Executive Summary This report and field study was produced as a result of the comments in the Santos 2016 Environmental Impact Statement that “no stygofauna were collected during the sampling regime by
Eco Logical” and therefore “there is an uncertainty regarding the presence of stygofauna at the project areas, especially Leewood”. The aim of this report is to provide certainty by demonstrating via a more extensive survey of bores across the Pilliga that stygofauna do indeed exist in the shallow aquifers of the Pilliga Forest, are at risk from the current and proposed future development of Coal Seam Gas production and therefore need to be considered and included in the environmental management program.
The current condition of the stygofauna community is considered good, based on available evidence (number and range of species in samples). The occurrence of this community within an unregulated catchment that has had very little water extraction for irrigation is considered to be a contributing factor in its condition. However, the proposed expansion of the coal seam gas exploration within the Pilliga Forest area including the Bohena Creek catchment poses an imminent threat to this community through likely changes in water table levels and water chemistry. The additional disturbances and demands by mining on the groundwater aquifer and potential changes to the aquifer water chemistry from gas exploration in the Pilliga is a serious and demonstrable threat to this GDE community. Potentially these activities, should they proceed, will place the Pilliga groundwater dependent ecosystems that include the endemic stygofauna, baseflow stream communities and the Terrestrial Vegetation community at risk of serious and irreparable environmental damage.
Australia is biogeographically distinct in its groundwater fauna (Humphreys, 2002) and the subterranean fauna of NSW is biogeographically distinct from other Australian ‘hotspots’ (Eberhard and Spate, 1995; Serov, 2002; Thurgate et al, 2001). In addition to the diversity aspect, our ecological perspective of groundwaters has broadened to consider the subsurface system as having a complex and interactive boundary with surface ecosystems at a range of scales. Groundwater fauna, especially stygofauna are extremely sensitive to the environmental characteristics of the water they inhabit and thus potentially are useful indicators of groundwater health (Tomlinson & Boulton, 2008, Serov et al, 2009).
The importance of aquifer ecosystems in terms of biodiversity is that groundwater environments within unconsolidated alluvial and fractured rock aquifers (as well as karstic aquifers) harbour a dynamic and diverse range of invertebrate communities that are composed of most of the major taxonomic groups (i.e. Crustacea, Oligochaete, Mollusca, Insecta) found in the surface water habitats, however, many of the lower (Order to species) are no longer found in surface environments or have surface water relatives (Humphreys, 2002; Marmonier et al,. 1993; Rouch and Danielopol, 1997; Sket 1999b; Danielopol et al., 2000). There is also a marked bias towards the crustacean and oligochaete groups (Marmonier et al,. 1993; Rouch and Danielopol, 1997; Sket 1999b; Danielopol et al., 2000 Tomlinson & Boulton, 2008). Most of these species are new to science.
In 2012 the first surveys were carried out within the Pilliga in order to determine the presence of Stygofauna within the Pilliga Sandstone Aquifer. The initial surveys were conducted on the pastoral property of ‘Rockdale’ located approximately 20km south of Narrabri, within the Pilliga State Forest. This first survey was in response to the property owner experiencing a rapid decline in water quality from the house bore used for domestic consumption. This was the second recorded change in groundwater condition, with the first occurring in 2006 with the failure of the original house bore. In order to investigate the cause behind the decline in water quality, a biological survey of the bores on the property was included as an indicator of the groundwater conditions to complement the water chemistry analysis conducted in the same period by Divstrat Pty Ltd. to provide advice on the possible cause of the water quality change. This was the first environmental assessment of the aquatic ecosystems of the Pilliga sandstone aquifer within the Pilliga Forest area
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