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SITE CLOSURE REQUEST POMBO PROPERTY 1755 WEST 11TH STREET TRACY,CALIFORNIA This report requests closure of the Pombo Property site on behalf of Chevron Environmental Management Company(CEMC). The site is located in San Joaquin County, California(Figure 1). CEMC conducted soil and groundwater investigations at the site from 1999 to 2004 to characterize and delineate weathered petroleum found in soil resulting from historical operations of the abandoned Old Valley Pipeline(OVP), which carried crude oil from the early 1900s to the late 1950s. This closure request was initiated pursuant to a March 8,2005 letter by the Central Valley Region of the California Regional Water Quality Control Board(RWQCB),which is included as Appendix A. In this letter,the RWQCB noted that the lateral and vertical extent of petroleum hydrocarbon-impacted soil has been delineated,as well as the off-site groundwater plume,and appear to be both limited in extent and stable. The decision to request closure has been based on technical data indicating that criteria have been met to support a"low-risk"case closure by the RWQCB in accordance with applicable State resolutions. This request includes a summary of general site conditions,previous environmental activities,results of a human health and ecological risk screening evaluation,and documentation required for case closure by the RWQCB in accordance with Appendix B of the Tri-Regional Guidelines. 1. GENERAL SITE CONDITIONS The Pombo Property is located at 1755 West 11`h Street in Tracy,California. A site vicinity map is included on Figure 1,and pertinent site features and sample locations are included on Figure 2. The Pombo Property is currently developed with one office building,a storm water retention pond, a fire station,and associated parking lots and driveways. The general topography of the site can be described as gently sloping to the north. The San Joaquin County Assessor's Office identifies the site as parcel number(APN)232-170-07 and as being 3.15 acres in size. The site and the adjacent properties on the block are bounded by Corral Hollow Road to the west, West I Ph Street to the south,and the Union Pacific Railroad(UPRR)right of way(ROW)to the north and east. The site's land use designation is General Highway Commercial(GHC),granted by the City of Tracy. The GHC zoning designation is intended to permit a pattern of varied automobile-oriented uses of property adjacent to major arterial streets as shown on the City of Tracy Zoning Map(City of Tracy,2005)and as described in the City of Tracy Municipal Code,Title 10,Article 19(City of Tracy,2004). Surrounding properties to the west include a shopping center. Areas to the south and north are primarily residential. The UPRR and West Side Irrigation District(WSID)easement bound the Pombo property to the north,and a public storage facility is located east of the site. The former OVP was located along the northern boundary of the Pombo Property, adjacent to the UPRR ROW. The former OVP was used to transport crude oil and Bunker C fuel oil from Bakersfield to Richmond,California from the early 1900s to 1950s. 1.1 REGIONAL/LOCAL HYDROGEOLOGY Based on previous investigations,subsurface soils were observed to be dark yellowish brown clay that extended to depths ranging from 7 to 17 feet below ground surface (bgs). The water table is approximately 7 feet bgs on the northern portion of the site. Depth to groundwater ranged from 6.2 to 17 feet bgs. The groundwater flow direction is inferred to be to the north based on well information from a 2,000 foot-radius well survey(SAIC,2005). Shallow groundwater in the Tracy area is of poor quality in general and prohibited for use as domestic or municipal supply in accordance with the Tracy Municipal Code(Section 11.1.16)due to reasons unrelated to the presence of degraded crude oil or Bunker C fuel 1