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Memo to Antonia Vorster -2- 21 April 1986 second to verify a southerly gradient before drilling the east and west wells. Whichever well (or wells) on the site becomes the upgradient well must be placed far enough away from the landfill that it would not pick up any leachate from the landfill if it were to occur. 3. To ensure that accurate ground water elevations are determined as ground water is encountered, proposed well locations must be surveyed before drilling begins, and a monument should be established near each well site. Elevations of completer) wells must subsequently be determined to a 0.01 foot accuracy. 4. At each quarterly sampling, ground water levels in the wells must be determined prior to purging or sampling. In accordance with Section 2556 A.4 of Subchapter 15, ground water contours, ground water velocity, and direction of flow must be plotted on a site map and submitted each quarter to the Regional Board. 5. The proposed casing hammer/dual tube reverse circulations air rotary drilling procedure looks like a good method for logging the hole and identifying water-bearing zones. If foam is to be used, will the geologist on-site be able to identify the water-bearing zones? Air should be filtered to prevent oil from the compressor from entering the wells. 6. Proposed materials for well construction are acceptable. Slotted pipe should be installed at least two feet above highest expected water levels. The sand backfill , bentonite pellets, and cement grout should be installed using a tremie pipe to prevent bridging. Will water by added to the bentonite pellets after placement or will they be mixed with a cement grout prior to placement? Filter pack design must be compatible with both the screen sizing and the geologic materials in the screened zones. 7. The proposed sampling program is acceptable. What quality control/quality assurance procedures are proposed? JLE:Jec