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SFPUC June 10, 2020 Page 3 tend to methylate HgII are aqueous, organic-rich, and anoxic. McHg is highly bioaccumulative and toxic to humans and wildlife. Most mercury in environmental water samples will be in the elemental form, and is analyzed as total mercury (total Hg). In all of these forms, mercury does not greatly dissolve in water or move through soil to contaminate groundwater. Useful general references on mercury in the environment are USDHHS (1999), USEPA (1997), and Wiener et al. (2002). Regulatory Thresholds Thresholds relevant to water and soil to consider for this situation are summarized in Table 1. The emergency, small-volume, and temporary nature of these discharges must be recognized. The risk to human health and the environment from the mercury in UV lamps used in the treatment of drinking water is exceedingly small, and can be addressed through engineering and administrative methods used to prevent UV lamp breaks and exposure to mercury if breaks do occur (USEPA, 2006). In particular, the water thresholds are merely reference points for on-site monitoring—none specifically apply to this situation. Table 1.Regulatory thresholds of interest for addressing mercury released from UV lamp breaks at the Tesla Facility. Applic- Source Value ability Water California Code of Regulations Title 22, Division 4.5, Chapter 11,Article 3, Section 200 [1] 66261.24 for Soluble Threshold Limit Concentration (STLC)test ug/L [https://dtsc.ca.gov/title22/1 Safe Drinking Water Act maximum contaminant level (MCL)for mercury in drinking 2 ug/L [2] water [www.epa.gov/ground-water-and-drinking-water/national-primary-drinking- water-regulations#Inorganic] DTSC's Screening Levels for Tap Water [dtsc.ca.gov/wp- 0.063 [3] content/uploads/sites/31/2019/04/HHRA-Note-3-2019-04.pdf] µg/L California Toxics Rule criteria for surface waters, protective of chronic human 0.050 [4] health consumption of water and organisms [www.epa.gov/wqs-tech/water- ug/L quality-standards-establishment-numeric-criteria-priority-toxic-pollutants-state] San Francisco Bay Regional Water Board's Environmental Screening Levels (Tier 1 0.025 [5] ESL) at sites with contaminated groundwater µg/L [www.waterboards.ca.gov/sanfranciscobay/water issues/programs/esl.htmll Soil NOAA Probably Effects Concentration sediment quality screening level for total 1.060 [6] mercury [response.restoration.noaa.gov/sites/default/files/SQuiRTs.pdf] mg/kg California Code of Regulations Title 22, Division 4.5, Chapter 11,Article 3, Section 20 [1] 66261.24 Total Threshold Limit Concentration (TTLC) mg/kg [www.dtsc.ca.gov/LawsRegsPol icies/Title22/upload/OEARA-REG-Title22-Ch11-Art3-2.pdf1