20 year old 18 x 40 x16 vinyl liner, galvanized steel side walls with concrete bottom.

This is the 4th liner we have had installed in this pool.

The concrete coping edge was cut off flush with the wall of the pool in order to install new composite decking coping. (We installed the new composite decking on top of the existing concrete pool deck). To construct new coping 2 x 6 composite decking joist were installed flush into the existing concrete pool deck. This was done in order to replace the old concrete coping( that was saw cut off) so that the new composite coping could be screwed into the composite joists and square up the edge of the pool.

Currently water is getting between our new vinyl liner and the galvanized side walls. We are not sure how it is getting there. We know we have groundwater issues and are putting in a new french drain system to alleviate water leaching into the side walls from underneath the old concrete pool deck. However, we are wondering if water could be getting behind the liner track because of installation of the composite coping. We suspect water is leaking through the coping and getting behind the track of the pool liner. Do we need to cover the composite joist area with a waterproof membrane (such as a roofing ice and water shield) before installing the surface coping made from composite decking? We have water tested the new coping and determined that water is coming from the old concrete coping area going down the surface of the liner but cannot determine if it is going behind the liner track? Has anyone experienced water getting behind the liner from leaking behind the liner track?