Well Siting and Geology
Siting questions blend Michigan's glacial and bedrock geology with the isolation distances that decide whether a location is legal. The exam tests whether you can match an aquifer to a well design and defend a location before the rig moves.
Michigan's aquifer framework
- Glacial drift supplies most domestic wells: outwash sand and gravel yield the most; clay till yields little and transmits water slowly.
- Bedrock units include the Marshall Sandstone, the Saginaw aquifer, the Michigan Formation, and karstic limestone in the northeast Lower Peninsula.
- Groundwater moves toward surface water and down the hydraulic gradient, so a well down-gradient of a manure stack, fuel tank, or septic system pulls those impacts toward its intake.
Siting rules that carry points
- Confirm isolation distances first: roughly 50 ft from a septic tank and 100 ft from an absorption field, plus separation from barnyards, silos, and chemical storage.
- Prefer upland, well-drained ground; a low spot collects runoff at the casing.
- In a floodplain the wellhead must stay above expected floodwater, which usually means extending and sealing casing.
Worked example
A proposed well measures 35 ft from a septic tank and 80 ft from the absorption field. Reasoning: both distances are short, and the tank is the nearer hazard. The driller relocates upslope to 55 ft from the tank and 105 ft from the field, confirms no other source is closer, and records the final coordinates and distances on the well record.
Traps
- Treating yield and water quality as one question; a high-producing sand can still sit in a bad location.
- Ignoring gradient: distance alone does not protect a well that draws contaminants toward itself.
- Assuming a variance can be obtained after the hole is drilled.