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the tail tank and allowed to escape through the water reservoir. This step is performed for <br />approximately five minutes to ensure that all air is purged from the tail tank prior to leaching <br />the sample. The sample was then saturated with primary leaching fluid introdpced through the <br />head tank. By opening the bottom valve on the column, the leaching procetllure is initiated. <br />Pore liquid from within the sample was allowed to drain by gravity into the tail tank. <br />The tail tank was monitored daily until the volume of leachate collected eglualled one pore <br />volume. Once a pore volume was collected, the liquid was placed in preser~+ed, laboratory- <br />supplied bottles and shipped to Core Laboratories for analysis. The outlined leashing procedure <br />was continued until three pore volumes had passed through the column. <br />2.5 Additional Data Collection <br />2.5.1 Underdrain Water Quality Monitoring <br />• The tailings water collects on the surface in the free water pond and beneatMt the deposited <br />tailings in the underdrain system. The underdrain system exits the tailitgs area at the <br />downstream tce of the main embankment and flows into the collection pond4 Flows in the <br />collection pond have been and will continue to be treated with hydrogen peroxide until the level <br />of cyanide in the flows exiting the underdrain falls below 4.4 pacts per million ~(ppm) total and <br />3.8 ppm WAD. Water quality is monitored both at the underdrain exit and after treatment in <br />the collection pond. <br />Daily samples of water exiting the underdrain system were collected and analyzed at the San <br />Luis on-site lab from June through November, 1992. Bi-weekly samples from) the underdrain <br />system were collected beginning in October, 1992, and are presently on-goings The monthly <br />WAD cyanide averages for the underdrain flows are presented in Table 2.2. During the bi- <br />weekly sampling, the flow rate from the underdrain discharge culvert is calculated using the <br />Manning Equation. Flow rate monitoring was initiated in August, 1992, aqd is on-going. <br />Monthly flow rate averages are also presented in Table 2.2. <br />is <br />