Håndtering av forurenset overvann i Norge – Analyse av et prosjektområde i Asker kommune ved hjelp av programvaren StormTac
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This bachelor thesis discusses the current structures and prevalent knowledge and methods surrounding the general management and treatment of polluted stormwater in Norway. The content is divided into an overall theoretical and a practical part. Part one of this bachelor thesis begins by describing the different sources of pollution in stormwater. Because roads account for the largest contribution in this regard, a division of this source of pollution into its construction and operational phase was necessary. Part one then continues by explaining some of the short-term and long-term effects that the release of polluted stormwater can have on the environment. Among the more serious consequences are eutrophication and pH change (causing the recipient water to become more basic or acidic), as well as generally reducing biomass and biodiversity in recipients. Further, a description of various methods through which stormwater can be treated locally before being released into a recipient, is given. Part one then ends with an exploration of the current laws and requirements related to treatment of polluted stormwater in Norway and criteria for its release into recipients with various degrees of vulnerability. Part two gives a presentation of StormTac as the main modelling software used in this bachelor thesis. StomTac can be used for calculation of various quantities and compositions of pollution-discharges from a watershed area, simulation of pollution- reduction effects of various treatment methods and analysis of the sensitivity and capacity of different recipients for handling stormwater runoffs with various levels of pollution. An explanation of the prerequisites for further development and large-scale implementation of StormTac or similar software in Norway is also given. The above explanation is based on a short survey which includes feedbacks from 12 different private and public enterprises. The main conclusion drawn from this survey, is that there is a need for a twofold development process if use of software in managing polluted stormwater is to gain any significant momentum. On the one hand, there is a need for digital software to adapt to the Norwegian standards and methods for calculating pollution levels in stormwater runoffs. On the other hand, a more accurate and detailed collection of various data is needed in Norway, which then can be used as input for simulations in StormTac and similar software. The latter development process is essential for providing reliable results when using digital software. Part three is based on a case study in connection to an ongoing development project in Slemmestad in Asker municipality, in cooperation with AFRY. The central focus of this development project is the extension of a section of Slemmestadveien, which is the main county road in the region. Slemmestadveien connects a few other smaller roads and several areas in the region, including two development areas, and is planned to have an annual average daily traffic (AADT) of 20000. Part three uses StormTac in order to simulate and calculate pollution loads and pollution reduction effects of treatment facilities. The pollution calculation shows for instance that even though Slemmestadveien is only around 3 % of the total surface area, it accounts for 20 % of the total pollution in the case area. The simulation consists of multiple treatment methods, including two dry ponds and several macadam, grass and swale ditches. Results from this simulation provides a basis for evaluation of treatment methods and the effect that polluted stormwater from the case area has on local recipients.