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CALIFORNIA GEOPHYSICAL GROUP , INC . P . O . Box 578341 , Modesto , CA 95357 Tel : (209) 527- 1247 March 21 , 2006 2D�6 HAR 27 Pq [(!k (209) 527-4810 l : p ; - T Ei� 7- h' D p.i Fi i A L Environmental Health Department tIEALT } ; p �NP,= , ,. , San Joaquin County ti hEFdT 304 East Weber Avenue Third Floor Stockton , CA 95202-2708 Attn : Mr. Nuel Henderson Re: Updated Monitoring Well Installation Work Plan (MW- 17 , MW - 18) Beneto Inc, 749 East Charter Way, Stockton, CA Site No . 1060 Introduction The San Joaquin County Environmental Health Department (EHD) has requested a work plan addressing verification of the CPT results of Soil Boring # 4 drilled on July 20 , 2005. The total depth of this CPT was 160 feet. As indicated in the field logs submitted for this boring , a discrete sand / gravel interval exists at approximately 132 — 135 feet bgs. The two monitoring wells we now propose will be installed in an effort to complete several goals . Proposed Tasks: 1 . ) Further define the vertical geology at the site; 135 ft. bgs. and confirm the vertical extent of the soil / groundwater contamination plume per the initial findings and analytical results of the CPT completed on July 20, 2005. 2 . ) Sampling and assessment of the newly discovered gravel/ sand stratification at 132 — 135 ft. bgs . 3. ) Evaluation if there is a potential for an off-site deep source from the documented contaminate releases surrounding this site through the sand/gravel interval at 132 — 135 ft. bgs . 4. ) MW- 17 will complete the tasks required to evaluate the 135 foot sandy zone of interest and it will allow evaluation of this sand zone for the movement of contaminates in a lateral direction . 5 . ) MW- 18 will verify the presence of contaminates at the 158 foot depth (indicated in the CPT analytical results) and it will serve as secondary verification of the consistency of ! the 135 foot zone. It could also provide the desired information as to the vertical definition of this contamination plume. 6. ) All the tasks completed will generate valuable current Geological and Analytical data which will be incorporated in the requested Feasibility Study for the site .