Agenda 03-07-24; 6-a - Amendments to the Water and Sewer Management, Planning, and Boundary Agreement

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18 Impact of proposed water and sewer boundary expansion in Southern Orange County on OWASA Water Distribution and Wastewater Collection Systems November 9, 2023 Page 2 broke this assumption down based on whether a parcel was developed or not, and the acreage if it was developed. Our assumptions are further described in Table 1 below. Lot type # Dwelling Units # Dwelling Units Low density scenario High density scenario Undeveloped 3 per acre 6 per acre Developed, less than or equal to 2 acres 2 total (1 new) 2 total (1 new) Developed, greater than 2 acres 3 per acre 6 per acre Total number of dwelling units 1170 2202 Table 1: Development Assumptions for Water Demand Projections We did not evaluate the validity of these assumptions on a parcel-by-parcel basis but we did eliminate OWASA property from the analysis as well as another parcel designated as a utility right-of-way in the County's parcel data. This resulted in a total of 1170 new dwelling units under the low density scenario and 2202 new dwelling units under the high density scenario. We assumed that each unit would use an average of 110 gallons of water per day (gpd) which aligns with average multi-family residential water use and median residential water use throughout the OWASA service area. Wastewater flow for a dwelling unit under an average dry weather condition was estimated at 88 gpd (aligning with multi- family residential use) plus 10 percent of the future flow increase to account for groundwater infiltration. The resulting water demands for the low density and high density scenarios were analyzed using our hydraulic models to determine their impact on the existing water distribution system and wastewater collection system capacity.The results are described in the following sections. Water Distribution System Freese and Nichols conducted the water distribution system analysis, which incorporated the additional demands under average day, maximum day and peak hour conditions and determined the resulting impacts on existing system capacity, pressure, fire flow and resilience. Without the additional development, buildout projections of average day demands for the entire service area are 12.99 million gallons per day (MGD). Based on the assumptions listed in the prior section, additional demand from the expanded service area would equate to between 0.13 and 0.24 MGD for the low and high density scenarios, respectively. A desktop analysis of water storage requirements showed that adding the projected service area expansion had minimal impact on overall system storage requirements, with the high density scenario requiring an additional 0.20 MGD of storage within the 640 pressure zone that feeds this area, based on peak hour — average day demands. Available fire flow capacity in the area decreased on average by 7%with the high density demands.