During a fluorescein dye trace in central Kentucky karst, we saw first arrival at a spring 7.8 km away just 14 hours after injection — about 9 m/min — compared to about 0.3 m/day Darcy velocity I see in a nearby sandy unconfined aquifer. That contrast is exactly why the same pumping rate can be sustainable in one system and risky in another, depending on conduit versus matrix flow and recharge timing. What’s your best subsurface speed record, and did it change your pumping or protection strategy?
Fluorescein hit ‘14 hours’ here too; dry-season pulses lagged to 3 days.
Quick tip: in karst I stopped relying on charcoal packs — , they miss peaks — salt slug plus a cheap EC logger at 1‑min resolution caught the “first arrival” near 7.8 km in about 15 h, but the tail ran two days and changed the mass balance. I’m with you on the about 9 m/min headline velocity; small caveat is that for pumping I weight the recession tail and low‑flow windows because conduit storage/backflooding can make the effective rate much slower. Handy overview from KGS if anyone wants a refresher: Page not found, Kentucky Geological Survey, University of Kentucky.