Foundation Design - Role of Surcharge

Hi All,

I am designing an Isolated Footing and got confused in certain parameters under Cover & Soil - " Depth of water Table" and  "Surcharge for Loading". I tried to found out the definition in Foundation Toolkit but it didn't specify in detailed matter. Kindly help me to answer the certain questions.

1. Loads being considered under surcharge? 

2.  Role of surcharge when depth of water table is below the soil and when depth of water table is above the soil ?