A lot of people in Australia use a bore pump for irrigating their gardens and farms, drinking water for animals and livestock and sometimes for house water. Have you ever looked at that strange looking white pipe sticking up out of the ground in your garden and wondered how it actually works?
What is a bore?
There are actually 2 parts to a bore water supply, the bore (some people also call it a well or spearpoint) and the bore pump. In simple terms, a bore is a hole drilled in the ground that fills up with groundwater that can then be pumped out to use for various things. A bore pump is either an above ground pump and motor that sucks water out of a bore or a submersible pump and motor that sits underwater down in the bore and pumps the water up and out to be used.
A bore is usually drilled by a water well driller but sometimes it can be done by the property owner if the water is fairly shallow (less than 10m deep). Once you get much beyond 10m then the machinery and power you require to drill a hole means that you need to get a specialist drilling contractor in.
The bore itself is constructed of the following parts:
- The hole.This is the large hole sometimes 300-400mm across that is drilled in the ground to create the bore. The depth of the hole varies to suit what water is there, it can be 15m deep up to 400m deep for the largest commercial bores.
- The bore casing. This forms the main pipe structure of the bore and holds back all the earth and rock and stops the hole from collapsing. This also provides a space for the power cables and outlet pipes to be fed down into the water to the pump so the water can be pumped out. A bore casing is usually made out of PVC pipe with common sizes being 4 inch (100mm), 6 inch (150mm) and 8 inch (200mm). Sometimes the casing is steel, stainless steel or fibreglass reinforced polyethylene (FRP) which is sometimes called permaglass.
- The bore screen, sometimes called a well screen. This is a section of pipe that is usually at the bottom of the bore sitting in the groundwater that the driller finds. The screen is used to hold the same round structure of the bore case but has perforations in it and this lets water flow in so the pump can pump it. Bore screen is usually the same size as the casing but sometimes can be smaller. In most domestic bores its actually made out of PVC pipe with lots of fine slots cut into it. It can also be made out of stainless steel mesh which is expensive but very strong and can let in a very high flow rate of water.
- The gravel packing. When the bore hole is drilled and the casing pipe is lowered into the hole, then there is an annular space between the case and the sides of the hole. This needs to be filled up so that the earth doesn’t collapse and block the screen and also to give the bore structural strength. In the screen area where the bore is trying to get the ground water to flow in, the driller usually pours a fine graded gravel grit to fill this space up. This gravel packing give more air gaps around the screen from normal earth or rock and so allows lots of water to flow in, it also assists in filtering out sand and other grit so that the water that gets pumped is fairly clean. At the top of the groundwater zone, usually the driller simply fills the remaining hole up with the soil that was removed during the drilling process. Sometimes if they are trying to stop shallow surface water from falling down the sides of the bore and contaminating the deeper (and sometimes much better quality) aquifer water, then the driller pours a cement grout down the outside of the bore case and uses this to seal the different layers of groundwater from leaking.
How do you get water out of a bore?
Once a bore has been drilled, then the driller “develops” the bore, this is the process of starting to pump water out of the bore, cleaning out all the sand, clay and debris from the drilling process and then testing the depth of the water and the flow rate so the pump engineer can work out how to get water out of the bore efficiently.
This process is usually started by a process called “air lifting”. This process involves joining a tool with nozzles on it to an air line and then feeding this down to the bottom of the bore. When a high volume of compressed air is pumped down the bore, this expands rapidly and blows all the water in the tube up and out of the bore. This lifting process usually lifts all the dirt and debris up and out of the bore which cleans the pipe and the screen and gravel packing. It also starts drawing water in from the surrounding aquifer and gets the bore flowing.
After this has been done for a number of hours, then this is removed and a test pump is fed down into the bore on a pipe and is turned on. This test pump is selected to hopefully pump the bore faster than its capable of flowing so the driller can find the maximum flow rate that the bore is capable of. Once the bore sucks dry, the pump flow rate is slowed down so the bore can flow at a rate that keeps a level of water sitting just above where the pump is sitting. This flow rate is then maintained for 12 to 24 hours and if it keeps flowing for that period, then this is the “rated flow rate” of the bore which can be in liters/sec, gallons per hour, liters per minute or cubic meters per hour. For a domestic irrigation bore you usually find the driller will try and achieve about 50-100L/min, or 3m3/hr to 6m3/hr. For a larger irrigation or commercial bore, then the flow rate could be 10L/sec (600L/min) up to 50L/sec (3000L/min) or more.
Once this flow rate is tested and the bore constantly produces water, then the depth of the bore is measured. There are 4 important depth measurements in a bore:
- The total depth, this is the depth from the surface to the bottom of the bore.
- The depth of the scree, this is the point where the screen starts and also how deep this screen is.
- The static water level (or SWL), this is the level of water in the bore when everything is just sitting doing nothing.
- The pumping water level (or PWL), this is level that the water in the bore drops to when its pumped at the rated flow rate.
Usually in a properly constructed bore where there a no problems with things like rock or clay layers, the pump is then recommended to be set at a level 5-10m below the pumping water level. As submersible bore pumps have a motor that is water cooled, they need water to be drawn past the motor to keep them cool. To do this properly, the pump should be sitting at a place in the bore where its above the screen, not in the screen. If the pump has to sit in the screen area, then it can risk the motor getting hot as water is going straight into the pump suction and not past the motor. If this is the case then sometimes the pump has to have a shroud around it or you use a “bleed off” tube to take some of the outlet water and feed it out around the motor so there is always cool water there.
How do you set up a bore pump?
Once a bore is drilled, the driller will provide a “drill log”, this is all the measurements from the bore, the depth, SWL and PWL, flow rate and also the pump set recommendation.
With this information, our sales staff can then work out a suitable pump for both the bore but also to do the right job once the water comes up and out of the bore. With a recommended pump set depth, we look to place the pump on a riser pipe at that depth. We usually don’t match or exceed the flow rate of the bore unless its absolutely essential as sometimes conditions can change and the bore flow rate or depth drops and it stops working.
We look at if you need to pump to a storage tank or provide lots of pressure and flow (for irrigation or a house or factory). This means calculating what pressure you need at the surface and then adding in the lift you need to get water to the surface. We also look at the power supply you have available (single or 3 phase or nothing) and then work out the available options.
An example of this is a fairly standard average bore pump for garden irrigation in the Bunbury area.
The bore would be approximately 35-40m deep.
The water will sit 10-15m deep and then draw down to 20m when pumping.
A flow rate for this bore would be 4000L/hr or 70L/min and the pump should be set at around 25-27m.
If you want to use this for garden irrigation, then you will need 60-70L/min to run a good station of 4-5 gear drive sprinklers and you will need 350-400kpa at the sprinklers so they spray far enough and evenly water the lawn.
Generally speaking you only have single phase 240V power available for this sort of pump as 3 phase power in domestic areas is not common.
To get the sprinklers to work, the pump needs to produce 70L/min (or 4m3/hr) and approximately 650kpa. This pressure will get the water up and out of the bore at 450kpa and then with 50kpa of friction loss in the pipes then you will have around the 375-400kpa at the sprinklers. A 60L/min pump with a 1.5hp (1.1kw ) motor will do this job and if the right motor is used can be run on a 10A standard power circuit.
The pump is hung in the bore using a length of poly pipe and the outlet pipe can then be connected to the irrigation lines. It can also be easily automated using an irrigation controller and a pump start relay or a pressure switch and valves to control where the water flows.
I’ve heard that bore water is always bad quality?
Bore water can range from really bad quality to really good quality, this is luck of the draw when you drill a bore. Sometimes a driller can use a bit of experience to try and get better quality water, sometimes this works and sometimes it doesn’t. The general rule with bore water is that it is cheaper and easier to have a good bore than have to treat the water as this can be very expensive and also time consuming.
The main measurements of bore water quality are:
- pH or acidity. pH is a measure of how acidic or alkaline your water is. Good quality water is between 6.5 and 7.5 pH with 7.0 being neutral on the 0 (acid) to 14 (alkaline) scale. Bore water usually has a lot of carbon dioxide dissolved in it and so can be 4.0 to 6.0 when it is pumped out of the ground and this makes it corrosive, keep metals like iron dissolved and not taste very nice. Usually you aerate the water by spraying it into a tank or pond to neutralise the pH and sometimes you need to treat it with chemicals like calcite, lime or caustic soda.
- Salinity, TDS or conductivity. The most common mineral dissolved in water is plain old salt or sodium chloride. In most of our water in the South West it can be anything from 250ppm (0.25g/L) to over 1500 ppm (1.5g/L) with a “good” level for drinking or household use being 600ppm and a usable level or irrigation at about 800-1000ppm.
To remove salt from water is very expensive and requires desalination using a reverse osmosis plant so if you need fresh water its usually cheaper and easier to get a good drilling contractor and drill for a fresher source of water.
- Iron and manganese. We live in the iron ore mining centre of the world for a reason, there is a lot of iron in the ground. Because of this we very commonly have a lot of dissolved iron in our water. This is also usually paired up with dissolved manganese in much smaller amounts. These 2 metals are responsible for the horrible dark red and black staining we see on buildings and garden fences all over WA.
Iron and manganese are very hard to remove from bore water with the normal method being to spray the water over a bed of sand grit which catches the build up of iron and manganese and separates it from the water. This can be very labour intensive and usually means pumping the water twice.
- Hardness. Hardness is the measure of dissolved calcium and magnesium minerals in the water . This is predominantly calcium carbonate and magnesium carbonate and in large amounts (usually over 0.1g/L) this causes a build up of scale and white powdery stains on surfaces. Hardness can be removed from water using a filter plant called a water softener, this drags the minerals out of the water using an exchange resin.
Does a bore require maintenance?
If a bore is covered with a cap and regularly used, then it shouldn’t need too much maintenance. If it sits unused then it can get a build up of minerals and the screen can get blocked. If there is lots of iron in the water then there are products based on oxalic acid, generally called “Iron cleaner” or “bore cleaner” and when you mix up a solution of this and pour it down the bore it can clean up all the build up and make things flow again.
The other thing that can be done is to flush the bore using an air lift like the drillers use when they originally drilled the bore. An air lift will lift out all the debris sitting in the bore and get the screen flowing again. Sometimes this doesn’t work, it depends on what is causing the blockage and if the bore is damaged or collapsed.
For bore pumps and bores, the best maintenance is to use them regularly so everything is always moving and flowing. If you have an irrigation bore, this means turning it on for a couple of minutes per week during winter, just to give everything a run and keep things flowing. If you turn a bore off for 6 months and then expect it just work properly when it needs to run, don’t be surprised if the motor is jammed or only a little bit of water comes out. Treat your bore well and it will give you years of good quality water and all you need to pay for is the power.
If you want more advice or have more questions about your bore and it set up, then give us a call on 08 9721 3577 or send us an email and our experts can help out.