Development and implementation of a site‐specific water quality limit for uranium in a high conservation value ecosystem

ABSTRACT Water quality guideline values (GVs) are a key tool for water quality assessments. Site‐specific GVs, which incorporate data relevant to local conditions and organisms, provide a higher level of confidence that the GV will protect the aquatic ecosystem at a site compared to generic GVs. Site‐specific GVs are, therefore, considered particularly suitable for sites of high sociopolitical or ecological importance. The present paper provides an example of the refinement of a site‐specific GV for high ecological value aquatic ecosystems in Kakadu National Park, Northern Territory, Australia, to improve its site specificity and statistical robustness, thereby increasing confidence in its application. Uranium is a contaminant of concern for Ranger U mine, which releases water into Magela Creek and Gulungul Creek in Kakadu National Park. A site‐specific GV for U has been applied, as a statutory limit, to Magela Creek since 2004 and to Gulungul Creek since 2015. The GV of 6 μg/L U was derived from toxicity data for 5 local species tested under local conditions. The acquisition of additional U data, including new information on the effect of DOC on U toxicity, enabled a revision of the site‐specific U GV to 2.8 μg/L U and an ability to adjust the value on the basis of environmental concentrations of DOC. The revised GV has been adopted as the statutory limit, with the regulatory framework structured so the GV requires adjustment based on DOC concentration only when an exceedance occurs. Monitoring data for Magela Creek (2001–2013) and Gulungul Creek (2003–2013) downstream of the mine show that dissolved U has not exceeded 1 μg/L. Integr Environ Assess Manag 2017;13:765–777. © 2016 SETAC Key Points A site‐specific water quality limit for U was revised on the basis of new toxicity data and quantitative data on the influence of DOC. The revised U limit was 2.8 μg/L and can be adjusted on the basis of environmental DOC concentration. The U limit has been implemented in the regulatory framework for the Ranger U mine, surrounded by World Heritage– and Ramsar–listed wetlands, in northern Australia. This case study illustrates how site‐specific water quality limits can be derived and implemented in a rigorous manner.