SITE INFORMATION AND CORRESPONDENCE

Home Browse Search

Former Chevron Service Station No. 98632 September 5, 2014 575 West Grant Line Road Page 2 of 4 Tracy, California 95376 human health (criteria [b] or [c] above). The site has been occupied by a used car lot since the 1990s with no permanent structures . The only structure onsite is a portable office trailerwith crawl space beneath that would likely allow any upward migrating vapor to dissipate. Therefore, there do not appear to be any current receptors at the site at risk of potential vapor intrusion to indoor air. If the site is redeveloped , potential vapor intrusion concerns can be addressed or mitigated by the Responsible Parties (RPs) at that time, through measures such as additional excavation or installation of active or passive ventilation equipment as warranted . Additional evaluation would be needed to determine what would be necessary. Such a condition could be included in the case closure documentation ." In response to the third bulleted LTCP criterion above , CRA stated in LTC Evaluation: "The maximum detected concentrations of benzene and ethylbenzene in soil samples collected in the 0 to 5 fbg interval do not exceed the commercial limits shown above. No soil samples collected in the 0 to 5 fbg interval were analyzed for naphthalene or PAHs; however, extensive excavation was performed to 10 to 10. 5 fbg in the former used-oil UST/sump/hoist area (Figure 2) and the soil disposed offsite. Therefore , these constituents are not expected to be present in soil from 0 to 5 fbg ." "With regard to the 5 to 10 fbg interval , for which the only potential exposure pathway of concern for commercial receptors is inhalation of volatile emissions from soil to outdoor air, the detected benzene and ethylbenzene concentrations generally do not exceed the limits above with the exception of two or three samples collected in 1995 (Table 2) . The concentrations do not significantly exceed the limits, and are expected to have decreased in the almost 20 years since the samples were collected due to natural attenuation processes. Although naphthalene was detected in a sample collected at 7.5 fbg beneath the former used-oil UST, as mentioned above this area was excavated to at least 10 fbg. In addition , no naphthalene was detected in a sample collected at 6 fbg from the boring for nearby well MW-1 . Regarding vo atilizafion of enzene an ethylbenzene from soil to outdoor air, as stated in the LTCP technical justification for this pathway, the assumptions under which this exposure pathway would be a concern are very conservative and the actual exposure assumed in the risk calculations would be impossible to achieve. For example , it is assumed that the receptor is located onsite, directly over the impacted soil 24 hour/day for the entire exposure duration (30 years for a commercial worker) . Also, vertical dispersion (mixing with outdoor air) above the height of the breathing zone is not considered . Thus, given this information and the site conditions, this does not appear to be a realistic exposure pathway of concern and it is unlikely it would pose a significant risk to the health of commercial workers at the site. " "With regard to utility worker concerns, of the numerous soil samples collected within 0 to 10 fbg , only the benzene concentrations in three samples (up to 24 mg/kg) collected at 6 or 6. 5 fbg in 1995 exceeded the limit (14 mg/kg) . Again, the concentrations do not significantly exceed the limit and likely have decreased since sample collection . Given the information and the limited extent, the benzene in soil does not appear to be a significant concern for potential future utility workers. However, to provide further assurance a soil management plan could be prepared to provide notification and management procedures for any future subsurface work." The following are EHD responses to CRA's arguments presented in LTC Evaluation :