Long-term performance of hydraulic and purification characteristics of infiltration swales during summer and winter operation

Funding: Provincial Government of Tyrol

                  ADTL
Staff: Dr. Carolina Engelhard, Dr.-Ing. Stefan Fach
Funding period: 12/2008 - 12/2011

Synopsis:

The high proportion of impervious surfaces in urban areas has a negative impact on the local water cycle from the urban hydrology's point of view. A large part of the rain runoff is discharged in to the sewer system instead of being infiltrated on (partially) pervious areas. The rainwater therefore does not contribute to groundwater recharge but results in peak flows in sewer system and wastewater treatment plant. Further the evaporation is reduced. Local infiltration of roof or traffic area runoff can lead to a significant reduction of rain runoff in urban areas. Runoff from trafficked areas like streets or parking lots should be infiltrated via an active topsoil passage because of the pollutants in the runoff. The construction of infiltration devices is set in ÖNORM B 2506-1 (2000), ATV-DVWK-A 138 (2002) or OEWAV technical fact sheet 35 (2003).
Soil retains various pollutants during runoff infiltration by physical, chemical and biological processes. Many organic pollutants can be degraded during active topsoil passage, persistent pollutants, however, accumulate in the soil and pose a potential threat for soil and groundwater.
A research project of the Unit of Environmental Engineering in the year 2006 investigated soil samples from infiltration swales of different Tyrolean supermarket parking lots. The aim of the investigation was to estimate the pollutant loading of infiltration swales during their operation period. The results showed that during the normally permitted period of operation of 20 years pollutant concentrations in the soil would probably not exceed landfill act limits for excavation soil landfills. The research project further demonstrated that due to geogenic reasons heavy metal concentrations can be already high in the soil used for swale construction. These background concentrations were unknown, therefore it was not possible to identify relations between the age of an infiltration swale and its heavy metal loads.
Therefore the aim of the actual research project was to enhance the findings from 2006 by a consecutive project. Repetitive measurements allow theoretically determining the accumulation of pollutants in the time between the previous and the current measurement. Generally the inhomogeneous character of soils requires multiple measurements to reduce the uncertainty of the results. Thus the research project validates the results of the previous project and attains evidence about long-term retention of pollutants.

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Contact:
University Innsbruck
Dr. Carolina Engelhard
Technikerstrasse 13
6020 Innsbruck
carolina.engelhard@uibk.ac.at