AgdaPkt 2016-02-22 Closed and Interview and Joint SA PFA

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City of Redwood City, Public Works Division Initial Study & Mitigated Negative Declaration Document Date: October 15, 2015 Revision Date: January 25, 2016 Page 29 Blankinship & Associates, Inc. estimate risk of copper to the longfin smelt were found in the published literature. As copper applications are sufficiently intermittent and copper is not significantly persistent within the water column, only acute TRVs are derived. The U.S. EPA (2004) suggests applying a 20X safety factor to acute median toxicity values (LC50s and LD50s) for aquatic threatened or endangered species and a 10X safety factor for terrestrial threatened or endangered species. Often, no herbicide-specific toxicity results are available for various taxonomic groups. For example, database and literature searches for copper toxicity testing of saltwater fish species did not yield any useable studies. In this case, fish toxicity endpoints of a species with similar size and life history to the longfin smelt were used. Once a TRV has been derived, it may be compared to an exposure estimate to evaluate whether an adverse effect for a given species is likely to occur. Exposure was estimated assuming the copper containing algaecides and herbicides are applied at the maximum allowable label rate of 1 ppm metallic copper, equivalent to 1 mg/L metallic copper. If an estimated exposure is lower than the derived TRV, the exposure scenario is not considered to pose a risk. Risk is estimated by comparing the estimated environmental concentration (EEC) an organism may be exposed to the derived TRV to estimate a risk. Risk may be present when the EEC divided by the TRV is greater than or equal to 1.0. Risk is likely not present if the result is less than 1.0. Risk = EEC/TRV Where: EEC = Estimated Environmental Concentration TRV = derived Toxicity Reference Value Copper Discussion Copper toxicity is largely driven by its environmental concentration. However, water quality parameters such as pH, hardness, alkalinity, salinity, and dissolved organic carbon (DOC) affect the bioavailability of copper. These parameters affect the competitive binding of copper to other molecules in the water column, thereby altering the fraction of copper that is bioavailable to elicit toxic effects. The USEPA suggests the use of the Biotic Ligand Model to analyze and/or predict toxicity of bioavailable copper in freshwater systems. The free cupric ion (Cu2+) is the primary driver of copper bioavailability and toxicity in aquatic ecosystems (USEPA 2007). Because the Redwood Shores Lagoon is not a freshwater system, this model was not appropriate and therefore not used. Instead, the highly conservative assumption was made that 100% of the copper present in the water column is bioavailable. Since no adequate published TRVs for copper were available for fish, the approach used here was to select the most sensitive and applicable fish endpoint from studies available in the literature. Studies indicate that, although early life stages generally are most sensitive, size rather than developmental stage may be the more significant factor when evaluating 6.3.A. - Page 37