SITE INFORMATION AND CORRESPONDENCE 2011-2015

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Messrs Larson and Trommer January 10, 2014 104 W. Beverly Place, Tracy, CA Page 3 of 4 The EHD has shown above a concern that there may not be a 5-foot bioattenuation zone with TPH uniformly less than 100mg/kg and that there is likely to be at least 3 feet of impacted soil of unknown width that underlies the entire north/south length of the residence from the source area to MW-8. The consultant presented a Tier II health risk evaluation for indoor air concentrations showing a cancer risk of less than 10-7 and a hazard index of less than 1, which the Fund accepted as demonstrating an acceptable health risk level for site closure, but the cancer risk and health hazard quotient for shallow soil gas and air in the crawl space was not noted or discussed. Soil gas samples collected near the residence contained as much as 5,150,000 micrograms per cubic meter (pg/m3) TPHg and 2,700 lag/m3 benzene in September 2011. Resampling three soil gas probes in March 2012 detected TPHg at concentration as high as 400,000 lag/m3 and benzene as high as 240 lag/m3. The consultant utilized a Johnson and Ettinger model to calculate the cancer risk and hazard index for the average benzene concentration detected during the March 2012 event, and determined a cancer risk of 7.4E-7 and a hazard index of 0.037. The EHD notes that this calculation avoids the much higher concentrations detected in the September 2011 event and the individual highs of the March 2012 event. The final Guidance for the Evaluation and Mitigation of Subsurface Vapor Intrusion to Indoor Air (Vapor Intrusion Guidance) issued by the Department of Toxic Substances Control (DTSC), dated October 2011, in discussing use of the Johnson & Ettinger Model (1991) states on page 23 that the "Maximum contaminant concentrations should be used for modeling." The EHD considers the health risk model provided for soil gas contaminants to be invalid. The crawl space under the residence has also been sampled and analyzed during the sampling events conducted in May 2011, September 2011, March 2012 and August 2013. The consultant report of November 2011 presented data from the first two sampling events with a human health risk assessment for the 930 lag/m3 benzene detected in September 2011, which yielded a cancer risk of 0.00068 (6.8E-4) and a hazard index of 23. This information and additional sampling led to conducting indoor air sampling and installing and operating a mitigation system to remove the hydrocarbon vapor frorn the crawl space. In their report of 16 September 2013, the consultant recounted calculating a cancer risk of 4.8E-7 and Hazard index of 0.016 for the 0.65 lag/m3 benzene in the indoor air samples, but did not present a hazard index for the TPHg in indoor air that exceeded the ESL for indoor air. While the data can be used to show a cancer risk at an acceptable level within the residence, it has also been shown that the cancer risk and hazard index for benzene in the air in the crawl space greatly exceeds acceptable risk and hazard levels. The soil gas near the residence probably also exceeds acceptable risk and hazard levels, but was not calculated in accordance with authoritative guidance. Please note that the residence is of older construction (built in 1951) on a raised foundation with only the flooring and subflooring acting as the barrier between the crawl space and the living space. Natural deterioration or modifications made by future owners may compromise the barrier as it currently exists. The crawl space, which may fit the definition of a confined space, may be accessed by unwary owners, repairmen or children in the future. Due to the extraordinary known hydrocarbon vapor concentrations on this site, the EHD is of the opinion that this is a case where the site may narrowly fit the LTCP criteria as a low-risk site, but should not be closed. Therefore, the EHD cannot concur with the Fund recornmend ation for case closure. The EHD is of the opinion that additional corrective action is required to further 2014 SRS Response CUF Claim No 8502.doc