WO1998036154A9

WO1998036154A9 - Contaminant remediation method and system

Info

Publication number: WO1998036154A9
Application number: PCT/US1998/002886
Authority: WO
Filing date: 1998-02-12
Publication date: 1999-01-14

Abstract

The present invention provides a method and a system (80) for removing contaminants from contaminated matter. The particulate matter (50) is leached with a lixivant solution (70) to produce a contaminated leachate (80), which includes contaminants from the particulate matter. The contaminants are then extracted from the contaminated leachate. In this manner, the extracted contaminants are removed from the particulate matter (50). In one embodiment, a remediation system is provided that includes a lixivant delivery system (100), a leaching system (200), and a leachate processing system (300). The leaching system leaches the particulate matter (50) with lixivant solution (70) from the lixivant delivery system. From this leaching, a contaminated leachate (80), which includes dissolved contaminants from the particulate matter, is formed. The leachate processing system (300) is connected to the leaching system to receive the contaminated leachate. The leachate processing system (300) extracts the contaminants from the contaminated leachate in order to remove them from the particulate matter.

Description

Contaminant Remediation Method and System

This application claims the benefit of and hereby incorporates by reference earlier filed provisional application App. No. 60/038,363, filed on February 13, 1997.

1. Technical Field

The present invention relates generally to the removal of contaminants from contaminated particulate matter. In particular, the present invention relates to a contaminant remediation system that removes contaminants by leaching the contaminated particulate matter and extracting contaminants from the resulting contaminant leachate.

2. Background of the Invention

During the past century, nuclear weapons development, civilian nuclear energy programs, and rapid industrialization have created several million tons of soils, debris, sludge, and similar material contaminated with radioactive and non- radioactive hazardous contaminants in the United States of America (US) and other countries throughout the world. During the past three decades, the US Government [Department of Energy (DOE) and Department of Defense (DOD)] and other governments around the world have initiated programs to decontaminate or otherwise control sites where residual radioactive materials and other hazardous materials remain. The US Congress has authorized DOE to remedy about 46 such sites in 14 states as part of the Formerly Utilized Sites Remedial Action Program (FUSRAP); over 50,000,000 cubic yards of contaminated soil are associated with this program alone. The major contaminated media at these sites are soils contaminated with low levels of radionuclides. Similar quantities of contaminated media exist at sites associated with other programs such as the civilian energy program. Conventionally, at a majority of these sites, one of the following techniques is employed for remediating contaminated media: excavation and disposal, soil washing, and fixation.

With excavation and disposal, the contaminated soil and other material are excavated, piled at a temporary storage area, loaded onto a transport vehicle (truck or rail car), and transported to a permanent repository (landfill) often several thousand miles away from the waste origination site. This method is extremely costly, labor intensive, and has very high levels of environmental and health hazard risks associated with it. For example, at one of the DOE sites at Fernald, Ohio the cost of off-site disposal of about 2.4 million cubic yards of contaminated soil is estimated to be from $1.27 billion (to transport to Utah by rail cars) to $4.46 billion (to transport to Nevada by trucks), or $530 to $1,440 per cubic yard. In addition to the high costs, it is estimated that up to 9 transport fatalities, 173 mechanical and

transportation injuries, and a maximum cancer risk of 4.2 x 10^" to site workers (4 in

1,000 will get cancer) may result from this operation. It was estimated that it would take approximately 20 years to remove and dispose of the 2.4 million cubic yards of soil. Safe disposal of this soil at an on-site repository will cost $2.4 billion, or $420 per cubic yard.

The second method is called soil washing or soil sorting. The soil is excavated and either transported to a processing plant or stockpiled on site to await processing. Next, the soil is either dry sorted (sieved) or wet sorted (washed); both of these processes generate clean and dirty streams. The clean stream is returned to the site and the dirty stream is dispatched for off-site disposal. In both cases, the soil is processed to mechanically separate large particles (such as greater than 5 mm), and if clean, returned to the site as recovered soil. In most cases this soil may have to be washed with water or solvent before returning it to the site. The remainder of the soil is subjected to a contaminant-mobilizing solution in a concurrent flow stream or in a mixing tank. This process will dislodge the contaminants and soil particles from the main stream and carry them in slurry form via a separate stream, leaving the intermediate-sized particles behind; these particles are abraded and then subjected to size separation. The process is continued until all contaminants and fines are concentrated in an aqueous solution that is subsequently dewatered and dispatched to off-site disposal. The liquid is processed to separate any dissolved or settled contaminants. This process is extremely laborious and costly. It also generates a substantial amount of secondary waste and contaminated equipment. The costs and time associated with this process are comparable to the off-site or on- site disposal described above.

With the fixation process, the contaminated particulate medium is mixed with a fixing agent such as grout or silica-based cation sieves such as zeolites to fix the contaminants within the matrix of the particulate medium. The soil is mixed with an immobilizing material in a slurry format and allowed to settle and solidify. Another method of fixing the contaminants within a particulate medium is to vitrify the medium, contaminants, and a glass-forming medium, either in situ or in a container, to form a solid mass that can then be disposed in an off-site or on-site repository. Solidification is achieved by using an extremely high rate of energy in the form of high voltage electricity, microwave energy, or oxidation energy such as fossil fuel or other form of combustible material to melt the constituents into a viscus material that is subsequently solidified into glass blocks. None of these three fixation processes actually removes the contaminants from the particulate medium; they only modify the contaminant location (off-site or on-site disposal), status (stabilization), or concentration level (soil washing). Since fixation processes require both processing and disposal costs, they often cost more than the off-site disposal and soil washing options.

Employing these technologies to clean up and remediate low level radioactive and non-radioactive hazardous waste tends to be ineffective and expensive. Technology gaps exist and large volumes of waste has been and will continue to be generated when there is only limited space in the planned waste repositories for storing such wastes. Even if adequate space is made available, disposal of the waste is expensive since disposal of a ton of this material can cost up to $1,400 using current technologies. The contaminant extraction process described in this document demonstrates treatment and remediation technologies that potentially could address the needs and requirements of some or all of the sites in the US and overseas.

Accordingly, the present invention provides a new method for actually extracting the contaminants from particulate matter without having to excavate or move the matter. 3. Summary

The present invention provides a method and system for remediating contaminants from contaminated particulate matter. The particulate matter is leached with a lixiviant solution to produce a contaminant leachate, which includes contaminants from the particulate matter. The contaminants are then extracted from the contaminant leachate. In this manner, the extracted contaminants are removed from the particulate matter.

In one embodiment, a remediation system is provided that includes, a lixiviant delivery system, a leaching system and a leachate processing system. The leaching system leaches the particulate matter with lixiviant solution from the lixiviant delivery system. From this leaching, a contaminant leachate, which includes dissolved contaminants from the particulate matter, is formed. The leachate processing system is connected to the leaching system to receive the contaminant leachate. The leachate processing system extracts the contaminants from the contaminant leachate in order to remove them from the particulate matter. 4. Brief Description of the Drawings

Figure 1 schematically depicts one embodiment of a remediation system. Figure 2A shows one embodiment of a leaching system with vertical point application.

Figure 2B shows a cross-sectional top view of the leaching system of Figure 2A.

Figure 3A shows one embodiment of a leaching system with horizontal point application.

Figure 3B shows a cross-sectional view of the leaching system of Figure 3A taken along line 3B-3B.

Figure 4A shows one embodiment of a leaching system with non-point application. Figure 4B shows a cross-sectional view of the leaching system of Figure 4A taken along line 4B-4B.

Figure 5 shows one embodiment of a leaching system in an ex-situ operation.

Figure 6 schematically depicts a remediation system for an ex-situ operation.

Figure 7 shows one embodiment of a horizontal point applicator. 5. Detailed Description The present invention provides a remediation system and method for removing contaminants, e.g., radioactive and non-radioactive hazardous elements, from contaminated particulate matter. The term particulate matter includes but is not limited to soil, debris, and sludge. The removal of contaminants may occur through an in-situ, as well as through an ex-situ process. Thus, contaminated particulate matter need not be displaced for contaminants to be removed.

A lixiviant solution is applied to the contaminated particulate matter to leach (i.e., dislodge and mobilize) the contaminants into a contaminant leachate, thereby making them available for extraction. An excursion containment system is provided to control off-site and subsurface migration of the lixiviant solution and resulting contaminant leachate. The dissolved contaminants are then extracted from the contaminant leachate solution using extracting agents such as precipitants, cation sieves, organic extractants (e.g., hexane), and evaporators. Once extracted, the contaminants may then be properly disposed, and the remaining leachate solution may be treated to transform it into recycled lixiviant solution, which is injected back into the lixiviant delivery system for further contaminant remediation. 5.1 Remediation System

Figure 1 shows a contaminant remediation system 10 for removing contaminants from contaminated particulate matter 50. The remediation system 10 includes a lixiviant delivery system 100, a leaching system 200, and a leachate processing system 300. The lixiviant delivery system applies a controlled amount of lixiviant solution 70 to the contaminated particulate matter 50, which is surrounded by the leaching system 200. The lixiviant solution is leached through the contaminated particulate matter 50 to yield contaminant leachate 80, which includes dissolved contaminants from the contaminated particulate matter 50. The leaching system 200 collects the contaminant leachate 80 and conveys it to the leachate processing system 300. The leachate processing system 300 demobilizes the contaminant leachate 80 to extract the contaminants from the leachate solution 80. Other particulate matter is also separated form the contaminant leachate 80. This particulate matter, along with the demobilized contaminants, is appropriately disposed. The remaining liquid is chemically augmented and into recycled as lixiviant solution, which is fed back into the lixiviant delivery system 100 where it is again used for leaching contaminated particulate matter 50. 5.1.1 Lixiviant Delivery System With reference to Figures 1 and 2, a lixiviant delivery system 100 is shown.

The lixiviant delivery system 100 includes a lixiviant metering system 110, a mixing tank 120, a delivery pump 130, a lixiviant transfer pump 134, and a dispensing system 140. Delivery pump 130 is in fluid connection with mixing tank 120 through supply line 132 to provide to mixing tank 120 water 62 and recycled lixiviant solution 64 from water line 105 and lixiviant recycling line 340, respectfully.

Lixiviant metering system 110 is also connected to mixing tank 120 for providing it with a controlled amount of lixiviant 68. Mixing tank 120 has an operably connected mechanical agitator 122 for mixing the lixiviant 68 with the water 62 and recycled lixiviant 64 to produce lixiviant solution 70. Transfer pump 134 is coupled between mixing tank 120 and delivery system 140 to provide lixiviant solution 70 to the delivery system 140, which in turn applies the lixiviant solution 70 to the contaminated particulate matter 50. In one embodiment, the lixiviant metering system 110 is implemented with a peristaltic pump of suitable make or model (e.g., a Spectra /Chrom Macroflow pump available from Baxter Scientific Products, McGaw Park, Illinois). The mixing tank 120 has appropriate capacity and is constructed of a suitable material, such as stainless steel, to withstand corrosion caused by the lixiviant.

5.1.1.1 Dispensing System With reference to Figures 1-6, various dispensing system configurations are depicted. The type of dispensing system 140 varies according to the type of contaminated particulate matter 50, along with its associated location and whether or not it is in an in-situ or ex-situ operation. In general, a dispensing system 140 includes a lixiviant delivery line 150 connected to an applicator (or applicators). The applicator conveys the lixiviant solution 70 to the contaminated particulate matter 50. An applicator could be but is not limited to a vertical point applicator 152, a horizontal point applicator 154, or a non-point applicator (e.g., a sprinkler) 156.

5.1.1.1.1 Vertical Point Application

Figures 1, 2A, and 2B illustrate dispensing systems 140 with vertical point applicators 152. A vertical point applicator could be a perforated pipe (e.g., 100 to 150 mm in diameter) or a combination of distributed perforated pipes that are designed for insertion into the ground at the center of the contaminated particulate matter 50. The length of the perforated section (e.g, between 500 and 1,000 mm) will define the active delivery length of the vertical point applicator 152.

5.1.1.1.2 Horizontal Point Application Figures 3A and 3B show a dispensing system 140 with a horizontal point applicator 154. The horizontal applicator 154 comprises at least one perforated pipe (e.g., 100 to 150 mm in diameter) that is designed to be positioned at or below (e.g., 200 to 300 mm) ground level and above the contaminated particulate matter 50. The perforations need only occur on one side of the applicators 154 in order to provide lixiviant solution 70 to the contaminated particulate matter 50. Figure 7 shows a horizontal point applicator 154 that includes concentric outer and inner pipes 157 and 158, respectively. This configuration enables lixiviant solution 70 delivery to be strategically concentrated at certain critical areas of the contaminant particulate matter 50. This horizontal point applicator 154 may be constructed by inserting a solid wall inner pipe 158 (e.g., 25 mm in diameter) into a fully perforated outer pipe 157, typically 100 mm in diameter. The horizontal point applicator 154 is extended to the points where maximum contamination levels are expected. At these points one or two perforations are made in the internal pipe 158 so that the majority of the liquid is delivered to the area of highest contamination within the contaminant particulate matter 50.

5.1.1.1.3 Non-Point Application Figures 4A, 4B, 5, and 6 show dispensing systems 140 with non-point applicators 156. The non-point applicators 156 may be implemented with conventional sprinklers that have large enough orifices for the lixiviant solution 70, as well as for the recycled lixiviant solution 64 (which may contain some impurities). For example, sprinklers 156 could be implemented with the Baghdad Wiggler or Senninger Wobbler. The Wiggler is made of a short piece of surgical tubing. As the lixiviant solution 70 flows through it, the tube flops around to produce fairly uniform coverage. The Wobbler is an off-center rotary action sprinkler that provides a coarse spray, which, in turn, significantly reduces evaporation. When using an organic lixiviant solution 70, minimizing evaporation is important to meet air quality requirements and to reduce the cost of lost lixiviant solution 70. The number of sprinklers 156 and their associated placement pattern should conform to the type of terrain and to climatic conditions. 5.1.1.1.4 Application Selection Spraying or dripping the solution on the surface is more suitable for in situ remediation of sites with small spatial variability of the contamination, and vertical point delivery systems (injection wells) are more suited to sites with localized contamination pockets (hot spots). Injecting the solution through horizontal pipes is most suitable for sites with excavated (stockpiled) medium. An additional advantage of using horizontal pipes for sites with excavated medium is that the pile can be covered during the remediation process, and dilution of the lixiviant by rain and runoff is significantly reduced. However, either of the applicators 152, 154, or 156 may be used in both in-situ and ex-situ remediation operations. 5.1.2 Leaching System

Figure 1 schematically depicts a leaching system 200 interconnected between lixiviant delivery system 100 and the leachate processing system 300. In general, leaching system 200 may comprise an excursion containment system 255 and a collection system 205. The excursion containment system 255 surrounds a contamination zone 280 for containing contaminated particulate matter 50, lixiviant solution 70, and contaminant leachate 80 in order to maintain environmental integrity and create a contaminant leachate basin for the collection system 205. The collection system 205 collects the contaminant leachate 80 and conveys it to the leachate processing system 300. 5.1.2.1 Excursion Containment System

An excursion containment system may be any system used to control off-site and subsurface migration of lixiviant solution 70 and contaminant leachate 80. Figures 2A and 2B show one embodiment of an excursion containment system 255. It includes a pressure pump 260, containment fluid 262, fluid supply lines 265, horizontal fluid barriers 270, and vertical fluid barriers 275. Pressure pump 260 is connected to horizontal fluid barriers 270 and vertical fluid barriers 275 through fluid supply lines 265 in order to supply them with pressurized containment fluid 262 (e.g., air, water, or nitrogen). The horizontal and vertical fluid barriers, 270 and 275, respectively, may be perforated pipes that are capable of transmitting a front of pressurized containment fluid 262 in a particular direction. In one embodiment, these pipes are 50 to 100 mm in diameter and constructed from steel or high strength PVC. The vertical fluid barriers 275 are inserted into the ground 40 to form a curtain of pressurized containment fluid 262 that is directed inward toward the contaminated particulate matter 50. Similarly, horizontal fluid barriers 270 are positioned beneath the contaminated particulate matter 50 to form a wall of pressurized containment fluid 262 that is directed upward toward the contaminated particulate matter 50. The horizontal fluid barriers 270 may be positioned with a conventional horizontal boring machine, which is capable of boring up to 500 feet in length and up to 40 feet in depth. The boundaries of contamination zone 280 are defined by the positions of the horizontal and vertical fluid barriers 270 and 275. The number and configuration of these horizontal and vertical fluid barriers 270 and 275 depend on the physical properties (e.g., permeability) of the contaminated particulate matter 50, the type of lixiviant delivery system 100, and on whether the remediation operation is in situ or ex situ. For example, with contaminated particulate matter 50 having a relatively high porosity, a greater number of horizontal fluid barriers 270, spaced closely together, may be required. Horizontal and vertical fluid barriers 270 and 275 may be positioned: as shown in Figures 2A and 2B for an in-situ operation with a vertical point applicator 152; as shown in Figures 3A and 3B for an in-situ operation with a horizontal point applicator 154; or as shown in Figures 4A and 4B for an in-situ operation with a non-point applicator 156.

However, both horizontal and vertical fluid barriers may not always be necessary. For example, as shown in Figures 5 and 6, a suitable excursion containment system 255 could be constructed with just horizontal fluid barriers 270, along with a number of earthen berms 45. With such a configuration, the horizontal fluid barriers 250 may be horizontally positioned along the interface between the contaminated particulate matter 50 and the uncontaminated ground 40 or at a depth just below ground surface (e.g., 200 to 300 mm). The berms 45 may be constructed around the contaminated particulate matter 50 at ground level to capture any surface runoff that may occur during the leaching process or by excessive rainfall. These berms 45 may be lined with low permeability liners (e.g., synthetic or clay) to prevent seepage to groundwater. Water collected in these berms 45 can then be directed to the leachate processing system 300 for decontamination and reuse.

Any suitable pressure fluid 262 (e.g., air, water, or nitrogen) may be used as a curtain depending on the type of particulate matter 50 and desired application technique. For example, a water injection curtain may be generated by the excursion containment system 255 to confine the lixiviant solution 70 and contaminant leachate 80 by surrounding the contamination zone 280 with a zone of high water hydraulic head. Since the hydraulic gradient is toward the contaminated particulate matter 50, the applied lixiviant solution 70 does not migrate outside the contamination zone 280; rather, it migrates to the collection system 205, which will be discussed in greater detail below. The use of air as pressure fluid 262 utilizes the principle of reduction of water saturation along the boundary surrounding the contaminated particulate matter 50.

High air pressures in the contamination zone 280 prevents water migration into the surrounding boundary area since the capillary pressures are high. The high capillary pressures maintain the water saturation at low values and, consequently, the water's hydraulic conductivity is kept very low.

The air curtain system is the most suitable and cost effective technology for most sites. In an in situ system, an air curtain is installed so that the entire contaminated particulate matter 50 is enclosed by a high pressure air curtain. In an ex-situ on-site system, an air curtain is installed at the contaminated particulate matter 50 pile-ground surface interface and a constant positive head is maintained during the leaching process.

The influence of initial moisture distribution in the flow domain should be examined in an analysis of the transient flow phases during system start-up. During this examination, uniformly low, intermediate, and high initial moisture conditions and nonuniform initial moisture distribution should be considered.

The flow region is assumed to be homogeneous and isotropic for all of the analyses.

To assess the potential for contaminant migration outside the contaminated area, a random walk particle tracking technique may also be used to trace fluid pathways and travel times. Depending on the results of these tests, all necessary safety precautions should be taken to protect the groundwater on a site. 5.1.2.2 Leachate Collection System Figures 1, 2A, and 2B show one embodiment of a leachate collection system

205, which is used in an in-situ operation with a lixiviant delivery system 100 that has a vertical point applicator 152. This leachate collection system 205 may comprise metering equipment 250, a collection pump 240, collection pipes 230, and vertical collection wells 210 that include submersible collection pumps 220. The metering equipment 250 and collection pump 240 are connected through collection pipes 230 to an end of each vertical collection well 210. A submersible collection pump 220 is connected to the other end of each vertical collection well 210. The leachate collection system 200 is connected to the leachate processing system 300 via collection pipes 230. Both the collection pump 240 and submersible collection pumps 220 provide the vertical collection wells 210 with sufficient vacuum suction for collecting the contaminant leachate 80 from within the contamination zone 280 and delivering it to the leachate processing system 300. The collected contaminant leachate 80 is metered by a flow meter 250 to control mass balance. In one embodiment, collection pump 240 is a liquid ring pump, which allows collection system 205 to be a tri-phasal material handling system. This enables the collection system 205 to handle gaseous, liquid, and solid phases, and convey a collected mixture that includes contaminate leachate 80, complexing agents, released contaminants, excess water, and some fines while exerting a negative pressure within the contamination zone 280.

The vertical collection wells 210 are inserted within and distributed throughout the contaminated particulate matter 50. When vertical point applicators 252 are being utilized, the vertical collection wells 210 may be positioned around each vertical point applicator 252, as shown in Figure 2B. In the depicted embodiment, the vertical collection wells 210 are installed at a radial distance of approximately 5 to 10 m from the vertical point applicators 252, with four collection wells 210 for each applicator 252. In addition, the depicted vertical collection wells 210 are 150 to 200 mm in diameter and are screened between the upper and lower perimeters of the contaminated particulate matter 50.

In another embodiment, collection system 205 could include horizontal collection wells 215 in place of or in addition to the vertical collection wells 210. Like vertical collection wells 210, the horizontal collection wells 215, through collection pipes 230, are connected to the collection pump 240, which creates a vacuum at the horizontal collections wells 215 for collection of the contaminant leachate 80.

The choice between vertical and horizontal collection wells is primarily dependent on the type of application (i.e., in situ or ex situ), the topography of the ground 40 and contaminated particulate matter 50, and the heterogeneity of the contaminated particulate matter 50.

Figures 3A, 3B, 4A, 4B, and 5 show collection system 205 with horizontal collection wells 215. These wells are installed horizontally at the deepest extent of

the contaminated particulate matter 50. For example, a DitchWitch^® pipe installer

may be used to place the horizontal collection wells 215 that are 500 feet in length to depths of up to 40 feet. This enhances the collection system's ability to prevent off- site migration of the contaminants and applied chemicals. Additional information regarding horizontal well technology is provided in: "The Green Book,

DitchWitch^®, Horizontal Directional Drilling Systems: A New Direction For

Remediation", Charles Machine Works Inc., Perry, Oklahoma, 73077-0066, and "In situ Stripping Using Horizontal Wells", Innovative Technology Summary Report, April 1995, US DOE Publication, DOE/EM-0269, which are hereby incorporated by reference into this specification. 5.1.3 Leachate Processing system The leachate processing system 300 (1) receives contaminant leachate (which may also include particulate matter) from leaching system 200, (2) demobilizes the dissolved contaminants with chemical processes, (3) extracts and disposes contaminant particles, and (4) transfers recycled lixiviant solution 64 back to the lixiviant delivery system 100.

With reference to Figure 1, the leachate processing system 300 includes a settling tank 310, a chemical treatment tank 320, a chemical delivery system 330, a lixiviant recycling line 340, an auger /conveyor system 350, and a temporary storage container 360. Chemical delivery system 330 could include a peristaltic pump for delivering liquids or a metering auger for delivering solids. Settling tank 310 is connected to the leaching system 200 through collection pipes 230 for receiving the contaminant leachate 80 from the leaching system 200. Settling tank 310 is also connected to chemical treatment tank 320 to provide it with supernatant 85 (i.e., the contaminant leachate solution over the settled particulate in settling tank 310) through gravitational force. The chemical delivery system 330 is connected to the chemical treatment tank 320 to provide it with various chemicals for demobilizing and extracting contaminants from the contaminant leachate 80. The lixiviant recycling line 340 is connected between the chemical treatment tank 320 and the delivery pump 130 for delivering recycled lixiviant solution 64 to the lixiviant delivery system 100. The auger /conveyor system 350 includes augers (not shown) and a conveyor. The augers are operably mounted within both the settling tank 310 and chemical treatment tank 320 to withdraw contaminant solids and sludge. In turn, a conveyor is aligned to convey the contaminant sludge away from the settling tank 310 a d chemical treatment tank 320 and into the temporary storage container 360. This sludge may be dewatered by adding, e.g., 3% clinoptilolite for stabilization and then removing water from the stabilized sludge by using a filter press (not shown) or solar or thermal evaporators (not shown) to evaporate the water. The resultant contaminant material 90 may then be collected, packed in appropriate containers, and shipped to a final disposal site. In the depicted embodiment, settling tank 310 is a corrosion resistant container with an inclined bottom, which enhances the auger/conveyor system's ability to withdraw settled sludge and solids. The capacity of settling tank 310 should conform to the size of the project and type of soil. Settling time and consequently extraction time are much longer when soils include significant amounts of fine-grained material, as opposed to silts and larger particles, which settle in a shorter period of time. Therefore, the longer the settling time requirement, the larger the settling tank 310 (or tanks). In one embodiment, the chemical treatment tank 320 is about two times larger than the settling tank 310 because a longer residence time is required for the chemical reactions, which occur in the chemical treatment tank 320.

5.2 Site Assessment and Characterization

A comprehensive site assessment and characterization may be performed to enhance the design and performance of the contamination remediation system 10. The relevant site characteristics can be assessed in order to effectively model the leaching and contaminant extraction process. The particulate matter 50 may be tested to derive a comparison of the permeability of soil at different locations within the contaminated particulate matter 50. A soil permeability measure can be used to determine lixiviant application rates, as well as pump and tank sizes. Other relevant site characteristics that affect flow and transport may also be analyzed to effectively model the leaching of radioactive and other contaminants. These characteristics include: soil bulk density, distribution coefficient, grain size distribution, hydraulic conductivity, moisture content, organic carbon content, porosity, radioactive content, saturated hydraulic conductivity, specific gravity, and void ratio. These site characteristics and the modeling efforts may be valuable in designing the lixiviant delivery system 100, application pattern, and collection system 205 configuration, as well as for estimating the leaching duration and expected leaching pattern. In order to assess these characteristics, a series of field and laboratory analyses can be conducted on samples gathered at the site. These samples include the contaminated particulate matter 50 and the surrounding ground 40. 5.2.1 Field Investigations and Sampling

The field investigation is directed to the spatial distribution of physical properties in the contaminated particulate matter 50. In an in situ application, surface samples may be collected at a depth of approximately 10 cm across several transacts. In addition, several samples may be collected from boreholes drilled into the radioactive and other wastes. In an ex-situ application, one soil sample may be collected from multiple positions within the contaminated particulate matter 50 —

about one position for every 100 m³'

A soil suction measurement may be taken immediately after coring using, e.g., a hand-held moisture probe. By plotting field suction and volumetric moisture content measurements with a retention function derived from average parametric values, heterogeneities may then be identified. It is more useful, however, to note the correlation of these two sets of measurements. If the bivariate field data scatter about the expected retention function, then the scaling of properties will normally not be an issue. Heterogeneity values derived from this effort may be used in determining whether a non-point, vertical, or horizontal application system should be implemented. These values may also be used to determine the locations and patterns of the components of the leaching system 200. 5.2.2 Laboratory Investigations In addition to field tests, various laboratory tests may also be performed on the contaminated particulate matter 50 with their results incorporated into a design for the contaminant remediation system 10. Some of these laboratory tests include soil bulk density, grain size distribution, hydraulic conductivity, organic carbon, moisture retention, and structural analysis. Soil samples may be collected using bulk density cores. Soil bulk densities may then be determined in laboratory settings using conventional methods such as those recommended by the American Society for Testing and Materials (ASTM) or American Society of Agricultural Engineers (ASAE). In addition, volumetric moisture content, porosity, and void ratio may also be determined using these samples.

Determining soil-moisture characteristic curves can be expensive and time consuming. Rather than direct determination of soil-moisture characteristic curves, one of several standard methodologies may be used to predict moisture retention for certain soil types from textural and structural properties associated with the grain size distribution. In one embodiment of this invention, a statistical relationship and a physicoempirical model are used instead of the conventional laboratory dessorption technique. In using the statistical approach, regression models are fitted to curves based on sand, silt, clay, organic matter, and bulk density of the contaminated particulate matter 50. In the physicoempirical approach, particle size distribution is used to derive pore size distributions. From this, cumulative pore volumes are divided by sample bulk volumes to give the volumetric water content. Pore radii are then converted directly to suction values assuming a capillary bundle model.

Flow and transport may be modeled in the contaminated particulate matter 50 by using a closed-form analytic expression to predict hydraulic conductivity from more easily measured soil-moisture data. Implementation of this approach still may require independently measured soil- moisture retention properties. Soil- moisture release curves can be determined by fitting dissorption data to a power function described by Van Genuchten. In turn, these empirical parameters can then be used in the analytic conductivity expressions derived by Van Genuchten. For example the relative conductivity, as a function of suction and effective saturation, is as follows:

(l - (αh )^mn [ l + (α )ⁿl K, (h) = -^ ' ^{l κ} mOi '

1 + (ah )"_.

which is an empirical equation used to predict soil moisture values from hydraulic conductivity and moisture retention properties; and

12

K_r (S_e , 0.5 1 1 /m

1 - 1

which is an empirical equation used to predict hydraulic conductivity in soil.

To arrive at the actual unsaturated conductivity function, the relative conductivity function is multiplied by the saturated conductivity value. Laboratory measurements of saturated and unconfined conductivity are carried out on undisturbed cores obtained from field sampling. Testing is conducted along the core axis using a constant head parameter. The core is soaked in tap water while under a vacuum for approximately two days prior to performing a test. The use of distilled water is discouraged as it may cause expansion of the adsorbed cations around clay particles and reduce the hydraulic conductivity. The effect of consolidation on hydraulic conductivity is not considered when the total depths of the contaminated particulate matter 50 are less than 5 m. The total organic carbon content of the contaminated particulate matter can be determined using standard laboratory procedures. This variable is used to determine absorption coefficients of the soil matrix with and without the presence of a lixiviant solution 70

Moisture release curves describe the retention properties associated with a particular particulate matter type. Moisture as a function of suction is also known as negative pressure head or matrix potential. Particulate matter moisture retention properties may be determined with laboratory dissorption experiments at 0, 10, 20, 30, 40, 60, 80, 100, 300, 500, and 1,000 centibars suctions. This becomes important when numerically simulating time dependent flow and transport behavior in the contaminated particulate matter 50. Previous studies demonstrate that the Brooks and Corey equation produced reasonable results for particulate matters characterized by a relatively narrow pore or grain size distribution. In contrast, the van Genuchten equation, characterized as a power function with five parameters

α, n, m, Θ_s, Θ_r ), is more robust for wide pore or grain size distributions and is as

follows:

θ= (Θ_s- Θ_r )[ (l - h )ⁿ + Θ

which is an empirical equation used to predict particulate matter moisture values from hydraulic conductivity and moisture retention properties. Although either of these procedures can be employed to achieve this objective, because the contaminated particulate matter 50 retention properties are likely to span a rather wide particle size distribution the latter function is used to fit parameters to each sample. A nonlinear curve fitting routine may be used to fit dissorption data to the

Van Genuchten expression. When performing the nonlinear fit, initial parameters are provided for all five constants. The best curve fits are obtained by not imposing any constraints. This is reasonable since the dissorption experiments tend to overestimate the porosity. Similarly, the approximate value for residual moisture content is obtained by plotting the laboratory moisture-suction data. Summary tables of fitted parameters are provided for each sample and for sample population statistics. The first and second moments are used in a Turning bands algorithm to generate spatial realizations of moisture and relative conductivity. Spacial realization of moisture and conductivity may be used to determine the solute and particulate transport patterns, which can be used for the estimation of leaching time and the design of the leaching system 200.

The flow and transport properties of a mine waste impoundment are heterogeneous, and it is therefore possible that these properties may also display similar characteristics at other sites. While summary statistics give temporal data, they do not provide a means to quantify the spatially dependent processes that may exist at a site. A variogram, which is a measure of dissimilarities as a function of separation distance, can be computed to determine the spatial structure associated with these properties and to use in modeling the impact of heterogeneities on an in situ operation. Using the classical variogram function, the spatial continuity is modeled as a random function. Any change in the variogram model as a function of direction indicates the presence of anisotropy. If anisotropy is present, care should be taken in the design of the application and collection systems to accommodate variations in the contaminant leachate 80 flow through the particulate matter 50 in order to avoid flooding or breakdown of steady state flow patterns.

5.3 Contaminant Removal Operation

Once the excursion containment system 255 is in place and pressurized, the remediation system 10 may be activated. In dispensing lixiviant solution 70, the transfer pump 134 is started and a determined amount of fresh water 62 is pumped into the mixing tank 120. Lixiviant 68 having an appropriate concentration (e.g., 0.1 to 1.0 moles per liter) is injected, when necessary, using the lixiviant metering system 110 to achieve a desired concentration (which depends upon the particular system 10 in connection with a particular site) for the lixiviant solution 70. The lixiviant solution 70 is agitated using the mechanical agitator 122 before it is pumped into the dispensing system 140 using the transfer pump 134. Suitable lixiviant 68 could be but is not limited to nitric, citric, sulfuric, or similar acid. Suitable lixiviants 68 could also include salts which are degradable by elements available in the environment such as biota (flora and fauna), bacteria, fungi, light, and redox potential. These salts are also benign to human health and are regularly used in the medical industry as agents to flush harmful metals from the human body.

In one embodiment, a 0.1 M/l solution of diethylenetriamine-N, N, N', N", N'-pentaacetic acid may be used as a lixiviant 68 to mobilize the contaminants in the contaminated particulate matter 50. (For additional information regarding demobilization, reference may be made to Pribil, R. and V. Vesely, 1967. Determination of rare earths in the presence of phosphate; Chemist-Analyst, 56, 23, and Norvell, W. A., 1984, Comparison of chelating agents as extractants for metals in diverse soil materials, Soil Sci. Soc, Am. J., 48, 1285, which are hereby incorporated by reference into this specification.) This chemical has the following specifications: Assay: > 99% (titration); Appearance: white crystals; Sulfated ash: < 0.2%; Heavy metal (as Pb): < 0.001%; Fe: < 0.001%. In another embodiment depending on the target contaminant, ethylenediamine-N,N,N',N'-tetraacetic acid may be used as a lixiviant 68 to mobilize the contaminants in the contaminated particulate matter 50. This acid has the following specifications: Solubility: 0.34

g/100 ml, at 25° C; Assay: > 99% (titration); Appearance: white powder; Sulfated ash:

< 0.2%; Heavy metal (as Pb): < 0.0005%; Fe: < 0.0005%. Persons of ordinary skill will recognize that other salts of this acid can be used such as: 2Na, ethylenediamine- N,N,N',N'-tetraacetic acid, disodium salt, dihydrate; 3Na, ethylenediamine- N,N,N',N'-tetraacetic acid, trisodium salt, trihydrate; 4Na, ethylenediamine- N,N,N',N'-tetraacetic acid, tetrasodium salt, tetrahydrate; 2K, ethylenediamine- N,N,N',N'-tetraacetic acid, dipotassium salt, dihydrate; 2Li, ethylenediamine- N,N,N',N'-tetraacetic acid, dilithium salt, monohydrate; and 2NH4, ethylenediamine-N,N,N',N'-tetraacetic acid, diammonium salt for this purpose. Each of these salts is suitable for extraction of a particular contaminant ion. The dispensing system 140 applies the lixiviant solution 70 onto the contaminated particulate matter 50. The required capacities of the pumps 130, 134 may be determined from the site characterization and modeling, which can also determine the rate at which the lixiviant solution 70 is to be dispensed to the contaminated particulate matter 50. Because the contaminated particulate matter 50 may contain inhomogeneous areas with widely varying permeabilities and contamination levels, the solution should be dispensed carefully so as to wet the entire contamination zone 280, but so as not to waste lixiviant solution 70 on uncontaminated pockets. Data from the spacial variability tests and variograms may be used to determine the heterogeneity of the contaminated medium and contaminants within the contaminated particulate matter 50. Lixiviant solution 70 is delivered to areas where a removable amount of contaminants exists.

The contaminant leachate 80 is collected and transferred to the leachate processing system 300. Contaminant leachate 80 is allowed to settle in settling tank 310. Supernatant 85 is transferred (e.g., decanted) from the settling tank 310 into the chemical treatment tank 320. After the supernatant is in tank 320, the solution's pH is adjusted to facilitate precipitation of the dissolved ions as insoluble salts. The supernatant 85 from the chemical treatment tank 320 is monitored for target compounds. If any target compounds remain in the supernatant 85 at this point, it may be passed through a bed of zeolites, or any other cation exchange medium, e.g., clinoptilolite, to extract the remaining contaminants from the supernatant 85. If any target contaminants remain in the supernatant 85 following this act, a predetermined amount of hexane or another organic complexing agent may be added to the supernatant 85 to extract the contaminants and to form a floating phase that will separate from the supernatant 85. The floating material can then be skimmed from the supernatant 85 and evaporated; the vapors may then be captured and condensed for reuse in the lixiviant delivery system 100 and concentrated contaminants are left for disposal. Settled sludge 90 from the settling tank 310 and settled salts /solids 90 from the chemical treatment tank 320 are withdrawn from the tanks by the auger /conveyor system 350 and are deposited as sludge into the temporary storage container 360. This sludge 90 may be tested for target compounds. The sludge, which may contain 40 to 60% water, can be stabilized, e.g., by adding a cation exchange medium such as 03% clinoptilolite. The sludge 90 may then be dewatered by using, e.g., a filter press (not shown) to extract the water or solar/ thermal evaporators (not shown) to evaporate the water. The resultant material may then be packed in appropriate containers and shipped to the final disposal site. In this manner, contaminants are extracted from the contaminant leachate 80.

Once contaminants have been extracted from the demobilized supernatant 85 in chemical processing tank 320 and disposed via auger /conveyor system 350, the remaining supernatant 85 may be chemically treated for reuse as recycled lixiviant solution 64. For example, a base may be added to return its pH value back to its original value prior to demobilization.

In one embodiment, the remediation system 10 is initially operated without the addition of lixiviant 68 into mixing tank 120 (i.e., the contaminated particulate matter 50 is leached with water only) for an appropriate amount of time, e.g., 60 days. This is done to leach out all free and water soluble contaminants, as well as competing ions from the contaminated particulate matter 50. The contaminant leachate 80 is monitored, sampled, and assayed for various ions (target or non-target elements). When an asymptotic level for these elements is reached, suitable lixiviant 68 is mixed with water 62 to form lixiviant solution 70. This lixiviant solution 70 is dispensed into the contaminated particulate matter 50 in a steady state manner for a minimum period, e.g., of 90 days. During the beginning phase (e.g., within the first week or so) of this lixiviant solution 70 application period, supernatant 85 from either the settling tank 310 or chemical processing tank 320 may be tested for a target contaminant. A sufficiently high level of the target contaminant indicates that the process is properly functioning to remove the target contaminant from the particulate matter 50. Conversely, if this level is sufficiently low, the system 10 may not be properly removing the target contaminant from the particulate matter 50, or it may have already exhausted the contaminants from the particulate matter 50. One solution to this inadequately low level would be to try a different lixiviant 68 that may be better suited for leaching the target contaminant. Once it is determined that the lixiviant solution 70 is adequately leaching contaminants, the process may be operated in the steady state manner for a period of time (e.g., 90 days). At the end of this period, the contaminated particulate matter 50 can be assayed for the target contaminant(s) to ensure that they have been sufficiently removed. If the expected level for a target contaminant is not achieved, the process may be adjusted (e.g., modify lixiviant solution 70, adjust dispensing system 140), and the system 10 may again be operated until the contaminant has been sufficiently removed.

It will be seen by those skilled in the art that various changes may be made without departing from the spirit and scope of the invention. Accordingly, the invention is not limited to what is shown in the drawings and described in the specification but only as indicated in the appended claims.

Claims

6. ClaimsWhat is claimed is:

1. A method for removing contaminants from particulate matter, the method comprising: (a) leaching the particulate matter with a first lixiviant solution to produce contaminant leachate, the contaminant leachate including contaminants from the particulate matter; and

(b) extracting the contaminants from the contaminant leachate, whereby the extracted contaminants are removed from the particulate matter.

2. The method of claim 1 further comprising:

(i) testing the contaminant leachate for a target contaminant;

(ii) responsive to said testing, leaching the particulate matter with a second lixiviant solution for leaching the target contaminant into a second contaminant leachate that includes the target contaminant; and (iii) extracting the target contaminant from the second contaminant leachate.

3. The method of claim 2, wherein responsive to said testing, the particulate matter is leached with the second lixiviant solution if the tested contaminant leachate includes a sufficiently low amount of the target contaminant.

4. The method of claim 2 further comprising leaching the particulate matter with water before leaching the contaminated material with the first lixiviant solution.

5. The method of claim 1, wherein the act of extracting the contaminants from the contaminant leachate includes demobilizing the contaminants in the contaminant leachate, whereby at least a portion of the contaminants precipitate into solid contaminant matter.

6. The method of claim 5 further comprising removing the solid contaminant matter from the contaminant leachate.

7. The method of claim 1, wherein the act of leaching the particulate matter with a first lixiviant solution includes containing the particulate matter with an excursion containment system.

8. The method of claim 7, wherein the act of containing the particulate matter with an excursion containment system includes:

(i) defining a contamination zone that includes the particulate matter, and (ii) applying a pressurized fluid inward upon the contamination zone toward the particulate matter.

9. The method of claim 8 further comprising collecting the contaminant leachate with at least one collection well that is within the contamination zone, wherein said collecting includes applying a negative pressure from said collection well.

10. The method of claim 1 further comprising recycling the contaminant leachate into a recycled lixiviant solution after contaminants have been removed from the contaminant leachate.

11. The method of claim 10 further comprising leaching the particulate matter with the recycled lixiviant solution.

12. The method of claim 1 further comprising:

(i) testing the particulate matter for a target contaminant;

13. The method of claim 12, wherein responsive to said testing, the particulate matter is leached with the second lixiviant solution if the tested particulate matter includes a sufficiently high amount of the target contaminant.

14. The method of claim 1, wherein the acts of leaching the particulate matter and extracting the contaminants from the contaminant leachate are repeated until the particulate matter is sufficiently void of contaminants.

15. A contaminant remediation system for removing contaminants from particulate matter, the system comprising:

(a) a leaching system for leaching the particulate matter with a lixiviant solution to produce a contaminant leachate that includes contaminants from the particulate matter;

(b) a lixiviant delivery system in connection with the leaching system to apply the lixiviant solution for leaching the particulate matter; and

(c) a leachate processing system in connection with the leaching system to receive the contaminant leachate, wherein the leachate processing system extracts the contaminants from the contaminant leachate.

16. The system of claim 15, wherein the leaching system includes:

(i) an excursion containment system for containing the particulate matter, lixiviant solution and contaminant leachate, whereby the excursion containment system defines a contamination zone that includes the particulate matter, and (ii) a collection system in connection with the leachate processing system, wherein the collection system collects contaminant leachate within the contamination zone and delivers it to the leachate processing system.

17. The system of claim 16, wherein the excursion containment system comprises a plurality of fluid barriers in connection with a pressure pump for pressurizing the fluid barriers with a pressurized fluid, wherein the plurality of fluid barriers are positioned about the contamination zone to apply the pressurized fluid toward the particulate matter.

18. The system of claim 16, wherein the collection system includes a collection well and a collection pump, wherein the collection well is inserted into the particulate matter and in connection with the collection pump and the leachate processing system, wherein the collection pump applies a negative pressure to the collection well to remove contaminant leachate from the contamination zone and deliver the contaminant leachate to the leachate processing system.

19. The system of claim 18 further comprising a submersible collection pump, wherein the collection well includes a pipe with a first end and a second end, the first end being connected to the collection pump and the second end being connected to the submersible collection pump.

20. The system of claim 15, wherein the leachate processing system includes a settling tank for separating solid particles from the contaminant leachate, whereby the settling tank yields sludge and supernatant.

21. The system of claim 20, wherein the leachate processing system further comprises a chemical treatment tank in connection with the settling tank and a chemical delivery system in connection with the chemical treatment tank, wherein the chemical treatment tank receives the supernatant from the settling tank and the chemical delivery system provides the chemical treatment tank with a chemical for demobilizing the contaminants within the supernatant.

22. The system of claim 21, wherein the chemical treatment tank is in connection with the lixiviant delivery system, wherein the supernatant is treated to yield recycled lixiviant solution, which is delivered to the lixiviant delivery system.