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3.02 SLURRY BATCHING PLANT The slurry botching plant shall include the necessary equipment including a mixer capable of producing a colloidal suspension of bentonite in water, pumps, valves, hoses, supply lines, and all other equipment as required to adequately supply slurry to the trench. Storage ponds shall be provided to store initially mixed slurry to allow hydration and to serve as a reserve in cases where substantial slurry loss from the trench through underlying pervious zones or other reasons may occur. The slurry shall be agitated or recirculated in the storage ponds as required to maintain a homogeneous mix. All slurry for use in the trench shall be prepared using a suitable mixer. No slurry is to be made in the trench. Mixing of water and bentonite shall continue until bentonite particles are fully hydrated and the resulting slurry appears homogeneous. 3.03 BACKFILL MIXING AND PLACING EQUIPMENT Equipment for mixing and placing backfill may consist of a suitable type of earthmoving or grading equipment, such as bulldozers, or blade graders, or blenders such as a pug mill, that are capable of ' thoroughly mixing the backfill materials into a homogeneous paste having the required gradation and properties and placing the material in the trench as hereinafter specified. 3.04 SLURRY TRENCHING Excavation shall be carried to final depth at the point where excavation is started and then the final depth of cut shall be carried along the line of the trench. Excavation shall proceed continuously from the starting point to the finishing point. Slurry shall be introduced into the trench at the same time trenching is begun and shall be maintained in the trench during excavation and until backfilled. The Contractor shall maintain the stability of the excavated trench at all times for its full depth. The level ' of bentonite slurry shall not be permitted to drop more than 2-fee[ below the surface of the slurry trench working platform except as approved by the Engineer. The Contractor shall have personnel, equipment, and materials ready to raise the slurry level at any time. To this end, the Contractor shall have personnel on call to raise the slurry level, weekends and/or holidays included. 3.05 TRENCH BOTTOM Unless otherwise directed by the Engineer, the bottom of the slurry trench will be extended a minimum of 3-feet below bedrock surface. Weathered rack of uncertain quality overlies bedrock. The Contractor shall provide sufficiently powered excavation equipment capable of penetrating through the bedrock to the prescribed depth. The final depth and penetration of the trench shall be measured and checked by the Contractor and approved by the Engineer immediately following excavation. 3.06 CLEANING TRENCH BOTTOM ' Upon completion of excavation, any loose material or cuttings shall be removed from the bottom of the trench with the excavation tools or other suitable means such as air lift pumps. If the unit weight of the slurry in the trench exceeds the specified limits, or becomes unworkable, the heavy slurry shall be removed from the trench by airlift pump, clamshell, or other methods approved by the Engineer or the excess solids shall be removed from the slurry by screening or centrifugal-type desander. 3.07 BACKFILL MIXING ' Material from borrow shall be mixed and blended in mechanical blenders or by windrowing, disk harrowing, bulldozing, blading or by other approved methods. Mixing and blending shall be ' performed in such a manner as to produce the required gradation of backfill. The backfill material 07/97 Section 02168 -Page 3 of 5