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1 <br />' Homestake Mining Company -Bulldog Mine-Lower Tailing Pond <br />' Construction started in June 1982 and was completed in August 1982. /n January 1983, <br />D'Appolonia provided a draft As-built Report on the remediation work; a final report <br />was completed in February 1983. The remedial activittes implemented in 1982 are <br />reflected on Figure I.i and are explained in more detail in section 3.1. <br />On September 3, 1982 the WQCD modified the CDPS Permit because of a concern for <br />cyanide in the ground water down-gradient from Lower Tailing Impoundment. The modification <br />stipulated that HMC provide, by June 1, 1983, all ground water data collected to date and a <br />summary of the remedial measures employed to correct the seepage problem. It was also <br />' requested that all ground water data generated in the future be provided in CDPS annual reports <br />due by September 1 of each year. <br />' On June 23, 1982 an MSHA inspection resulted in a concern for the stability of the <br />Lower Tailing Embankmettt. In response, in September 1982, D'Appolonia was retained by <br />HMC to evaluate the stability of the embankment. A February, 1983 Stability Report concluded <br />' that because of piping below the embankment, stability was below the factor of safety of 1.5. <br />Plans were presented in the Stability Report to improve stability by reducing seepage through the <br />' installation of a sluny wall through the embankment core. On May 26, 1983 the MLRD <br />approved the proposed construction activities as modifications to MLR Permit No. 77-215. On <br />May 20, 1983 HMC notified the Stale Engineer of the proposed slurry wall construction. <br />' From June -November 1983, D'Appolonia constructed a slurry trench below the bottom <br />of the embankment core along its entire length (approximately 200 feet). In addition, nine <br />' additional piezometers were installed to monitor seepage pressures beneath the embankment. <br />The remedial measures inplemented in 1983 are reflected on Figure 16 and explained in more <br />detail in section 3.1. <br />t Following the remedial construction activities of 1982 and 1983 the following events <br />occurred: <br />' • January 1985, HMC suspends mining and ore processing operations; mine de- <br />watering and treatment continues with some effluent going to the Lower Tailings <br />' Impoundment. <br />• August 1985, HMC notifies the WQCD that mine water will no longer be pumped <br />to the Lower Tailing Impoundment. <br />' • January 1987, HMC notifies the WQCD that mine de-watering will cease. <br />• March 31, 1989 HMC notifies MLRD of Temporary Cessation of Operations at <br />the Bulldog Mine under Rule 1.62. <br />' • May 18, 1989 MLRD notifies HMC that the request for Temporary Cessation will <br />be on the Board Agenda June 2l -22, 1989, and ,unless the Board has questions, <br />the five-year Temporary Cessation monitoring period will begin March 31, 1989. <br />' • November 1989, the last time monitoring well WP 15 contains water - CN (free) is <br />measured at 0.2 ppm <br />• In the summer of 1990, fresh water is added to the Lower Tailings Impoundment <br />1 <br />1 <br />