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representative to determine if mechanical anchoring is required. Each jobsite has varying soil and water conditions. It is the Unpaved responsibility of the tank owner and its technical representative �. . . 4 in. reinforced concrete to determine actual size and thickness of either the concrete anchor pad or concrete deadmen used at a specific jobsite. n..:` Some installations will be considered"wet hole areas"where the water table must be kept at the lowest possible level in the excavation by pumping out water with or without a well point system. Consult "filter fabric" section of these installation instructions to determine if filter fabric is necessary. In the event water is used to fill or "ballast" the tank so installation can be accomplished, the following guidelines apply: •After tank is placed in hole add enough water to sink 77 tank. • Water level inside tank should be approximately the same level as water outside the tank. TANK ANCHORING, • In no event shall the water inside the tank be more than HIGH WATER TABLE 12" above the water level outside the tank. •Backfill excavation with pea gravel or crushed stone High water tables or water entering tank excavation will create making sure to push backfill under the bottom 120 significant uplift or buoyant force on underground tanks. These degrees section of tank to maintain proper support of buoyant forces can be partially overcome by the tank's weight, tank weight of backfill used and the amount of pavement or reinforced concrete applied over tank. Modern Welding Company publishes a guideline of holddown strap sizes based on tank's capacity and diameter. Refer to this When additional buoyant restraint is required, flat metal guideline when determining number of anchor points required holddown straps used in conjunction with concrete deadmen or for concrete pad or deadmen use. Holddown straps in concrete holddown pads maybe used. conjunction with backfill weight and concrete pad or deadmen When holddown straps are used, an inert dielectric isolation design work together to overcome the buoyant force of the material is required to separate the tank's exterior surface from underground tank. Once tank and holddown straps are installed the flat metal holddown strap. This isolation material should be it is imperative to apply remaining compacted backfill over tank shipped with the holddown straps from the tank manufacturer. before water has a chance to enter the excavation. The holddown strap guideline is for information only. Final anchoring system should be designed by approved engineer qualified in the area of soils and structural strengths of steel and THE USE OF STEEL concrete. CABLE AND ROUND BAR AS HOLD DOWN STRAPS Filter Fabrics / IS PROHIBITED Unstable Soil Environments When tank installations are subjected to the following conditions,filter fabric is required to prevent backfill migration. •Excavation Area is subjected to frequent ground water level changes. •Excavation is in a Tidal Area. •Excavation is in a swampy area were bog, muck, peat or where other soft expansive clay type, unstable soils are CAUTION: Never use steel cables or round bar as holddown present. strap material. This configuration of holddown will cut into and • Soils that have less than 750 lbs./sq.ft. cohesion and a damage exterior protection coating of your underground storage ultimate bearing capacity of 3500 lbs/sq.ft. are considered tank unstable excavations. Soil conditions, ground water and storm water runoff must be When filter fabric is used, clean sand is not an acceptable considered when anchoring tanks. backfill material, only crushed rock or pea gravel may be used. It is the responsibility of the tank owner or tank owner's Minimum bedding depth for backfill under tank in these conditions shall be 18".