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,..._......_. ___ _ . 31 Duly __ 89 `LI)' � t � I This mencranduM was generated by t`:e DHS-TSSD ?.egicn 1 Technical and Support Services Unit to address proper procedures for mixing grout for we':l ,and borehole seals . -t is of upmost concern that the exact proportions and volumes of grout ingredients and the mixing procedures used for each batch of grout be documented. This documentation should be available for regulatory review. DHS , at present, is preparing formal recommendations for formulating and mixing grout that will specify exact. procedures. Technical specifications presented in this memorandum will be incorporated in future more formal performance standard recommendations. The following are some DHS concerns and preliminary recommendations regarding grouting procedures : - Grout blending should be done thoroughly using a mechanical mixer or recirculating the slurry through a high-shear pump to insure that the mixture is uniform and "lump free. " Qrcut containing "lumps" of unmixed bentonite and/or cement should not be used (California Department of Water Resources Bulletin 74-88 , in preparation) . - If bentonite-cement grout is used, the preferred method is to orehydrate the bentonite in water before adding cement to the mixture. - The bentonite used in bentonite-cement grout should be pure, non-beneficiated bentontite (no polymers) . - For bentonite-cement grout, DHS recommends that the percentage of bentonite to cement be in the two (2) to four (4) percentage range. If this amount of bentonite is used, DHS also recommends that the amount of water used be between eight (8) and ten gallons per 94 pound sack of cement. The percentage of bentonite must not exceed six (6) percent of the cement weight or excessive shrinkage is likely to occur (Driscoll, 1986) . The Environmental Protection Agency RCRA Technical Enforcement Guidance Document (TEDD) recommends that the addition of bentonite to the cement admixture be between two (2) and five (5) percent of the cement weight. - Grout should be installed through a tremie (small diameter) pipe. Before grouting, the tremie pipe should be placed from two (2) to seven (7) feet above the bottom of the hole or above the top of the sand or bentonite bridge. The tremie pipe should remain in this position during grouting. Grout should be pumped down the tremie pipe to fill the well annulus or borehole from bottom to top. If the tremie pipe must be raised during grouting, it should remain submerged at least 20 feet within the grout being emplaced.