Graphical Methods for Huntley's LNAPL Baildown Test

This paper presents six new graphical methods to assist the analyst in the selection of the correct data required for use in Huntley's (2000) baildown test method to determine LNAPL transmissivity based on the Bouwer and Rice (1976) slug test which is referred to here as Huntley's Method 1. Huntley (2000) did not develop his Method 1 from experimental data. Instead, he derived equations relating the change in the air‐LNAPL interface elevation to the change in LNAPL‐water interface elevation under the conditions where the potentiometric surface elevation in the well remains constant. Our new graphical methods use features of Huntley's (2000) equations and the updated conceptual understanding of the gradients causing fluid flow during a baildown test identified by Hamper and SeyedAbbasi (2023) to assist with identifying the data required for use with Huntley's Method 1. These graphical methods use the following features of Huntley's Method 1: during recovery Period 1 of the baildown test, all fluid interface elevations rise; and during Period 2, the air‐LNAPL interface elevation rises, the LNAPL‐water interface elevation declines, and the potentiometric surface elevation in the well is constant. The relative density of the LNAPL can be determined from the slope of the best fit line of the graph of drawdown vs. change in LNAPL thickness. The graphical methods presented here represent the ideal as predicted by Huntley's Method 1 equations as applied to unconfined formations. While not all graphs are needed for every data set, the methods provide analysts with multiple tools for interpreting less‐than‐ideal field data and for gaining a deeper understanding of Huntley's Method 1.