Estimating the Potential for Urban Mining in Paris Region

Construction materials are the largest flows entering urban areas after water, while they constitute the top waste deposit (Matthews et al., 2000). The consumption of these mostly non-renewable materials generates environmental impacts and land-use conflicts, from extraction to end-life management and especially storage. Moreover, urbanisation strongly constrains local mineral resources extraction, which leads to the extension of the supplying areas. Materials contained in a city today, in the form of buildings and networks, could potentially be recycled tomorrow through urban mining and so partly substitute for primary resources in highly urbanised countries (Brunner, 2011). The joint analysis of flows and stock of construction materials is therefore an important issue in terms of understanding and managing the metabolism of socioeconomic systems. This is bound up with significant methodological challenges concerning the knowledge of flows and stock of existing materials, in terms of quantity and location, along with short-term forecasting which is essential to anticipating and acting on metabolism. A three years research project launched in 2014 by Géographie-Cités laboratory aims at helping regional authorities to set urban mining objectives until 2030. It is financed by the regional council (Région Ile-de-France) which is in charge of the C&D waste management plan, and the regional office for environment (DRIEE) responsible of the quarries regulation plan. First, construction materials flows were studied through a top-down material flow analysis for Paris Region and its administrative divisions (départements) in 2001 and 2013. The Eurostat top-down MFA method adapted to urban and regional scales by Barles (2009) was used. Then the stock contained in buildings and networks was studied in terms of quantity and location for the entire region through a bottom-up assessment. For buildings, a 3D geographical database called BD Topo® was matched with local tax records which contain information on construction years, economic activities and materials in wall structures. Materials stocked in road, rail, electricity, gas, heat and water networks were estimated with BD Topo® and data from networks managers. Domestic material consumption (DMC) of Paris region reaches 2.5 t/inhab. in 2013. Annual net addition to stock amounts for 2.0 t/inhab. while total stock estimation is 226 t/inhab. While non metallic minerals form 95 % of the DMC, used domestic extraction of these materials decreases and only amounts for 85 % of non metallic minerals imports in 2013. Paris urban area (city and petite couronne) has the lowest DMC (1.8 t/inhab.) in the region, but also the most important local and exported processed outputs (0.8 t/inhab.). Regional development plan for 2030 (SDRIF) sets high annual construction objectives for Paris urban area that imply a strong increase of building renewal. Buildings form 79 % of material stock in this area with a building stock density that reaches 12,277 t/ha in 2013. Objectives of the development plan and statistics on demolition during the last decade are used to estimate future input and output flows until 2030 and hence the potential for urban mining.