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CALIFORNIA GEOPHYSICAL GROUP, INC. - 12709 Poway Road, Suite 202, Poway, CA 92064 Tei: (619) 486-1323 January 28, 1992 _ Public Health Service San Joaquin County RECEIVfl ,� 0 P. O. Box 2009 JAN 3 Stockton, Ca 95201 1992 ENVIRONMENTAI_ HEALTH Attn: Mr. Steve Schneider PERM.! ADDENDUM TO WORK PLAN _ 749 E. -CHARTER WAY - STOCKTON, CA. - DECEMBER 11, -1991 = Pursuant- to our telephone conversation of Jan. 28 1992, we are submitting this addendum to clarify and modify some of the procedures mentioned in the original work plan. 1. We plan to use slotted casing fromthe bottom of the well to within 10 feet of the surface. We are aware we are opening a possible conduit to the water table from- the upper zones which may be contaminated. We will only place the slotted casing as designed if no pearched water zones are encountered there were none in the original wells) and if the material drilled is mostly clean, according to our OVA readings taken during drilling. We would feel a middle range reading on the OVA meter in a clay unit as not dangerous- for future contamination, whereas the same reading in a sand or- silt would . cause us to cancel the present design and complete the well with slotted casing only 5 to 10 feet above the water table. 2. The soil and water samples will be tested as follows : ITEM Detection Limits Soil BTEX - EPA 8020 , - Benzene 5- 0 ppb -oluene 5 .p ppb -� Ethyl Benzene 5. 0 ppb Each Xylene -5. 4 ppb -- TPH Soils - D. O. H. S. /LUFT Manual - 1. 0 ppm D Water BTEX - EPA 802 Benzene 0. 5 ppb Toluene 0. 5 ppb Ethyl Benzene 0. 5 ppb _ Each Xylene 0. 5 ppb TPH Water - D. O. H. S. /LUFT Manual 50. 0 ppb - 3. We have rewritten our QA/QC Controls and incorporated your ideas for well surging prior to placing the bentonite seal.