Tool T02 · Pump Test
The cone of depression.
When you pump a well, you don't just move water at the well — you create a cone-shaped depression in the water table for thousands of feet around. This tool uses the Theis (1935) equation to show how that cone forms.
Parameters
500 gpm
MLGW wells: 500–1500 gpm typical
60 ft/day
Memphis Sand: ~60 ft/day
200 ft
Memphis Sand: ~600 ft
1 × 10⁻⁴
Confined aquifer: 10⁻⁴ to 10⁻³
1 days
Watch the cone spread over time
Drawdown at well face
9.5 ft
Transmissivity T = 12,000 ft²/day
Cone reaches 5,000 ft
0.95 miles out
Beyond this distance, drawdown is less than 1 ft.
Cross-section through the well
Why this matters for POA
A large cone of depression can pull water — and contamination — from further away than expected. If a proposed industrial well sits near a contamination plume, its cone could pull the plume into the drinking water supply.
This is central to POA's 2017 fight to stop TVA from drilling cooling wells next to arsenic-contaminated coal ash ponds. The cone of depression would have reached directly into the plume.
Data:Theis (1935)·USGS Groundwater Notes·CAESER