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GeosyntecO consultants 2. VAPOR INTRUSION CONCEPTUAL SITE MODEL The following subsections presents the current understanding of the vapor intrusion conceptual site model (VI CSM) for the SG-100 area. 2.1 Historical Site Use and Sources The SG-100 sample is located in the parking lot north of Benjamin Holt Drive and south of the former Village Cleaners and is bound to the north, east, west and south by commercial buildings. The former Village Cleaners borders the Site to the north. Past dry-cleaning waste disposal practices included the disposal of wastewater containing dissolved dry-cleaning fluids into the sanitary sewer lines. The sanitary sewer lateral that connected the former Village Cleaners suite to the main sewer lateral along Benjamin Holt Drive transects the northern part of the Shopping Center. These historical waste disposal practices and documented spills from dry cleaning businesses resulted in VOC impacts to soil and groundwater. Historical investigations have identified PCE as the primary COC in soil vapor with TCE, cis-1,2-DCE and VC reported at lower concentrations and lower frequencies. 2.2 Vadose Zone Stratigraphy Information on the regional geology and hydrogeology can be found in the RI Report (Levine Fricke Recon [LFR], 1999), historical investigation data(Arcadis, 2013) and existing boring logs and subsurface interpretations. As previously described by others (mostly on the basis of on-Site data)the geology of the Site is highly stratified with interbedded layers of fine to coarser grained material. Boring logs from the installation of the SVE wells near SG-100 were not available for review; however, during the installation of SG-100, a sandy clay layer was observed from 9 feet bgs to 15 feet bgs, followed by a clay layer from 15 feet bgs to 17.5 feet bgs. 2.3 Previous Investigations Between 1988 and 1990, soil and soil vapor samples were collected along the sewer lateral transecting the Site and beneath the slab of the former Village Cleaners suite. PCE was reported in soil samples collected beneath the sanitary sewer lateral at concentrations up to 100 micrograms per kilogram (gg/kg) and at concentrations up to 8,400 gg/kg in soil samples collected from beneath the slab at the former Village Cleaners (LFR, 1999). PCE was reported in soil vapor samples collected along the sanitary sewer at concentrations ranging from 280 to 770 micrograms per liter(µg/L). A sanitary sewer line video survey was conducted in the sewer lateral transecting the Site in 1999. Numerous obstructions, rootballs, breaks, and offset sections of pipe were observed along the entire length of the lateral during the video section (LFR, 1999). In 1999, soil vapor samples were collected between 0 and 5 feet bgs (shallow), 5 to 16 feet bgs (intermediate) and 16 to 41 feet bgs (deep) in the SG-100 area. Shallow soil vapor samples were collected around the former Village Cleaners suite, along the sewer lateral, and adjacent to the surrounding buildings. Concentrations of PCE were reported at a maximum concentration of 363 gg/L in shallow soil vapor samples collected. The highest concentrations of PCE in shallow soil vapor were generally reported near the former Village Cleaners suite and the area southeast of the 202012 Lincoln Center Soil Vapor Assessment Work Plan 2 December 2020