COSTS AND PRICES
The cost of drilling a bore-hole is based on a combination of factors, all of which originate in the geology of the site. This can normally be found by reference to a BGS (British Geological Survey) Prognosis. This will usually say what materials will be encountered, the depth of each layer, if any are likely to contain water, whether it is under pressure, the chemical composition - will it be drinkable, contain excessive hardness or sulphates - and the most suitable depth at which to find an acceptable water supply. A BGS Prognosis may be obtained by going to the GeoReports page of the BGS website via the following link - British Geological Survey. Alternatively, for a nominal administrative charge, we can arrange a prognosis on your behalf.
The building blocks of a quotation are made up as follows:-
A lump sum, which reflects the distance from our nearest depot to the site, setting up and clearing site, and the cost of preparing any special casing, screens and tools and materials for the specifics of the site.
Drilling costs reflect the productivity anticipated in the materials at the site and might include charges for the non productive time taken to install temporary and any sacrificial casing that may be dictated by the materials and the conditions. Where the drilling conditions are difficult, and the installation of temporary casing occupies significant amounts of time relative to the removal of material in advancing the hole, additional or higher drilling costs will be included in the quotation. Driven casing also has to be removed, and this can take more time than even installation and attracts a rate for the work involved.
CASING and CONSUMABLES
Water wells normally require sand screens to allow water to pass, but which retain sand on the outside. Above the screen is plain casing, the size of which is dictated by the pump it is intended to install. Unless there are other requirements, we normally install 4-inch pumps, which are sized to enter a casing having an inside diameter of some 100mm. Around the screen, in some conditions it is necessary to place gravel of a certain grain size, in order to protect the pump from the inflow of harmful sand and silt through the screen.
Plain casing requires the support of 'casing stabiliser' material such as sand, and for a distance below ground level this is replaced by a clay seal to prevent the ingress of surface water into the well. Gravel pack, casing stabiliser and clay are materials of a special type and the quantities involved are charged depending on the amounts used in finishing the well.
At ground level it is usual to place a concrete surround - again as protection to the water supply and the aquifers.
Not all wells will require the use of a submersible pump. When a confining layer of material causes the yielding aquifer to be pressurised, the standing and pumping water levels may be close enough to the surface to allow the use of pumps having the motors - or engines - above ground level. It may also be convenient to use jet pumps rather than submersibles. Some wells can be pumped using normal suction pumps. There are circumstances where a hand pump may be the best method of abstracting water - allotment gardens and pony fields are examples. In discussion with the Customer, we will supply and fit the most appropriate pump for the situation. 4-inch submersible pumps cost from about £250 each. There is an additional cost if the pump is required to operate automatically, by timer or pressure regulation. The cheapest option is by manual control using a simple on/off switch. Any electrical work necessary for pumps is required by law to be done by a qualified electrician.