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�i 2-2 o Investigation of the seepage problem by D'Ap- polonia in 1981 with recommended remedial measures. o Installation of collection and control systems in areas downstream of the dam by D'Appolonia in 1982. The engineering.firm:of-record for design of the dam is Davis Engineer - Ing Services, Inc. Geotechnical subsurface investigations and recom- mendations for dam design were provided by Lincoln-Devore (1973). The dam was designed to be a zoned earthfill dam with a, fine-grained soil core and key trench; and sandy soil, shell zones on both the upstream jand downstream sides of the core. The design specified a chinmey drain to control seepage to be located between the core and downstream shell zone. The chimney drain was to be connected with a blanket drain placed beneath the downstream shell zone. The fill'was to be compacted and was i to be within specific grain size distributions, i.e., fine grained material in the core and coarse grained material in the shell. A cutoff excavated through alluvial soils and backfilled with sand was specified to be placed beneath the embankment. Construction inspection of the dam was performed by Davis Engineering Services. Daily construction records kept b9 site coAstruction.person- nel indicated that suitable fine-grained core material in the -required quantities was difficult to obtain (Davis, 1974). As -built cross sections of the dam (Homestake, 1974) do not indicate delineation between core and shell material zones within the dam. The as -built drawings indicate that the chimney drain, embankment slopes and 'key trench were constructed essentially as specified. t Stability of the lower tailings dam as originally designed was evaluated by Lincoln-Devore. Test borings in the dam and pond area, and labora- tory testing of samples from those borings were conducted as part of the investigation. The evaluation was reviewed by Francis-Meador-Gellhaus,