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Source-tracking approach for detecting and identifying sources of wastewater in waters of Hawaiʻi

Elevated concentrations of nutrients and the fecalindicator bacteria enterococci are occasionally detected in Hawai‘i’s surface waters by the State of Hawai‘i Department of Health Clean Water Branch. Management efforts to improve the water quality of surface waters are complicated by the fact that nutrients and enterococci can originate from several sources, including wastewater, animal waste, and soils. Wastewater often is the suspected source of nutrients and bacteria, but the source may not always be unequivocally identifiable from the Clean Water Branch’s routine monitoring efforts. This report—prepared in cooperation with the State of Hawai‘i Department of Health Clean Water Branch—describes a source-tracking approach for Hawai‘i that is meant to help investigators determine whether wastewater is present in the environment and where wastewater might be originating, if it is present. Wastewater sources include domestic wastewater entering the environment through on-site disposal systems and municipal wastewater entering the environment through leaky sewer systems or injection-well disposal systems. The source-tracking approach relies on the use of field-measured water properties and multiple chemical tracers of wastewater, including optical brighteners, nutrients, hydrogen and oxygen isotopes in water, nitrogen and oxygen isotopes in nitrate, organic waste compounds, and human-use pharmaceutical compounds. The source-tracking approach proposes the following sequence of steps for investigators to execute: (1) gather background information on the study area, (2) conduct trolling-instrument surveys of physical properties of surface water and identify groundwater-discharge locations, (3) collect water samples at reconnaissance sites and analyze the samples for detergent optical brighteners and specific conductance, (4) collect water samples at targeted sites and have appropriate laboratories analyze the samples for chemical tracers of wastewater, and (5) evaluate analytical results for chemical tracers of wastewater and conclude whether wastewater is present in sampled waters. The conclusions can guide management and stakeholder efforts to protect and improve the quality of Hawai‘i’s water resources. Introduction The State of Hawai‘i Department of Health Clean Water Branch (CWB) is responsible for protecting and restoring the ecosystem health of Hawai‘i’s surface waters for marine life and wildlife (State of Hawai‘i, 2017). The CWB assesses the ecosystem health of surface waters by monitoring several nutrients and other properties such as turbidity, total suspended solids, and chlorophyll a. Waters that have concentrations of these properties that exceed applicable State of Hawai‘i (2014) water-quality standards are considered impaired. In a recent assessment (State of Hawai‘i, 2017) of the ecosystem health of Hawai‘i’s surface waters, results of nutrient monitoring in waters of 24 coastal watersheds indicated that 10 of the 24 assessed watersheds were impaired for one or more nutrients. The CWB also is responsible for notifying the public about which surface waters in Hawai‘i may contain harmful pathogens that can sicken people. Pathogens harmful to humans include bacteria and viruses that typically originate from the fecal matter of humans and other warm-blooded animals. People who recreate in fecal-contaminated water risk exposure to pathogens that can cause gastrointestinal illnesses and may lead to diarrhea, nausea, stomach aches, and vomiting. The CWB infers the presence of fecal pathogens in water and associated health risks to humans by monitoring the fecal-indicator bacteria enterococci. The U.S. Environmental Protection Agency (2012) recommended monitoring enterococci to assess potential health risks of pathogens to humans recreating in fresh and marine waters because enterococci concentrations in water impacted by wastewater have been correlated with the risk of humans contracting gastrointestinal illnesses. Currently (2020), enterococci are monitored by the CWB at dozens of sites on Kaua‘i, O‘ahu, Maui, and Hawai‘i Island; most of the sites are near or along the coastlines of these islands. The CWB notifies the public of the potential health risks of recreating in waters that have enterococci levels that exceed the State of Hawai‘i (2014) recreational water-quality standards. 2 Source-Tracking Approach for Detecting and Identifying Sources of Wastewater in Waters of Hawaiʻi