Eagle Mine: Power Outage on September 13th Resulted in pH Limit Exceedance of Water Treatment Plant Effluent Discharge

On Tuesday September 13th, Eagle Mine experienced a power failure that resulted in the temporary shutdown of the water treatment facility. During the outage, water was not discharged.  During outages, Eagle’s standard operating procedure (SOP) requires operators to shut down the flow of water to the inline pH meters located on the discharge line.  Upon restoration of power, effluent was discharged for fifteen minutes before it was noted that the flow to the pH meters was never restarted. The pH of the effluent at the time of the power outage was 7.6 SU; however, once flow to the meters was restarted, the pH of the treated effluent was measured to be 9.3 SU, above the permit level of 6.5-9.0 SU. During that fifteen minute timeframe, approximately 4,500 gallons (300 gallons per minute) of effluent was discharged. The total volume discharged at a pH outside of the permit limit was 4,500 gallons or less but the exact amount is not known since it’s unknown at what point the pH changed from 7.6 SU to 9.3 SU. This incident has resulted in a change in Eagle Mine’s standard operating procedure, removing the requirement to shut off flow to the pH meters in the event of a power outage. SWP will continue to monitor this event and will provide any updates when/if available.