Below The Water Table
For sampling below the water table it requires specialised equipment to hold the fluid samples and to prevent the hole collapsing.
One-off samples can be achieved using one of the special samplers but for continuous sampling the hole will need Casing (a liner to prevent the hole collapsing) and if the material is fluid, a Sludger/Baler is required.
We make casing from lightweight steel, or aluminium with brass threads in sizes 50mm, 62mm, 75mm and 90mm OD and either 1.0 or 1.5 metre lengths.
- Casing Cutters
Used to protect the thread, give clearance to the casing and to assist penetration when the casing is turned.
- Casing Collars
To protect the threads at the top of the casing while working inside and for attaching casing recovery equipment.
- Casing Clamp and Strap Wrench
Installed on the upper part of the casing for rotating the casing and as a platform to apply downward pressure (some operators stand on them or add sand bags).
- Sludgers or Bailers
We have 3 types: SLR (Rope connection only) and SLW (Whistletop – rigid threaded connection) and SLS (Swivel threaded connection). All use a ball valve and on the standard versions the ball valve is not removable. All are available in 38mm, 45mm, 50mm, 62mm, 70mm & 75mm diameters and either 1.0m or 1.5m long. Standard versions are painted steel and can be made from stainless steel. They all can be made with removable ball valves.
BELOW THE WATER TABLE INFORMATION
To continue drilling or sampling below the watertable most often requires casing the hole( a rigid lining). Any type of tubing which can be joined and advanced down the hole with the drilling process can be used.
The problems with the improvised casing are: joining the casing so that it does not hinder the installation; protecting the leading edge; and removing (or sacrificing) the tubing. It can be done and has been done on many occasions.
However, for us to sell a professionally made product we need to address the issues.
Our Casing is specially made so that the threaded joints are flush fitting on the outside while not impending work inside, there are hardened tooth Casing Cutters threaded to the leading edge and through design features it is easier to recover our reusable casing.
We have customers who re-use our casing job after job for years. The biggest risk with casing is getting it stuck and not being able to recover all or part of it.
Casing needs to be installed over the full depth of the hole and can be done using either of two methods.
One method is to install the casing from the beginning of the hole and to drill inside the casing using a smaller diameter auger. This is slower because of the effort required advancing the casing in hard ground and unless the auger takes out full cross-section inside the casing, contamination of the sample can occur.
Also, there is more surface friction on the outside when it comes to removing the casing.
The second and more popular method is to drill the hole initially down to the watertable using an auger slightly larger than the casing OD and then install the casing.
This reduces the friction on the outside and allows the casing to inserted much more easily. When adding lengths of casing, use the Strap Wrench to tighten the joints while holding the lower section with the Casing Clamp.
When the casing reaches the bottom of the auger hole, fit a Casing Collar to the top thread to protect it. Insert an auger and remove any fall-in or surplus and discard it.
When the sample proves two wet to extract using an normal auger, a Sludger or Bailer is used.
By pumping the sludger up and down in short vigorous or long rhrythmic movements using either a the rope type of the extention rod type sludger, while adding downward weight(standing on or hang sandbags on the Casing Clamp) onto the casing via the Casing Clamp, a sample will fill the sludger and the casing will penetrate.
Care needs to be taken to ensure the sample is not taken from below the end of the casing and to watch for “welling up” caused by the water pressure pushing materials into the end of the casing.
It helps to withdraw the sludger slowly so as to reduce the suction effect, and to keep the inside of the casing topped up with the water to balance the pressure.
Depths of upto 30 metres below the watertable have been achieved but on average, 8 metres.
Other hints are:
- Never leave the equipment in the hole unnecessarily as it may get stuck.
- If gravel or stones are encountered, chop them up using the Star Drill or Chisel and remove the pieces with theStone Catcher and the Slide Hammer to force-fill it.
- Remove the casing as soon as possible or it will need mechanical extraction. Using a jack (the highlift jacks used by the 4WD’ers are good) under the casing clamp or a tripod (we make them) connected to the Casing Collar helps remove difficult casing.
- Regularly rotate the casing clockwise only, using the Casing Clamp to help penetration or removal. Do not turn more than half a turn anticlockwise or the joints may undo.
Do not use pipe wrenches (stilsons) on the casing as it damages the lightweight walls and the threads may go out-of-round. Our Strap Wrenches are an infinitely better choice by far.