Material source to be used for building back filling having high chloride content. What shall be remedial action if no choice to use?

The substructure exposed to the filling material shall be protected with some type of chemical treatment as barrier against incoming moisture and/or waterproof protective boards/sealant or tapes in order to protect the rebar and restoring concrete durability

Since Chloride content will be high and react invariably to the conditions present, you must determine treatment strength outcome based on this. Rebar with proper irrigatiion must be present in order to reinforce the structure. 

All concrete contct surfaces with back filling material having haigh chloride content must have the following:

1. Chathdic protection to protect reiforcemet st. rebars against corrossion (Piles and deep/shallow foundations and concrete/non concrete walls).
2. Using water proofing insulation for sides surfaces and bottom side of foundation).