Storage Vaults

by Gil Larson

 

Above ground vault system


The Nebraska senate voted that only above ground vaults would be allowed for any site that was chosen by Bechtel and their subcontractor U.S. Ecology. This system was being used in France although no reason was given except I feel that the senators wanted vaults that would be easier to find. This method was supposed to be cheaper than burring the vaults, and engineering-wise it is easier and less expensive to build above ground. The danger is settlement of the boxes, which can cause cracking. The reason other sites in Nebraska were not used was because of excessive settlement possibilities do to thick and multi layer overburden. Figure one shows what the typical box would look like. The more settlement that was expected the thicker the walls of the vaults must be, thus creating a higher cost. In Boyd County there was only approximately 15' of overburden thus very little settlement was expected.

Some of the problems of building above ground are of course settlement plus concrete weathers. Concrete slowly deteriorates under freezing and thawing. Above ground is also a better and easier target for vandals. The settlement factor is the worst cause especially in the light of high ground water. The water table was going to be near the surface on part of the site thus designed walls would be very thick and thus very expensive. If the design was based on dry conditions and the water table rose to the bottom of the sand major problems would occur with the saturated clay fill. This would lend to uneven settlement and cracking. Once problems started occurring the fix would be very expensive. Below ground vaults founded on rock would be choice of most engineers if no outside forces were involved, Figure two shows a typical below ground installation. The cost of digging the holes would be more than offset by the cheaper structures. As in all modern dry landfills the rubber liner would keep any leakage from entering the groundwater.

The case of the rubber, sand, and collection system along with excavation is minor. This design eliminates the chance for settlement along with a lot of the worry of leakage into the ground water. It is less sightly and safer from vandals. This system of burial is the new way of handling landfills, which take garbage, but also for ones that take industrial waster and no storage vault is built. If the site had been built 3 to 4 miles north of the chosen site, water problems would have been greatly reduced.