A Constant-Head Well Permeameter Measurement of Saturated Hydraulic Conductivity in the Vadose Zone and the Capabilities of Carbon Dioxide Injection

Abstract

The constant-head well permeameter (CHWP) method is a single-borehole infiltration test for in situ measurements of field-saturated hydraulic conductivity (K fs) in the vadose zone. A measuring instrument was designed for the determination of K fs at greater depths using a pipe-in-pipe overflow system with a submersible pump. The entrapment of air in the soil pore system inhibits truly saturated conditions during infiltration tests. A proven method to reduce the influence of entrapped air is the displacement of soil air with carbon dioxide. In this study, the designed CHWP was put to the test in a field experiment in a sandy soil. Injection of CO2 was applied in 7 out of 11 tests for varying durations and flow rates in order to find an optimal combination. The experimental results show a considerable increase in K fs by about a factor of 1.5 due to the application of CO2. An average hydraulic conductivity of 1.6E−06 m/s was determined in tests without CO2-injection, 2.4E−06 m/s in tests with sufficient CO2-injection, and 2.8E−06 m/s in laboratory falling-head hydraulic conductivity tests. The optimal setting for the injection of CO2 was duration of 1 h with a flow rate of 20 L/min.