Miljökonsekvenser av dagvattendamm i Skebäck, Örebro : en fallstudie hur miljöpåverkan av en dagvattendamm intill ett Natura 2000-område kan bedömas

Abstract: Stormwater is surface runoff water that originates from precipitation or snowmelt and that on hardened surfaces prevents to infiltrate the ground. In city areas stormwater can consists of major amounts pollutants and when reaching a lake or watercourse it can cause damages on vegetation and animals. Therefore it is important to treat polluted stormwater before it reaches the recipient. The municipality of Örebro have since the 90ies an extensive work with treatment of stormwater in sedimentation ponds. A new stormwater treatment project is planned in an industrial estate in Skebäck, Örebro. The pond will become the largest so far in Örebro with an area of three hectare and will be able to treat stormwater from almost one third of the area of Örebro. However, because of limited available space in the area, the pond will be located to the borders of a natural reserve area that also includes a Natura 2000 site with protective nature values. Due to its nature the project has to be registered to the county administrative board with an environmental impact assessment (EIA) included. As a part of this examination report this EIA document has been carried out commissioned by the municipality of Örebro. The purpose of this examination report is to investigate how the environmental impact can be assessed in this project of stormwater treatment pond adjacent to a nature reserve and Natura 2000 site. Four problem areas were to be investigated in the report: 1) which environmental effects can be caused by the project, 2) what will the impact be on the nature reserve and Natura 2000 site, 3) which measures will be needed to prevent negative effects, 4) what do different groups of people consider about the benefits and appropriation of the project? This examination report is a case study that includes mainly three methods: studies of literature, interviews and the making of an EIA. Literature of principles behind treatment of stormwater and its effect on the environment were studied to get a better knowledge about the problem and to be able to predict what consequences the project could cause. To investigate the effects of this particular project an EIA where carried out. Interviews were made in order to gather different opinions. Seven persons representing three different groups were addressed: the public, experts and non-governmental-organisations. The environmental effects of this project are expected to be both positive and negative, and both short-term and long-term. The major positive effect is expected to be improved water quality in Svartån and Lake Hjälmaren when polluted stormwater is treated. To get a long-term treatment efficiency in the pond a continuous management is demanded with sediment and vegetation removal. The major negative effects would be the risk of impact on vegetation and animal life in the nature reserve and the risk of toxic effects on an established animal life in the pond. At a start the biodiversity in the area could be positive if a vegetation and animal life is established in the pond despite the harsh water quality. In long-term there is a risk that toxic effect occurs on organisms in the pond. Four alternative outlet ditches from the pond have been investigated of which one have been dismissed. Of the remaining alternatives the first ditch will pass through a biological rich alder marsh in the Natura 2000 site and there is a risk of negative impact on this sensitive biotope. Measures needs to taken in order to assure that the high water table are not affected. The second ditch will pass by an old dump in the Natura 2000 site and there is a major risk that this will cause leak of toxics into the ditch. The other alternatives boost this risk as well. The last ditch will pass in a northern direction and connect to an existing outlet from the sewage treatment plant and will not affect the Natura 2000 site. This ditch is regarded as the best alternative with the least negative impact. If negative effects occurs mainly depends on how the project is carried out and how the service of the pond is managed. The negative impacts can be minimal if measures are drawn. An important measure for project success and preventing damage is to obtain a management plan that regulates sediment and vegetation removal. Doing so will secure the long-term function of the pond, and the project will be controlled. Results from the interviews showed that all respondents, except one expert, had positive attitudes towards the project and thought the advantages would outweigh the disadvantages. One of the experts stood out from the rest with his sceptical approach towards the benefits of the project and thought the negative effects would be severe. Despite a general positive opinion some worries among the respondents came to light. Expected negative impacts would be; increased insecurity, that the pond would attract animal life that in long-term could endure toxic effects, that the alder marsh could be damaged, that an important feeding place for birds in the winter would disappear and that some barrier effects for animals would occur. The project in itself is a positive measure but because of complications with the protective values the benefits are not obvious. Great measures need to be implemented to prevent negative environmental impact and this will be decisive if the benefits with the project will outweigh the negative effects.