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IIJ 1.0 INTRODUCTION 1.1 Purpose This report describes the investigation of hydrocarbon contamination on property located at 711 N. Pershing Avenue in Stockton, California. The�'rinvestigation was authorized by Mrs. Marianne Snell, one of the property owners, and was undertaken at the request of the Swett & Crawford Group, tenants of the building on the site. The Central'"Valley Region Water Quality Control Board delegated regulatory oversight responsibility to the San Joaquin County Public Health Service, Environmental Health Division. Mr. Michael Infurna of PHS/EHD has supervised the investigation. 1.2 Site Location and Description The site is located in western Stockton, near the Pershing Avenue off-ramp to Interstate 5 (Figure 1). The Stockton Deep Water Channel is located approximately one-half mile to the south of the site. The area was marshland until about 1945, when it was drained, cleared, and developed by the U. S. Navy. Naval housing units were constructed on the site and were occupied until 1965. They were demolished in 1979. The Swett& Crawford Group redeveloped the site in 1980 and constructed the present office building. The area is zoned primarily for residential use, although commercial buildings are located along Oak Street and other nearby streets to the`south of the site.: 2.2 Background , As part of an intended property purchase in 1993, Swett & Crawford retained RESNA Industries of Sacramento to perform a limited soil investigation to determine whether any contamination might be present. RESNA personnel drilled four shallowrholes with a hand auger and collected soil samples for laboratory analysis (Figure 2). These samples were analyzed for diesel and petroleum hydrocarbons as oil& grease, both of which were detected at fairly low concentrations, and for pesticides, two of which (chlordane and 4,4 DDT)were detected at high`concentrations in one of these samples (Appendix A). This prompted Swett&Crawford to delay the property transaction pending further investigation. I The investigation was continued by Upgradient Environmental, when five more borings (SP-1 through SP-5)were drilled in November 1994 (Figure 3). Four of these were drilled on adjacent properties to determine whether contamination was localized or widespread..A sixth boring (SP-6) was drilled in December near RESNNs boring B4, in an attempt to verify the RESNA results. Neither chlordane nor i DDT was detected in any of these samples, and Upgradient recommended case closure with no further work. The Central Valley Board rejected this recommendation, citing its concern that a very localized ' pesticide spil might have been missed. The CVRWQCB directed PHS/EHD to recommend further drilling, groundwater sampling, and excavation of any pesticide-contaminated soil that might be present. A work plan addressing these issues was submitted by Upgradient in late 1995, and the work was performed in November and December 1995. The results of that work are presented in the following sections.