Evaluation of the effectiveness of wrapping filter drain pipes in geotextile for pollution prevention in response to relatively large oil releases

French drains or infiltrating filter drains are commonly fitted with slotted plastic pipe to act as an overflow mechanism when rainfall is too great to allow complete infiltration. The release of the effluent from such pipes is commonly to surface water courses. Whilst there is expected to be some slight degree of protection against hydrocarbon release because of interaction with the drain’s stone infill material this will be severely limited. This paper reports an experiment in which model filter drains with or without geotextile sleeves around the slotted drain are challenged with lubricating oil. The textile was a surface-treated non-woven geotextile manufactured from polyester. The models were challenged with very high loadings of oil, as would be anticipated in a motor vehicle collision occurring close to the drain. A series of simulated 10-20mm rain events over 1 hour were applied and two sample types were collected which either included or excluded any free product. Additional aliquots of oil were added at each rain event. The un-sleeved models were found to release visible free product with the addition of as little as 100ml of oil per linear meter of drain. For the models with geotextile sleeves there was no such release with as much as 2000ml per linear metre. Analysis showed that under these conditions the geotextile sleeved pipes continued to produce effluent with hydrocarbon concentrations well below the 5000g/l limit usually accepted in the UK.