Plugging a Hand-Dug Well Near a Sinkhole
An old farmstead has a 36-inch-diameter hand-dug well, 30 feet deep, with a brick liner and about 10 feet of water. The owner wants to fill it with fieldstone and dirt and cap it with a concrete slab. A 2-inch driven sand-point well 20 feet away is still used for livestock, and a flowing artesian condition was reported in the area. The hand-dug well is 70 feet from a septic tank and 40 feet from a sinkhole that accepts surface runoff. The casing top is flush with the ground, and the well has been open for years. The owner has a quote from a landscaper to 'fill it to grade' and asks whether that is acceptable. You are the driller called for a second opinion.
1. Is filling the hand-dug well with fieldstone and dirt acceptable? Identify the pathways and hazards.
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Fieldstone and dirt are not an acceptable plugging method for a hand-dug well. The fill is highly permeable, will settle over time, and leaves voids through which surface water and contamination can move downward. The brick liner can also collapse, creating a larger opening and a safety hazard. The well is only 40 feet from a sinkhole that accepts runoff, so surface water can enter the well directly and carry sediment, bacteria, and nutrients into the aquifer. The nearby sand-point well and the reported artesian condition increase the risk that the hand-dug well is a conduit between aquifers or a pathway for upward flow. The open top and flush casing make the well a physical safety hazard as well. The correct approach is to remove debris, evaluate the liner, and place a continuous low-permeability seal from the bottom to the surface, with the seal designed for any artesian flow. A concrete slab alone does not address the subsurface pathway.
2. Outline a plugging sequence and materials for this well, including how to handle possible artesian flow and the brick liner.
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First control access and test the atmosphere; no one should enter the well. Remove floating debris and any loose liner material that could interfere with a seal. Disinfect the well and, if flow is present, install a temporary standpipe or cap to control the artesian head rather than letting water wash out the seal. For a 36-inch hand-dug well, place a clean, stable base of gravel or crushed stone only if needed to support the seal, then introduce a continuous seal by tremie: cement grout, bentonite-sand slurry, or properly placed bentonite chips in increments. The seal must extend from the bottom of the well to the surface and must cross the water-bearing zone without bridging. If artesian flow is strong, use a weighted cement plug or extend casing and grout under pressure so the flow cannot channel through the seal. The brick liner can remain if it is stable, but voids behind it should be filled. Finish with a concrete cap, slope the ground away, and divert runoff from the sinkhole.
3. What notifications and records are required, and what should be done about the nearby sand-point well?
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The plugging should be reported to the Iowa DNR on the required form, with the owner's information, well location, diameter, depth, static water level, flow condition, materials used, seal intervals, and final cap details. The landowner should receive a copy, and local authorities should be notified if the county requires it. The nearby 2-inch sand-point well must be evaluated separately. If it is properly constructed, sealed at the surface, and still needed for livestock, it can remain, but it should be protected from surface water and sampled if the hand-dug well is found to be contaminated. If it is an old driven point with a poor surface seal or a gravel pack open to the surface, it may also be a conduit and should be upgraded or plugged. The two wells should not be connected or used to relieve artesian pressure. Documentation should show that the hand-dug well was sealed, not merely filled, and that the sinkhole runoff was diverted.