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i LOWRY & ASSOCIATES Page 4 August 17, 1990 L & a No. 90-190 CONCLUSIONS Ground Water It is anticipated that high water stages of the Mokelumne River would raise ground water levels below the existing Tracy Lake bed and, depending upon whether the Mokelumne River crested its bank, Tracy Lake would flood. It is our understanding that the 100-year flood level for this project is at elevation +28 feet. Since the building pad areas that are below the 100 year flood plain will be raised above that level, ground water should not l adversely affect the completed building lots. 1 Surface Water During and shortly following the wet season, run-off water may saturate surface soils. If grading is to proceed during the winter and spring months, a saturated soil condition may severely impede grading operations and soil may become unstable. In addition, saturated soils may require considerable time to dry out in order to reach a moisture content at which the specified minimum degree of compaction can be obtained. Bearing_Capacity Surface silts and sands are considered suitable for support of the proposed residential construction. Engineered fill placed and compacted in accordance with the recommendations of this report will also be suitable for support of the proposed construction. Support for the proposed bridge abutments can be achieved either by shallow i foundations based within on-site soils recompacted as engineered fill or by deeper foundations such as drilled piers or piles. If shallow foundations are to be considered, it is concluded that scour from flood stages of the Mokelumne River should be analyzed so that these foundations are not placed in potential scour zones. Potential Settlement It is not anticipated that native soils or engineered fill constructed to support residential houses will consolidate with time. However, the soils directly under the proposed berm location that will traverse Tracy Lake are prone to consolidation with the addition of the proposed 20 to 25-foot depth of engineered fill. It is concluded that these soils may consolidate from 12 to 16 inches and consolidation could take from 9 to 12 months to reach 90 percent of the maximum calculated settlement.