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SEMI-PERMANENT SOIL VAPOR PROBE INSTALLATION WORK PLAN STAND Affordable Housing 2222 and 2244 S.Airport Way Stockton,CA 95206 1.0 INTRODUCTION Condor Earth (Condor) has prepared this work plan to install 4 semi-permanent soil vapor probes for STAND Affordable Housing (Client), to further characterize potential constituents of concern in the subsurface of the property located at 2222 and 2244 S. Airport Way, Stockton, California(the Site). This proposed scope of work includes the installation and sampling of four semi-permanent soil gas sampling probes and associated permitting and reporting. 2.0 SITE GEOLOGY AND HYDROGEOLOGY The Site is located approximately 18 to 20 feet above mean sea level with relatively flat topography that slopes very slightly to the west. A regional groundwater pumping depression east of Stockton influences the groundwater gradient such that near the Site, groundwater generally flows toward the east-northeast. The nearest surface water is the San Joaquin River, approximately 1.7 miles southwest of the Site. Geologic materials encountered beneath the Site are characterized by silty clays to clayey silts typical of braided alluvial channel deposits in non-marine delta environments. The Site soil type as mapped by the US Department of Agriculture is Stockton Clay with Class D hydrologic group(slow infiltration rate) and Jacktone Clay with Class D hydrologic group (slow infiltration rate). Groundwater typically ranges between 29-32 feet below ground surface (bgs) based upon previous groundwater monitoring associated with the Ralph's square-BUI'. Shallow groundwater was encountered at a depth of approximately 30 to 32 feet bgs during drilling conducted as part of this Phase H ESA. Figure 1 (Appendix A) presents a Site Vicinity Map. 3.0 SITE BACKGROUND The Site is comprised of two adjoining parcels,designated as APNs 169-163-010-000 and 169-151-010-000, totaling approximately 1.61 acres, located in a mixed commercial-residential area. The Site is currently vacant, with 60 percent of the ground surface paved and the remaining bare land/dirt.The Site was used as an agricultural field during the early 20th Century until the early 1950s. The Site was developed in the early 1950s with four buildings on the northern portion of the Site and asphalt surrounding the buildings in a mixed residential and commercial neighborhood. The shops operating on the Site vicinity included a drug store (2202), variety store(2222 and 2226), grocery (2222 and 2244), and various service-related and retail shops. A dry-cleaning shop operated at 2230 Sharps Lane (Airport Way) from 1950 until the early 1970s which corresponds to the small shop that was located immediately north of the former large market (southernmost building) at 2244 Airport Way. The buildings were removed sometime between 2010 and 2012 with the asphalt driveways and parking lots remaining. There are six former fueling stations within 600 feet of the Site. Two have been investigated and remediated under regulatory oversight. The other four have no public record of investigation. Two former fuel stations are directly upgradient (west-southwest) with respect to the Site. Three monitoring wells were present adjacent to the southwestern margin of the Site associated with the former gas station at 2255 S.Airport Way. Gasoline was detected in groundwater immediately adjacent to the Site at concentrations ranging from 55 ' Groundwater Monitoring Report — First Quarter 2017, Ralph's Square, 2122 South Airport Way, Stockton, California,dated March 2,2017,Advanced Geo Environmental �� CONDOR