T4 PM Endangered Species and Environmental Contaminants: Status of the Science (Part 2)
Tuesday, 15 November 2005: 1:50 PM - 5:30 PM in Ballroom 4

(HAL-1116-007432) Deriving Chloride Aquatic Life Thresholds - Upper Santa Clara River (CA): Protecting Endangered Species.

Hall, S¹, Byrn, K¹, Beeson, D¹, Lockwood, R¹, Ruffell, K², Gully, J², ¹ ADVENT-ENVIRON, Brentwood, TN, USA² County Sanitation Districts of Los Angeles County, Whittier, CA, USA

ABSTRACT- BSTRACT. The Upper Santa Clara River (USCR) supports a variety of aquatic life, including Threatened and Endangered (T&E) species, such as the unarmored three-spine stickleback. The river is effluent dominated and habitat limited. We examined the chloride sensitivity of several aquatic and riparian species, with special emphasis on resident species, T&E species, and important riparian plants (e.g., cottonwoods). The primary objective of this study was to recommend appropriate acute and chronic aquatic chloride thresholds for the USCR incorporating new data since the federal chloride criteria were developed. Several methods were used to develop a weight-of-evidence in support of proposed thresholds. The methods included review of federal criteria, recalculation of the criteria and the acute-to-chronic ratio (ACR), verification of the site-specific applicability of candidate thresholds using the Salinity Toxicity Relationship model, application of ACRs to estimate safe chronic thresholds, chloride toxicity testing of surrogates for key T&E species, habitat assessment, and a review of the salinity tolerance of cottonwoods. Recalculation of chloride aquatic life criteria resulted in a lower acute threshold and higher chronic threshold of 544 mg/L and 278 mg/L, respectively, as compared to respective federal criteria of 860 mg/L and 230 mg/L. Additional threshold derivations indicated that an acute threshold of 605 mg/L chloride was protective of USCR aquatic life, including T&E species. The recalculated chronic threshold of 278 mg/L is well below chronic chloride levels protective of Upper SCR biota, including T&E species and cottonwoods.

Key words: Chlorides, Criteria, Endangered, Species