The trench keeps filling with water

I keep dreaming of the same trench—unfinished, open, and the water table rising around my boots. Every time I bend to lift a coin it's warm, like someone held it just before I got there. I keep troweling and the walls keep slumping. There's no supervisor, no finds box, no end of day. Just the water and the coin and me, not quite backfilling, never quite drowning either.