Coos Bay advising of two leaks at wastewater plants

On the evening of Monday July 29, 2024, a power failure occurred at Plant 1. The power failure only occurred for a few seconds, however the plant sent out an alarm (as designed) to the city’s operators. This alarm system ensures that a prompt response occurs to make sure everything is working correctly.

Nationwide, wastewater treatment plants have a National Pollutant Discharge Elimination System (NPDES) permit. These permits have strict water quality limits for discharging effluent to receiving waters. One limit in the permit for Plant 1 (located at 680 Ivy Ave) is disinfection prior to discharge. Plant 1 utilizes chlorine to disinfect and sodium bisulfite to dechlorinate the effluent prior to sending it to the receiving waters.

Upon inspection of the plant, the operator discovered that the sodium bisulfite (de-chlorination) pump did not go back online and was not dosing sodium bisulfite to dechlorinate the effluent prior to discharge.

As a result, approximately 137,500 gallons of treated and chlorinated effluent was discharged to the bay. Based on the plant’s monitoring equipment the chlorine levels in the effluent were 0.4 milligrams per liter (mg/L). To put this into perspective, the allowable limit of chlorine in drinking water is 4.0 mg/L. While this discharge was ten times less than drinking water standards it is still above the city’s NPDES permit limits and must be reported to both the Oregon Department of Environmental Quality (DEQ) and the Oregon Emergency Response System (OERS).

On the night of July 30, 2024, city staff received an alarm from the pump station, upon arrival all pumps were operating correctly. Coos Bay pump station 6, located at S. 5th Street and Kruse Avenue, is currently under construction. As a result, sewer flows must be bypassed around the pump station until construction is complete.

Staff went back out the following morning on July 31, 2024, to check all the pumps to ensure they were still working properly, which they were. While out on inspection staff observed the bypass pumping pipeline was leaking. Staff immediately stopped the leak and then replaced the section of damaged pipe and disinfected the surrounding area with lime. Approximately 2,880 gallons left the pipe through the leak and discharged to the Coal Bank Slough via outfall at the south end of S. 5th Street. Oregon Department of Environmental Quality and the Oregon Emergency Response System were notified of the incident. Any questions can be directed to the Coos Bay Public Works Department at 541-269-1181 extension 3565.