Drilling on Dolomite: Risks Joburg Homeowners Should Know

Dolomite sits beneath a large portion of Greater Johannesburg and stretches across parts of several other provinces. It is a sedimentary rock that dissolves slowly when acidic groundwater moves through it, leaving cavities that can — under the right (wrong) conditions — collapse toward the surface. That process is the origin of sinkholes.

If your property sits on a dolomite risk zone, drilling a borehole is not simply a matter of calling a driller and picking a spot. There is a specific regulatory framework, and ignoring it creates legal, financial and physical risks. Here is what you need to understand before you go any further.

What Makes Dolomite Different Underground

Dolomite looks solid from the surface. The problem is what groundwater does to it over decades or centuries. As water percolates through joints and fractures in the rock, it gradually dissolves the carbonate minerals, widening those joints into voids. The overburden — the soil and rock sitting above — can bridge those voids for years until it cannot, at which point material drops suddenly.

Sinkholes in dolomitic areas are not always dramatic. Some open slowly; others drop without warning. Either way, an open excavation or borehole shaft changes the subsurface hydrology: it creates a new pathway for water movement. If that pathway directs water toward an existing void or accelerates dissolution in a weak zone, the risk profile of that piece of ground changes.

This is the core reason why drilling on dolomite is treated differently from drilling on granite, shale or sandstone. It is not that boreholes are impossible on dolomite; it is that they require more investigation, more care, and specific approvals.

The Regulatory Position

The Department of Water and Sanitation (DWS) regulates the use of groundwater nationally, and the National Water Act requires that boreholes above certain yield or depth thresholds are registered. That obligation applies everywhere in South Africa, not only on dolomite. You can find the registration detail explained in our post on borehole registration with DWS.

For dolomite specifically, an additional layer of control applies at municipal level. Most affected municipalities — including Johannesburg — require a dolomite risk assessment before issuing any building or earthworks approval on dolomite-zoned land. Drilling a borehole constitutes earthworks. Proceeding without the correct approvals can void your home insurance, create liability if a neighbour’s property is later affected, and potentially result in a council instruction to decommission the borehole at your own cost.

The responsible approach is to establish your property’s dolomite risk classification before you do anything else.

Dolomite Risk Classifications

South African practice (informed by standards developed through bodies including the Council for Geoscience) assigns dolomite land to risk categories. These typically run from lower-risk zones where limited development is permitted with precautions, through to high-risk areas where surface development is severely restricted or prohibited.

Your local municipality’s town planning or geotechnical department should hold zone maps. A professional geotechnical engineer or engineering geologist can interpret your site’s classification and advise whether a borehole is permissible, what investigation is needed first, and what construction method a driller must use.

Do not rely on a neighbour’s assessment or a driller’s verbal reassurance. Dolomite risk can change significantly from one stand to the next.

What a Dolomite Risk Assessment Involves

A formal dolomite risk assessment for a residential stand is carried out by a suitably qualified geotechnical professional. It typically involves:

• A review of existing geological and municipal records for your area
• A site inspection examining surface features, vegetation die-off, and visible cracking
• In some cases, geophysical survey techniques (such as electrical resistivity or ground-penetrating radar) to detect subsurface anomalies without excavation
• A written report classifying the risk and recommending whether and how drilling may proceed

The cost of this assessment varies by site complexity and the extent of geophysical work required. Get a written scope and quote from the professional before committing. Do not ask a borehole driller to provide this assessment — it is a geotechnical function, not a drilling function.

If you're ready to find drillers with dolomite experience in your area, compare 3 free quotes — vetted installers, no obligation.

Choosing a Driller for Dolomite Ground

Not every borehole contractor has experience working on dolomite, and that experience matters. The drilling method, the casing specification, and the grouting of the annulus (the gap between the casing and the borehole wall) all affect how much water is directed into the formation and whether the borehole shaft could become a preferential pathway for subsurface erosion.

When speaking to contractors, ask directly:

• Have they drilled on dolomite before, and in which risk zones?
• What casing and grouting method do they use on dolomite sites?
• Are they familiar with your municipality’s approval process for dolomite earthworks?
• Can they provide references from dolomite projects?

A contractor who is vague or dismissive about these questions is not the right person for this job. Our broader guide to borehole drilling covers what to look for in a contractor generally; on dolomite, the geotechnical awareness criterion moves from desirable to essential.

For context on why Johannesburg’s geology varies so significantly across short distances — and why this affects drilling decisions — the post on Johannesburg geology and drilling is worth reading before you speak to contractors.

What Happens if You Drill Without Assessment

Beyond the physical risk — which is real — there are practical consequences worth spelling out:

Risk category	Consequence
Insurance	Many home insurers exclude sinkhole damage if earthworks were carried out without required geotechnical approvals
Resale	A non-compliant borehole must typically be disclosed or decommissioned before transfer
Municipal enforcement	Councils can require decommissioning and remediation at the owner’s expense
Neighbour liability	If your borehole contributes to a sinkhole affecting adjacent property, you carry significant legal exposure

None of these outcomes are hypothetical. They are documented consequences of ignoring the assessment requirement.

Dolomite or not, getting the right installer makes a real difference. Request quotes from three vetted drillers and compare what they recommend for your site.

The Bottom Line for Dolomite Properties

A borehole on dolomite is not automatically off the table. Many have been drilled safely on lower-risk dolomite land, where the ground conditions and proper practice made it viable. The point is not to deter you — it is to make sure you go in with accurate information rather than assumptions.

The sequence that makes sense is: establish your risk classification, commission a geotechnical assessment if required, obtain the necessary municipal approval, and then appoint a driller with demonstrated dolomite experience. Cutting any of those steps to save time or money creates risks that dwarf the cost of doing it properly.