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2. STUDY AREA CHARACTERISTICS discharge to the McKenzie and Willamette rivers. Other activities upstream of the study area may result in water quality changes. These activities and possible altered parameters include forestry (sediment, herbicides, temperature), agriculture (sediment, herbicides, nutrients, pesticides, bacteria, temperature), rural residences (sediment, bacteria, nutrients, temperature), and old mines (heavy metals). Water Temperature In Oregon the water temperature standard in a basin for which salmon and steeLhead spawning is a designated beneficial use is 55.4° F from October 15 through May 15 (OAR 340-041-0028(4)(a)). The Oregon water temperature standard in a basin for which salmonid fish rearing and migration is a designated beneficial use is 55.4° F from October 15 through May 15 (OAR 340-041-0028(4)(c)). Although the natural temperature regime of many water bodies will exceed 64° F at various times of the year, the aim of the standard is to protect beneficial uses most sensitive to water temperature--in this instance, fish and aquatic life. The mainstem Willamette River exceeds the numeric criteria and, therefore, the river has been identified as water quality-limited for temperature. In order to determine the magnitude of the temperature change on the Willamette River, the WPCF wastewater staff collected in-stream temperature data in 2003 at locations upstream and downstream of the diffuser outfall, and of WPCF effluent6. The sections below discuss results of the in-stream temperature monitoring program. Management staff at the WPCF believe the temperature effects of the effluent from the facility are insignificant because: · Temperature-monitoring results for the period of April to November 2003 show that river temperatures downstream of the outfall are less than those measured upstream. These results are consistent with those reported to the DEQ for river temperature monitoring done in 2002. · Under conditions of 7Q10 river flow? and maximum measured effluent temperature, the calculated temperature increase of the Willamette River downstream of the WPCF outfall at the edge of the mixing zone is 0.3 F°, less than the 0.5 F° human use allowance specified under OAR 340-41-0028(12)(b)(A). · Daily regulatory mixing zone (RMZ) calculated temperatures using upstream temperature and plant effluent data, and a mixing ratio of Willamette River flow to effluent flow of 12:1, indicate no exceedance of the 0.5 F° human use allowance over the monitoring period. Similarly, no exceedance was observed for maximum 7-day average temperatures. 6 In addition, probes were deployed throughout the plant to evaluate the relative temperature change over each treatment stage. Monitoring locations included the influent waste stream, preliminary treatment, primary clarification, activated sludge return, aeration, and secondary clarification. These data were used to assess waste stream thermal loads due to treatment processes, and to aid E-S wastewater management staff in assessing options for process temperature management. 7 The 7010 refers to the lowest consecutive 7 day streamflow that is likely to occur in a ten year pedod. It is used by many states and the federal government in setting discharge limits in NPDES water quality permits. A permit will only be granted if the proposed amount of pollutant that will be discharged into a river will not significantly impair the designated uses, such as drinking or swimming, when the streamflow falls to the 7010 level. MWMC_ZO_REV23.DOC 2-19