retention wall slab settlemen

huangyhg

retention wall & slab settlement
we have a rentention wall slab that is 65' long, 7 ' tall with an attached, supported poured concrete slab. the slab area is a pool deck with the pool being 25' from the retention wall. approximately 6' of the rentention wall has settled about 2" on just one side. the supported slab that is attached to that portion of the rentention wall settled recently about 1" down, on the inside area,(away from the wall) where the slabs come together to form an overflow drain line for the pool. it is the only area that has settled. the retention wall also has 5 - 2" drain holes, drilled out several years ago, for some unknown reason, 2 of the drain holes that are inline with the slab that has settled, have been recently letting the sand/backfill drain out of them  at an increasing amount. i suspect a major shift in the back fill under that portion of the slab(s) however most of the other suggestions say it was just a small wash out and that the slab can be fixed without any major work. i would like some comments or suggestions on this.thanks larry
were not because you talk of the drain holes showing action precisely where the problem is, i would have thought of inspecting the pool for leaks (measuring loss of level etc). however, it seems is coming from above and washing the ground for both the drain holes and the fact of there being settlement indicate loss of material. is there any important or stable source of water above, such rains, excessive watering, or must be looking for sewage failures etc?

it is impossible to give an informed opinion about something like this when the problem is just expressed in words.  some visual information is required.
hokie66, i am working on getting a picture that shows this, thanks for the suggestion.
ishvaaag, we did look at all water issues, and suspect rain water, however we never thought of the sewer, that would be worth checking will let you know.
we tried a garden hose, there was not enough water to show us anything though.