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Santa Maria ReservOir. my October 28, 1993 Page - 3 .. . Seepage found 82 feet from the spillway and 47 feet below the dam crest. . A second 47 feet below the dam crest and 162 feet from the spillway. . Seepage found in 1993 near the left abutment at elevation 246.1 and 247.7 as well as lower at 223.7 and 226.2. These recent seeps emit 10 gpm to 35 to 40 gpm individually. All seeps appear to be inactive or insignificant when reservoir levels are at or below gauge 64.5 feet The currently available repons do not indicate silty water emissions or silting. The recent whirlpool characteristics at high reservoir and the rapid flow (<2 hours) between the intake and the abutment piezometer and discharge zone provides clear indication that the seepage is potentially a serious problem. Considering this background info1lIllltion as well as the response characteristics during anempts to limit seepage (1993) as described in the Hydro-Triad, LTD repon, Harza is providing the following evaluation and recommendations. During the reservoir raise of 1993, May 31 to June 18, seepage increased progressively from elevation 10,225 upward into two areas adjacent to the plan location of the lateral toe drain and eastward about 50 feet. As seepage moved laterally from the initial zones more seeps became evident at elevations 10,292.5 and 10,297.5. These zones developed as the reservoir reached a gauge height of 69 feet. During this period piezometer observations indicated maximum rises of groundwater in the abutment within 7 days and within the core in 13 days. The piezometer responses relative to the dye migration rates indicate that peak velocities, e.g. largest fracture apertures are near the highest gauge heights recorded. Flow times at peak reservoir level were 2.5 hours and 1 hour and 50 minutes respectively. Anempts to plug the seepage intake zones were made. Bentonite, cement and straw were used. At the same time, the reservoir was lowered to gauge height 60.5 feet. These actions resulted in the drying of the upper seepage zones. Testing and observations throughout July and August confirmed that the seeps progressively dry up as the reservoir water level drops. It's noted that the abutment piezometer, CA-1, dried up on July 13th at gauge level 65.4 feet. The piezometer, CE-2, located in the core dried up on July 17th at gauge height 62 feet. It appears that the discharge point of the groundwater gradient in the downstream shell of Continental Dam starts to rise above the toe of the dam as the reservoir level rises above 58 to 59 feet (gauge). As the reservoir level reaches gauge levels of 64 feet the velocity of the seepage increase dramatically and is measured in hours. This response infers that the critical abutment seepage is occurring between elevation 58 and the dam crest, a height of 32 feet. This does not presume no seepage below height 58 but that the Page 7 of 15