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SFPUC June 10, 2020 Page 5 <br /> UV Building <br /> 12 UV Reactors ^' Weir <br /> Trench drain <br /> " <br /> ��— Sump <br /> Baker tanks <br /> �� i <br /> �� -0 100 <br /> offsite <br /> i <br /> Disposal <br /> i Inlet <br /> Grit Pond #1 <br /> Seepage irafioln <br /> Eua�PatransP <br /> outlet <br /> Figure 1.Plan view schematic of the current Tesla Facility's UV Building and UV lamp break containment system <br /> UV Lamp Break Event Description <br /> The Tesla Facility uses ultraviolet(UV) light to disinfect water travelling through the Hetch <br /> Hetchy raw water supply system. Lamps are installed in 12 parallel, above-ground"UV reactor" <br /> pipelines in the UV Building. There are 9 lamps per reactor. <br /> Each medium pressure mercury arc UV lamp used to treat the water contains approximately 2 <br /> grams of Hg0 (Figure 2). For comparison, 2.3 grams of liquid mercury is the amount of mercury <br /> in four oral thermometers, or the volume of three droplets of water. In fact, all of the UV lamp <br /> breaks in the past two years combined have not amounted to the volume of a standard marble. <br />