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1. INTRODUCTION, PURPOSE AND NEED characteristics and groundwater table. It occurs throughout the system, and is attributable to newly developing areas as well as older developments. While some of the I/I can be removed through repair and rehabilitation of pipes, and inspection and enforcement of plumbing code standards, water pollution control facilities must be designed to handle the remaining peak wet weather flows in the sanitary system with adequate treatment prior to discharge. 1.6.2 Regulatory Drivers Regulatory drivers include existing conditions contained in the NPDES wastewater discharge permit, and new regulations or changes in regulatory policy that affect the overall treatment capacity rating, treatment strategy, or effluent requirements. Regulations that were newly included in the 2002 reissuance by DEQ of the WPCF discharge permit include the requirement for a dry season effluent ammonia limitation, a thermal load limit, and implementation of the Temperature Management Plan and WWFMP, which were included as part of the NPDES permit renewal materials. New requirements, expected beginning in 2004 and 2005, include total maximum daily loads (TMDLs) for effluent constituents, such as temperature. Pending changes in federal regulatory policy also include the elimination of SSOs resulting from certain storm events, and changes to current effluent blending practices or new effluent blending policy currently under consideration. Dry Season Effluent Ammonia Limitation The current NPDES permit includes a requirement for dry weather nitrification. The permit requires a dry weather average month and maximum day effluent ammonia concentration limit of 12 milligrams per liter (mg/L) and 22 mg/L, respectively. Wintertime nitrification is not required. The treatment facility must partially or completely nitrify on a peak month basis in the dry season to meet permit. The addition of a nitrification requirement has the overall effect of reducing the design dry weather capacity of the facility because more wastewater treatment volume is required to achieve ammonia removal than is required solely for BOD removal. Additionally, a modification to the biological process is required to provide an environment suitable for nitrification while maintaining capacity. CBOD and TSS Limitations Dry season mass limitations for both carbonaceous biological oxygen demand (CBOD) and TSS as outlined in the NPDES permit are based on the average dry season flow of 49 mgd. Concentration limits as well as percent removal requirements are also specified in the NPDES permit. The mass limit requirements must also be met for the highest 30-day flow period in the dry season (maximum month basis). Even if the constant concentration limits for CBOD and TSS are met, the mass limits imply a lower concentration requirement if the wastewater flows exceed the dry weather design capacity of 49 mgd. Because actual DSMM flows from 1992 through 2003 ranged from 52 percent to 100 percent of the design capacity rating, this indicates that the plant is at or near its dry weather capacity at certain critical dry periods. Additional secondary clarifier capacity and tertiary filtration is anticipated as necessary to meet these more stringent effluent requirements. Similarly, wet season mass limitations for both CBOD and TSS, as outlined in the NPDES permit, are based on the average wet season flow of 75 mgd. Although significantly higher, concentration limits as well as percent removal requirements are also specified in the MWMC_I .O_REV13.DOC 1-7