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Mr'. Tinj Smith County of Los Angeles %..0 Department of Public Works October 19, 2009 Page 2 This area includes three islands, each containin petroleum product and three product line runs exgtending beneath the dispensers.three dispensers for h �sD e. and diesel activities the dispensers were removed and product piping was exposed. ring upgrade > p p pp, g P Flying J contracted the services of Nichols Consulting Engineers, Chtd. (NCE) to mobilize to the site to observe soil conditions and to collect soil samples from beneath seven of the nine dispenser locations and along product line runs for the RV islands. A total of 15 soil samples were submitted to a State of California certified laboratory for analysis of total petroleum hydrocarbons (TPH), gasoline and diesel range organics, and fuel oxygenates using the EPA Test Methods 8015 and 826013, respectively.- Results of these analyses indicated 1 of the 15 samples analyzed contained TPH-diesel range organics at a concentration of 240 milligrams per kilogram, rThe sample was collected from approximately 1 to 2 feet beneath the diesel dispenser located on the south'side'of the center RV island. No other constituents were detected in any of the samples analyzed. In response to these findings, San Joaquin County issued a correspondence dated September 15, 2009 requesting "a work plan to investigate the lateral and vertical extent of the soil and groundwater contamination at your site...." This work plan is being provided pursuant to this request. Area Geology The subject site lies within the Central or Great Valley of California.' The Great Valley is an elongated lowland located between the Sierra Nevada on the east and the Coast Ranges on the west. The southern portion of the Great Valley drained by the San Joaquin River is referred to as the San Joaquin Valley and the northern portion drained by the Sacramento River is referred to as the Sacramento Valley. Rocks of the Great Valley consist of sedimentary deposits ranging in age from late Mesozoic through Holocene (Recent).' Unconsolidated continental deposits constitute the primary source of groundwater in the Great Valley' The continental deposits consist primarily of alluvium; however, some areas consist of permeable lake bed sediments. 4 Norris, Robert M. and Robert W. Webb, 1990. Geology of California, 2nd edition, John Wiley & Sons, Inc., USA, 541 pages. 2 Norris, Robert M. and Robert W. Webb, 1990. Geology of California, 2nd edition, John Wiley & Sons, Inc., USA, 541 pages. Geologic Map of California, Compilation by Charles W.Jennings, California Division of Mines and Geology, 1977. Davis, G. H.,J. H. Green, F. H. Olmstead, and D.W. Brown, 1959. Ground-Water Conditions and Storage Capacity in the San Joaquin Valley,California, United States Geological Survey Water-Supply Paper 1469. 3 F. H.Olmstead and G.H. Davis, 1961. Ground-Water Conditions and Storage Capacity in the Sacramento Valley, California, United States Geological Survey Water-Supply Paper 1497.