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1.0 INTRODUCTION This report presents the results of the initial phase of an investigation of the soils in the vicinity of the Union Pacific Railroad diesel pipeline in Stockton, California. The investigation was performed at the direction of Union Pacific Railroad (UPRR). The study area is located on Sixth Street between Harrison Street and El Dorado Avenue in Stockton, L. California (Plate 1). The 4-inch diesel pipeline runs along the northern side of Sixth Street in the study area (Plate 2) and was reportedly taken out of service in 1986. The pipeline is located approximately 6 to 6.5 feet from the street curb at a depth of about 3.5 to 4 feet. The objectives of this investigation were to: (1) locate areas known to have been contaminated by diesel hydrocarbons; (2) evaluate the applicability of a soil gas technique in L investigating possible diesel soil contamination in the vadose zone by comparing the results from the soil gas survey with the results from discrete soil samples obtained at the same location; and (3) assess the feasibility of employing the soil gas method to other portions of L.• the pipeline. The scope of work, field methodologies, county approvals and contract services were prepared by USPCI. PES Environmental Services was contracted to provide on-site support, sample and data compilation, and preliminary interpretation. p 2.0 SCOPE OF INVESTIGATION A workplan was submitted to the San Joaquin County Department of Environmental Health in November, 1990. In May, 1991 USPCI received notice of the conditional approval of the L' workplan with a list of additional documents and permits that were required by the county. The additional documents primarily concerned the county's contractor approval process and required that USPCI document our California State Contractor license and insurance coverage. In addition, the county requested further information about final closure . procedures. The closure of the pipeline as proposed consists of the following stages: • Test the soil gas method in an area of a known leak to determine the feasibility of the method for assessing the entire line. During the test, the soil gas results will be verified with soil sampling and analysis. • If the test is successful, a soil gas survey with limited verification sampling will be designed and conducted over the entire length of the line. • Prior to closure, the line will be rinsed and final rinsate collected and analyzed to ensure that the line is clean. Water will be pumped through the line from %W the port and collected and treated at the UPRR yard. ` • After rinsing the line, areas with confirmed soil impact, if any, will be L excavated and that portion of the pipeline removed. Remaining portions of the line will be closed in place by pumping the line full of grout. L+ f:e"TocKTON.SO 1 �w