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Phase II Environmental Site Assessment Multi-Modal Station Stockton,San Joaquin County,California Page 25 • of the soils encountered in CPTl, the salt and clayey silt soils are more prevalent in this zone than the clay-rich soils In CPT1, primarily silty soils and clayey soils were encountered in roughly equivalent abundance Sand and silty sand layers that may correspond to water-bearing zones were generally encountered at or near the basal portions of this uppermost subsurface zone Sand and silty sand layers encountered between approximately 27 5 feet and 39 feet bgs in the CPT borings appear to represent a continuous sand and silty sand unit and likely correspond to the first groundwater at depth across the site Sand and silty sand layers were encountered at approximate depths of 28 to 32 feet bgs and 108 to 115 feet bgs in CPT1, 30 to 31 feet bgs and 43 feet bgs in CPT2, 28 to 33 feet bgs in CPT3, 36 to 39 feet bgs and 115 to 120 feet bgs in CPT4, and 34 to 36 feet bgs, 95 to 97 feet bgs, 109 to 115 feet bgs, 119 to 121 feet bgs, 134 to 137 feet bgs, and 170 to 174 feet bgs in CPT5 The detection and hydropunch borings were advanced to approximate depths of 45 feet bgs to collect groundwater samples from this shallow zone Interbedded silts, clayey silts, silty clays, and clays comprise the majority of the subsurface between approximately 39 feet and 110 feet bgs With the exception of CPT2, the primarily silty soils and clayey sods were encountered in roughly equivalent abundance to a depth of approximately 110 feet bgs The soils encountered in CPT2 were predominantly salts and clayey silts with sparsely interbedded clay-rich soil layers A semi-continuous sand layer was encountered at an approximate depth of 117 to 119 feet bgs in borings CPT4 and CPT5 In CPT5, this sand layer was separated from another sand layer between approximate depths of 109 feet and 115 feet bgs by a predominantly salty Iayer This upper member of the lower sand unit was also encountered in CPT1 at an approximate depth of 108 to 115 feet bgs Boring PA1 and hydropunch boring HBK4-730-1 were advanced to approximate depths of 114 feet bgs and 110 feet bgs, respectively, to collect groundwater samples from the deeper zone The logs for borings CPT2 and CPT3 do not indicate the presence of a potentially water-bearing semi-continuous sand unit at these depths Other discontinuous sand and/or silty sand layers were encountered at approximate depths of 43 feet bgs in CPT2 and 95 to 97 feet bgs in CPT5 Based on the soils encountered in CPT5 at depths greater than 120 feet bgs, the site subsurface is comprised primarily of interbedded salts, clays, and transitional soils between these types to an approximate depth of 170 feet bgs Additional deep sand and silty sand layers were encountered in CPT5 at approximate depths of 134 to 137 feet bgs and 170 to 173 feet bgs In general, the CPT and direct push borings indicated similar soil types and units The water-bearing zones generally consist of predominantly sandy soil types, as identified in the CPT borings, located at depths ranging from approximately 27 5 to 39 feet bgs and 108 to 119 feet bgs 6.2 GROUND PENETRATING RADAR INVESTIGATION A total of 936 GPR data lanes were collected from 28 of the private properties within the site For the purposes of this report, only 66 of the 936 collected data lanes are discussed in Appendix C A map of the GPR study area and data line locations is provided in Figure 4, Appendix A GPR lines were traversed from west to east or south to north unless otherwise indicated on the included figures A detailed discussion of the GPR investigation, including technology, investigation methodology and instrumentation, is provided in Appendix C Appendix C also contains the radargrams for data lines 1-66, and an index grouping the radargrams by property and block and providing the corresponding data file number for each radargram Each data file number represents a walked line for a given property The primary objective of the investigation was to garner additional information pertaining to the subsurface conditions at the proposed boring locations on selected private properties within the site The secondary objective was to investigate certain properties or portions thereof for evidence of suspect environmental conditions, such as the potential presence of USTs and other buried objects �� CONDOR