ARCHIVED REPORTS_SOIL AND GROUNDWATER INVESTIGATION

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' 1.0 INTRODUCTION This report documents a recently-completed soil and groundwater investigation ofthe clarifier area ' at 15700 South McKinley Avenue in Lathrop, California(see Figure 1 and Figure 2). The soil and groundwater investigation included the drilling and sampling of eight investigative soil borings(I3-1 through IB-8) at the site using direct-push coring equipment. The goal of this investigation was to ' assess soil and groundwater quality adjacent to the clarifier, both for planning purposes for the anticipated removal of the clarifier and to address regulatory concerns. ' 1.1 Site Background Based on information provided to us by Scott Company, it is our understanding that: (1)During an ' investigation of the clarifier by Advanced GeoEnvironmental in October 1997, one boring, B-3, located near the inlet pipe on the south end of the clarifier,encountered 350 parts per million(ppm) of Total Petroleum Hydrocarbons as Gasoline (TPH-G), 10,000 ppm of Total Petroleum ' Hydrocarbons as Diesel(TPH-D), and 0.094 ppm of Tetrachloroethene(PCE)in soil at five feet in depth, with no detection of these constituents in a ten-foot soil sample and no groundwater sample collected; and (2) During an investigation of the clarifier by Dames & Moore in June 1998, one ' boring, B-9, located immediately south from the clarifier and west from previous boring B-3, encountered 0.082 ppm of TPH-D,with no detection of Volatile Organic Compounds(VOCs). Soils ' encountered in the clarifier area consisted primarily of sands and silts, and groundwater was encountered in B-9 at a depth of about eight feet below surface grade. It is our understanding that Scott Company is planning to remove the clarifier. In order to further evaluate hydrocarbon releases priorto removal ofthe clarifier,Gribi Associates prepared aworkplan, dated January 5, 2000, proposing to conduct a soil boring investigation using direct-push coring ' equipment. This workplan was approved by San Joaquin County Public Health Services Department on January 27, 2000, with the provision that additional VOC analysis be run for soil samples collected near the soil groundwater interface. A copy of the workplan approval facsimile ' is included in Appendix A. 1.2 Scope of Work ' Gribi Associates was contracted by for Scott Company to conduct the following scope of work: ' 0 Task 1 Conduct prefield activities. ■ Task 2 Conduct drilling and sampling activities. ' ■ Task 3 Conduct laboratory analyses. • Task 4 Prepare report of findings. ' These tasks were conducted in accordance with applicable environmental sampling guidelines and statutes. ' GRIBI Associates Page I REPORT OF SOIL AND GROUNDWATER INVESTIGATION 15700 SOUTH MCKINLEY AVENUE/GA 11"5.01