SUDS pollution degradation: final report

Background to the Research
SNIFFER Project UEUW01 SOURCE CONTROL OF POLLUTION published in February 2008 included field monitoring and artificial dosing experiments. It demonstrated the effectiveness of various SUDS techniques in attenuating and degrading a range of diffuse source pollutants arising from motor vehicles. The project established an evidence base to aid future policy development in this area.

Two aspects of the work could not be finalized by February 2008 and it was decided to continue with these and, since additional work was being undertaken, a third aspect was undertaken. All three aspects are reported in this supplementary report.

Objectives of the Research
The three aspects reported in this supplementary report form the objectives which were;

1. To continue the degradation study. Samples had been stored and it was
decided to analyse the soil samples after a further period of approximately six
months of degradation.
2. To integrate results from two research programmes. A separately funded
research programme was carried out in parallel with the work undertaken for report UEU01 but was not reported there. This report includes a preliminary integration of the research outputs of both programmes.
3. To develop a risk assessment flowchart. A speculative design flowchart was
included in the first draft of the final report of UEUW01. It was considered that
some further work developing this flowchart was merited.

Key Findings and Recommendations
It is concluded that it is better to control oils and Poly Aromatic Hydrocarbons (PAHs) in soil based SUDS at locations which are periodically wet and dry such as in the base of detention basins, swales or infiltration basins. Basins and swales are good for sediment removal and, by association, oils and PAHs will also be best removed there and not in ponds or wetlands.

This research supports guidance that a soil based system should be used as the primary control of sediments, with the pond or wetland as a polishing component where required.

For the traffic loadings in this study, the degree of contamination found suggests road traffic is a significant source of oil, but SUDS are effectively trapping them, protecting the receiving water environment.

Waste arisings from SUDS serving busy highways will most probably have to be treated as contaminated waste and reduced and recycled. However, the amount of waste which might arise can certainly be minimised using the results of this research.

Results from this study suggest that source control measures such as grass filter strips, swales, and detention areas, should be priority features of sustainable drainage networks serving urbanised areas and highways, where oil contamination may be significant. This is entirely consistent with the treatment train and stormwater management concepts for sustainable drainage systems.

Information to assist in preparing a design flowchart to meet the environmental and other risks posed by pollutants from highways has been considered in this report. A diagram has been included which shows the type of research/ studies required to develop this flowchart.

Recommendations for Uptake
The results will be best used to inform the ongoing improvements to the Design Manual for Roads and Bridges. This work will be taken forward by the Highways Agency.