Publication Summary

The is a DRAFT report for review only. Do not cite or quote.

DRAFT ABSTRACT

The Yakima River, along with several of its tributaries and irrigation returns, is on the Clean Water Act 303(d) list for not meeting water quality standards for a range of chemical contaminants. The chemicals include seven chlorinated pesticides or breakdown products (DDT, DDE, DDD, dieldrin, endosulfan, chlordane, and alpha-BHC), the organophosphorus insecticide chlorpyrifos, polychlorinated biphenyls (PCBs), and dioxin (2,3,7,8-TCDD). All of these chemicals have exceeded Washington State water quality criteria for protection of human health for fish consumption or criteria for protection of aquatic life. Except for endosulfan and chlorpyrifos, these legacy pollutants are no longer produced or used in the United States.

The Clean Water Act requires a Total Maximum Daily Load (TMDL) be developed for every waterbody and pollutant on the 303(d) list. A TMDL is a written, quantitative assessment of water quality problems and pollutant sources that cause the problems. The TMDL determines the amount (load) of a pollutant that can be discharged to the waterbody and allocates the load among sources.

A water quality study was conducted in the Yakima River basin during 2007-08 to aid in developing a TMDL for the 303(d) listed pesticides and PCBs. Dioxin was excluded from the study due to budget constraints and because human health criteria were very close to being met.

The water quality study analyzed 303(d) pesticides, PCBs, suspended sediment, and turbidity in surface waters, municipal wastewater treatment plant effluents, fruit packer & vegetable processor effluents, and urban stormwater runoff. This report describes how the study was conducted and analyzes the data in terms of compliance with water quality criteria, temporal and seasonal patterns, trends, pollutant loading, and the relative importance of sources.

Numeric water quality targets are described for bringing the Yakima River into compliance with water quality standards for DDT compounds, dieldrin, chlorpyrifos, PCBs, toxaphene (an unlisted legacy pesticide), and turbidity. The river′s loading capacity is calculated for these pollutants. Endosulfan, chlordane, and alpha-BHC are now meeting standards and should be removed from the 303(d) list during the next listing cycle. The report concludes with additional recommendations for source tracing and monitoring.