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�i SECOR www secor com INTERNATIONAL 3017 Kilgore Road Suite 100 S E C ® R INCORPORATED Rancho Cordova CA 95670 916$61-0400 TEL 916-861-0430 FAx March 18, 2004 HEMMED MAR 2 2 2004 ENMUNMENT HEALTH Mr Mike Infurna San Joaquin County Public Health Services PERMIT/SERVICES 304 East Weber Avenue Stockton, California RE Addendum to Work Plan for Vertical Assessment dated February 26, 2004 Former 76 Service Station 4409 1502 North EI Dorado Street Stockton, California SECOR Project No 77CP 64409 05 0001 Dear Mr Infurna This letter, prepared by SECOR International Incorporated (SECOR) on behalf of ConocoPhillips, presents an addendum to Work Plan for Vertical Assessment dated February 26, 2004 for Former 76 Service Station 4409, located at 1502 North EI Dorado Street, Stockton, California (Figure 1) The addendum is being submitted to propose the drilling of deep borings utilizing sonic drilling equipment The purpose of the proposed work is to gather soil lithology and soil and groundwater samples to delineate the vertical extent of petroleum hydrocarbons beneath the site prior to the installation of wells proposed In the work plan PROPOSED SCOPE(OF WORK 3 The scope of work for this addendum will Include the drilling of deep soil borings onsite utilizing sonic drilling equipment (Figure 1) a The specific scope of work is discussed below ' Site Specific Health and Safety Plan As required by the Occupational Health and Safety fkO Administration (OSHA) Standard "Hazardous Waste Operations and Emergency Response" guidelines (29 CFR 1910 120), and by California Occupational Health and Safety Administration (Cal-OSHA) "Hazardous Waste Operations and Emergency Response" guidelines (CCR Title 8, Section 5192), SECOR will prepare a Site-Specific Health and Safety Plan prior to the commencement of fieldwork The Site-Specific Health and Safety Plan will be reviewed by the field staff and contractors before beginning field operations at the site h yt Permitting Soil boring permits will be obtained from SJCEHD prior to initiating work d Sonic Borings Two sonic borings will be advanced to approximately 120 feet below ground ^ surface (bgs) to assess soil lithology in each location Continuous soil cores will be collected from 80 to 120 feet bgs One sonic boring location will be advanced through the area of highest contamination (based on Figure 10 of the Site Conceptual Model) and one will be placed directly downgradient of the highest contamination (Figure 2) Adjacent to each borehole, a second sonic borehole will be advanced to collect discrete soil and groundwater samples The depth of soil and groundwater grab samples will be based on the borehole lithology and field observations Sand layers likely to contain water will be targeted for groundwater grab samples Groundwater grab samples will be collected beneath existing deep wells (80 feet bgs) Based on soil borehole