When the plumbers made the trench from the slab to the main sewer line it filled up with water. They believe that ground water was moving along the outside of the main sewer pipe and that when they disturbed the soil, it gave the water an easier path to follow.

My question is how often does this situation occur and is the normal fix to fill and compact the fill dirt in the trench and would this force the water to continue down the O/S of the main sewer line and not under the slab.

No water was found in the footings trenches or the natural gas service trench.

Thank you for your assistance. TL

It does sound suspicious.

All the other excavations were at the same time and weather conditions? (did it rain? landscape irrigation?...)

Usually sewer trench will be deeper than the gas, but not necessarily the footings.  If it was not deeper and the area is the same then there is no reason for this trench to attract water.

I have two concerns:

1. Where did the water come from?  Is it possible you have a leak under the slab somewhere?

2. Did they fill and compact the trench properly?  Trenches are a big problem because it is difficult to compact even under ideal conditions.  Usually, there is an inspector that verifies that the compaction was proper (90 to 95%).  Improperly compacted trenches can cause the soil above to subside, concrete to fail, and cause cracking of flatwork.

I am not really concerned about the water traveling backwards to the footings - unless I am missing something.

 A geotechnical engineer is the person who should be designing and supervising compaction work.  You will find them on larger projects because it is difficult to justify the cost for a single house.  However, it may be worthwhile to consult a local one at this time.

 Hope this helped.