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CLAIM OF PRIORITY 
     This application is a continuation of U.S. patent application Ser. No. 13/724,559, filed Dec. 21, 2012, now U.S. Pat. No. 8,667,717, which is a continuation of U.S. patent application Ser. No. 13/175,510, filed Jul. 1, 2011, now U.S. Pat. No. 8,336,231, which is a continuation of U.S. patent application Ser. No. 12/361,242, filed Jan. 28, 2009 (abandoned), which is a continuation of U.S. patent application Ser. No. 10/971,455, filed Oct. 22, 2004, now U.S. Pat. No. 7,484,322, the entire disclosures which are incorporated by reference herein. 
    
    
     FIELD OF THE INVENTION 
     This invention relates generally to a reduction system for removing soil to expose underground utilities (such as electrical and cable services, water and sewage services, etc.), and more particularly to a system for removing materials from the ground and backfilling the area. 
     BACKGROUND OF THE INVENTION 
     With the increased use of underground utilities, it has become more critical to locate and verify the placement of buried utilities before installation of additional underground utilities or before other excavation or digging work is performed. Conventional digging and excavation methods such as shovels, post hole diggers, powered excavators, and backhoes may be limited in their use in locating buried utilities as they may tend to cut, break, or otherwise damage the lines during use. 
     Devices have been previously developed to create holes in the ground to non-destructively expose underground utilities to view. One design uses high pressure air delivered through a tool to loosen soil and a vacuum system to vacuum away the dirt after it is loosened to form a hole. Another system uses high pressure water delivered by a tool to soften the soil and create a soil/water slurry mixture. The tool is provided with a vacuum system for vacuuming the slurry away. 
     SUMMARY OF THE INVENTION 
     The present invention recognizes and addresses disadvantages of prior art constructions and methods, and it is an object of the present invention to provide an improved drilling and backfill system. This and other objects may be achieved by a mobile digging and backfill system for removing and collecting material above a buried utility. The system comprises a mobile chassis, a collection tank mounted to the chassis, a water pump mounted to the chassis for delivering a pressurized liquid flow against the material for loosening the material at a location, a vacuum pump connected to the collection tank so that an air stream created by the vacuum pump draws the material and the fluid from the location into the collection tank, and at least one backfill reservoir mounted to the chassis for carrying backfill for placement at the location. 
     In another embodiment, a mobile digging and backfill system for removing and collecting material comprises a mobile digging and backfill system for removing and collecting material. The system has a mobile chassis, a collection tank moveably mounted to the chassis, and a digging tool comprising at least one nozzle and a vacuum passage proximate the nozzle. A water pump mounted on the chassis has an output connected to the nozzle for delivering a pressurized liquid flow against the material for loosening the material at a location. A vacuum pump mounted on the chassis has an input connected to the collection tank so that an air stream created by the vacuum pump draws the material and the fluid from the location into the collection tank. A motor mounted to the chassis and is in driving engagement with the water pump and said vacuum pump. A first backfill reservoir is moveably mounted on the chassis for carrying backfill for placement at the location. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A full and enabling disclosure of the present invention, including the best mode thereof directed to one of ordinary skill in the art, is set forth in the specification, which makes reference to the appended figures, in which: 
         FIG. 1  is a perspective view of a drilling and backfill system constructed in accordance with one embodiment of the present invention; 
         FIG. 2  is a perspective view of a key hole drill for use with the drilling and backfill system of  FIG. 1 ; 
         FIG. 3  is a perspective view of a reduction tool for use with the drilling and backfill system of  FIG. 1 ; 
         FIG. 4  is bottom view of the reduction tool shown in  FIG. 3 ; 
         FIG. 5  is a partial perspective view of the reduction tool of  FIG. 3  in use digging a hole; 
         FIG. 6  is a perspective view of a key hole drilling tool base for use with the key hole drill of  FIG. 2 ; 
         FIG. 6A  is a bottom perspective view of the tool base shown in  FIG. 6 ; 
         FIG. 7  is a perspective view of the reduction tool of  FIG. 3  in use digging the hole; 
         FIG. 8  is a perspective view of the drilling and backfill system of  FIG. 1 , showing the hole being backfilled; 
         FIG. 9  is a perspective view of the drilling and backfill system of  FIG. 1 , showing the hole being tamped; and 
         FIG. 10  is a schematic view of the hydraulic, electric, water, and vacuum systems of the drilling and backfill system of  FIG. 1 . 
     
    
    
     Repeat use of reference characters in the present specification and drawings is intended to represent same or analogous features or elements of the invention. 
     DETAILED DESCRIPTION 
     Reference will now be made in detail to presently preferred embodiments of the invention, one or more examples of which are illustrated in the accompanying drawings. Each example is provided by way of explanation of the invention, not limitation of the invention. In fact, it will be apparent to those skilled in the art that modifications and variations can be made in the present invention without departing from the scope and spirit thereof. For instance, features illustrated or described as part of one embodiment may be used on another embodiment to yield a still further embodiment. Thus, it is intended that the present invention covers such modifications and variations as come within the scope of the appended claims and their equivalents. 
     Referring to  FIG. 1 , a drilling and backfill system  10  generally includes a water reservoir tank  12 , a collection tank  14 , a motor  16 , a drilling apparatus  18 , and back fill reservoirs  20  and  22 , all mounted on a mobile chassis  24 , which is, in this embodiment, in the form of a trailer. Trailer  24  includes four wheels  38  (only three of which are shown in  FIG. 1 ) and a draw bar and hitch  40 . Drilling and backfill system  10  generally mounts on a platform  42 , which is part of trailer  24 . It should be understood that while drill and backfill system  10  is illustrated mounted on a trailer having a platform, the system may also be mounted on the chassis of a vehicle such as a truck or car. Further, a chassis may comprise any frame, platform or bed to which the system components may be mounted and that can be moved by a motorized vehicle such as a car, truck, or skid steer. It should be understood that the components of the system may be either directly mounted to the chassis or indirectly mounted to the chassis through connections with other system components. 
     The connection of the various components of system  10  is best illustrated in  FIG. 10 . Motor  16  is mounted on a forward end of trailer  24  and provides electricity to power two electric hydraulic pumps  30  and  172 , and it also drives both a water pump  26  and a vacuum pump  28  by belts (not shown). Motor  16  is preferably a gas or diesel engine, although it should be understood that an electric motor or other motive means could also be used. In one preferred embodiment, motor  16  is a thirty horsepower diesel engine, such as Model No. V1505 manufactured by Kubota Engine division of Japan, or a twenty-five horsepower gasoline engine such as Model Command PRO CH25S manufactured by Kohler Engines. The speed of motor  16  may be varied between high and low by a wireless keypad transmitter  108  that transmits motor speed control to a receiver  110  connected to the throttle of motor  16 . 
     The water system will now be described with reference to  FIG. 10 . Water reservoir tank  12  connects to water pump  26 , which includes a low pressure inlet  44  and a high pressure outlet  46 . In the illustrated embodiment, water pump  26  can be any of a variety of suitable pumps that delivers between 3,000 and 4,000 lbs/in 2  at a flow rate of approximately five gallons per minute. In one preferred embodiment, water pump  26  is a Model No. TS2021 pump manufactured by General Pump. Water tank  12  includes an outlet  50  that connects to a strainer  52  through a valve  54 . The output of strainer  52  connects to the low pressure side of water pump  26  via a hose  48 . A check valve  56  is placed inline intermediate strainer  52  and low pressure inlet  44 . High pressure outlet  46  connects to a filter  58  and then to a pressure relief and bypass valve  60 . In one preferred embodiment, pressure relief and bypass valve  60  is a Model YUZ140 valve manufactured by General Pump. 
     A “T”  62  and a valve  64 , located intermediate valve  60  and filter  58 , connect the high pressure output  46  to a plurality of clean out nozzles  66  mounted in collection tank  14  to clean the tank&#39;s interior. A return line  68  connects a low pressure port  69  of valve  60  to water tank  12 . When a predetermined water pressure is exceeded in valve  60 , water is diverted through low port  69  and line  68  to tank  12 . A hose  70 , stored on a hose reel  73  ( FIG. 1 ), connects an output port  72  of valve  60  to a valve  74  on a digging tool  32  ( FIG. 3 ). A valve control  76  ( FIG. 3 ) at a handle  78  of digging tool  32  provides the operator with a means to selectively actuate valve  74  on digging tool  32 . The valve delivers a high pressure stream of water through a conduit  80  ( FIGS. 3, 5, 7, and 10 ) attached to the exterior of an elongated pipe  82  that extends the length of digging tool  32 . 
     Referring to  FIG. 3 , digging tool  32  includes handle  78  for an operator  34  ( FIG. 7 ) to grasp during use of the tool. A connector  84 , such as a “banjo” type connector, connects the vacuum system on drilling and back fill system  10  ( FIG. 1 ) to a central vacuum passage  86  ( FIG. 4 ) in digging tool  32 . Connector  84  is located proximate handle  78 . Vacuum passage  86  extends the length of elongated pipe  82  and opens to one end of a vacuum hose  88 . The other end of hose  88  connects to an inlet port  90  on collection tank  14  ( FIG. 7 ). It should be understood that other types of connectors may be used in place of “banjo” connector  84 , for example clamps, clips, or threaded ends on hose  88  and handle  78 . 
     Referring to  FIGS. 4 and 5 , a fluid manifold  92 , located at a distal end  94  of digging tool  32 , connects to water conduit  80  and contains a plurality of nozzles that are angled with respect to one another. In one preferred embodiment having four nozzles, two nozzles  96  and  98  are directed radially inwardly at approximately 45 degrees from a vertical axis of the digging tool, and the two remaining nozzles  100  and  102  are directed parallel to the axis of the digging tool. During use of the drilling tool, nozzles  96  and  98  produce a spiral cutting action that breaks the soil up sufficiently to minimize clogging of large chunks of soil within vacuum passage  86  and/or vacuum hose  88 . Vertically downward pointing nozzles  100  and  102  enhance the cutting action of the drilling tool by allowing for soil to be removed not only above a buried utility, but in certain cases from around the entire periphery of the utility. In other words, the soil is removed above the utility, from around the sides of the utility, and from beneath the utility. This can be useful for further verifying the precise utility needing service and, if necessary, making repairs to or tying into the utility. 
     Digging tool  32  also contains a plurality of air inlets  104  formed in pipe distal end  94  that allow air to enter into vacuum passage  86 . The additional air, in combination with the angled placement of nozzles  96  and  98 , enhances the cutting and suction provided by tool  32 . Returning to  FIG. 6 , digging tool  32  may also include a control  106  for controlling the tool&#39;s vacuum feature. Control  106  may be an electrical switch, a vacuum or pneumatic switch, a wireless switch, or any other suitable control to adjust the vacuum action by allowing the vacuum to be shut off or otherwise modulated. An antifreeze system, generally  190  ( FIGS. 1 and 2 ), may be provided to prevent freezing of the water pump and the water system. Thus, when the pump is to be left unused in cold weather, water pump  26  may draw antifreeze from the antifreeze reservoir through the components of the water system to prevent water in the hoses from freezing and damaging the system. 
     Turning now to  FIGS. 7 and 10 , vacuum pump  28  is preferably a positive displacement type vacuum pump such as that used as a supercharger on diesel truck. In one preferred embodiment, vacuum pump  28  is a Model 4009-46R3 blower manufactured by Tuthill. A hose  112  connects an intake of the vacuum pump to a vacuum relief device  114 , which may be any suitable vacuum valve, such as a Model 215V-H01AQE spring loaded valve manufactured by Kunkle. Vacuum relief device  114  controls the maximum negative pressure of the vacuum pulled by pump  28 , which is in the range of between 10 and 15 inches of Hg in the illustrated embodiment. A filter  116 , located up stream of pressure relief valve  114 , filters the vacuum air stream before it passes through vacuum pump  28 . In one preferred embodiment, the filter media may be a paper filter such as those manufactured by Fleet Guard. Filter  116  connects to an exhaust outlet  118  of collection tank  14  by a hose  120 , as shown in  FIGS. 1, 7, 8, and 9 . An exhaust side  122  of vacuum pump  28  connects to a silencer  124 , such as a Model TS30TR silencer manufactured by Cowl. The output of silencer  124  exits into the atmosphere. 
     The vacuum air stream pulled through vacuum pump  28  produces a vacuum in collection tank  14  that draws a vacuum air stream through collection tank inlet  90 . When inlet  90  is not closed off by a plug  127  ( FIG. 1 ), the inlet may be connected to hose  88  leading to digging tool  32 . Thus, the vacuum air stream at inlet  90  is ultimately pulled through vacuum passage  86  at distal end  94  of tool  32 . Because it is undesirable to draw dirt or other particulate matter through the vacuum pump, a baffle system, for example as described in U.S. Pat. No. 6,470,605 (the entire disclosure which is incorporated herein), is provided within collection tank  14  to separate the slurry mixture from the vacuum air stream. Consequently, dirt, rocks, and other debris in the air flow hit a baffle (not shown) and fall to the bottom portion of the collection tank. The vacuum air stream, after contacting the baffle, continues upwardly and exits through outlet  118  through filter  116  and on to vacuum pump  28 . 
     Referring once again to  FIG. 1 , collection tank  14  includes a discharge door  126  connected to the main tank body by a hinge  128  that allows the door to swing open, thereby providing access to the tank&#39;s interior for cleaning. A pair of hydraulic cylinders  130  (only one of which is shown in  FIG. 8 ) are provided for tilting a forward end  132  of tank  14  upwards in order to cause the contents to run towards discharge door  126 . A gate valve  140 , coupled to a drain  142  in discharge door  126 , drains the liquid portion of the slurry in tank  14  without requiring the door to be opened. Gate valve  140  may also be used to introduce air into collection tank  14  to reduce the vacuum in the tank so that the door may be opened. 
     Running the length of the interior of collection tank  14  is a nozzle tube  132  ( FIG. 10 ) that includes nozzles  66  for directing high pressure water about the tank, and particularly towards the base of the tank. Nozzles  66  are actuated by opening valve  64  ( FIG. 10 ), which delivers high pressure water from pump  26  to nozzles  66  for producing a vigorous cleaning action in the tank. When nozzles  66  are not being used for cleaning, a small amount of water is allowed to continuously drip through the nozzles to pressurize them so as to prevent dirt and slurry from entering and clogging the nozzles. 
     Nozzle tube  132 , apart from being a conduit for delivering water, is also a structural member that includes a threaded male portion (not shown) on an end thereof adjacent discharge door  126 . When discharge door  126  is shut, a screw-down type handle  134  mounted in the door is turned causing a threaded female portion (not shown) on tube  132  to mate with the male portion. This configuration causes the door to be pulled tightly against an open rim (not shown) of the collection tank. Actuation of vacuum pump  28  further assists the sealing of the door against the tank opening. Discharge door  126  includes a sight glass  136  to allow the user to visually inspect the tank&#39;s interior. 
     Backfill reservoirs  20  and  22  are mounted on opposite sides of collection tank  14 . The back fill reservoirs are mirror images of each other; therefore, for purposes of the following discussion, reference will only be made to backfill reservoir  22 . It should be understood that backfill reservoir  20  operates identically to that of reservoir  22 . Consequently, similar components on backfill reservoir  20  are labeled with the same reference numerals as those on reservoir  22 . 
     Referring to  FIG. 1 , back fill reservoir  22  is generally cylindrical in shape and has a bottom portion  144 , a top portion  146 , a back wall  148 , and a front wall  150 . Top portion  146  connects to bottom portion  144  by a hinge  152 . Hinge  152  allows backfill reservoir  22  to be opened and loaded with dirt by a front loader  154 , as shown in phantom in  FIG. 1 . Top portion  146  secures to bottom portion  144  by a plurality of locking mechanisms  156  located on the front and back walls. Locking mechanisms  156  may be clasps, latches or other suitable devices that secure the top portion to the bottom portion. The seam between the top and bottom portion does not necessarily need to be a vacuum tight seal, but the seal should prevent backfill and large amounts of air from leaking from or into the reservoir. Front wall  150  has a hinged door  158  that is secured close by a latch  160 . As illustrated in  FIG. 8 , hydraulic cylinders  130  enable the back fill reservoirs to tilt so that dirt can be off loaded through doors  158 . 
     As previously described above, backfill reservoirs  20  and  22  may be filled by opening top portions  146  of the reservoirs and depositing dirt into bottom portion  144  with a front loader. Vacuum pump  28 , however, may also load dirt into back fill reservoirs  20  and  22 . In particular, back fill reservoir  22  has an inlet port  162  and an outlet port  164 . During normal operation, plugs  166  and  168  fit on respective ports  162  and  164  to prevent backfill from leaking from the reservoir. However, these plugs may be removed, and outlet port  164  may be connected to inlet port  90  on collection tank  14  by a hose (not shown), while hose  88  may be attached to inlet port  162 . In this configuration, vacuum pump  28  pulls a vacuum air stream through collection tank  14 , as described above, through the hose connecting inlet port  90  to outlet port  164 , and through hose  88  connected to inlet port  162 . Thus, backfill dirt and rocks can be vacuumed into reservoirs  20  and  22  without the aide of loader  154 . It should be understood that this configuration is beneficial when backfill system  10  is being used in an area where no loader is available to fill the reservoirs. Once the reservoirs are filled, the hoses are removed from the ports, and plugs  166  and  168  are reinstalled on respective ports  162  and  164 . 
     Referring once more to  FIG. 10 , hydraulic cylinders  130 , used to tilt collection tank  14  and backfill reservoirs  20  and  22 , are powered by electric hydraulic pump  30 . Hydraulic pump  30  connects to a hydraulic reservoir  170  and is driven by the electrical system of motor  16 . A high pressure output line  171  and a return line  173  connect pump  30  to hydraulic cylinders  130 . Hydraulic pump  172 , mounted on trailer  24 , is separately driven by motor  16  and includes its own hydraulic reservoir  174 . An output high pressure line  175  and a return line  186  connect pump  172  to a pair of quick disconnect couplings  182  and  184 , respectively. That is, high pressure line  175  connects to quick disconnect coupling  182  ( FIGS. 1 and 2 ) through a control valve  178 , and return line  186  connects quick disconnect coupling  184  to reservoir  188 . A pressure relief valve  176  connects high pressure line  175  to reservoir  188  and allows fluid to bleed off of the high pressure line if the pressure exceeds a predetermined level. A pressure gauge  180  may also be located between pump  172  and control valve  178 . 
     Quick disconnect coupling  182  provides a high pressure source of hydraulic fluid for powering auxiliary tools, such as drilling apparatus  18 , tamper device  185 , or other devices that may be used in connection with drilling and backfill system  10 . The high pressure line preferably delivers between 5.8 and 6 gallons per minute of hydraulic fluid at a pressure of 2000 lbs/in 2 . Hydraulic return line  186  connects to a quick disconnect coupling  184  ( FIGS. 1 and 2 ) on trailer  24 . Intermediate quick disconnect coupling  184  and hydraulic fluid reservoir  174  is a filter  188  that filters the hydraulic fluid before returning it to hydraulic reservoir  174 . While quick disconnect couplings  182  and  184  are shown on the side of trailer  24 , it should be understood that the couplings may also be mounted on the rear of trailer  24 . 
     Referring to  FIGS. 1 and 2 , drilling apparatus  18  is carried on trailer  24  and is positioned using winch and crane  36 . Drilling apparatus  18  includes a base  192 , a vertical body  194 , and a hydraulic drill motor  196  slidably coupled to vertical body  194  by a bracket  198 . A high pressure hose  200  and a return hose  202  power motor  196 . A saw blade  204  attaches to an output shaft of hydraulic motor  196  and is used to drill a coupon  206  ( FIG. 7 ) in pavement, concrete or other hard surfaces to expose the ground above the buried utility. The term coupon as used herein refers to a shaped material cut from a continuous surface to expose the ground beneath the material. For example, as illustrated in  FIG. 7 , coupon  206  is a circular piece of concrete that is cut out of a sidewalk to expose the ground thereunder. 
     Body  194  has a handle  220  for the user to grab and hold onto during the drilling process. Hydraulic fluid hoses  200  and  202  connect to two connectors  222  and  224  ( FIG. 10 ) mounted on body  194  and provide hydraulic fluid to hydraulic drill motor  196 . A crank  226  is used to move the drill motor vertically along body  194 . Drilling apparatus  18  is a Model CD616 Hydra Core Drill manufactured by Reimann &amp; Georger of Buffalo, N.Y. and is referred to herein as a “core drill.” 
     In prior art systems, base  192  was secured to pavement or concrete using lag bolts, screws, spikes, etc. These attachment methods caused unnecessary damage to the surrounding area and required additional repair after the utility was fixed and the hole was backfilled. Additionally, having to drill additional holes for the bolts or screws or pounding of the spikes with a sledge hammer presented unnecessary additional work. Thus, the drilling apparatus of the present invention uses the vacuum system of drilling and backfill system  10  to secure base  192  to the pavement. 
     Referring to  FIGS. 6 and 6A , base  192  includes a flat plate  195  having a connector  206  attached to a top surface thereof. Connector  206  attaches to an outlet port  208  formed in a top surface of plate  195  that is in fluid communication with a recessed chamber  210  ( FIG. 6A ) formed in a bottom surface  212  of plate  195 . That is, outlet port  208  has a passageway therethrough that extends between the top and bottom surfaces. A groove  230  formed in bottom surface  212  receives a pliable gasket  232  that forms a relatively air tight seal between the bottom surface  212  and the pavement or concrete being drilled. It should be understood that while a gasket is shown, it may not be necessary depending on the strength of the vacuum air stream being pulled through connector  206  since bottom surface  212  can form a sufficient seal with the pavement or concrete. A bracket  214  coupled to a top surface of plate  195  fixedly secures body  194  ( FIG. 2 ) to base  192 . A bolt or screw  216  is received through body  194  and into a threaded bore  218  to secure the body to the base. Wheels attached to the base allow the drilling apparatus to be moved around the work area after it has been off loaded the trailer by winch and crane  36 . The term “base” as used herein refers to a drill support structure that maintains a secure connection of the drill to a surface proximate the area to be drilled. The drill base should have a generally planar bottom surface, and the remaining structure of the base may be of any suitable shape to secure the drill motor to the base. 
     Referring to  FIG. 2 , hose  88  connects to connector  206  by a suitable clamp (not shown). Once core drill  18  is positioned, vacuum pump  26  is turned on and a vacuum is pulled through hose  88  into chamber  210 , providing a vacuum of between 12-15 inches of Hg, which is sufficient to fixedly secure base  192  to the pavement or concrete during the drilling process. Prior to moving core drill  18 , vacuum pump  28  is shut down to eliminate the vacuum produced in chamber  210 . 
     The operation of the drilling and backfill system will now be described with reference to  FIGS. 2, 7 to 9 and 10 . Prior to using drilling and backfill system  10 , water is added to water tank  12 , and valve  54  is opened to allow water to flow to water pump  26 . Motor  16  is powered up, and water pressure is allowed to build in the system. 
     Referring to  FIG. 2 , if a utility is located under concrete, core drill  18  is positioned over the utility, and vacuum hose  88  is connected from inlet port  90  on collection tank  14  to connector  206  on base plate  195 . Hydraulic hoses  200  and  202  are connected to hydraulic motor  196  at connectors  222  and  224 , and vacuum pump  28  and hydraulic pump  172  are powered up. Saw  204  is used to cut coupon  206  ( FIG. 7 ) from the concrete to expose the ground over the utility. Hose  70  connects to saw  204  and provides a steady stream of water that flushes the drill bit during the drilling process. Coupon  206  is removed from the hole and placed aside so that it can be reused in repairing the hole after it is backfilled. 
     Next, and referring to  FIG. 7 , the user disconnects vacuum hose  88  from connector  206  and connects the hose to digging tool handle  78  using banjo connector  84 . High pressure water hose  70  is also connected to valve  74  to provide water to the digging tool. As tool  32  is used, it is pressed downwardly into the ground to dig a hole. For larger diameter holes, digging tool  32  is moved in a generally circular manner as it is pressed downward. Slurry formed in the hole is vacuumed by tool  32  through vacuum passage  86  ( FIGS. 4 and 5 ) and accumulates in collection tank  26 . Once the hole is completed and the utility exposed, the vacuum system can be shut down, and the operators may examine or repair the utility as needed. 
     After work on the utility is completed, and referring to  FIG. 8 , the operator may cover the utility with clean backfill from backfill reservoirs  20  and  22 . In particular, trailer  24  is positioned so that one of backfill reservoirs  20  or  22  is proximate the hole. Hydraulic cylinders  130  are activated, causing the tanks to tip rearward so that backfill can be delivered through door  158  into the hole. Once the hole is sufficiently filled, hydraulic cylinders  130  return reservoirs  20  and  22  to their horizontal position, and door  158  is secured in the closed position. 
     With reference to  FIG. 9 , operator  34  may use a tamping device  185  to tamp the backfill in the hole. Tamping device  185  connects to hydraulic pump  172  through quick disconnect couplings  182  and  184  via hydraulic lines  200  and  202 . Tamping device  185  is used to pack the backfill in the hole and to remove any air pockets. Once the hole has been filed and properly packed, coupon  206  is moved into the remaining portion of the hole. The reuse of coupon  206  eliminates the need to cover the hole with new concrete. Instead, coupon  206  is placed in the hole, and grout is used to seal any cracks between the key and the surrounding concrete. Thus, the overall cost and time of repairing the concrete is significantly reduced, and the need for new concrete is effectively eliminated. 
     Drilling and backfill system  10  can be used to dig multiple holes before having to empty collection tank  14 . However, once collection tank  14  is full, it can be emptied at an appropriate dump site. In emptying collection tank  14 , motor  16  is idled to maintain a vacuum in tank  14 . This allows the door handle to be turned so that the female threaded member (not shown) is no longer in threading engagement with the male member (not shown) on nozzle rod  132 , while the vacuum pressure continuing to hold the door closed. Once motor  16  is shut down, the vacuum pressure is released so that air enters the tank, thereby pressurizing the tank and allowing the door to be opened. Once opened, hydraulic cylinders  130  can be activated to raise forward end  132  upward dumping the slurry from the tank. 
     Collection tank  14  may also include a vacuum switch and relay (not shown) that prevents the tank from being raised for dumping until the vacuum in the tank has dropped below a predetermined level for door  126  to be opened. Once the vacuum in the tank has diminished to below the predetermined level, tank  14  may be elevated for dumping. This prevents slurry from being pushed up into filter  116  if door  126  can not open. 
     It should be appreciated by those skilled in the art that various modifications and variations can be made in the present invention without departing from the scope and spirit of the invention. It is intended that the present invention cover such modifications and variations as come within the scope and spirit of the appended claims and their equivalents.

Summary:
A mobile digging and backfill system for removing and collecting material above a buried utility. The system comprises a mobile chassis, a collection tank mounted to the chassis, a water pump mounted to the chassis for delivering a pressurized liquid flow against the material for loosening the material at a location, a vacuum pump connected to the collection tank so that an air stream created by the vacuum pump draws the material and the fluid from the location into the collection tank, and at least one backfill reservoir mounted to the chassis for carrying backfill for placement at the location.