Interim progress report - Geochemistry monitoring program (draft)

Abstract

The geochemical monitoring program has undertaken two related responsibilities: 1) Conduct a detailed analysis of the chemistry and dynamics of the shallow groundwater system on the Lower East Rift (LERZ); and 2) Evaluate the chemical composition of the geothermal fluids from the geothermal reservoir currently under development on the Kilauea East Rift Zone (KERZ). The objectives of the first effort are to characterize the baseline compositions of the shallow groundwater in the LERZ, to assess whether the geothermal development is having an adverse affect on the groundwater resources, develop a conceptual model for groundwater flow and mixing on the LERZ and to provide a data base with which to develop and validate a numerical model of this groundwater system. Analysis of the geothermal fluid compositions will provide us with the data necessary to determine whether shallow groundwater contamination is occurring and will enable us to assess some of the impacts that fluid production may be having on the long term viability of the geothermal reservoir. The shallow groundwater monitoring program has employed both continuous downhole monitoring instruments as well as repeated sampling of a variety of shallow groundwater sources located within and near the KERZ. Groundwater sources were chosen for monitoring included wells that were in close proximity to or down-gradient from, the geothermal system as well as sources that could provide baseline data that were unlikely to be affected by geothermal activities. Analysis of reservoir fluids have included both the liquid and steam phases generated by the geothermal production wells supplying steam to the PGV facility. The results that have been obtained to date for the groundwater monitoring program have shown that the groundwater system in lower Puna is very complex and is much different from those found elsewhere 4t Hawaii. Comparison of the variations in groundwater chemistry with the compositions of the geothermal fluids has not shown any detectable impact on groundwater quality from the geothermal development activities up to the present time. Analyses of the geothermal fluids has also shown that the fluids produced by the commercial production wells in the reservoir currently under development are quite different from those produced by the earlier HOP-A well, but have also found that substantial changes in production chemistry have occurred since production began in early 1993.