This project consisted of site research and preliminary geotechnical engineering evaluations for a proposed regional wastewater treatment plant for Mobile Water and Sewer System to be constructed at the former ALCOA spoil disposal site (mud lakes). The historical research for this project included the review of seven previous geotechnical studies performed by GET in the area. The review indicated that the natural soils underlying the spoil material within the pond were highly compressible. The spoil material within the ponds was found to contain a bauxite residual slurry that is highly caustic and highly compressible with low shear strengths.
Soils explorations were performed within the dikes around the perimeter of the pond to evaluate dike materials and strengths. Soil explorations were performed with a pontoon mounted drill rig from within the pond. GET performed laboratory testing of the highly compressible spoil materials within the pond and soft soils beneath. This test data was evaluated with regard to design/settlement issues. Settlements in the order of 3 to 5 feet were projected. Samples were also collected and tested for potential contaminants. GET developed preliminary constructability options and provided the results to the design team. Various foundation options were also provided for the anticipated structures that would be required for the WWTP. GET noted potential benefits and drawbacks of each option.