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borehole is capable of discharging up to 500 gpm of mine water. Discharge through the boreholes will occur on an <br />alternating basis, with the potential of discharging simultaneously. <br />Note: The following information relative to caustic soda treatment system has been superseded by the updated <br />treatment information for the electro-coagulation system beginning on page 2.05 -65.4. The treatment ponds <br />remain in use, and the related information remains relevant - The chemistry of the mine discharge has changed so <br />that the primary focus of treatment is for iron removal. In order to accomplish this, the pH of the mine discharge <br />must be raised to a range of 8.8 to 9.0. Sodium hydroxide is used by TCC to cause the upward pH adjustment. <br />TCC's experience shows that when the pH is in this range, that iron is dropped out at a rate to meet the 0.5 mg /1 <br />total recoverable iron limit in CDPDSpermit number CO- 0042161. <br />The as -built drawing for the system, based upon the survey data, is presented in Exhibit 8K. The storage capacity <br />of each cell was calculated. Pond 1 (west cell) has a capacity of 374,730 gallons, Pond 2 has a capacity of 348,530 <br />gallons, and Pond 3 (east cell) has a capacity of 277,000 gallons. The total capacity of all three ponds is <br />approximately 1,000,260 gallons. The flow rate for varying detention time is as follows: <br />DETENTION TIME (hrs) <br />FLOW RATE <br />(gpm) <br />POND 1 <br />(374,730 gallons) <br />POND 2 <br />(348,530 gallons) <br />POND 3 <br />(277,000 gallons) <br />TOTAL <br />DETENTION <br />300 <br />20.8 <br />19.4 <br />15.4 <br />55.6 <br />350 <br />17.8 <br />16.6 <br />13.2 <br />47.6 <br />400 <br />15.6 <br />14.5 <br />11.5 <br />41.6 <br />450 <br />13.9 <br />12.9 <br />10.3 <br />37.1 <br />500 <br />12.5 <br />11.6 <br />7.2 <br />31.3 <br />750 <br />8.3 <br />7.7 <br />6.2 <br />22.2 <br />1000 <br />6.2 <br />5.8 <br />4.6 <br />16.6 <br />1250 <br />5.2 <br />4.8 <br />3.8 <br />13.8 <br />ACZ Laboratories, Inc. conducted a titration study on the mine discharge and showed that raising the pH to 9 <br />would result in an effluent concentration of 0.63 mg /1 of the total recoverable iron after 12 hours, and a <br />concentration of 0.21 mg11 at 24 hours. TCC has operated the system and has achieved compliance with its <br />discharge permit for total recoverable iron by maintaining the pH at 8.8 to 9.0 in the discharge. At a pH of 10, the <br />total recoverable iron was reported at 0.01 mg /l after 12 hours, and at 0.01 mg /1 at 24 hours. This shows that by <br />elevating the pH, the iron will precipitate at a faster rate. TCC used this information as a starting point and then <br />fine -tuned it at the site. At higher flows, TCC would be required to apply additional sodium hydroxide to achieve <br />the same pH level. <br />The settling cells (impoundment) were constructed prior to discharge of underground mine water at the Fish Creek <br />Borehole Area. This installation consists of three adjacent cells, each measuring 123 x 37 feet, with a final depth of <br />8 feet. A 15 -foot light -duty road runs around the entire structure and on the berms separating the cells. <br />The sodium hydroxide is housed in the Electrical Control Building along with the metering pumps used to inject the <br />sodium hydroxide into the mine discharge. A third portable structure is located adjacent to the Electrical Control <br />Building for more efficient storage and handling of the NaOH. A chemical feed -line extends from the metering <br />pumps in the Electrical Control Building to the east cell of the impoundment, near the outlet of the borehole pump <br />discharge line. An aerator has been placed downstream of the inlet into the pond so that the sodium hydroxide is <br />dispersed throughout the cell, promoting the precipitation of iron from the mine discharge water. <br />TR09 -66 2.05 -80 04/11/09 <br />