Peak production generates surges in waste water. Also, chemical spills could require large volumes of clean up water. To deal with these events, the treatment plant would have to be enlarged. The alternative (used by many city sewage plants) is to send the rare high flows untreated into local rivers. Emergency Recovery Basins are a better solution. These tanks are normally empty. But in emergencies, waste is accumulated in these reservoirs, giving the treatment facility time to catch up. In this way, a treatment plant sized for normal flows can still deal with emergencies.