Abstract:
The apparatus of the invention comprises a plurality of vessels, each vessel having a soil intake opening, a soil discharge opening, and a soil motivator associated therewith. The apparatus also has a liquid delivery system configured to deliver a liquid into at least one of the vessels, and a drainage system configured to collect the liquid and the contaminants. The vessels are arranged in sequence so that soil discharged from the discharge opening of one vessel is directly deposited into the intake opening of the next vessel. The method of the invention comprises the steps of: introducing the contaminated soil into a first vessel; washing the soil with a first liquid cleaning agent; passing the soil through a plurality of vessels in sequence wherein said first liquid cleaning agent is removed by a second liquid cleaning agent and water; draining said second liquid cleaning agent and water from the soil; and, rinsing the soil with water.

Description:
TECHNICAL FIELD  
         [0001]    This invention relates to treatment of contaminated soil, particularly to methods for remediating soil at the site of a spill of oil or other environmentally hazardous material and mobile apparatus for practising such methods.  
         BACKGROUND  
         [0002]    It is an unfortunate truth that when people handle materials which have the potential to damage the environment, sooner or later accidents will result in such materials being spilled on to the ground. For example, in oil fields, spills can occur as a result of leaking well heads. In this case, the fluids spilled are generally crude oil, salt water, or a mixture of the two called an “emulsion”. Fortunately, the deleterious effects of such accidents can be minimized if appropriate steps are timely taken to remove any contaminants from the soil upon which the spill has occurred. Cleaning contaminated soil is becoming an increasingly serious problem for business as environmental protection regulations become more strict.  
           [0003]    One way to deal with spills is to load all of the contaminated soil into trucks and drive the soil to a reclaimer or “land farm”. At the reclaimer the soil is processed to remove contaminants. Contaminated soil is dumped into the open top of a vessel known as a reclaimer, where it is agitated by high pressure steam. Oil tends to collect at the top of the vessel and salt water near the mid section. After the oil and salt water have been skimmed off, the soil is further processed at a land farm. At a land farm the soil is placed in a clay pit and allowed to dry. The soil is turned periodically to allow sunlight to reach every portion of the soil. Ultraviolet light from the sun helps to break down hydrocarbons. Manure and straw may be mixed in with the soil to replace organic matter. Land farms may take years to process soil, and as a result, this method of dealing with spills is inefficient. Furthermore, land farms are few and far between. It is very expensive to haul tonnes of soil back and forth from spill sites to land farms in trucks.  
           [0004]    There are various prior art apparatus and methods for treating soil at the site of a spill. This avoids the need to haul soil to a remote location for treatment. For example, U.S. Pat. No. 4,919,570 discloses a portable on-site soil treatment system that includes one or more soil treatment vessels cyclically connected to a pumping station and a treatment station. Fluid is pumped upwardly through the vessels to clean the soil. The vessels are tilted to dump the soil once the soil meets the necessary environmental standards.  
           [0005]    U.S. Pat. No. 5,244,308 discloses a mobile apparatus for removing contaminants from soil. The soil is fed into a processor along with a liquid agent for separating the contaminants from the soil. The soil is then separated from the liquid agent containing the contaminants.  
           [0006]    U.S. Pat. No. 5,637,154 discloses a method and portable apparatus for remediating soil using only water. The soil is fed into a hopper where it is screened and passed to a series of reactors by an auger. The soil is passed through the reactors by further augers. The number of washing stages is variable. The reactors are connected by transfer pipes in such a way that each subsequent reactor has a lower water level than the previous one.  
           [0007]    U.S. Pat. No. 6,155,276 discloses a portable apparatus and method for removing soil contaminants that uses water and a biodegradable soap mixture. Soil, water and soap are fed into cylindrical chambers that have channels on the inside for capturing the soil. The chambers are arranged end to end and soil is moved between them by conveyors.  
           [0008]    A general problem with current portable soil cleaning systems is that they are either slow (i.e. low throughput), or they themselves use large amounts of hazardous chemicals to remove the contaminants.  
           [0009]    There exists a need for a mobile apparatus for efficiently treating contaminated soil at the site of a spill. There further exists a need for a method of soil treatment that is environmentally friendly, that is, one that does not use large amounts of toxic chemicals in removing contaminants from soil.  
         SUMMARY OF INVENTION  
         [0010]    One aspect of the invention provides an apparatus for treatment of soil that contains contaminants. The apparatus is made up of a plurality of vessels, each vessel having a soil intake opening and a soil discharge opening. Each vessel has a soil motivator associated therewith. The motivators are operable to move soil from the intake opening to the discharge opening. The apparatus also has a liquid delivery system configured to deliver a liquid into at least one of the vessels, and a drainage system configured to collect the liquid and the contaminants. The vessels are inclined so that the intake opening is at a lower level than the discharge opening. The vessels are arranged in sequence so that soil discharged from the discharge opening of one of the vessels is directly deposited into the intake opening of the next vessel.  
           [0011]    Each of the intake openings is preferably near a first end of one of the vessels. Each of the discharge openings is preferably near a second opposite end of one of the vessels. The second end of one vessels is preferably above the first end of the next vessel, so that soil exiting the discharge opening of one vessel falls directly into the intake opening of the next vessel.  
           [0012]    The vessels are preferably inclined at angles between 10 and 40 degrees, and more preferably between 25 and 30 degrees. The second end of one vessels is preferably above the first end of the next vessel.  
           [0013]    The soil motivators preferably comprise rotatable shafts with a plurality of paddles attached thereto. The paddles may be symmetrically disposed around the rotatable shafts. The paddles may extend radially outward from the shafts in pairs. Adjacent pairs of paddles may be perpendicular to each other.  
           [0014]    The paddles are oriented so that when the shafts are rotated in a forward sense (the forward sense is clockwise when looking out of the drum through the discharge opening), the paddles move soil towards the discharge opening.  
           [0015]    The motivator preferably further comprises a motor operably coupled to the shaft. The motor is capable of rotating the shaft in a forward sense.  
           [0016]    The vessels preferably comprise cylindrical drums.  
           [0017]    The first end of at least one of the drums is preferably closed and the second end of at least one of the drums is preferably open.  
           [0018]    The drainage system may comprise a screened portion on an underside of at least one of the vessels.  
           [0019]    The screened portion is preferably adjacent to the discharge opening. The screened portion preferably has a mesh size in the range of 20 to 80 mesh.  
           [0020]    The drainage system may further comprise at least one slot on the underside of at least one of the drums. The slot is preferably oriented generally horizontally along a side of the drum, the slot extending from the screened portion towards the first end. The drainage system may alternatively comprise a series of holes in the underside of at least one of the drums.  
           [0021]    The paddles may have replaceable wear plates attached thereon.  
           [0022]    The motivator may comprise a screened cylinder attached to a rotatable shaft. The screened cylinder may have a plurality of paddles therein.  
           [0023]    The drainage system may comprise a plurality of slots on the underside of at least one of the drums.  
           [0024]    The apparatus may further comprise a trailer having an intake conveyor and a discharge conveyor mounted thereon. The drums may be positioned on the trailer so that soil placed on the intake conveyor deposits soil into a first drum, and soil exiting the last drum is deposited on the discharge conveyor.  
           [0025]    The drainage system may comprise a skimming system, the skimming system comprising gutters and skimming plates, wherein the liquid and contaminants are delivered to the gutters and flow over the skimming plates, while any remaining soil mixed in with the liquid and contaminants is caught by the skimming plates.  
           [0026]    An alternative aspect of the invention provides a single vessel in which soil may be treated.  
           [0027]    Another aspect of the invention provides a method of treating soil that contains contaminants. The method comprises the steps of: inserting the contaminated soil into a first vessel; washing the soil with a first liquid cleaning agent; passing the soil through a plurality of vessels in sequence wherein said first liquid cleaning agent is removed by a second liquid cleaning agent and water; draining said second chemical and water from the soil; and, rinsing the soil with water.  
           [0028]    Further features and advantages of the invention are described below. 
       
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0029]    In drawings which illustrate non-limiting embodiments of the invention:  
         [0030]    [0030]FIG. 1 a  is a top plan view of apparatus according to a preferred embodiment of the invention;  
         [0031]    [0031]FIG. 1 b  is a right side elevation view of the apparatus of FIG. 1 a;    
         [0032]    [0032]FIG. 1 c  is a left side elevation of the apparatus of FIG. 1 a;    
         [0033]    [0033]FIG. 2 is a rear elevation view of the apparatus of FIG. 1 a  with a rock washer attached to the side of the trailer.  
         [0034]    [0034]FIG. 3 is a perspective view of one of the drums according to a preferred embodiment of the invention;  
         [0035]    [0035]FIG. 4 is a perspective view of one of the drums according to a preferred embodiment of the invention, showing drip trays that form part of a drainage system;  
         [0036]    [0036]FIG. 5 is a perspective view of one of the drums according to a preferred embodiment of the invention, showing a rotating screened drum inside of the forward portion of the drum;  
         [0037]    [0037]FIG. 6 is a right side elevation view of the drum of FIG. 5, with an expanded view of the intersection of the rearward and forward portions of the drum;  
         [0038]    [0038]FIG. 7 is a perspective view of one of the drums according to a preferred embodiment of the invention, showing a rotating screened drum inside the entire length of the drum;  
         [0039]    [0039]FIG. 8 is an end view of a funneling member used to guide soil into the drums;  
         [0040]    [0040]FIG. 9 is a side view of the funneling member of FIG. 8;  
         [0041]    [0041]FIG. 10 is a side view of a chute used to connect the fourth drum to the fifth drum;  
         [0042]    [0042]FIG. 11 a  is a side view of a set of paddles mounted on a shaft constructed according to a preferred embodiment of the invention;  
         [0043]    [0043]FIG. 11 b  is a side view of a larger set of paddles mounted on a shaft constructed according to a preferred embodiment of the invention;  
         [0044]    [0044]FIG. 12 a  is an exploded view of one of the paddles, showing a wear plate which may be attached thereon;  
         [0045]    [0045]FIG. 12 b  shows the paddle of FIG. 12 a  with the wear plate attached thereon;  
         [0046]    [0046]FIG. 13 is an end view of one drum according to a preferred embodiment of the invention, showing a motor and a chain used to turn a sprocket;  
         [0047]    [0047]FIG. 14 is a perspective view of a gutter with a skimmer plate therein;  
         [0048]    [0048]FIG. 15 a  is an end view of the gutter and skimmer plate of FIG. 14 with the skimmer plate lowered;  
         [0049]    [0049]FIG. 15 b  is an end view of the gutter and skimmer plate of FIG. 14 with the skimmer plate raised; and,  
         [0050]    [0050]FIG. 16 is a perspective view of a sump.  
     
    
     DESCRIPTION  
       [0051]    Throughout the following description, specific details are set forth in order to provide a more thorough understanding of the invention. However, the invention may be practiced without these particulars. In other instances, well known elements have not been shown or described in detail to avoid unnecessarily obscuring the invention. Accordingly, the specification and drawings are to be regarded in an illustrative, rather than a restrictive, sense.  
         [0052]    The invention provides an apparatus  10  and method for removing contaminants from soil. Apparatus  10  preferably includes a trailer  12  as shown in FIGS. 1 a ,  1   b ,  1   c  and  2  so that it can be easily taken to the site of a spill where it can be used to clean contaminated soil. Apparatus  10  comprises a series of drums  20 . Soil is moved continuously through drums  20  of apparatus  10  along a path  13  in the direction indicated by arrows  19 . As it passes through drums  20 , the soil is washed with liquids, which may include first and second liquid cleaning agents and water. Each drum  20  is inclined so that soil and liquid tend to accumulate at its lower end  201 .  
         [0053]    Drums  20  are preferably all inclined at substantially the same angle, with one end of each drum  20  positioned above the next drum  20 . The angle of drums  20  is preferably in the range of 10 and 45 degrees, most preferably in the range of about 25 to 30 degrees. Each drum  20  has a soil motivator  17 . Soil motivator  17  urges soil up and eventually out of drum  20  at a discharge opening  202 . Due to the incline of drum  20 , fluids tend to drain out of the soil before it reaches discharge opening  202 . As soil exits one drum  20 , it falls directly into an intake opening  200  of the next drum  20  along path  13 . Some drums  20  have a drainage system, as described below, to remove liquids from the soil and the drum  20  before the soil leaves drum  20 . Such liquids are carried to a sump  25  by a gutter  22 .  
         [0054]    [0054]FIGS. 1 a ,  1   b ,  1   c  and  2  show a soil treatment apparatus  10  according to a preferred embodiment of the invention. This embodiment is described in detail herein so as to fully explain the best mode of the invention currently contemplated by the inventor. The embodiment described herein should be considered to be an example only. Apparatus  10  comprises a hopper  14 , intake conveyor  16 , five drums  20 A,  20 B,  20 C,  20 D and  20 E, and a discharge conveyor  18 .  
         [0055]    In operation, soil is fed continuously into hopper  14  from where it is deposited onto intake conveyor  16 . Alternatively, a vacuum hose and tank (not shown) could be used to suck soil and contaminants up from the ground into hopper  14 . Intake conveyor  16  deposits soil into first drum  20 A through an intake opening  200 A. There may be a grate  44  over intake opening  200 A to prevent large rocks from entering first drum  20 A, as discussed below.  
         [0056]    Each drum  20  has a forward direction as indicated by arrow  19  (see FIG. 1 a ). Soil is moved in sequence through first through fifth drums  20 A- 20 E in the direction of arrows  19 . As the soil moves through drums  20 , liquids are added, as described below. In each drum  20 , a soil motivator  17  agitates the soil along with the liquids and urges the soil in the “forward” direction indicated by arrow  19 .  
         [0057]    Apparatus  10  is configured to process a steady flow of contaminated soil.  
         [0058]    FIGS.  3  to  7  illustrate the basic structure of drums  20 . Each drum  20  has an intake opening  200  near its lower end  201 , which is covered by end plate  204 . The upper end  203  is open and forms a discharge opening  202 . End plate  204  has a drain hole  206  near its bottom edge. During operation, drain hole  206  is plugged by a drain plug (not shown). There may be an access hatch (not shown) provided on the top of drum  20 , to allow for maintenance and inspection when the apparatus is not in operation.  
         [0059]    First drum  20 A may have various forms but preferably comprises an elongated cylinder with a lower end  201 A covered by an end plate  204 A, and an upper end  203 A, as shown in FIG. 3. Intake opening  200 A is formed in the top of first drum  20 A near lower end  201 A. Upper end  203 A is open and forms discharge opening  202 A.  
         [0060]    A first liquid cleaning agent is introduced into first drum  20 A from first liquid cleaning agent tank  27  by means of a hose (not shown). The first liquid cleaning agent is preferably a Xylene-based cleanser.  
         [0061]    First drum  20 A is inclined so that the soil and the first liquid cleaning agent tend to accumulate at the bottom of first drum  20 A near end plate  204 A. First drum  20 A has a soil motivator  17  therein which agitates the soil and first liquid cleaning agent. The motivator urges the soil up drum  20 A towards discharge opening  202 A, while allowing the first liquid cleaning agent to drain back to the bottom of first drum  20 A to form a pool  15  of liquid. Motivator  17  preferably comprises a rotatable shaft  224 A. Shaft  224 A may be rotated by any suitable means, but is preferably turned by a motor  220 , as described below. In the illustrated embodiment shaft  224 A is rotatably supported at its lower end by suitable bearings in a shaft receiving hole  208 A through the middle of end plate  204 A.  
         [0062]    Shaft  224 A preferably has a set of paddles  240 A attached thereto, as shown in FIGS. 3 and 11 a . It would be possible to use an auger in place of paddles  240 A. However, paddles  240 A allow liquid to more readily seep back towards the bottom of first drum  20 A as the soil is moved upwards than would an auger. This is desirable because contaminants become dissolved in the liquid. By separating the liquid from the soil some of the contaminants are removed. Furthermore, an auger would likely require more power to turn than paddles  240 A (since an auger would force soil continuously towards end  203 A, while paddles  240 A allow soil to move from one paddle  240  to the next). Paddles  240 A are spaced apart around shaft  224 A.  
         [0063]    In the preferred embodiment shown in the drawings, paddles  240 A extend radially outwardly from shaft  224 A in pairs, although other arrangements of paddles  240 A are possible. The paddles  240 A of each pair extend from shaft  224 A in opposite directions. Adjacent pairs of paddles  240 A are preferrably oriented perpendicularly relative to one another. Each paddle  240 A has a blade  242 A that is at an angle of approximately 45 degrees to shaft  224 A. Blades  242 A of one pair of paddles  240 A are at opposite angles to shaft  224 A. Paddles  240 A are spaced apart so that blades  242 A of adjacent pairs just overlap. Blades  242 A are shaped and sized to pass within a short distance, for example, within about {fraction (1/16)}″ to ⅛″ or so (1.6-3.2 mm) of the interior walls of drum  20 A when shaft  224 A is placed therein.  
         [0064]    As shown in FIG. 3, one end of shaft  224 A is inserted through a shaft receiving hole  208 A in endplate  204 A, while the opposite end is supported by a shaft support (not shown) at discharge opening  202 A. The shaft support has a bearing (not shown) therein to allow shaft  224 A to rotate freely.  
         [0065]    When shaft  224 A is rotated, any soil in first drum  20 A is agitated by paddles  240 A. The orientation of blades  242 A is such that when shaft  224 A is rotated in a forward sense, (clockwise when looking out through discharge opening  202 A), soil is moved upward and out through discharge opening  202 A, while the majority of liquids in first drum  20 A drain back into pool  15  and remain in first drum  20 A.  
         [0066]    Some of the first liquid cleaning agent will remain with the soil when it leaves first drum  20 A. Preferably a majority of the first liquid cleaning agent drains back into pool  15  as the soil is carried upward through first drum  20 A. First liquid cleaning agent may be relatively expensive, so it is desirable to retain the majority of the first liquid cleaning agent in first drum  20 A. Preferably only small amounts of the first liquid cleaning agent must be replenished as soil is processed.  
         [0067]    Once the soil leaves discharge opening  202 A of first drum  20 A, it falls directly into intake opening  200 B of second drum  20 B. There may be a funneling member  30  connecting discharge opening  202 A and intake opening  200 B, as shown in FIGS. 8 and 9.  
         [0068]    [0068]FIGS. 8 and 9 show a funneling member  30  which may be fitted over discharge opening  202  of a drum  20  to guide soil into intake opening  200  of the next drum  20 . The opening at the bottom of funneling member  30  is placed in intake opening  200 . A liquid supply  33  may be provided in funneling member  30  so that water or the first or second liquid cleaning agents may be added to the soil as it passes through funneling member  30 .  
         [0069]    Water from fresh water tank  29  is added to second drum  20 B by means of a hose (not shown) connected to liquid supply  33 , along with the soil. The water may be heated before being added to second drum  20 B, to increase its ability to accept solutes. Water may be supplied to drums  20 C,  20 D and  20 E in a similar fashion.  
         [0070]    Second drum  20 B comprises a rearward portion  205 B and a forward portion  207 B as shown in FIGS. 5 and 6. Rearward portion  205 B has a diameter equal to that of first drum  20 A. Forward portion  207 B has a diameter approximately 1 to 2 inches greater than that of rearward portion  205 B to accommodate a rotating screened drum  209 B, as described below. Rearward portion  205 B of second drum  20 B functions in much the same way as first drum  20 A, except that rearward portion  205 B has a liquid removal system that comprises part of a drainage system for second drum  20 B.  
         [0071]    Shaft  224 B extends through the entire length of second drum  20 B. Paddles  240 B in rearward portion  205 B are the same as paddles  240 A of first drum. Paddles  240 B in forward portion  207 B are shown in FIG. 11 b , and are larger than paddles  240 B in rearward portion  205 B. Rotating screened drum  209 A is attached to the outer edges of blades  242 B of forward portion  207 B. Rotating screened drum  209 A preferably has a mesh size of approximately 20 to 80 mesh. Rotating screened drum  209 B preferably overlaps rearward portion  205 B by approximately {fraction (1/16)}″ to {fraction (3/16)}″ (1.5 mm to 4.5 mm) and extends forward to approximately 1″ (25 mm) beyond discharge opening  202 B. Forward portion  207 B may have sprayers  211 B along an upper portion thereof. Forward portion  207 B has slots  213 B along a lower portion thereof which comprise the liquid removal system of forward portion  207 B, as described below.  
         [0072]    In operation, soil and liquids enter intake opening of drum  20 B and are urged forward through rearward portion  205 B. A significant portion of the liquids will drain back into pool  15  as the soil and liquids are agitated by paddles  240 B. The soil and any remaining liquids then pass into rotating screened drum  209 B. As seen in the expanded circle in FIG. 6, rotating screened drum  209 B is slightly larger than, and partially overlaps, rearward portion  205 B, so that none of the soil will fall between rearward portion  205 B and rotating screened drum  209 B. The soil is urged forward through forward portion  207 B, and most of the liquids migrate through the rotating screened drum  209 B and out slots  213 B, as described below. Once the soil exits discharge opening  202 B it falls out of screened drum  209 B into intake opening  200 C of third drum  20 C, possibly with the assistance of funneling member  30 .  
         [0073]    The drainage system of second drum  20 B comprises a liquid removal system and a liquid collection system. The liquid removal system comprises slots  213 B in the underside of forward portion  207 B. Sprayers  211 B spray water (which may be heated) down through rotating screened drum  209 B. The water from the sprayers keeps the screened drum  209 B from clogging. The majority of the liquids and water from sprayers  2111 B drains through slots  213 B.  
         [0074]    The liquid collection system of second drum  20 B preferably comprises right drip tray  218 B and gutter  22 . As best seen in FIG. 5, right drip tray  218 B is configured to collect any liquid exiting second drum  20 B through slots  213 B and deliver it to gutter  22 . Gutter  22  collects liquid from drums  20  and delivers it to sump  25 .  
         [0075]    Soil is agitated and moved forwards and upwards through second drum  20 B by paddles  240 B, while most of the liquid drains into gutter  22 . The liquid carries away with it most of the remaining first liquid cleaning agent. Soil exits second drum  20 B through discharge opening  202 B and falls from rotating screened drum  209 B into intake opening  200 C of third drum  20 C, possibly with the assistance of funneling member  30 . A mixture of a second liquid cleaning agent from second liquid cleaning agent tank  28 , and water from fresh water tank  29  are added to third drum  20 C by means of hoses (not shown) connected to liquid supply  33 , along with the soil. The water may be heated. The second liquid cleaning agent is biodegradable, and preferably comprises citric acid. The second liquid cleaning agent may be derived from orange peelings.  
         [0076]    The soil and liquid mixture passes through third drum  20 C in substantially the same way as it passes through second drum  20 B. The drainage system of third drum  20 C is preferably substantially the same as that of second drum  20 B. By the time the soil and liquid mixture reaches discharge opening  202 C of third drum  20 C, there is typically no detectable amount of the first liquid cleaning agent or the contaminants remaining mixed in with the soil.  
         [0077]    Fourth and fifth drums  20 D and  20 E are used to rinse the majority of the second liquid cleaning agent from the soil and drain most of the water from the soil. As the soil and liquid mixture is deposited into intake opening  200 D of fourth drum  20 D, more fresh water is added from fresh water tank  29  by means of a hose (not shown) connected to liquid supply  33 .  
         [0078]    Fourth drum  20 D is shown in FIG. 4, and functions in much the same way as first drum  20 A, except that fourth drum  20 D has a drainage system, and water from fresh water tank  29  is added to fourth drum  20 D by means of a hose (not shown) connected to liquid supply  33 , along with the soil. The water may be heated before being added to fourth drum  20 D, to increase its ability to accept solutes.  
         [0079]    The drainage system of fourth drum  20 D comprises a liquid removal system and a liquid collection system. The liquid removal system of fourth drum  20 D preferably comprises a fine mesh screen  212 D and a slot  214 D. Screen  212 D forms the underside of fourth drum  20 D in a portion near its upper end  203 D. Screen  212 D is fine enough to retain soil particles while letting liquids pass through. For example, a suitable mesh size for screen  212 D is in the range of 20 to 80 mesh. Slot  214 D extends along the right side (when looking in direction of arrow  19 D) of drum  20 D. Slot  214 D is oriented generally horizontally when fourth drum  20 D is in its inclined position. In the preferred embodiment slot  214 D extends from screen  212 D partway to end plate  204 D. As paddles  240 D rotate clockwise (when looking in direction of arrow  19 B), soil is pushed up the left side of drum  20 D, away from slot  214 D. Liquids, however, will collect more or less in the middle of drum  20 D. Any liquids above the level of slot  214 D will drain through slot  214 D.  
         [0080]    Liquid collection system of fourth drum  20 D preferably comprises left drip tray  216 D, right drip tray  218 D and gutter  22 . As best seen in FIG. 4, left and right drip trays  216 D and  218 D are configured to collect any liquid exiting fourth drum  20 D through screen  212 D or slot  214 D and deliver it to gutter  22 .  
         [0081]    A chute  32  is attached to discharge opening  202 D. Chute  32  connects discharge opening  202 D of fourth drum  20 D to intake opening  200 E of fifth drum  20 E. Chute  32  is different from funneling member  30  to accommodate the structure of fifth drum  20 E, as described below.  
         [0082]    [0082]FIG. 10 shows how chute  32  connects fourth drum  20 D to fifth drum  20 E. One end of chute  32  is fitted over discharge opening  202 D of fourth drum  20 D to receive soil. The other end of chute  32  is fitted into intake opening  200 E of fifth drum  20 E to deliver soil into fifth drum  20 E. A hose (not shown) delivers water from water tank  29  to a sprayer  34  in chute  32 . Sprayer  34  delivers a pressurized stream of water down chute  32  so that chute  32  does not get clogged with soil.  
         [0083]    [0083]FIG. 7 shows the structure of fifth drum  20 E. Drum  20 E is similar to the forward portions of drums  20 B and  20 C. In addition to paddles  240 E, shaft  224 E has a screened cylinder  241 E mounted thereon. Screened cylinder  241 E has a diameter slightly less than the interior diameter of fifth drum  20 E. Soil is introduced into the interior of screened cylinder  241 E through intake opening  200 E which is formed through the upper portion of end plate  204 E. The liquid removal system of fifth drum  20 E preferably comprises slots  215 E in the bottom thereof. Liquid collection system of fifth drum  20 E preferably comprises drip trays  216 E,  218 E attached to the sides thereof to direct drained liquid into gutter  22 . Paddles  240 E are preferably larger than other paddles  240 A-D, and shaft  224 E may be rotated faster than other shafts  224 A-D for increased drainage of liquids from soil in fifth drum  20 E.  
         [0084]    After passing through fifth drum  20 E the soil, which is now clean but may have some water mixed in with it, exits fifth drum  20 E through discharge opening  202 E and is dumped onto discharge conveyor  18 . Discharge conveyor  18  deposits the clean (and possibly wet) soil on to the ground, or into a suitable soil transportation device (e.g. a truck) for return to the environment. Discharge conveyor  18  may be stored on trailer  12 , as indicated by dotted lines in FIG. 1 a.    
         [0085]    Returning briefly to FIG. 1 a , gutter  22  runs just below the left side of second through fifth drums  20 B-E. Gutter  22  is sloped so that liquids flow in the direction of arrows  21 . Reference numeral  23  in FIG. 1 a  indicates skimmer plates  23 , the operation of which is best described with reference to FIGS. 14, 15 a  and  15   b.    
         [0086]    As seen in FIGS. 14, 15 a  and  15   b , gutter  22  has slots  24  into which removable skimmer plates  23  may be inserted. Skimmer plates  23  prevent any fine soil particles that escape drums  20  from reaching sump  25 . Liquid builds up upstream of skimmer plates  23 , and then flows over skimmer plates  23 , while solid particles are collected at the bases of skimmer plates  23 .  
         [0087]    As seen in FIG. 16, gutter  22  drains into sump  25  through a fine screen  26 . Screen  26  is designed to remove any remaining solid particles from the liquid entering sump  25 . Screen  26  preferably has a mesh size of 80 to 120 mesh. Liquid from sump  25  is pumped into holding tank  31 , where it is stored until it can be hauled by a tank truck to an appropriate processing facility, such as a digester.  
         [0088]    As shown in FIG. 13, in the preferred embodiment, shafts  224  are each turned by a suitable drive means. In the illustrated embodiment the drive means comprises a motor  220 . Motor  220  has a driving sprocket  222  attached thereto. Each drum  20  has a shaft  224  extending through the center thereof and out shaft receiving hole  208 , and a bearing assembly  226 . Bearing assembly  226  serves to allow shaft  224  to rotate freely in shaft receiving hole  208 . Driven sprocket  236  is non-rotatably attached to shaft  224 .  
         [0089]    Driving sprocket  222  is operably coupled to driven sprocket  236  by means of a chain  238 . When in operation, motor  220  turns driving sprocket  222 . This rotational motion is transferred to driven sprocket  236 , and thus shaft  224 , through chain  238 . Driving sprocket  222  may be selected to be smaller than driven sprocket  236  so that shaft  224  rotates much slower than motor  220 . It will be apparent to one skilled in the art that there are many other functionally equivalent ways to turn the shafts  224 , any of which may be used.  
         [0090]    Shaft  224 E is turned by motor  220 E in the same way as for drums  20 A-D. However, shaft  224 E is longer, and extends farther away from end plate  204 E, than other shafts  224 A-D This allows sprocket  236 E to keep clear of chute  32 . Sprocket  236 E is smaller than sprockets  236 A-D so that shaft  224 E rotates faster than shafts  224 A-D.  
         [0091]    [0091]FIGS. 12 a  and  12   b  show how a replaceable wear plate  250  may be attached as the end of a blade  242  by means of a nut and bolt assembly  251 . As soil is fed through apparatus  10 , blades  242  may become worn. Wear plates  250  simplify maintenance by allowing replacement of the ends of blades  242 , rather than replacement of the entire paddle  240 , which is preferably permanently attached, for example by welding, to shaft  224 . The ends of blades  242  are the portions that will likely wear out first.  
         [0092]    Returning to FIG. 2, a rock washer  40  may be used in conjunction with the drums  20 . Rock washer  40  may be attached to trailer  12  adjacent first drum  20 A by means of bracket  41 . The position of rock washer  40  relative to drums  20  can be seen in FIG. 2. Alternatively, rock washer  40  may be mounted on the rear of trailer  12 , so that it may remain attached to trailer  12  during transport. Occasionally, large rocks  42  that could damage drums  20  may fall into hopper  14 . To prevent rocks  42  from entering drums  20 , a grate  44  is placed at the end of intake conveyor  16 , above intake opening  200 A of first drum  20 A. Grate  44  is angled so that rocks  42  fall into rock washer  40 .  
         [0093]    Rock washer  40  comprises funnel  46 , screen  48  and walls  50 . Rocks  42  are dropped onto screen  48  and walls  50  prevent rocks  42  from falling to the ground. Rocks  42  may be washed while sitting on screen  48 . Any liquid used in washing rocks  42  falls through screen  48  into funnel  46  to be collected in bucket  52 . Rocks  42  may be returned to the ground when they are clean.  
         [0094]    As shown in FIG. 1 a , drums  20  may be arranged on trailer  12  so that path  13  has a generally “U” shape when viewed form above. This provides a reasonably compact and easily transportable configuration.  
         [0095]    As will be apparent to those skilled in the art in the light of the foregoing disclosure, many alterations and modifications are possible in the practice of this invention without departing from the spirit or scope thereof. For example:  
         [0096]    a different number of drums could be used;  
         [0097]    the drums need not be cylindrical—they could have a rectangular cross-section as long as the motivators are adapted to move soil along the rectangular drums, for example, by moving the paddles longitudinally up along the bottoms of the drums;  
         [0098]    other drive means may be provided to drive the soil motivators;  
         [0099]    one motor or engine could drive multiple soil motivators by way of a suitable power transmission system;  
         [0100]    the motors may be operably connected to the shaft in a number of different manners;  
         [0101]    the shafts may be turned by means other than the motors described above;  
         [0102]    the motivators may comprise augers with interrupted blades;  
         [0103]    the first and second liquid cleaning agents could comprise chemicals other than those described herein having similar characteristics;  
         [0104]    the first and second liquid cleaning agents could both comprise the same biodegradable agent;  
         [0105]    the intake and discharge conveyors could be replaced with chutes;  
         [0106]    the trailer could have sides and a roof for use in cold temperatures;  
         [0107]    apparatus according to the invention could comprise separate trailers, one trailer for the drums and another trailer for the tanks;  
         [0108]    apparatus according to the invention could be mounted or placed on a barge for use in cleaning up shoreline spills;  
         [0109]    the invention could be practiced as a stationary treatment facility with larger drums, storage tanks, gutters and sump;  
         [0110]    the screens may be replaced with screens having a different mesh size for use with different types of soil.  
         [0111]    Accordingly, the scope of the invention is to be construed in accordance with the substance defined by the following claims.