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Groundwater and Surface Water Interactions in the Ewa Shaft Area, Oahu, Hawaii
Changes in land use in the Ewa area of Oahu have increased current and projected demand for potable water. Groundwater from the Ewa shaft is needed to meet future potable water needs in the Ewa area. However, high bacteria counts in water pumped from the shaft indicate possible surface-water contamination at the site. The source of the bacteria contaminating the pumped water is unknown, although previous field inspections indicate that groundwater may be interacting with surface water near the site.
The objectives of this study are to (1) describe the hydrogeological setting and (2) evaluate the groundwater and surface water connection near the Ewa Shaft.
Relevance and Benefits
The results from this study are necessary to determine if surface water may be infiltrating and contributing to groundwater recharge near the study area. Information generated by this study is needed to make an informed decision on how to best manage groundwater resources. Therefore, the study is consistent with the USGS Science Strategy and its broader theme of developing a Water Census of the United States to provide the public and decision makers with information on freshwater resources.
To meet the objectives of this study, the USGS will (1) compile existing discharge records and collect new discharge measurements from Honouliuli Stream to evaluate streamflow loss rates, (2) measure water levels in Ewa Shaft to evaluate any surface-water contribution to groundwater, and (3) analyze the extent of the interaction between surface water and groundwater in the area of interest. Results from this study will be published in the USGS Scientific Investigations Report series and made available on the internet.