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Effects of Irrigation with Treated Wastewater on Groundwater Quality in North-Central Oahu

Project Chief: Robert Anders
Project Period: 2013 through 2015
Cooperator: Honolulu Board of Water Supply
Location: Island of Oahu


As the reuse of wastewater treatment plant (WWTP) effluents increases to meet growing freshwater demands, the need to better understand the potential impacts of these complex chemical sources on aquatic environments also increases. Direct reuse of treated WWTP effluent as a source of irrigation water or indirect reuse by spreading in managed artificial recharge ponds has benefits for augmenting the water supply and limits the adverse effects of wastewater disposal on receiving surface-water bodies, but the potential to degrade groundwater quality needs to be carefully assessed. Although land use, wastewater treatment, and anthropogenic chemicals in wastewater have changed during the period of operation, the North-Central Oahu reuse project represents a valuable case study for evaluating whether chemical signatures from treated wastewater can be identified in groundwater in Hawaii because of the long duration and large areal extent of the irrigated area.


The objective of this study is to assess the effects of irrigation with treated wastewater on groundwater quality in North-Central Oahu, particularly in regards to emerging contaminants of concern including endocrine disrupting chemicals, pharmaceuticals, and trace elements.

Relevance and Benefits

Completion of the proposed work will provide the USGS with additional water-quality information on emerging contaminants of concern in drinking-water aquifers. Therefore, the study is consistent with the USGS Science Strategy and its broader themes of the role of environment and wildlife in human health, and a Water Census of the United States. Furthermore, results from this study can be used to design monitoring and proactive risk-assessment modeling efforts to evaluate the potential impacts of wastewater-reuse projects on groundwater supplies used for drinking water or other beneficial uses.


To meet the objective of this study, the USGS will sample the irrigation water and groundwater upgradient of, beneath, and downgradient of the area of application of treated wastewater as irrigation in North-Central Oahu. Samples will be analyzed for a wide variety of emerging contaminants and potential tracers, including organic, inorganic, and isotopic analytes.

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