Use LNAPL transmissivity metrics for LNAPL remediation in dual pososity and fractured aquifers — a case study

LNAPL remediation in dual porosity and fractured bedrock aquifers is a challenge in both understanding the extent of LNAPL in the subsurface as well as identifying practical and efficient remediation options to remove LNAPL to the extent practicable. LNAPL transmissivity (Tn) is a useful metric to assess LNAPL abundance, saturation and recoverability, and hence the relative suitability of remedial techniques, as well as the practicability of ongoing remedial activities in accordance with the regulatory guidelines (i.e. Clean Up to The Extent Practicable (CUTEP)). The American Petroleum Institute (API) Transmissivity Workbook is a widely used method to undertake Tn calculations. However, these calculations may not be accurate in dual porosity aquifers or highly variable strata, such as infilled ground, siltstone, or fractured bedrock such as Victorian basalt. This is due to the assumptions on aquifer hydraulic characteristics underlying the estimation of Tn and practicalities with obtaining and interpreting quality LNAPL recovery data. This case study outlines the challenges encountered in the use of LNAPL Tn in the development of LNAPL conceptual site models (CSMs) and remediation options at a number of LNAPL remediation sites with dual porosity and fractured aquifers, including the applicability and use of LNAPL Tn calculations as a remediation metric. (author)