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ENVIRONMENTAL INVESTIGATION REPORT <br /> Unocal Service Station No 5886 <br /> 2701 west March Lane <br /> Stockton California <br /> Delta Project No D091-066 <br /> Page 2 <br /> 3.0 REGIONAL GEOLOGY <br /> The site is located in the San Joaquin Valley portion of the Central Valley of California The Central <br /> Valley lies west of the Coast Ranges and extends approximately 400 miles in a northwest-southeast <br /> orientation with an average width of 50 miles This basin is an asymmetric synclinal trough containing <br /> Jurassic to Holocene sedimentary rocks and sediments with a maximum thickness of approximately <br /> 33,000 feet in the San Joaquin Valley (Repenning, 1960) <br /> ' The sedimenta rocks and deposits consist of siltstone, cla stone, sandstone, and conglomerate that are <br /> sedimentary p Y g <br /> of predominantly marine origin (Hackel, 1966) The source area for these sediments was most probably <br /> the Klamath and Sierra Nevada Mountains (Bailey et al , 1964) Pleistocene and Holocene sedimentation <br /> ' of predominantly fluvial and lucustrme mechanisms has resulted in generally unconsolidated sediments <br /> of 330 to 3,300 feet in thickness (Poland and Evenson, 1966) <br /> 4.0 INVESTIGATION RESULTS <br /> � 4.1 Dispenser_Island,_Product Line�and_Canopy_Footing Soil Sampling <br /> On July 27, 1995, representatives of Unocal, San Joaquin County Environmental Health Division <br /> (SJCEHD), Delta and several employees of both Valenzuela Engineering and Advanced Environmental <br /> ' Services, Inc were on-site to examine and remove the piping connecting the USTs to the former product <br /> dispensers The product lines and tanks were rinsed by Erickson Inc of Richmond, California prior to <br /> the line removal A copy of Erickson's rinseate manifest for the material removed from the dispensers, <br /> lines, and tanks is attached in Appendix A No observable holes or cracks were apparent in the exposed <br /> ' lines Spalling of epoxy resin was observed at several locations along the lengths of the piping, however <br /> no failures were observed In addition, a fresh oily substance affecting approximately two square surface <br /> ' feet was observed on pea gravel present within the piping trench associated with the southern dispenser <br /> island This material appeared to be inconsistent with prior activities at the site and appeared to have <br /> been recently dumped or leaked from heavy machinery The location of the former dispensers and the <br /> associated piping trenches are presented in Figure 3, Trench and Dispenser Sample Locations <br /> RPT 160 SJS <br />