Siting a Piedmont Domestic Well Near a Drainfield and a Neighbor's Declining Well
A 2.5-acre homesite in Walton County, Georgia, is underlain by 30 ft of sandy clay, 60 ft of saprolite, and fractured granite gneiss beginning at about 90 ft. The homeowner wants a domestic well and has proposed a location in a shallow swale that holds water for a day after rain. Distances are 25 ft to the property line, 60 ft to the septic tank, 95 ft to the edge of the drainfield, and 80 ft to an intermittent creek. A neighbor's well 175 ft away has a static level of 40 ft, a pumping level of 110 ft at 6 gpm, and was recently deepened after losing yield. The proposed well would be drilled to 300 ft with 6-inch casing set 20 ft into rock and grouted to surface. The homeowner is eager to begin and says the swale is 'just where the water is.' The driller must decide whether to accept the location or require a change before mobilizing.
1. Evaluate the proposed well location against Georgia siting requirements and hydrogeologic good practice. What would you recommend, and why?
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The proposal should be rejected as staked and relocated upslope. Georgia's well-location rule requires at least 50 ft from a septic tank and 100 ft from the drainfield or absorption field; 95 ft to the drainfield is short of the 100-ft separation, and the 60-ft tank distance is only marginally acceptable. The intermittent creek at 80 ft is not automatically disqualifying, but the swale is: ponded surface water can enter the annular space during drilling, saturate the grout, and create a direct pathway from the surface. The property-line distance may also conflict with local ordinance even if it meets the state minimum. A better location is on the upland side of the house, at least 100 ft from the drainfield, with the pad graded so runoff drains away from the casing. Because the saprolite is thick and permeable, casing should be seated at least 20 ft into competent rock and the annulus grouted continuously to land surface. The driller should document the setback decision and the homeowner's concurrence in writing before drilling.
2. How would you assess the likelihood that the new well will interfere with the neighbor's well, and what test would you run before committing to a pump setting?
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Start with the neighbor's specific capacity: 110 ft pumping level minus 40 ft static equals 70 ft of drawdown at 6 gpm, or about 11.7 ft per gpm. That is a low specific capacity and suggests a tight fracture system, so a new pumping well 175 ft away could add several feet of drawdown even at a modest rate. Estimate transmissivity from the specific capacity using a standard relationship, then use a distance-drawdown or Theis calculation to bound the additional drawdown at 175 ft; treat the result as an order-of-magnitude estimate, not a permit-grade prediction. Before setting the pump, run a 24-hour constant-rate test at the intended rate, with the neighbor's permission to measure their water level or at minimum to record their pump cycling. A step-drawdown test first will show whether turbulence is significant. If the test shows the neighbor's pumping level dropping toward the pump inlet, reduce the design rate, deepen the pump setting, or relocate the well farther from the property line.