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4. WASTEWATER CHARACTERISTICS The response of the sewer system to immediate and antecedent rainfall during the wet weather events of the 1997-1998 monitoring period was analyzed as part of the WWFMP. As a first gtep in analyzing the monitoring data, the diurnal base flow hydrograph for selected storms was subtracted to obtain the RDII hydrograph. For the WWFMP study, flow inputs were developed from regression equations, and were modified to reflect the experience of MWMC operations personnel and the observations of return ratio at monitor locations. The regression equations provided a method to generate the RDII component of the flow input hydrograph for each monitoring location for any storm of interest. Although the method is a good one, it can be deficient if the equation is applied to storms that differ significantly in character (intensity, pattern, and volume) from the storm for which the equation was created. As part of the task of updating the MWMC MOUSE hydraulic model for 2003-2004, the model was recalibrated using the latest flow monitor data from six permanent MGD Technologies monitor installations (herein referred to as MGD monitors) within the collection system and one at the WPCF. Changes to the collection system pipes and pump stations were also incorporated into the updated model. The methodologies used to generate model flow inputs were different than those used for the WWFMP, although the relative distribution of flows within the collection system and the peak flow at the WPCF were consistent with the WWFMP. The MOUSE dry weather flow module was used to create the diurnal sanitary flow based on population, and the MOUSE RDII module was used to generate system RDII flows from rainfall. This change in methodology allowed all of the flow inputs to be generated within the hydraulic model rather than as separate computations external to the MOUSE model. More detailed information on the subject of the wastewater collection system hydraulic modeling analysis is given in the March 2004 "MWMC Wastewater Facility Plan--Wet Weather Peak Flow Analysis" technical memorandum (see appendix). Assumptions for system rehabilitation identified under the WWFMP were incorporated in the future conditions model rims (2025 and buildout). The WWFMP used a peak rainfall dependent infiltration and inflow (RDII) rate of 2,000 gallons per additional future developed acre per day for the 5-year storm event. The updated MOUSE model also uses the 2,000 gallons per acre per day peak RDII rate for all future developed areas. This value was derived as part of the WWFMP and was based on measured data in areas considered to represent future system conditions. System rehabilitation recommendations included in the WWFMP for existing and future conditions were assumed to have been implemented for the 2025 peak flow estimates. These rehabilitation projects were included in the plan as a result of the cost-effectiveness analysis that identified projects to reduce peak flows in the collection system. 4.2 Wastewater Loading Characteristics BOD and TSS concentrations at the WPCF are measured using 24-hour composite samples collected and analyzed by plant personnel. IVIWMC_4.0_REV8. DOC 4-7