At the peak of pear packing season, Daniel Wilson's Sacramento County operation is bustling. Pears are sorted wrapped and prepared for shipments to stores across the country. "I get so buried in it, I don't think about it too hard. We just go until we're done," Wilson said.It's an operation that sits a few feet below sea level, so flooding is always in the back of Wilson's mind. His orchards and packing plant is surrounded by levees. "If you look, all the equipment is up high and that's why," Wilson explained, adding, "100 percent of what we farm is protected by levees anywhere from five feet below sea level (to) five feet above sea level. If the levees break, we're out of business."That's why many farmers, like Wilson, and engineers are concerned about the state's proposal to dig two four-story tall water tunnels under the Delta. Engineers are concerned that the below-ground construction could disrupt vital levees and other infrastructure above it."We really don't know the competency of that soil," said Chris Neudeck, an engineer who works with irrigation districts that maintain many of the levees along the Delta. "If you dig a hole and then pull out, would it collapse?" He pointed to smaller projects that had a difficult time getting through this part of the state."We've had similar situations in the Delta, with boring machines that are more like four feet in diameter that have failed initially because of soft soil," Neudeck said."Generally speaking, they'll be working within that muck setting that's very soft, almost if you think of San Francisco Bay mud -- very sticky, we think," Wilson said. "The one thing they don't have is gravel, rock, things of that nature."The proposed tunnel path stretches 35 miles from west of Elk Grove to just below Discovery Bay. The tunnels would take water from three intakes along the Sacramento River to existing aqueducts south of Discovery Bay, and then the water will be sent to Southern California.Along the proposed path, there are at least 22 levees that would sit above the tunnels, Neudeck said. The concern is not so much the levees themselves, but the kind of soil that is below the levees. Neudeck said it's possible a tunnel boring machine could weaken the levees. As the machine goes under the levees, it could cause the soft soil above the machine to move around or settle, leaving the levees weakened. Another possibility: The digging could lower parts of the levees, leaving areas more prone to flooding."Any displacement of that fill vertically down would be a risk to the flood protection," Neudeck said.The threat of flooding is evident even in the state's own project animation. A clip shows how the state plans to use fill dirt to build up the construction site."The elevated pad would be raised high enough to protect vital equipment and the tunnel from flooding in case of a levee breech during construction activities," a narrator says in the video."The rate at which the actual tunnels are constructed and bored out is actually very slow. They take years to go through and dig," said Mike Mierzwa, a civil engineer for the Department of Water Resources.Mierzwa said the tunnels are being planned 15 stories below ground because it's what the state considers solid ground."It's deep enough where you are getting below the rivers where that we will be fine for the construction," he said.Mierzwa said the depth is similar to what's been used in other big civil projects, including the Channel Tunnel between England and France. He also said the state has already taken 200 soil samples along the proposed route."There's been an assessment of the levees themselves to make sure that they are shored up and can handle whatever happens during construction," Mierzwa said.Neudeck said the state's assessment is not complete and there are still questions."Every time you try to pin them down on a on a levee stability issue, they go, 'Well, we haven't made the plans yet, and we so we can't give you a straight answer,'" Neudeck said. "So that the target is very squishy. There is no there, there for lack of a better term."The DWR said there is still more planning to do. There would also be monitoring of the levees during construction to ensure if there was an issue with a levee, it could be addressed immediately.