Challenge: To decommission the Caltech Submillimeter Observatory (CSO) while minimizing environmental and cultural impacts from wastewater and fill material.  

Solution: In support of the CSO decommissioning activities on Maunakea, a sensitive cultural and biological mountain, INTERA completed a hydrogeological and geological evaluation as part of the overall environmental assessment (EA) conducted by the California Institute of Technology (Caltech). We analyzed the potential environmental impacts from wastewater associated with the decommissioning, including impacts on downgradient drinking water aquifers, Lake Waiau, and springs in Pōhakuloa Gulch The analysis incorporated a literature review, visual hydrologic inspections, travel time and attenuation estimates, examination of nitrate data from water supply wells, and dilution factor calculations. INTERA also conducted a geochemical analysis of the fill material that was brought to the site during construction of the CSO.  

Results: INTERA’s work helped ensure the successful decommissioning of CSO. We demonstrated that wastewater from decommissioning the CSO posed negligible risks to the regional aquifers, springs, and Lake Waiau. The collection and analysis of samples from the fill material and a nearby lava flow were used to inform decisions about potential fill removal and return to its source based on the selected decommissioning alternative.