ENFORCE20318 - Laserfiche WebLink

Home Browse Search

Memo to the BMRI File Long-Term Tailings DETOX page 3 revisions, with the exception of precipitates resulting from th} CYTOX treatment. The CYTOX precipitates are a minor component of the overall tailings volume, which will be addressed by BMRI in its respons to abatement requirement Item (8>. Upon entry into the tailings pond, the tailings solids begin se tling to the bottom of the impoundment immediately. As the solids settl they increase their density. The excess liquids remain in the free tanding pool, infiltrate into the coarse sand collector layer, enter th collection pipe network, flow into the collection pond, and are pumped back to the tailings pond, from which they are recycled to the re processing plant. These liquids are processed through the plan and detoxified along with the tailings, after which they return to he active tailings pond in compliance with the permit requirements. For his reason the liquids within the free standing pool will not repre ent a hazard when compliance has been achieved at the spigot outfall. The porosity of the tailings is projected by laboratory modelin to decrease from 59% to 49% as the tailings consolidate. The liqu d which remains in the interstitial pore space of the solid tailings wi 1 migrate downwards until it passes into the coarse sand collector layer, enters the collection pipe network, flows into the collection pond, an is pumped back to the tailings pond, from which it is recycled thr ugh the ore processing plant and detoxified. The pore space of the solid tailings deposited pre-July, 1992 c~ntain liquids with cyanide concentrations in violation of the permit standards. Those liquids have not been exposed to the H2O2 tai ings treatment. They probably retain the majority of total and WAD yanide they contained upon exiting the ore processing plant spigot. B cause the tailings solids are stable in contact with the liquids, and the' environment is devoid of oxygen and sunlight, the cyanide will ~ot naturally degrade. However, once the normal downward migration has purged the cyanide contaminated fluid from the tailings pore sp ce, the tailings will be detoxified with regard to cyanide. The Division completed a conservative flow projection assuming uniform cylindrical tai~ings configuration (thickness 58.5 feet) and th hydraulic conductivity of S x 10-6 cm/sec, contained in the approved permit. This analysis projects an anticipated cycle time of 7. years to purge one pore volume from the accumulated solid tailings. Whe the last of the pre-July, 1992 liquid exits the tailings, the tailings w 11 be detoxified and the collection pond will return to compliance. Conversely, when the collection pond returns to compliance, the !tailings will have been detoxified.