SITE INFORMATION AND CORRESPONDENCE

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Revised Soil and Groundwater Investigation Work Plan Mountain House Development Site#6 July 2007 2. BACKGROUND 2.1 LOCATION AND SITE DESCRIPTION The site is located in an agricultural area northwest of the City of Tracy in San Joaquin County, California (Figure 1). Locally,the Mountain House study area is situated at elevations ranging from approximately 40 to 50 feet above mean sea level in relatively flat-laying areas. 2.2 HISTORICAL AND EXISTING PIPELINES The site includes ROWS associated with a former Standard Oil of California(Standard)Wait-Mendota- Richmond pipeline(the OVP), and a former TAOC pipeline. The OVP is located on the west side of Byron Road, and the TAOC ROW is located within the UPRR ROW on the east side of Byron Road. The OVP was installed between 1902 and 1904 as a"hot line"(i.e.,the oil was heated to facilitate transmission)and carried San Joaquin Valley(SJV)crude oil north from the Kern River Oil Fields (in and near Bakersfield)to Standard's Richmond Refinery. The pipeline and associated pump stations operated from 1903 until the early to mid 1930s. The pipelines were again used during the early 1940s to primarily transmit Bunker C fuel oil from the Richmond Refinery to railroad hubs in Tracy. The pipelines northwest of Tracy may have also been used to transport crude oil to various markets within the Bay Area until the late 1960s, and they were reportedly abandoned in 1970. Where the pipelines were not abandoned in place they were removed, and their trenches were likely backfilled with native soil. The TAOC pipeline system was constructed in 1907, and like the OVP,transmitted heated crude oil from Bakersfield to the Bay Area. The pipeline reportedly transmitted a cutter stock with the crude oil between Coalinga and the Bay Area to reduce oil viscosity. The TAOC pipeline was abandoned in the 1970s. Active pipelines within the UPRR ROW include an 8 inch-diameter Bay Area Products Line(BAPL) and a Kinder Morgan Energy Partners pipeline,both of which transport refined products. 2.3 EXISTING AND PLANNED DEVELOPMENT Currently,Byron Road is a two-lane thoroughfare serving southwest San Joaquin and eastern Contra Costa counties between Tracy and the Sacramento River Delta. The site is located among agricultural areas in the community of Mountain House, California. Nearby development of the area consists of agricultural and light-industrial facilities. Mountain House is a master-planned development where single-family homes are under construction in areas north of the site. Because the site is located within the Byron Road and UPRR ROWS, future residential, industrial, or commercial land use is not anticipated. Excavation for utility maintenance and future construction associated with roads and utilities is likely to occur. 2.4 PREVIOUS ENVIRONMENTAL ACTIVITIES In Condor's 2001 Chevron Pipeline Easement Assessment Report, affected soil was documented at the site in borings GP-152, GP-156 through GP-15 8,GP-160, and GP-161 at depths ranging from 4.5 to 20 feet bgs. Soil samples were collected at the boring locations shown on Figure 2 and submitted to a laboratory for analytical testing. Laboratory analytical results indicated detectable total petroleum hydrocarbons quantified as crude oil(TPHc) at concentrations ranging from 880 milligrams per kilogram (mg/kg) in boring GP-152 at 15.5 feet bgs to 29,000 mg/kg in GP-156 at 12 feet bgs. Grab groundwater samples were collected at the boring locations shown on Figure 2 and submitted to a laboratory for analytical testing. TPH quantified as diesel(TPHd)were detected at concentrations ranging from 2,200 micrograms/liter(µg/L) in GP-152 to 260,000 gg/L in GP-161. TPH quantified as gasoline(TPHg)were also detected at concentrations ranging from 8,500 in GP-156 to 9,900 gg/L in GP-161. 2 ��i`® From Schee to Solutions