Side-by-Side Comparison of Two Groundwater Sampling Methodologies: A Quantitative Review of Analytical Data From Groundwater Samples Collected Simultaneously Using Micropurge ‘Low-Flow' and Traditional Standard Groundwater Sampling Techniques

Micropurge, or “low-flow” groundwater monitoring is a relatively new field sampling method that is gaining increasing technical and regulatory acceptance.  The effectiveness of this groundwater sampling technique was evaluated under “real project” conditions at a closed RCRA surface impoundment subject to a compliance groundwater monitoring program.  Groundwater samples were collected in the field simultaneously using the micropurge method that employed dedicated pumps, together with the traditional standard sampling method that employed bailers.  A brief description of both sampling methodologies will be provided as background.  The primary focus of the presentation will be the comparison of analytical results from groundwater samples collected using the two sampling methods, analyzing the disparities found when comparing the results, and offering discussion on the presumed reasons for the different results. 

Results indicated that fourteen (14) individual semi-volatile organic compounds that were identified at concentrations greater than the permit limits using the traditional standard groundwater sampling methods were less than the permit limits using the micropurge sampling technique.  In summary, the micropurge sampling methodology is considered to provide more representative results, and state regulators have approved the new micropurge sampling techniques to replace the old sampling methods.  The change to the new micropurge sampling method (and it’s more accurate measurements) has saved the permittee significant costs because data collected using the traditional standard sampling method was indicating a need to initiate a potentially costly corrective action program, but data from more recent groundwater samples collected using the micropurge method indicate such action is unnecessary.  The collection of representative groundwater samples will continue to be of critical importance at this facility and many others like it, given the fact that it is subject to a minimum of 30 years of post-closure groundwater monitoring.