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SECTION 1.0 INTRODUCTION The predominant structures Iocated on the site include two shop buildings, a storage building, and an office building One shop building was recently completed in the center of the site near the former UST location This new shop building is reportedly intended for equipment maintenance The majority of the site is overlain with b to 10 inches of concrete and asphalt, or irrigated landscaping 1.2 OBJECTIVES The overall project objectives are to complete the delineation of petroleum hydrocarbons in the subsurface beneath Shop 10 and use the additional data to (1) complete the human health and groundwater risk assessment for the site and (2) assess potential remedial alternatives to mitigate residual petroleum hydrocarbon concentrations, if necessary, based on the risk assessment results, CVRWQCB Basin Plan objectives, and Caltrans objectives The objectives accomplished by the tasks described in this report include the following • Evaluate the stratigraphy beneath the site, • Assess the magnitude and extent of petroleum hydrocarbons in soil and in groundwater through the evaluation of previous subsurface investigation data and horizontal and vertical groundwater sampling, • Evaluate the hydraulic characteristics of the saturated zone(s), and • Monitor the dissolved-phase petroleum hydrocarbons in groundwater tThe results of this investigation will be used to complete the draft Human Health Rask Assessment and Groundwater Impact Analysis Report, which was submitted in October 1998 (Woodward-Clyde, 1998) The draft report estimated risks for complete exposure pathways, and discuss CVRWQCB Basin Plan water quality objectives and site-specific corrective action goals to achieve site closure In addition, in accordance with Caltrans objectives and Task Order agreements, a separate report that includes an evaluation of potential remediation alternatives and the respective magnitude of costs will be prepared 1.3 APPROACH URSGWC prepared a scope of work that outlined sax tasks to achieve the above objectives (Woodward-Clyde, 1999) The scope of work was partially completed under the previous contract (Number 43X929), that expired on April 30, 1999 A new scope of work (URSGWC, 1999) was submitted and approved by Caltrans in June 1999, concurrent with the approval of the new contract (Number 43A0019) The tasks are outlined in the scope of work described below $IPRO.84144o100044SHOP1OISHOPIOSA.DOC 1-2 URS Greiner Woodward Clyde