Comparative Analysis for Reuse & Disposal of Concrete Residuals from Hydrodemolition, Diamond Grinding, & Diamond Grooving Operations
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Abstract
Large quantities of concrete residual slurries, solids, and liquids are currently being produced from hydrodemolition, diamond grinding, and diamond grooving operations within North Carolina. North Carolina Department of Transportation (NCDOT) and environmental organizations, such as North Carolina Department of Environmental Quality (NCDEQ), are working to identify and implement strategies to promote the most environmentally friendly, economically viable, and most risk averse methods for disposal/reuse of these residual materials. The available methods for slurry handling are containment in a fractioning tank, or Frac Tank, or creation of a Decanting Pond for settlement. The available options for Liquid disposal is insertion into a Wastewater Treatment Plant (WWTP)/Publically Owned Treatment Works (POTW) or reuse via deposition onto a state certified Land Application site. The available options for Solid disposal/reuse are beneficial fill onsite or offsite, or placement into one of the three available landfills: Land Clearing and Inert Debris (LCID), Construction and Demolition (C&D), or Municipal Solid Waste (MSW).The currently feasible reuse/disposal methods have been combined into 20 total combinations of options. The objective of the project was to create a Cost Benefit Model (BCM) using Multi-Criteria Decision Making (MCDM) to compare these 20 options in order to find the most favorable option. The BCM used the Monte Carlo Method to simulate 5000 iterations of the model to estimate the most likely costs based on the available cost data gathered from various available sources. The model allows for specific project information to be input to reliably estimate the costs of residual management for that unique project. The model differs in cost depending upon the region of North Carolina that the work is taking place in: Mountain, Piedmont, or Coastal. Each option has specific costs associated with it, which varied depending on project specific information; such as the quantity of the residual materials, and how and where the residuals would be disposed. Once the costs for each option are calculated, they can be viewed side-by-side to compare costs directly. The user will then provide the model with a rating of the risks and environmental benefits of each option for disposal /reuse based on the user’s specific capabilities, and will then place a level of comparative importance between risk, environmental benefit, and cost. The model will use of these inputs to provide a ranking of the 20 available options of disposal/reuse. The Cost data was gathered from contacting the facilities, either by phone or email, which would accept the residuals. The risks and environmental benefits incorporated into the model were gathered by contacting the contractors that were performing the work, either within North Carolina, or throughout the United States and Canada. Those contractors also provided ranges for the most likely rate of slurry generation resulting from the previously mentioned construction projects. The model was then validated and approved by an environmental consultant that had previously performed the environmental compliance portion of the work in North Carolina. The model shows that for a typical project within North Carolina the most cost effective options of slurry handling was the creation of a decanting pond. The most cost effective method of liquid management was deposition into a WWTP/POTW. The most cost effective method of solid residual management is beneficial fill onsite. The options perceived to be the most environmentally friendly and least risky options were determined based on the specific inputs based on the user’s opinion of their capabilities. Generally the options that did not involve the creation of waste, the transportation of the residual material, or the lowest possibility of releasing the residual material into the environment were determined to be the most environmentally friendly and most risk averse. The ranking of the options provided by the BCM allows the flexibility to select the second most desirable option in the case where the most desirable option is not available.