25B - METRO WATER DISTRICT FUTURE SUPPLY

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Exhibit A- Scope of Work Restoration of Local Recharge Sources from Invasive Dreissenid Mussels 1.0 Study Objective The purpose of the Study is to evaluate a potential treatment method, other than desiccation, that can be used to eradicate existing quagga mussel infestations and prevent the potential spread of quagga mussels. If such a method is identified, it could lead to restoring the use of facilities for recharge of local water sources, such as stormwater. 2.0 Background Information In January 2007, quagga mussels (Dreissena bugensis) were discovered at a marina in the Nevada portion of Lake Mead, and two other lakes on the Colorado River, Lake Mohave and Lake Havasu. Soon thereafter, the mussels spread through the Metropolitan Water District of Southern California's (MWD's) Colorado River Aqueduct (CRA) as far south as Lake Skinner, near Temecula. As of December 2017, quagga mussels have been detected in 43 locations in California. So far, State Water Project (SWP) aqueducts and reservoirs have not been impacted, although there were detections of quagga mussels in Pyramid Lake and other areas of the SWP in December 2016. To minimize the spread of quagga mussels, MWD chlorinates CRA water, starting at Copper Basin reservoir, close to the eastern end of the CRA and at other locations, such as Lake Matthews. Despite this effort, quagga mussels have infested reservoirs used for capture of local runoff as well as rivers, streams and canals used to convey both local supplies and imported supplies to groundwater replenishment facilities. This is important because multiple entities that recharge local water sources, such as storm water, use many of the same facilities to recharge imported water. As a result, the presence of quagga mussels presents a barrier to the efficient use of these dual use facilities and has affected the ability to maximize the capture and recharge of local supplies, such as storm water. As an example, Irvine Lake, which is owned and operated by the Irvine Ranch Water District (IRWD), receives both imported CRA water and local storm flow. Downstream of Irvine Lake are OCWD's Santiago Basins which are open gravel pits that were converted to groundwater replenishment facilities in the early 1990s. In the 1990s, water from Irvine Lake was discharged to Santiago Basins via Santiago Creek for groundwater replenishment. These deliveries are no longer possible due to the presence of the quagga mussel in Irvine Lake and the potential for infesting Santiago Creek and Santiago Basins. On the San Gabriel River, multiple entities, including the Main San Gabriel Basin Watermaster and the Water Replenishment District of Southern California (WRD) divert storm water from the San Gabriel River into spreading grounds adjacent to the river. In October 2017, MWD found City of Santa Ana 24 Agreement No. 189280 25B-27