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9.3.3.2.4 Sand-Sumo. There shall be a 2-foot minimum length "sand-sump" <br /> placed below the base of the screen. The sand-sump shall be a blank section <br /> of riser conforming to the requirements of riser to be placed below the table <br /> as described in paragraph 10.3.3.2.1. The sand-sump will be installed only if <br /> the screen can be placed at the appropriate interval without the sand-sump <br /> penetrating the aquitard. <br /> 9.3.3.2. 5 Joining Screen and Riser. Screen and riser sections shall be <br /> joined by threaded, flush-joint couplings, to form watertight unions, that <br /> retain 1008 of the strength of the screen. Solvent glue shall not be used at <br /> any time in construction of the wells. The bottom of the deepest screen or <br /> casing section shall be sealed with a threaded cap or plug of inert, noncor- <br /> roding material similar in composition to the screen itself. <br /> 9.3.3.2.6 Well Plumbness and Alignment. All risers and screens shall be <br /> set round, plumb, and true to line. Centralizers shall be used to assure <br /> plumbness and alignment of the wells. Centralizers shall not be installed on <br /> the well screen. <br /> 9.3.3.3 Gravel Pack. The AE shall select and use clean, inert, noncar- <br /> bonate materials to construct a uniform and continuous gravel pack designed to <br /> prevent migration of fines into the screen. The gradation shall be chosen by <br /> the AE to suit the well screen slot size and the expected gradation of the <br /> aquifer materials and submitted for approval as part of the Work Plan. The <br /> gravel pack shall be placed by tremie pipe from the bottom of the boring to at <br /> least two (2) feet above the top of the well screen. <br /> 9.3.3.4 Bentonite Seal and Grout. A minimum five (5) foot seal, con- <br /> sisting of tamped bentonite pellets or bentonite slurry shall be placed into <br /> the annular space between the riser and boring wall at the top of the gravel <br /> pack. Non-shrinking cement grout shall then be placed from the top of the <br /> bentonite seal to the ground surface. The cement grout shall consist of a <br /> mixture of portland cement (ASTM-C 150) , and water in the proportion of not <br /> more than seven (7) gallons of clean water per bag of cement (One cubic foot <br /> or 94 pounds) . Additionally, 38 by weight of bentonite powder shall be added <br /> if permitted by State regulations. <br /> 9.3.4 Soil Sampling for Geotechnical Analysis. During drilling of in- <br /> jection wells, soil samples shall be collected and geotechnical analysis shall <br /> be performed as outlined below. <br /> AA-29 <br />