Risk assessments – trader activities and water pollution
4.5 RELATIVE CONTRIBUTION TO WIDER CATCHMENT POLLUTIONPOLLUTION
Which level of pollution control measures is required was based on the relative contribution of each industrial estate to the wider catchment. The study considered
Risk assessments – trader activities and water pollution 61 how significant the discharge from the industrial estate was by determining its overall contribution to the WFD monitoring point downstream of the surface water discharge. The comparative loads of pollutants arising from the estate were calculated using literature values for a light industrial estate (Rule et al. 2006) so as to determine if it were likely to result in failures or contribute to failure at the WFD monitoring point. The methodology adopted was to:
• Determine the geographical area of the industrial estate and assess the impermeable area to determine the run-off area: This was achieved by using satellite map data and drainage plans.
• Determine the hydrological definition of the catchment geographical area of the WFD monitoring point and flows at the point: LowFlows V1.0.6 was used to define the catchment boundaries upstream of the discharge.
This is a programme developed by Wallingford Hydrosolutions (UK) to estimate flows at specified locations on a watercourse. A second programme was also used to estimate flows called Flood Estimation Handbook (FEH) (Centre for Ecology and Hydrology [CEH], 1999) which has been designed for the purpose of estimating high flows for flooding studies. These programmes use different digital terrain models (DTMs) to define the catchment draining to a specified location on a watercourse.
The catchment boundary obtained using LowFlows was validated by comparing it with FEH. These were found to be in agreement (±10%) for all but the localised catchment.
• Consider the % urbanisation, including likely contributions such as motorways, railway lines and potential contaminated land: This was achieved by overlaying the boundary from the hydrological map determined above on a satellite map of the urban area, including significant contributions from highways, rail or significant other industrial areas.
• Determine the chemical and ecological status at both the WFD monitoring point and the trader discharge point. Water quality data were available from the Scottish Environment Protection Agency for the pollutants identified in the literature. River Basin Management Plans (RBMPs) prepared as part of the WFD look not only at the chemical status of surface water bodies but also their ecological status. The ecological status is an integrated assessment which includes biology, chemistry (physico-chemical and specific pollutants), hydrology and morphology. The classification upstream of the discharge and downstream were considered.
There are instances where the size of the estate compared to the whole WFD catchment and the intense urbanisation of the overall catchment will clearly indicate that the contribution of the estate, in which the high risk activities have been identified and controlled, will be of very little significance to the WFD monitoring point. However, the impact on the local receiving water may need to
be considered, especially for the impact of fuel oil that can substantially visually impact receiving water.
In most cases the initial assessment of the site indicated that post ‘normalisation’
the sites would be considered no more impactful than a typical urban area so the selection matrix for SUDS solutions that are conventionally used for other urban areas were deemed appropriate.
4.6 CONCLUSIONS
Although the nature of the economic activity of the traders was related to the risk of diffuse pollution on site, the management of processes involved have a much bigger impact on the surface water quality.
There are some ubiquitous activities, such as vehicle washing, that are largely uncontrolled and potentially locally impactful.
Having ‘normalised’ the quality through the improved risk identification and control, the surface water runoff is similar to that anticipated from other urban areas.
Having in mind sizes of the industrial estates in comparison to the area of the wider catchments, the contribution of pollution to the WFD waterbody in most cases was relatively low, though local streams may need higher levels of protection, especially from the hydrocarbons such as oil, as small spills may have a disproportionate visual impact.
However, accidental spillage risks need to be managed through site specific measures (for example bunded areas for chemical holding, etc.) and need site specific review and if necessary monitoring of water quality to design site specific measures.
The SUDS technologies that are commonly used within the domestic space are effective options after risk normalisation at industrial estates and could improve water quality that is discharged into the watercourses.
The collaboration of multiple stakeholders in a Surface Water Action Plan is critical and can drive improvement through behaviour and site management practice (e.g., storage areas, gully pot cleaning etc.).
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© IWA Publishing 2017. Wealth Creation without Pollution: Designing for Industry, Ecobusiness Parks and Industrial Estates
Brian D’Arcy, Lee-Hyung Kim, Marla Maniquiz-Redillas doi: 10.2166/9781780408330_65
Lee-Hyung Kim and Marla C. Maniquiz-Redillas
Department of Civil and Environmental Engineering, Kongju National University, Cheonan, Chungnamdo, Korea (E-mail: leehyung@kongju.ac.kr, marlcmani@kongju.ac.kr)