A Method for Conducting Simultaneous Convergent Tracer Tests in Multilayered Aquifers

Abstract

Forced gradient tracer tests between two boreholes can be used to study contaminant transport processes at the small field scale or investigate the transport properties of an aquifer. Full depth tests, in which tracer samples are collected just from the discharge of the abstraction borehole, often give rise to breakthrough curves with multiple peaks that are usually attributed to different flow paths through the aquifer that can rarely be identified from the test results alone. Tests in selected levels of the aquifer, such as those between packer-isolated sections of the boreholes, are time consuming, expensive; and the identification of major transport pathways is not guaranteed. We present a method for simultaneously conducting multiple tracer tests covering the full depth of the boreholes, in which tracer sampling and monitoring is carried out by a novel multilevel sampling system allowing high frequency and cumulative sampling options. The method is applied to a tracer test using fluorescein conducted in the multilayered sandstone aquifer beneath the city of Birmingham, UK, producing six well-defined tracer breakthrough curves.

Borehole Flowmeter Logging for the Accurate Design and Analysis of Tracer Tests

“…Ptak et al () adopted a multilevel fiber optic fluorimeter to obtain a high temporal and spatial resolution, with a high installation cost that can be a limiting factor for this technique. In complex aquifer systems with significant vertical variation in permeability, a series of cross‐hole tracer tests between homogeneous intervals can be performed, but this approach is extremely time‐consuming (Greswell et al ). On the other hand, a single well tracer dilution test (Brainerd and Robbins ) can be used to characterize the flow in unconnected fractures, but such tests require the pumping and treatment of significant quantities of water.…”