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F" F OEQMATR1X SUMMARY OF SOIL AND GROUNDWATER INVESTIGATION AND RECOMMENDATION FOR SITE CLOSURE 1 . Highiet/Monterosso Parcel FiTracy, California 1.0 INTRODUCTION This report was prepared by Geomatrix Consultants, Inc. (Geomatrix) on behalf of Chevron Pipe Line Company(CPL) to present the results of previous assessments and recent groundwater monitoring per- formed at the Highiet/Monterosso parcel and to recommend appropriate further action, if any. The F. Highiet/Monterosso parcel (assessor's parcel number [APN] 238-040-02) is being developed for resi- dential use and is located at the southwest corner'of the intersection of Corral Hollow and West Byron roads in Tracy, California (Figure 1). Environmental assessments at the parcel have focused on the F presence of degraded petroleum hydrocarbons in the subsurface soil. F2.0 BACKGROUND AND SUMMARY OF PREVIOUS INVESTIGATIONS The Highiet/Monterosso parcel (the site) fronts the south side of West Byron Road. Two former pipe- Fline systems (including CPL'S former Wait-Mendota-Richmond pipeline) were located along the north and south side of West Byron Road parallel to the site's boundary as shown on Figure 2. These pipe- line systems were used to carry crude oil and Bunker C oil from the early 1900s to the late 1950s. t . Three phases of environmental assessment were previously performed at the site and are described in Section 2.1. The Highiet/Monterosso parcel is located east of a property known as the Dividend property (APNs F1238-020-10113114), which is shown on Figure 1. CPL has recently completed an extensive site assess- ment and human health risk assessment for the Dividend property in response to the presence of de- graded crude oil/Bunker C in subsurface soil. The assessments for the Dividend property indicated that 1 the residual petroleum in soil is not a threat to shallow groundwater quality and does not pose a signifi- cant health risk to future on-site residents. Because the residual petroleum at the Dividend property Fand Highiet/Monterosso parcel is likely the same or similar material, comparison of environmental conditions and resultant risks between the two properties is appropriate. Such a comparison is useful for interpreting the potential risk posed by the residual petroleum at the Highiet/Monterosso parcel. A F summary of environmental assessments and the human health risk assessment for the Dividend prop- erty is provided in Section 2.2. P F I P