Item A-MWMC Facilities Plan - Laserfiche WebLink

Home Browse Search

9. ENVIRONMENTAL REPORT 9.5 System Alternative 4 - High-Rate Clarification 9.5.1 Affected Environment As with System Altemative 1 and Alternative 5, the affected environment associated with Altemative 4 includes areas where direct and indirect impacts could occur. Similar to the other alternatives, impacts could occur in the vicinity of the WPCF and along the Willamette River downstream from the WPCF outfall. The larger Eugene-Springfield area could experience indirect effects, such as noise or air quality impacts. The features that would be added to the WPCF under Alternative 4, and the wastewater treatment process trader this alternative, are described below. Potential environmental impacts under this alternative are discussed in sections 9.5.2 through 9.5.10. Water Pollution Control Facility Under the High-Rate Clarification (HRC) alternative (System Alternative 4), as with the Parallel Primary/Secondary Treatment altemative (System Alternative 5), the peak wet weather flow capacity of the WPCF would increase from approximately 160 mgd to 300 mgd. Following preliminary treatment, influent to the plant in excess of 160 mgd (up to 140 mgd) would be diverted around the existing primary clarifiers to a new HRC facility. Primary-treated wastewater from the HRC will be blended with secondary-treated wastewater that has passed through the existing primary and secondary treatment stages, before discharge to the Willamette River. Additionally, as with System Alternative 5, a new tertiary filtration system would be built to treat 30 mgd of plant effluent prior to disinfection. The influent flow-dependent treatment steps for wastewater entering the WPCF are described below for Alternative 4. · 0-160 mgd: Total influent flows to the plant of 0-160 mgd would undergo preliminary screening, primary treatment, secondary treatment (with two new secondary clarifiers; 10 total), and disinfection prior to discharge. · 160-300: With plant influent flows of 160-300 mgd, preliminary-treated wastewater (0- 140 mgd) would bypass the existing primary treatment system and be treated in a new, HRC facility. Implementing System Alternative 4 at the WPCF would involve constructing the following features (Figure 9.5.1-1): · Pretreatment expansion · Clarifier upgrades: primary clarifier baffles, primary clarifier blending structure, secondary clarifier baffles · Two new secondary clarifiers · Bypass pump station high rate clarifier · High rate clarifier (HRC) facility · New high-rate disinfection basin · New effluent blending and outfall structure New bioscrubbers for odor control · New tertiary filtration system MWMC_9.0_REV14.DOC 9-19