If your O'Fallon home draws from a private well, one of the most useful papers you may own is the well log. This record is made when the well is drilled, and it is sometimes called a drillers' log or well completion report. It describes what the crew found underground and how the well was finished. Reading it before you choose a filter, softener, or other treatment can keep you from guessing at the problem.
Not every home has one. If you bought an older house, check your closing papers, the seller's disclosure, or any file the previous owner left behind. Well construction records are often kept by the state agency that oversees wells, so a copy may exist for your property even if you never received it.
What to Look For on the Log
- Total depth and casing depth. Shallow wells and deep bedrock wells often draw from different water-bearing layers, and that difference affects which tests make sense.
- Where water enters the well. Look for a screen, an open bedrock section, or a gravel pack. An open bedrock section can allow water from more than one zone to mix.
- Sealing at the top of the casing. A poorly sealed well can let surface water in, which matters when you are looking at bacteria or nitrates.
- Formation notes. Entries about clay, sand, limestone, or shale can hint at where iron or sulfur sources might sit.
- Water observations. Some logs note odor, color, or taste when the well was first pumped. Treat these as clues, not conclusions.
- Water level and pumping notes. These help you and a service technician understand pump and pressure tank needs.
How the Log Points Toward Treatment
Use the log to narrow your questions. A shallow well near a septic field or row-crop land raises questions about bacteria and nitrates. A deep bedrock well raises questions about naturally occurring radium, gross alpha, and uranium. Iron and sulfur problems can show up in wells that draw from certain rock layers, but the log alone cannot confirm them.
Radium is a naturally occurring element found in some rock and groundwater. Gross alpha is a broad screening measure a lab can run to indicate whether more specific radionuclide testing is worth doing. Uranium is a naturally occurring metal that can also be present in groundwater. The log can suggest these are worth checking, but only a lab result tells you what is in your water.
Turning the Log Into a Testing Plan
- Make a copy of the log and keep the original in a safe folder.
- Note the well depth, casing depth, and any odor or color comments.
- Start with coliform and E. coli testing. The MO State Public Health Lab offers free or low-cost coliform, E. coli, and iron bacteria testing, so check their current options before you collect a sample.
- Test for nitrates if the well is shallow or sits near row-crop fields or a septic system.
- Ask a certified lab about radium, gross alpha, and uranium if the well is deep in bedrock.
- Compare the results with the log before you choose any treatment.
Questions to Bring to a Technician
- Does the log match the well as it sits today?
- Was the well ever repaired, extended, or re-cased?
- Which water-bearing zone supplies most of the water?
- Does the proposed plan address your actual test results, not just a smell or a stain?
When the Log Is Missing
If no log can be found, ask neighbors on similar lots in O'Fallon and the surrounding area whether they know their well depths. Nearby properties may share similar geology, so their details can offer a rough clue. Still, a fresh test panel is a more reliable path than assumptions drawn from a neighbor's well.
The well log is a starting point, not a verdict. Pair it with current test results, and make treatment decisions based on those results rather than on the log alone.