The purification performance of infiltration basins fitted with pretreatment facilities: a case study J.P. Bardin, A. Gautier, S. Barraud and B. Chocat U.R.G.C. Hydrologie Urbaine, I.N.S.A de Lyon, 20 avenue Albert Einstein, 69621 Villeurbanne Cedex, France Abstract In the south-east of France, the evacuation of stormwater by infiltration into the ground is being developed for large aquifer systems such as the ground water in the Rhône valley and in the eastern part of Lyons. A study proposal has been presented to the water management department of the conurbation of Lyons, aimed at quantifying, within a reasonably short space of time, the effects, in terms of transport of pollutants, of the stormwater infiltration system in the underground water in eastern Lyons. To this end, a one year duration experiment was carried out on the Vénissieux infiltration basin which drains stormwater from a 380 hectares industrial catchment area. Its peculiar configuration also made it possible to acquire new knowledge on the qualitative operation of a few pretreatment facilities. After describing the operation of the basin and the experimental protocol, we shall present a body of data that we monitored and our conclusions about the behaviour of the pollution throughout the facilities. Then, we present methods used to assess the pollution removal performance of the infiltration basin and its pretreatment devices, the results obtained, and our conclusions about the impact of the infiltration basin on groundwater and soil. Keywords Best management practices; experiment; infiltration; pollutant removal performance; urban drainage Introduction For several years, the water management department of the conurbation of Lyons had wished to know the impact on soil and groundwater (in terms of pollution) of its stormwater infiltration systems. The water management department decided, to begin with, to focus its attention on one particular infiltration basin, namely that of the industrial estate of Venissieux, where incoming water is probably the most polluted, and which is fitted with pretreatment facilities. In order to estimate the impact of this infiltration basin and to improve knowledge about the qualitative functioning of its facilities, a one year experiment was carried out in 1995. The object of this paper is to present the experiment, the methods used in order to assess the performance of the facilities, and the main results obtained. Site description The Venissieux basin was built in 1975. From 1975 to 1988, the structure only consisted of an infiltration basin of 80,000 m 3 over 2 hectares. The bottom of the structure was covered with a geotextile which was covered with a forty-centimetre layer of sand. The structure was divided into two basins in 1988, the first one comprising a settling impervious area of 1.1 ha and the second one comprising an infiltration area of 0.9 ha. The volume of each basin is about 40,000 m 3 . The geotextile and the sand of the infiltration basin were removed in 1990 and respectively replaced by a new geotextile and a fifty-centimetre layer of gravel. The Vénissieux basin drains stormwater from a 380 ha catchment area whose impervious- ness coefficient is about 43%. The utilisation of the site can be defined as: industrial: 77%, agricultural: 20%, housing: 3%. The groundwater is situated between 3 and 5 metres beneath the bottom of the infiltration basin. Water Science and Technology Vol 43 No 5 pp 119–128 © 2001 IWA Publishing and the authors 119 Downloaded from https://iwaponline.com/wst/article-pdf/43/5/119/429516/119.pdf by guest on 03 November 2018