Question: how do you dig a hole when there are cables or pipes in the ground and you don't want to hit them? Well speaking as one who has dug through a power cable (in my short-lived career as a fence erector) Biglorryblog is rather taken by ADP Group's 
Its Vector HDD vacuum excavators and the hand-held AIR-SPADER provide complementary techniques for tackling a wide range of ground conditions, from porous and semi-porous substrates, to impervious soils and clay. And according to ADP they both provide: "substantially safer - and in many applications, faster - ground excavation compared with conventional excavators and hand-dig methods: pick axes, shovels, mechanical buckets. And by using a high pressure air-stream to dislodge and dissipate materials, they pose zero risk of damage or fracture to buried services, such as electricity cables, gas mains, drainage pipes, fibre-optics, etc."
New for 2009, it the latest 35hp Vector HDD650, an even lighter weight addition to the Vector range of compact trailer-, skid-, or truck-mounted vacuum excavators for digging and disposal of spoil. It has an adjustable 16" HG vacuum pull, 650 cfm airflow, and 4000 psi water jet for loosening hard compaction and conveying spoil, and is light enough to be towed by a Land Rover or mounted on a 3.5-tonne truck.
And this is what it looks like when it's 'dug' a hole...neat eh? 
ADP boss Adrian Page tells me: "Although vacuum excavation and compressed air spades are relatively new concepts to the
Now click through here for the techie-stuff....
The systems use a positive displacement Roots rotary lobe blower, ranging between 650 and 4000 cfm, with up to 28"hg pull. The hydro system works off a pump rating of 18l per minute at 4000 psi, discharging to spoils tanks ranging from 1000---3200 litres. Applications include slit trenching, trial pitting, horizontal boring, bulk excavation, environmental spill clear-up, gully cleaning, safe root exposure, UXO exposure, pot holing, bulk excavation and a variety of materials removal applications including railway ballast, mud, slurry and silt.
Working off a maximum size 6 inch (150mm) hose, a boom is not necessary (although still available as an option) so work can be staged with pipe up to 300m away from the vacuum unit. The use of a hydro system - specifically a high pressure turbo water jet - alongside the vacuum allows a wider range of soil conditions to be tackled, and conveys spoils to the storage unit for disposal. In contrast to larger, more cumbersome suction excavators, Vector units can be moved around and between sites more easily, and off-load deposits more cleanly into the skip. Although not bulk excavators, HDD machines are capable of excellent, and above all, safe, strike-free work-rates. Depending on ground conditions, up to 25m of slit trenching can be excavated to a depth of 1m in a day, or 20 boreholes at 150mm in diameter down to 1.2m. Meanwhile, weighg just 3kg, the standard AIR-SPADE 2000 has a 1.2m non-conductive, insulated barrel, ergonomic handle with thermal shield, and uses interchangeable supersonic nozzles made from hard-wearing, non-sparking stainless steel.
The GUARD-AIR patented supersonic nozzle turns compressed air into a high speed, laser-like jet moving at twice the speed of sound: Mach 2. All of the energy and momentum of this air, moving at approximately 1500 mph, is focused on the soil, dislodging it in a fraction of a second. The aggregate nature of soil aids the ability of the air to fracture it. Stronger materials and non-porous ones, such as metal, plastic pipes, cables or even tree roots, are unaffected. Standard AIR-SPADE nozzles are designed to work at an optimum 90 psi, corresponding to a Mach 2 jet. This suits the typical output of most portable air compressors, which operate at 90 to 100 psi for running standard air tools such as paving breakers. Working with compressed air at greater pressures is costly, more difficult for the operative and does not provide any proportional gains in excavation capability. There is a choice of nozzles (15 up to 250 cfm) to match different air compressors, plus interchangeable extensions to 2.4m and reducers to 600mm. All nozzles run at 90 psi so the same hardness of soil can be excavated. The 45 degrees nozzle adapter quickly changes the angle of work and excavated soil is ideal for re-compaction. AIR-SPADE'S reduced effort, vibration-free operation produces less worker fatigue and reduces the risk of injury in comparison to a pick or shovel. The modular design is assembled from parts that screw together without tools.
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