SITE INFORMATION AND CORRESPONDENCE 2011-2015

Home Browse Search

Nwl ..i Weldon Church Property Page 2 104 West Beverly Place November 22, 2011 Tracy, California 95376 Although the reporting limits for TPH-g and benzene were above the ESLs, concentrations of contaminants of concern were non-detect for the field blank sample. Concentrations for TPH-g (250 Ng/m3) and benzene (0.47 pg/m3) in Ambient-East air sample were above the ESLs; and although the reporting limit for TPH-g was above the ESL, only the concentration of benzene (0.44 Ng/m3) was reported above the ESL in the Ambient-West air sample. Based on these results, AGE proposes collecting "monthly air samples in the crawl space at 104 West Beverly Place to evaluate the trend of petroleum hydrocarbon concentrations detected in air samples, refine the risk estimates, and to characterize temporal and seasonal variations;" and preparing "a work plan to reduce subsurface vapor intrusion into the crawl space of the residence at 104 West Beverly Place, Tracy, CA until the contaminant source is remediated or is no longer a significant risk to human health." The EHD reviewed various sources of guidance regarding the inhalation risks associated with the BTEX exposure created by vapor intrusion into the crawl space. The California Office of Environmental Health Hazard Assessment lists the Reference Exposure Levels (RELs) for benzene at 1,300 Ng/m3 for acute exposure (maximum for 1 hour) and 60 pg/m3 for chronic exposure (long duration up to lifetime); the detected benzene concentration exceeds the chronic exposure REL. Exposure at concentrations exceeding these RELs can lead to carcinogenic risk to the hematopoietic system and also have toxic effects on the neurological, reproductive, and developmental systems. The chronic exposure RELs are also exceeded for toluene (300 pg/m3) and xylenes (700 Ng/m3), which can lead to nervous and respiratory systems risks. As the chronic exposure REL is greatly exceeded for benzene, toluene and xylenes in crawl space samples, the EHD considers it critical to expeditiously protect the resident of the house by assessing the actual indoor concentrations of the chemicals of concern, mitigating the high contaminant concentrations in the crawl space, and remediating impacted soil and/or groundwater; therefore the EHD does not approve the collection of monthly air samples in the crawl space to refine the risk further — we already know excessive concentrations of several chemicals of concern intrude into the crawl space. Instead, the EHD directs: 1. Collection of an air sample within the residence at this site. Following the Technical and Regulatory Guidance — Vapor Intrusion Pathway: A Practical Guideline (Guidance), dated January 2007, prepared by the Interstate Technology & Regulatory Council, or other authoritative guidance document, submit a work plan for the collection of an indoor air sample along with a crawl space sample and ambient air sample/s. The EHD recommends the inclusion of an indoor air sampling questionnaire and building inventory form similar to that found in Appendix G of the Guidance. 2. Submission of a work plan for a vapor intrusion mitigation system, designed by a qualified professional, such as a civil engineer, with mitigation experience to abate the soil gas intrusion within the crawl space. Submit the work plan to the EHD by 23 December 2011. 3. Evaluation of the vapor intrusion risk/hazard posed to adjacent residences.