Many low lying coastal areas have naturally occurring materials known as acid sulfate soil, including the Bayside Council.
Acid Sulfate Soils
Acid Sulfate Soils
These soils, when inappropriately disturbed, can become very acidic due to exposure to oxygen. Areas likely to be affected include the Botany Bay foreshore, creek lines and reclaimed areas. Excavation can also disturb acid sulfate soils further afield from these locations.
Acid Sulfate Soils and DA's
Any developments or civil works that involve the disturbance of soil below the groundwater table or the disturbance of sediments within Botany Bay have the potential to disturb actual or potential acid sulfate soils. The soils can form sulfuric acid that can leach into the surrounding area acidifying neighbouring drains, wetlands, creeks, estuaries and bays, causing severe environmental damage. It can also impact on infrastructure by causing serious damage to steel and concrete structures such as the foundations of buildings.
There are five classes of land when categorising risk from acid sulfate soils. Each Class has corresponding acid sulfate soil risk management requirements. Further information can be found at:
- Acid sulfate soil risk maps
- Acid sulfate soil classes
- Fact Sheet – Acid Sulfate Soils Upload document
All Development Applications are assessed for the likelihood of acid sulfate soils onsite, and depending on the risk class, appropriate management measures are required during demolition, excavation and construction.
Further general information on acid sulfate soils can also be found at:
Building & Construction Sites - Sediment and Erosion Control
Discharge of water containing sediment and contaminants can have a significant harmful effect upon the environmental health and amenity of creeks, wetlands, ponds and Botany Bay.
Disturbance of soil for building, construction and landscaping can cause pollution if not managed correctly. Bayside Council requires the implementation of controls for soil and water management for developments, as outlined in the Part 3G of the Development Control Plan 2013. (Link to new location of Botany DCP)
The following information must be provided as part of documentation of Development Applications to Council:
A Development Application must include an:
- Erosion and Sediment Controls Plan for sites with an area of 2500m2 or smaller, or
- Soil and Water Management Plan for sites with an area greater than 2,500m2.
Managing Urban Stormwater - Soils and Construction 4th ed. March 2004 and Planning for Erosion and Sediment Control on Single Residential Allotments provide guidelines for the preparation of these plans.
Bayside is located in the Botany Sands Aquifer with groundwater less than two metres below ground level in many other areas. Where a development is proposed to extend into the existing groundwater, it is critical that adequate site investigation is undertaken at an early stage.
To enable the work area to be kept dry while construction is being undertaken, groundwater inflows into any basement excavation are generally managed through dewatering. Dewatering is the process of removing groundwater from an aquifer to lower the water table below the lowest level of excavation. This allows construction to proceed safely by limiting the potential for excavation instability and preventing waterlogged ground conditions.
Dewatering within the Botany Sands Aquifer generally requires continuous pumping of groundwater for a prolonged period. Where significant dewatering is required to allow construction to proceed, you will need to apply for a licence from the Department of Primary Industries – Water .
Tailwater is the water produced through the extraction of groundwater during dewatering. To meet the requirements of the Protection of the Environment Operations Act 1997 tailwater must be disposed of in a manner that doesn’t contaminate surface waters.
If the dewatering system is not carefully designed and managed it can lead to adverse impacts on the environment including:
- inflow of contaminated groundwater resulting from excessive or prolonged pumping
- discharge of contaminated water into stormwater systems and waterways
- detrimental ‘downstream’ environmental impacts by potential chemical and physical contamination
- impacts on local businesses or residents due to the appearance of the discharge or the odours generated by the tailwater.