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SantaMariaReservOire any October 28. 1993 Page - 4 .. groundwater gradient at reservoir levels below this point only daylights at the toe of the dam Evaluation of Seepage Detailed analyses of the seepage conditions attributes seepage to migration through the highly fractured abutment rocks. The outcrops observed during our site visit make this process likely. Early seepage on the right abulment points to the possibility of seepage under the spill way invert as well. The lat<:ra1 distribution of seepage zones across the downstream face indicates that the dam shell has developed stratification either during construction or through in situ weathering of the embankment materials. Seepage appears at the toe of the downstream section and rises to elevation 10,247 as the reservoir rises. With reservoir lowering the seeps dry up in the reverse sequence. The latest episode indicated that the core saturation rises only slightly and climin;shes slowly as well. These responses tend to confirm saturation from the abutments and general satisfactory integrity of the core. While the threshold elevation for increased g.eepage appears to be elevation 58 feet (gauge), opinion has been offered that seepage is <:ontributing to the stilling basin at lower gauge levels. This opinion is reasonable and indic:ates that the flow path and gradient for gauge heights below 58 feet stay well within the dam shell. The response of the piezometer, CE-2, during plugging of the seepage intake zone infers possible compromise of the clay corelfoundation in the immediate vicinity of the base of that piezometer. It also indicates that a grouting program could have the potential to shunt flow paths in an uncontrolled manner if care is not taken. Proposed exploration It is our opinion that there is stratification of the downstream emb~n 1cmp.nt both horizontally and on planes inclined parallel to the original dam outer slope. Zones of lower permeability are forcing seepage water from the abutments into the downstream shell and across the face of the dam We propose, that a series of five cored and sampled bore holes be drilled and observation piezometrn. installed. These boring should be located as shown on Figure 1-3. Boring 1,2, 3, and 4 should extend through the embankment to a depth of at least 5 feet above the base of the dam. The fifth boring :;hould be an inclined borehole from the left abutment inclined towards the canyon at an angle of 60 degrees. It will penetrate at least 90 feet. I?uring drilling ,falling head tests will be performed on the embankment materials; pressorie testing will be performed on the foundation rock in the fifth boring.. - Page 8 of 15