SITE INFORMATION AND CORRESPONDENCE

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Soil and Groundwater Investigation Report Vernalis Pump Station August 2006 • Conducted a search of California Department of Water Resources (DWR) files to obtain information on water supply wells and prepared a summary table,which is provided in this report. • Advanced six soil borings from which soil and groundwater samples were collected and tested by Lancaster Laboratories in Lancaster,Pennsylvania for the constituents of concern: BTEX by EPA Method 826013; TPHg by EPA Method 8015 Modified; TPHd(carbon range CIO to C25)by EPA Method 8015 Modified with and without silica-gel cleanup; and PAHs by EPA Method 8270C SIM. • Installed three groundwater monitoring wells. • Evaluated project data to determine the extent of affected soil and groundwater. • Prepared this Soil and Groundwater Investigation Report,which describes the investigation results and makes recommendations for future investigation activities. The field investigation was implemented in accordance with the RWQCB-approved work plan, except for the following variations: • Because site access could not be obtained from the owner of the San Joaquin Valley Hay Grower's Association(SJVHGA)property,which is located east and down gradient of the Arcos property,proposed borings SB-26 through SB-29 were not advanced. • Because flowing sands encountered during drilling made it impossible to collect high-quality grab groundwater samples from the borehole and to install monitoring well MW-6 in the borehole, a groundwater sample was not collected from boring SB-24. Instead,monitoring well MW-6 was installed in boring SB-23. For more information regarding the field and sampling methods employed during the field investigation, refer to Appendix A. 4. FINDINGS 4.1 SUBSURFACE CONDITIONS Soils encountered during the investigation ranged from low-plasticity clays and silts,to clayey or silty sands,to poorly graded sands and gravels with fine-grained sediments. Soil boring logs and monitoring well construction data are provided in Appendix B. Based on the depths at which saturated soils were noted on boring logs and the depths at which static water levels were measured in each borehole,the top of the uppermost groundwater ranged from approximately 30 to 35 feet bgs. Additionally,the shallow groundwater is unconfined. Because the top- of-casing elevations of the newly installed monitoring wells were surveyed at a later date, coinciding with subsequent groundwater monitoring and sampling activities,the direction and gradient of groundwater movement were not determined during the field investigation. However,based on the depth-to-water measurements of multiple quarterly groundwater monitoring and sampling events completed since this field investigation, it has been concluded that the shallow groundwater beneath the site flows to the east at a gradient of 0.001 ft/ft. 4.2 DWR FILE REVIEW RESULTS SAIC conducted a search of DWR files to identify water supply wells within a '/z-mile radius of the site. The search covered portions of Township 3-South,Range 6-East, Sections 24 and 34. AMEN 4 From Science to Solutions-