The big question is – what kind of soil lies under the levees? 

"Depending on how thick that is and how permeable the soils beneath that are there may be a concern or there may not." 

Steve Mahnke heads urban levee evaluations for the state Department of Water Resources. He says they hope to find clay or some other kind of water resistant soil.

What they don’t want to find is sand or gravel. Those materials could cause water to seep under the levees…and sand to bubble up on the inland side. 

"You can get boils which can lead to movement of material and eventual failure." 

Crews will be collecting soil samples for another week or so. Mahnke says if the samples show deficiencies, they’ll come up with a plan for repairing the levees. 

Similar soil tests found under-seepage problems in Natomas. That led FEMA to order a building moratorium in Natomas until the levees are upgraded.