Abstract
This paper presents a means of estimating in-situ groundwater pH and oxidation-redox potential (ORP), two very important parameters for species migration analysis in safety assessments for radioactive waste disposal or carbon dioxide sequestration. The method was applied to a pumping test in a deep borehole drilled in a tertiary formation in Japan for validation. The following application examples are presented: when applied to several other pumping tests at the same site, it could estimate distributions of the in-situ groundwater pH and ORP; applied to multiple points selected in the groundwater database of Japan, it could help estimate the in-situ redox reaction governing the groundwater conditions in some areas.
Highlights
Geochemical characteristics of deep groundwater are essential information for safety assessments for the geological disposal of radioactive wastes [1], and the sequestration of carbon dioxide [2], one of the known greenhouse gases, because groundwater chemistry could affect migration of the species included in disposal wastes
When pumped up to the surface, it could be degassed with depressurisation to increase its pH and it could be oxidised by contact with the atmosphere to increase its oxidation redox potential (ORP) [3,4,5,6]
The geochemical test consisted of pumping the groundwater, monitoring of physical-chemical parameters including water pressure, pH, temperature, dissolved oxygen (DO), electrical conductivity (EC) and ORP, and in-situ water sampling which had the capability of maintaining the in-situ water pressure with stainless steel containers
Summary
Geochemical characteristics of deep groundwater are essential information for safety assessments for the geological disposal of radioactive wastes [1], and the sequestration of carbon dioxide [2], one of the known greenhouse gases, because groundwater chemistry could affect migration of the species included in disposal wastes. Existing investigations of groundwater chemistry so far have involved drilling a borehole, purging the drilling mud, pumping up the groundwater, sampling it at the surface and conducting analyses in the laboratory. In order to procure quality data on the pH and ORP of the deep groundwater, it is recommended to measure them in-situ [7, 8], and some apparatus has been developed for. A realistic solution is considered as follows: (1) perform in-situ measurements, and the existing ones; (2) develop a method for estimating the in-situ pH and ORP using existing data in comparison with in-situ data; (3) estimate the in-situ values of test intervals where in-situ measurements are not conducted; (4) economically obtain data on the in-situ pH and ORP across a wide area. As application examples, the following is estimated: distributions of the in-situ pH and ORP at a site in Japan; a predominant redox reaction governing the in-situ groundwater conditions in use of the groundwater database of Japan
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