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Geosptec consultants 3. SCOPE OF WORK 3.1 Rationale and Approach Groundwater monitoring wells located between the Site and the domestic wells to the north have been installed at multiple depths ranging between 20 and 100 ft bgs. Concentrations of PCE reported in the domestic wells are generally over a magnitude higher than in Site monitoring wells,indicating that the Site is not the source and the cause of the domestic well impacts are likely a separate source(s).A sanitary sewer main located along West Hammer Lane between the Site and the domestic wells flows from east to west. Multiple historical dry cleaners have been identified upstream along the sewer main near the intersection of West Hammer Lane and Thornton Road. Since PCE is generally not reported or has been reported at very low concentrations in shallow and deep groundwater on-Site,the sanitary sewer main is the most likely source of the PCE concentrations reported in the domestic supply wells. Therefore, co-located soil vapor and groundwater samples are proposed in three locations along the sewer main to evaluate this source. Two locations are proposed on the north side of West Hammer Lane,between the sewer main and the domestic supply wells and one location is proposed on the south side of West Hammer Lane, near the sewer lateral connecting to the Site. Soil vapor samples are proposed at approximately 5 and 15 ft bgs in these borings to evaluate potential VOC releases from the sewer. Grab groundwater samples from first encountered groundwater are also proposed in the three locations to evaluate if potential impacts have migrated to groundwater and to compare groundwater VOC concentrations to those collected on Site and at other sources. Previous VI evaluations at the Site have consisted of shallow soil vapor and indoor air sampling in the current and former dry cleaner suites.No sub-slab samples have been collected with the indoor air samples and, indoor air samples have only been collected in the winter season. PCE was not reported at concentrations above reporting limits during the initial indoor air sampling event. A summer sample is needed to assess potential seasonal variability of indoor air concentrations. This additional VI data will be used to complete the VI-Conceptual Site Model(CSM). A minimum of three, collocated sub-slab soil vapor and indoor air sample locations are proposed recommended for small buildings (less than 1,500 square feet) to evaluate VI (California Environmental Protection Agency[CalEPA],2023).Indoor air samples will be collected simultaneously with the sub-slab soil vapor samples. Three indoor air samples will be collected in each of the former dry cleaner suites. Indoor air data will be used to evaluate current VI potential in the buildings while sub-slab soil vapor data will be used to evaluate potential future VI in the buildings.The paired concentrations of chemicals reported in the indoor air and sub-slab samples will be compared to evaluate attenuation of vapors across the slab. In addition, three outdoor air samples will be collected from areas near the buildings to assess potential background concentrations of VOCs. Sub-slab soil vapor and indoor air samples are proposed for each of the three suites located in the 1174 West Hammer Lane building, which are occupied by the Parkwoods Cleaners,a barber shop, and a nail salon, as well as the former Parkwoods Cleaner suite. While no dry-cleaning activities currently take place in the Parkwoods Cleaners suite, there is a higher potential for off-gassing of PCE from recently dry-cleaned clothes in this suite. Similarly,products used in the barber shop and nail salon also have potential for off-gassing VOCs, therefore, detailed chemical inventories will be conducted in these suites during the building surveys prior to indoor air/sub-slab vapor 5 September 2025