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

Browse Search

City of Redwood City, Public Works Division Initial Study & Mitigated Negative Declaration Document Date: October 15, 2015 Revision Date: January 25, 2016 Page 57 Blankinship & Associates, Inc. operating procedures that will be used by City or contractor personnel, there is a less than a significant potential for impact. Item b): Less Than Significant Impact. The cumulative impacts of continued application of copper-based herbicides is not precisely known. However, studies examining the relationship between sediment copper concentration and toxicity support the conclusion that sediment- bound copper is not bioavailable. Deaver et al. (1996) compared limnetic water and copper- amended sediment toxicity to Hyalella azteca, an epibenthic detritivore sentinel species, and found that sediment concentrations were not predictive of copper toxicity across various water and sediment conditions. The limnetic water median lethal concentration (LC50) of the free cupric ion, however, varied by <4% in the sediment-toxicity tests, indicating that the form of copper associated most strongly with toxicity (i.e. the bioavailable fraction) in its aquatic phase rather than sediment-bound copper. These results are corroborated by those of Suedel et al. (1996) which showed that copper toxicity to several aquatic organisms, including fish, water fleas, a midge, and an amphipod species, were correlated with overlying (limnetic) water concentration rather than sediment or pore water concentration. As noted in the IS/MND, copper-containing herbicides rapidly dissipate and/or become permanently insoluble, and as a result, are not bioavailable shortly after application (CDFA 2002; Trumbo 1997, 1998; WA DOE 2004). Toxicity studies have also been conducted using water and sediment samples from copper herbicide application sites. Gallagher et al. (2005) collected water and sediment samples from a 20,234 hectare lake treated for 10 years in some areas with Komeen, a form of chelated copper applied annually at concentrations of 1 mg Cu/L. This rate of application is similar to the rate and application interval to what the City or contractor anticipates using. The Gallagher study also looked at untreated areas to assess bioavailability to Hyalella azteca and Ceriodaphnia dubia. No statistical differences in response of either H. azteca or C. dubia to treated (16.3-18.0 mg Cu/kg) and untreated (0.3 mg Cu/kg) sediments were observed when compared to control sediments. In a 10-day exposure study by Huggett et al. (1999), sediments were collected from Steilacoom Lake (WA) and amended with CuSO4 (800-2,000 mg Cu/kg dry weight) to assess copper bioavailability to H. azteca, Chironomous tentans,and C. dubia. When comparing the no observable adverse effect concentrations (NOECs) derived under these experimental conditions (906-2,010 mg Cu/kg) with the current concentrations of copper in the lake sediment (180-1,110 mg Cu/kg), it is apparent that the sediment-bound copper in the lake is not bioavailable to the three species. Mitigation has been incorporated into the Project (HWQ-1). This mitigation reduces the impact to a less than a significant. Item c): Less Than Significant Impact. As a result of implementation of City or contractor standard procedures as described in the Hazards and Hazardous Materials section, any hazard/hazardous material impacts to the human beings is reduced to a less than a significant level. 6.3.A. - Page 65