Wet-Weather Lift Station Failure and Imminent SSO
A wastewater collections crew responds to a lift station during a 2-inch rainstorm. The station has three 350-gpm pumps: two duty and one standby, with a wet well 10 ft in diameter and a high-level alarm at 9 ft. The overflow point is at 12 ft. On arrival, the wet well level is 10.8 ft and rising about 0.3 ft every 10 minutes; SCADA estimates inflow at 370 gpm. Only one pump is running, and its discharge pressure is normal at 22 psi. The second pump does not start; the control panel shows a blown 120-V control fuse. The standby pump is available but the automatic transfer switch has a fault. A portable 500-gpm bypass pump is on the truck, and the force main has a 4-inch bypass connection. Rain is forecast to continue for two hours. The last SSO at this station was five years ago, and the state requires immediate notification of any overflow to surface water or streets. The wet well is 300 ft from a storm drain.
1. What immediate actions should the crew take to prevent an overflow, and in what order?
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Order: (1) Make the scene safe and keep people away from the wet well; treat it as a confined space. (2) Replace the blown 120-V control fuse and try to start the second pump immediately; if it starts, verify discharge and level trend. (3) If it does not, set the portable 500-gpm bypass at the 4-inch connection and start it before the level reaches 12 ft; at the observed 0.3 ft/10 min rise from 10.8 ft, there is only about 40 minutes. (4) Notify the supervisor and call for electrical support. (5) If overflow occurs or is imminent, notify the state and local health authority as required and begin cleanup. Do not wait for the automatic transfer switch repair if a bypass can be set.
2. If a small overflow occurs before the bypass is set, what notifications, documentation, and public protections are required?
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If a small overflow occurs: notify the state within the required time, notify the local health department, and post signs if there is public access. Contain and clean up with vacuum truck or absorbent, do not hose it into the storm drain; the drain is 300 ft away. Estimate and document volume, duration, location, and receiving water. Collect samples if required, and follow the utility's SSO response plan. Provide public notice if required by the permit. Record all pump status, fuse failure, and bypass start times.
3. What root causes and follow-up would you investigate to prevent recurrence?
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Root causes: the second pump failed to start because of a control fuse, and the ATS fault disabled standby. Investigate why the fuse blew (control circuit short, moisture, pump overload) and why the ATS was not maintained. Review preventive maintenance for pump testing, fuse/control checks, ATS exercise, alarm testing, and spare parts. Evaluate I/I because the station received high wet-weather flow; the last SSO was five years ago. Check wet-well capacity and emergency storage, and consider a permanent backup pump or generator. Update the SSO plan and train crews on bypass setup.