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Appendix C Ground Penetrating Radar Investigation Phase 11 ESA Multi-Modal Station"Six-Block ProjecY January 6,2003 Page 6 of 9 . 1.3 7 Block 4 730 E Channel Street EHD records indicated ten USTs were present at the former Stockton Metropolitan Transit District facility at 145 N Grant Street (current address 730 E Channel Street) in 1985 Two USTs were reportedly removed in 1987, but no additional information regarding the remaining eight USTs was observed in the EHD records The property was investigated on August 27 and 28, 2002, by a total of 117 GPR lines Radargrams of the property's subsurface suggest that there was some past disturbance of the soil The southeastern exterior corner of the property was investigated by 23 GPR lines, the northwestern exterior corner of the property was investigated by 54 GPR lines, and the interior portion of the property excluding the underlying basement was investigated by 40 GPR lines The GPR investigation was performed to identify suitable areas for boring locations and to investigate the property for possible USTs and other Issues of potential concern The former parking area comprising the southeastern portion of the property was investigated on August 27, 2002 Radargram 28 depicts a typical data line from this portion of the property The subsurface conditions in this radargram, like many others from this portion of the property, suggest that the soil was the subject of some past disturbance Radargram 29 shows similar subsurface conditions with small buried objects GPR data collected from within the vicinity of an asphalt surface patch located in this portion of the property did not indicate the presence of potential issues of concern The interior portion of the property, excluding the underlying basement, was investigated on August 28, • 2002 This area was formerly used as a maintenance bay for buses and has two approximately five-foot deep maintenance bays that provided access to the undercarriages of buses The GPR data indicated several issues of potential concern in this area A possible burled object, void, or vertical conduit was identified immediately west of the northern maintenance bay and is shown in Radargrams 30 and 31, which are perpendicular and intersect at this feature Radargrams 32 and 33, parallel to Radargram 30, show a burled pipe or conduit that runs north from this object or void towards the northwestern exterior portion of the site Radargrams: 34 and 35 show two additional features that may be buried objects, voids, or vertical conduits located east of the maintenance bays No potential issues of concern were identified in the area between the two pits, as shown in Radargram 36, parallel to the length of the bays The distinct high-amplitude feature in this radargram is a low-ceilmged tunnel that connects the two bays The cast end of this radargram also indicates that parts of this portion of the property are characterized by reinforced concrete surfacing containing rebar The variable subsurface suggests that portions of the property may have been excavated for unknown reasons subsequent to original construction at the property The northwestern exterior corner of the property was investigated on August 28, 2002 This area appeared to previously have been used as a bus washing area and possible bus yard A large concrete patch and four existing vent pipes suggested that this portion of the property might be the current or former location of one or more USTs The collected GPR data contained several features of interest throughout this portion of the property Radargrams 37 and 38 show a Imear feature that runs north from a drain in the bus wash area toward E Channel Street The drain and this feature of the GPR data were collinear with burled utilities markings on the E Channel Street sidewalk and roadway indicating the location of a sewer line, suggesting the bus wash drained into the sewer system Data presented in Radargrams 39 and 40 indicate buried pipes running northeastward from an aboveground industrial filter located in the southeastern . corner of this portion of the property to a small concrete patch area Data collected from the large i