Method and apparatus for in-situ chemical oxidation for soil and groundwater remediation

Abstract

A method for treating groundwater and soil with a chemical oxidant, such as potassium permanganate, is provided. A chemical is placed in a powdered or pellet form into injection wells. Baffles are inserted into the ground to direct groundwater flow toward the injection wells. The groundwater flows through the injection wells to pick up the chemical oxidant. A second set of baffles are placed between the injection wells and the contaminated zone to disperse the chemical oxidant laden water. The chemical oxidant laden water flows through the contaminated field, the oxidant acting on the contaminated soil and groundwater to treat same. The injection wells can be pressurized to increase groundwater flow. Tests can be conducted on the other side of the contaminated field to measure the effectiveness of the treatment.

Description

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a method and apparatus for in-situ saturated soil and groundwater remediation by chemical oxidation, and more particularly, to a method and apparatus for delivering an oxidant, such as potassium permanganate (KMnO4) to a contaminated site. The KMnO4 is solubilized into the groundwater in an injection well and then transported through a contaminated area using the natural groundwater gradient.

[0003] 2. Related Art

[0004] In-situ chemical oxidation remediation techniques involve treatment of organic contaminants by oxidizing single-chained hydrocarbon compounds, as well as double-bonded chlorinated compounds, into carbon dioxide and water. Chemical oxidants such as Fenton's Reagent are known oxidizing agents used, in part, for groundwater remediation. Typically, in-situ remediation using Fenton's Reagent consists of serially injecting catalysts and reagents into the subsurface of a contaminated site. Other oxidants such as potassium permanganate are known for use in water treatment plants. Additionally, it is known to inject a potassium permanganate solution into groundwater for groundwater remediation.

[0005] What would be desirable, but has not heretofore been provided, is a process whereby a powdered or pelletized oxidant can be placed into an injection well, dissolved, and carried by groundwater through a contaminated soil and groundwater area for remediating same. Specifically, it would be desirable to use such a process for remediating contaminated, saturated zone soil, i.e., the soil zone below the water table, and groundwater.

OBJECTS AND SUMMARY OF THE INVENTION

[0006] It is an object of the present invention to provide a system for in-situ chemical oxidation of contaminated saturated zone soil and groundwater.

[0007] It is an additional object of the present invention to provide a method and apparatus for passively remediating contaminated saturated zone soil and groundwater by solubilizing a chemical oxidant into groundwater.

[0008] It is a further object of the present invention to provide a method and apparatus for using groundwater to deliver a chemical oxidant to contaminated saturated zone soil and groundwater.

[0009] It is still a further object of the present invention to place powder or pelletized potassium permanganate into an injection well and allow same to dissolve in groundwater flowing through the well, the groundwater delivering the potassium permanganate to contaminated saturated zone soil and groundwater for remediating the contaminated zone.

[0010] It is still a further object of the present invention to direct groundwater flow through injection wells to dissolve a chemical oxidant and carry the chemical oxidant through contaminated saturated soil for soil and groundwater remediation.

[0011] It is even an additional object of the present invention to diffuse the flow of groundwater bearing a chemical oxidant so that the oxidant is dispersed through contaminated saturated soil and groundwater for remediating same.

[0012] The present invention relates to a method and apparatus for treating contaminated groundwater and soil with a chemical oxidant, such as potassium permanganate. More specifically, the present invention relates to a delivery system for delivering a chemical oxidant to groundwater for treatment of contaminated media. The chemical oxidant is placed in a powdered or pelletized form into injection wells upstream of the contaminated site. Baffles may be inserted into the ground upstream of the injection wells to channel groundwater flow toward the injection wells. The groundwater flows through the injection wells and solubilizes a portion of the chemical oxidant. A second set of baffles may be placed between the injection wells and the contaminated zone to disperse the chemical oxidant laden water. The chemical oxidant laden water flows through the contaminated field, the oxidant acting on the contaminated media to treat same. Tests can be conducted on the other side of the contaminated field to measure the effectiveness of the treatment. A preferred chemical oxidant is potassium permanganate in powder or pellet form. Flow of groundwater through the wells can be increased by altering the natural hydraulic gradient and/or pressurizing the wells.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Other important objects and features of the invention will be apparent from the following Detailed Description of the Invention taken in connection with the accompanying drawings in which:

[0014] FIG. 1 is a cross-sectional view of an injection well with groundwater flowing therethrough according to the present invention

[0015] FIG. 2 is a schematic diagram of groundwater directed by baffles to flow through injection wells, then about baffles and through a contaminated area.

[0016] FIG. 3 is a detailed view of an injection well used in the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0017] The present invention relates to a delivery system for delivering a chemical oxidant to groundwater for treatment of contaminated media. The oxidant is placed in a powdered or pellet form into one or more injection wells. Baffles may be inserted into the ground to channel groundwater flow toward the injection wells. The groundwater flows through the injection wells whereby the chemical oxidant is solubilized into groundwater. A second set of baffles may be used to disperse the chemical oxidant laden water. The chemical oxidant laden water flows through the contaminated field, the oxidant chemically reacting with the contaminated media to treat same. Tests can be conducted on the other side of the contaminated field to measure the effectiveness of the treatment. A preferred oxidant is potassium permanganate (KMnO4), which is manufactured by Carus Chemical Company of Peru, Ill., and sold under the registered trademark Cairox. This oxidant is described in U.S. Pat. No. 5,152,804 dated Oct. 6, 1992 to Eissele, et al.

[0018] As shown in FIG. 1, a soil profile typically includes the following layers: ground surface 9, overburden 10, silt 12, gravel 14 and bedrock 16. Water, shown by arrows A, flows around baffle 20 into injection well 30 which contains a chemical oxidant 32 within sleeve 34. The groundwater A flows through apertures 36 in the well 30 and the sleeve 34 and becomes laden with the chemical oxidant. The water leaving the injection well 30 is laden with the chemical oxidant as indicated by arrow B. Thereafter, the chemical oxidant laden water B is dispersed by baffle 40 for flow through the contaminated field.

[0019] As shown in FIG. 2, water A is directed by baffles 20 through injection wells 30. The groundwater A picks up the chemical oxidant and leaves the injection well 30 laden with chemical oxidant as shown by arrows B. The chemical laden water B is then dispersed over a desired area by baffles 40 and then flows through the contaminated field 19. Typically, a concentration of 1% to 4% KMnO4 solution is desired.

[0020] The injection wells 30 may be installed to bedrock depth using a backhoe or drilling rig as is known in the art. The wells may be screened from the top of the bedrock to the top of the length above the seasonal high water table. The wells can be sized as desired. In an embodiment of the invention, a 24-inch diameter schedule 80 PVC pipe with 5-foot screen intervals and a 9-inch sump could be used. It may be desirable to utilize a plurality of wells in rows. The wells could be placed about 15 to 20 feet from each other depending on the rate of groundwater flow and concentration of the contamination to achieve the desired retention time. In an embodiment of the invention, the wells have radii of influence of 5 feet that overlap each other by 2 inches. It is to be understood, however, that various other radii of influence and overlap factors are considered within the scope of the invention and can be calculated using known equations to achieve a maximum delivery of potassium permanganate for a given treatment area.

[0021] FIG. 3 shows a detailed view of an injection well 30 of the present invention. The well extends from the ground surface 9 to the bedrock 16. The well can be capped with a cover 31 such as a thirty-six inch manhole cover. The well 30 includes a well riser portion 33 which could be twenty-four inch diameter corrugated PVC pipe SCH 80, the height of which will vary depending on site stratography. A screened interval 35 extends preferably about five feet above the bedrock 16. The screened interval 35 could be twenty-four inch diameter corrugated PVC SCH 80 with a 0.025 inch slot size. A sump 37 interconnects with the screened interval 35 and is partially embedded in the bedrock 16. The sump 37 could be nine inches and have a twenty-four inch diameter corrugated PVC pipe SCH 80 construction with an end cap. Of course, dimensions and materials can be varied to accommodate different conditions. Wells with smaller diameters (approximately 2 inches) may be appropriate given the geologic setting. Small wells may also be desirable if pressure needs to be increased to increase groundwater flow, as will hereinafter be discussed.

[0022] The baffles 20 and 40 are preferably constructed of sheet piling driven to bedrock with a sheet-pile-driving rig. The baffles are placed at locations based on groundwater conditions and potassium permanganate loading requirements. The amount of sheet pile installed for funnel baffles 20 depends on the thickness of the most transmissive layer within the impacted area, the saturated thickness, the change in groundwater velocities, and the thickness of unsaturated soil.

[0023] The progress of the treatment, including travel time and oxidant concentration, can be monitored through monitor and/or observation wells, which can be positioned between the injection wells 30 and the contaminated field, within the contaminated field, and/or beyond the contaminated field.

[0024] As is readily apparent, treatment times will vary depending upon groundwater flow rates, the contaminant mass volume, and the oxidant demand rate at a given site. The flow of groundwater through the injection wells can be controlled by varying the pressure differential. To accelerate the groundwater flow rate, the present invention can be modified by pressurizing the injection wells. For example, the flow rate can be increased by pumping air into the injection wells to force the groundwater out. Air could be injected through a manifold with a valve. A pressure gauge could be used to monitor and maintain a desired pressure. In another embodiment of the present invention, the injection well can be pressurized by introducing water into the well to increase the hydraulic groundwater head, causing increased flow out of the well. Conversely, the gradient can be increased by lowering the gradient in a downgradient well. Advantageously, due to an increase in groundwater flow, the delivery of potassium permanganate will also be accelerated, and treatment time reduced. In order to determine how much water or air to add to the injection well to achieve a desired increase in groundwater flow, standard flow calculations known in the art can be used.

[0025] In order to determine the hydraulic head necessary in an injection well to create a desired groundwater flow, and accordingly, a desired delivery of potassium permanganate, it is necessary to first determine the hydraulic conductivity of the material through which groundwater flows without the introduction of water into the injection well, as well as the hydraulic gradient. This can be achieved by using a standard groundwater velocity equation listed below, in conjunction with observed parameters: 1 q = K n × Δ ⁢   ⁢ H Δ ⁢   ⁢ L ( 1 )

[0026] where q=the observed average velocity of potassium permanganate (measured in feet per day), K=the hydraulic conductivity of the material through which the potassium permanganate flows (measured in feet per day), n=the porosity of the material through which the potassium permanganate flows (measured in percentage), &Dgr;H=the observed change in hydraulic head between the injection well and a monitoring well (measured in feet), and &Dgr;L=the linear distance between the injection well and the monitoring well (measured in feet). It is assumed, in the above calculation, that since potassium permanganate is completely solubilized in water and moves the same rate as the groundwater, no retardation occurs. Thus, q represents both the groundwater seepage velocity and the rate of dispersion of potassium permanganate.

[0027] Solving for K, Equation 1 can be represented as follows: 2 K = q · n · Δ ⁢   ⁢ L Δ ⁢   ⁢ H ( 2 )

[0028] Accordingly, using Equation 2 above, the hydraulic conductivity of the material through which potassium permanganate flows, without the introduction of water into the injection well, can be determined. For purposes of illustration, the following example is provided:

[0029] Assume that potassium permanganate is observed to have moved 2.5 feet in 60 days from the injection well prior to the introduction of water therein. Accordingly, q=2.5/60=0.041667 feet/day. Further, assume that, based on the grain size of the aquifer, the porosity of the material through which the potassium permanganate moves is estimated to be 22%. Accordingly, n=22% or 0.22. Also, assume that the distance between the injection well and a monitoring well is 48.75 feet; therefore, &Dgr;L=48.75. Finally, assume that the observed change in hydraulic head between the injection well and monitoring well is 0.05 feet; therefore, &Dgr;H=0.05. Applying these observed parameters to Equation 2, the hydraulic conductivity K can be determined as follows: 3 K = ( 0.041667 ⁢   ⁢ feet/day ) ⁢ ( 0.22 ) ⁢ ( 48.75 ) 0.05 = 8.9375 ⁢   ⁢ feet/day ( 3 )

[0030] Thus, given the above observations, the hydraulic conductivity of the material through which permanganate flows, prior to the introduction of water into the injection well, is 8.9375 feet/day.

[0031] For further purposes of illustration, assume that it is desired to increase the average velocity of potassium permanganate 1 foot/day, instead of 0.041667 feet/day, as stated above. To achieve such an increase, the hydraulic gradient can be altered by adding water to the injection well. Therefore, the hydraulic gradient must be determined, based upon the above-derived hydraulic conductivity of the material through which potassium permanganate is presently flowing. Solving for &Dgr; H, the required change in hydraulic head in the injection well, Equation 1 can be transformed such that: 4 Δ ⁢   ⁢ H = q · n · Δ ⁢   ⁢ L K ( 4 )

[0032] Accordingly, because the desired average velocity of the potassium permanganate is 1 foot/day, q is equal to 1. K, already determined from prior observation, is equal to 8.9375 feet/day. Finally, n and &Dgr;L, already determined, are 0.22 and 48.75, respectively. Solving for &Dgr;H, the required change in hydraulic head in the injection well will be: 5 Δ ⁢   ⁢ H = ( 1 ) ⁢ ( 0.22 ) ⁢ ( 48.75 ) 8.9375 = 1.2 ⁢   ⁢ feet/day ( 5 )

[0033] Thus, in order to increase the average velocity of potassium permanganate being delivered from the injection well, it is necessary to introduce a quantity of water into the injection well that will result in an increase of the hydraulic head of the injection of 1.2 feet.

[0034] The above calculations can also be made/verified using a two-dimensional groundwater flow modeling program, such as the computer program sold under the name “WinFlow” by Environmental Simulations, Inc.

[0035] Having thus described the invention in detail, it is to be understood that the foregoing description is not intended to limit the spirit and scope thereof. What is desired to be protected by Letters Patent is set forth in the appended claims.

Claims

1. A method for treating a contaminated site including soil and groundwater comprising:

providing one or more injection wells located upstream of the contaminated site in the flow of groundwater to the contaminated site;

directing groundwater to flow through the one or more injection wells prior to flowing through the contaminated site;

dissolving a chemical oxidant in the groundwater as the groundwater flows through the one or more injection wells;

dispersing the groundwater with dissolved chemical oxidant for flow through the contaminated field; and

allowing the ground water with the dissolved chemical oxidant to flow through the contaminated field, the dissolved chemical oxidant reacting with and treating the contaminated site.

2. The method of claim 1 wherein the chemical oxidant is potassium permanganate.

3. The method of claim 1 wherein the step of directing the water to flow through the injection wells comprises installing first baffles upstream of the one or more injection wells.

4. The method of claim 3 wherein the first baffles are angled to direct groundwater flow through the one or more injection wells.

5. The method of claim 1 further comprising monitoring the treatment by testing groundwater downstream of the contaminated site.

6. The method of claim 1 wherein the step of dispersing the groundwater with dissolved chemical oxidant comprises installing second baffles between the one or more wells and the contaminated site for dispersing water.

7. The method of claim 6 wherein the second baffles are oriented perpendicular to the direction of groundwater flow.

8. The method of claim 1 further comprising increasing groundwater flow from the one or more wells by pressurizing the one or more wells.

9. The method of claim 8 wherein the one ore more wells are pressurized by injecting air into the wells.

10. The method of claim 8 wherein the one or more wells are pressurized by injecting water into the one or more wells.

11. An apparatus for treating a contaminated site including soil and groundwater comprising:

at least one injection well positioned upstream of the contaminated site;

a chemical oxidant injected within the at least one injection well;

means for directing groundwater to flow through the at least one injection well to pick up the chemical oxidant; and

means for dispersing the groundwater with chemical oxidant to flow through contaminated site.

12. The apparatus of claim 11 wherein the chemical oxidant comprises potassium permanganate.

13. The apparatus of claim 12 wherein the chemical oxidant comprises pellets.

14. The apparatus of claim 12 wherein the chemical oxidant comprises powder.

15. The apparatus of claim 11 wherein the means for directing groundwater flow through the at least one injection well comprises first baffles positioned upstream from the wells to funnel groundwater flow into the wells.

16. The apparatus of claim 15 wherein the means for dispersing the groundwater comprises second baffles positioned in the ground between the wells and the contaminated site.

17. The apparatus of claim 16 wherein the second baffles are positioned perpendicular to the flow of groundwater.

18. An injection well for delivering an oxidant to a site including contaminated soil and groundwater comprising:

a sump partially embedded in bedrock;

a screened interval interconnected with the sump;

a well riser interconnected with the screened interval and extending from the screened interval to ground surface; and

a cover positionable over the well riser.

19. The injection well of claim 18 wherein the screened interval extends approximately five feet from the sump.

20. The injection well of claim 18 wherein the sump comprises a pipe with a bottom end cap.

21. The injection well of claim 18 further comprising means for pressurizing the well.

22. The injection well of claim 21 further comprising a pressure gauge for monitoring and maintaining pressure in the injection well.

23. A method for treating a contaminated site comprising:

providing an injection well upstream of the contaminated site;

introducing a solid chemical oxidant into the injection well;

allowing groundwater to flow into the injection well;

dissolving the chemical oxidant into the groundwater;

allowing the groundwater with dissolved chemical oxidant to flow out of the injection well; and

allowing the dissolved chemical oxidant to treat the contaminated site.

24. The method of claim 23, wherein the chemical oxidant is potassium permanganate.

25. The method of claim 24 wherein the chemical oxidant is in pellet form.

26. The method of claim 25 wherein the chemical oxidant is in powder form.

27. The method of claim 23, further comprising:

sampling the groundwater downstream of the contaminated site; and

selectively increasing or decreasing the amount of chemical oxidant in the injection well based on the results of the sampling.

28. The method of claim 23 further comprising directing the groundwater to flow into the injection well by installing baffles upstream of the injection well.

29. The method of claim 28 further comprising dispersing the groundwater with dissolved chemical oxidant by installing a second baffle between the injection well and the contaminated site.