount of the agent for controlling ORP sufficient to control the ORP of pore water in the matrix.

3. A method as claimed in claim 2 further comprising the step of determining the permanence of the stabilized matrix in contact with the agent for increasing the ANC.

4. A method as claimed in claim 3 wherein the permanence is determined by a method selected from the group consisting of a Multiple Extraction Test (MEP) or a groundwater analysis.

5. A method as claimed in claim 2 wherein the agent for increasing the ANC comprises calcium carbonate.

6. A method as claimed in claim 5 wherein the agent for increasing the ANC comprises limestone.

7. A method as claimed in claim 2 further comprising, prior to the placing step, the step of intimately mixing the stabilized matrix and a reserve amount of the agent for increasing the ANC.

8. A method as claimed in claim 2 wherein the agent for increasing the ANC flows into contact with the stabilized matrix in flowing groundwater.

9. A method as claimed in claim 8 wherein the flowing groundwater permeates a permeable barrier that comprises the agent for increasing the ANC.

10. A method as claimed in claim 9 wherein the permeable barrier comprises limestone.

11. A method as claimed in claim 2 wherein the leaching-stabilized matrix leaches heavy metals at a level sufficiently low to meet a regulatory test.

12. A method as claimed in claim 11 wherein the regulatory test is selected from the group consisting of a Toxicity Characteristic Leaching Procedure [TCLP], a Multiple Extraction Test [MEP], a Synthetic Precipitation Leaching Procedure [SPLP], an ASTM water leach test, a California Wet Extraction Test [WET], and a site-specific test to meet a federal drinking water standards.

13. A method as claimed in claim 2 wherein the heavy metal is selected from the group consisting of lead, cadmium, arsenic, zinc and chromium.

14. A method as claimed in claim 2 wherein the stabilized matrix is stored at a subsurface site.

15. A method as claimed in claim 14 wherein the agent for increasing the ANC flows into contact with the stabilized matrix in groundwater.

16. A method as claimed in claim 14 wherein the agent for increasing the ANC is provided on top of the stabilized matrix, so that water that contacts the stabilized matrix comprises the agent for increasing the ANC.

17. A method as claimed in claim 14 wherein the matrix is stored in a mine tailings impoundment.

18. A method as claimed in claim 2 wherein a plurality of barriers comprising the agent for increasing the ANC is spaced from the matrix.

19. A method for storing in a saturated zone a leaching-stabilized heavy metal-containing matrix that leaches heavy metal at no more than a preselected level, the method comprising the steps of:

placing the leaching-stabilized matrix in a saturated zone, wherein the matrix is spaced apart from an agent for increasing the acid neutralization capacity (ANC) of the stabilized matrix, and wherein the matrix is also spaced apart from an agent for controlling oxidation reduction potential (ORP) of the matrix; and

flowing an amount of the agent for increasing the ANC sufficient to increase the permanence of the stabilized matrix to a preselected level, wherein the stabilized matrix is also contacted with an amount of the agent for controlling ORP sufficient to control the ORP of pore water in the matrix, and wherein the matrix is stored at a location above a groundwater level.

20. A method as claimed in claim 19 wherein the agent for increasing the ANC is spaced apart from and on top of the stabilized matrix, so that water that contacts the stabilized matrix from above comprises the agent for increasing the ANC.

21. A method as claimed in claim 20 wherein the matrix is stored in a mine tailings impoundment.