I was digging next to where the pipes run between the pool and the equipment pad and found wet dirt down at pipe level - about 24" below grade. At first I thought I must have cracked one of the PVC pipes while digging but now I'm not sure. I dug a trench to expose about 3 feet of the pipes so I could find the leak and have enough room to do a repair, but I can't find any crack or damage in any of the pipes.
Here's what is happening: There is about 1" of water in the bottom of the trench, just enough to cover the pipes. When I suck this water out with a Shop Vac, the bottom inch will refill in less than 5 minutes but the trench does not fill any more than that bottom inch. The pool is about 15' away and the water level in the trench is about 18" below the level in the pool, so the head in the pool doesn't seem to be operating on the water in the trench. Running the pump and switching the valves between pool and spa, and running the booster pump for the cleaner, doesn't change anything. If I run the pump and then Shop Vac the water out of the trench, the bottom of the trench will refill with an inch of water in about 5 minutes even while the pump is running.
I'm thinking that if a return line was cracked, then the trench would fill with water while the pump was running. If a suction line was cracked, then the water in the bottom of the trench would get sucked into the suction line. Because running the pump doesn't change what is happening with the water in the trench, I'm thinking that the water must not be coming from any of the pool lines. Am I correct in thinking that a crack in either a suction or return line would cause the water in the trench to go down or up when the pump was running? Please offer suggestions because I can't figure this one out. We don't have high groundwater in my area, so that can't be the source.