Agenda - 02-16-2021; 4-b - OWASA Annual Update Presentation

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Information on OWASA's Long-Range Water Supply Plan 12 January 29,2021 Page 6 Is there also uncertainty in our yield estimates? Yes. The following factors contribute to uncertainty in the yield estimates: • Streamflow records—the stream flow records available to estimate the yield of our reservoirs have measurement errors and limited spatial and temporal extent. They may not be representative of long-term historical flows. • Estimates in storage volume—potential errors in storage volume include (1) the accuracy of the original survey data, and(2)the rate of sedimentation into the reservoir • Climate change—climate change will impact flows into our reservoirs and evaporation rates. The majority of climate change models indicate that the southeast will receive approximately the same or more rainfall on an average basis,but we will have more frequent high flow events. Some of those models also indicate there will be more intense droughts. More intense droughts and different types of droughts will impact our estimated yield. Because of the difficulty in estimating uncertainty around climate change and the cost to develop an analysis similar to the one completed for the demand projections, OWASA opted not to perform a similar analysis for yield. However, our consultant did perform a sensitivity analysis around the inputs and noted that changing inflows to the reservoir have the highest impact on our estimated yield. Based on the sensitivity runs performed, OWASA's estimate yield after the expanded Quarry Reservoir is online could vary between 11.5 and 15 mgd(baseline estimated yield is 12.6 mgd). What role does water conservation and water recycling and reuse play in our water needs? Water conservation and recycling water have played a very important role in OWASA's service area resulting in reduced drinking water demands and energy use. As illustrated in Figure 4, we are using the same amount of water that we were using in the early 1990s despite an increase of about 70 percent in customer accounts. Following the droughts of 2001-02 and 2007-08, our customers conserved water and have continued to save water. In addition, UNC partnered with us to develop a reclaimed water system that allows them to use highly treated wastewater to meet non-drinking water needs such as for cooling buildings and irrigation. Our reclaimed water system now meets over 10 percent of the community's water needs. OWASA also developed a system to recycle water within its Jones Ferry Road Water Treatment Plant(WTP), which saves approximately 7 percent of our drinking water.