MXPA99001133A - Method for directing groundwater flow and treating groundwater in situ - Google Patents

Abstract

A method for treating groundwater in situ in rock or soil. An elongate permeable upgradient zone (2) and an elongate permeable downgradient zone, each in hydraulic communication with a permeable subsurface treatment zone (14) and having a major axis parallel to a non-zero component of the general flow direction (8), are provided in the subsurface by any of a number of construction methods. The upgradient zone, downgradient zone, and treatment zone are situated within the subsurface medium (4) and have permeabilities substantially greater than the adjacent subsurface medium's permeability.

Description

METHOD FOR DIRECTING THE FLOW OF UNDERGROUND WATER AND TREATING UNDERGROUND WATER ON THE SITE FIELD OF THE INVENTION This invention relates to a method for directing the flow of groundwater and with a method for treating groundwater.

BACKGROUND OF THE INVENTION Most efforts to attack groundwater contamination in subsurface media have historically involved pumping to extract contaminated groundwater from the subsurface for treatment above the ground. This process is commonly known as "pump and treat." However, pumping and treating systems are limited in their ability to remediate groundwater, dirt, and contaminated rocks (Mackay et al., Environmental Science and Technology 23 (6): 630-636 (1989) and Travis and collaborators, Environmental Science and Technology, 24: 1464-1466 (1990)). Remedial lifetimes are commonly in the order of decades to centuries. During pumping, there are continual energy and cost requirements, and the need to adequately treat groundwater for disposal at the surface poses an additional problem.

Conventional pump and treat systems are particularly ineffective in collecting and treating groundwater from low permeability fractured rock. Groundwater contaminated in low permeability fractured rock is commonly extracted for surface treatment by actively pumping from one or more conventional vertical recovery wells, typically installed at or near the source source for the source remedy and at the source. descending gradient end of a pollutant plume to control the migration of pollutant. Control of conventional migration in low permeability fractured rock typically requires the installation of a sufficient number of recovery wells to capture all the groundwater that would otherwise pass through. However, when fractures in low permeability rock are irregularly separated and poorly interconnected, as is commonly the case, a large number of conventional vertical recovery wells should be placed fairly close together to ensure that the majority of groundwater contaminated be captured. Sometimes, the potential capture range of groundwater in low permeability fractured rock for a single well can be only 3 meters to 9 meters, especially under unconfined conditions, and attempting to achieve effective capture over a wide region may require several dozens of wells with pumps and pipes, all of which must be installed and maintained at considerable expense. Moreover, in cold climates, associated surface lines and other equipment must be protected from freezing with other additions to the expense. Even with an installation of nearby wells, some fractures or large faults can go unnoticed between the wells and allow significant migration of contaminants past the pumping area. In recent years, unconventional horizontal wells, rather than conventional vertical wells, have sometimes been used for the recovery of groundwater, but in general, this also requires active pumping to extract contaminated groundwater and is very face its construction. Moreover, horizontal wells often fail to capture contaminated groundwater in low permeability fractured rock, because the presence of certain extremely low permeability horizontal rock layers prevents groundwater from flowing at an appreciable speed in the vertical direction, except through widely spaced isolated fractures. Under the hydraulic tension of the pumping, there could be negligible or very small vertical components of flow through these layers of low permeability up to the screens of the horizontal wells, preventing the effective recovery of groundwater from the horizontal rock layers that are separated from the ground. the screen of the well by the layers of low permeabilida. A comparatively new method for recovering ground water from low permeability fractured rock involves pumping groundwater from a linear bedrock-flow area or from a radial set of bedrock-flown zones (Begor et al., Ground Water, 27: 57-65 (1990); Smith et al., Proceedings of the 5th Annual Hazardous Materials and Environmental Management Conference / Central, Chicago, pp. 103-117 (1992); Gehl, Proceedings of the Focus Conference of Eastern Regional Groundwater Issues, National Water Well Association, pp. 265-273 (1994); and McKown and collaborators, Proceedings of the 21st Annual Conference on Explosives and Blastina Techniques, International Society of Explosives Engineers, pp. 305-322 (1995) ("McKown")). Linear zones of shattered rock, commonly known as "trenches," along with one or more pumping wells, can form an extraction system that effectively connects otherwise unconnected fractures and greatly increases the effective region of influence of pumping. Since a flowbed bedrock trench has a much greater hydraulic conductivity than the surrounding natural rock, groundwater flows in from many directions when the pump in a trench recovery well is operating. The average expenditure of one or more recovery wells installed in a flown bed trench exceeds the hypothetical cost of more than 60 and 70 traditional recovery wells installed in the same type of rock (McKown). However, as indicated above, the flow in the trench is effected only when the trench is actively pumped. A common feature of the methods of "pumping-and-treating" groundwater, regardless of whether the well used is a horizontal well, a vertical well, or a rocky bed hole, is the need to carry the water collected by the Well to the surface for your treatment. Generally, this requires more or less continuous pumping operation, and this pumping process, as well as the surface treatment processes, is expensive in terms of operating and maintenance costs. In addition, the groundwater treatment effluent from groundwater should typically be discharged to an allowable discharge point or to a publicly owned wastewater treatment facility. Since groundwater is discharged above the ground, chemicals other than those contaminants that needed groundwater treatment in the treatment process must also be managed and remediated to acceptable levels for discharge above the ground. For example, when Fe (II) in the anaerobic groundwater is brought to the surface and exposed to air, it is commonly oxidized to Fe (III) which then forms a precipitate, which can cause water quality problems and the incrustation of the equipment and the lines of treatment. Another example of this problem is the need to allow colloidal materials and fine dust to settle in the groundwater before treatment and / or discharge. In this way, the acriba treatment of the earth frequently needs the installation of systems to treat substances that would never have needed remedy if the water remained in the subsurface. The long-term costs of treating and disposing effluent above ground, coupled with the long-term costs associated with the maintenance and operation of pumps and related equipment, make expensive top-down treatment of the land. Therefore, there is a continuing need for methods to direct the flow of groundwater and treat groundwater. The present invention is directed to satisfy this need.

SUMMARY OF THE INVENTION The present invention relates to a method for treating groundwater flowing in a general flow direction through a subsurface environment. The method includes providing an elongate permeable upward gradient zone and an elongate permeable downward gradient zone. The ascending gradient zone is hydraulically located uphill from and in hydraulic communication with a treatment zone and has a major axis parallel to a non-zero component of the general flow direction. The descending gradient zone is hydraulically located downhill from and in hydraulic communication with the treatment zone and has a major axis parallel to a non-zero component of the general flow direction. Each one of the ascending gradient zone, the descending gradient zone, and the treatment zone is located within the subsurface environment and has a substantially greater permeability than the permeability of the surrounding subsurface environment. Groundwater is allowed to move from the surrounding subsurface medium to the ascending gradient zone towards and through the ascending gradient zone, to, through, and out of the treatment zone. It is then allowed "for the groundwater to move inward, through, and out of the gradient downward toward the middle of the subsurface surrounding the downward gradient zone. The method also includes treating the groundwater in the treatment zone. The present invention also relates to a method for directing groundwater flowing in a general flow direction through a subsurface environment around a particular subsurface location. The method includes providing an elongate permeable upward gradient zone and an elongate permeable downward gradient zone. The ascending gradient zone is hydraulically located uphill from the particular location and has a major axis parallel to a non-zero component of the general flow direction. The descending gradient zone is hydraulically located downhill from and in hydraulic communication with the ascending gradient zone, is located downstream of the particular location, and has a major axis parallel to a non-zero component of the general flow direction. Each of the ascending gradient zone and the descending gradient zone is situated within the subsurface environment and has a substantially greater permeability than the permeability of the surrounding subsurface environment. The method further includes allowing the groundwater to move from the subsurface environment surrounding the upward gradient zone towards and through the upward gradient zone towards, through, and away from the gradient zone downwardly towards the middle of the gradient zone. the subsurface surrounding the descending gradient zone. The method of the present invention is particularly convenient for directing contaminated groundwater without pumping it to one or more subsurface treatment zones in rock or soil where the groundwater can be treated at the site. Because the method allows groundwater treatment at the site, pumping is not required, and costs associated with pumping are avoided. Moreover, the problems associated with discharging effluent from groundwater treatment above ground are avoided. The method of the present invention can also be used to direct relatively uncontaminated groundwater around a relatively contaminated subsurface site to avoid contamination of relatively uncontaminated groundwater. Alternatively, the method of the present invention can be used to protect a relatively uncontaminated sub-surface site from being contaminated by a contaminated groundwater flow by directing relatively contaminated groundwater around the relatively uncontaminated sub-surface location.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a plan view of a subsurface medium containing an ascending gradient zone. Figures 2A-2F are plan views of various configurations of ascending gradient and descending gradient according to the present invention. Figures 3A-3C are plan views of various configurations of gradient up and gradient zones according to the present invention. Figure 4 is a diagram illustrating a groundwater stream line in an ascending gradient zone. Figure 5 is a computer-generated contour plot showing lines of the same hydraulic head in an ascending gradient and descending gradient zone configuration according to the present invention. Figure 6 is a diagram illustrating a groundwater stream line in an ascending gradient zone and the transverse separation of optional additional treatment zones in accordance with the present invention. Figure 7 is a graph showing the ratio of the transverse spacing of the treatment zone (S), the hydraulic conductivity ratio (k ^ / K ^, and the thickness of the ascending gradient zone (T).

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for treating groundwater. Groundwater includes water located below the surface of the earth at pressures of caliber greater than zero atmospheres. Groundwater is located in a subsurface environment. The subsurface medium may be any that occurs naturally or artificially, including, for example, earth, rock, and filler. The subsurface medium may include only one type of material, or may include two or more types of materials. Furthermore, the subsurface medium may have a substantially uniform permeability or may vary in permeability. Groundwater flows through the subsurface environment along the current lines affected by permeability v. local in the middle of the subsurface. Macroscopically, the groundwater has a general flow direction, which is the weighted average of microscopic flows along the current lines in a particular spatial region of the subsurface environment. It is not critical to the practice of the method of the present invention that the precise direction of flow for the practice of the method of the present invention is known, although this knowledge would facilitate the optimization of the method for a particular spatial region. The directions of the general flow can be determined by well-known techniques, such as those described in Freeze et al., Groundwater, Englewood Cliffs, New Jersey: Prentice-Hall, Inc. (1979) and Domenico et al., Physical and Chemical Hydrogeology, New York: John Wiley and Sons (1990) ("Domenico"), which are incorporated herein by reference. The method includes providing an ascending gradient zone and a descending gradient zone located in the middle of the subsurface in which the groundwater to be treated is located. The ascending gradient zone is hydraulically uphill from and in hydraulic communication with a permeable treatment zone which is also located within the subsurface environment. The descending gradient zone is hydraulically downhill from and in hydraulic communication with the treatment zone. That is, the water in the ascending gradient zone, as time passes, will flow from the ascending gradient zone to and through the treatment zone and the treatment zone to the descending gradient zone. Each one of the ascending gradient zone, the descending gradient zone, and the treatment zone has a permeability (i.e., an inherent capacity to transmit fluid) substantially greater than the permeability of the medium. subsurface. In particular, it is preferred that each of these regions have a substantially greater permeability than the permeability of the subsurface environment surrounding the zone. To provide a margin of safety to take into account unknown permeability variations in the subsurface environment, it is more preferred that the permeabilities of the rising gradient, the falling gradient, and the treatment zones are all substantially greater than the permeability of the most permeable portion of the subsurface environment. Absolute values of the permeabilities of the ascending gradient, descending gradient, and treatment zones are not critical to the practice of the present invention. The important factor is that the permeabilities of the ascending gradient, descending gradient, and treatment zones are substantially greater than that of the subsurface environment. For a substrate medium with relatively low permeability, such as some types of rock or soil, very large permeability contrasts can be easily reached between the ascending gradient, descending gradient and treatment zones, collectively and the subsurface environment. Areas of ascending gradient, gradient descent and treatment can be constructed of permeable materials, such as porous or fractured media, whose permeability is well increased on the permeability of the rock, surrounding earth or other subsurface media, through a process designed technically. Convenient porous medium includes materials that contain open spaces between grains, pebbles, or blocks of the solid portion of the medium. More particularly, the porous medium suitable for use as permeable materials in the practice of the present invention include, but are not limited to, consolidated materials, such as broken or fractured rock, and unconsolidated materials, such as sand or gravel. The compositions and permeabilities of the materials in the areas of ascending gradient, descending gradient, and treatment may be the same or different. Generally, for ease of construction, these materials are the same, and, consequently, their permeabilities are also similar. However, in some cases, such where the geometry of the ascending gradient and descending gradient zones are different or where the permeabilities of the subsurface environment surrounding the rising gradient and the falling gradient zones differ, areas of ascending gradient and descending gradient made of materials that have different permeabilities. The permeability of the permeable materials in the areas of ascending gradient, descending gradient, and treatment are preferably at least two or three orders of magnitude greater than the permeability of the subsurface environment surrounding the ascending gradient zones, desce gradientndent, and treatment. For example, in the case where the subsurface medium has a hydraulic conductivity of the order of 10 centimeters / second, suitable permeable materials for use in the construction of the ascending gradient, descending gradient, and treatment zones are those that they have hydraulic conductivities of from about 10"3 centimeters / second to about 10 centimeters / second, preferably from about 10" 2 centimeters / second to about 10"1 centimeters / second, where the subsurface medium has a hydraulic conductivity of the order of 10"centimeters / second, suitable permeable materials are those that have hydraulic conductivities of from about 10 centimeters / second to about 10" 1 centimeters / second, preferably from about 1 "centimeters / second to approximately 10 centimeters / second, where the subsurface medium has a hydraulic conductivity of the order of 10 centimeters / second, the suitable permeable materials are those that have hydraulic conductivities of from approximately 10" ^ centimeters / second to about 10 centimeters / second, preferably from about 10 centimeters / second to about 10 centimeters / second. Furthermore, it should be noted that the ascending gradient zone does not necessarily have to have uniform permeability or composition, although substantial uniformity is generally preferred. Likewise, the zones of descending gradient and of treatment may each have permeability and uniform or non-uniform composition. The ascending gradient zone is elongated along a major axis parallel to a non-zero component of the general groundwater flow direction, that is, in a direction which is not perpendicular to the general flow of groundwater. A convenient orientation of the ascending gradient zone with respect to the general direction of groundwater flow is shown in Figure 1. The ascending gradient zone 2, located in the middle of the substrate 4, is elongated along the major axis 6. The major axis 6 and the general direction of groundwater flow 8 form an angle, designated OI. The angle a can take any value from 0o to slightly less than 90 °. The preferred orientations of the elongated gradient zone with respect to subsurface groundwater flow are those where the angle a is from about 30 ° to about 60 °. The optimal orientations depend on a variety of factors, such as the permeability of the ascending gradient zone, the permeability of the subsurface environment, particularly the permeability of the subsurface environment surrounding the ascending gradient zone, and the form of the ascending gradient zone. The optimization of these variables is discussed later in greater detail. The descending gradient zone is also elongated along a major axis parallel to a non-zero component of the general direction of groundwater flow, that is, in a direction that is not perpendicular to the general flow of groundwater.

The elongated ascending gradient zone and the falling gradient zone may have any aspect ratio greater than 1. Convenient aspect ratios are generally much greater than one, usually from about 10 to about 100. The optimum aspect ratios are determined by several factors, including the orientation of the zones with respect to each other, and the direction of the general flow of groundwater, the permeability of the zones of ascending gradient and descending gradient, and the permeability of the subsurface environment. The areas of ascending gradient and descending gradient may be any elongated shape when viewed in a plane parallel to the surface of the earth, including, for example, elliptical, rectangular, or triangular. Preferred shapes are those which are substantially rectangular, although non-uniform permeabilities along the length of the ascending gradient zone or the falling gradient zone may cause other shapes to be favored. Preferably, the areas of ascending gradient and descending gradient are of substantially uniform width over a substantial portion of their lengths. Typically and especially in cases where the permeabilities of the subsurface media surrounding the zones of ascending gradient and descending gradient are substantially the same and where the permeabilities of the ascending gradient and descending gradient zones are substantially equal, it is preferred that zones of ascending gradient and descending gradient have the same shape, more preferably rectangular, each having the same width, substantially uniform and substantially the same length. The areas of ascending gradient and descending gradient can be oriented in various spatial configurations in the practice of the present invention. Several convenient orientations are shown in Figures 2A, 2B, and 2C. The flow lines 10 show the trajectory that the groundwater, which has the general direction of the flow 8, takes through the middle of the subsurface 4 under the influence of the ascending gradient zone 2, descending gradient zone 12, and zone of treatment 14 when the ascending gradient zone 2 is elongated along the major axis 16 and the descending gradient zone 12 is elongated along the major axis 18. In a convenient orientation, shown in Figure 2A, the major axes of the zones of ascending gradient and falling gradient coincide, and the zones of ascending gradient and descending gradient form a line oriented in any direction other than perpendicular to the general direction of groundwater flow. In a particular illustration of this orientation, shown in Figure 2B and designated the "I-shape", the major axes of the ascending gradient and descending gradient zones coincide with each other and are parallel to the general direction of groundwater flow. Another advantageous way is that of "V corridors", as shown in Figure 2C. The V-shaped corridor shape has an apex in the treatment zone and legs, which represent the areas of ascending gradient and descending gradient, pointing away from a line parallel to the general direction of flow. As indicated above, the major axis of the ascending gradient zone forms an angle, a, with the direction of flow. In the V-aisle orientation, the descending gradient zone is preferably elongated along an axis that forms an angle equal to 180-Q !, as indicated in Figure 2C. When configured in this way, the angle between the major axes and the gradient and rising gradient zones is 180-2a. As previously indicated, the zones of ascending gradient and descending gradient are in hydraulic communication with the treatment zone. For the purposes of this application, two zones have the quality of being "in hydraulic communication" when the zones meet one another or are separated by some intervention material that does not significantly reduce the movement of fluid from one area to the other. Preferably, the intervention material has a permeability at least equal to the permeability of one of the two zones in hydraulic communication. However, intervention materials of somewhat lower permeability may be acceptable. Having provided the areas of ascending gradient and descending gradient, the groundwater is allowed to enter the ascending gradient zone and move through the ascending gradient zone to the treatment zone. Groundwater is then allowed to move from the treatment zone to the descending gradient zone, through the descending gradient zone, and out of the gradient descending zone towards the middle of the subsurface surrounding the descending gradient zone . The movement of groundwater to, through, and outside the zones of ascending gradient, descending gradient and treatment occurs without pumping, governed by the forces created by the existence of zones of ascending gradient, descending gradient and treatment of greater permeability than the permeability of the subsurface environment. Subsurface groundwater flowing in a general direction of flow contacts the interface of the rising gradient zone and the subsurface environment and moves into the zone. Subsurface groundwater within the ascending gradient zone is then moved under hydraulic forces within and through the ascending gradient zone for some distance in the direction semi-parallel to the major axis of the ascending gradient zone towards and within the treatment area. The water is then directed by hydraulic forces outside the treatment zone, towards the descending gradient zone, through at least a portion of the descending gradient zone, and outside the descending gradient zone toward the middle of the subsurface? e surrounds the descending gradient zone. Optimally, the shape and orientation of the areas of ascending gradient and descending gradient is such that the regime of movement of groundwater outside the gradient descending zone is the same as the regime of movement of groundwater from the subsurface to the zone of ascending gradient, avoiding by this the accumulation of hydraulic head of the zones of ascending gradient and descending gradient. The method of the present invention can also be practiced using a plurality of zones of ascending gradient and descending gradient. In this embodiment the method further includes providing one or more additional elongated gradient zones and one or more additional elongated gradient zones. Each zone of rising gradient and further down gradient has a permeability that is substantially greater than the permeability of the subsurface environment, and each has a major axis parallel to a non-zero component of the direction of flow. Preferably, the number of additional upward gradient zones is equal to the number of additional downward gradient zones so that the total number of upward gradient zones is equal to the total number of downward gradient zones. In a particularly preferred embodiment, each descending gradient zone is elongated along a major axis which coincides with the major axis of one of the ascending gradient zones, so that each descending gradient zone has exactly one gradient zone corresponding ascending along whose major axis is elongated. The orientation of the additional gradient and rising gradient zones is not critical to the practice of the present invention. However, it is preferred that the downward gradient zone and the further down gradient zones be the mirror images of the upward gradient zone and the additional upward gradient zones reflected in a plane perpendicular to the general direction of flow and that They pass through the treatment area. Optimally, the total number of zones of ascending gradient is 2, and the total number of zones of descending gradient is 2. In this configuration the zones of gradi € inte ascending and descending gradient form two corridors in V that have a common apex, representing the apex is the treatment area to which the groundwater is directed. This configuration, designated the X configuration due to the shape defined by the two ascending gradient zones and the two descending gradient zones when viewed in a plane parallel to the surface of the earth, is represented in Figure 2D. As indicated above, the preferred configuration of each V-corridor forming the X is such that the angle between the general direction of flow and the major axis of the descending gradient zone is 180-a !, where a is the angle between the major axis of the ascending gradient zone and the general direction of flow. In a more preferred configuration, the descending gradient zone and the additional descending gradient zone are mirror images of the ascending gradient zone and the additional ascending gradient zone reflected in a plane perpendicular to the surface of the earth, parallel to the general direction of flow, and that passes through the treatment area. As will be appreciated by one skilled in the art, additional configurations are possible including, for example, multiple, laterally adjacent configurations. The method of the present invention can be used to direct the groundwater to a series of treatment zones employing a series of zones of ascending gradient and descending gradient paired with each pair of zones hydraulically connected to a single treatment zone. An example of such a configuration is a series of laterally adjacent V corridors where each V in the series points in the same direction. Another example of such a configuration is a series of laterally adjacent X's, as illustrated in Figure 2E. Using multiple treatment zones, a wider area of groundwater flow can be directed to a series of treatment treatment zones. Other combinations of V and X corridors can be employed, including those where the descending gradient zone of a treatment center is used as the ascending gradient zone of a second treatment center, as depicted, for example, in Figure 2F. Optionally, additional treatment zones can be located at various locations along the gradient and up gradient zones. The areas of ascending gradient and descending gradient can be formed by any convenient method, many of which are known to those skilled in the art. The preferred method for installation in the earth (ie, when the subsurface environment is earth), in most cases, is to remove the earth from the gradient or up gradient zone, such as excavation, and fill the trenches with permeable materials, such as sand, gravel, broken rock, or other porous media with high permeability. When gravel is used, it is preferably used in conjunction with a protective geotextile fabric or sand barrier to prevent the movement of fines from the soil into the porous spaces of the gravel so as to avoid the reduction of permeability. When the subsurface medium through which the groundwater is to be directed is a bedrock, suitable gradient and upward gradient zones can be produced by flying the bedrock under effective conditions to produce areas of upward gradient and falling rock gradient. fractured. Areas of fractured rock (commonly referred to as "rock-blown zones" or "shatter zones") are preferably formed by blasting the subsurface using explosive charges within multiple shot holes bored several meters apart and oriented in the desired shape of the ascending gradient zone or; descending gradient. The firing holes used to fracture the rock typically separate along the areas to be flown in a staggered manner in order to create a large fracture zone. Typically, explosive charges are separated vertically from each other within each shot hole using belay stone or other suitable material, and charges are detonated using millisecond delays to reduce vibrations and the vertical drag component of the land to acceptable levels. . The methods for providing the treatment zones are varied and depend on the nature of the subsurface environment. For example, when the pre-existing subsurface medium was land, the treatment zone can be constructed by removing soil from the area of the treatment zone, such as by digging or drilling a hole or series of holes, and filling the area of treatment with a material having a substantially greater permeability than that of the earth, such as sand, gravel, broken rock, zero-valent iron or other metal particles, or combinations of these materials. It should be noted that, as used herein, drilling includes any process whereby holes having a circular or substantially circular cross-section are produced, including, for example, spiral drill-hole. Injection wells or piezometers may be installed within the filling material of the treatment zone, as appropriate for the subsequent injection or placement of treatment agents. Alternatively, the treatment zone can be constructed by drilling a large hole or a series of smaller holes in a contact between the ascending gradient and descending gradient zones and installing a well screen and a vertical pipe in the drilled hole or in each of the drilled holes. Still another process to build the treatment zone involves removing soil from the area of the treatment zone, such as by digging the soil, and installing permeable, preferably flat, walls to support the soil surrounding the treatment zone. Suitable permeable walls include those made of permeable sheet stacking. When the subsurface environment is rock, the treatment zone can be provided by flying the rock under effective conditions to fracture the rock in the area of the treatment zone. Injection wells or piezometers can be installed within the fractured rock of the treatment zone, as appropriate, for subsequent injection or placement of the treating agents. Alternatively, the treatment zone can be constructed by drilling the rock to produce a hole or a series of holes in the treatment zone. Typically, a single large hole can be bored, or a series of smaller holes can be used. Bored holes can be filled with a material that has a greater permeability than that of the surrounding rock, such as broken rock, gravel, or zero-valent iron or other metal particles. Alternatively, especially in the case where a surrounding subsurface medium is intact and stable and where the treatment method does not require filling the holes with a permeable material, the bored holes may be left empty. The method of the present invention is particularly suitable for the on-site treatment of groundwater containing one or more contaminants. Examples of contaminants that can be treated using the methods of the present invention include: toxic or hazardous chemical substances, such as dissolved organic halogenated compounds, pesticides, carbohydrates, heavy metals, cyanides, nitrates, radioelements, or combinations thereof; undesirable physical substances, such as colloids; and dangerous or potentially dangerous biological substances, such as pathogenic bacteria, parasites, or viruses. Subsurface groundwater treatment is done at the site, below the ground, in the treatment area to which the groundwater is directed through the ascending gradient zone and is directed outward through the gradient descending zone. The treatment is carried out by contacting one or more contaminants with a treatment agent under effective conditions to treat at least one or more contaminants present in the groundwater of the subsurface. Several treatment agents and technologies can be used to treat groundwater in the treatment zone. The particular technology used for the treatment depends on several factors, such as the geology, the types and concentrations of the pollutants, the size of the polluting plumes, the speed of the migration of pollutants, and the physical, chemical, biological, legal restrictions , regulatory, political, and social that may exist in relation to the design and implementation of the treatment area. The contacting of the contaminants with the treatment agent can be effected by injecting a treatment agent in the vapor, liquid or solid phase directly into the treatment zone. The treatment agent can be brought to the treatment zone by any convenient injection vehicle, such as several small diameter wells or piezometers. Under certain site-specific circumstances, several treatment agents can be injected into the treatment zone to treat contaminated groundwater. For example, oxygenators such as air, oxygen, hydrogen peroxide, ozone, or solid substances that release oxygen slowly over a period of time can be used to oxygenate the groundwater and facilitate aerobic biodegradation of the contaminant or contaminants, to the extent that which can be biodegraded under aerobic conditions. Oxygenators are particularly useful for treating simple, non-chlorinated hydrocarbons and other substances amenable to ordinary aerobic biodegradation. Alternatively, air or oxygen can be used in combination with a co-metabolite (such as methane, propane, or ammonia) to oxygenate the water and to facilitate aerobic biodegradation of the co-metabolite and, at the same time, co-metabolize of the pollutant. This combination is particularly useful for treating halogenated organic compounds. In many cases the use of co-metabolites requires specific safety precautions (particularly with regard to concentrations that are well below the lower explosive limits ("LEL")). The treatment agent may also be an electron acceptor other than oxygen, such as nitrate, particularly in cases where the contaminants are susceptible to biodegradation under anoxide or anaerobic conditions. Injectable reductants, such as sodium dithionate, underfed iron-reducing bacteria, or colloidal iron, can also be used to create conditions that lead to the treatment of contaminated groundwater. In some cases the reducer becomes the Fe (III) that occurs naturally in minerals in Fe (II) which in turn facilitates the degradation of, for example, organic pollutants. In other cases the reducer can reduce inorganic contaminants, such as hexavalent chromium, and facilitate its precipitation. In particular, the use of colloidal iron to treat contaminated water is described in U.S. Patent Number: 5,266,213 to Gillham ("Gillham"), which is incorporated herein by reference. Injectable oxidants, such as potassium permanganate or ozone, can also be used to directly attack and decompose a variety of contaminants, including halogenated hydrocarbon compounds and other organic contaminants. As one skilled in the art will notice, in some cases, the use of injectable treatment agents would require specific safety precautions as well as regulatory approval. As will also be recognized by one skilled in the art, not all contaminants can be treated with all the treatment methods described above. Alternatively to injecting the treatment agent, the treatment agent can be placed in the holes or cavities formed in the treatment zone. Frequently this requires the construction of a subsurface cavity, such as a rock cavity or earth excavation, to house the treatment agent. The subsurface cavity may be a hole or cavity constructed in the treatment zone, constructed, for example, by the processes described above. Several promising treatment processes can be used in a rock cavity or earth excavation. A method, particularly suitable for the treatment of groundwater containing halogenated organic compounds ("HOC"), such as perchloroethene ("PCE"), trichloroethene ("TCE"), dichloroethene ("DCE"), and trichloroethane ("TCA") "), is described in Gillham, which is incorporated herein by reference. Briefly, the method involves contacting the halogenated organic compounds with zero-valent iron or other zero-valent metals placed under the water table. The metals preferably have a high specific surface area, such as when the metal is in the form of filaments, particles, or fibers. In the case where zero-valent iron is used, yes, some years after the initial metal placement, it is discovered that there is loss of permeability caused by the chemical precipitation in the iron of the ascending gradient, an electromagnet can be used to remove all or something of iron. The iron can then be reactivated, for example, by acid washing or redistribution, and then replaced. This method of treatment can also be effective for groundwater that contains excessive concentrations of nitrate. Groundwater treatment containing halogenated organic compounds or volatile organic compounds ("VOC"), such as benzene, toluene, ethylbenzene, and xylenes, (collectively known as "BTEX"), can be accomplished by dispersing the halogenated organic compounds or Volatile organic compounds from groundwater and collecting vapors dispersed in, for example, the vadose zone over groundwater. This method involves contacting the contaminated groundwater with a gaseous treatment agent, such as compressed air or some other harmless gas separator. The gaseous treatment agent can be delivered in tubes installed at the base of a treatment zone and then forced through microporous bubblers such as dispersion tubes, to create small bubbles. The movement of the bubbles upwards through the contaminated groundwater in the treatment zone divides the volatile organic compounds, and then the splitting gas rich in volatile organic compounds is collected, for example, by steam extraction, and stirred to remove the separation or subsequent treatment. Yet another method for treating contaminated groundwater, particularly convenient for removing contaminants that tend to be absorbed onto solids or splitting into organic matter, involves contacting contaminated groundwater with a sorbent material. Suitable sorbent materials include activated carbon, resins, or polymers. Preferably the sorbent material is removable or regenerable. Many other on-site methods can be used to treat groundwater directed to the treatment zone. These include, for example, the precipitation of metal or radioelements by, for example, pH adjustment; electrochemical methods to cause chemical changes to groundwater contaminants or to precipitate metals, preferably at an electrode; large-scale ultrasonic cavitation; and treatment by ultraviolet light, optionally used together with hydrogen peroxide or ozone treatment. The present invention also relates to a method for directing the flow of groundwater in a general direction of flow through a subsurface environment around a particular location in the subsurface. The method includes providing an elongate permeable upward gradient zone and an elongate permeable downward gradient zone, each of which has a major axis parallel to a non-zero component of the general direction of flow. The ascending gradient zone is hydraulically located uphill from the particular place. That is, the ascending gradient zone is located in a manner that intercepts the groundwater that is flowing to the particular location or which, in the absence of the ascending gradient and descending gradient zones, would flow to the particular location. The descending gradient zone is hydraulically located downhill from and is in hydraulic communication with the ascending gradient zone. The descending gradient zone is located downhill from the particular location, so that the groundwater flowing out of the descending gradient zone does not flow to the particular location. Groundwater is allowed to move from the subsurface medium surrounding the rising gradient zone to and through the ascending gradient zone. The groundwater is then moved from the upward gradient zone to, through and out of the downward gradient zone towards the middle of the subsurface surrounding the downward gradient zone. Each of the zones of ascending gradient and descending gradient is situated within the subsurface environment and has a permeability substantially greater than the permeability of the environment of the surrounding subsurface. The suitable orientations for each of the zones of ascending gradient and descending gradient includes those described above in relation to the method of treating groundwater. The method of the present invention for directing groundwater around a particular location can also be practiced using several zones of ascending gradient and descending gradient. In this embodiment the method further includes providing one or more additional elongated gradient zones and one or more additional elongated gradient zones. Each additional zone of ascending gradient or descending gradient zone has a permeability that is substantially greater than the permeability of the subsurface environment and each has a major axis parallel to a non-zero component of the flow direction. Preferably, the number of additional upward gradient zones is equal to the number of additional downward gradient zones so that the total number of upward gradient zones is equal to the total number of downward gradient zones. The orientation of the additional gradient and rising gradient zones is not critical to the practice of the present invention. However, it is preferred that the downward gradient zone and the further down gradient zones be the mirror images of the upward gradient zone and the additional upward gradient zones reflected in a plane perpendicular to the general direction of flow and which pass through a particular place. Optimally, the total number of ascending gradient zones is 2, and the total number of descending gradient zones is also 2. In a more preferred configuration, the descending gradient zone and the additional descending gradient zone are mirror images of the zone of ascending gradient and the zone of ascending gradient reflected in a plane perpendicular to the surface of the earth, parallel to the general direction of flow, and passing through the particular place. Illustrative configurations suitable for the practice of the present invention are shown in Figures 3A, 3B, and 3C. The flow lines 10 show the path taken by the groundwater, which has a flow direction 8, through the subsurface means 4 around a particular location 20 under the influence of the ascending gradient zone 2 and the gradient zone. descending 12. The method of the present invention for directing groundwater around a particular location can be used in a variety of situations. For example, where groundwater contains a contaminant, and the particular place is relatively free of the contaminant, the method could be used to reduce the migration of contaminated groundwater through the particular site thereby reducing the degree to which the particular site becomes polluted by the pollutant. When a particular site contains the contaminant in the subsurface environment and when the groundwater is relatively free of the contaminant, the method of the present invention can be used to reduce the flow of uncontaminated groundwater through the particular contaminated site, reducing by this the degree to which uncontaminated groundwater becomes contaminated by the contaminant. In addition, the velocity of the groundwater in the particular place would be lowered to a large extent, by as much as an order of magnitude or more. Reducing the flow velocity through a particular contaminated site would have two potential advantages. First, by decreasing the movement of impacted groundwater, the rate of growth and development of pollutant plume would decrease, which could potentially be important since the difficulty and cost of remedying contaminated groundwater is generally an increasing function of length, width and depth of the plume. Second, decreasing the velocity of the contaminant would increase its residence time within a treatment center installed downhill from the particular region. This would allow the depletion of much less remedial agent (such as iron filaments for reductive dechlorination, or oxygen injected for oxidative biodegradation) per unit time. The downstream site treatment center may employ conventional treatment processes, such as funnel-and-door treatment process (Remediation Review, 8 (l): 6-7 (1995), which is incorporated herein). by reference) (in the case of soil contamination), or the treatment method of the present invention. In any case, decreasing the flow velocity through the particular contaminated region would have the advantage of requiring less space in the treatment center, since less treatment agent would be required. The optimization of the methods of the present invention involves several factors. These include: the permeability of the ascending gradient and descending gradient zones, including their width and length, the permeability of the subsurface environment, the orientation of the ascending gradient and descending gradient zones with respect to each other and with respect to the general direction of groundwater flow, and the size and shape of the treatment area. The interrelation of these factors is not fully understood. However, the following is a brief description of how the invention is believed to operate. This brief description is not intended to limit or otherwise affect the scope of the present invention but is only provided to guide the optimization of the invention in a particular situation. In accordance with the foregoing, the present invention is not considered to be limited by the following description. It is believed that changes in the direction of groundwater in the areas of ascending gradient and descending gradient and the convergence of groundwater flows to a treatment center are carried out through refraction of groundwater flow designed technically. When groundwater flows out of a medium and into a second medium that has a higher permeability, the current lines in that water tend to refract, or reorient, in different directions of the directions of the original streamlines. The process is similar but not identical to the refraction of light at the junction between two media of different refractive indices. One difference is that the refraction of light is expressed by a sine law, while the refraction of groundwater, under idealized circumstances, is expressed by a tangent law. However, refraction in real groundwater systems depends on three factors, only the first two of which are implied by the tangent law of refraction: (1) the orientation of the contact between the two different media in relation to the average direction of groundwater flow, (2) the difference in relative permeability between the two media, and (3) the geometry of the two media and their contact surface. The effects of the last factor in the refracted flow should generally be attacked through the numerical model of the flow. The basic concept of flow refraction can be understood in terms of groundwater flow through two subsurface porous media that have a vertically flat contact that, seen in plan, is oblique, but not perpendicular, to the direction of the flow. average flow (see Figure 4). The permeabilities of the two media differ, and the ratio of permeabilities is one of the important variables that govern the flow refraction. This proportion without dimensions has the same numerical value as the proportion of hydraulic conductivities, where the term "hydraulic conductivity" takes into account fluid parameters that affect the flow, such as viscosity and density, as well as the inherent transmission capacity of the porous medium (Domenico, which is incorporated herein by reference). In the common expression of the principles of flow refraction, the proportion of hydraulic conductivities is used; This practice is followed here. In the contact between the two media, the groundwater current lines flowing from a medium (with hydraulic conductivity K ^ towards the contact form an angle with the normal (or perpendicular) to the contact, and the current lines of the groundwater flowing from the contact to the hydraulic conductivity means K2 form an angle 02 with these normals, all of which can be expressed in accordance with the tangent refractive law (Freeze, which is incorporated herein by reference): tand ?!) / tan (02) = 1 / K2 (Equation 1) In qualitative terms, Equation 1 says that groundwater flowing from a medium of low permeability to a very long medium of high permeability through oblique contact will tend to be refracted almost parallel to contact if the high permeability ratio The low is very high (for example,> 100). If, for example, a narrow, very long, sand cell were placed 45 degrees oblique to the groundwater flow in a fine powder, where the K2 / KL ratio was 100, the refractive angle with respect to the normal contact would be ? 2 = arctan [an ((? 1) K2 / K1] = arctan [tan (45) 100] = 89.4 ° (Equation 2) which means that the flow would be almost parallel to the contact If ICL high permeability cell were of limited size, however, the flow to the more downward end of the cell may not continue to be refracted as it would be along the uphill portion of the cell, a concept that is not apparent from the inspection of the Equation 1. This equation assumes a set of two semi-infinite media in which there is no tendency for hydraulic head accumulation at any point.If the refraction were to continue all along the length of the finite-length cell, then the water The low-permeability medium would be compressed at the descending gradient end of the cell where the high permeability medium meets the low permeability medium.The flow in the initial direction of refraction would then be impeded. cause the hydraulic head to accumulate and stop the refraction process some distance away from the wall. That the flow would move away locally from the tangent refractive law near the end of the cell under conditions in which the high permeability zone is limited in its spatial extent has been demonstrated as part of this work, based on a flow representation of groundwater USGS MODFLOW. However, the flow can be made to converge to a location if there is an associated descending gradient region of dispersion that has an equal capacity to disperse the flow as the ascending gradient region has to collect flow. This is illustrated conceptually in Figure 2D, where the flow converges to a "flow-through" treatment zone through the two ascending gradient arms of the X-shaped refractive flow system. The upward gradient flow can converging in this zone due to the two symmetrical descending gradient arms of the refractory flow system bring the groundwater away from the treatment zone as fast as the upward gradient arms carry it inward. In Figure 5 (output of a MODFLOW model), the same hydraulic head lines, which are perpendicular to the local groundwater flow, are illustrated in detail for an X-shaped refractory flow system where the permeability of the system is 100 times that of the region of the surrounding medium. Representative lines of the groundwater stream 26 are also illustrated. Figure 5 shows that a groundwater flow is refracted from the general direction of initial flow 28 to an almost parallel direction to the rising gradient zones. The groundwater flow is then directed through a permeable treatment zone in the center of the X and towards the gradient descending zones. The groundwater is transported out of the gradient descending zones to resume its general gradient gradient course. Any groundwater flow that makes contact with the ascending gradient zone passes through the permeable treatment zone. The X-shaped refractory flow system has been demonstrated through a computer model that is highly efficient for directing groundwater through a known, central location where a treatment zone can be installed on the site. If there is a need for multiple treatment centers placed along the ascending gradient arms of a refractory flow system, it would be necessary to be able to estimate the separation between the treatment centers. This separation, interpreted in the equations as perpendicular to the average direction of groundwater flow, can be calculated with reference to Figure 6. S, the space between the treatment zones, is equal to T, the thickness of the duct of the subsurface of high permeability (that is, the thickness of the ascending gradient zones), multiplied by sew ^), the cosine "of the angle between the major axis of the ascending gradient zone and the average (ie, general) direction of the groundwater flow , multiplied by the term [(K2 / Kj) -1].

S = T [cos (Oí!)] [(K2 / K1) -1] (Equation 3] Figure 6 shows how the ratio (S / T) varies with (K2 / Kj) for different representative values of OÍJ. The values of T and K2 can be estimated from previous experience and, if necessary, can be confirmed, for example, by exploratory drilling and field testing after several firing holes have been flown. Adjustments can be made to blasting methods in the field as necessary to achieve the appropriate values for T and K2. The calculations should give reasonable estimates of (S / T) for refractory flow systems with adequate downward gradient flow dispersion. A reasonable safety factor should be applied in the design to take into account subsurface heterogeneities and other unknowns. Although the invention has been described for purposes of illustration, it is It will be understood that these details are solely for that purpose and those skilled in the art can make variations therein without departing from the spirit and scope of the invention.

Claims (47)

1. A method for treating groundwater flow in a general direction of flow through a subsurface means comprising: providing a hydraulically located elongate permeable upward gradient uphill slope of and in hydraulic communication with a permeable water treatment zone; subsurface and having a major axis parallel to a non-zero component of the general direction of flow; providing an elongated permeable gradient downward gradient zone hydraulically located downhill from and in hydraulic communication with the subsurface permeable treatment zone and having a major axis parallel to a non-zero component of the general direction of flow; and allowing the groundwater to move from the subsurface environment surrounding the upward gradient zone to and through the upward gradient zone to, through, and out of the treatment zone and inward, through, and outside the gradient zone descending into the middle of the subsurface surrounding the descending gradient zone; and treating the groundwater in the treatment zone, wherein each of the ascending gradient zone, descending gradient zone and treatment zone is situated within the subsurface environment and has a substantially greater permeability than the permeability of the medium. the surrounding subsurface.

2. A method in accordance with the claim 1, where the subsurface medium is earth.

3. A method in accordance with the claim 2, wherein each of the ascending gradient zone and the descending gradient zone indeently comprises a material selected from the group consisting of sand, gravel, and combinations thereof.

4. A method in accordance with the claim 3, wherein providing the ascending gradient zone and providing the descending gradient zone comprises: removing earth from the ascending gradient zone and the descending gradient zone and filling the ascending gradient zone and the descending gradient zone with a material selected from the group consisting of sand, gravel, broken rock, and combinations thereof.

A method according to claim 2, wherein the treatment zone is provided by a process comprising: removing soil from the treatment zone and filling the treatment zone with a material selected from the group consisting of sand, gravel , broken rock, and combinations thereof.

6. A method according to claim 5, wherein removing the soil from the treatment zone comprises: excavating soil from the treatment zone.

7. A method according to claim 5, wherein removing the soil from the treatment zone comprises: drilling a hole or a series of holes in the treatment zone.

A method according to claim 2, wherein removing the soil from the treatment zone comprises: drilling a hole or a series of holes in the treatment zone and installing a well and vertical pipe screen in the hole or each one of the series of bored holes.

9. A method in accordance with the claim 2, wherein the treatment zone is provided by a process comprising: excavating soil from the treatment zone and installing effective permeable walls to support the soil surrounding the treatment zone.

10. A method in accordance with the claim I, where the middle of the subsurface is rock.

11. A method according to claim 10, wherein each of the ascending gradient zone and the descending gradient zone comprises fractured rock.

12. A method in accordance with the claim II, wherein providing the ascending gradient zone and providing the descending gradient zone comprises: flying the rock under effective conditions to fracture the rock in the ascending gradient zone and the descending gradient zone.

13. A method according to claim 10, where the treatment zone is produced by a process that includes: flying the rock under effective conditions to fracture the rock in the treatment zone.

A method according to claim 10, wherein the treatment zone is produced by a process comprising: drilling the rock under effective conditions to produce a hole or a series of holes in the treatment zone.

15. A method according to claim 1, wherein the groundwater comprises a contaminant.

16. A method according to claim 15, wherein the contaminant is selected from the group consisting of toxic materials, hazardous materials, pathogens, malodorous materials, noxious materials, and combinations thereof.

17. A method in accordance with the claim 1, wherein the treatment comprises: contacting, within the treatment zone, the contaminant with a treatment agent under conditions effective to treat the contaminant.

18. A method in accordance with the claim 17, wherein contacting comprises.- injecting the treatment agent into the groundwater within the treatment zone.

19. A method according to claim 17, wherein contacting comprises: placing the treatment agent in the groundwater within the treatment zone.

20. A method according to claim 17, wherein contacting comprises: placing a material capable of releasing the treatment agent in the ground water in the treatment zone and allowing or causing the release of the treatment agent in the water underground in the treatment area.

21. A method according to claim 17, wherein the treatment agent is selected from the group consisting of air, oxygen, oxidants other than oxygen, co-metabolites, nutrients other than co-metabolites, electron acceptors, iron zero-valent, different reducers of zero-valent iron, acids, alkalis, surfactants, sorbents, heat energy, light energy, acoustic energy, and combinations thereof.

22. A method according to claim 1, wherein the general direction of flow forms an angle or. with respect to the major axis of the ascending gradient zone and where a. is from about 30 ° to about 60 °.

23. A method according to claim 22, wherein the general direction of flow forms an angle of 180-Q; degrees with respect to the major axis of the descending gradient zone and where there is an angle of 180 -2a degrees between the major axis of the descending gradient zone and the major axis of the ascending gradient zone.

24. A method according to claim 1, wherein the ascending gradient zone has a substantially uniform width, the descending gradient zone has a substantially uniform width, and the widths and lengths of the gradient and descending gradient zones are substantially the same.

25. A method according to claim 1, wherein the descending gradient zone is an image in the mirror of the ascending gradient zone reflected in a plane perpendicular to the general direction of flow and passing through the zone of treatment.

26. A method according to claim 1, further comprising: providing one or more additional elongate permeable rising gradient zones, each located hydraulically uphill from and in hydraulic communication with the treatment zone and each having a major axis parallel to a non-zero component of the general direction of flow and provide one or more additional elongate permeable gradient zones, each located hydraulically downhill from and in hydraulic communication with the treatment zone and each having a parallel major axis to a non-zero component of the general direction of flow, wherein each of the additional zones of ascending gradient and each of the additional zones of descending gradient is situated within the subsurface environment and has a substantially greater permeability "than the permeability of the surrounding subsurface medium.

27. A method of compliance with the claim 26, where the number of additional gradient zones ee equals the number of additional gradient zones.

28. A method according to claim 27, wherein the downward gradient zone and the further down gradient zones are mirror images of the upward gradient zone and additional upward gradient zones, reflected in a plane perpendicular to The general direction of flow and passing through the treatment area.

29. A method according to claim 28, wherein the number of additional ascending gradient zones is one and the number of additional descending gradient zones is one and wherein the descending gradient zone and the additional descending gradient zone are mirror images of the ascending gradient zone and the zone of additional upward gradient, reflected in a plane perpendicular to the surface of the earth, parallel to the general direction of flow, and passing through the treatment zone.

30. A method for directing the flow of groundwater flowing in a general direction of flow through a subsurface medium around a particular subsurface location comprising: providing an elongated permeable upward gradient zone hydraulically located uphill from the particular location and having a major axis parallel to a non-zero component of the general direction of flow; providing an elongate permeable gradient drop zone located hydraulically downhill from the particular location and having a major axis parallel to a non-zero component of the general direction of flow; and allowing the groundwater to move from the subsurface environment surrounding the upward gradient zone to and through the upward gradient zone up to, through, and out of the gradient downward zone into the middle of the subsurface surrounding the descending gradient zone, wherein each of the ascending gradient zone and the descending gradient zone is situated within the subsurface environment and has a substantially greater permeability than the permeability of the surrounding subsurface environment.

31. A method according to claim 30, wherein the subsurface means is ground.

32. A method according to claim 31, wherein each of the ascending gradient zone and the descending gradient zone independently comprises a material selected from the group consisting of sand, gravel, broken rock and combinations thereof.

33. A method according to claim 32, wherein providing the ascending gradient zone and providing the descending gradient zone comprises: removing earth from the ascending gradient zone and the descending gradient zone and filling the zone of gradient. ascending gradient and descending gradient zone with a material selected from the group consisting of sand, gravel, broken rock, and combinations thereof.

34. A method according to claim 30, wherein the subsurface medium is rock.

35. A method in accordance with the claim34, wherein each of the ascending gradient zone and the descending gradient zone comprises fractured rock.

36. A method in accordance with the claim 35, wherein providing the ascending gradient zone and providing the descending gradient zone comprises: flying the rock under effective conditions to fracture the rock in the ascending gradient zone and the descending gradient zone.

37. A method according to claim 30, wherein the groundwater comprises a contaminant and wherein the particular location is relatively free of the contaminant.

38. A method according to claim 37, wherein the contaminant is selected from the group consisting of toxic materials, hazardous materials, pathogens, malodorous materials, noxious materials, and combinations thereof.

39. A method according to claim 30, wherein the particular site comprises a contaminant and the groundwater is relatively free of the contaminant.

40. A method according to claim 39, wherein the contaminant is selected from the group consisting of toxic materials, hazardous materials, pathogens, malodorous materials, noxious materials, and combinations thereof.

41. A method according to claim 30, wherein the general direction of flow forms an angle with respect to the major axis of the ascending gradient zone and wherein OI is from about 30 ° to about 60 °.

42. A method according to claim 41, wherein the general direction of flow forms an angle of 180-GI degrees with respect to the major axis of the descending gradient zone and wherein there is an angle of 180-2O degrees between the major axis of the descending gradient zone and the major axis of the ascending gradient zone.

43. A method according to claim 30, wherein the ascending gradient zone has a substantially uniform width, the descending gradient zone has a substantially uniform width, and the widths and lengths of the gradient and descending gradient zones are substantially the same.

44. A method according to claim 30, further comprising: providing one or more additional elongate permeable gradient zones, each hydraulically located uphill from the particular location and each having a major axis parallel to a non-zero component of the general flow direction and providing one or more additional elongate permeable gradient gradient zones, each located hydraulically downhill from the particular location and each having a major axis parallel to a non-zero component of the general direction of flow, in where each of the additional zones of ascending gradient and each of the additional zones of descending gradient is situated within the middle of the subsurface and has a substantially greater permeability than the permeability of the surrounding subsurface environment.

45. A method in accordance with the claim 44, wherein the number of additional gradient zones ee equals the number of additional gradient zones.

46. A method according to claim 44, wherein the downward gradient zone and the further down gradient zones are mirror images of the upward gradient zone and additional upward gradient zones, reflected in a plane perpendicular to The general direction of flow and that pass through the particular place.

47. A method according to claim 46, wherein the number of additional upward gradient zones is one and the number of additional downward gradient zones is one and wherein the downward gradient zone and the additional downward gradient zone are mirror images of the ascending gradient zone and the additional ascending gradient zone, reflected in a plane perpendicular to the surface of the earth, parallel to the general direction of flow, and passing through the particular location.