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Well Abandonment Recommendations -2- 23 November 1992 DDRW, Tracy Your letter also expressed concern that an insufficient amount of water may have been used (5.3 gallons) per sack of cement with two pounds of bentonite. You state that a bentonite-cement grout cannot be mixed with less than 6.5 gallons of water per sack of cement. In order to yield a slurry of 14.7 pounds per gallon (lbs/gal ) , 6.5 gallons of water per sack of cement with two percent bentonite is needed. However, a bentonite-cement slurry may be mixed with less than this optimal water requirement and still remain pumpable. It is our understanding that representatives from the DTSC were not present in the field during the well abandonments. Concerns regarding insufficient or excessive water should have been presented during the field operation so that the water content of the slurry could have been adjusted. In the future, we recommend that a mud scale, which would measure the slurry weight in lbs/gal , be used as a quality control measure to assure that the slurry is mixed with the appropriate amount of water. 3. Comment No. 6 of your letter indicates that the perforated intervals should have been from 64 to 74 feet below ground surface (bgs) and from 100 to 110 feet bgs rather than from 15 to 25 feet bgs and 120 to 124 feet bgs. We are concerned with the untimeliness of this recommendation. Again, it is unfortunate that representatives of the DTSC were not present in the field during abandonment of the supply wells. We believe that the selection of the perforated intervals requires field decisions. Therefore, regulatory recommendations for changes in the perforated intervals is appropriate during the field operations rather than after the completion of the well abandonments. Second, DDRW, Tracy submitted the Final Work Plan for Well Evaluation and Abandonment on 18 February 1992. As you are aware, the State had conflicting comments on the Final Work Plan which resulted in a delay of the schedule for the Operable Unit No. 1 (OU-1) Remedial Investigation (RI) . Considering the past difficulty in reaching a consensus for the abandonment of Supply Well Nos. 1 and 2, we are disappointed that there was a lack of coordination prior to issuance of your letter. We are concerned that our differences in recommendations for well abandonment may again delay remedial activities if other deep supply wells must be abandoned at the DDRW, Tracy site. We hope that our technical differences will be resolved prior to any future well abandonments at the DDRW, Tracy site. We are willing to meet again to discuss specific recommendations for well abandonments so that a unified State position may be developed. If you have any questions, please call me at (916)255-3069. CAMILLA WILLIAMS Engineering Geologist CKW:cw