Effects of sampling well construction on H-2 measurements made for characterization of redox conditions in a contaminated aquifer

Measurement of hydrogen, H-2, has been suggested for characterization of redox levels in groundwater and has recently been used in the delineation of redox processes in contaminated aquifer. In this investigation, we evaluate the influence of materials and age of the well on the H-2 measurements performed in a leachate-contaminated sandy aquifer at the Grindsted Landfill, Denmark, Four types of small diameter wells were tested, covering a range of materials (teflon, PVC, black iron, and stainless steel) and installation methods (driven wells and bailer techniques). The results suggest that the following precautions are taken in order to obtain valid measurements of H-2: (1) all iron parts should be avoided as well materials, (2) PVC, teflon, and probabaly stainless steel are suitable materials for wells, (3) wells for monitoring H-2 levels shall rest for a period from installation till sampling (our experiences indicate approximately 3 months) before their readings can he trusted, and (4) installation of wells or heavy mechanical work in the subsoil can affect the H-2 levels in nearby wells.