How can refineries and chemical plants ensure the separation of rainwater and wastewater after rainfall? Implementation Plan for Separating Rainwater and Sewage in Refining and Petrochemical Facilities During the Rainy Season (Complete Version)

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Implementation Plan for Separating Rainwater and Wastewater in Refining and Petrochemical Facilities During the Rainy Season (Complete Version) I. General Provisions 1. Purpose To ensure that polluted rainwater during the rainy season is collected entirely at the initial stage, while clean rainwater can be discharged later; to prevent the discharge of rainwater containing oil or chemicals in excessive amounts, and to avoid overloading the wastewater treatment system. 2. Scope of application: All drainage areas such as the equipment area, tank farm, loading/unloading area, utility area, pipe gallery area, and circulating water plant. 3. Core principles: separation of rainwater and sewage, separation of clean water and waste water. The initial rainwater goes directly into the sewage system, while the later rainwater is discharged after meeting the standards. Zonal control, hierarchical switching, and full-process monitoring. Upon occurrence of an anomaly, effluent discharge is immediately cut off; all effluent enters the accident storage system. II. Organizational Structure and Responsibilities 1. Production Operations Department: Coordinates the switching between rainwater and sewage systems, manages drainage loads, and controls liquid levels. 2. The Quality, Safety, and Environmental Protection Management Department is responsible for water quality monitoring, control of wastewater discharge, and compliance oversight. 3. The device/area team is responsible for on-site valve position switching, inspections, sampling, and reporting of abnormalities. 4. The storage and transportation team is responsible for the fire dikes, cofferdams in the tank area, as well as the operation for switching between rainwater and wastewater systems. 5. The maintenance team is responsible for the maintenance of valves, water seal wells, pumps, and online instruments. III. Composition of the stormwater and sewage separation system 1. Sewage system: Collection of production wastewater, surface washing water, and initially polluted rainwater. Destination: Sewage treatment plant / retention tank. 2. Rainwater system: Collection of clean rainwater collected later, as well as rainwater from unpolluted areas. Destination: Rainwater monitoring tank → Discharge/reuse after meeting standards. 3. Emergency buffer system: Initial rainwater ponds, monitoring ponds, accident water ponds, and lift pump ponds. 4. Key facilities: water seal wells, oil separation tanks, switch gate valves, sampling ports, online oil content detectors, level gauges. IV. Preparatory work before rain (mandatory) 1. System clearance: Thoroughly clean rainwater drains, floor drains, water-sealed manholes, and oil separators to ensure there is no silt, debris, or accumulated oil. Check the drainage slope to ensure there is no water accumulation or backflow. 2. Facility inspection: The storm/sewage switching valve operates smoothly and there is no internal leakage. The emergency pump and lift pump have passed normal trial operation. The online monitor is properly calibrated. The cofferdam and water barrier are intact, with no breaks. 3. Liquid level control: Maintain low liquid levels (≤30%) in the initial rainwater tank, monitoring tank, and accident tank. High water levels during the flood season are strictly prohibited. 4. Material preparation: oil absorbent mats, oil booms, sandbags, portable oil analyzers, emergency repair tools. 5. Valve position verification (normal state prior to rainfall): Sewage valve: normally open; Rainwater valve: normally closed; Main discharge valve: closed. V. Detailed operating procedures during rainfall (1) Initial rainwater phase (first 0–30 minutes of rainfall): Objective: To collect all polluted rainwater without any discharge. 1. Maintenance: Keep the sewage valves fully open and the rainwater valves fully closed. 2. All water used for flushing the ground, cofferdams, pipe galleries, and equipment areas should be directed into the oily wastewater system. 3. Monitor at the sampling point every 10–15 minutes: presence of oil droplets, floating oil, an emulsified odor, color, oil content, pH, and COD (in accordance with corporate standards). 4. Rainwater within the fire dike of the tank area must not be directly discharged into the rainwater system. (II) Intermediate transition phase (after water quality meets the standards) Transition conditions (must be met simultaneously): 1. 2–3 consecutive samples show no oil spots, no floating oil, no unusual odors, and an oil content of ≤ 10 mg/L. 2. No obvious oil stains resulting from washing on the ground. Switching steps: 1. Slowly close the sewage inlet valve. 2. Slowly open the rainwater discharge valve. 3. Later, direct the clean rainwater into the rainwater monitoring tank. 4. Only after the water in the monitoring tank is found to be of acceptable quality can the external discharge valve be opened. 5. If the water quality is not acceptable, it should be directed entirely to the emergency tank or the sewage treatment system. (III) Stabilization phase: Conduct regular inspections; if oil spots are detected, immediately switch back to the sewage system. Control the discharge flow to avoid sudden surges. Inspect the switching wells and water seal wells every 30 minutes. VI. Special rainwater and sewage separation plan for the tank area: 1. Drainage within the fire dike: Initial rainwater → all goes into the sewage system. 2. Switching wells outside the fire dike: Once the water quality is acceptable → switch to the rainwater system. 3. In case of oil spots/emulsification/odd odors, immediately close the rainwater valve, fully open the sewage valve, and activate the oil skimming system. 4. It is strictly prohibited for the cofferdam to overflow or for oil-contaminated rainwater to enter the rainwater drainage system. VII. Emergency Response Plans for Abnormal Conditions
1. In the event of oil-containing wastewater discharge: Immediately close the rainwater discharge valves, fully open the sewage valves to divert all water into the sewage system. Activate oil barriers and absorbent pads to contain the oil. Report the situation to the environmental protection department and the operations team.
2. If the sewage system is overloaded: Reduce unnecessary flushing water. Prioritize collecting wastewater from highly polluted areas. Direct excess rainwater to initial rainwater tanks or accident tanks for temporary storage.
3. In case of waterlogging: Increase the use of temporary pumps for drainage. Raise dikes and seal floor drains to prevent backflow of sewage.
4. If a water seal well is damaged or there is backflow: Immediately close the rainwater valves in that area. Temporarily seal it off and restore normal operation after repairs.
5. If online instruments fail: Switch to manual sampling every 10 minutes. Strictly adhere to the principle of “sewage first, then rainwater”.

VIII. Recovery and Management After Rainfall
1. After the rain stops: Close the rainwater valves, restore the sewage valves to their normal open position, and return all valves to their standard settings.
2. Cleaning: Remove floating oil and debris from drainage channels; skim oil from oil separation tanks.
3. System restoration: Gradually transfer water from accident tanks and monitoring tanks to the sewage treatment system. Ensure that valves, pumps, and instruments are back in normal operation.
4. Documentation: Record rainfall duration, switching times, water quality data, and valve operation records.

IX. Control Parameters
- Initial rainwater: All should be directed into the sewage system.
- Oil content in discharged rainwater: ≤ 10 mg/L.
- Switching time: Generally 0–30 minutes. Discharge is allowed only after the water in monitoring tanks meets specified standards.
- In case of any abnormalities: Immediate cessation of discharge is required.

X. Safety Precautions
1. Be careful to avoid slips and electric shocks during rainy days; it is strictly forbidden to cross ditches illegally.
2. Perform switching operations slowly to prevent water hammer and pressure surges.
3. In areas prone to fire, it is prohibited to use metal tools or engage in unauthorized welding.
4. A two-person verification system must be implemented for discharge valves