Following the hydrodemolition process, the water produced will contain suspended solids (slurry), which are primarily cement particles. In addition to causing a milky white water, the cement particles will increase the pH of the water to between 10 to 12. The cement particles are heavy and settle out quickly if the water is ponded or passed through a filter media. The requirements for the disposal of the wastewater vary depending on where the project is performed. Generally the water cannot be discharged to any waterway, wetland, river or stream within the United States. However following removal of the suspended material the water may be discharged to the ground for absorption and evaporation or discharged to a sanitary system.
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Dry hydrodemolition. The water is collected directly from the hydrodemolition eliminating much of the “mess” of the typical hydrodemolition project. |
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Filter fabric and aggregate dams. |
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Existing bridge drainage used to direct water to settling tanks. |
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K-rails or Jersey barriers covered with plastic sheeting to create a settling pond. |
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Settling ponds dug at the end of the bridge to collect wastewater. |
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Wastewater Recycling System consisting of multiple settling tanks, storage tank, pH adjusting equipment, filtration and flocculating equipment. |
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During bridge restoration the wastewater is typically filtered and discharged to a ditch along the roadway where the water will be absorbed. Various methods have been used to filter the water including creating a series of dams or berms, using hay bales or filter fabric and gravel. These dams not only filter the water as it passes through but they also create retention ponds which allow for suspended material to settle out. Another method is to dig a small retention pond at the end of the structure and direct the flow of the water to that location where the suspended solids will fall out of suspension as the water passes through. Rampart recently introduced the concept of “dry hydrodemolition “ where a vacuum truck is connected directly to the hydrodemolition robot. The vacuum truck collects 95%+ of the wastewater during hydrodemolition eliminating the need to set up any wastewater collection system on the bridge. This method of water collection is particularly effective in environmentally sensitive areas or locations where the water must be completely contained to prevent it from crossing live traffic lanes. Parking Garage Restoration: Because parking garages are located in residential or commercial areas, the water must be contained within the structure. A water retention area can be established on the lowest level or slab on grade of the structure where the weight of the water is not a concern. In order to meet discharge requirements it may be necessary to reduce the pH. A typical wastewater handling system within a structure consists of a settling tank, a filter box and pH adjusting equipment. Rampart uses CO2 to reduce the pH, as it is not hazardous, can be easily bubbled in the wastewater and will not acidify the water if two much is added. It is also much more easily handled than acids such as muriatic or sulfuric.
Large water settling areas can be constructed using plywood, formwork materials, shoring or the structures columns and walls. All the wastewater including the wash water can be directed to this location. Once the work is complete the clear surface water can be pumped from the settling tanks and the slurry removed, dried and disposed. |