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l\/I. Scott Mansholt - 3 - 18 July 2008 Chevron OVP Former Tracy Pump Station Groundwater Groundwater samples were obtained from the four borings and submitted for analysis. Concentrations of TPH as diesel (TPHd) were reported at 1 ,000, 110, 650/680, and 4,400 micrograms per liter (pg/L), respectively for the SB-14, 15, 17/17 duplicate, and 18 samples. BTEX compounds were ND. SB-16 was not sampled due to the presence of an oil sheen noted during drilling. PAHs were ND except that the method detection limits (MDLs) used for the SB-18 sample, for some compounds, exceeded the ESLs/PRGs. The vertical extent of impacted groundwater has not been defined since the 32-foot interval in onsite boring SB-14 was dry, and a water sample could not be collected. A sample from the onsite domestic well, DW-1 was submitted for analysis of petroleum hydrocarbons, total dissolved solids (TDS), and general minerals. Results this event for TPHd, BTEX compounds, and PAHs were ND; TDS was 1,640 mg/L and the results for chloride, sodium, boron, and sulfate exceeded respective Water Quality Objectives (WQOs) described in the Central Valley RWQCB -Water Quality Control Plan (Basin Plan) for the Sacramento River Basin and the San Joaquin River Basin, 4th ed. (revised August 2006). Previously, groundwater samples from two 2004 onsite borings reported TDS values of 2,200 and 2,800 mg/L. According to the Basin Plan, an aquifer is considered a potential source of drinking water provided: a) TDS in groundwater is less than 3,000 mg/L; and, b) groundwater yield is greater than 200 gallons per day. The reported TDS values exceed the U.S. Environmental Protection Agency (EPA) Secondary Maximum Contaminant Level (MCL) for TDS (500 mg/L), which is based on aesthetic (taste and odor) and technical (staining and corrosion) characteristics*3. Based on the findings, SAIC concluded the following: • The vertical extent of affected soil has been delineated at approximately 31 .5 feet bgs in onsite boring SB-14. • Affected soil and groundwater has been delineated upgradient (south) and crossgradient, to the east and west; groundwater has been delineated to the north of the Site. • The lateral extent of affected soil and groundwater has not been delineated offsite- downgradient, east-northeast of the Site and additional characterization is needed. • Onsite well, DM-1 has not been affected by petroleum hydrocarbons. SAIC proposed to advance additional borings downgradient of the affected soil/groundwater areas. They proposed four step-out borings downgradient of SB-3, 16, and 18 which previously reported TPH as gasoline (TPHg) present in groundwater. An appropriate sample(s) would be collected and submitted for fuel fingerprint evaluation. *3— U.S. EPA, 1980, Suggested No Adverse Response Levels (SNARLs).