Rainwater Run-off
Australia has two key seasons wet and dry and when it rains it rains “heaps”. Garry and I were overseeing a project of the building of a large refinery expansion that would double our production rates at our site. The expansion was located on a site that was surrounded by a body of water on three sides. The first year we had done earth works that changed the profile of rainwater run off and we realized that this would likely have an impact on the adjacent receiving environment.
The initial construction environmental management planning did not fully incorporate stormwater run-off control management of the potentially large quantity of stormwater run-off new hard stand surfaces and it was agreed that it would have been a good idea to reuse this water in some of the construction activities (i.e. construction dust suppression). We revisited our project risk register and identified that we needed to act fast since the “wet” season was months away and we needed to build incremental catchment pondage and change the drainage profile of the site in order to redirect all rain water into these new storm sediment control areas.
Since the risk was ranked as high, it deservedly got senior management’s immediate attention and focus and we were able to secure funding from our board; so that, engineering could be conducted. The detailed design was completed in record time and we were able to contract and mobilize a contractor that specialized in such re-contouring earth works.
For us, the key learnings were:
1. Include a review of the project site “1:100-year ARI and flood profile” knowledge when designing storage areas and location of new plant (especially in a sub-tropic setting).
2. Look at rainwater downfall duration/ quantities to anticipate receiving environment impacts.
3. Look at incidents that record off-site releases and what lessons were learned.
4. Review and update the project site environmental risk registers, contour drawings and action plans.
5. Review records and inspect the brownfield stormwater sediment catch basins to ensure have they been cleaned-out and operational pumps/ pond level indicators are maintained to capture and reduce the impact from heavy or extreme rainfall. Update the inspection plan schedule and documentation.
The average rainfall as measured at the local airport was 1.45 metres (m) with annual evaporation of 2.15 m however, tropical lows and severe cyclones had lasted for several days and “dumped” up to 0.60 m in one event.
We learned that our activities and nature (severe tropical low-pressure storms/ cyclones) would have environmental impacts that could alter and impact our natural environment. Rainwater looks and is very benign and when it hits the surface of your site and could lift old oil stains and other chemicals that may have spilled on-site over time and it can be transported off-site. If you plan on doing an expansion on a brownfield or greenfield site, it would be prudent to include risked-based impacts form rainwater into your EIA and feasibility studies and execution of construction activities.
Presented by Roger Belair, C.E.T, C.R.S.P, C.R.M. and Garry Pearson, MAusIMM CP(Env), MSc EM NRM, GD EM, BApSc Ext (Chem) Met
Photo taken by David Cox, Northern Territory, Australia
