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<br />Ms. Carla Lznsky <br />NOTIFICATION FOR MAY 4,1999 DISCHARGE <br />May 10,1999 <br />BACKGROUND <br />Colowyo's Industrial Discharge Permit #CO-0045161 allows for the transfer of precipitation <br />induced water from an active mine pit to a permitted discharge point provided the pumped <br />water meets specific Primary Discharge Standards. <br />To facilitate this scenario in the West Pit area, an interim treatment cell was constructed on <br />overburden had been mined and re-deposited. The cell was lined with a native silty clay <br />material having a permeability of 1 x 106 cm/sec. <br />Prior to Iviay 4,1999 the treatment cell was successfully used to bring the pit pumped water to <br />the required discharge standards of the treatment cell, Outfall OIOB. Prior to May 4 there had <br />been no indication that the integrity of the treatment cell was in jeopardy. <br />SUIVIMAR'Y OF EVENTS <br />Between 3:30 and 4:00 a.m. May 4, 1999 [he Shift Production Supervisor made a routine <br />inspection of Colowyo's West Pit area. The inspection included the pumping system used to <br />pump water from the bottom of the West Pit to the treatment cell. The Shift Supervisor also <br />noticed water flowing out from the spoils along the access ramp for the West Pit and the ramp <br />leading to the treatment cell. He was not concerned with the observance of the water or amount <br />of water flowing because the area had been receiving a mixture of rain and snow for several <br />days. <br />During this inspection the Production Supervisor observed the water in the treatment cell with <br />the use of a spotlight. He noted that there was no observable change of the water level in the <br />treatment cell, and continued with his end of shift inspections. <br />Two and a half hours later, at approximately 6:30 a.m. May 4, 1999, a Day Crew employee <br />coming on shift observed water flowing from the spoil area near the treatment cell. He <br />proceeded to the treatment cell itself and observed that the water level in the treatment cell had <br />decreased by approximately 3.2 vertical feet. This fall in water level equates to approximately <br />2 acre-feet of water being released from the treatment cell. The water was released through a <br />breach on the east side of the treatment cell. <br />Once the semi-impermeable liner was penetrated, water traveled through the underlying <br />material. The downward migration of the water was intercepted by virgin, undisturbed ground <br />at two Locations along the haul road, where it was observed as seeps. The water from the <br />treatment cell followed the West Pit access road and then turned west and entered the East <br />Taylor drainage. The East Taylor drainage was carrying precipitation induced water in it from <br />the recent rain and snowmelt from the undisturbed area of the water shed. Water from the <br />natural drainage and the treatment cell co-mingled and entered the East Taylor Pond. <br />1 Precipitation records for April and May, 1999 are included at the end of this letter. <br />2 <br />