It’s really important to be aware of Phytophthora plant pathogens that can be spread via contaminated soil- any soil transfer activities or storage/stockpiling could introduce contamination unless phytosanitary procedures are followed.  In the Bay Area of California, we are very careful during any kind of soil handling (and growing plants or planting plants) and make sure that all tools, equipment, shoes, etc are sanitized before use (70% isopropyl alcohol solution for small tools/boots and use of commercial car washes for large equipment), as well as pasteurizing potting soil and other practices (if growing or dividing plants in a nursery).  If stockpiling soil, it should be placed on clean, sanitized tarps.  For more information you can visit http://www.calphytos.org.