SITE INFORMATION AND CORRESPONDENCE_PRE 2019

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Mr. Thomas Black Page 3 of 4 Tracy Office Plaza March 15, 2016 324 E. Eleventh St., Tracy CA feet bsg, which may represent the depth to the water table at and near the time of the unauthorized release. • Assuming that the B-7 lack of odor observation is representative of the deeper conditions for B-1, the contaminant distribution in soil is consistent with a limited release in which impacted soil extends to a depth of at least 15 feet below surface grade (bsg); the B-7 data suggests the depth of impact soil is limited to less than 24 feet bsg, consistent with the shallow depth to groundwater in the area which would limit the downward migration of separate phase liquid hydrocarbons. The EHD cannot concur with the recommendation of Pangea to consider closing the case on the subject site under the LTCP for the following reasons: • The actual usage of each of the six former USTs has not been documented; it is possible that one or more may have been utilized for waste oil. If one or more tanks were utilized for waste oil, or usage is unknown, the analytical protocols must include analysis for volatile organic compounds (VOCs), semi-volatile organic compounds (SVOCs); oil and grease, polychlorinated biphenyls (PCBs), and Title 22 metals. If pentachlorophenol (PCP) is detected, the sample should then be analyzed for dioxins and furans. • As the B-1 and B-6 soil data can be interpreted as having a shallow source and the groundwater data from borings B-1 and B-6 can be interpreted as potentially indicating two separate sources if groundwater flow is predominately north-northwest, additional data from the east margin of the site should be obtained to test the one-source model Pangea implied in their interpretation of the site. To address these concerns, the EHD directs the following additional assessment actions: Obtain an additional soil sample from approximately 10 feet bsg in the area of boring B-1 and analyze the sample to complete the unknown tank or waste oil tank analytical protocols, including: • Volatile organic compounds (VOCs) by EPA Method 826013; • Heavy metals (often referred to as the CAM 17 metals or the Title 22 metals) by EPA Method 6010B for most of the metals and by EPA Method 7062 for antimony and arsenic, EPA Method 7131 for cadmium, EPA Method 7421 for lead, EPA Method 7471A for mercury, EPA Method 7521 for nickel, EPA Method 7742 for selenium, and EPA Method 7841 for thallium (more current EPA methods may be utilized for each metal if appropriate); • Semi-volatile organic compounds (SVOCs) by EPA method 8270C; • Oil and grease by EPA method 1664A, and • Polychlorinated biphenyls (PCBs) by EPA method 8082. In the unlikely event that pentachlorophenol (PCP) is detected in the analysis for PCBs, analyze the sample for dioxins and furans by EPA method 8290 and for pesticides by EPA method 8081A. To asses for a possible second source area, obtain a soil sample 10 feet bsg from the flower bed on the east side of the building, approximately due east of B-1, and analyze the sample for