Mine Subsidence and Old Coal Workings in Oklahoma

A depression has appeared in the lawn that was not there last year, or a corner of the house has dropped and the usual explanation about Oklahoma clay does not quite fit the shape of it. In parts of eastern Oklahoma, including parts of Tulsa County, there is another possibility that most homeowners have never considered: there may be a mine under the property.

This article covers where coal was mined in Oklahoma, which agency does what, what actually determines the hazard, what help exists and its important limit, and what any of it means when you sell.

Where the mines are

Coal mining began in Oklahoma in 1872 and took place primarily across a sixteen county area on the eastern side of the state. Early production came almost entirely from underground mines before surface mining took over.

The scale is larger than people expect. Over thirty two thousand acres have been surface mined, and roughly forty thousand acres have been mined underground. It is the underground workings that produce subsidence, because a room and pillar mine leaves voids that can eventually collapse toward the surface.

This is not only a rural question. The Conservation Commission, the Department of Mines and the Geological Survey produced a fact sheet specifically about past coal mining in Tulsa County.

Those agencies state that they believe there is some potential geologic hazard for subsidence over abandoned underground coal mines in Tulsa County. In April 2019 an opening appeared a few feet from the back door of a Tulsa home.

What actually determines the hazard

Two factors, and understanding them tells you why one street can be affected and the next one is not.

Depth to the mine. A shallow working has less rock between the void and your foundation.

Whether a rigid sandstone bed sits between the mine and the surface. A competent sandstone layer bridges a void that softer rock would not.

So shallow depth combined with the absence of a rigid sandstone layer suggests a higher hazard, while greater depth with a rigid sandstone layer suggests a lower one. That is geology rather than anything you can assess from the garden, which is why the agencies below matter more than a contractor's opinion.

Who does what

Three state bodies, with distinct roles, and calling the wrong one wastes a fortnight.

The Oklahoma Conservation Commission, through its Abandoned Mine Land Division, reclaims abandoned coal mines. It has had statutory authority since 1981, it is one hundred per cent federally funded from fees on active coal production, and it deals with mines abandoned before 3 August 1977 under the federal surface mining legislation. This is the agency to ring about a subsidence event.

The Oklahoma Department of Mines permits and regulates active surface and underground coal mines.

The Oklahoma Geological Survey holds the geological information.

The programme's record includes 187 completed projects, more than 5,500 acres reclaimed and 223 subsidence sites reclaimed. This is a working programme rather than a theoretical one.

The help that exists, and its limit

This is the sentence to take away, because it decides your financial position entirely.

Where a home is damaged by subsidence from underground mining, the Conservation Commission can do work to stabilise the home's foundations, or in some situations move the home. That is real and substantial help.

But the programme does not provide funds to repair damage to the house caused by the subsidence.

So the ground can be dealt with and the cracked walls, the broken services and the ruined finishes are yours. Understanding that division early is what stops a homeowner assuming the state will make them whole.

Ask your insurer what your own policy covers, and ask specifically. Earth movement is a standard exclusion on ordinary homeowners policies, as our article on earthquake damage and selling a house in Oklahoma sets out, and some states operate specific mine subsidence insurance arrangements. Establish what applies to you before you need it rather than during a claim.

Telling it apart from ordinary movement

Most Oklahoma foundation movement is not mining related. Expansive clay, drought, drainage and guttering do far more damage across the state than voids do, and our articles on why Tulsa houses move and drainage, guttering and foundations cover the usual causes.

What points toward something else is the pattern. A localised depression rather than a general settlement. A hole rather than a slope. Movement that arrives suddenly rather than over years. Damage that does not correspond to where water goes.

Do not investigate a hole yourself, and do not fill it. An opening over a mine void is a safety hazard and the appropriate response is to keep people and animals away from it and ring the Conservation Commission.

Where the question is whether the structure has moved, get an engineer's report. Our article on which foundation cracks matter covers reading the damage.

What it means when you sell

Disclose what you know. Known subsidence, a known mine under the property, any reclamation work done and any claim made all belong on the disclosure form. Our article on Oklahoma seller disclosure requirements covers the position.

Documentation settles it. Where reclamation has been carried out, the records of that work are worth a great deal, because they convert a frightening idea into a completed project. Where an engineer has assessed the structure, the same applies.

Do not volunteer a diagnosis you do not have. Telling a buyer the movement is mine subsidence when nobody qualified has said so creates a problem you may not actually have. Describe what you observed and what was done about it.

Where we come in

Establish what you actually have before you decide anything. An engineer's report and a call to the Conservation Commission cost very little, and in most cases they establish either that the movement is ordinary or that it is a defined problem with a route through it. A great many houses in these counties never have a problem at all.

Where a cash sale genuinely fits: confirmed subsidence damage to the structure that you are not going to repair, a house where the ground has been stabilised but the building has not, or a buyer's lender or insurer that has already taken a view. We buy with the damage in place and take the repair on. Our page on selling a house with foundation problems sets out how the number is built.

The short version

• Coal mining began in Oklahoma in 1872, primarily across a sixteen county area in the east, with roughly 40,000 acres mined underground
• The Conservation Commission, the Department of Mines and the Geological Survey have produced a fact sheet on past coal mining in Tulsa County and see some potential hazard there
• Hazard depends on depth to the mine and whether a rigid sandstone bed lies between it and the surface
• The Oklahoma Conservation Commission's Abandoned Mine Land Division is the agency to ring, and it has reclaimed 223 subsidence sites
• It can stabilise foundations or in some situations move a home, but it does not provide funds to repair damage to the house
• Ask your insurer specifically. Earth movement is a standard exclusion on ordinary policies
• Most Oklahoma foundation movement is clay, drought and drainage rather than mining
• Do not investigate or fill a hole. Keep people away and ring the Commission