Publication Summary

An upper Yakima River basin suspended sediment and organochlorine pesticide total maximum daily load (TMDL) evaluation was conducted by the Washington State Department of Ecology as required by the federal Clean Water Act. This evaluation was an extension of the 1997 lower Yakima basin TMDL and addressed several organochlorine pesticide 303(d) listings of water column and fish tissue in the upper basin. Turbidity and suspended sediment were included as transport mechanisms for the pesticides and as pollutants themselves.

An upper Yakima River basin suspended sediment and organochlorine pesticide total maximum daily load (TMDL) evaluation was conducted by the Washington State Department of Ecology as required by the federal Clean Water Act. This evaluation was an extension of the 1997 lower Yakima basin TMDL and addressed several organochlorine pesticide 303(d) listings of water column and fish tissue in the upper basin. Turbidity and suspended sediment were included as transport mechanisms for the pesticides and as pollutants themselves.

Historical data and data collected during the 1999 irrigation season (April to October) were used for this TMDL. The data evaluation for the upper Yakima River basin indicated that:

1. In many tributaries and the mainstem, turbidity and suspended sediment (as total suspended solids) were too high for too long and could be harmful to salmon.

2. Dieldrin and total DDT (DDT+DDE+DDD) had decreased in mainstem fish, but some fish samples still exceeded total DDT and dieldrin criteria for human health. Concentrations of the individual compounds, 4,4′-DDT, 4,4′-DDE, and 4,4′-DDD, did not exceed fish tissue criteria.

3. Water column 4,4′-DDE, total DDT, and dieldrin exceeded chronic aquatic toxicity and human health criteria at two sites in the Cherry Creek sub-basin. Unfortunately, organochlorine pesticide concentrations were not well correlated with suspended sediment, turbidity, or organic carbon.

4. Upper basin water quality is improving (and is less severe than was reported for the lower basin in 1997), but nonpoint sources will require TMDL targets to protect aquatic communities and human health.

Turbidity targets were calculated for seven sub-basins to decrease suspended sediment loading. Meeting these targets will move the mainstem towards meeting a turbidity target of not more than a 5 turbidity unit increase from Nelson (river mile 191) to Harrison Bridge (river mile 121.7) by 2011. DDT and dieldrin targets were calculated so Cherry Creek will meet aquatic toxicity and human health criteria. A dieldrin target for the Cle Elum area, and DDT and dieldrin targets for the Yakima River at Umtanum, were calculated based on fish tissue concentrations. Reductions in the availability of organochlorine pesticides to fish are needed to meet human health criteria, especially to meet the dieldrin target at Umtanum.

Link to EIM data for User Study ID UPYAKIMA