grade beam with helical pile

huangyhg

grade beam with helical pile
i am designing reinforced concrete grade beam with helical piles below in an area with high water table and underground springs.
although beam can be 24 inches deep based upon loads, plan examiner tell me that 7 ft deep beams are generally used in underground spring areas and in coastal areas because of possible scour of soil below beam.  
is this so?  can an underground stream scour the soil and therefore impact the piles.  is this plan examiner correct.   
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scour is a definite problem in coastal areas where tidal ebb and flow causes almost continual changes in bottom contours. not familiar with this action from underground springs, but sounds like a reasonable concern.