Application of CCME Procedures for Deriving Site-Specific Water Quality Guidelines for the CCME Water Quality Index

Since its development in 2001, the Canadian Council of Ministers of the Environment (CCME) Water Quality Index (WQI) has established itself as a valuable tool for communicating ambient water quality data. Due to the high natural background levels of particular parameters in water bodies throughout the country it is often necessary to use Site-Spedfic Water Quality Guidelines (SS-WQGs) as opposed to generic national Water Quality Guidelines (WQGs) or provincial Water Quality Objectives (WQOs) in the CCME WQI model to obtain truly representative rankings. SS-WQGs have only been developed for a limited number of ambient water quality sites and this has been a major hurdle to the widespread use and acceptance of the CCME WQI. This paper presents the adaptation and implementation of an existing CCME-approved SS-WQGs derivation method called the background concentration (BC) procedure into a Site-Specific Water Quality Index (SS-WQI) calculator and tool. It discusses the application of the SS-WQI calculator to compute water quality indices for five pristine ambient water quality sites in Newfoundland and Labrador. The effects of using five different BC-based SS-WQGs (mean; median; mean ′ one standard deviation; mean ′ two standard deviations; 90 t h and 10 t h percentile) are examined. The paper also discusses the challenges and benefits of using this methodology and provides recommendations for further testing.