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1 r I ti I 1 Reservoir Site Characterization obtained from twelve test holes bored in and in the dam raise, and the proposed emergency spillway. 1 proposed borrow areas located around the reservoir Reclamation and Woodward-Clyde's laboratories. ' provide additional information on the dam embankn site for the proposed dam faise design; to characteri provide additional information on the availability an characterize the geologic setting of the reservoir are geology, and foundation strength; to examine the cl and to provide information on the phreatic surface t ;inity of the existing dam, the proposed ienty-three test pits were excavated in the The samples obtained were tested in both le objectives of the investigation were to nt and subsurface conditions near the dam the overburden soil and bedrock; to properties of construction materials; to in terms of seismic potential, structural racteristics of the existing embankment; ough the existing dam. The data obtained from this investigation we "Preliminary Geotechnical Investigation, Elkhead 1 prepared by Woodward-Clyde in January, 1994. 1 recommendations for the proposed enlargement of test hole and test pit logs from the previous geotecl prepared based on the understanding that the dam i that the new dam design would incorporate a new left abutment and an emergency spillway in the for right abutment. The executive summary and maps the Woodward-Clyde report are reproduced in Apl summarized in the report entitled n, Moffat County, Colorado"; was report presents the analyses and khead Reservoir along with the available cal investigations. The report was bankment would be enlarged 45 feet and vice spillway and outlet structure near the raphic saddle adjacent to the dam in the owing test hole and test pit locations from idix H. Also included in the Woodward-Clyde report are the results of geophysical surveys completed by Hadley and Hollingsworth, Ltd. Seven seismic lines (approximately 4,000 feet of seismic refraction profiling) were selected around) the existing dam to estimate the depth of unweathered bedrock and ripability of subsurface materials. The field work for this analysis was conducted between July 27 and July 31, 1993. Woodward-Clyde's investigation observed tha seepage through the right abutment and little seepage combined flow of approximately six gallons per min three weirs at the lower right abutment. Woodward this seepage flow could increase by one order of ma drain system in the embankment be designed to hanc dam raise designs which differ in regards to seepage Clyde's investigation. For the design of the appurtenant structures recommended that the emergency spillway be con on the results from the test hole logs and geophysi spillway will be founded into the underlying sand: recommended to be positioned closer to the left at can be installed on bedrock. Woodward-Clyde re be excavated or tunneled in bedrock and be partia below the core of the embankment. the dam currently experiences noticeable through the embankment. A total ite (gpm) of seepage was measured from Clyde estimated that with the dam raise nitude and recommended that the new le 10 to 50 gpm of flow. Two alternative remediation were proposed in Woodward- the dam, Woodward-Clyde tcted with 2:1 or flatter side slopes. Based survey it is anticipated the bottom of the ie bedrock. The service spillway was vent so that the spillway crest and apron amended that the primary outlet works to or fully encased in concrete for the length The geotechnical study also reviewed the investigations at the six potential borrow areas 1 Clyde estimated that there is adequate material ation obtained from the test pit around the reservoir site. Woodward- le for both the embankment fill and 3-7