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i ~ Mayflower Mill - Tailings Pond No. $ Seepage Control Plan Page 3 of the toe drain system at localized areas, and visual seepage frcm the embankment toe is occurring. Upon exiting the embankment toe, the seepage waters drain to the southwest corner of the embankment-highway abutment, are collected there, and returned to the pond interior. Concern was raised by Department of Health personnel during a site visit that seepage waters from the pond may be impacting adjacent ground and surface water quality. In compliance with requirements placed at Part D of the discharge permit issued for the mill facility, Standard Metals Corporation implemented a study to determine the quality of seepage waters, and efforts which could be effected to eliminate the seepage. Design criteria employed in the construction and operation of Tailings Pond No. 4 was completed by F. M. Fox and Associates, consulting engineers, in the summer of 1976. During the summer of 1982, F. M. Fox was contracted to perform an interim inspection of Tailings Pond No. 4 to determine the current status of tailirg pond construction, and in conjunction with Standard's seepage control study, to address the visual seepage occurring at localized points~of the tailings embankment. The seepage control part of the study performed by F. M. Fox consisted of two phases: a fi=_ld investigation, and laboratory analysis of samples collected in the field. Activities conducted during the field investigation included installation of water quality and phreatic monitoring wells at selected points oaf the tailrngs e a an es ole drilling to obtain samples for laboratoty analysis. Constant head and falling head permeability tests wereconducted in test wells 2, 11, 17, and 19 (see Figure 2 ) to dete ~ *'~^ ~^~.~~~, permeability of the toe drain. Upon completion of the field inves~ciga- tion, samples collected were transported to the laboratory to determine ~, moisture content, dry densities, and size class distribution of the embank- ~~,~)~ ment materials. ~ `~, ,i d-~'1 Results of the seepage study revealed that seepage waters occuring along the embankment were caused by three factors: 1. Hioh _phreatic levels in the berm. ~~ J7 . / 2.,)~1igration of pond water through the roadbed at the northea::t L~ abutment of the tailings pond with the roadbed. r Infiltration of the Animas River into the toe drain during periods of high run-off. Upon reviewing the results of the study determining the cause of seepage from Tailings Pond No. 9, Standard Metals Corporation has developed the following plan for controlling that seepage.