Groundwater Sampling: Flow-Through Bailer Passive Method Versus Conventional Purge Method

A study was conducted to assess the performance of the flow-through bailer groundwater sampling method against the conventional purge method based on the analysis of inorganic chemistry and total coliform parameters. Sampling was performed at three sites for a total of 43 monitoring wells. Samples were first collected by a bailer from inferred groundwater flow zones followed by the purging method. Analysis of variance of inorganic chemistry parameters measured in the bailered and purged groundwater samples was conducted at 99% confidence interval. Across the three sites, there was no statistically significant difference between all inorganic chemistry parameters measured in the bailered and purged samples. Further analysis was conducted to assess the probability (p) to which the observed difference among groups is attributable to the influence of random factors or the sampling methods (test factor). The probability that the observed differences between the tested groups is rather due to random chance and not to the influence of sampling methods. There are wells that show high influence of the sampling methods on the results and others showing minimum influence. The results suggest that well specific hydrogeology has an influence on the comparison of the sampling methods. Recommendations are therefore made for well specific evaluations prior to the adoption of the bailer passive sampling method. The total coliform counts in the bailered samples are much more elevated than in purged samples, which suggest that, for total coliforms and possibly other microbial analytes, purging is necessary.