43 RELIEF WELLS BEING DUG NEAR CHANNEL LEVEE

Workers Monday started digging 43 relief wells along the south side of the Diversion Channel levee to help prevent subsurface deterioration of the levee.

Phillip Boykins and Dave McCarty of United Geosciences of Villa Ridge, Mo., spent the morning taking soil samples along a 1-mile stretch at the base of the levee near Interstate 55 and Nash Road. After that they began digging a series of preliminary wells that will be lined with a screen and made permanent.

Boykins said he encountered about 70 feet of fine sand just below a level of clay. He was drilling to about 96 feet and taking samples every 2 1/2 feet. The samples will be used to determine the type of screen that will line the wells.

The engineers want to use a screen that allows the flow of water but keeps sediment out.

Boykins said the samples could not be used to determine the stability of the levee. He said they didn't encounter anything they didn't expect.

United Geosciences is subcontractor for Dewatering Service Co., which was awarded the job by the Corps of Engineers. Dewatering was given approval in December to start the project.

Deland Cooper, general superintendent of Dewatering Service Co., has been analyzing the more than 800 soil samples that have been taken.

Cooper said earthen levees allow seepage if they are exposed to high water levels for long periods. Water will run under the levee then rise to the surface on the other side. To seep through a levee, water has to break through a layer of clay near the top soil.

As the water breaks through cracks in the clay it weakens the clay and brings sand from underground to the surface in the form of sand boils.

Not only does the seepage deposit sand on topsoil, but it also weakens the protective clay layer and erodes the sand that forms the backbone of the levee.

"If it keeps taking away material the levee would just collapse," Cooper said. "If the water flows freely it will take the pressure off the clay cap. This area has sandboils all the time so it needs these wells."

Cooper said the wells will lessen the deterioration of the clay layer by providing an easier route for the water to flow to the surface. The screens along the well walls will also keep the water clean as it rises. Just as much water will be deposited on the protected side of the levee as would have seeped in, but the water will be free of sand.

The wells will be drilled about 80 to 100 feet deep. Cooper said samples will be taken later in the week to test the stability of the levee.