1996-05-20_HYDROLOGY - M1977493 - Laserfiche WebLink

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CLIMAY MOLYBDEr I� I� COLORADO OPERA Mme 999 Hwy.91 0429 / 7 -7' (� Climax,Colorado -2150 /� 719)486.2150 FOC7191486-2251 May 15,1996 " Certified Mail No: P 720 678 570 �Y 'Z Kathleen Sullivan /-tDPHE -WQCD 3400 Cherry Creek Drive South Denver, CO 80222 RE✓Stormwater upset - 4-Dam Seep Pump Station Dear Ms. Sullivan: This letter serves as 5-day notification of an upset condition relayed to you by phone on Sunday, May 12 at 2:40 p.m. involving stormwater conveyance in the Eagle River Valley below the Climax Mine. As stated in my 24 hour telephone notification, an upset occurred when a pipe conveying snowmelt stormwater in the Lower North Interceptor broke at the north abutment of 4-Dam. Stormwater in the conveyance flowed along the groin of the dam and reported to two seep collection ponds at the 4-Dam Seep Pumping Station located at the dam toe. The pump station facility is used as a contained collection station for delivery of water seeps beneath Eagle Park Reservoir back into the Climax Water Treatment System. Two pumps operate in the seep collection at a combined rate of 20 gallons per minute (gpm). An estimated 4500 gpm of snowmelt stormwater reported to the two ponds between routine inspections of the station conducted at 7:04 p.m. Saturday, May 11 and approximately 3:30 a.m. Sunday, May 12. With pump capacities limited to seep water inflow, the 4500 gpm stormwater input overwhelmed capability of the system to return seep waters to treatment. The inspection at 3:30 a.m. identified the fact that pump systems were operable during the event. Seep water combined with the snowmelt from the Lower North Intercept overtopped the ponds and reported to the East Fork of the Eagle River above the confluence of the Upper North Intercept. Corrective action was immediately initiated to divert stormwater away from the ponds. This action, completed by 4:30 a.m., reduced pond discharge volume to nominal levels. Pumping continued to lower the water level and the incident was corrected by 11:00 am on May 12. Worse case calculations for the 16 hour event show that no more than 21,000 gallons of seep water involved in the upset. At the confluence of the Upper North Interceptor with the stormwater and seep flow from the seep pump station (located approximately 50 yards downstream), the volume of flow in the stream channel was estimated at 10,900 gpm for a total volume of 4.57 million gallons. With seep contribution of 21 gpm, the maximum worse case based on pump capacity and potentially impounded water in the ponds, the effective ratio of snowmelt water to seep water is calculated to be 520:1. Chemistry of the seep water