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MWMC FACILITIES PLAN FIGURE 5.1.3-4 Wet Weather Maximum Week Effluent Concentration Requirements Based on Existing Mass Load Limitations and Projected Flows MWMC Facilities Plan, Eugene-Springfield 50.0 I ~. 190 45.0 · CurrentTSS Effluent Concentration Limit _ . 175 40.0 Current CBOD Effluent Concentration Limit 146.5 --'155~9~.~. _~-~"~*~ 160 26.3 25.0 2~.5 22.5 ~ lO0 15.0 85 62,0 5.0 55 0.0 [ 40 2005 2010 2015 2020 2025 Year C~OD Concentration ~ TSS Concentration ~-~ax Week Wet weather Flow ~-Average Wet Weather Flow' Ammonia The current NPDES permit (issued in 2002) includes a requirement for dry weather nitrification. Current Oregon water quality criteria drove previous reasonable potential findings ea~d the justification for a dry weather average month and maximum day effluent ammonia concentration limit of 12 milligrams per liter (mg/L) and 22 mg/L, respectively. If Oregon were to adopt EPA's 1999 update of water quality criteria, as recommended by the Triennial Review Policy Advisory Committee, there may be a relaxation of the acute and chronic criteria. However, in the absence of adoption of that criterion, and based on the premise that it will be difficult to relax the current effluent ammonia requirements, it is assttmed that the current ammonia effluent limitations will be implemented in future permits. The result is that the biological process at Eugene-Springfield will need to be modified to accommodate more sustainable nitrification, and thus de-nitrification will be required to address the alkalinity deficit currently experienced during nitrification. Excess Thermal Load Under the 1996 Oregon Temperature Stm~dard (Oregon Administrative Rule 340-41-0026), the WPCF was required to prepare m~d implement an approved Temperature Management Plem for the following reasons: 5-8 MWMC 5.0 REV&DOC