CORRESPONDENCE - Laserfiche WebLink

Home Browse Search

Additional Site Assessment Report and Human Health Risk Screening Evaluation www.arcadis.com 11 2021). If a 0.005 attenuation factor was applied, the corresponding TPH-g ESL would be 120,000 µg/m3. The detected TPH-g concentration at the 5-foot depth in B-13 was 140,000 µg/m3 in 2020, only slightly in excess of this revised ESL. TPH-g naturally attenuates and the TPH-g concentration in B-13 will reduce with time. 7 Summary and Recommendations The results of the site assessment conducted in December 2019 through February 2022 are summarized below. 7.1 Site Soils • In all affected soil samples, the highest TPH detections were in the TPH-d range, with lower concentrations in the TPH-g range. • There was little to no evidence of BTEX compounds in the soil samples. Low concentrations of toluene and total xylenes were reported in one primary sample. • Low concentrations of naphthalene were detected in only one primary sample. • Based on the boring locations, residents were identified as the most likely receptor that could be exposed to affected soils. All TPH, BTEX, and naphthalene detections in soil were less than applicable LTCP (SWRCB 2012) residential screening levels and SFBRWQCB residential soil ESLs (SFBRWQCB 2019), with exception of TPH-d. However, the TPH-d results with exceedances are in deeper soils (greater than 4 feet below grade) and are likely not available for direct contact. Therefore, contact with soil is not associated with unacceptable health risk. 7.2 Site Soil Vapor • TPH-g was analyzed for two of the samples and exceeded the SFBRWQCB residential ESL (SFBRWQCB 2019). If an attenuation factor of 0.005 was applied as recently recommended by the DTSC, the TPH-g concentration in the 5-foot probe at B-13 only slightly exceeds the revised ESL of 120,000 µg/m3. The TPH-g concentration at B-13 was measured in 2020 and is expected to naturally attenuate through time. • Low concentrations of 15 VOCs were observed. The VOC concentrations did not exceed applicable SFBRWQCB residential ESLs (SFBRWQCB 2019). • The nondetection of helium in the soil vapor samples ensured no leaks were present during sampling. 7.3 Conclusions and Recommendations • The TPH detections were predominantly in the TPH-d range. All hydrocarbon detections in soil were less than applicable LTCP (SWRCB 2012) residential screening levels and SFBRWQCB residential ESLs (SFBRWQCB 2019) with the exception of a few deeper locations. These TPH-d samples are likely too deep for direct residential contact. • The TPH-g concentration in soil vapor from 5 feet bgs slightly exceeded the revised ESL for residential exposure; however, the concentrations will naturally attenuate through time.