Eric,
This is an interesting technique you describe.  I'd like some clarification on
the use of the sand bags.  Do I understand you correctly that after you
cover the features with plastic and the larger excavated area containing
the features with filter cloth (agricultural type?) that you do not backfill the
excavations but place sand bags around the perimeter of the filter clothed
area?  Sorry, my mental picturing system is not working up to par today.
 
Jane Brown
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