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DRAFT slurry to allow hydration and to serve as a reserve incases 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 mixes 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 th 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. Slutry shall be introduced into the trench at the same time trenching is begun and shall be maintained in the trench dwing 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 [his 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- feetbelow bedrock surface or as shown on the plans. Weathered rock 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 de-sander. 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 shall be thoroughly mixed into a homogeneous mass, free from large lumps or pockets of fines, sand, or gravel. Occasional lumps of up to 6 inches in their largest dimension will be permitted. No frozen material, ice, or frost bearing soil shall be mixed into the backfill or allowed to be placed in the trench. Just prior to placing, the backfill material shall have a slump of 2 to 6 inches. To this end, the material shall be sluiced with slurry during blending operations. Sluicing with water will not be permitted. Containment berms will be cons[mc[ed where necessary to prevent slurry from entering rivers or ditches or flowing across the project boundary. 7/04 Section 02168 -Page 3 of 5