SANTOS is building a groundwater monitoring system for its coal seam gas (CSG) operations in the Pilliga Forest as its starts exploratory drilling.
The monitoring system will report the impact of CSG activities on water levels and quality in aquifers underneath the Pilliga and more broadly, around Narrabri.
Santos faces an uphill battle in the court of public opinion and CSG’s potential impacts on groundwater is a key concern for local farmers in the Namoi catchment.
The company will collect baseline data to paint a picture of the current state of the groundwater system in the Namoi catchment and then monitor to detect impacts from CSG activity as production ramps up.
Santos hydrogeologist Glenn Toogood says monitoring bores will act as “heart-rate monitors” of groundwater systems.
In 2013, the company will sink as many as 20 bores to monitor the Great Artesian Basin porous rock aquifer as well as deeper water bearing rocks between 500 and 1000 metres across the project area.
Santos will combine the data collected with that collected by the NSW Office of Water (NOW) in its real-time groundwater monitoring bores.
NOW reports there are “several dozen” of these bores in the catchment.
Santos will combine baseline data from an additional 123 NOW non-live monitoring bores.
The results will be publicly available on the Santos Water Portal website.
During production, Santos will extract CSG from depths between 700m and 1100m.
Farmers’ bores in the Namoi catchment, on the other hand, tap into aquifers which bottom out at a maximum of 350m, with the majority targeting rich alluvial groundwater sources between 20 to 100m deep, Mr Toogood said.
Fears abound that shallow (alluvial) aquifers that groundwater could be depleted as water is pumped out of deep coal seams in preparation for gas production.
CSG opponents argue that when Santos drills its wells to tap into the underlying CSG, previously impermeable layers will be cracked, allowing precious irrigation water to run away or be contaminated with the saline water and methane from below.
Santos says the wells it drills will be reinforced to “mitigate the risk” of impacts on groundwater systems.
Mr Toogood said Santos’ modelling of groundwater systems shows shallow aquifers will not be effected, when it de-waters the deep coal seams in preparation for CSG extraction.
“The modelling shows there won’t be any effect to the overlying groundwater systems, even at the Pillaga project’s full production – meaning there will be no greater drop than half a metre, which is within the accuracy tolerance of the models.”
Mr Toogood said water levels in the alluvial and hard rock aquifers in the Namoi catchment “regularly drop by 1m to 2m” during periods of drought or heavy irrigation extraction.
