When There’s a Borehole, There’s a Way – Drilling for Groundwater
Do you require an alternative water supply? Do you want to go off-grid and tap out of the municipal supply? Do you wish to never rely on burst bulk water pipelines? Then we have a solution for you! Installing a borehole is a relatively quick and easy solution (provided groundwater development is undertaken properly) that can be used to target aquifers for groundwater supply, which can range in depths from surface to thousands of metres.
What is a borehole?
A borehole is a vertical or horizontal shaft that is narrow in diameter and can be constructed for different purposes, such as the extraction of liquids, gases and/or groundwater, or even for geotechnical investigations before any construction of buildings can take place. Boreholes are constructed using a drill rig, which can drill through both unconsolidated sediment as well as consolidated rock. These are usually wider diameter and can range in depths, but are generally greater than ~15 m deep. Wellpoints are usually a shallow (generally <15 m deep) and narrow diameter irrigation pipe or PVC that is jetted in through unconsolidated sediment or material, and are cheaper (although generally lower yielding) to construct compared to boreholes. Wellpoints can only be installed where you have ~5-20 m thick surface layers of sand and silt, whereas boreholes can be installed into any type of geological material.
What is an aquifer?
An aquifer is an underground geological body of rock or sediment that holds groundwater, and are what wellpoints and boreholes target for water supply. The main types of aquifers you get in South Africa are intergranular or primary aquifers, secondary aquifers (either fractured or karstic aquifers), and basement aquifers (which are a combination of intergranular and fractured aquifers).
Intergranular or primary aquifers are generally comprised of sandy to gravelly sediment and are associated with coastal dune deposits and river floodplain gravel deposits. They are called primary aquifers because groundwater is found in the primary pore spaces between sediment grains. Secondary aquifers form when either tectonic processes (faulting, folding, or volcanic intrusions causing fracturing of the rock in the case of fractured aquifers) or chemical dissolution (in limestones or dolomites, in the case of karstic aquifers) form secondary pore spaces for groundwater to flow in – in this case there is generally very limited to no free-flowing groundwater present in the solid rock matrix itself. Basement aquifers usually form within very old granites and metamorphic rocks such as gneisses, where weathering up to depths of 50-100 m produces both intergranular sediment and opens any pre-existing fractures (allowing for the flow of groundwater).
The aquifer types outlined above can also either be confined or unconfined. Confined aquifers are capped off by an impermeable rock or sediment (e.g., shale or clay) called an aquiclude or aquitard, which does not allow groundwater to pass through and results in groundwater within the aquifer being under pressure (sometimes causing “artesian” conditions, where groundwater flows out at surface under its own pressure). Unconfined aquifers are those that have water seeping into the ground from surface and are in contact with the atmosphere.
The steps to take before drilling and testing a borehole
Because drilling can be a life-long expensive investment, it is important to ask yourself these relevant questions before deciding to drill a borehole:
- Why do you require groundwater?
- Groundwater can be used to provide an alternative supply to municipal water, but it can also provide an option to go completely off the grid therefore not relying on any municipal supply. It is important that any municipal by-laws dealing with alternative water supplies (e.g. with regard to plumbing and effluent discharge) are understood and complied with before attempting to go off-grid.
- What would you like to use groundwater for?
- Groundwater can be used for agricultural irrigation, toilet flushing or sanitation, industrial and commercial processes, and even drinking water. What groundwater is used for is dependent on both the quantity and quality of groundwater present e.g. you might have a very high yielding borehole with poor water quality that might not be fit for agricultural use without extensive water treatment, but can be used for specific industrial processes without treatment.
- Depending on the quality of the groundwater, it can be used for medium to large scale agricultural activities to sustain crop production and livestock, therefore keeping up with the demand especially during drought or water shortages.
- Commercial and industrial activities can make use of groundwater for process and/or cooling water, as well as supplying on-site sanitation facilities and drinking water to staff. This can replace municipal supply, reducing large municipal water costs.
- Can you afford a borehole?
- This is an important question. Even though it is a life-long investment, there is usually a relatively high initial capital cost outlay to drilling/testing a borehole and completing it with the necessary pump installations, electrical and water reticulation connections, and treatment options that could be required (depending on what you want to use the groundwater for).
- It is important to note that there is no guarantee that your borehole will yield groundwater or that the yield will be sufficient for supply. Any driller, “diviner” (which is disproven pseudoscience) or consultant who say they can predict the precise depth and yield of water strikes in an aquifer is at best ignorant and at worst a liar. An experienced and professionally registered hydrogeologist (with the South African Council for Natural and Scientific Professions [SACNASP]) will be able to give you a best estimate of the likely drilling depth (depending on the aquifer targeted), possible depth of water intersection and possible yields that might be encountered during borehole drilling, but they will (or should at least) never promise you a precise borehole yield as they know that this is not possible to determine 100% without actually drilling and testing.
The next phase, once the decision to drill and test a borehole has been taken:
- Do your homework
- Find out from neighbours or people within your area if they have any boreholes. Ask them necessary questions such as:
- What is the groundwater quality like?
- What do they use groundwater for?
- What yields do they get?
- How deep is the borehole?
- Which drilling contractor did they use?
- These questions will help understand the likelihood of finding groundwater and whether the quality will be good for your intended use.
- Find out from neighbours or people within your area if they have any boreholes. Ask them necessary questions such as:
- Consult a SACNASP-registered hydrogeologist or geologist (experienced in groundwater work)
- They will be able to determine the groundwater potential and assist with the possible outcomes of drilling a borehole in your area, and will be able to advise on the next steps to take. They also usually know experienced and reputable drillers who will be able to drill a properly designed borehole using the correct drilling technique (based on the aquifer type present).
- Understand that drilling a borehole is a messy process, and it’s possible that further work such as repaving will be necessary on your property.
- Have a look around your property to make sure that there is access for a drill rig. The drilling company will also advise if they will be able to access the property with the drill rig. Some drilling companies have smaller mobile rigs that can get into difficult access areas.
- Borehole positioning also needs to consider infrastructure as drill rigs (especially rotary air percussion drilling) can cause vibrations which could possibly crack nearby walls. Also make sure you don’t drill through any service infrastructure (water and sewage pipes, buried electrical lines, fibre cable etc.) passing through your property.
- Let your neighbours know that you plan to drill a borehole and that there will be noise for a few days.
- Make sure you are compliant with any municipal by-laws prior to undertaking any drilling (some municipalities require that they be notified prior to drilling commencing).
There are two options which you can choose from to complete the drilling and testing of your borehole:
- Allowing a hydrogeological consultancy to complete the process
- Will undertake the full hydrogeological assessment and cover all points from above.
- A hydrogeologist can provide information on the likelihood of drilling the area and whether you will benefit from it.
- A hydrogeologist will advise on the most appropriate way to operate your borehole, therefore ensuring sustainability over the long term.
- This option is more costly as there are usually professional fees associated with a hydrogeologist, but a high standard of work can be expected and all aspects of drilling and testing a borehole will be completed on your behalf therefore leaving you stress free.
- Undertaking the process without the input from a hydrogeologist/geologist
- This option, even though cheaper, might not be the most appropriate. With this option, you will be in charge of finding and contacting an appropriate driller, choosing the position to drill, trusting the driller to drill the borehole correctly and designing it appropriately.
- With this option, you will also have to undertake the necessary tests to determine if the quality of water is suitable for usage.
- There is a risk involved with this option. You will be in charge and will have to trust the expertise of the driller. You could incur extra unnecessary costs should the work not be conducted properly.
The steps that a hydrogeologist would undertake with respect to groundwater assessment and development:
Step 1 – Desktop Study
A desktop study will be undertaken to review available geological and hydrogeological maps of the area to understand the geology underlying the property and the likelihood of any structures where groundwater could be flowing through. Known hydrogeological databases will be consulted as well to identify known groundwater users and interrogate existing borehole data. This will then allow for a hydrocensus to be completed in which surrounding neighbours and known water users will be visited to collect more groundwater data (borehole depth, yield, water level, usage etc.) and necessary infield measurements such as pH and electrical conductivity (EC). Collection and analysis of such desktop and field data enables further understanding on the potential success of drilling on your property and have a better idea on the groundwater quality.
Step 2 – Borehole siting, borehole design and contractor selection
Scientifically proven geophysical methods such as electrical resistivity tomography (ERT) or magnetic surveys can also be undertaken prior to drilling. The geophysical method used depends on the type of material that underlays the property. For example, magnetic surveys are good for identifying dolerite intrusions (with drilling usually taking place in the fractured material either side of the intrusion), whereas ERT surveying measures the resistivity of material and can be used to determine the thickness of unconsolidated sediments or the presence of potentially water-bearing fractures within hard rock. These surveys therefore assist with identifying potential groundwater bearing zones or structures, allowing for better identification of borehole sites where the best chance of intersecting groundwater is present. Undertaking geophysical surveys depends on if there is big enough open/unsurfaced natural ground present, as geophysical lines with decent depth penetration are usually 150-200 m in length or more. Although undertaking geophysics will increase costs, it also reduces the risk of drilling dry or very low yielding boreholes, as a combination of geophysical survey data and desktop study results will indicate the best possible site for drilling.
This data also assists the hydrogeologist in designing how the borehole should be drilled based on the likely lithology (i.e. rock or sediment) that will be intersected during drilling and estimated final borehole depth (depending on the aquifer depth and amount of aquifer to be intersected). Once the borehole has been sited and designed (i.e. drilling technique[s] to be used, drilling diameters, casing type and diameters, casing annulus [space between the borehole wall and casing] infill etc.), then the hydrogeologist can identify the best drilling contractor to use, based on the available space for the drilling equipment.
Step 3 – Drilling of the borehole
It is crucial that an experienced, reputable and competent driller is selected, especially since there are major costs involved and you would not want to spend money to have a job done incorrectly. Some drilling contractors are also capable of designing boreholes, as competent drillers have many years of experience and understand the underlying geology to some extent. It is advisable to have a hydrogeologist supervising the drilling process as this can ensure all relevant information is captured (e.g. the lithology intersected per metre as indicated by rock chips, and the depth and estimated yield of water strikes) and that the borehole is drilled to the specified design. This is crucial for the longevity of the borehole. Having a hydrogeologist on-site will also allow for timeously and scientifically informed decisions to be made during the drilling process e.g. if a borehole needs to be stopped at a shallower depth or drilled deeper than originally planned for whatever reason, additional casing needs to be installed because of extreme collapsing conditions etc.
Step 4 – Testing your borehole and groundwater quality sampling
Once the borehole is drilled, development takes place in which the borehole is cleaned out. During this step, a blow yield is recorded which provides an approximate reading of how much water there is. The general rule of thumb for secondary and basement aquifers is that the recommended (also sometimes called the “safe” or “sustainable”) pumping yield is only a third to a quarter of the blow yield i.e. if the blow yield of the borehole was ~10 litres per second (l/s) or 36 000 litres per hour, then the recommended pumping yield would be ~2.5-3 l/s or ~9 000-12 000 l/hour. The best practice to determine the recommended yield of a borehole is to undertake scientific test-pumping however, based on “South African National Standard (SANS) 10299-4-2003 – Test Pumping of Water Boreholes”. For this a temporary test-pump is installed, and the borehole is pumped at a derived rate for a specified period based on what the planned water use is (but usually for 24-72 hours). Test-pumping provides scientific yield and pumped water level drawdown data, which can then be analysed to determine the recommended yield and how to best operate your borehole. Groundwater quality samples should be taken at the end of the test-pumping process (to make sure a flushed and representative groundwater sample is collected) and sent to a South African National Accreditation System (SANAS)-accredited laboratory for testing. This will provide data on the quality of the groundwater, from which a hydrogeologist and/or water treatment specialist can advise on whether the water will be applicable for planned usage and what sort of treatment may be required (if any).
Step 5 – Installation of pumps
The type of pump will depend on the diameter of the casing installed and the yield of the borehole. Selecting the right pump and operating it correctly is important for the management of the aquifer.
For all boreholes (but especially low to very low yielding ones), it is better to pump the borehole at a lower yield but over a longer period, to ensure the pumped water level remains relatively stable and does not fluctuate significantly (i.e., not having water levels fluctuate from the rest water level to the pump inlet during pumping, and back to the rest water level during non-pumping periods constantly). This is for two reasons:
- if the pump inlet is at the base of the borehole, and water levels are drawn constantly to the pump inlet, there is a risk of permanently dewatering fractures (fractured aquifers), solution cavities (karstic aquifers) or sediment (primary aquifers) that bear major water strikes – this would negatively affect the aquifer integrity i.e., reduced storage capacity within the aquifer, possible surface subsidence and reduced borehole yields; and
- constant water level fluctuation results in oxygen introduction into the borehole, groundwater and aquifer as a whole during pumping, which can lead to biofouling if iron/manganese concentrations are elevated (i.e. the development of iron/manganese oxide/hydroxide sludge via iron/manganese bacteria processes) – this can cause clogging of pumps and water reticulation systems, as well as reduce the yield of the borehole if casing screens, gravel packs or sediment/fractures get clogged (which would then require annual borehole cleaning).
Step 6 – Finalisation of your new borehole
Ensure that all relevant information (drilling depth, casing depth and type, lithology information, yields, water quality results) is handed over to you by either the driller or the hydrogeologist in charge. Surface plinths should be installed after borehole completion, to ensure the stability of and prevent damage to the casing at surface. Boreholes should be capped appropriately with a tamper-proof, lockable steel/PVC cap or manhole to avoid any vandalism, and labelled correctly with information such as borehole name, borehole depth, date drilled and contractor. The borehole information should be submitted to the Department of Water and Sanitation to be recorded on the National Groundwater Archive, as well as to the relevant municipality (if the latter has by-laws requiring this, for example the City of Cape Town).
Step 7 – Regulation of groundwater use
The National Water Act (NWA) (No. 36 of 1998) stipulates that any water use requires authorisation from the national Department of Water and Sanitation (DWS) (or their appointed regulatory authority, such as a catchment management agency). It should be noted that groundwater (and surface water) in South Africa is not privately but publicly owned i.e. belongs to all citizens of the country. DWS therefore regulates water use on behalf of the citizenry of the country, ensuring that the resource is used sustainably and to the beneficial use of all (in theory).
The requirement of a water use license (WUL) is dependent on the type of activity stipulated in Section 21 of the NWA. Groundwater usage for “reasonable” domestic and non-commercial use is referred to as Schedule 1 use, which is excluded from this licensing requirement. However, domestic and non-commercial users which fall part of Schedule 1 are still required to register with the DWS if abstraction is over 10 m3/day (averaged over the year). A General Authorisation (GA) registration or WUL is required for commercial usage, depending on the size of the property and the volume of groundwater to be abstracted.
Certain municipalities might have various by-laws that will require you to register your borehole (but not the actual water use) with them. It is important to ensure that all regulations and by-laws of the municipalities are known prior to drilling and that necessary procedures are followed.
Involving a hydrogeologist throughout the life cycle of a groundwater development project can ensure that all regulatory measures are met, and the user can be registered or licensed with the DWS (if required). Umvoto has 30 years’ experience in the groundwater industry and has undertaken numerous groundwater development projects across all aquifer types throughout South Africa and Africa. This includes small-scale residential houses, medium-scale estates, commercial and industrial properties, agricultural irrigation projects, mining supply, and large-scale municipal wellfield development and groundwater management projects such as the City of Cape Town New Water Programme. Umvoto has an experienced team of geologists and hydrogeologists that can assist with any groundwater development requirements, whether it be groundwater assessments, borehole siting and design, borehole drilling and testing, yield and hydrochemical analysis, groundwater registration or water use licensing, groundwater monitoring, numerical groundwater modelling and/or contamination assessments.
Contact us if you’d like to inquire about our drilling a borehole!