We have recently been tasked with carrying out refurbishments and upgrade works to a number of borehole head works.
A borehole is a narrow shaft drilled into the ground, vertically or at an angle for a number of purposes such as water extraction, gas or petroleum extraction, mineral exploration, site assessment, geotechnical investigation, groundwater monitoring and a number of other purposes. The borehole may be a few meters or hundreds of meters deep. Typically the hole is drilled into an aquifer and then lined with a solid pipe over part of its depth and then a mesh screen or filter pipe to support the bore and keep the hole open through fissured rock, sands or gravel.
The head works can take various forms, from simply a steel pipe protruding from the ground, to a walk in kiosk set on a concrete base. Most commonly, monitoring boreholes tend to be accessed via a shallow chamber with a removable access cover.
Artesian boreholes occur when the aquifer in to which they are drilled is under pressure. This is usually due to the confinement of the aquifer beneath an impermeable layer which is at a lower level than the hydrostatic equilibrium of the aquifer as a whole.
Aquifers can occur at any depth but for monitoring purposes in the UK boreholes are commonly drilled to depths of 10m – 90m. One of the deepest boreholes ever drilled is the Kola Superdeep in Russia. This borehole was drilled in the 1970”s by the Soviet Union as part of a scientific experiment and achieved a depth of 12,262m – that’s over seven and a half miles!
The boreholes we help to maintain are used by our client to monitor groundwater levels. Groundwater level data is an important aid for flood forecasting as the more water that is in the ground, the less rain water can be absorbed. High groundwater levels can also mean high river levels and therefore less drainage capacity. It is also useful to know when groundwater levels are low, as this can often indicate the possibility of an impending water shortage.
The groundwater level has traditionally been measured by lowering a weighted tape measure with two electrodes in the bottom of the weight down the borehole tube. When the weight touches the water, the circuit is completed and a buzzer on the tape reel sounds. The depth is measured against a fixed datum point.
Many boreholes now are fitted with telemetry systems which enable the groundwater levels to be monitored remotely and consistently, with a reduced requirement for manned site attendance.
We are often tasked with the modification of existing borehole head works to enable the installation of automated measuring and telemetry systems.
The picture shows the cabinet mounted over the top of the headworks, an adjacent earthing point with a copper pin driven into the ground, and four marker posts to locate the installation in the verge. On the back of the cabinet is a solar panel to power the data logger and telemetry equipment.