Well Siting, Geology, and Hydrogeology
Well Siting, Geology, and Hydrogeology
This domain tests whether you can predict where usable groundwater occurs in Georgia and whether a proposed location meets isolation requirements before the rig moves. Items favor practical judgment: province-level geology, aquifer type, contamination pathways, and setback distances.
Georgia's provinces and what they mean at the rig
- Blue Ridge and Piedmont - crystalline bedrock beneath saprolite. Water is stored in fractures, not in the rock matrix. Yields are variable and often low; one dry hole does not condemn a site. Saprolite must be cased off before drilling rock.
- Valley and Ridge / Appalachian Plateau - folded carbonates and shale; karst terrain. High yields from solution conduits, fast turbid response after rain, and high risk of surface contamination moving straight down. Sinkholes are both a siting hazard and a drilling hazard.
- Coastal Plain - unconsolidated sand, clay, and limestone in layered, often confined aquifers (Upper Floridan, Midville, Dublin, Cretaceous). Flowing artesian wells are possible, and saltwater intrusion is a real constraint near Savannah and Brunswick.
Siting rules that decide the exam question
- Locate upslope and upgradient of septic systems, animal pens, fuel tanks, and chemical storage. A well downslope of a drainfield fails regardless of linear distance.
- Meet the state minimum isolation distances from pollution sources, property lines, and rights-of-way; keep the wellhead out of drainage paths and above flood level, or properly sealed and vented.
- Ensure rig access and a stable pad - a setback that a rig cannot reach is not a usable site.
- Confirm permit status with the county health department, and check for existing or abandoned wells and buried utilities (call 811) on the parcel.
Worked example
A 5-acre Piedmont lot slopes down toward a creek. The house drainfield sits mid-slope, and the only flat pad is 40 feet downslope of it. Reasoning: the pad is convenient but downgradient of a biological contamination source, so reject it. Move to the uphill side of the house, meeting the required distances from the drainfield and property line, with the wellhead above the floodplain and drainage diverted away. Note in the plan that fractured-rock yield may require drilling deeper or a second attempt.
Traps that cost marks
- Treating distance alone as protection while ignoring slope and gradient.
- Assuming a high-yield neighbor guarantees yield across a fault or lithologic contact.
- Relying on dowsing or "water veins" instead of fracture mapping and nearby well records.
- Siting in a karst depression or obvious surface-water collection point.