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• i <br /> Memo to Antonia Vorster -3- 12 December 1985 <br /> 3. According to the report submitted on 11 June 1985, wells 6, 8, 9 and 10 <br /> have large amounts of sand in the casing. Our letter of 12 March 1985, and <br /> good well construction technique, require that the screen/packing rela- <br /> tionship be designed to preclude native materials. The material in the <br /> well logs of wells 6, 8, 9, and 10 was described as very fine sand. <br /> According to the soil survey manual , USDA, 1951, the diameter of such sand <br /> is 0.1 - 0.05 mm. The gravel/sand pack used was 15 - 20% medium sand and <br /> 80 - 85% 1/4" pea gravel . The screen used was "perf 1/16 inch saw slot <br /> groups at 6 inch intervals". The saw slots, at 1/16 inch (or 1.6 mm) are <br /> large enough to allow even the medium sand in the packing to pass through <br /> to the casing. The native material , having only to pass through 1 inch of <br /> pea gravel , would also pass through to the casing. These wells were <br /> constructed incorrectly, and formation materials as well as packing ma- <br /> terials will continue to enter the well . <br /> Attachment <br /> DTW:jec <br />