Sand-Laden Gravel Pack on a 6-Inch Domestic Well
A driller completes a 6-inch PVC domestic well to 180 ft through fine sand and gravel. The screen (80-slot, 0.080 in) runs from 150 to 175 ft, and the annulus is gravel-packed with washed 8/16 mesh material. After development, the well is test-pumped at 15 gpm and produces visibly sandy water that has not cleared after 90 minutes. Static water level is 60 ft; pumping level is 95 ft. The driller's client demands a pump be set immediately because the household is out of water. The driller suspects the pack is undersized relative to the screen opening and that development was cut short. The driller has a surge block, a bailer, and a temporary test pump on site, and enough daylight for roughly four more hours of work.
1. Evaluate the sand-production problem and decide whether the pump should be installed today.
Read the worked answer
No. Persistent sand after 90 minutes at 15 gpm indicates the gravel pack and screen are not yet filtering the formation, and a pump set now would be abraded by sand and could seize. The first check is the pack-to-slot relationship: 0.080 in slot with 8/16 mesh washed gravel is a reasonable pairing, so the more likely cause is incomplete development rather than a sizing error. The driller should resume development with the surge block and bailer, alternating surge and bailing until the discharge clears, then re-test at a controlled rate. Install only after the water runs clear at the design rate. Document the sand content; if it persists after proper development, the screen or pack must be reconsidered before any pump goes in.
2. Given the pumping level of 95 ft and a 15 gpm target, what setting depth and pump considerations apply, and what constraints does the 6-inch casing impose?
Read the worked answer
With a pumping level of 95 ft at 15 gpm, the pump intake must sit well below that - typically at least 10–20 ft of submergence - so a setting around 115–125 ft is sensible, kept above the screen top at 150 ft to avoid drawing sand directly off the pack. A 6-inch casing limits the pump outside diameter; a 4-inch pump leaves only about 1 inch of annular clearance, so a 3-inch or slim 4-inch unit is safer, and the drop pipe and cable must be sized to fit. The driller must also check that the well can sustain 15 gpm without the pumping level dropping to the intake, and select a pump whose head curve delivers 15 gpm at roughly 95–125 ft of lift, not a pump chosen only by horsepower.