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HORIZON ENVIRONMEN AL INC. Specialists in Site Assessment,Remedial Testing, Design and Operation December 22, 2003 Mr. Michael Infurna San Joaquin County Environmental Health Department 304 East Weber Avenue, Third Floor Stockton, California 95202-2708 Subj ect: Work Plan Addendum Beacon Station No. 12474 3440 East Main Street, Stockton, California Mr. Infurna: At the request of Ultramar Inc., Horizon Environmental Inc. (Horizon) is submitting this work plan addendum and a well permit application for additional monitoring wells at the subject site (Figure 1). This work plan addendum to Preliminary Results of Additional Subsurface Investigation and Work Plan Addendum dated February 26, 2003 was developed on the basis of stratigraphic evaluation and analytical results of soil and groundwater samples collected during a cone-penetrometer (CPT) investigation conducted on August 28, 2003. The February 26, 2003 addendum proposed the installation of five monitoring wells (MW- 13 through MW-17). The San Joaquin County Environmental Health Department (EHD) requested additional stratigraphic and analytical data before siting monitoring wells MW-15 and MW-16. The CPT investigation was proposed in Revision to Work Plan Addendum dated June 16, 2003 and approved by the San Joaquin County Environmental Health Department (EHD) in a letter dated June 25, 2003. Two CPT-log borings were advanced at the CPT-2 and CPT-3 locations as shown on Figure 2. Groundwater samples were collected from separate borings placed adjacent to the CPT- log borings. Boring B I 1 was advanced for the purpose of collecting a soil sample at approximately 80 feet bsg. All borings were backfilled with neat cement. The CPT logs are attached to this letter. The CPT logs generally indicated coarse-grained, water-bearing zones,between 85 and 100 feet bsg in both borings, and also at approximately 105 feet bsg in CPT-2 and 146 feet bsg in CPT-3. Groundwater sampling adjacent to the CPT-2 boring was attempted at five intervals: 55 to 60 feet below surface rade (bsg); 60 to 65 feet bsg; 85 to 90 feet bsg; 103 to 108 feet bsg; g g ; g; g; g; - and 143 to 148 feet bsg. Groundwater samples were successfully collected from the three intervals 60 to 65 feet bsg (sample CPT2-65), 85 to 90 feet bsg (sample CPT2-90) and 103 to 108 feet bsg (sample CPT2-108). The intervals 55 to 60 feet bsg and 143 to 148 feet bsg iwere dry. 5011 Golden Foothill Parkway, Suite 7 • EI Dorado Hills, CA 95762 (916) 939-2170 • FAX (916) 939-2172 P.O. Box 5283 9 Bakersfield, CA 93388 • (661) 589-8389 • FAX (661) 589-1456