Presentations 2016

Analysis of some 20 years of monitoring data in the municipality of Aarhus, has shown pesticides in about every third well, with the drinking water threshold being exceeded in about one in every six wells. This article illustrates the efforts undertaken in Aarhus to map the vulnerability of groundwater to pollution and in finding solutions to deal with the pesticide pollution.Groundwater in the Aarhus Municipality can only be protected against pesticide/nutrient contamination by a long-term, holistic effort involving water service providers, management agencies and stakeholders. This has necessitated development of: new geophysical methods to map clay thickness to assess the risk to aquifers from surface activities (both agricultural and urban); extensive monitoring of both groundwater level and quality; extensive stakeholder liaison and communication; and the development of multiple pieces of legislation including multiple amendments. This has taken decades at a considerable cost, but without this level of endeavour, optimal groundwater management would not be possible to protect Denmark and in particular, Aarhus’s groundwater resources. During the course of the 1990s it was acknowledged that approx. 1/3 of the general abstraction wells in Aarhus Municipality were contaminated with pesticides. Aarhus University, Aarhus County and Aarhus Water Inc. collaborated extensively in the period on technology development and mapping. In 1998 a new act was passed in Denmark on mapping of vulnerable areas, identification of groundwater protection zones and action plans for such zones. The experiences from the Aarhus area were employed in the preparation of the Act. The methods to map groundwater vulnerability initially focused on nitrate, which was a known pollution issue as early as the 1980s both in Denmark and in the EU.Throughout the process there has been an understanding that pesticide vulnerability is a more complex issue than nitrate vulnerability. However, as they both commonly occur together, the presence of nitrate in groundwater may be a good indicator of pesticide risk. The mapping activities have shown that in the Aarhus area pesticide vulnerability and nitrate vulnerability coincide extensively. It was decided to designate the nitrate vulnerable areas as groundwater protection zones with respect to nitrate as well as pesticides. At the political level there is an ambition that all vulnerable areas should be protected by imposing a ban on the use of pesticides in these areas. Such a ban may be implemented under the provisions of the 1998 Act. Initially, the water works are to offer voluntary agreements, but if stakeholders fail to enter into a voluntary agreement, the municipality can issue a pesticide ban. Bans can be issued in well protection zones as well as groundwater protection zones. Since 1998 Aarhus Water Inc. as well as other water service providers have been offering voluntary agreements and providing advice on conversion into pesticide free farming. The efforts have been prolonged and persistent, and many agreements have been made. But nevertheless, the voluntary agreements only cover a fraction of the vulnerable areas. The local authorities have decided to exploit the facilities of the legal framework to introduce binding requirements on pesticide free production and in 2013 passed the first ever action plan, which makes use of injunctions. Based on the experience in Aarhus water quality protection through voluntary agreement is unlikely to succeed. A significant percentage of land holders in this jurisdiction only changed behaviour as a result of enforced pesticide bans and injunctions. Costs for voluntary measures and injunctions will be equivalent to 0,07 Euro per m³ abstracted water over the next 20 years. Additionally, all publicly owned areas are kept pesticide-free, and the authorities have initiated measures targeting historical point sources.