Building Dewatering In The Botany Sands And The Aquifer Interference Policy

The Department of Primary Industries (DPI) Water is responsible for the management of groundwater across NSW. The management of groundwater extraction impacts including those associated with dewatering for building developments which predominate in Sydney within the Botany Sands Groundwater Source is one of the primary roles of the agency. There are an increasing number of residential and commercial developments that need to accommodate construction below the water table for basements and other functions. These have to be built in a way that mitigates adverse impacts on other building developments or other groundwater users, sensitive ecosystems or structures. Parts of Sydney’s development are remarkably high-density and construction must be well planned to prevent such effects as unintentional groundwater mounding, obstruction of natural flows by the completed building, and potential basement inundation caused by periodic elevated water levels.

In order to demonstrate sustainable development principles, the Aquifer Interference Policy (AIP) requires the proponent to account for all groundwater take during both construction and occupation. This may include the proponent taking measures to avoid or prevent the take of groundwater where possible and include mitigation or avoidance strategies to reduce take of water. The proponent should demonstrate that adequate arrangements will be in place to ensure the minimal impact considerations of the AIP are met. The information needed for assessments of the groundwater impacts of proposed developments under the AIP requires a comprehensive evaluation of the hydrogeological environment. This information is required to allow DPI Water to balance the management of the groundwater resource with facilitating sustainable development.

In some instances, the use of secant piled cut-off walls to enclose an entire site may not be the optimum solution without other engineering measures because the walls effectively work like dams to groundwater flow. Alternate methods of construction might be more appropriate and facilitate flows both beneath and around structures. The dewatering considerations are not limited to individual properties as there are significant interferences from major infrastructure projects, as well as other nearby concurrent building developments, which need to be accommodated at the same time. This paper discusses requirements for proponents and their consultants that relate to the assessment of dewatering proposals in Sydney’s Botany Sands Groundwater Source, which is part of the Greater Metropolitan Region Water Sharing Plan area.