Stormwater quality performance of a macro-pervious pavement car park installation equipped with channel drain based oil and silt retention devices

AbstractThis paper reports the results of a two year field monitoring exercise intended to investigate the pollution abatement capabilities of a novel system which offers an alternative to the, now well established, pervious pavement system as a source control device for stormwater management. The aim of this study was to determine the effectiveness of a live installation of a macro-pervious pavement system (MPPS) (operated as a visitors' car park at a prison in Central Scotland) in retaining and treating a range of pollutants which originate from automobile use or become concentrated on the parking surface from the wider environment. The MPPS is a sub-class of pervious pavement system where the vast majority of the surface is impermeable. It directs stormwater into a pervious sub surface storage/attenuation zone through a series of distinct infiltration points fast enough to prevent flooding during the design storm. In the particular system studied here the infiltration points consist of a network of oil/silt separation devices with extensive further pollutant retention/degradation provided during the passage of stormwater through the sub surface zone. Approximately 12 months after the car park was completed a sampling regime was instigated in which grab samples were collected at intervals from each of the three sub catchments whilst, simultaneously, samples were collected directly from the, pollutant retaining, infiltration devices. Through investigation of samples collected at the upstream end of the system, the retention of significant amounts of hydrocarbons and heavy metals in the initial collection devices has been illustrated and the analysis of effluent samples collected at the outlet points indicate that the system is capable of producing effluent which is of a standard comparable to that expected from a traditional pervious pavement system and is acceptable for direct release into a surface water receptor. The system offers the opportunity to accrue the benefits of a pervious pavement when the use of traditional paving surfaces is the preferred option

The Microbiology of Permeable Pavements

SUMMARY Pervious pavement systems (meaning permeable pavements within this context and used interchangeably) are known to retain and degrade hydrocarbons within the structure of the pavement. The key to this decontamination has been shown to be the naturally occurring microbial communities living on the pavement building materials. Research by Formpave and Coventry University has shown that once oil is trapped on a suitable strongly oil-retaining geotextile membrane layer, the oil rapidly becomes a food source for the microbial communities. Oil is metabolised by aerobic bacteria and fungi that convert the oil into sugars such as glucose for growth and reproduction. Over time, a network of microbial growth spreads over the surface of Inbitex forming a biofilm, further improving the filtration and purification properties of the system. The presence of a large food source growing on the oil attracts larger predatory organisms such as protozoa and metazoa to the biofilm. These organisms play an important role in maintaining the free-draining characteristics of the geotextile and also the vigorous growth of the oil degrading organisms. An understanding of the processes underpinning the environmental benefits of permeable pavements is essential in order to optimise the operation of the system

The sources, impact and management of car park runoff pollution: a review

Traffic emissions contribute significantly to the build-up of diffuse pollution loads on urban surfaces with their subsequent mobilisation and direct discharge posing problems for receiving water quality. This review focuses on the impact and mitigation of solids, metals, nutrients and organic pollutants in the runoff deriving from car parks. Variabilities in the discharged pollutant levels and in the potentials for pollutant mitigation complicate an impact assessment of car park runoff. The different available stormwater best management practices and proprietary devices are reported to be capable of reductions of between 20% and almost 100% for both suspended solids and a range of metals. This review contributes to prioritising the treatment options which can achieve the appropriate pollutant reductions whilst conforming to the site requirements of a typical car park. By applying different treatment scenarios to the runoff from a hypothetical car park, it is shown that optimal performance, in terms of ecological benefits for the receiving water, can be achieved using a treatment train incorporating permeable paving and bioretention systems. The review identifies existing research gaps and emphasises the pertinent management practices as well as design issues which are relevant to the mitigation of car park pollution