according to the present invention , the general area of a leak in a pipeline is first located . generally , this is accomplished using conventional techniques , with television cameras or the like . the particular way in which the general location is determined is not significant to the invention , nor is the precise location of the leak . after the general location is determined , a opening into the ground is made to more accurately locate the pipe . preferably , the opening is relatively small in size , ranging from 6 inch by 6 inch , up to 12 inch by 12 inch . the hole need not be of regular size or shape . rather than using a boring implement , such as a drill or auger , the invention makes use of a vacuum excavation technique . this technique utilizes a combination of a high velocity fluid nozzle or jet and a vacuum line . the fluid typically is supplied at a volume of about 100 to 250 cubic feet per minute at a pressure of less than 100 psi . the fluid jet dislodges material in the hole , while the vacuum line removes excess fluid and dislodged material . the fluid used may be air or water or other appropriate fluid . water , soil , rock and various other materials removed from the hole by the vacuum line are placed into a suitable receptacle , such as a tank . the entire system may be mounted on a truck , and the excavated material may be vacuumed into tank on the truck for collection and removal . optionally the removed material may be reused . using this vacuum excavation technique , only a small diameter hole is made into the ground . this hole can be used as a visual inspection hole . further , this technique will not damage the sewer line or other utility lines which might be encountered during the excavation , and the work crew is not exposed to dangers of working around excavating equipment or working in excavations . should an obstruction be encountered during the vacuum excavation operation , a simple redirecting of the direction of the jet nozzle will enable the operator to go around the object without damaging it . once the hole is at the proper depth , again by redirecting the jet nozzle , the excavation may be directed in order to precisely locate the pipe and the leak . indeed , unlike the prior art methods , the excavation around the pipe can be easily enlarged so as to expose more of the pipe , whereby a visual inspection could reveal a large hole , break or other deterioration which would require removal and replacement of the pipe . in most cases , the pipe will not need to be replaced , and the present process may be continued in order to stop the infiltration into the pipe . once the general location of the leak has been reached by the vacuum excavation step , a water swellable material is introduced into the hole . preferably this water swellable material is powdered or granular in nature , and is of such a physical characteristic that the swelling is not instantaneous , but occurs over a relatively short period of time . this will allow the material to flow in dry form into the interstices in the ground , and then be carried some distance into the pores of the ground , gradually swelling until it blocks the flow . a preferred type of water swellable material is a naturally occurring argillaceous material which by nature is non - polluting and can be simply poured into the hole in dry , bulk form . the argillaceous material is one , or a mixture of more than one of the class of naturally occurring clays which are well known to expand by hydration upon contact with water . one of the most commonly known of such clays is bentonite . another common water swellable clay is attapulgite , and still other such clays are known and useable , although they are generally not as readily available . the clay is generally packaged in bulk , granular or powdered form , for example in bags of 50 to 100 pounds for ease of handling . the clay is a low cost , naturally occurring material mined in various parts of the world . thus , this material is not considered to be a contaminant to soils or groundwater . the quantity of the material poured into the hole will vary slightly depending upon the size of the excavation , but generally would be used to a depth of at least about 1 foot above the pipe . the use of excess material is not harmful , and because of the low cost , an excess is not a significant factor . generally , excess material should be used over the minimum needed to accomplish the purpose . after placement into the hole , the clay may be tamped in place , and a quantity of gravel is then placed over the clay material . preferably , the hole is completely backfilled with gravel . when the backfilling of the hole is completed , any small resurfacing of a street may be done by a simple patch . within a short period of time , groundwater will again reach the area of the leak , but will first encounter the argillaceous compound . upon contact , the clay may migrate slightly toward the leak with the water and will begin to swell . with the swelling , the flow into the pipe will gradually diminish , and in a short period of time , the flow will stop . at this time , the leak is repaired . at this point , it should be pointed out that it is not necessary that the clay material be in contact with the pipe or the leak when it is placed into the hole , since the migration will always be toward the leak and into the pipe , and the swelling of the clay while it fills the interstices in the soil will stop the flow of the water . with excess clay in place , the swelling will ensure a complete blockage of the flow of water into the pipe . thus , the clay does not necessarily plug up the hole or leak in the pipe , but may also prevent the groundwater from reaching the pipe , accomplishing the same purpose . in the event that insufficient clay was introduced into the hole , the excavation may be re - opened in the same manner . at this time , however , the vacuum excavation will be through the gravel backfill material , and will be more easily accomplished , and there will be no hardened cement or other material or product ( i . e . clamps ) surrounding the pipe to impair the process . instead , the original clay will be removed by the vacuum excavation process , and may then be replaced in greater quantity than before . through trial and error , at very low cost , the proper amount of clay for a given hole may be readily determined . in a preferred embodiment , a water soluble , and environmentally suitable dye is incorporated into the water swellable material . the dye may be a simple food coloring type of dye , or may be a fluorescent dye visible under ultraviolet light . with the use of such a dye , the effectiveness of the leak stoppage may be readily determined by inspection through a downstream manhole . as the inflow of groundwater into the pipe diminishes , the dye will gradually disappear in the sewer line , until the inflow is completely stopped , at which time no dye will be present in the water flowing through the pipe . experience has shown that by using this method , the inflow into a sewer line can be completely stopped in less than 24 hours after the work begins . further , since such a small hole is used , very slight disruption of traffic flow or other surface uses is encountered . any repair of a street surface is minimal , and can be accomplished simply with a small patch , rather than a repaving operation . further , the materials introduced to accomplish the goal do not contaminate the soil or the groundwater . the invention has the additional advantage that the process performed externally of the sewer pipe , can also function without additional work , to stop exfiltration , or outflow , from the sewer pipe . generally , exfiltration is not a problem , since the hydrostatic pressure surrounding the sewer pipe is ordinarily greater than the pressure within the pipe . however , it is possible that the pressure within the pipe will increase , particularly if the water is blocked from reaching the pipe externally . when this happens , the water in the pipe can flow outwardly through the leak in the pipe . however , when it does so , it will contact the water swellable material external to the pipe , and will be blocked by essentially the same mechanism . thus , any exfiltration is effectively blocked by the process as well . the invention will be described further in reference to the accompanying , drawings showing non - limiting examples of the invention , and in which : fig1 is a schematic cross - sectional view of an excavation in the vicinity of a sewer pipe ; fig2 is a view similar to fig1 showing another excavation near various obstructions such as a building and existing underground utilities ; and fig3 is a schematic plan view of a typical layout of buildings on opposite sides of a street with utility lines buried therebelow . referring firstly to fig3 a typical street layout is shown in which a street 10 has buildings or houses 12 on both sides of the street . buried beneath the street are utility lines such as a sewer main 14 , a water main 16 , a gas line 18 and an electric line 20 . the relative positions of these lines are merely exemplary of the way in which such lines are often placed in a street . other obstacles such as large rocks or the like are indicated at 22 . the various lateral lines which connect the houses 12 with the main utility lines are designated as l . of course it will be noted that the water line 16 is above the sewer line 14 , and thus would present an obstacle which must be avoided by any digging . fig1 and 2 illustrate the manner in which a hole may be vacuum excavated , either directly vertically or at an angle . a truck 24 is shown which would include the vacuum excavation equipment which would include a pressure line 26 and a vacuum line 28 appropriately connected to the pumps , filter equipment , and spoil receiving receptacles on the truck . the excavation is commenced using the pressure line 26 which is gradually lowered into the hole 30 as the excavation proceeds . the excavation continues until the sewer main 14 is located . at this point , it may be desirable to enlarge the lower portion of the hole 30 to the dotted line position 30 &# 39 ;, even around the pipe , to increase access to the sewer main 14 . depending upon the depth of the normal water table , the excavation process can affect the level of the water table . the normal water table level is illustrated at 32 in fig1 . it will be appreciated that while a leak allows inflow to the sewer line 14 , the water table will lower to the point indicated by the line 34 . during repair of the pipe , the water table level will drop even further to the level indicated by the line 36 . after the hole has been excavated to reveal the sewer main 14 , workers simply pour into the hole 30 ( 30 &# 39 ;) the water swellable material described above . preferably , this material is introduced into the hole to a depth of 1 - 2 feet above the sewer main 14 . in some cases , it is desirable to lower a pneumatic tamper into the hole 30 ( 30 &# 39 ;) to compact the clay in the lower portion of the hole around the main 14 . next , gravel is poured into the hole on top of the clay to a depth of at least several feet above the clay level , and then the hole can be backfilled with fill material . preferably , the backfilling is completely gravel . finally , the street surface may be patched with a small patch in a conventional manner . within a short period of time , the water swellable material or clay will be moistened by the water in the ground , causing the material to swell , and then forming a nonpermeable &# 34 ; plug &# 34 ; around the pipe in the space surrounding the leak , thus preventing the water from reaching the pipe . it should be noted that the leak may still exist in the pipe , but the water cannot reach the leaking portion of the pipe . it is also possible that some of the clay will flow into the leak in the pipe and in essence plug up that leak . in either case , the inflow stops . in the preferred embodiment using a clay material with an appropriate water soluble dye blended with the clay , inspection of the water flowing through the sewer pipe to a downstream manhole will reveal whether the leak is stopped . initially , and shortly after the clay has been placed around the pipe , the downstream inspection will reveal the dye in the flowing water , but after a short period of time , the quantity of dye will decrease and ultimately there will be no dye flowing , providing a visual indication that the inflow of water through the leak has been stopped . in fig2 the ability of the process to proceed around obstacles is illustrated . an excavation may be made starting in close proximity to a building 12 , and may go downwardly at any appropriate angle . as seen , the hole 30 &# 34 ; can avoid building foundations 50 , rocks 22 , underground utility lines 16 , 18 and 20 , tree roots and the like in reaching the sewer pipe 14 . also , it will be appreciated that the angle of the excavated hole 30 &# 34 ; could reach beneath the building to some extent with equal ease . clearly , the present process enables repair of sewer lines without the need for having people in an excavation , as is the case in many prior techniques . aside from the inherent danger of such manual repairs , the cost is quite high since various regulations require substantial shoring of excavations when workers are to be in the excavation . the size of the opening in the street is essentially determined by the size needed to accommodate the pressure and vacuum lines , typically less than 3 square feet , a size which may be readily patched without large paving equipment , in order to keep the repair cost at a minimum . the process may also be used to repair other utility lines which are subject to water seepage and damage . for example , jacketed telephone lines or electric lines , and particularly those lines which are in conduits , can be damaged by the presence of water in the jackets or conduits , and the present process will be equally effective in preventing the inflow of water into such lines . while this invention has been described as having certain preferred features and embodiments , it will be understood by the skilled artisan that the invention is capable of still further variation and modification without departing from the spirit of the invention , and this application is intended to cover any and all variations , modifications and adaptations of the invention that fall within the spirit of the invention and the scope of the appended claims .