Arrow Energy has advised regulators that routine monitoring tests have detected minute traces of benzene, toluene and xylene in five of 14 shallow bores at Arrow’s Tipton West and Daandine gas fields, approx 25 kilometres from Dalby. These monitoring bores are 50mm in diameter, they are not coal seam gas (CSG) production wells, and are not used to produce coal seam gas or supply water.
The samples were taken over three days from 14 purpose installed monitoring bores constructed around CSG dams. These monitoring bores are required to be routinely sampled every six months. No traces of any chemical were found in the remaining nine bores, or a further six dams also tested.
The water in this aquifer, where the shallow bores are drilled, is not suitable for drinking water, nor to water stock or irrigate crops.
At Tipton West, samples were taken from eight monitoring bores. Laboratory test results showed a minute trace of benzene at 6 parts per billion (ppb) in one bore. Given the close proximity and similar age of the other three bores which were tested, this reading was considered an error.
Secondary testing was carried out on all six bores as well as two dams. These results showed a reduced minute trace of benzene in the same affected bore, at 2 ppb and a minute trace of toluene in two other bores at 2 ppb.
Further testing is planned, with the Department of Environment and Resource Management (DERM), to determine whether the chemicals are naturally occurring or introduced through grease used in the bore drilling process. There is no connection between this process and CSG production activities.
At Daandine, samples were taken from six monitoring bores. Laboratory results showed one bore contained benzene at 15 ppb, toluene at 16 ppb and xylene at 4 ppb. Duplicate samples (which are not secondary testing, but in fact second immediate analysis of the same sample) showed the same bore with benzene at 6 ppb, toluene at 8 ppb and xylene at 3 ppb.
In the initial testing, a second bore was shown to contain toluene at 2 ppb. Duplicate samples showed no trace of toluene, or any other chemical.
Secondary testing was carried out on all six Daandine bores and four dams. The results showed no BTEX chemicals in any of the bores, or the dams. Further testing is planned, with DERM, to confirm the results of the secondary testing. Arrow has notified the relevant landholders.
BTEX is an acronym for the group of chemicals benzene, toluene, ethylbenzene and xylenes. Arrow does not use hydraulic fracturing (fraccing) in its Surat Gas Project area.
[mappress] Source: Arrow Energy, August 26, 2011;