Searching for Groundwater Pollution at Oneuli

Groundwater is a common way for pollution and other harmful substances to enter coastal waters. It can carry anything from toxic chemicals to nutrients that cause excessive algae growth into the ocean, wreaking havoc on marine ecosystems and coral reefs. Our team took the first step to test for pollution by towing Manta devices along the Makena coastline to identify if and where groundwater could be entering the sea.

Groundwater will typically rise to the top of the ocean, and its temperature is cooler than that of seawater. The graph below shows the results of our Manta survey with areas in white representing cooler water temperatures, indicating that groundwater is likely present. Areas in blue or green are where temperature readings were warmer and consistent with that of normal seawater. The lighter shades of blue or green show temperatures between normal ground and seawater readings, indicating areas where the two are mixed.

Salinity at Maluaka. Credit: John Starmer

Making sure Maui’s waters are healthy is vital to our economy and day-to-day lives. By confirming the presence of groundwater, we’ve taken the critical first step to being able to test for harmful pollutants in our coastlines. Once we’re able to identify where groundwater is entering the ocean, we can focus our testing efforts around those areas to identify what kinds of pollutants are being brought in (if any) and then determine where the source or cause of those pollutants are originating on land.