ill be used, reducing to around 35 mm by around 4 m to 5 m depth. The full samplers are either jacked out manually or pulled from the hole using a hydraulic jacking system.
A full sampler will reveal a complete or partial ground profile although guidance from the driller will be needed on any compression that may have occurred and resulted in, for example, a 1.5 m sample occupying a 1 m space in the sampler. With some window sampling systems, samples can be recovered in a thin walled transparent liner placed inside the steel tubes. The liner is removed for visual inspection or capped at each end for transporting to the laboratory. Whatever system is used, the quantity of soil within the sampler is small and, particularly where the analytical suite is extensive, a sample may have to be taken from a 0.5 m or so section to ensure sufficient quantity. The advantage, however, is that once soil is taken for samples and backfilling purposes, there is rarely any excess requiring disposal.
Narrow diameter groundwater/gas monitoring installations can be constructed in the borehole once all samplers are withdrawn. Whilst the diameter of the standpipe is ultimately dictated by the diameter of the smallest (and lowest positioned) sampler, in practice it is usually possible to install a 19 mm or 35 mm standpipe with a fine gravel pack surround. With some systems, it is possible to drive a water well in through unsampled ground using the hammer unit.
This method is not suitable where there is a need to drill through an aquiclude into an aquifer as there is no way of protecting the aquifer from downwards migration of any contaminants from the ground above the aquiclude during drilling.
The equipment is generally brought to site in a van or four-wheel drive vehicle and from then on, it can be carried by hand around the site. In many circumstances the fact that this is largely a manual method is its advantage over even the smallest drilling rigs. Window sampling causes minimal disturbance to the ground surface (e.g. useful for investigations inside buildings, in a landscaped car park or between the sleepers of rail lines. The method can be used where access is very restricted (e.g. small operational sites and in gardens). It can also achieve rapid coverage to shallow depth (e.g. useful for establishing the thickness of a landfill cap over a large area).
Electric Dynamic (Window) Sampling
We also offer an electrical powered drilling unit which is capable of Windowless sampling, SPT’s etc., the same as a diesel/petrol powered rig. We replace the diesel power source with a unit that is electrically driven.
The power pack simply plugs into a 13amp socket/generator which in turn runs the hydraulics on the rig but, (being electric) it does not produce any fumes.
This is ideal for working in buildings, restricted area’s and petrol chemical plants etc.
We can also offer an electric powered hand held sampling unit for height/restricted areas.