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Draft Addendum to Draft UST Data Gap Investigation Work Plan <br /> November 9, 2018 <br /> Page 3 <br /> GEOSYNTEC'S RESPONSE <br /> Geosyntec concurs with the CVRWQCB's recommendations for the collection of additional data <br /> in soil. The current concentrations of TPH-g, TPH-d, and benzene in the soil at UST Site 817B <br /> will be assessed with the collection of one soil sample from a depth of 4 feet bgs from a boring <br /> advanced adjacent to each of the 2008 borings 817-D2, 817-133, and 817 D4. These three soil <br /> samples will be analyzed for TPH-9 by United States Environmental Protection Agency <br /> (USEPA) Method 8260B and benzene,toluene,ethylbenzene, and xylenes by USEPA Method <br /> 8260B. <br /> With respect to the sampling of the three groundwater monitoring wells, 917-3, 917-4, and 917- <br /> 10, these wells were sampled on June 28, 2018 pursuant to the RRI Groundwater Sampling <br /> Work Plan dated June 1, 2018. The groundwater samples were analyzed for volatile organic <br /> compounds (VOCs) and TPH-g, TPH-d, and TPH (C28-C40 range). The concentrations for <br /> benzene, TPH-g, TPH-d, and TPH(C28-C40 range) ranges were: <br /> • Benzene: 0.21 (J) µg/L (Well ID 917-03)to 38 µg/L (Well ID 914-10); <br /> • TPH-g: <50 µg/L (Well ID 917-3)to 3,200 µg/L(Well ID 914-10); <br /> • TPH-d: 120 µg/L (Well ID 917-3) to 220 µg/L (Well ID 914-4); and <br /> • TPH(C28-C40 range): <160 µg/L (Well ID 917-4)to<170 µg/L (Well IDs 914-3 <br /> and 917-10). <br /> Based on the recent sampling of the three wells, 917-3, 917-4, and 917-10, it is Geosyntec's <br /> recommendation that the June 2018 groundwater monitoring results be evaluated in conjunction <br /> with the soil data that will be collected as part of the UST Data Gap investigation. Therefore, we <br /> recommend that additional groundwater sampling not be conducted from wells 917-3, 917-4, and <br /> 917-10. <br /> CVRWQCB COMMENT 2: UST SITE 916B <br /> Issues: In 2008, soil sample C-5 at 5-8 feet bgs had a TPH-d detection of 790,000 mg/kg. A <br /> concentration this elevated may indicate the presence of free product in groundwater. The <br /> groundwater-specific criteria of the LTCP requires there to be no free product. <br /> Recommended Actions: CVRWQCB staff recommend the Port also collect a grab groundwater <br /> sample at the 2008 C-5 sample location to determine if concentrations have attenuated and <br /> evaluate the existence of free product. <br /> engineers I scientists I innovators <br />