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4 the well followed by check-valve bailer sampling, waiting 2 hours and resampling each well using the KABIS Sampler T'. The results of the test indicated the following o There was no appreciable difference in the TPH ccentrations between the pre-purge samples collected by the KABIS SamplerTM and post-purge samples collected by the check-valve bailer o The test showed overall lower TPH concentrations in the post-purge KABIS SamplerTM samples when compared to the post-purge check-valve bailer samples, due to an improperly designed field method (i e, the KABIS Sampler was delivered to a depth of 4 feet BGW, while the bailer sampled the upper 11/2 feet of the water column.) o Comparison of relative recovery values indicated as much as a 54% increase in recoverable dissolved chemicals of concern (CoCs) in the pre-purge KAB15 Sampler TM samples as compared to the post-purge check-valve bailer samples o Comparison of overall costs showed a considerable difference between the two methods employed at the site Savings of more than 80% were shown when using the KABIS SamplerTM in a no-purge methodology scenario The WSPA Study — In 1995, under pressure to reduce the ever-increasing costs of environmental cleanup at petroleum contaminated sites, the Western States Petroleum Association sponsored the "California Well Purging Study" to evaluate the need for purging of groundwater monitoring wells prior to sampling It should be noted that several methods of purging (lugh-flow, low-flow, and passive) were compared in this study, as were several types of passive and active sampling devices Analysis of the collected data set supports the following three conclusions: o The results of analyzing the entire data set indicate that there is a systematic tendency toward slightly higher petroleum hydrocarbon concentrations in the no-purge sample than in the post-purge sample with the median value of the relative percent difference between no-purge and post purge samples being approximately 9.5 percent o The degree of variability introduced into the sampling process by the absence of purging is no larger than, and in many cases much smaller than, the variability introduced by the choice of a purging method In simpler terms, the decision to select a no-purge sampling methodology will not effect the overall variability in chemical data, and will provide a comparable, and in many cases more conservative, estimate of petroleum hydrocarbon concentrations in groundwater. o In a small population of wells/sites, an especially large discrepancy between no-purge and post- purge concentrations was found This effect appears to be due to site-specific conditions/mechanisms, is reproducible, and such wells/sites can be identified using the sampling methodologies presented in their Study.