Measures for Water Environmental Pollution Control

7.5 Measures for Water Environmental Pollution Control

7.5.1 Measures for water pollution control during the construction period

Living wastewater within the construction area mainly comes from the camps and offices of the Employer, contractor and subcontractors. Use the Anaerobic Bio-treatment Process to treat the living wastewater.

Anaerobic Bio-treatment is the most widely used means of treatment on construction sites. The facilities for treatment are septic tanks. Living wastewater is discharged after being treated in septic tanks. During the process of use, depending on the design parameters of the septic tank, excavate and clear it regularly. The wastes shall be transported to the treatment yard where they will be exposed to strong sunlight and be sterilized.

(2) Measures for treatment of production wastewater within the construction area

Production wastewater within the construction area mainly comes from the washing water of the sand, machinery, vehicles, the floor for concrete agitating and mixing, tank cars, etc.

During the process of separating the sand and stones materials, huge amounts of water will be used for washing. The washing water contains a lot of sand but no other toxic or hazardous matter. Materials washing water shall be recycled by the contractor. Sediment it in the deep pits from which the sand and/or stone is excavated. Production-used water will be supplied from Beigang and be sediment for recycled use. Part of the wastewater, after sedimentation, can be sprayed on the worksite to prevent dust. This can not only help reduce the cost of water supply and save water resources, but also lower the cost of pit backfilling.

Wastewater from washing machinery and vehicles contains not only huge amounts of oil but also suspended substances, such as sand, etc. These kinds of wastewater are usually treated in sedimentation cells and oil/water separation systems. In order to treat the production wastewater on the worksite, the contractor has already built multi-level sedimentation cells near the place for vehicle washing. Wastewater of the heavy-vehicle shop, the light-vehicle shop and maintenance shop is discharged via hidden pipes into sedimentation cells. In order to ensure the effectiveness of treatment, oil/water separation cells have been made behind the maintenance shop to pretreat the production wastewater from the maintenance shop. Production wastewater from the maintenance shop is small in volume but high in oil content. After treatment, the oil content in production wastewater is usually below 5 mg/L and conforms to the national Class I standard for wastewater discharge.

The concrete agitating and mixing system has been set up on the site. The wastewater from concrete agitating, mixing and washing is alkaline. The content of suspended matter is high and, besides, the pH value is above 11. After being treated in sedimentation cells, the pH value still exceeds the index. However, because the flow is small, it has a small degree of impact on the main stream of Beigang.

(3) Prevention and treatment of wastewater from construction of the pile foundation and bridge deck

When excavating the pier foundation, sediment/filter the slurry to prevent it from silting in the river basin.

So, during the construction period, the constructor shall strictly implement the Temporary Rules for Civilized Construction and Environmental Management on Construction Site and design the system for discharge of ground water to prevent pollution of the roads and environment.

1) Wastewater from maintenance of concrete. To maintenance the concrete, directly spray/brush the plastisol on the surface of the concrete. After the plastisol has volatized, a plastic film will form on the surface of the concrete to isolate the concrete from air.

2) Enhance construction management, especially monitoring over the quality of Minjiang River during the construction period.

3) The piling yard for construction materials shall be far away from ground waters. It shall be free of rainwater flow. The piling yard for powder materials shall be covered with canvas, etc. In addition, an open channel shall be dug around the yard to prevent rainwater flow.

4) When constructing a structure under the water, set up a steel cofferdam around it. At the same time, to prevent slag and oil from falling into the water, set up a preventive net, etc at the place where the cofferdam extends towards the waters.

5) Do not discard the slag from construction of the pier directly into the waters. Transport it to the bank for proper disposal. When transporting the slag up to the bank, effective measures shall be taken to prevent slag from falling in the waters. After being transported to the bank, slag shall be disposed in time. When possible, use it as the roadbase material. Otherwise, after obtaining agreement from related authorities, dispose it in a cove where the rainflow is small. Besides, corresponding measures shall be taken to prevent soil loss.

6) Enhance management of construction machinery. Prevent oil leakage from construction machinery and construction vessels.

7) During the construction of underwater structures, enhance communications with the navigation management authorities and reasonably arrange the construction time. Structures at the point of pier construction shall use the warning red color. When necessary, ask the navigation management authorities to dispatch dedicated personnel to guide passing vessels.

7.5.2 Prevention and treatment of water pollution during the operation period

During the operation period, the impact of road surface source pollution on the water is small. Obvious pollution often comes from vehicles carrying hazardous goods. Experiences show that the probability of accidents on the bridge that lead to water pollution is very low. However, in order to prevent pollution, corresponding measures shall also be ready in place. During the construction period, rainflow on the bridge deck shall not be directly discharged into the river. It shall be guided into the dike. In addition，buffering cells shall be built at the point of discharge, namely at the both ends of Kuiqi Bridge, so that when pollutants are leaked, they can be guided into the cells for treatment. Surveying and comparison shows that, at the worst, two 5T vehicles might collide with each other and cause leakage of 10T toxic substances, so one 10-m³ buffering cells shall be built at each end of the bridge.

For management of accidents, please refer to the chapter dedicated to risk assessment.

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