SR0085478 (2) - Laserfiche WebLink

Home Browse Search

Draft Addendum to Draft UST Data Gap Investigation Work Plan November 9, 2018 Page 2 historical data highlights additional issues the Port will need to consider in their evaluation for "no further action" eligibility under the LTCP that the Draft Work Plan may not fulfill. This includes: • Petroleum vapor intrusion to indoor air: It is necessary to comply with the LTCP media-specific criteria for petroleum vapor intrusion to indoor air. As specified in the LTCP, the media-specific criteria for petroleum vapor intrusion to indoor air can be accomplished by either: (1) collecting TPH data, in addition to the benzene data,to demonstrate that TPH concentrations in the upper 5 feet of soil have attenuated to less than 100 milligrams per kilogram(mg/kg); or(2) collecting soil vapor data to demonstrate compliance with the threshold values provided in Appendix 4a or 4b of the LTCP; or(3) conduct a site-specific risk assessment for the vapor intrusion pathway; or(4) control exposures through the use of mitigation measures. ■ Groundwater benzene data: 2008 groundwater samples at UST Site 817B yielded benzene concentrations of 2,500 micrograms per liter(µg/L) at monitoring wells 917-3 and 917-4. The benzene concentration at monitoring well 917-10 was also elevated at 600 µg/L. The LTCP media-specific criteria for vapor intrusion to indoor air requires benzene concentrations in groundwater to be less than 1,000 µg/L and have a sufficient bioattenuation zone in soil. ■ TPH in soil: The 2008 soil samples also had exceedances of 100 mg/kg at 4 feet below ground surface (bgs) at samples 817-D2, 817-D3, and 817-D4. However, soil samples adjacent to these locations are not proposed in the Draft Work Plan. A sufficient bioattenuation zone according to the LTCP requires the upper 5 feet of soil to be less than 100 mg/kg to meet the media-specific criteria for vapor intrusion to indoor air. • 2008 Soil Sample 817-D4 benzene: The Draft Work Plan does not propose sampling adjacent to the 817-D4 location from 2008. However,the benzene concentration from this sample (8.7 mg/kg) also exceeded the media-specific criteria for direct contact and outdoor air exposure for commercial/industrial settings (8.2 mg/kg) in the LTCP. RECOMMENDED ACTIONS 1. CVRWQCB staff recommend the Port also collect soil samples for TPH and benzene analyses adjacent to the 2008 soil samples at 817-D2, 817-D3, and 817-D4. 2. CVRWQCB staff recommend the Port also collect groundwater samples from monitoring wells 917-3, 917-4, and 917-10 simultaneously with soil sampling to evaluate concentrations of TPH and benzene in groundwater. Groundwater samples should be collected following protocols appropriate for volatile organic carbon analysis. engineers I scientists I innovators