Tier II SCV

These are secondary chronic values that are conservative estimates of water quality criteria for those chemicals for which available data are insufficient to derive criteria. EPA developed Final Water Quality Guidance for the Great Lakes System. The final Guidance contains numeric acute and chronic criteria to protect aquatic life for 15 pollutants, and a two_tiered methodology to derive criteria (Tier I) or values (Tier II) for additional pollutants. Tier I aquatic life criteria for each chemical are based on laboratory toxicity data for a variety of aquatic species (e.g., fish and invertebrates) representative of species in freshwater. The Guidance also includes a Tier II methodology to be used in the absence of the full set of data needed to meet Tier I data requirements. The Tier I aquatic life methodology includes data requirements similar to current guidelines for developing national water quality criteria. For example, both require acceptable toxicity data for aquatic species in at least eight different families representing differing habitats and taxonomic groups. The Tier II aquatic life methodology is used to derive Tier II values, which can be calculated with fewer toxicity data than Tier I. Tier II values can be based on toxicity data from a single taxonomic family, provided the data are acceptable. The Tier II methodology generally produces more stringent values than the Tier I methodology, reflecting greater uncertainty in the absence of additional toxicity data. The final Guidance expresses the criteria for metals in dissolved form because the dissolved metal more closely approximates the bioavailable fraction of metal in the water column than does the total recoverable metal. The dissolved criteria are obtained by multiplying the chronic and/or acute criterion by appropriate conversion factors.

The final Guidance also contains numeric criteria to protect wildlife for four pollutants and a methodology to derive Tier I criteria for additional persistent bioaccumulative pollutants. Wildlife criteria are derived to establish ambient concentrations of chemicals which, if not exceeded, will protect mammals and birds from adverse impacts from that chemical due to consumption of food and/or water from the Great Lakes System. The methodology focuses on endpoints related to reproduction and population survival rather than the survival of individual members of a species. The methodology incorporates pollutant_specific effect data for a variety of mammals and birds and species_specific exposure parameters for two mammals and three birds representative of mammals and birds in the Great Lakes basin that are likely to experience significant exposure to bioaccumulative contaminants through the aquatic food web.

EPA. 40 CFR Parts 9, 122, 123, 131, and 132. (http://www.mvaconsulting.com/glwqi.html#intro)