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SFPUC June 10, 2020 Page 2 assessing and cleaning up abandoned mine sites. McCord Environmental is subcontracted for this work to Baseline Environmental Consulting. Scope of Work The overall project objectives are to ensure regulatory compliance and to protect the environment. Specific project goals are to: (1) analyze UV lamp break conditions, (2) compare mercury levels in discharge water to various regulatory thresholds, and(3) evaluate and suggest improvements to the Interception Plan previously developed and implemented by SFPUC (discussed in more detail below). The work performed to produce this memorandum included the following key tasks. • Compile and review available reports and datasets. • Visit the facility and interview key staff to understand site-specific conditions. • Estimate relevant concentrations and loads of mercury emanating from a UV lamp break. • Evaluate mercury conditions relative to regulatory thresholds. • Evaluate current practices to contain mercury-contaminated waters. • Determine if mitigation is necessary based on mercury levels in the discharge water. • Recommend changes/improvements for managing mercury from UV lamp breaks. Background Information This section provides relevant information about mercury chemistry and regulatory thresholds considered in this memorandum's assessment and recommendations. Basic Mercury Forms and Characteristics Important characteristics determining mercury fate in the environment under the Tesla Facility's conditions depend on its form. The three general forms of mercury(Hg) are described as follows. • Elemental mercury(Hg0) remains in liquid form at normal ambient temperatures, which is unusual for metalloids. It is extremely dense (more than 13.5 times denser than water), yet it volatilizes even at room temperature. It has an octanol—water partition coefficient of log Kota-6, meaning at equilibrium Hg is one million-fold more concentrated on lipids (representing organic material) than dissolved in water(i.e., Hg0 tends to adhere to particles much more than it tends to dissolve in water). This is the form used in UV lamps, as well as in thermometers, dental amalgam fillings, batteries, and other electrical switches. It is released into the atmosphere globally from volatilization, fossil fuel burning, forest fires, and volcanoes. • Inorganic or ionic mercury(HgII) compounds occur when Hg0 oxidizes to HgII. Being highly reactive, it combines with elements such as chlorine, sulfur, or oxygen. It has been used as a fungicide, skin-lightening cream, and antibacterial. Hg0 can be oxidized by sunlight, thus emissions of Hg0 tend to be deposited wet(in rain) and dry(in dust) as HgII complexes. • Organic or methylmercury(CH3Hg+, or McHa) is formed primarily as a byproduct of bacterial respiration, reducing iron and sulfur compounds. Environmental conditions that