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I I I I I I I I I I I I I I I I I I I JCHA Rueter-Hess Reservoir Project Description March 1999 reservoir area. Knight-Piesold (KP) conducted a preliminary geotechnical inv1estigation for the proposed Rueter-Hess dam axis in 1994 that included the drilling of four boreholes along the proposed dam alignment to evaluate subsurface conditions. In 1996, KP conducted a follow-up subsurface exploration that included the drilling of an additional four exploratory boreholes along the abutment areas of the proposed dam alignment and the digging of 23 test pits in the reservoir basin and embankment footprint areas to gain additional knowledge about the near- surface soils and bedrock, in addition to obtaining a. cursory material assessment. The results of the KP studies that have been conducted to date indicate that there are no geotechnical factors that preclude the ability to build the desired structure based on the data available to date. Specific findings of these studies include: (1) The proposed dam abutments contain some non-cemented sandstones and possibly some unconsolidated sand, as well as being underlain by hard to very hard, low-permeability claystone. (2) The porous materials on the abutments may require some engineering treatment, such as injection grouting, a slurry wall, or a diaphragm wall cutoff through the sandstone to the underlying claystone. (3) The valley bottom contains significant quantities of porous sand and gravel, which likely will have to be removed from the dam footprint prior to construction. (4) Areas outside of the valley bottom are underlain by silty to dayey sand and sandstone, which offer good embankment founding conditions.. Further geotechnical work will need to be done for a complete assessment of the Ruelter-Hess Reservoir area, as well as the dam axis. However, these preliminary studies were used in developing initial cost estimates for the Rueter-Hess Dam. 5611i.rpt -8-