The San Diego County Water Authority (SDCWA) is planning a tunnel connection between Lake Hodges and Olivenhain Reservoir as part of its Emergency Storage Project (ESP). This tunnel and an associated hydroelectric turbine will allow for operation of the two reservoirs as part of a pumped storage project to 1) transfer water from Lake Hodges to the Second San Diego Aqueduct (Second Aqueduct) via Olivenhain Reservoir or 2) generate income from a pumpback scheme between the two reservoirs that takes advantage of reduced off-peak energy costs. Currently, inflows to Lake Hodges consist solely of runoff. Conversely, Olivenhain Reservoir is filled with higher-quality water from the Second Aqueduct. Due to this difference in water quality between the two reservoirs, the SDCWA is concerned that the planned pumped storage project could adversely impact water quality in Olivenhain Reservoir, the Second Aqueduct, and at several downstream water filtration plants. In order to evaluate the water quality impacts of the planned pumped storage operations on Olivenhain Reservoir, Flow Science developed an ELCOM model of temperature and salinity and several tracers to characterize the extent of mixing of the pumped storage inflow water from Lake Hodges within Olivenhain Reservoir and the percentages of Lake Hodges and Olivenhain Reservoir water throughout each reservoir due to the ESP pumped storage operations and subsequent mixing.