The application and revision of a new relationship to calculate effective porosity from specific capacity on a well database in the Pacific Northwest

Abstract

Previous unpublished research led to the establishment of a relationship between effective porosity and specific capacity, based on well construction data in a series of laboratory experiments. In this paper the relationship was tested on a regional aquifer system using data from 609 wells which met certain criteria. The relationship was applied to each well, with results showing that the relationship needed revision. The relationship was thus reevaluated and revised to produce results that reflected the conditions in the aquifer system which consisted of 9 layers of aquifers and aquitards of various lithologic descriptions, ranging from unconsolidated sediments to volcanic rocks. Average values of effective porosity could be calculated and the distribution of effective porosity was determined for each unit and compared with the original estimates. The result was a new relationship to determine effective porosity directly from specific capacity, which can be applied without detailed information on well construction or lithology. The new relationship is useful for distributing effective porosity within 2 or 3 dimensional groundwater and particle tracking models on a cell-by-cell basis. More importantly, the new relationship can be used to determine effective porosity for contaminant transport models.