2007-11-01_PERMIT FILE - C1982056A (3)

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Note: The following information relative to caustic soda treatment system has been superceded by the updated treatment information for the electro-coagulation system beginning on page 2.05-65.4. The treatment ponds remain in use, and the related information remains relevant -The chemistry of the mine discharge has changed so • that the primary focus of treatment is for iron removal. In order to accomplish this, the pH of the mine discharge must be raised to a range of 8.8 to 9.0. Sodium hydroxide is used by TCC to cause the upwazd pH adjustment. 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 total recoverable iron limit in CDPDS permit number CO-0042161. The as-built drawing for the system, based upon the survey data, is presented in Exhibit 8K. The storage capacity of each cell was calculated. Pond 1 (west cell) has a capacity of 374,730 gallons, Pond 2 has a capacity of 348,530 gallons, and Pond 3 (east cell) has a capacity of 277,000 gallons. The total capacity of al] three ponds is approximately 1,000,260 gallons. The flow rate for varying detention time is as follows: DETENTION TIME (hrs) • FLOW RATE (gpm) POND I (374,730 gallons). POND 2 (348,530 gallons) POND 3 (277,000 gallons) TOTAL DETENTION 300 20.8 19.4 15.4 55.6 350 17.8 16.6 13.2 47.6 400 15.6 14.5 11.5 41.6 450 13.9 12.9 10.3 37.1 500 12.5 11.6 7.2 31.3 750 8.3 7.7 6.2 22.2 1000 6.2 5.8 4.6 16.6 1250 5.2 4.8 3.8 13.8 ACZ Laboratories, Inc. conducted a titration study on the mine discharge and showed that raising the pH to 9 would result in an effluent concentration of 0.63 mg/1 of the total recoverable iron after 12 hours, and a concentration of 0.21 mg/t at 24 hours. TCC has operated the system and has achieved compliance with its discharge pemrit for total recoverable iron by maintaining the pH at 8.8 to 9.0 in the discharge. At a pH of 10, the total recoverable iron was reported at 0.01 mg/1 after 12 hours, and at 0.01 mg/1 at 24 hours. This shows that by elevating the pH, the iron will precipitate at a faster rate. TCC used this information as a starting point and then fine-tuned it at the site. At higher flows, TCC would be required to apply additional sodium hydroxide to achieve the same pH level. The settling cells (impoundment) were constructed prior to dischazge of underground mine water at the Fish Creek Borehole Area. This installation consists of three adjacent cells, each measuring 123 x 37 feet, with a final depth of 8 feet. A 15-foot light-duty road runs around the entire structure and on the berms separating the cells. The sodium hydroxide is housed in the Electrical Control Building along with the metering pumps used to inject the sodium hydroxide into the mine discharge. A third portable structure is located adjacent to the Electrical Control Building for more efficient storage and handling of the NaOH. A chemical feed-line extends from the metering pumps in the Electrical Control Building to the east cell of the impoundment, near the outlet of the borehole pump discharge line. An aerator has been placed downstream of the inlet into the pond so that the sodium hydroxide is dispersed throughout the cell, promoting the precipitation of iron from the mine discharge water. The water flow through the cells was modified to take advantage of additional retention time in the system. The original flow-path focused on using two of the three cells at any one time. Presently, all three cells aze utilized, .with a new inter-pond baffle system routing flows between the center and western cell. The baffles reduce the potential for short-circuiting, increasing the efficiency of the pond. The final component added to the system was placement of an aerator in the western cell. This aerator maybe turned off after the one in the eastern cell is turned on. MR07-216 2.05-77 05/28/07