Direct comparison of bore purge and low-flow groundwater sampling techniques in high yield areas

The objective of groundwater sampling is to extract a representative water sample from underground; however this is difficult due to inaccessibility. Two methods are used routinely to obtain groundwater samples; the bore purge and the low-flow methods. The bore purge method has been shown to be highly disruptive, introducing turbulence to the groundwater and mobilising contaminants. The low-flow method was introduced to provide more accurate results. Bores in three high yield areas in Maribyrnong, Victoria, Dunmore, New South Wales and Queanbeyan, New South Wales were sampled to compare the two methods. The bores were sampled using the low-flow method and then immediately after using the bore purge method. Any excessive disruption using the bore purge should result in significantly different contamination levels. Several analytes such as BOD, COD, ammonia, TOC and total dissolved solids were analysed and the average relative percentage difference in results across the 10 different bores was only 14.2 and not considered to be significantly different. The low-flow method returned slightly higher readings 100 times, and the bore purge method, 84 times. Even results were returned 112 times. This finding is unexpected and significant, and differs from the results of earlier studies. However, issues associated with the bore purge method may be more pronounced in areas with low recharge and this could be tested in a later study.