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M. Scott Mansholt - 4 - 17 December 2M& Chevron Catellus Property results for TPHd at depths of 30, 34, and 36 feet bgs, respectively for the North, Central, and South study areas. Based on the report, SB-66 was drilled approximately 150 feet east of the Singh well, and SB-67 was less than 50 feet northwest of SB-66, both very close to the OVP alignment. However, SAIC concluded that the TPHd detected in SB-66 was an anomaly and not attributable to the historical OVP or TAOC pipelines since groundwater samples from the surrounding and downgradient borings were ND for TPH compounds. Total dissolved solids (TDS) concentrations ranged from approximately 1,200 to 9,680 milligrams per liter (mg/L) for 11 groundwater samples, including the Singh well. As reported by SAIC, the Singh property owner indicated that the well is not used for domestic purposes. Except for the two highest values of 6,170 and 9,680 mg/L, the TDS values are consistent with those documented in groundwater at nearby Mountain House and City of Tracy OVP projects. The reported TDS values exceed the U.S. Environmental Protection Agency Recommended Secondary Maximum Contaminant Level of 500 mg/L, which is based on aesthetic (taste and odor) and technical (staining and corrosion) characteristics. Use of the shallow groundwater in Tracy is prohibited by Municipal Code for domestic or municipal use for reasons unrelated to the historical OVP/TAOC pipelines. SAIC concluded and recommended the following: • The lateral and vertical extent of affected soil has been defined for the three different areas of the Site. Vertically, affected soil has been defined at approximate depths of between 30 and 36 feet bgs. • The vertical extent of affected groundwater has been delineated. • The lateral extent of affected groundwater has been delineated except northeast of the North area. A separate workplan will be prepared to address the affected groundwater at the former Tracy Pump Station. Based on my review, I have the following comments: • 1 concur that the lateral and vertical extent of affected soil has been delineated. • Groundwater has been defined up and downgradient of the Singh private well and the associated borings. However, additional investigation is needed in the vicinity of boring SB-66 to confirm if the petroleum hydrocarbons detected are diesel fuel or crude oil. • 1 concur that the lateral and vertical extent of affected groundwater has been delineated except as noted for the area downgradient of the former Tracy Pump Station facility. Except for confirmation in the area around SB-66, additional characterization is not needed at Catellus.