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Mr. Brendan Kenny October 7, 2020 Page 7 "The measured mercury concentration is about 0.0007 mg/L in the trench, which is more than two orders of magnitude below the federal and state hazardous waste thresholds listed in Table 1. Thus, the discharge water is not a toxic hazardous waste [and] can be classified as a non-hazardous waste..." Table 1. Summary of toxic substance regulatory threshold for Toxicity Characteristic. Toxic Test method Regulatory Source substance Threshold Toxicity Characteristic Article 3 of Chapter 11 Leaching Procedure 0.2 mg/L of 22 CCR, section (TCLP) 66261.24 (a)(1) Waste Extraction Test (WET), Soluble Article 3 of Chapter 11 Mercury Threshold Limit 0.2 mg/L of 22 CCR, section Concentration (STLC) 66261.24 (a)(2)(A) Waste Extraction Test (WET), Total Threshold Article 3 of Chapter 11 Limit Concentration 20 mg/kg of 22 CCR, section 66261.24 (a)(2)(A) (TTLC)wet-weight Based on Abelli-Amen's conclusion that the water collected in the Baker tanks is not a hazardous waste, hazardous waste management protocols, including limiting on-site storage to less than 90 days and transport under uniform hazardous waste manifest, do not apply to the water. Baseline's technical memorandum, which elaborates on this conclusion, is attached for your review. Conclusions and Drainage Plan Update Based on the information summarized in this letter and in the attached memoranda, SFPUC has concluded that continuing the collection of the lamp break releases in Baker tanks and transporting it for disposal under uniform hazardous waste manifest is not necessary or appropriate. Instead, the best practice for handling water released from any future UV lamp break is to re- initiate discharge to the grit pond. This protocol will have no significant impact on water quality and is consistent with the Facility's design. The grit pond was designed to capture and treat discharges from the Facility. This design was evaluated under the California Environmental Quality Act in a 2008 environmental impact report (EIR) prepared for the facility,' prior to the construction of the Facility. The certified EIR found that the potential impacts related to release of mercury from UV lamp breaks were less than significant. 7 San Francisco Public Utilities Commission. 2008. San Joaquin Regional Water Quality Improvement Project Final Environmental Impact Report, San Francisco Planning Department Case No.2007.0427E, State Clearinghouse No. 2007052109,EIR Certification Date: December 18,2008.