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27 September 2024 AdvancedGeo <br /> p An Employee-Owned Company <br /> Project No. 23-7573 _ <br /> Page 2 of 6 <br /> Proposed sampling locations are illustrated in Figure 1. The scope of work is described <br /> in detail below. <br /> 2.0. PROPOSED SCOPE OF WORK <br /> The proposed scope of work for this investigation includes the following: <br /> • Installation of a soil-vapor sampling point to a depth of 6.5 feet below surface grade <br /> (bsg) on the central-western side of the residential structure located at 1122 <br /> Graffigna Avenue. A co-located crawl space sample will be collected underneath <br /> the structure. <br /> • Installation of a soil-vapor sampling point to a depth of 6.5 feet bsg on the western <br /> side of the residential structure located at 1203 West Lockeford Avenue. A co- <br /> located crawl space sample will be collected underneath the structure as part of <br /> this initial investigation. <br /> • Installation of a soil-vapor sampling point to a depth of 6.5 feet bsg on the western <br /> side of the commercial structure located at 1213 West Lockeford Avenue. A co- <br /> located indoor air (IA) sample will be collected within the currently vacant building. <br /> • Installation of a soil-vapor sampling point to depth of 6.5 feet bsg on the eastern <br /> side of the commercial structure located at 1225 West Lockeford Street. A co- <br /> located IA sample will be collected within the common area of the ARCO-branded <br /> convenience store. <br /> • Collection of single ambient air sample at the rear of the subject property facility. <br /> All four boings will be advanced with a 3-inch hand auger. The proposed sampling <br /> locations are illustrated in Figure 1. <br /> 3.0. SOIL-VAPOR POINT INSTALLATION, SAMPLING AND ANALYSIS <br /> Soil gas sampling will be conducted in accordance with the DTSC Advisory (DTSC et al., <br /> 2015). Soil gas sampling will not be performed during rainfall or within 48-hours of a <br /> significant rain event of more than a half of an inch of rain during a 24-hour period. <br /> 3.1. SOIL-VAPOR POINT INSTALLATIONS <br /> Following boring advancement, single-completed soil-vapor sampling points will be <br /> installed in the locations described in each of the above-described locations. A total of 8.5 <br /> feet of/4-inch diameter Teflon® tubing and a 2-inch-long polyethylene soil-vapor implant <br /> will be lowered to the bottom of the borehole. A filter pack of#2/12 sand will be added to <br /> approximately 4 feet bsg. Following placement of the filter pack, approximately 12 inches <br />