WORK PLANS - Laserfiche WebLink

Home Browse Search

analyzed for VOCs using EPA Method 8260B. Refer to Figure 3 for proposed temporary well locations and existing monitoring well locations. 3.2.2 Soil Vapor Sampling To assess data gaps in soil vapor results as noted in DTSCs March 18th email and August 31 st memorandum and recognizing the results of the offsite soil gas sampling along Scarlett Place, Roux proposes to complete a Site-wide soil vapor sampling event so that a comprehensive spatial and temporal soil-vapor dataset can be generated. The following 21 existing soil gas probes are proposed to be sampled: SG-11, SG-14, SG-15, SG-16, SG-17, SG-18A, SG-19A, SG-24, SG-25, SG-26, SG-27, SG-28, SG-29, SG-30, SG-31, SG- 34, SG-35, SG-36, SG-37, SG-40, and SG-41.Additionally, one permanent soil gas probe(SG-44; re-named from SG-42 in original work plan) will be installed and sampled along the western property boundary as shown in Figure 4. Four additional soil gas probes (SG-42, SG-43, SG-45, and SG-46) will be installed adjacent to the residential homes located immediately south and west of the Site (Figure 4). Probe SG-45 will provide step-out data from soil gas well SG-16, located 60 feet to the north of proposed SG-44 and SG-15, located 110 ft east of proposed SG-44. Ali soil vapor samples will be collected at approximately 5 feet bgs and analysed for VOCs by EPA Method TO-15 for VOCs and fixed gases (helium, methane, oxygen, and carbon dioxide) by ASTM Method D-1946. Consistent with the Draft February 2022 Supplemental Guidance:Screening and Evaluating Vapor Intrusion,soil vapor data proximate to the buildings will first be assessed, indoor air and sub-slab sampling will be proposed under separate cover if results of the soil vapor sampling indicate soil vapor intrusion is a potential concern. 3.2.3 Indoor Air Sampling Indoor air quality samples will be collected from the former Quality Cleaners suite and the supermarket building. The dry cleaner indoor air sampling event will consist of two indoor samples, one duplicate, and two outdoor ambient samples. The supermarket indoor air sampling event will consist of three indoor samples, one duplicate, and one outdoor ambient sample. All samples will be analysed for VOCs by EPA Method TO- 15. Roux has assumed that the supermarket will have at least three rooms with sewer connections. If the actual number of rooms with sewer connections is greater than three, then the number of indoor air samples collected from the supermarket building will be increased accordingly. 3.3 Screening Level Comparison In general, soil gas and indoor/ambient air sample results will be compared to the DTSC Human and Ecological Risk Office (HERO) most up to date Human Health Risk Assessment (HHRA) Note Number 3 DTSC-modified Screening Levels (HERO Note 3 Screening Levels), which, as of the date of this document, are June 2020 revised in May 2022. If no HERO Note 3 Screening Level has been promulgated for a given compound, the most up to date EPA Regional Screening Level (RSL) for that compound will be utilized, which as of the date of this document, are May 2022. Should soil gas sample results exceed HERO Note 3 Screening Levels, an additional work plan for a step-out investigation will be submitted to DTSC for review and approval. Groundwater data will be compared to the California EPA Maximum Contaminant Levels (MCLs). Should groundwater sample results exceed MCLs, an additional Work Plan for a step down/step out investigation will be submitted to DTSC for review and approval. 3989.0001S101/R Revised Data Gap Investigation Work Plan I ROUX 17