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Groundwater Tracers to Evaluate Connection Between Inland and Coastal Groundwater Systems, Kona Area, Island of Hawaii

Project Chief: Delwyn Oki
Project Period: May 2012 through September 2014
Cooperator: Hawaii State Commission on Water Resource Management
Location: Island of Hawaii

Problem

Since 1970, west Hawaii has experienced a population increase of about 83 percent and the fastest economic growth on Hawaii Island, although the effects of development on groundwater resources remain uncertain. At issue among stakeholders is whether urban development over, or withdrawals of freshwater from, the high-level groundwater system will adversely affect the coastal groundwater system, which itself is developed for municipal, agricultural, and industrial uses and which sustains aquatic resources.

Objective

The objective of this 2.5-year study is to evaluate whether groundwater from the high-level system discharges into the coastal groundwater system, and whether there are characteristic chemical or isotopic signatures that aid in making this discrimination.

Relevance and Benefits

The results from this study will help water managers and other stakeholders to better understand potential risks to coastal water resources associated with groundwater withdrawals from, and development over, the inland high-level groundwater system. This study is consistent with the USGS mission to provide a clearer knowledge of the status of water resources; specifically, the likely changes in land use, land cover, and water use on water quality and ecosystem health.

Approach

The following approach will be used to meet the study objective: (1) collect water samples from existing wells and anchialine pools in western Hawaii during both dry and wet seasons; (2) measure water-quality parameters at the time of sampling; (3) analyze water samples for selected constituents, including water isotopes, major ions, silica, selected metals, and salinity; and (4) collect rain samples to establish a local meteoric line for water isotopes and to quantify isotopic differences associated with different rain-producing mechanisms.

Progress

USGS staff collected water-quality samples from about 25 sites, and deployed 4 rain collectors.

Fiscal Year 2013

Continue sampling and start analyzing data.