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February 19, 2021 Mr. Olivier Theard Page 2 SLR International Corporation slrconsulting.com significant impact which represents a REC to the Site; however it should be noted that there has been no report or evidence of a release having had occurred. Additionally, there is no indication that Save Mart Supermarkets caused any release at the property. Based on the above described REC, the primary chemicals of potential concern (COPCs) are tetrachloroethylene (PCE), trichloroethene (TCE), and potential daughter products of PCE natural attenuation. In January 2021, SLR performed an Additional ESA to evaluate the potential for vapor intrusion affecting Tenant buildings and if Site soil and/or groundwater were impacted by the dry cleaner operation. Investigative activities included the advancement of nine direct-push soil borings to a maximum of 20 feet below ground surface (ft bgs), the installation of temporary dual-nested soil vapor probes at each boring location, and the installation of two sub slab vapor monitoring points; along with the collection of soil, groundwater, and soil vapor samples at the Site. Sampling results indicated the following: • Low levels of acetone and methylene chloride were detected in several soil samples. No other VOCs, including PCE and TCE, were detected in the soil samples collected. Acetone and methylene chloride are considered common laboratory contaminants. • PCE was detected in three of the five groundwater samples collected. One sample (B-1) exceeded the maximum contaminant limit (MCL) of 5.0 µg/L for PCE and the San Francisco Regional Water Quality Control Board (SFRWQCB) Commercial/Industrial Environmental Screening Level (ESL) of 2.8 µg/L for vapor intrusion from groundwater. • PCE was detected above the SFRWQCB Commercial/Industrial ESL of 67 µg/m3 in both sub slab soil vapor samples, four of the nine 5 ft bgs soil vapor samples, and five of the nine 10 ft bgs soil vapor samples. The highest concentrations were observed in the 10 ft bgs samples at B-8 and B-9 near the alignment of the sanitary sewer line that runs in the alley along the west side of the Site. Other volatile organic compounds (VOCs) detected in soil vapor above the SFRWQCB Commercial/Industrial ESLs included benzene, ethylbenzene, chloroform, and bromodichloromethane. Nineteen other VOCs were detected in the soil vapor samples, and concentrations were generally higher in the 10 ft bgs samples. Based on the results of the January 2021 Additional ESA, SLR proposes to conduct the following scope of work to identify potential source areas for contamination along the sanitary sewer alignment and to determine the extent of impacted soil, soil vapor, and groundwater beneath the Site. The scope of work is presented as a tiered approach for supplemental site characterization. In Tier I, SLR proposes to use a semi- quantitative, field-screening device known as a Membrane Interface and Hydraulic Profiling Tool (MiHPT) probe that can detect VOCs in soil, soil vapor, and groundwater to determine the extent of groundwater and soil vapor impacts. MiHPT technology is capable of sampling VOCs and some SVOCs in the vadose and saturated zones. Its ability to rapidly locate and identify contaminants reduces uncertainty in management decisions, and it may be used to produce reliable estimates of contaminated mass, which is crucial to achieving cost-effective cleanups. (Additional details about MiHPT technology are included in Attachment A of this Work Plan.) SLR also proposes to install and sample additional soil vapor probes and sub slab vapor pins at the Site. Based on the results of Tier I, SLR proposes to conduct indoor and outdoor air sampling as part of Tier II. The tasks and sampling locations defined in Tier II will be adjusted based on the results of Tier I.